JP2007298314A - Method for measuring nondestructive film thickness, and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To nondestructively measure a thickness of an ultrathin film residue of the next-generation semiconductor nanoimprint by utilizing near-field photons. <P>SOLUTION: A measurement object 10 is irradiated with light by a light source 16, and a near-field light probe 15 makes an approach to a surface of the measurement object 10 to measure the air gap value between the measurement object 10 and the probe 15. A near-field photon field is generated by the presence of the measurement object in a near-field photon localized area formed at the tip of the probe 15, near-field photon response light that is a propagating light according to the near-field photon field is radiated, and the near-field photon response light is measured by a light-receiving part 17. A PC 21 acquires film thickness information of the measurement object, on the basis of the intensity of the measured near-field photon response light and the measured air gap value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nondestructive film thickness measuring method and apparatus, and more particularly to a nondestructive film thickness measuring method and apparatus using near-field photons.

  Nanoimprint technology can be mass-produced at low cost without the need for large-scale equipment such as a vacuum process, so it can be applied as a high-precision two-dimensional fine pattern formation technology that replaces conventional optical lithography in next-generation semiconductor processes. Is expected. According to the technology strategy roadmap formulated by the Ministry of Economy, Trade and Industry, 2013 (32 nm technology node) is the target year for applying nanoimprint technology to semiconductor processes. It is positioned as one of the specific industrial needs in the industry.

FIG. 25 is an explanatory diagram of the remaining film in nanoimprint.
In general, the nanoimprint technology removes the residual film in the semiconductor process because after the mold release, an ultra-thin residual film (thickness of about several tens of nanometers) remains in areas other than the resist cured part (desired fine pattern forming part). The process to do is needed. Since the resist hardened part (fine pattern forming part) functions as an etching mask, if this residual film varies, the pattern size after etching will vary, resulting in variations in the characteristics of the semiconductor device, which may cause defects. Is being viewed. In order to solve such problems and apply the nanoimprint technology to a semiconductor process with high reliability, a highly accurate control technology for the film thickness of an ultrathin residual film having a thickness of about several tens of nanometers, which is generated at the time of nanoimprinting. Establishment is needed. For this purpose, it is indispensable to measure the film thickness of the ultrathin residual film with high accuracy.

  Today, the importance of in-process measurement and evaluation technology has been reaffirmed as semiconductor microfabrication technology continues to become smaller and more accurate. Sampling measurement of microfabrication dimensions with an atomic force microscope (AFM) has also been introduced. With the introduction of AFM, it has been pointed out that even with measurement methods that are essentially difficult to perform 100% inspection, performing appropriate sampling measurement at critical points will greatly help improve process reliability and production device yield. ing.

  On the other hand, conventionally, near-field photons are generally used to acquire local attributes of adjacent substances, focusing on their non-propagating characteristics and local characteristics. Local attribute acquisition focusing on this localization characteristic means high-resolution measurement that transcends the diffraction limit. From this point of view, it is often used as a high-resolution attribute measurement method for only a region limited by near-field photons among bulk material attributes.

  In semiconductor manufacturing, oxide films, nitride films, and metal films are used as the vertical structure of semiconductor devices, and there are many methods for measuring the film thickness. Thickness measurement methods based on various measurement principles are available. Proposed and used. The main items are listed below and their characteristics are described.

[1] FT / IR interference film thickness measurement method This method analyzes the interference spectrum in the infrared region to analyze the molecular structure and composition at high speed and with high accuracy in a non-destructive and non-contact manner. Measure. In the measurement, an interference spectrum having a period corresponding to the thickness of the film is obtained, the interference spectrum is converted into a spatial gram by a frequency analysis method, and the film thickness is calculated with high accuracy from the peak position. However, normally only a few tens of μmφ can be squeezed and the lateral resolution is low.
[2] Confocal method / white interferometry The confocal microscope has a high height resolution even for samples with different heights by moving the pinhole up and down, and the inside of the multilayer film can be observed by changing the illumination wavelength. can do. However, measurement of a thin film with a thickness of 100 nm or less is impossible due to the wavelength limitation. The white interferometer has a very high resolution of 0.1 nm, but the lateral resolution is limited to about half of the wavelength due to the diffraction limit, and there is a limit to the measurement of tens of nm patterns.
[3] Prism coupling method If the thickness of the thin film is 300 to 500 nm, the film thickness and refractive index can be determined from the mode propagating in the film. In addition, for a bulk material, a highly accurate refractive index extremely close to an absolute value can be obtained by the critical angle method. It is difficult to apply to a nanoimprint ultrathin residual film that requires a film thickness range of 100 nm or less.
[4] Eddy current sensor method A method of measuring the thickness and sheet resistance of a metal thin film in a non-contact and non-destructive manner using an eddy current sensor. The measurement range of the film thickness is 0.03 to 5 μm. It is a method of measuring the sheet resistance of the measurement principle, and the thickness of the insulating film that does not conduct electricity cannot be measured in principle.
[5] Ellipsometer (see Non-Patent Documents 1 and 2)
Using the principle of ellipsometry (polarization analysis), the film thickness and refractive index of a thin film can be measured at high speed and with high accuracy. It is possible to measure the film thickness and refractive index of semiconductor oxide film, nitride film, resist, ITO, etc., the method of changing the incident angle using a laser, and the reflection of each wavelength of broad light such as 190 nm to 830 nm There are methods to detect rates. The ellipsometer can measure a film thickness of several nanometers, but it also has an incident angle of about 60 °, and the diameter of the object is about 50 μm. The average thickness of the entire area is measured. Will be.

Brian Trotter et al. , “Fixed-polarizliprisome: a simple technique to measure the thickness of very thin films”, Optical Engineering Vol. 38 No. 5 May 1999. Steven A. Henck et al. "In situ special ellipsis for real-time thickness measurement and control", SPIE Vol. 1803. X. Zhu et al. , “A Nobel ultrasonic resonance sample-tip distance regulation for near field optical microscopy and shear force microscopy”, Solid State Community. 98 No. 7 pp. 661-664 1996.

