JP2009539064A - Contamination monitoring and control technology for use in optical metrology equipment - Google Patents

Abstract

  Create a controlled environment in the optical metrology device to minimize absorbent material in the optical path of the metrology device and to minimize contaminant buildup on the optical element surface that can cause performance degradation. Subsequent monitoring techniques are provided. Both exhaust and refill techniques can be used with monitoring techniques to determine whether the environment is suitable for measurement or whether the environment should be regenerated. The optical measurement device may be a device that operates at wavelengths including vacuum ultraviolet (VUV) wavelengths.

Description

  This application relates to the field of optical metrology, and more specifically to optical metrology performed in vacuum ultraviolet (VUV).

  In one embodiment, a means is provided that can perform accurate and reproducible optical measurements in vacuum ultraviolet (VUV). In one embodiment, the techniques disclosed herein ensure that a vacuum ultraviolet reflectometer produces highly stable and reproducible results in the presence of both gaseous and surface contaminants. Can be used for. In other embodiments, the techniques disclosed herein provide a means for obtaining accurate reflectance data from the sample itself, whose surface may be contaminated.

  Optical metrology technology has long been adopted for process control applications in the semiconductor manufacturing industry due to its non-contact, non-destructive and generally high-speed processing nature. The majority of these devices operate in a portion of the spectral region ranging from deep ultraviolet to near infrared wavelengths (DUV-NIR, generally 200-1000 nm). The constant effort towards developing smaller devices with thinner layers has been a challenge to the sensitivity of such devices. There has been an effort to develop an optical measurement device using a short wavelength (less than 200 nm) that can realize greater sensitivity to minute changes in process conditions. An approach to performing optical measurements at short wavelengths, such as a system and method for a vacuum ultraviolet (VUV) reflectometer, is currently available in US patent application Ser. No. 10 / 668,642, filed Sep. 23, 2003. Patent Document 1 and US Patent Application No. 10 / 909,126 filed on July 30, 2004 are described in the present Patent Document 2, and the contents of both of these are explicitly described in this specification. Included in the book.

  Contamination of optical surfaces such as windows and mirrors is a serious obstacle to the operation of optical devices in VUV. Moisture and residual molecules, especially hydrocarbon compounds, can accumulate on such surfaces over time and can significantly reduce the performance of the device. These effects have been the focus of past research due to their impact on the design, development and performance of 193 and 157 nm lithographic exposure apparatus.

  A device with the essential function of reducing, eliminating, or eliminating all the build-up of contaminants on the optical surface of the device, in order to ensure that the great sensitivity improvements that are theoretically provided by the VUV optical metrology device are actually achieved. It is highly desirable to develop. Furthermore, if this self-cleaning function can be realized without the addition of potentially expensive and complex parts, it would be very beneficial to the owner of the device.

  The presence of a contaminant layer on the surface of the sample under investigation can significantly affect the measurement of the optical response in the VUV and may give inaccurate and / or incorrect results. If the sample contains a very thin film (<100 mm), this thickness itself is equivalent to the thickness of the contaminant layer, and these effects are of particular concern.

  One possible technique for improving the measurement of semiconductor wafers by removing the contaminant layer in the cleaning stage involves the use of microwave radiation and / or radiator heating prior to measurement. Although this approach has been reported to improve measurement repeatability, this method requires that another cleaning system be coupled to the existing measurement system, resulting in system cost and design considerations. Complexity will increase.

  In view of these disadvantages, it is desirable to develop a measurement system that has its own function of removing contaminants from the surface of the sample, and that can reliably obtain accurate and reproducible results. Such devices can simultaneously clean and measure specific locations on the sample without the need for additional components beyond what is normally required for measurement, thereby reducing system cost and design complexity. It should be possible to reduce sex. Furthermore, such an apparatus should not require separate cleaning and alignment of the auxiliary measurement system. Furthermore, such an apparatus should ensure that a stable cleaning result is obtained at all measurement positions, while at the same time avoiding unnecessary “cleaning” of the entire sample.

US Pat. No. 7,067,818 US Pat. No. 7,126,131

  One embodiment of the disclosed technology creates a controlled environment within the VUV optical metrology device to minimize or eliminate any accumulation of contaminants on the surface of the optical element that can cause performance degradation. Next, provide the technology to monitor.

  In another embodiment, techniques are disclosed for reducing surface contamination from optical elements housed in the optical path (or auxiliary path) of an optical metrology device. This technique can be used in one embodiment in such a way that no additional components and / or devices need to be coupled or integrated into an existing metrology device.

  In another embodiment, a technique is disclosed in which surface contaminants on optical elements in an optical metrology device are monitored so that a cleaning process can be performed when deemed necessary. This technique will further allow the separate optical paths of the device to be monitored independently of each other and subsequently cleaned.

  In yet another embodiment, techniques are disclosed for removing contaminants from the surface of the sample to ensure that accurate results are obtained before the optical response is recorded from the sample. Alternatively, this technique can be implemented in a manner that does not require additional components and / or devices to be coupled or integrated into existing metrology equipment.

  In yet another embodiment, a technique for characterizing contaminants on the surface of a sample is disclosed. In addition to providing knowledge of the nature of the contaminant itself, this technique also provides a means by which accurate sample measurements can be performed taking into account the contaminant layer that may be present on the surface of the sample.

  In another embodiment, a method for controlling an atmosphere in an optical measurement device is provided. The method includes providing at least a first environment controlled room and a second environment controlled room, wherein the first and second environment controlled rooms are lower than the DUV wavelength. Configured to pass a light beam having a wavelength. The method includes the step of reducing the concentration of the optically absorbing material in at least one of the chambers in which the first and second environments are controlled using a vacuum evacuation technique. The method may further include the step of at least one of the controlled atmosphere chambers being a controlled atmosphere chamber. The method includes refilling a controlled atmosphere chamber with a non-absorbing gas and improving the optical performance by increasing the pressure of the controlled atmosphere chamber above the vacuum exhaust pressure level; Transmitting a light beam having a wavelength lower than the DUV wavelength while the atmosphere-controlled chamber is in a refilled state.

Another embodiment includes a method for controlling an atmosphere in an optical metrology device, the method comprising providing at least an environment-controlled sample chamber and an environment-controlled optical chamber,
Each of the sample chamber and the optical chamber may include a step configured to pass a light beam having a wavelength lower than the DUV wavelength. The method includes reducing the concentration of moisture or oxygen in at least one of the sample chamber and the optical chamber from ambient conditions using a vacuum evacuation technique, wherein the reducing step occurs. At least one of the chambers may further comprise a step where the atmosphere is a controlled chamber. This method also allows the diffusion of contaminants by refilling the controlled atmosphere chamber with a non-VUV absorbing gas and increasing the controlled atmosphere pressure above the evacuation pressure level. And transmitting a light beam having a wavelength lower than the DUV wavelength while the atmosphere-controlled chamber is in a refilled state.

  In another embodiment, a method for controlling an atmosphere in an optical measurement device is the step of providing at least an environment-controlled sample chamber and an environment-controlled optical chamber, each of the sample chamber and the optical chamber. Can be configured to pass a light beam having a wavelength lower than the DUV wavelength. The method may further include providing a sample beam optical path and a reference beam optical path, wherein the optical path lengths of the sample beam optical path and the reference beam optical path are coincident. The method also includes reducing the concentration of moisture or oxygen in at least one of the sample chamber and the optical chamber from ambient conditions using a vacuum evacuation technique, wherein the reducing step occurs. And at least one of the optical chambers may include a step in which the atmosphere is controlled. The method includes refilling a controlled atmosphere chamber with a non-VUV absorbing gas and increasing the optical performance by increasing the pressure in the controlled atmosphere chamber above the evacuation pressure level. And transmitting a light beam having a wavelength lower than the DUV wavelength while the atmosphere-controlled chamber is in a refilled state.

  In another embodiment, a method is provided for determining an environmental contamination condition within an optical metrology device. The method may include obtaining a first intensity measurement from the reference sample at a first time and obtaining a second intensity measurement from the reference sample at a second time. The method is based on analyzing the first and second intensity measurements and the variation between the first intensity and the second intensity to determine whether the environmental contamination state of the optical measurement device is suitable for further use. Determining from analyzing the first and second intensity measurements.

  In another embodiment, a method is provided for determining an environmental contamination condition in an optical metrology device operating at a wavelength that includes at least a wavelength lower than the DUV wavelength. The method includes obtaining a first intensity spectrum measurement from a reference sample at a first time, wherein the first intensity spectrum measurement includes at least a plurality of wavelengths lower than the DUV wavelength; Obtaining a second intensity measurement from the reference sample at a time of two, wherein the first intensity spectrum measurement includes at least a plurality of wavelengths lower than the DUV wavelength. The method is based on analyzing the first and second intensity measurements and the variation between the first intensity and the second intensity to determine whether the environmental contamination state of the optical measurement device is suitable for further use. Determining from analyzing the first and second intensity measurements.

  The advantages of the nature of the concepts disclosed herein will be further understood by considering the following description and the associated drawings.

In order to increase the sensitivity of optical metrology devices for challenging applications, it is desirable to expand the wavelength range in which such measurements are performed. Specifically, it is advantageous to utilize short wavelength (high energy) photons in and beyond the electromagnetic spectral region called vacuum ultraviolet (VUV). Vacuum ultraviolet (VUV) wavelengths are generally considered deep ultraviolet (DUV), ie wavelengths below about 190 nm. There is no universal boundary at the lower limit of the VUV range, but in the art VUV may be considered where the extreme ultraviolet (EUV) region begins (eg, wavelengths below 100 nm may be defined as EUV). right. Although the principles described herein are applicable to wavelengths above 100 nm, such principles are generally applicable to wavelengths below 100 nm. Accordingly, as used herein, it will be appreciated that the term VUV generally refers to wavelengths below about 190 nm, but is not meant to exclude lower wavelengths. Thus, as used herein, VUV generally means to encompass wavelengths generally below about 190 nm, without excluding the lower limit of wavelengths. Furthermore, the lower limit of VUV may be generally considered to be a wavelength below 140 nm.

  It is generally correct that virtually all material forms (solid, liquid, and gas) exhibit stronger optical absorption properties at VUV wavelengths. This is, to some extent, rather an intrinsic property of the material, and the high sensitivity available in the VUV optical metrology technique is due to the material itself. Small changes in process conditions are undetectable optical behavior changes of materials at long wavelengths, but VUV wavelengths can induce sufficiently and easily detectable changes in the measurable properties of such materials. Become. This highly non-linear dependence of the photon absorption cross section with respect to wavelength presents a tremendous opportunity for VUV optical metrology equipment, but unfortunately also introduces associated complexity.

One such complexity is related to the fact that VUV radiation cannot propagate through normal atmospheric conditions. Since VUV photons are strongly absorbed by O ₂ and H ₂ O, these materials are at a sufficiently low level (eg, typically below PPM) to allow transmission along the optical path of the instrument. Must be maintained. For this purpose, a purge method using vacuum or a non-absorbing purge gas (such as nitrogen, argon or helium) is generally used. Although the purge method can be reasonably effective in reducing gaseous O ₂ and H ₂ O concentrations, it is very difficult to remove adsorbed water in a timely manner without using vacuum techniques. The vacuum method is more efficient at removing adsorbed H ₂ O, but unintentionally diffuses surface contaminants as a result of the increased mean free path generated by such materials under reduced pressure. Facilitate.

  Given these conflicting issues, vacuum or purge alone alone constitutes the most effective means of creating and continuing to maintain the controlled environment necessary to perform optical measurements in VUV. It will be impossible. Rather, it is desirable to utilize a process that combines elements of both technologies to ensure optimal device performance. That is, a vacuum is first used to quickly reduce the concentration of moisture and oxygen materials to acceptable levels and then refill the device with a non-absorbing gas.

In one embodiment, it is generally desirable to reduce the pressure in the device to around 1 × 10 ⁻⁵ to 1 × 10 ⁻⁶ Torr in order to reduce the concentration of adsorbed moisture to an acceptable level. During this time, care should be taken to ensure that the optical surface of the device is not exposed to VUV radiation, as a photodeposited contaminant layer may form. This situation is easily avoided by either shutting off the VUV light source or turning off the power prior to exhaust.

  The time required to reach the required vacuum conditions depends on many aspects of the system (ie, temperature, internal surface area of the instrument volume, vacuum pump speed, etc.), but the internals during the sample loading process It is greatly affected by atmospheric exposure on the surface. Thus, the system pump depressurization time is minimized by devising the use of a load lock mechanism, which increases system throughput and reduces contaminant diffusion.

The pump vacuum cycle can also be shortened by applying energy to the water-adsorbed base via mechanical, thermal, or radiative methods. Mechanical energy can be added by introducing a controlled purge gas during the initial portion of the pump decompression cycle. Although it is possible to apply thermal energy by heating the walls of the device, this approach may promote the diffusion of contamination and may be mechanically unstable. It is possible to transfer energy directly to adsorbed water molecules using a UV lamp, but at the same time it can cause photodeposition of contaminants.

  When the concentration of the absorbent material in the device volume is sufficiently reduced, the controlled (ie, VUV photon) required to assist operation is provided by refilling the device volume with high purity non-absorbing gas. Environment) is obtained. Considering the contaminants will promote maintaining a high level of equipment pressure, but mechanical considerations generally limit practical operating pressures to near atmospheric conditions. As a result, pressures typically in the range of 300-700 Torr are used. Thus, optical performance can be improved by increasing optical transmission. Optical transmissibility can be increased by reducing the oxygen and / or moisture content through the use of vacuum technology. In addition, optical performance can also be improved by suppressing the diffusion of absorbent materials (ie, contaminants) from the surface through the use of refill techniques. Adsorbent contaminants that diffuse from the device surface and adhere to the optical surface can significantly degrade the performance of such elements, resulting in reduced mirror reflectivity and reduced window transfer characteristics.

  Over time, the quality of the controlled environment within the device can be expected to deteriorate due to various causes, including vaporization from internal surfaces, permeation through materials, and penetration through leaks (in practice). And practically both), and vaporization from the sample itself, but is not limited to these. Either of these mechanisms results in an increase in the concentration of absorbent material in the device, and thus a corresponding reduction in system optical transmission. It is advantageous to monitor the environmental conditions, and if necessary, appropriate measures can be taken to regenerate the environment, thereby ensuring that the accuracy of the measurement is not compromised.

There are many stand-alone methods, systems, and sensors to monitor the quality of the enclosed space, but the most direct and perhaps the most useful approach is to combine and measure with a reference sample to detect optical transmission The use of the optical elements of the device. The flowchart 100 of FIG. 1 illustrates how environmental monitoring can be achieved in this manner. First, in step 110, device volume is evacuated to a predetermined pressure P _L using a suitable vacuum system. Next, in step 120, the device is refilled with a non-absorbing gas to a predetermined measuring pressure P _H. When the measured pressure is reached, the intensity spectrum from the reference sample at time t ₁ is recorded immediately, as shown in step 130. The concentration of the absorbent material is assumed to be at the minimum level that can be reached by this point. Next, in step 140, the measurement of the test sample is performed for a predetermined period of time, followed by, as shown in step 150, the intensity spectrum of the reference sample is collected again at time t _2. As indicated by steps 160 and 170, the ratio of the _two intensity spectra (time t ₁ and time t ₂ ) from the reference sample is then calculated and analyzed to determine the concentration of the absorbent material. Next, in step 180, the determined concentration is then compared to a user defined threshold to determine whether the environment within the device is suitable for further measurements. As shown in step 190, if the environment is suitable, then control returns to step 140, and the measurement of the test sample is again performed for a predetermined time. Conversely, if the environment is no longer appropriate (as indicated by step 195), then the environment is regenerated by starting the exhaust / refill process again at step 110.

  FIG. 2 shows trace concentrations of oxygen and water (1, 5, 10 as shown in plots 200, 205, 210, and 215, respectively, for reference measurements collected in the presence of pure non-absorbing gas. And the ratio of the reference measurements collected in the presence of a non-absorbing gas atmosphere containing 20 PPM). As can be seen in the figure, as oxygen and water concentrations increase, the transmissibility through the controlled environment decreases significantly at wavelengths below 190 nm. Using the already known optical path length information, device pressure, and oxygen and water absorption cross sections, the concentrations of these materials can be easily determined through analysis.

  Alternatively, it is possible to simply monitor the quality of the controlled environment using the ratio of the reference measurements at discrete wavelengths. FIG. 3 shows VUV wavelengths 124.6 nm, 144.98 nm, and 177.12 nm (represented by plots 300, 305, and 310, respectively), for reference measurements collected in the presence of pure non-absorbing gas. The ratio of the reference measurements carried out in the presence of a non-absorbing gas containing trace amounts of oxygen and water is plotted as a function of oxygen and water. In practice, the measured transmissibility value can be compared with a user-defined threshold to determine the state of the controlled environment. The actual wavelength used for comparison can be selected based on the absorption cross section of the absorbing material of interest.

  The environmental monitoring process described herein assumes that the spectral intensity of the VUV light source has no appreciable change between the first and last reference measurements. While this may be a reasonable assumption in many instances, it should be noted that in situations where significant fluctuations are expected, the spectral intensity of the light source can be monitored independently to account for intensity fluctuations.

  The time that such a device can be operated (and reliable sample measurements can be performed) before a controlled environment regeneration is required can vary significantly depending on the design of the device and the manner in which the device is operated. For well-designed (ie, leak-free) systems that are operated to minimize the exposure of internal (ie, samples are introduced through a loading and securing mechanism), generally control Changes in the generated environment occur on a time scale that is significantly longer than the time required to measure a given sample. Therefore, many of these samples can often be measured before requiring a controlled environment regeneration. In any case, a short interval can be used if the environment is less stable and a longer interval can be used if the environment is more stable. The interval is adjustable.

  A controlled “measurement” environment established in the process outlined in the flow diagram of FIG. 1 may be created by refilling the device volume to a predetermined pressure. When this state is reached, purge gas flow to the apparatus may be stopped. Another way of operating such a device could be to have a purge valve set at a specific “release” pressure in the device so that the purge gas flows continuously into the device. In principle, it would be possible to reduce or eliminate the need for “regeneration” of the measurement environment, since the accumulation of absorbable substances such as oxygen and water may be limited. Implementation of this approach is difficult in practice because high flow rates are required to keep the concentration of absorbent material low enough (due to backflow of contaminants through the purge exhaust). In addition, continuous purge can induce pressure fluctuations and can adversely affect measurement stability.

  In connection with the use of VUV photons in optical metrology devices, the next difficulty is with respect to problems with surface contamination. A thin contaminant layer can only have a minor effect on the performance of the optical surface at longer wavelengths, but can significantly reduce the response of such elements at VUV wavelengths. In addition to adsorbed layers that are expected to form easily on optical surfaces under normal atmospheric conditions, organic and silicone-based thin films, when irradiated with VUV photons in the presence of contaminant-containing atmospheres, Unintentional photodeposition can occur on such surfaces.

With respect to the VUV response of the optical surface, FIG. 4 shows an example of the effect that a contaminant layer can have, but as shown in plots 400, 405, and 410, respectively, the reference value for the “clean” silicon surface is Against the reference values of the “contaminated” and “more contaminated” surfaces. As is apparent from the figure, the reflectivity of the Si surface in the VUV region decreases significantly as a function of contaminant accumulation. The photons in the optical metrology device typically hit many such surfaces as they travel from the light source to the sample and finally to the detector, so that the optical performance of the individual surfaces is only slightly reduced, The overall optical transmission of the device can be severely affected.