  Nanoimprint technology is expected as the most promising alternative to photolithography in next-generation semiconductors. At that time, in order to manufacture a semiconductor device with high reliability, the film thickness of the ultrathin residual film (thickness: several 10 to 100 nm) generated during nanoimprinting is measured nondestructively, and based on the measurement evaluation result Optimization of nanoimprint process conditions is essential. However, there is currently no method capable of nondestructively measuring the film thickness for such an ultrathin residual film in a fine structure.

  As a result, in order to evaluate the thickness of the ultrathin residual film, it is now necessary to rely on a destructive evaluation method in which the wafer is cut and the cross section is observed with a scanning electron microscope (SEM). . Moreover, since the cross-sectional SEM measurement is a destructive measurement, the sample cannot be used again. Therefore, in order to put it into practical use in line with the technology strategy roadmap for nanoimprint technology, there is an urgent need to develop a nondestructive film thickness measurement technology that can provide process feedback.

Further, the conventional non-destructive measurement technique is not applicable to a pattern of several tens of nm due to the low lateral resolution. In addition, since the optical method causes multiple interference, a film thickness of several tens of nm cannot be measured.
Therefore, the present invention aims to nondestructively measure the film thickness of a nanoimprint ultrathin residual film for next-generation semiconductors by using near-field photons localized in a small region of about several tens of nanometers, for example.

  Note that, as in the present invention, the method of capturing the near-field photon contribution range itself as a measurement parameter is different from the conventional near-field photon application measurement method, and the thickness of the ultrathin film thickness itself is the measurement parameter. No measurement example has been known so far.

According to the first solution of the present invention,
Irradiate the measurement target with a light source
Bring the near-field optical probe closer to the surface to be measured,
Measure the air gap value between the object to be measured and the near-field optical probe,
By making the measurement object exist in the near-field photon localized region formed at the tip of the near-field optical probe, the interaction between the dipole at the tip of the near-field probe and the dipole in the substance to be measured To generate a near-field photon field, and emit a near-field photon response light that is a propagating light corresponding to the near-field photon field,
Measure the near-field photon response light,
There is provided a nondestructive film thickness measurement method for obtaining film thickness information of a measurement object based on the measured intensity of the near-field photon response light and the measured air gap value.

According to the second solution of the present invention,
A light source that illuminates the measurement object;
A near-field optical probe for detecting the near-field photon response light by approaching the surface of the measurement object;
An air gap measuring unit for measuring an air gap value between the measurement object and the near-field optical probe;
A light receiving unit for measuring the near-field photon response light detected by the near-field light probe;
By making the measurement object exist in the near-field photon localized region formed at the tip of the near-field optical probe, the interaction between the dipole at the tip of the near-field probe and the dipole in the substance to be measured A near-field photon field is generated by, and a near-field photon response light that is a propagating light corresponding to the near-field photon field is emitted, and the intensity of the near-field photon response light measured by the light receiving unit is measured. There is provided a nondestructive film thickness measurement apparatus including a processing unit that obtains film thickness information of a measurement object based on the air gap value.

  According to the present invention, since it is an optical method, it can be measured non-destructively, and since it is locally focused by a fiber probe, it is possible to measure a minute region. The lateral resolution mainly depends on the aperture of the probe. If a small aperture is selected, for example, a high resolution of several tens of nm can be expected.

1. Hardware of Film Thickness Measuring Device 1-1 Outline of Film Thickness Measuring Device FIG. 1 shows a conceptual diagram of a film thickness measuring device.
Below, the outline | summary of a film thickness measuring apparatus is demonstrated. In this embodiment, a description will be given using c mode as an example. However, the present invention is not limited to this, and the present invention can be applied to an apparatus configured in accordance with various modes described later.

  This film thickness measurement apparatus includes a near-field light response detection optical system 1 and a near-field light response control system 2. The near-field light response detection optical system 1 includes stages 11 to 13, a tuning fork 14, a probe 15 such as a fiber probe, a light source 16, and a light receiving unit 17. The near-field light response control system 2 includes a computer (PC) 21, a stepping motor controller 22, a fine movement stage controller 23, a lock-in amplifier 24, and a storage unit 25.

  An XY coarse movement stage 11 is used as a sample stage. The air gap is brought close to the movable range of the fine movement stage 13 by piezo (PZT) or the like by the Z axis coarse movement stage 12. Shear force control is used for high-precision height control with the sample 10 to be measured. A sample is illuminated by a light source (for example, laser) 16, a near-field optical response is detected by a probe 15, and light is received by a light receiving unit (for example, PMT) 17. Since the probe 15 vibrates at the resonance frequency of the tuning fork 14 and the near-field optical response detected by the probe 15 also vibrates at the same frequency, a signal is obtained by performing lock-in detection. This reduces noise.

  In the description of the embodiment, the air gap, which is the distance between the probe 15 and the sample (measurement target) 10, is measured using the tuning fork 14. An air gap measuring means may be provided to measure the air gap. In that case, the configuration of the tuning fork 14 and the like can be omitted as appropriate.

1-2 Examples of main functions The main functions required for the film thickness measuring apparatus of the present embodiment are the following two points.
(I) The air gap is controlled in units of several tens of nanometers, for example.
(Ii) detecting a very weak optical signal traveling in the probe.

  Regarding (i), as an example, the air gap control uses shear-force control (see Non-Patent Document 3, etc.). In addition to the shear force technique, an appropriate air gap control technique can be used.

FIG. 2 is an explanatory diagram of the shear force.
As shown in the figure, the probe 15 is moved closer to the sample while vibrating in the horizontal direction with an excitation piezo or the like. When the air gap is 50 nm or less, the amplitude is attenuated by the viscosity of water molecules adsorbed on the sample surface. The air gap is controlled by monitoring and controlling the amplitude. As shown in the figure, there is a method of detecting the amplitude with a detector placed behind by applying a light source 16 such as a laser to the vibrating probe 15 as shown in the figure, but the light becomes stray light and the sensitivity deteriorates. Therefore, in this embodiment, the amplitude is detected using a sound type tuning fork (quartz crystal resonator) which is a piezoelectric element.

FIG. 3 shows a diagram of an amplitude detection method using a tuning fork.
As shown in the figure, the probe 15 is attached to the sound portion of the tuning fork 14, and a voltage is applied from the internal oscillation circuit of the lock-in amplifier 24 at the resonance frequency of the tuning fork 14 to resonate. When resonating, the tuning fork 14 vibrates with an amplitude of several nanometers in the lateral direction, and the probe 15 also vibrates simultaneously. In this state, when approaching the sample and the air gap becomes 50 nm or less, the amplitude of the probe is attenuated by the shear force, and at the same time, the amplitude of the tuning fork is also attenuated. By monitoring the amplitude and keeping it constant, the air gap can be kept constant.

  With regard to (ii), the near-field optical response that has traveled through the probe is detected using a detector such as a photomultiplier tube (PMT) having high sensitivity and high response speed. In addition, a final signal is obtained by performing lock-in detection for noise reduction.

1-3 Detailed Configuration A detailed configuration of the film thickness measuring apparatus will be described below.
(1) Near-field light response detection optical system 1
As an example, the stage drive part has an XY-axis stage 11 installed on a vibration isolation table, a Z-axis stage 12 installed on the upper part of the basic frame, and a head part including a probe 15 on the stage 12. Created. With respect to the Z axis, it is necessary to control the air gap with high accuracy, and the coarse movement stage 12 and the fine movement stage 13 are used. The XY-axis stage 11 can be used for sample stage scanning, so that the film thickness can be continuously evaluated.

  In the head portion, the tip of the probe 15 such as a fiber probe is connected to the tuning fork 14 so that it is, for example, about several mm. When a voltage is applied from the internal oscillation circuit of the lock-in amplifier 24, the tuning fork 14 vibrates at the resonance frequency, and the probe 15 also vibrates.

  As an example, the external illumination optical system portion is a c mode of a near-field light microscope, and a light source 16 such as a laser illuminates a zone including the tip portion of the probe 15. As the light source 16, for example, a laser such as a linearly polarized He—Ne laser having a wavelength of 633 nm can be used. The external illumination optical system portion can be configured using, for example, a linearly polarized laser as the light source 16 and using a λ / 4 wavelength plate and a polarizer as the polarizing unit 18. Furthermore, the tip of the probe may be illuminated by being reflected by a mirror with a fine angle adjustment.

  In the thin film thickness evaluation of the present embodiment, illumination can be performed with P-polarized light and S-polarized light by the polarizing unit 18, and the film thickness can be evaluated by examining the intensity change. Regarding the external illumination optical system, since it is desired to detect a difference due to polarization with the same laser intensity, the intensity of the incident laser needs to be the same for both polarizations. For example, since the laser oscillates with linearly polarized light, first, the laser beam is transmitted through the λ / 4 wavelength plate. Then, since it becomes circularly polarized light, it is possible to adjust P-polarized light and S-polarized light with the same intensity when transmitted through the polarizer. Switching between the P-polarized light and the S-polarized light may be performed manually or by the PC 21.

  The near-field light response detection unit can use, for example, an integrated photosensor module in which a low power consumption type high-voltage power supply circuit and an amplifier are built in a photomultiplier tube as the light receiving unit 17. An FC connector is attached to the light receiving surface of the light receiving unit 17 such as PMT, and an end surface opposite to the fiber probe 15 is inserted therein to detect an optical signal propagating through the fiber. Also, the PMT was placed in a shielding box so that only the optical signal that passed through the fiber could be received, so that other light was not required as noise.

(2) Near-field light response detection control system 2
In this apparatus, it is necessary to control the stepping motor controller 22 for scanning the sample stage, the fine movement stage controller 23 for controlling the probe height, and the lock-in amplifier 24 for signal detection. Therefore, the PC 21 communicates with and controls the controllers 22 and 23 and the lock-in amplifier 24 using an interface such as GPIB (General Purpose Interface Bus).

The stepping motor controller 21, the piezo controller 23, and the lock-in amplifier 24 are connected to the PC 21 with a cable.
The storage unit 25 can store propagation light intensity distribution reference data indicating the intensity of near-field photon response light with respect to the air gap value for a plurality of film thicknesses whose film thicknesses are known in advance.

  Alternatively, the storage unit 25 irradiates the P-polarization propagation light intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value for each film thickness when the polarization unit irradiates the P-polarized light, and / or the S-polarized light. It is possible to store the S-polarized light propagation intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value for each film thickness. At this time, the storage unit 25 can further store characteristic data indicating the film thickness with respect to the air gap value at the intersection of the P-polarized light propagation intensity distribution and the S-polarized light intensity distribution. Note that only the propagation light intensity distribution for one polarization may be stored.

2. Measurement Principle 2-1 Basic Principle FIG. 4 shows a conceptual diagram of the principle of film thickness measurement. This figure shows an enlarged view of the probe tip. An example of the basic principle of the present embodiment is as follows.
The aperture type fiber probe is brought close to the vicinity of the surface of the sample. A near-field probe having a near-field light formed at the probe tip is brought close to the surface of the remaining film, and the near-field light acts on the remaining film of the sample. Its size depends on the tip size and is localized at the probe tip. A near-field optical response that includes film thickness information and is emitted as propagating light is locally focused by a probe, and film thickness information is extracted from the response signal.

2-2 Basic principles of near-field light microscopes (for example, Genichi Otsu, Kiyoshi Kobayashi "Near-field light basics-New optics for nanotechnology" (issued January 5, 2003), Ohm Corporation , P.29-35 etc.)
FIG. 5 is an explanatory diagram of the principle of the probe.
The basic property of near-field light is non-propagating light that is localized on the surface of the fine particle and has a thickness of about the size of the fine particle. In order to detect this, as shown in the figure, the second fine particle is inserted into the near-field light and converted into propagating light, and this second fine particle is called a probe.

  At this time, the volume to be converted is preferably as small as possible in order to take advantage of the dimension-dependent localization characteristics of the near-field light. However, since the conversion efficiency is maximized when the two fine particles have the same size, the size of the second fine particles. Is advantageously equivalent to the first fine particles. Further, since the conversion efficiency is determined by the scattering efficiency of the near-field light by the two fine particles, it also depends on the structure of these fine particles.