  Fortunately, in many cases, non-destructively reducing, removing or eliminating the accumulation of such contaminants on the optical surface through VUV irradiation in the presence of an atmosphere containing a trace concentration of oxygen. Is possible. When exposed to VUV wavelengths, diatomic oxygen dissociates into atomic oxygen, which then reacts with diatomic oxygen to form ozone. Both atomic oxygen and ozone are very reactive and can oxidize surface contaminants and form and release gaseous products.

  This photoetch cleaning process is schematically illustrated in FIG. FIG. 5A shows a contaminated optical surface 500 having a contaminant 505. In FIG. 5B, the contaminated optical surface 500 is exposed to VUV radiation 510 in the presence of an oxygen-containing atmosphere so that the contaminant 505 is removed from the surface via the reaction outlined above. FIG. 5C shows the resulting “clean” optical surface 520.

  For certain contaminants (eg, halogenated organics and organosilicon compounds), the photodeposition reaction may be irreversible and may not be sufficiently removed through photoetching. In such a case, irradiating the surface with VUV photons in the presence of an atmosphere consisting mostly of oxygen results in a continuous growth of the contaminant layer, even with a slight level of contaminant compounds. there is a possibility.

  In the more general case, oxygen, contaminants that lead to both photodeposition and photoetching (ie, those formed via a reversible reaction), and contaminants that photodeposit but not photoetch (ie, The surface is exposed to VUV radiation in the presence of an atmosphere containing (which is formed via an irreversible reaction). In such a situation, at least three different processes occur: a reversible deposition process, an irreversible deposition process, and a reverse reaction process via etching. These three processes are illustrated in FIG. 6 by white circles 610 moving toward the surface, black circles 620 (reversible and irreversible deposition, respectively), and white circles 610 moving away from the surface (etching), respectively, in FIG. Is represented graphically. The relative velocities associated with these processes depend on a variety of factors, including the surface concentration of the adsorbed contaminant, the oxygen concentration, the absorption cross-section of the contaminant, and the associated VUV photon flux.

  Since oxygen plays an important role in the photoetching process, it may be advantageous to monitor and control the concentration of oxygen contained within the device volume. Thus, the trace concentration of oxygen (or clean dry air) is deliberately added to the refilling non-absorbing gas to facilitate the cleaning process for measurement purposes without significantly compromising the VUV photon flux. To be added. Depending on the relative rates of contamination and etching, it may be possible to operate the VUV optics such that it does not promote the onset of unwanted material accumulation (ie, the etching rate exceeds the contamination rate). If a significant amount of contaminants is already present on the optical surface, the cleaning time required to remove such a thin film will temporarily exceed the level of oxygen normally used for data acquisition. By increasing it, it can be greatly reduced.

A trace amount of oxygen concentration intentionally added to the controlled environment of the device can be monitored, as can unintentional oxygen and moisture accumulations be detected using the environmental monitoring technique of FIG. . A gas such as a trace concentration of oxygen could be accurately added to the device volume using a mass flow controller. It could be practically implemented by modifying the technique of FIG. 1 so that a certain amount of oxygen is added to the device volume just before the start of sample inspection. To verify that the proper amount of oxygen has been added to the system, the spectral intensity from the reference sample will be recorded and can be compared with the spectral intensity obtained immediately after refilling with a non-absorbing gas. Thus, for example, to facilitate various cleaning mechanisms, a trace concentration of oxygen, for example in the range of 1 ppm or less, and more preferably in the range of 0.1 ppm or less, can be added to the controlled environment. In one embodiment, the controlled environment may be subatmospheric.

  In principle, all optical surfaces in a VUV measuring device are susceptible to contamination effects. This includes not only the optical elements (ie windows, beam splitters, mirrors, etc.) but also the surface of the sample itself. Contaminant concentrations in the instrument are expected to vary significantly with changes around the instrument and with sample introduction, so that appropriate cleaning measures can be taken to achieve optimal system performance. It may be advantageous to monitor the accumulation (or removal) of major contaminants over time.

  If such a surface can be effectively cleaned by a photoetching process, the relative luminous flux profile of the VUV that the optical surface undergoes during cleaning matches very well with that experienced during the initial photodeposition process. It should be. As a result, in order to obtain an optimal cleaning result, the VUV cleaning system is precisely configured and the position of the VUV optical measuring device and the position is ensured so that the VUV luminous flux profile received by the optical surface can be matched very well. It would be desirable to fit.

  Therefore, it would be advantageous if it could be integrated into an optical metrology device in such a way that precise configuration and alignment of the VUV cleaning function is not required. Furthermore, if such a function can be integrated in a way that requires few additional components in addition to those already present in the optical metrology device, the need for system design and cost will be greatly reduced. Let's go. An innovative means of accomplishing this is to detect the contamination status of the system using the optical elements of the measurement device itself in combination with a reference sample.

  The flowchart 700 of FIG. 7 illustrates how a contaminant monitor can be achieved in this manner. Initially, as shown in step 710, n consecutive reference sample intensity monitor measurements are performed and recorded on the reference sample. For each measurement, the optical path of the device (and each optical element on the path) is exposed to a certain VUV radiation flux within a known time interval. Thus, each measurement can be considered to give a specific dose of VUV radiation on the optical surface in the device. The reference sample strength may then be measured as a function of measurement number n. For example, as shown in step 720, the reference sample intensity may be plotted as a function of measurement number n. Thus, by recording the intensity at the detector as a function of the number of measurements, it is possible to effectively detect the optical transmission of the system as a function of the VUV exposure dose. In one embodiment, the number of measurements may be 10 or less. If the system environment is well controlled, only two measurements are required.

Following these reference measurements, the recorded results can be analyzed to determine if the cleaning process is complete and therefore the optical transmission of the device is stable. For example, as shown in step 730, a plot of the reference sample intensity as a function of the number of measurements n is analyzed to determine the contamination status, and if unstable, the exposure time t _clean required to reach stability is It is determined. Once it is determined that the system is in a stable state, a sample measurement can then be performed. As shown in step 740, for example, within a range where the difference in reference sample strength between two consecutive measurements (n and n-1) is within the desired measurement reproducibility associated with the “clean” state. If so, the state may be considered stable. However, as shown in step 745, for example, the difference between the reference sample intensities between two consecutive measurements (n and n-1) is within the desired measurement reproducibility associated with the "cleaned" state. If it is greater than the range, the state may be considered unstable. If the system is determined to be unstable (including when the cleaning process is incomplete)
Next, the exposure dose required to achieve system stability can be estimated. This exposure dose can be converted into an effective measurement time that may expose the system (and the reference sample). In one embodiment, the exposure is performed alone, as opposed to exposure via consecutive individual reference measurements. After exposing the system to the required cleaning dose, a continuous monitor measurement on the reference sample can be performed again, as shown in the reassessment step 760. This process may be repeated until the device is confirmed to be in a substantially “cleaned” state. As shown in the representative technique of FIG. 7, the change between two intensity measurements may be determined by subtracting one intensity measurement from another intensity measurement. However, it is recognized that the difference or change between two intensity measurements can be identified by a wide range of methods comparing the two measurements, and thus the variation of the two measurements can be quantified in a wide range of ways. Will be done. For example, a ratio may be used to quantify variation. Thus, although using a wide range of mathematical methods, it will also be appreciated that the measurement data can be analyzed, compared and quantified using the concepts described herein. Furthermore, although described with respect to the evaluation of two consecutive measurements (n and n-1), the two measurements need not be consecutive, but rather, simply evaluate any two measurements. It will be appreciated that the variation from one measurement to another may be determined.

  Details related to the cleaning process (so as a function of time, usage, etc.) to ensure efficient equipment cleaning and the resulting improved system stability ( That is, the frequency of reference measurements, the effective dose per exposure, the trace concentration of oxygen present in the device volume, etc.) can be adjusted. In this way, the device can be operated to optimize device performance.

  An example of the results that can result from this process is shown in plot 800 of FIG. 8, where the intensity from a normalized reference sample at a single VUV wavelength is plotted as a function of effective dose. As is apparent from the figure, the intensity from the reference sample generally increases linearly with exposure for a period before stabilization. If such cleaning is not performed, the ability of the optical device to perform accurate measurements prior to completion of such cleaning process will be significantly impaired.

  It should be considered that non-optical surfaces in such devices can also function as a source of contaminants, which can be adsorbed onto the optical surface and later released. Therefore, it is desirable to produce such a surface so as to minimize the potential for potential contaminants to adhere. This may include application of specific machining processes and / or appropriate coatings to ensure vacuum compatibility.

  In order to reduce the diffusion of contaminants from extraneous surfaces into the optical element within the device, it is advantageous to operate the device to minimize the evaporation rate of such materials. At a given temperature, the rate of molecular evaporation increases as the atmospheric pressure decreases. Furthermore, under such conditions, the mean free path of these molecules will also increase. As a result, contaminant molecules have a greater tendency to diffuse throughout the available volume, increasing the likelihood that the molecules will hit the optical surface and adhere to it. Therefore, from a contamination perspective, it is desirable to minimize the time that the volume of the VUV optical device is maintained at a reduced pressure.

Just as the optical elements in a VUV measuring device are susceptible to contamination effects, just as the sample being measured is also susceptible. The degree of sample contamination is highly dependent on both the environment to which the sample is exposed after creation and the duration of the exposure. Therefore, it is desirable to quickly detect a surface contaminant layer that may be present to help achieve an accurate measurement of sample characteristics. This is particularly important when the sample under investigation contains a very thin film with a thickness comparable to the thickness of the layer of the contaminant itself. This importance is even more emphasized in situations where the contaminant layer exhibits a higher degree of absorbency than the ultrathin film under study.