3. Thin film evaluation method using near-field light Next, we will describe how to evaluate the thin film thickness.
FIG. 6 is a diagram summarizing the relationship between the air gap and the probe electric field for P-polarized light and S-polarized light for each film thickness.

  As shown in the figure, when the film thickness changes, the probe electric field intensity basically shifts to the left, but the probe electric field intensity changes differently due to the influence of the thin film and the influence of the polarization. It should be noted here that there are places where the intensity of P-polarized light and S-polarized light are reversed.

FIG. 7A shows a relationship between the air gap and the film thickness that are reversed so that the intensity of the P-polarized light is increased.
In FIG. 6, the intensities of P-polarized light and S-polarized light are reversed within a square indicated by a dotted line. For example, the film thickness is not yet reversed at a film thickness of 10 nm, but is reversed at an air gap of 90 nm at a film thickness of 20 nm. When the film thickness is 30 nm, the air gap is 60 nm, when the film thickness is 40 nm, the air gap is 30 nm, and when the film thickness is 50 nm, the air gap is 10 nm. In other words, it is considered that the film thickness can be evaluated using an air gap in which the intensity of P-polarized light is greater than the intensity of S-polarized light.

FIG. 7B shows a relationship between the air gap and the film thickness that are reversed so that the intensity of S-polarized light is increased.
However, there are cases where a film thickness of 20 nm or less cannot be measured by the above method. In this case, attention is paid to the other squares in FIG. Within the square, the intensity of S-polarized light is greater than the intensity of P-polarized light. When the film thickness is 0 nm, the air gap is 70 nm, when the film thickness is 10 nm, the air gap is 45 nm, and when the film thickness is 20 nm, the reversal occurs at the air gap of 25 nm.

From this graph, for example, if the air gap can be controlled at 5 nm or less, the film thickness can be measured with a resolution of 2-3 nm.
If necessary, the film thickness can be measured by examining the air gap whose intensity is reversed by using either one of the polarization graphs or the two graphs at the intersection as described above.

4). Flowchart FIG. 8 shows a flowchart of the first embodiment for nondestructive film thickness measurement.
First, the PC 21 measures near-field photon response light, and stores the measurement data in the storage unit 25 (S101). This will be specifically described below. For details, see “5. Details of control and measurement” described later.

  The measurement object 10 is irradiated by a light source 16 such as a laser, the near-field light probe 15 is brought close to the surface of the measurement object 10, and the air gap value between the measurement object 10 and the near-field light probe 15 is measured. Then, by making the measuring object 10 exist in the near-field photon localized region formed at the tip of the near-field optical probe, the dipole at the tip of the near-field probe 15 and the dipole in the substance of the measuring object 10 The near-field photon field is generated by the interaction of the near-field photon, and the near-field photon response light that is the propagating light corresponding to the near-field photon field is emitted. Then, the near-field photon response light is measured by the light receiving unit 17.

  During the measurement in step S101, the P-polarized light is irradiated by the polarization unit 18 automatically or manually by the PC 21 to measure the P-polarized light propagation intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value. S-polarized light is irradiated, and the S-polarized light propagation distribution indicating the intensity of the near-field photon response light with respect to the air gap value is measured. The PC 21 stores the measurement result in the storage unit 25. See, for example, FIG. 6 for the propagation light intensity distribution.

Next, based on the measured intensity of the near-field photon response light and the measured air gap value, the PC 21 obtains the film thickness information of the measurement target 10 as follows.
In this embodiment, first, the PC 21 obtains the air gap value at the intersection of the P-polarized light propagation intensity distribution and the S-polarized light intensity distribution, and stores the intersection data in the storage unit 25 as necessary ( S103).

  The PC 21 reads predetermined characteristic data indicating the film thickness with respect to the air gap value at the intersection from the storage unit 25, and obtains film thickness information according to the air gap value at the intersection obtained using the characteristic data (S105). . Further, the PC 21 can display the film thickness information on the storage unit 25 or the display unit.

  At this time, using this apparatus, each sample having a plurality of known film thicknesses is irradiated with P-polarized light, and P-polarized light propagation indicating the intensity of near-field photon response light with respect to the air gap value for each film thickness. Measure the light intensity distribution, and irradiate each sample of a plurality of film thicknesses whose thicknesses are known in advance with S-polarized light, and indicate the intensity of the near-field photon response light with respect to the air gap value for each film thickness. The S-polarized light intensity distribution is measured in advance. The PC 21 stores these propagation light intensity distributions in the storage unit 25. And PC21 calculates | requires the characteristic data which showed the film thickness with respect to the air gap value of the intersection of P polarization | polarized-light propagation light intensity distribution and S polarization | polarized-light propagation light intensity distribution based on reading propagation | transmission light intensity distribution from the memory | storage part 25, The characteristic data is stored in the storage unit. For characteristic data, see, for example, FIG.

  In this example, the characteristic data includes the first characteristic data when the P-polarized light is stronger than the S-polarized light and the second characteristic data when the S-polarized light is stronger than the P-polarized light with respect to the decrease or increase of the air gap. In addition, the PC 21 determines the film thickness according to the first and second characteristic data. However, the present invention is not limited thereto, and any one of the polarization characteristic data may be provided, and the film thickness may be measured using only the polarization characteristic data.

FIG. 9 shows a flowchart of the second embodiment for nondestructive film thickness measurement.
In the second embodiment, when obtaining the film thickness information, the propagation light intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value is measured as in the first embodiment (S201). Next, the PC 21 inputs various setting values determined for measuring the wavelength, the incident angle, the polarization, and the like (S203). Next, the PC 21 obtains the film thickness information of the measurement object 10 as follows based on the measured intensity of the near-field photon response light and the measured air gap value (S203).

  In this embodiment, the PC 21 reads out propagation light intensity distribution reference data indicating the intensity of the near-field photon response light with respect to the air gap value from the storage unit 25 for each known film thickness obtained in advance according to the set value. The propagation light intensity distribution reference data for each film thickness is compared with the measured propagation light intensity distribution, and the film thickness is obtained according to the similarity. With regard to the similarity, an appropriate correlation is taken, and reference distribution data having a predetermined film thickness can be specified by the correlation, similarity, dissimilarity, etc. of the distribution. See, for example, FIG. 19 (described later) and FIG. 6 for the propagation light intensity distribution reference data. Further, the PC 21 can display the film thickness information on the storage unit 25 or the display unit.

  At this time, using this apparatus, predetermined various set values are determined, laser light is irradiated to a plurality of film thicknesses whose thicknesses are known in advance, and the intensity of near-field photon response light with respect to the air gap value is indicated. The propagation light intensity distribution reference data is measured, and the PC 21 stores the propagation light intensity distribution reference data in the storage unit 25 for each film thickness corresponding to various setting values.

  Further, the P-polarized light propagation distribution indicating the intensity of the near-field photon response light with respect to the air gap value when irradiating the P-polarized light and / or the S-polarized light with respect to a plurality of film thicknesses that are known in advance Based on the S-polarized light propagation distribution indicating the intensity of the near-field photon response light with respect to the air gap value at the time of irradiation, the PC 21 can obtain the film thickness. See, for example, FIG. 6 for the propagation light intensity distribution.

  Note that the propagation intensity distribution and the reference data used in the first and second embodiments described above are data obtained as a result of measurement on a sample having a known film thickness by actually using this apparatus. However, the present invention is not limited to this, and distributions and data obtained by various settings by simulation may be used.

5). Details of Control and Measurement 5-1 Air Gap Control Program FIG. 10 is a diagram showing the air gap and the probe amplitude when the probe amplitude is attenuated due to the influence of the shear force.

  In this example, if the region (1), that is, the air gap is, for example, several hundred nm or more, the amplitude of the probe does not change. However, when the area (2), the air gap, is 50 nm or less, for example, the amplitude of the probe is attenuated. The air gap can be controlled by monitoring the amplitude of the probe in the region (2) and keeping the amplitude at a certain threshold. This is the principle of shear force control.

FIG. 11 shows a flowchart of the air gap control program. For example, the PC 21 executes the following processing.
The PC 21 monitors the amplitude of the tuning fork 14 with the lock-in amplifier 24 (S301). The PC 21 determines whether the amplitude is greater than or less than a threshold value (S303). If it is equal to or greater than the threshold value, the air gap is still large, so the PC 21 lowers the Z-axis piezo stage 13 by the controller 23 (S305). The PC 21 then returns to step S301 and basically repeats this operation. However, the stroke of the piezo stage 13 is, for example, 25 μm, and it is difficult to bring the air gap close to the working distance of the shear force. When the movable range becomes equal to or greater than a certain range (S307), for example, when the PC 21 moves to about half of the stroke, the PC 21 returns the piezo stage 13 to the origin by the controller 23 and lowers the same distance by the step 12 of the stepping motor (S309). .

  On the other hand, when the amplitude is equal to or smaller than the threshold value in step S303, that is, when the air gap is equal to or smaller than 50 nm, for example, the PC 21 stops the lowering of the tuning fork 14 and the Z coordinate at that time is stored in the storage unit 25. Writing to a file (S311), the tuning fork 14 is raised by a predetermined distance, for example, about 200 nm (S313). Thereafter, the PC 21 does not use the stepping motor stage 12 and raises and lowers the tuning fork 14 using only the piezo stage 13. This is because the stepping motor stage 12 is less accurate than the piezo stage 13 and the air gap may change significantly due to vibration.

  As described above, in the air gap control using the shear force, the oscillation circuit of the tuning fork that is a piezoelectric element is oscillated, and the probe is oscillated at the resonance frequency. The air gap is controlled by monitoring and feeding back the tuning fork amplitude with the air gap control program.

5-2 Tuning fork amplitude attenuation measurement by shear force Since the circuit oscillates even when the probe is sandwiched between tuning forks, in this embodiment, the probe is brought closer to the sample surface in the oscillated state, and the tuning fork amplitude is increased by shear force. Measure the decay.

FIG. 12 shows a relationship between the air gap and the tuning fork amplitude.
This figure shows the relationship between the air gap and the tuning fork amplitude when the probe is lowered by the Z-axis piezo stage while monitoring the tuning fork amplitude with the air gap control program.

  In the area (1) in the figure, where the air gap is sufficiently large, even if the probe is brought closer, the amplitude fluctuates due to the effect of electrical noise, but attenuation cannot be confirmed. When the area (2) and the air gap were 50 nm or less, the amplitude began to attenuate. As it was lowered, the amplitude became 0, and even when lowered further by 200 nm, the amplitude remained at 0. In this state, it was determined that the tip of the probe was hitting the sample, and the position where the amplitude first became 0 was defined as an air gap of 0 nm.

  From this result, it was found that the air gap can be controlled at a position of several tens of nanometers by setting a certain threshold value and stopping when the amplitude falls below that value. For example, the air gap can be stopped at a position around 25 nm by controlling the threshold value to 0.3.

5-3 Near-field light response detection program FIG. 13 shows a block diagram of a near-field light response detection program.
First, the PC 21 uses the above-described air gap control program to check the amplitude of the tuning fork 14 (S401), and closes the air gap to a certain value, for example, 50 nm or less (S403). When approaching a certain value, the descent is stopped and the PC 21 measures the air gap by writing the coordinate value at that time to a file in the storage unit 25 (S405). The PC 21 stops the piezo stage 13 and keeps the same coordinates (S407). Here, the PC 21 performs laser illumination with the light source 16, and the near-field light response (light reception intensity) detected by the light receiving unit 17 such as the PMT with the fiber probe 15 is transmitted to the lock-in amplifier 24, where lock-in detection is performed. The PC 21 reads the signal and writes it in a file in the storage unit 25 (S409). This is a series of work. Since the near-field light response detection is performed while changing the air gap, when a series of operations are completed, the coordinates are increased by a predetermined value, for example, several tens of nm (S411), and the same operations of steps S407 and S409 are repeated. Thus, the PC 21 detects the near-field light response while changing the air gap.