  Prior approaches to this problem have attempted to completely remove the contaminant layer from the entire surface of the sample before starting the measurement. In general, cleaning of the entire wafer is performed using thermal heating, microwave radiation, UV radiation, or some combination of these or other techniques. There are many difficulties associated with such a whole wafer cleaning technique. Such systems are often relatively large and are therefore likely to be configured as stand-alone systems outside the controlled environment of the VUV optical metrology apparatus. As a result, the sample must move between the cleaning system and the measurement device, increasing the possibility of recontamination.

  In addition, although moisture will be easily removed using whole wafer cleaning techniques, it can be seen that removing other contaminants completely and uniformly is problematic. This is due to the difficulties associated with generating an output beam of sufficient energy, amplitude, and spatial uniformity to ensure that contaminants are sufficiently removed from all parts of the sample. Residual contaminants after cleaning can lead to inaccurate measurement results as well as false conclusions regarding the spatial uniformity of sample characteristics.

  Stand-alone partial cleaning techniques have many drawbacks, even when integrated into the controlled environment of a VUV metrology device. In order to ensure that accurate measurement results are obtained, it is likely that the partial cleaning system is accurately aligned with the optical metrology device so that the position of the cleaning part and the position of the partial measurement coincide. ,desirable.

  Therefore, it would be advantageous if a partial cleaning function could be integrated into the optical metrology device so as to avoid alignment concerns through the use of a common optical module. Furthermore, if such a function can be integrated in a way that requires few additional components in addition to those already present in the optical metrology device, the need for system design and cost will be greatly reduced. Let's go.

  A novel means of achieving this is to utilize the measurement radiation itself for both cleaning and sample characterization. Thus, the discrete positions of the sample can be cleaned through exposure to measurement radiation immediately prior to measurement. In addition to completely eliminating the concern of cleaning / measurement alignment, this approach avoids unnecessarily “treating” large sample surface areas. However, the techniques provided herein are still available using another light source for the light source used for cleaning and measurement. One, both or any of such light sources may be a VUV light source.

  A further advantage of this technique is that the contaminant layer itself can be easily measured and characterized. The manner in which this can be achieved is illustrated in the flowchart 900 of FIG. Determine the properties of the contaminant layer (thickness, optical properties, composition, roughness, etc.) by obtaining the optical response from the contaminated sample and analyzing the results before and after removal of the contaminant layer It is possible. Using this acquired information, data is then collected and analyzed from other contaminated locations on the sample to characterize the characteristics of the sample. In other words, once the nature of the contaminant layer on a given sample is determined, in principle, other locations of the sample can be accurately characterized without first being cleaned. In addition to the obvious processing speed advantages, the combined cleaning / measurement period is reduced, so this technology can also provide valuable information on the contaminant layer itself that can be used to improve sample processing techniques. It is.

As shown in step 910 of FIG. 9, reflectance data will first be collected from a first location of a “dirty” sample in which a contaminant film is present. Next, in step 920, the first on the sample.
This position is cleaned by exposing the position to measuring radiation. In step 930, after the contaminant film is removed in step 920, the "clean" data will then be collected from the first location. In step 940, clean data from the first location of the sample will be analyzed and the characteristics of the sample will be determined. In step 950, the sample characteristics measured in step 940 can be utilized to analyze the dirty data from the first location (data from step 910) to determine the characteristics of the contaminant film. Next, at step 960, “dirty” data will be collected from another location on the sample where the contaminant film is present. Next, in step 970, this is done in step 970 by using the “dirty” data from another location obtained in step 960 and the characteristics of the contaminant film obtained in step 950. Sample characteristics can be determined for this other location without the need for another location cleaning. Multiple positions can be analyzed in this manner by returning control from steps 970 to 960 and repeating the process.

  The method of FIG. 9 determines the nature of the contaminant layer at one or several locations of a given sample, or multiple consecutive samples, once this approach has been validated. It is also possible to adopt a mode in which this is used during analysis at a position to be continuously measured on the sample or another sample. In this way, the contaminant layer need not be analyzed at all measurement locations. Alternatively, in situations where the contamination layer properties are expected to vary significantly from one location to another, all measurement locations can be cleaned prior to data collection. Furthermore, it is possible to measure the position of each of the samples before and immediately after cleaning to determine the nature of both the contaminant layer and the underlying sample.

  Of course, the use of this integrated partial cleaning technique can also be combined with other stand-alone, full wafer or partial cleaning techniques. This approach may be advantageous in situations where the sample is highly contaminated and / or many locations on a given sample should be measured. Under such circumstances, this combination of cleaning methods will help speed up the cleaning process.

  The same sample cleaning techniques outlined in this specification can also be used for calibration and / or reference sample preparation utilized by optical metrology systems, ensuring high levels of measurement accuracy. In addition, the nature of these “cleaned” samples can be monitored over time to detect the “soundness” of such samples. Such sample repair and / or replacement could thus be planned to occur concurrently with other preventive maintenance activities.

  In one example, through observation of the response of such a layer to the cleaning process, further knowledge about the characteristics of the contaminant layer itself can be obtained. That is, it may be possible to determine part of the chemical nature of the contaminant by recording the removal rate of the contaminant thin film as a function of the cumulative dose. If a correlation is obtained with additional analytical data, a library of cleaning response profiles could be created. This library can then be referenced during subsequent measurements to characterize unknown contaminants.

  As an example, representative cleaning response profiles for three different contaminant layers 1000, 1010, and 1020 are shown in FIG. This representative cleaning response profile illustrates the profile changes that can be observed from different contaminant layers. Using these profiles stored in the cleaning response library, profiles from unknown contaminant films could be classified by comparison. The profiles could be directly comparable, or could be fitted using a parameterized model and the resulting parameter values could be used to distinguish between contaminants.

Thus, as described above, the characteristics of the sample layer can be altered by exposing the sample to optical radiation, and this change can be characterized through the use of measurements performed before and after exposure to optical radiation. In the example described above, the change may include removing a contaminant layer from the sample. However, it will be appreciated that other changes in the sample may be characterized. Thus, for example, a contaminant layer need not be present, but rather some other layer or part of the sample may be characterized. In one embodiment, the characteristics of the sample layer or part of the sample to be analyzed through the use of an optical metrology device will be characterized. In such embodiments, the sample layer or part of the sample may remain after exposure to optical radiation, but some state of the sample layer or part of the sample may change. By characterizing the changes that occur, information about the intrinsic properties of the sample layer or part of the sample can be obtained.

  For example, exposure to optical radiation can change the binding structure, substance concentration, or other physical characteristics of the sample. In such examples, the intrinsic binding structure, substance concentration / diffusion, or other physical characteristics can be quantified based on the amount of change detected for a dose of optical radiation. Thus, how a layer responds to optical radiation can provide useful information about the intrinsic properties of the layer. Changes in layers are analyzed through quantified measurements of detected changes, alternatively compared to known optical response profiles (such as those stored in response profile libraries), or through other techniques Is possible.

  In one example, a silicon oxide film containing nitrogen can be characterized through such techniques. For example, VUV optical exposure can selectively affect the nitrogen contained in such thin films by causing nitrogen diffusion and / or changing the binding structure that retains nitrogen in such thin films. give. Changes in the optical response detected before and after exposure to optical radiation thus provide useful information about the original state, such as nitrogen binding (tightly bound, loosely bound, etc.) or nitrogen concentration. obtain. Thus, in general form, the techniques provided herein can characterize a sample through analysis of the thin film before and after the thin film characteristics change due to exposure to optical radiation. It will be recognized to detect.

  To help obtain accurate and reproducible results from optical metrology devices operating in VUV, the environmental monitoring technique of FIG. 1, the contaminant monitoring technique of FIG. 7, and the sample cleaning technique of FIG. 9 are combined. Thus, it is possible to form the basis of basic operation for such a device.

  An example of a VUV optical metrology device that fits well with the advantages of using the methods described herein is US patent application Ser. No. 10 / 668,642, filed Sep. 23, 2003. No. 7,067,818 and U.S. Patent Application No. 10 / 909,126, filed July 30, 2004, and described in current U.S. Pat. No. 7,126,131, The contents of both are expressly incorporated herein by reference. This metrology device may be a broadband reflectometer designed specifically to operate over a wide wavelength range including VUV.

An example of such an apparatus 1100 is shown in FIG. As is apparent, the light source 1110, the beam conditioning module 1120, the optical system (not shown), the spectrometer 1130, and the detector 1140 are housed in a device room 1102 (or optical system) in which the environment is controlled. Sample 1150, additional optics 1160, motor driven stage / sample chuck 1170 (optionally with integrated desorber function), and reference sample 1155 are independent controlled environment The sample is accommodated in the sample chamber 1104, and the sample can be attached and detached without contaminating the quality of the device chamber environment. The instrument chamber and the sample chamber are connected via a controllable coupling mechanism 1106, which can transmit photons and can exchange gas if desired. Both the instrument chamber 1102 and the sample chamber 1104 are fully equipped with suitable vacuum connections 1176, valves, purge connections 1177, and pressure gauges 1178 so that environmental control can be performed independently within each chamber. Connected to vacuum / purge assist system 1175. Thus, the environmental vacuum and refill techniques described above may be accomplished independently or together in each chamber. Thus, environmental vacuum and refill techniques (one or both) may be performed in the instrument / optical chamber, sample chamber, and / or both chambers.

  In addition, a processor (not shown) located outside the controlled environment may be used to facilitate automated monitoring techniques and to analyze measurement data. It will be appreciated that the processor may be any of a wide variety of computing means capable of providing appropriate data processing and / or storage of collected data.