6). Modeling Analysis Here, the present embodiment is modeled into a form suitable for simulation analysis. Then, the electric field behavior at the probe tip is analyzed. First, we analyze the model without a thin film, and elucidate the mechanism of the electric field behavior near the sample. Next, we apply the mechanism to a model with a thin film, and analyze what electric field behavior occurs depending on the film thickness.

6-1 Modeling Below, modeling of this Embodiment is demonstrated.
FIG. 14 is an explanatory diagram of the simulation model.
In the FDTD simulation, since the analysis area is limited, it is not realistic to model the entire probe. Also, in this embodiment, in order to analyze in detail the electric field behavior at the probe tip and the electric field traveling inside the probe, the length of the probe itself is secured for several wavelengths, and the probe tip is several μm cubic Set the area as the analysis area. Actually, a fine pattern is engraved as shown in the figure, but in this paper, the purpose is to detect changes in the near-field light response due to the change in film thickness. . In other words, although it was impossible to measure a thin film thickness of 50 nm or less with the conventional method, a simulation analysis is performed for the purpose of showing that this method is possible.

  In general, the FDTD method (Finite Difference Time Domain method: time domain difference method) can analyze the electric field behavior in a micro area. In the FDTD method, an electromagnetic field is temporally and spatially arranged in the analysis region. That is, an analysis region is taken so as to surround the wave source and the scatterer, the entire analysis region is divided into cells, and Maxwell's partial differential equation is applied to all the cells and formulated. And it is an algorithm that advances the time step and calculates the electric and magnetic fields alternately. The basic algorithm at this time is the Yee algorithm.

6-2 Analysis of probe tip electric field behavior The electric field behavior of the probe tip is divided into two regions. The first is a region where the air gap exerted by the tip electric field is very small, and the second is a region where the air gap where the tip electric field is not effective is large. Thereafter, the mechanism of the tip electric field is estimated by dividing into these two regions.

(1) Region in which the air gap is very small FIG. 15 shows an explanatory diagram of the relationship between the air gap and the probe electric field.
It is considered that there are two factors in the interaction between the tip electric field and the probe electric field.
(A) When the air gap is increased, the shielding effect of the probe itself is reduced, and illumination is effectively performed from the outside, and the tip electric field is increased.
(B) Since the tip electric field is localized at the probe tip, if the air gap is too far away, the effect on the probe electric field is expected to decrease rapidly.

FIG. 16 is an explanatory diagram showing the effect of the tip electric field. In this figure, the above-mentioned (a) and (b) are put together to illustrate the effect on the probe electric field.
Regarding (i) in the figure, as the air gap increases, the shielding effect of the probe itself decreases and the tip electric field increases. When the distance is more than a certain distance, the external illumination on the probe tip constantly hits, and the strength of the tip electric field becomes constant. Regarding (ii), the effect on the probe electric field is attenuated as the air gap becomes larger than the localization of the tip electric field. The sum of these two effects is as shown in (iii). The probe electric field increases as the air gap increases. However, it becomes maximal at a certain air gap and then decays.

(2) Region with Large Air Gap FIG. 17 is a diagram showing the relationship between the interference wave caused by external illumination and the probe electric field. As shown in the figure, it is expected that the effect of the interference wave by the external illumination is increased in a region where the air gap is large.

FIG. 18 is an explanatory diagram showing the effect of interference waves caused by external illumination. The effects of interference from external illumination on the probe electric field are summarized as shown in the figure.
Regarding (i) in the figure, a constant interference wave is always generated by external illumination, and the state of interference is stable when viewed from the far field. However, considering the effect on the probe electric field as in (ii), when the air gap is small, the effect on the probe electric field is very small due to the shielding effect of the probe itself. However, as the air gap increases, the shielding effect of the probe itself decreases, and the effect on the probe electric field increases. It is considered that (iii) is obtained by combining these two points. When the air gap becomes larger and the effect of the tip electric field becomes smaller, the effect of external illumination gradually becomes larger and becomes dominant.

(3) Electric field at the probe tip Above, (1) The effect of the tip electric field in the region where the air gap is very small, (2) The effect of the interference wave due to external illumination in the region where the air gap is large, these two points are summarized. This will be the final probe electric field.

FIG. 19 is a diagram showing the relationship between the air gap and the probe electric field.
The effects of these two points are summarized as shown in the figure.
That is, when the air gap is small, the probe electric field is very small due to the shielding effect of the probe itself. As the air gap gradually increases, more external lighting is applied and the influence of the tip electric field becomes stronger. However, since the tip electric field is localized, the effect becomes smaller as the air gap becomes larger. After that, the influence of interference by external illumination becomes dominant. This is presumed to be the mechanism of the electric field behavior at the probe tip.

Next, FIG. 20 shows an explanatory diagram of the nature of the tip electric field (left is P-polarized light, right is S-polarized light, the upper figure is the horizontal viewpoint, and the lower figure is the upper viewpoint).
The changes in the behavior of the tip electric field due to the difference in polarization are summarized as shown in the figure.
That is, P-polarized light is polarized light whose electric field oscillates perpendicularly to the probe end surface, and it is considered that a tip electric field oscillating in that direction, that is, in the length direction of the probe is generated at the probe tip. Also, regarding the S-polarized light, the direction of vibration of the electric field is perpendicular to the P-polarized light, so it is considered that the tip electric field is also oscillating in the direction perpendicular to the P-polarized light. Although the state of vibration is different, both are electric fields localized at the tip, so the mechanism of the electric field behavior at the probe tip due to the difference in polarization is considered to be the same.

  FIG. 21 is a diagram showing the relationship between the air gap caused by polarized light and the probe electric field. The final signal strength summarizing the effects of polarization is as shown.

(4) Electric field behavior analysis in a model with a thin film Next, electric field behavior will be described according to simulation analysis in a model with a thin film. The simulation was performed by changing the film thickness and the air gap.

FIG. 22 shows a diagram of a simulation model when there is a thin film.
As shown in the figure, the probe electric field is analyzed by changing the film thickness. The film thickness was changed from 0 nm to 50 nm in increments of 10 nm, and the air gap was changed from 10 nm to 100 nm in increments of 10 nm. A simulation was performed for each of P-polarized light and S-polarized light, and the probe electric field was examined.