  Although not explicitly shown in FIG. 11, the system is equipped with a robot and other related mechanized parts to assist in the loading and unloading of the sample in an automated manner, thereby further increasing the processing speed of the measurement. It is possible. Further, as is known to those skilled in the art, it is possible to utilize a load lock chamber along with the sample chamber to improve control of the environment for sample replacement and increase system processing speed for sample replacement.

  In operation, light from the light source 1110 is conditioned through the beam conditioning module 1120 and is distributed through the coupling mechanism 1106 through the distribution optics into the sample chamber where it is focused onto the sample 1150 by the focus optics 1160. Tie. The light reflected from the sample 1150 is collected by the focus optical system 1160, passes through the coupling mechanism 1106, is distributed again outside, where it is dispersed by the spectrometer 1130 and recorded by the detector 1140. The entire optical path of the device is maintained in a controlled environment that functions to remove absorbing material and allow transmission of VUV photons.

  A more detailed schematic diagram of the optical configuration of the apparatus is shown in FIG. The apparatus is configured to collect reference broadband reflectance data in the VUV and two additional spectral regions. In operation, light from these three spectral regions may be acquired in a parallel or serial manner. When operating in a serial fashion, reflectivity data and reference data from the VUV are first acquired, and subsequently reflectivity data from the second and third regions are collected and referenced. Once all three data sets are recorded, they are combined together to form a single broadband spectrum. In parallel operation, reflection data from all three regions is collected, referenced and recorded simultaneously before data combination.

The apparatus is divided into two chambers in which the environment is controlled: an apparatus chamber 1102 and a sample chamber 1104. The device room 1102 contains most of the system optics and is not normally exposed to the atmosphere. The sample chamber 1104 contains the sample, as well as the sample and reference optics, and is usually open to facilitate sample exchange. For example, device room 1102 may include mirrors M-1, M-2, M-3, and M-4. Flip-in mirrors FM-1 and FM-3 may be used to select which light source 1201, 1202 and 1203 (each having a different spectral region) to use. Flip-in mirrors FM-2 and FM-4 may be utilized to select one of spectrometers 1204, 1216 and 1214 (also depending on the selected spectral region). Mirrors M-6, M-7, M-8, and M-9 may be utilized to assist the light distribution as illustrated in the light beam. Windows W-1 and W-2 connect light between the measurement chamber 1102 and the sample chamber 1104. Windows W-3, W-4, W-5, and W-6 connect light into and out of the measurement chamber 1102. The beam splitter BS and shutters S-1 and S-2 are used to selectively distribute light to the sample 1206 or reference 1207 with the aid of mirrors M-2 and M-4, as shown. (In one embodiment, the reference may be a mirror). The sample beam passes through the correction plate CP. The correction plate CP is included to eliminate a phase difference that may occur between the sample path and the reference path, and due to the nature of the beam splitter action, this phase difference causes the light transmitted through the sample channel to pass through the beam splitter substrate. The light passing through the reference channel is due to the fact that it passes through the beam splitter substrate three times, whereas it passes only once. Therefore, the correction plate may be made of the same material as the beam splitter and have the same thickness. This ensures that the light transmitted through the sample channel also passes through the beam splitter substrate material of the same thickness in total.

  When operated in a serial manner, the flip-in light source mirror FM-1 in the second spectral region and the flip-in light source mirror FM-2 in the third spectral region are switched to the “outer” position. The light from the VUV light source is collected, collimated and can be redistributed by the focus mirror M-1 towards the beam splitter element BS, and VUV data is acquired first. The light striking the beam splitter is split into two components, a sample beam 1255 and a reference beam 1265, using a near-balanced Michelson interferometer arrangement. The sample beam is reflected from the beam splitter BS and transmitted to the sample chamber 1104 through the correction plate CP, the sample shutter S-1, and the sample window W-1, where the light is redistributed through the focus mirror M-2. Light is focused on the sample 1206. During this time, the reference shutter S-2 is closed. The sample window W-1 is made of a material that is sufficiently transparent to the VUV wavelength so as to maintain a high optical transmission amount.

  The light reflected from the sample is collected, collimated, redistributed through the sample window by the sample mirror M-2, and returned through the sample shutter and the correction plate. The light is then constrained by a first spectral domain flip-in detector mirror FM-2 and a second spectral domain flip-in detector mirror FM-4 (switched to the “outer” position). It proceeds without being received, is redistributed, and is focused on the entrance slit of the VUV spectrometer 1214 by the focusing mirror M-3. At this point, the light from the sample beam is dispersed by the VUV spectrometer and recorded by the associated detector.

  After collection of the sample beam, the reference beam is measured. This is accomplished by closing the sample shutter S-1 and opening the reference shutter S-2. This allows the reference beam to be transmitted through the beam splitter, reference shutter S-2 and reference window W-2 into the sample chamber 1104 where it is redistributed and by mirror M-4. Focus on a flat reference mirror 1207 that serves as a reference. The reference window is also made of a material that is sufficiently transparent to the VUV wavelength to maintain a high optical transmission.

  The light reflected from the surface of the flat reference mirror 1207 returns toward the focal reference mirror M-4, is collected, collimated, and passes through the reference window W-2, the reference shutter S-2, and the beam splitter BS. Redistributed light. The light is then reflected by the beam splitter toward the focusing mirror M-3, redistributed and focused on the entrance slit of the VUV spectrometer 1214.

  The path length of the reference beam 1265 is specifically designed to match the sample path length of the sample beam 1255 in each of the environmentally controlled chambers. The quality of the controlled environment of the device can be assessed by monitoring the intensity from the reference path, as previously described in FIG. As described above with reference to FIG. 7, the amount of optical radiation to which the various optical elements of the system are exposed can affect the amount of surface contaminants that can be present on the various optical elements. Accordingly, it may be desirable to balance the amount of optical radiation to which each path is exposed to facilitate further balancing the reference path transmitted by the reference beam and the sample path transmitted by the sample beam. Thus, in addition to balancing the optical path length and optical element, contaminants associated with the optical element may be relatively balanced between both paths. Furthermore, the techniques for determining the contamination status of an optical path described herein may be performed separately for each path to monitor the status of each path.

  After measurement of the VUV data set, a data set of the second spectral region is acquired in the same way. During the collection of spectral data in the second region, the light source flip-in mirror FM-1 in the second spectral region and the detector flip-in mirror FM-2 in the second spectral region are switched to the “inner” position. It is done. As a result, the light from the VUV light source 1201 is blocked and the light from the light source 1203 in the second spectral region can pass through the window W-3, and after the light is collected, it is collimated and the focus mirror Redistributed by M-6. Similarly, when detector flip-in mirror FM-2 in the second spectral region is switched to the “inner” position, the light from the sample beam (when the sample shutter is open and the reference shutter is closed) and the reference The beam (when the reference shutter is open and the sample shutter is closed) is distributed through the associated window W-6 onto the mirror M-9, which transmits the light to the spectrometer in the second spectral region. Focus is placed on the 1216 entrance slit where the light is split and collected by the detector here.

  The data from the third spectral region also switches the light source flip-in mirror FM-1 in the second spectral region and the detector flip-in mirror FM-2 in the second spectral region to “outside” while Are collected in the same manner by switching the inner spectral region source flip-in mirror FM-3 and the third spectral region detector flip-in mirror FM-4 "inside".

  Once the samples and reference measurements for each spectral region have been performed, a referenced reflectance spectrum can be calculated in each of the three regions using a processor (not shown). Finally, these individual reflectance spectra are combined to produce a single reflectance spectrum that encompasses the three spectral regions.

  When operated in a parallel manner, the source and detector flip-in mirrors are replaced with appropriate beam splitters and data for all three spectral regions is recorded simultaneously.

  In situations where it may be desirable, just as an auxiliary light source can be easily added to the reflectometer of FIG. 12, certain VUV light sources are also integrated with a common optical module for system and / or sample cleaning purposes. It is possible, for example, to use one additional auxiliary VUV light source for system and / or sample cleaning. Such an auxiliary VUV light source may be a light source with a higher intensity than the main VUV light source. Such an auxiliary VUV light source may be a single wavelength line light source or may have other wavelength characteristics different from the main VUV light source. The use of a high intensity light source can improve the cleaning process speed. In one embodiment relating to the use of an auxiliary VUV light source, such a light source such that the light from the light source is distributed toward the mirror M-1 via a flip-in mirror, shutter, etc. (not shown). It would be desirable to configure. This will allow the mirror M-1 to be cleaned. In such a configuration, most if not all of the elements in the optical path of the main VUV light source used to make the sample measurement will be hit by the auxiliary light source. While it would be desirable to hit many such elements, it will be recognized that the advantages of the techniques disclosed herein can be achieved without hitting all the elements of the optical path of the main VUV light source. Let's go. Further, when an auxiliary VUV light source is utilized, it is recognized that it would be desirable to couple such a light source into the system so that the path of such a light source is contained within an optical path in which the environment is controlled. right.

The system of FIGS. 11 and 12 may be used as a stand-alone device or may be integrated with other process devices. In one embodiment, the system of FIGS. 11 and 12 may simply be attached to the process equipment using some mechanism that allows the sample to be transferred between the process equipment and the sample chamber of the metrology equipment. Alternatively, the sample chamber may be configured to be shared among the process devices so that the measurement device and the process device can be more closely integrated with each other. For example, the device / optical chamber may be integrally connected with the sample chamber formed with the process device through the use of windows, gates, valves, or other coupling mechanisms. In this way, the sample need not be separated from the environment of the process equipment, but rather the sample may be contained in a region of the process equipment, such as a processing chamber, transfer area, or other area within the process equipment.

  As is apparent, the systems shown in FIGS. 11 and 12 facilitate the environmental monitoring approach outlined in FIG. 1, the system contamination monitoring approach outlined in FIG. 7, and the contaminated sample measurement approach shown in FIG. Contains typical parts. In general, all three effects (ie, accumulation of absorbing material within the device volume, contamination of the optical surfaces within the device, and sample contamination) can significantly affect the optical data in the VUV, and thus this spectral region It may be desirable to employ all three approaches simultaneously to achieve optimal system performance from the equipment operating in it. The operational flow diagram 1300 shown in FIG. 13 provides an example of how this can be achieved.

Initially, at step 1305, the device volume is evacuated to a predetermined pressure. The device is then refilled 1310 with a non-absorbing gas to a predetermined measured pressure. When the measured pressure is reached, the system is prepared for measurement using the system contamination monitoring technique outlined in FIG. 7, as shown in step 1315. Thus, step 1315 may perform steps 710-760 for the various system contaminants of FIG. If, at step 1315, the system condition is considered stable and “clean”, an intensity spectrum from the reference sample at time t ₁ is immediately acquired at step 1320. The concentration of the absorbent material is assumed to be at the minimum level that can be reached by this point. The intensity spectrum acquired at this time may be used as part of the environmental monitoring process corresponding to step 130 of FIG. Next, in step 1325, a measurement on the test sample is performed for a predetermined time in step 1325 using the contaminated sample measurement technique outlined in steps 910-970 of FIG.

Once the predetermined measurement time has elapsed, the state of the environment controlled at step 1330 is again evaluated by preparing the system for measurement utilizing the system contaminant monitoring technique outlined in FIG. When the system contaminant monitoring and cleaning steps are performed again, the various optical surfaces can be in the same state as at step 1315. Thus, when the environmental monitoring step is completed under certain conditions, it is possible to more closely match the system status to the first intensity measurement recorded in step 1320. Thus, after step 1330, the intensity spectrum from the reference sample is recorded again in time t ₂ as shown in step 1335. The ratio of the _two intensity spectra from the reference sample (time t ₁ and time t ₂ ) is then calculated and analyzed in steps 1340 and 1345 to determine the concentration of absorbent material N ₁ , N _2, etc. In step 1350, the determined concentration is then compared to a threshold value to determine if the environment within the device is suitable for further measurements. If the environment is deemed suitable (ie, the determined contaminant is below the threshold), then, if ready for measurement via the process of FIG. Measurement may be performed. Conversely, as shown in step 1360, if it is determined that the environment is unsuitable for making further measurements, the environment is regenerated by returning control to step 1305 and restarting the process of FIG. Thus, steps 1335 to 1360 correspond to environment monitoring steps 150 to 195 in FIG.

  As shown in FIG. 13, the various measures of environmental monitoring and regeneration of FIG. 1, system contamination monitor and cleaning of FIG. 7, and sample cleaning of FIG. 9 are integrated with each other for use in controlling optical metrology equipment. You can do it. It will be appreciated that the adoption of various technologies can vary, and FIG. 13 is merely illustrative of one way of combining these various strategies. For example, these strategies may be performed in series rather than integrating the steps together as shown in the technique of FIG. Furthermore, these strategies do not have to use all of each other. For example, in alternative embodiments, only one or two of these strategies may be utilized.

  The degree of contamination effects (both environment and surface / sample) that degrade the performance of a VUV optical metrology device generally depends on a wide range of factors, including device design, operating method, measurement frequency, sample loading technique, and sample Including but not limited to properties. As a result, it is anticipated that the operating process outlined in FIG. 13 can be modified as appropriate to ensure that optimal device performance is maintained.

  Further modifications and other embodiments of the invention will be apparent to those skilled in the art in view of the description herein. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the manner of carrying out the invention. The forms of the invention shown and described herein are to be understood as presently preferred embodiments. As will be apparent to those skilled in the art who have the benefit of the invention described herein, elements illustrated and described herein can be substituted with similar elements, and the features of the invention are Available independently of the use of other spot colors.

A more complete understanding of the present invention and its advantages may be obtained by reference to the following description, taken in conjunction with the accompanying drawings, in which like reference numerals indicate like features, and in which: However, the accompanying drawings only illustrate exemplary embodiments of the present invention and there are other equally effective embodiments, and therefore should not be considered as limiting the scope of the present invention. It should be noted that there is no.
It is a flowchart of a typical environmental monitor. FIG. 6 illustrates the results of a representative environmental monitor using a broadband VUV data set. FIG. 6 illustrates the results of a typical environmental monitor using a selected wavelength VUV data set. FIG. 5 illustrates exemplary reflectance data obtained from clean and contaminated silicon surfaces. FIG. 6 illustrates an optical surface with a contaminant layer. FIG. 6 illustrates VUV exposure in an oxygen-containing atmosphere that provides cleaning. It is a figure which illustrates the clean optical surface after a process. FIG. 6 illustrates reversible deposition and etching of one contaminant and irreversible deposition of another contaminant as a result of VUV irradiation in the presence of a contaminant and oxygen-containing atmosphere. 2 is a flow diagram of an exemplary system contaminant monitor. FIG. 5 illustrates exemplary contaminant monitor data using selected VUV wavelengths. 2 is a flowchart of a representative contaminated sample measurement. FIG. 4 illustrates a typical cleaning response profile for three contaminant films. It is a figure which illustrates the VUV reflectometer of a typical schematic expression. FIG. 6 illustrates a broadband reference reflectometer that includes three spectral regions including VUV. 3 is a representative operational flow diagram for a VUV optical measurement device.

Claims (162)