FIG. 23 is a diagram illustrating the intensity of the probe electric field in the P-polarized light and the S-polarized light when the film thickness is changed.
In this example, both the P-polarized light and the S-polarized light reach a maximum when the air gap is around 70 nm when the film thickness is 0 nm. Since the magnitude of the tip electric field depends on the probe tip diameter, it is localized in a region around 70 nm. In other words, it is a region where the influence of the advanced electric field is dominant.

  In a model with a thin film, it can be read that the graph shifts to the left with respect to the graph with a film thickness of 0 nm as the film thickness increases. The resist is more transparent to light than Si. Therefore, even if the thin film thickness changes, it is considered that it eventually depends on the distance from the Si surface. In other words, increasing the thickness of the thin film is considered to be synonymous with increasing the air gap by the increased thickness.

  Further, the degree of intensity change and the magnitude of shift differ depending on the difference in polarization. That is, with respect to the electric field behavior elucidated when the film thickness is 0 nm, the air gap and the graph shape that reach the peak value shift to the left as the film thickness increases.

7). Modifications (1) Modes of the near-field optical microscope The near-field optical microscope has the following various modes.
FIG. 24 is an explanatory diagram of fiber probe modes ((A) i mode, (B) c mode, (C) i-c mode).

  There are i mode (illumination mode), c mode (collection mode), and i-c mode (illumination-collection mode) modes depending on the method of condensing illumination.

  The i mode is a method in which light is incident on the probe, and evanescent light that has oozed out from the probe tip is scattered by the sample and received by an external detector. Since it is used in a general near-field optical microscope and can be focused by an optical system having a large numerical aperture, a highly sensitive response can be obtained. Used for processing and fluorescence analysis.

  The c mode is generally a method of illuminating a sample with total reflection, scattering evanescent light generated on the sample with a probe, and condensing the scattered light with the probe. Evanescent light with less noise can be detected and high contrast can be obtained. Used for living body observation. Further, in c mode, when the sample stage is made of Si or the like and is opaque, illumination is performed from outside the top.

  The i-c mode is a method in which light is incident on the probe, evanescent light oozing from the probe tip is scattered by the sample, and detected by the probe. It is used for spectroscopic analysis of an opaque sample stage.

  In the above-described embodiment, the c mode has been particularly described. However, the present invention may be appropriately realized by other modes such as i mode and i-c mode. For example, in the case of i mode, it can be realized by replacing the arrangement of the light receiving unit (detector) 17 and the light source 16 with respect to the fiber 15 as illustrated. In the case of i-c mode, light may be irradiated from the light source 16 to the measurement object 10 via the fiber 15.

(2) Metal Scattering Probe In addition to the above three probe modes, a metal scattering probe as shown in FIG. In this case, for example, the light source 16 and the light receiving unit (detector) 17 can be arranged as shown in the drawing, and a metal-like probe 15 can be used instead of the fiber probe 15.

(3) Utilization of only one of S-polarized light and P-polarized light Depending on the target film thickness range, it is possible to measure the film thickness by measurement using one of S-polarized light or P-polarized light.

  In other words, the non-destructive film thickness measurement technology for ultra-thin residual film using near-field photons according to the present invention is positioned as an indispensable industrial technology seed to meet the industrial needs of applying nanoimprint technology to semiconductor processes. Can do.

  In addition, the present invention is not limited to the industrial seeds that are indispensable in the practical application of nanoimprint technology to semiconductor processes, but can also be regarded as having industrial seeds as an in-process sampling measurement evaluation technology after practical application. It is.

The conceptual diagram of a film thickness measuring apparatus. Explanatory drawing of shear force. The figure of the amplitude detection method using a tuning fork. The conceptual diagram about the principle of film thickness measurement. Explanatory drawing of the principle of a probe. The figure which put together the relationship between the air gap and probe electric field in P polarization | polarized-light and S polarization | polarized-light for every film thickness. (A) Relationship between air gap and film thickness reversed so that the intensity of P-polarized light becomes stronger, and (b) Relation between air gap and film thickness reversed so that the intensity of S-polarized light becomes stronger. Figure. The flowchart of 1st Embodiment about nondestructive film thickness measurement. The flowchart of 2nd Embodiment about nondestructive film thickness measurement. The figure which showed the air gap and the amplitude of a probe when the amplitude of a probe attenuate | damps by the influence of a shear force. The flowchart of an air gap control program. The figure of the relationship between an air gap and the amplitude of a tuning fork. The block diagram of a near-field light response detection program. Explanatory drawing of a simulation model. Explanatory drawing of the relationship between an air gap and a probe electric field. Explanatory drawing about the effect of a tip electric field. The figure which shows the relationship between the interference wave by external illumination, and a probe electric field. Explanatory drawing about the effect of the interference wave by external illumination. The figure which shows the relationship between an air gap and a probe electric field. Explanatory drawing about the nature of the tip electric field (left is P-polarized light, right is S-polarized light, upper figure is horizontal viewpoint, lower figure is upper viewpoint). The figure which shows the relationship between the air gap by polarization, and a probe electric field. The figure of the simulation model when there is a thin film. The figure which shows the intensity | strength of the probe electric field in P polarized light and S polarized light when changing a film thickness. Explanatory drawing of the mode ((A) i mode, (B) c mode, (C) i-c mode) of a fiber probe. Explanatory drawing of the remaining film in nanoimprint.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Near field light response detection optical system 2 Near field light response control system 11 Stage 12 Stage 13 Stage 14 Tuning fork 15 Probe (fiber probe)
16 Light source 17 Light receiver 21 Computer (PC)
22 Stepping motor controller 23 Fine movement stage controller 24 Lock-in amplifier 25 Storage unit

Claims (16)