Providing at least a first environment-controlled room and a second environment-controlled room, wherein the first and second environment-controlled rooms have a wavelength lower than the DUV wavelength. A step configured to pass a light beam;
Reducing the concentration of the optically absorptive substance in at least one of the chambers in which the first and second environments are controlled using a vacuum evacuation technique, the first and second environments; The at least one of the controlled chambers is a controlled atmosphere chamber; and
Refilling the atmosphere-controlled chamber with a non-absorbing gas and improving the optical performance by increasing the pressure in the atmosphere-controlled chamber above the pressure level of evacuation; and
Transmitting the light beam having a wavelength lower than the DUV wavelength while the atmosphere controlled chamber is in the refilled state.
A method for controlling the atmosphere in an optical measurement device.   The method of claim 1, wherein the optical performance is improved by increasing optical transmissibility.   The method according to claim 2, wherein the optical transmissibility is increased by suppressing vaporization of a substance absorbed from the surface of the optical device.   The method of claim 1, wherein the optical performance is improved by reducing contaminant diffusion.   5. The method of claim 4, wherein the diffusion of contaminants is reduced to limit degradation of the reflective properties of the optical surface due to contaminants attached to the optical surface.   The method of claim 4, wherein the optical performance is also improved by increasing optical transmissibility.   The first chamber is a sample chamber, the second chamber is an optical chamber, and the step of reducing the concentration of the optically absorbing substance and the step of refilling are performed in the sample chamber; The method of claim 1.   The method of claim 1, wherein the optical measurement device is a stand-alone optical measurement device.   The first chamber is a sample chamber, the second chamber is an optical chamber, and the step of reducing the concentration of the optically absorbing substance and the step of refilling are performed in the optical chamber; The method of claim 1.   The method of claim 9, wherein the sample chamber is integrated into a process apparatus.   The first chamber is a sample chamber, the second chamber is an optical chamber, and the step of lowering the concentration of the optically absorbing substance and the step of refilling both the sample chamber and the optical chamber. The method according to claim 1, wherein   The method of claim 1, wherein the optically absorptive substance is moisture or oxygen. The apparatus of claim 1, wherein a pressure level of the evacuation is lower than 1 × 10 ⁻⁵ Torr.   The method of claim 1, further comprising applying energy to the optically absorptive material during the lowering step.   The method of claim 1, wherein the energy is applied via a mechanical, thermal, or radiative method.   The method of claim 1, wherein the refilling step increases the pressure in the atmosphere controlled chamber to a range of 300 to 700 Torr.   The method of claim 1, further comprising continuously supplying a purge gas to the atmosphere controlled chamber after the refilling step.   The method of claim 1, further comprising adding a trace level of gas to the atmosphere controlled chamber.   The method of claim 18, wherein the tracking level gas facilitates a surface cleaning process. Providing at least an environment-controlled sample chamber and an environment-controlled optical chamber, each of the sample chamber and the optical chamber configured to pass a light beam having a wavelength lower than the DUV wavelength Step,
Reducing the concentration of moisture or oxygen in at least one of the sample chamber and the optical chamber from ambient conditions using a vacuum evacuation technique, wherein the reducing step occurs; and The at least one of the optical chambers is a controlled atmosphere chamber; and
Refilling the atmosphere-controlled chamber with a non-VUV absorbing gas and reducing the diffusion of contaminants by increasing the pressure in the atmosphere-controlled chamber above the evacuation pressure level. When,
Transmitting the light beam having a wavelength lower than the DUV wavelength while the atmosphere controlled chamber is in the refilled state.
A method for controlling the atmosphere in an optical measurement device.   21. The method of claim 20, wherein the diffusion of contaminants is reduced to limit degradation of reflective properties of the optical surface due to contaminants attached to the optical surface.   The method of claim 21, wherein the step of reducing the concentration of moisture or oxygen and the step of refilling are performed in the sample chamber.   The method of claim 21, wherein the optical measurement device is a stand-alone optical measurement device.   The method of claim 21, wherein the step of reducing the concentration of moisture or oxygen and the step of refilling are performed in the optical chamber.   25. The method of claim 24, wherein the sample chamber is integrated into a process apparatus.   The method of claim 21, wherein the step of reducing the concentration of moisture or oxygen and the step of refilling are performed in both the optical chamber and the sample chamber.   21. The method of claim 20, further comprising continuously supplying a purge gas to the atmosphere controlled chamber after the refilling step.   The method of claim 21, further comprising adding a trace level of gas to the atmosphere controlled chamber.   The method of claim 21, wherein the tracking level gas facilitates a surface cleaning process. Providing at least an environment-controlled sample chamber and an environment-controlled optical chamber,
Each of the sample chamber and the optical chamber is configured to pass a light beam having a wavelength lower than the DUV wavelength;
Providing a sample beam optical path and a reference beam optical path, wherein the optical path lengths of the sample beam optical path and the reference beam optical path match; and
Reducing the concentration of moisture or oxygen in at least one of the sample chamber and the optical chamber from ambient conditions using a vacuum evacuation technique, wherein the reducing step occurs; and The at least one of the optical chambers is a controlled atmosphere chamber; and
Refilling the atmosphere-controlled chamber with a non-VUV absorbing gas and increasing the optical performance by increasing the pressure in the atmosphere-controlled room above the pressure level of evacuation; and ,
Transmitting the light beam having a wavelength lower than the DUV wavelength while the atmosphere controlled chamber is in the refilled state.
A method for controlling the atmosphere in an optical measurement device.   32. The method of claim 30, wherein the optical performance is improved by increasing optical transmissibility.   32. The method of claim 31, wherein the optical transmissivity is increased by inhibiting vaporization of a material absorbed from the surface of the optical device.   32. The method of claim 30, wherein the optical performance is improved by reducing contaminant diffusion.   34. The method of claim 33, wherein contaminant diffusion is reduced to limit degradation of the reflective properties of the optical surface due to contaminants attached to the optical surface.   34. The method of claim 33, wherein the optical performance is also improved by increasing optical transmissibility. A method for determining an environmental contamination state in an optical measuring device,
Obtaining a first intensity measurement from a reference sample at a first time;
Obtaining a second intensity measurement from the reference sample at a second time;
Analyzing the first and second intensity measurements;
Based on the variation between the first intensity and the second intensity, the first and second intensity measurements are analyzed to determine whether the environmental contamination state of the optical measurement device is suitable for further use. Determining from the steps.   37. The method of claim 36, wherein the first and second intensity measurements have an intensity spectrum having at least a portion of wavelengths below the DUV wavelength. 37. The method of claim 36, further comprising performing a first evacuation and refilling operation of a chamber in which at least one environment of the optical metrology device is controlled prior to obtaining the first intensity measurement. the method of.   37. The method of claim 36, further comprising adjusting the environment of the optical metrology device if the environmental contamination state of the optical metrology device is determined to be unsuitable for further use.   40. The method of claim 39, wherein the step of adjusting the environment comprises performing a chamber evacuation and refill operation in which at least one environment of the optical metrology device is controlled. The exhaust and refill operation is
Configuring the chamber in which the first environment is controlled to pass a light beam having a wavelength lower than the DUV wavelength;
Lowering the concentration of the optically absorptive substance in the chamber in which the first environment is controlled using a vacuum evacuation technique;
Optical performance is improved by refilling the first environment controlled chamber with a non-absorbing gas and increasing the pressure in the first environment controlled chamber above the pressure level of the evacuation. Steps to improve,
41. The method of claim 40, comprising transmitting the light beam having a wavelength lower than the DUV wavelength while the first environment is in a refilled chamber.   41. The method of claim 40, further comprising performing an initial evacuation and refilling operation of the at least one environment controlled chamber of the optical metrology device prior to obtaining the first intensity measurement.   38. The method of claim 36, wherein the concentration of the absorbent material is determined at least during the second time.   37. The method of claim 36, wherein the variation between the first intensity measurement and the second intensity measurement is analyzed by calculating a ratio of the first and second intensity measurements. .   45. The method of claim 44, wherein the measured concentration of the absorbent material is determined at the first time and the second time.   46. The method of claim 45, wherein the determination regarding the environment is based on comparing at least the measured concentration of the absorbent material to a threshold value for the absorbent material at the second time.   The plurality of optical components used for obtaining the first intensity spectrum measurement value and the second intensity spectrum measurement value are also used for measuring a sample with the optical measurement device. 36. The method according to 36.   38. The method of claim 36, wherein at least the plurality of optical components utilized to obtain the first intensity spectrum measurement and the second intensity spectrum measurement are dedicated monitor components.   40. The method of claim 36, wherein the optical metrology device has a reference optical path and a sample optical path.   50. The method of claim 49, wherein the reference optical path is optically coincident with the sample optical path. A method for determining an environmental contamination state in an optical measurement device operating at a wavelength having at least a wavelength lower than a DUV wavelength,
Obtaining a first intensity spectrum measurement from a reference sample at a first time, wherein the first intensity spectrum measurement has at least a plurality of wavelengths lower than a DUV wavelength;
Obtaining a second intensity measurement from the reference sample at a second time, wherein the first intensity spectrum measurement has at least a plurality of wavelengths lower than a DUV wavelength;
Analyzing the first and second intensity measurements;
Based on the variation between the first intensity and the second intensity, the first and second intensity measurements are analyzed to determine whether the environmental contamination state of the optical measurement device is suitable for further use. Determining from the steps.   The plurality of optical components used for obtaining the first intensity spectrum measurement value and the second intensity spectrum measurement value are also used for measuring a sample with the optical measurement device. 51. The method according to 51.   52. The method of claim 51, wherein at least the plurality of optical components utilized to obtain the first intensity spectrum measurement and the second intensity spectrum measurement are dedicated monitor components.   52. The method of claim 51, wherein the optical metrology device has a reference optical path and a sample optical path.   55. The method of claim 54, wherein the reference optical path is optically coincident with the sample optical path.   52. The method of claim 51, further comprising performing a first evacuation and refilling operation of a chamber in which at least one environment of the optical metrology device is controlled prior to obtaining the first intensity measurement. the method of.   57. The method of claim 56, further comprising adjusting the environment of the optical metrology device if the environmental contamination state of the optical metrology device is determined to be unsuitable for further use.   58. The method of claim 57, wherein the step of adjusting the environment comprises performing a second evacuation and refilling operation of a chamber in which at least one environment of the optical metrology device is controlled.   52. The method of claim 51, further comprising adjusting the environment of the optical metrology device if the environmental contamination state of the optical metrology device is determined to be unsuitable for further use.   60. The method of claim 59, wherein the step of adjusting the environment comprises performing a chamber evacuation and refill operation in which at least one environment of the optical metrology device is controlled.   61. The method of claim 60, wherein the refilling operation comprises adding a trace level of gas to the environment controlled chamber.   64. The apparatus of claim 61, wherein the tracking level gas facilitates a surface cleaning process.   The method of claim 18, wherein the gas comprises oxygen.   The method of claim 19, wherein the gas comprises oxygen.   30. The method of claim 28, wherein the gas comprises oxygen.   30. The method of claim 29, wherein the gas comprises oxygen.   64. The method of claim 61, wherein the gas comprises oxygen.   64. The method of claim 62, wherein the gas comprises oxygen. A method of monitoring the level of surface contaminants on an optical element in an optical measurement device, comprising:
Performing a plurality of intensity measurements;
Analyzing at least two intensity measurements of the plurality of measurements;