Irradiate the measurement target with a light source
Bring the near-field optical probe closer to the surface to be measured,
Measure the air gap value between the object to be measured and the near-field optical probe,
By making the measurement object exist in the near-field photon localized region formed at the tip of the near-field optical probe, the interaction between the dipole at the tip of the near-field probe and the dipole in the substance to be measured To generate a near-field photon field, and emit a near-field photon response light that is a propagating light corresponding to the near-field photon field,
Measure the near-field photon response light,
A nondestructive film thickness measurement method for obtaining film thickness information of a measurement object based on the measured intensity of the near-field photon response light and the measured air gap value. Irradiate P-polarized light, measure the P-polarized light propagation distribution indicating the intensity of the near-field photon response light against the air gap value,
Irradiate S-polarized light, measure the S-polarized light propagation distribution indicating the intensity of the near-field photon response light with respect to the air gap value,
The processing unit obtains the air gap value at the intersection of the P-polarized light propagation intensity distribution and the S-polarized light intensity distribution,
The processing unit reads predetermined characteristic data indicating a film thickness with respect to an air gap value at the intersection from the storage unit, and obtains film thickness information according to the obtained air gap value at the intersection. The nondestructive film thickness measuring method described. Irradiate each sample of a plurality of known film thicknesses with P-polarized light, measure the P-polarized light propagation intensity distribution indicating the intensity of near-field photon response light with respect to the air gap value for each film thickness,
S-polarized light is irradiated to each sample of a plurality of thicknesses that are known in advance, and an S-polarized light intensity distribution indicating the intensity of near-field photon response light with respect to the air gap value is measured for each thickness. ,
The processing unit obtains characteristic data indicating a film thickness with respect to an air gap value at an intersection of the P-polarized light propagation intensity distribution and the S-polarized light intensity distribution, and stores the characteristic data in the storage unit. Item 3. The nondestructive film thickness measuring method according to Item 2. The characteristic data includes first characteristic data when P-polarized light is stronger than S-polarized light and second characteristic data when S-polarized light is stronger than P-polarized with respect to the decrease or increase of the air gap,
The nondestructive film thickness measurement method according to claim 3, wherein the processing unit determines the film thickness according to the first and second characteristic data. When finding film thickness information,
Measure the propagation light intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value,
The processing unit reads propagation light intensity distribution reference data indicating the intensity of the near-field photon response light with respect to the air gap value from the storage unit for each known film thickness obtained in advance, and refers to the propagation light intensity distribution for each film thickness. The nondestructive film thickness measuring method according to claim 1, wherein the film thickness is determined according to the similarity by comparing the data with the measured propagation light intensity distribution. Irradiate light to a plurality of film thicknesses whose thicknesses are known in advance, measure propagation light intensity distribution reference data indicating the intensity of near-field photon response light with respect to the air gap value,
The nondestructive film thickness measuring method according to claim 5, wherein the processing unit stores the propagation light intensity distribution reference data in the storage unit for each film thickness.   P-polarized light intensity distribution indicating the intensity of near-field photon response light with respect to the air gap value when P-polarized light is irradiated and / or S-polarized light with respect to a plurality of film thicknesses that are known in advance. The nondestructive film thickness measuring method according to claim 5, wherein the processing unit obtains the film thickness based on the S-polarized light propagation light intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value. The nondestructive film thickness measuring method according to claim 1, wherein one of the following is used as a measurement mode by the near-field optical probe.
(1) A microfiber aperture illumination mode that uses a near-field optical probe with a sharp tip to illuminate a measurement target and propagate and detect scattered light from the limited region in free space;
(2) Illuminate the object to be measured with free-space propagating light, use a near-field optical probe with a sharp tip, convert the near-field from the limited area of the object to be measured into propagating light, and propagate the probe to detect it Microfiber aperture type collection mode, or
(3) Using a near-field optical probe with a sharp tip, subject the measurement object to limited illumination, and also use the illumination near-field optical probe for detection, and convert the near-field from the measurement target limited area to propagating light. , Illumination collection mode of microfiber aperture type that is detected by propagating inside the probe   The nondestructive film thickness measuring method according to claim 1, wherein the near-field optical probe is of a metal scattering probe type.   The nondestructive film thickness measuring method according to claim 1, wherein the processing unit obtains the air gap value by shear force control using a tuning fork coupled to the near-field optical probe.   The non-destructive film thickness measuring method according to claim 1, wherein the measurement target is a nanoimprint ultrathin residual film for a semiconductor. A light source that illuminates the measurement object;
A near-field optical probe for detecting the near-field photon response light by approaching the surface of the measurement object;
An air gap measuring unit for measuring an air gap value between the measurement object and the near-field optical probe;
A light receiving unit for measuring the near-field photon response light detected by the near-field light probe;
By making the measurement object exist in the near-field photon localized region formed at the tip of the near-field optical probe, the interaction between the dipole at the tip of the near-field probe and the dipole in the substance to be measured A near-field photon field is generated by, and a near-field photon response light that is a propagating light corresponding to the near-field photon field is emitted, and the intensity of the near-field photon response light measured by the light receiving unit is measured. A nondestructive film thickness measuring apparatus comprising: a processing unit that obtains film thickness information of a measurement object based on the air gap value. A storage unit that stores propagation light intensity distribution reference data indicating the intensity of near-field photon response light with respect to the air gap value for a plurality of film thicknesses that are known in advance,
The nondestructive film thickness measuring apparatus according to claim 12, wherein the processing unit obtains a film thickness with reference to the storage unit. A polarization unit that converts irradiation from the light source into P-polarized light or S-polarized light;
P-polarization propagation light intensity distribution indicating the intensity of near-field photon response light with respect to the air gap value for each film thickness when irradiated with P-polarized light by the polarizing section, and / or for each film thickness when irradiated with S-polarized light A storage unit storing an S-polarized light propagation intensity distribution indicating the intensity of the near-field photon response light with respect to the air gap value;
The nondestructive film thickness measuring apparatus according to claim 12, wherein the processing unit obtains a film thickness with reference to the storage unit. The storage unit further stores characteristic data indicating the film thickness with respect to the air gap value at the intersection of the P-polarized light propagation intensity distribution and the S-polarized light intensity distribution,
The nondestructive film thickness measuring apparatus according to claim 12, wherein the processing unit obtains a film thickness based on an intersection point indicated by the characteristic data. A tuning fork coupled to the near-field optical probe;
The nondestructive film thickness measuring apparatus according to claim 12, wherein the processing unit obtains an air gap value by shear force control using the tuning fork.