Determining the stability of the surface contaminant level from a comparison of the at least two intensity measurements of the plurality of measurements.   70. The method of claim 69, wherein the surface contaminant level condition is determined to be stable if the comparison is within a desired range.   70. The method of claim 69, wherein the surface contaminant level condition is determined to be unstable if the comparison is not within a desired range.   72. The method of claim 71, further comprising performing a cleaning operation to clean at least some surfaces of the optical element after the surface contaminant level condition is determined to be unstable.   73. The method of claim 72, wherein the cleaning operation comprises exposing the optical surface to radiation.   74. The method of claim 73, wherein the exposure to optical radiation occurs in the presence of a gas.   75. The method of claim 74, wherein the gas is present in a sub-atmospheric environment.   75. The method of claim 74, wherein the gas facilitates the cleaning operation.   75. The method of claim 73, wherein the radiation comprises light having at least some wavelengths that are lower than deep ultraviolet (DUV) wavelengths.   70. The method of claim 69, wherein the optical metrology device has a reference optical path and a sample optical path.   79. The method of claim 78, wherein the intensity measurement is performed utilizing the reference optical path.   79. The method of claim 78, wherein the intensity measurement is performed utilizing the sample optical path.   79. The method of claim 78, wherein the reference optical path is optically coincident with the sample optical path.   84. The method of claim 81, wherein a radiation exposure dose is balanced between the reference optical path and the sample optical path. 70. The method of claim 69, further comprising performing a first evacuation and refilling operation of the chamber in which at least one environment of the optical metrology device is controlled.   84. The method of claim 83, further comprising adjusting the environment of the optical metrology device if the environmental contamination state of the optical metrology device is determined to be unsuitable for further use.   85. The method of claim 84, wherein the step of adjusting the environment comprises performing a second evacuation and refilling operation of a chamber in which at least one environment of the optical metrology device is controlled. A method of monitoring the level of surface contaminants on an optical element in an optical metrology device that utilizes at least some wavelengths below a deep ultraviolet (DUV) wavelength, comprising:
Providing a reference optical path and a sample optical path, wherein the reference optical path and the sample optical path are optically balanced;
Performing a plurality of intensity measurements utilizing at least some wavelengths below the DUV wavelength;
Analyzing at least two intensity measurements of the plurality of measurements;
Determining stability of the surface contaminant level based at least in part on an analysis of the at least two intensity measurements of the plurality of measurements.
The method wherein the intensity measurement is performed utilizing at least one of the reference optical path or the sample optical path.   90. The method of claim 86, wherein the intensity measurement is performed utilizing the reference optical path.   90. The method of claim 86, wherein the intensity measurement is performed utilizing the sample optical path.   87. The method of claim 86, wherein the stability of the surface contamination level of both the reference optical path and the sample optical path is determined.   90. The method of claim 89, wherein similar radiation exposure doses are provided to both the reference optical path and the sample optical path.   90. The method of claim 86, wherein similar radiation exposure doses are provided for both the reference optical path and the sample optical path.   87. The method of claim 86, wherein the analyzing the at least two intensity measurements of the plurality of measurements comprises performing the at least two comparisons of the plurality of measurements.   94. The method of claim 92, wherein the surface contaminant level condition is determined to be stable if the comparison is within a desired range.   95. The method of claim 92, wherein the surface contaminant level condition is determined to be unstable if the comparison is not within a desired range.   94. The method of claim 92, wherein the comparison identifies a variation between the at least two of the plurality of measurements.   94. The method of claim 92, further comprising performing a cleaning operation to clean at least some surfaces of the optical element after the surface contaminant level condition is determined to be unstable.   99. The method of claim 96, wherein the cleaning operation comprises exposing the optical surface to radiation.   98. The method of claim 97, wherein the exposure to optical radiation occurs in the presence of a gas.   99. The method of claim 98, wherein the gas is present in a sub-atmospheric environment.   99. The method of claim 98, wherein the gas facilitates the cleaning operation. A method for cleaning surface contaminants on an optical element in an optical metrology device, comprising:
Performing a plurality of intensity measurements, the intensity measurements exposing the optical element to radiation under conditions suitable to remove the surface contaminants;
Analyzing at least two measurement intensities of the plurality of measurements;
Determining whether surface cleaning of the optical element is desirable based on the analyzing step of the measured intensity;
A method wherein surface cleaning is performed by exposing the optical element to additional radiation if it is determined that surface cleaning is desired.   102. The method of claim 101, wherein the surface contaminant condition is determined to be acceptable if an intensity variation between the at least two of the plurality of measurements is within a desired range.   102. The method of claim 101, wherein surface cleaning of the surface contaminant level is determined to be desirable if the intensity variation between the at least two of the plurality of measurements is not within a desired range.   102. The method of claim 101, wherein the radiation has a wavelength comprising at least a DUV wavelength.   105. The method of claim 104, wherein at least a plurality of optical components utilized to perform the surface cleaning are also utilized to perform optical metrology sample measurements.   106. The method of claim 105, wherein a light source for performing an optical metrology sample measurement is also utilized as the light source for the radiation utilized to clean the optical element.   105. The method of claim 104, wherein the optical metrology device has a reference optical path and a sample optical path.   108. The method of claim 107, wherein the reference optical path is optically coincident with the sample optical path.   102. The method of claim 101, wherein the exposure to additional radiation occurs in the presence of a gas.   110. The method of claim 109, wherein the gas is present in a sub-atmospheric environment.   110. The method of claim 109, wherein the gas facilitates the cleaning operation.   75. The method of claim 74, wherein the gas comprises oxygen.   76. The method of claim 75, wherein the gas comprises oxygen.   77. The method of claim 76, wherein the gas comprises oxygen.   99. The method of claim 98, wherein the gas comprises oxygen.   100. The method of claim 99, wherein the gas comprises oxygen.   101. The method of claim 100, wherein the gas comprises oxygen.   110. The method of claim 109, wherein the gas comprises oxygen.   111. The method of claim 110, wherein the gas comprises oxygen.   112. The method of claim 111, wherein the gas comprises oxygen. A method for cleaning a sample where it is desired to obtain optical data through the use of an optical metrology device, comprising:
Distributing light beams to discrete locations on the sample and cleaning contaminants from the discrete locations on the sample;
Measuring the characteristics of the sample at the discrete locations;
By utilizing at least the common part of the optical module of the optical metrology apparatus for achieving the cleaning and measurement, the same discrete position measurement and cleaning is achieved, the cleaning step and the measuring step; A method that minimizes alignment errors between.   122. The method of claim 121, wherein separate light sources are used for the cleaning light source and the measurement light source.   123. The method of claim 122, wherein at least one of the cleaning light source and the measurement light source comprises light having a wavelength lower than the DUV wavelength.   122. The method of claim 121, wherein a common light source is used for both the cleaning light source and the measurement light source.   129. The method of claim 124, wherein the cleaning light source comprises light having a wavelength lower than the DUV wavelength.   122. The method of claim 121, wherein the optical metrology device is a reflectometer that utilizes at least a portion of light having a wavelength lower than the DUV wavelength.   122. The method of claim 121, further comprising performing a pre-cleaning operation on all samples before distributing the light beam to the discrete locations.   128. The method of claim 127, wherein the precleaning operation comprises exposing the sample to light.   122. The method of claim 121, wherein the sample is a calibration standard.   129. The method of claim 129, wherein the optical metrology device is a reflectometer that utilizes at least in part light having a wavelength lower than the DUV wavelength.   122. The method of claim 121, wherein the sample is in a chamber in which the environment of the optical measurement device is controlled, and the chamber in which the environment is controlled is subjected to a vacuum evacuation process. A method for cleaning a sample where it is desired to obtain optical data through the use of an optical metrology device, comprising:
Distributing a light beam having a wavelength at least partially including a wavelength lower than the DUV wavelength to discrete positions of the sample to clean contaminants from the discrete positions of the sample;
Measuring characteristics of the sample at the discrete locations, wherein the characteristics are obtained by utilizing at least in part information relating to wavelengths where the characteristics are lower than the DUV wavelength;
By utilizing at least the common part of the optical module of the optical metrology apparatus for achieving the cleaning and measurement, the same discrete position measurement and cleaning is achieved, the cleaning step and the measuring step; A method that minimizes alignment errors between.   135. The method of claim 132, wherein the sample is in a chamber in which the environment of the optical measurement device is controlled, and the chamber in which the environment is controlled is subjected to a vacuum evacuation process.   134. The method of claim 133, wherein separate light sources are used for the cleaning light source and the measurement light source.   143. The method of claim 133, wherein a common light source is used for both the cleaning light source and the measurement light source. Collecting first optical data from the discrete locations and then subsequently distributing the light beam to the discrete locations of the sample to clean contaminants from the discrete locations of the sample; ,
Collecting second optical data from the discrete positions after cleaning the discrete positions;
Determining at least one characteristic of a contaminant layer on the sample by at least partially utilizing the first optical data and the second optical data;
134. The method of claim 133.   138. The method of claim 136, further comprising determining at least one characteristic of the sample by analyzing the second optical data.   138. The method of claim 137, further comprising determining at least one characteristic of the sample at a plurality of locations on the sample. Collecting third optical data from a second position of the sample, wherein the second position of the sample does not receive the light beam distributed to the discrete positions of the sample; When,
137. The method of claim 136, further comprising analyzing the third optical data utilizing the determined characteristic of the contaminant layer to determine the characteristic of the sample at the second location. A method of acquiring optical data from a sample through the use of an optical measurement device,
Collecting first optical data from a first position of the sample;
Cleaning the first position of the sample through exposure to light radiation after collecting the first optical data;
Collecting second optical data from the first position of the sample after the step of cleaning the first position of the sample;
Determining at least one characteristic of a contaminant layer on the sample by at least partially utilizing the first optical data and the second optical data.   141. The method of claim 140, further comprising determining at least one characteristic of the sample by analyzing the second optical data.   142. The method of claim 141, further comprising determining at least one characteristic of the sample at a plurality of locations on the sample.   143. The method of claim 142, wherein the characteristics are determined at the plurality of locations of the sample without requiring that all of the plurality of locations be cleaned by exposure to light radiation. Collecting third optical data from a second position of the sample, wherein the second position of the sample does not receive the light beam distributed to the discrete positions of the sample; When,
143. The method of claim 140, further comprising analyzing the third optical data utilizing the determined characteristic of the contaminant layer to determine the characteristic of the sample at the second location.   145. The method of claim 144, wherein the light radiation has at least a portion of a wavelength that is lower than a DUV wavelength.   141. The method of claim 140, wherein determining at least one characteristic of a contaminant layer on the sample comprises utilizing a cleaning response profile. A method of acquiring optical data from a sample through the use of an optical measurement device,
Collecting first optical data from the sample;
Modifying the characteristics of the sample through exposing at least a portion of the sample to light radiation after obtaining the first optical data;
Collecting second optical data from the sample after modifying the characteristic of the sample;
Determining at least one characteristic of the sample by at least partially utilizing the first optical data and the second optical data.   148. The method of claim 147, wherein the step of altering the quality of the sample comprises removing at least a portion of a contaminant layer.   149. The method of claim 148, wherein the light radiation has at least a portion of a wavelength below the DUV wavelength.   148. The method of claim 147, wherein the step of altering a property of the sample comprises the step of altering a physical property of a layer, wherein at least a portion of the layer remains on the sample.   165. The method of claim 150, wherein the characteristic is determined at least in part by a variation between the first optical data and the second optical data.   152. The method of claim 151, wherein the characteristic is determined by utilizing a predetermined optical response profile.   152. The method of claim 151, wherein additional collected optical data is utilized in combination with the first optical data and the second optical data to determine the at least one characteristic of the sample.   153. The method of claim 151, wherein the modified characteristic comprises a modified coupling characteristic.   153. The method according to claim 151, wherein the altered attribute is due at least in part to diffusion of material within the sample.   153. The method of claim 151, wherein the light radiation has at least a portion of a wavelength that is lower than a DUV wavelength.   165. The method of claim 150, wherein the light radiation has at least a portion of a wavelength that is lower than a DUV wavelength.   158. The method of claim 157, wherein the characteristic is determined at least in part by a variation between the first optical data and the second optical data.   158. The method of claim 157, wherein the characteristic is determined by utilizing a predetermined optical response profile.   158. The method of claim 157, wherein additional collected optical data is utilized in combination with the first optical data and the second optical data to determine the at least one characteristic of the sample.   158. The method of claim 157, wherein the modified characteristic comprises a modified coupling characteristic.   158. The method of claim 157, wherein the altered attribute is due at least in part to diffusion of material within the sample.

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