KR101907965B1 - Dynamically or adaptively tracking spectrum features for endpoint detection - Google Patents

Abstract

A method of controlling polishing includes polishing a substrate and receiving an identification of a selected spectral feature, a wavelength range having a width, and a characteristic of the selected spectral feature for monitoring during polishing. While the substrate is being polished, a sequence of spectra of light from the substrate is measured. A sequence of values of the characteristics of the selected spectral feature is generated from the sequence of spectra. For at least some of the spectra from a sequence of spectra, a modified wavelength range is generated based on the location of the spectral feature within the previous wavelength range used for the previous spectrum in the sequence of spectra, The selected wavelength range is searched for the selected spectral feature, and the value of the characteristic of the selected spectral feature is determined.

Description

[0001] DYNAMICALLY OR ADAPTIVELY TRACKING SPECTRUM FEATURES FOR ENDPOINT DETECTION [0002] FIELD OF THE INVENTION [0003]

The present disclosure relates to optical monitoring during chemical mechanical polishing of substrates.

An integrated circuit is typically formed on a substrate by sequentially depositing a conductive layer, a semi-conductive layer, or an insulating layer on a silicon wafer. One fabrication step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive filler layer may be deposited on the patterned insulating layer to fill the trenches or holes in the insulating layer. After planarization, portions of the conductive layer that remain between the raised patterns of the insulating layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains on the non-planar surface. In addition, planarization of the substrate surface is generally required for photolithography.

Chemical mechanical polishing (CMP) is one acceptable planarization method. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. Typically, the exposed surface of the substrate is disposed relative to the rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. An abrasive polishing slurry is typically supplied to the surface of the polishing pad.

One problem with CMP is to determine whether the polishing process is complete, i.e. whether the substrate layer has been flattened to the desired flatness or thickness, or when the desired amount of material has been removed. The slurry dispensing, polishing pad conditions, the relative speed between the polishing pad and the substrate, and variations in load on the substrate can result in variations in material removal rate. These variations as well as variations in the initial thickness of the substrate layer cause variations in the time required to reach the polishing endpoint. Accordingly, the polishing end point can not be determined simply as a function of polishing time.

In some systems, the substrate is optically monitored in-situ during polishing, e.g., through a window in a polishing pad. However, existing optical monitoring techniques may not satisfy the growing demands of semiconductor device manufacturers.

Some optical endpoint detection systems track selected spectral feature characteristics in spectral measurements to determine an end point or to vary the polishing rate. In the spectrum, spectral features similar to the selected spectral feature may make it difficult to track the selected spectral feature. Once the wavelength range is identified for the optical endpoint detection system to search for the selected spectral feature, such an optical endpoint detection system will be able to accurately identify the selected spectral feature with reduced processing resources.

In some polishing processes, a second layer of a second material, for example a barrier layer, such as a nitride, for example tantalum nitride or titanium nitride, is removed from the substrate to form another first material, for example a dielectric material, Exposes a first layer or layer structure comprising a low-k material and / or a low-k cap material. Often, it is required to remove the first material until the target thickness remains. Some optical endpoint detection techniques that track selected spectral feature characteristics in spectral measurements to determine an endpoint or to change the polishing rate have problems in their polishing process because they are not well known for the initial thickness of the second material . These problems, however, can be solved by other monitoring techniques that can reliably detect the removal of the second material and exposure of the underlying layer or layer structure, for example, by motor torque, eddy current, or optical intensity monitoring, If triggered, can be avoided. Also, for the thickness of the layer or layer structure, there may be substrate-to-substrate variations (deviation from substrate to substrate). In order to improve the substrate-to-substrate uniformity of the final thickness of the layer or layer structure, the initial thickness of the layer or layer structure can be measured prior to polishing and the target feature value is calculated from this initial thickness and the target thickness .

In one aspect, a method of controlling polishing includes polishing a substrate, receiving an identification of a selected spectral feature, a wavelength range having a width, and a characteristic of the selected spectral feature for monitoring during polishing . While the substrate is being polished, a sequence of spectra of light from the substrate is measured. A sequence of values of a characteristic of a selected spectral feature is generated from a sequence of spectra. Such generating may comprise calculating a modified wavelength range based on the location of the spectral feature within the previous wavelength range used for the previous spectrum in the sequence of spectra, for at least some spectrums from the sequence of spectra Searching the modified wavelength range for the selected spectral feature, and determining the value of the property of the selected spectral feature. At least one of the adjustment to the polishing endpoint or the polishing rate is determined based on the sequence of values.

Implementations may include one or more of the following features. The wavelength range may have a fixed width. The step of creating a modified wavelength range may include centering the fixed width at a position of the characteristic within the previous wavelength range. The step of generating a modified wavelength range includes determining the position of the characteristic within the previous wavelength range and adjusting the wavelength range so that the characteristic is located closer to the center of the modified wavelength range in the modified wavelength range Step < / RTI > The step of generating a modified wavelength range includes determining a wavelength value for the selected spectral feature for at least a portion of the spectra in the sequence of spectra to produce a sequence of wavelength values, And calculating an expected wavelength value for the selected spectral feature for subsequent spectral measurements from the function. The function may be a linear function. The step of creating a modified wavelength range may include centering the width of the wavelength range to the expected wavelength value. The method may include fitting a function to a sequence of values and determining at least one of an adjustment to a polishing endpoint or a polishing rate based on the function. Wherein determining the polishing endpoint comprises: calculating an initial value of a characteristic from the function; calculating a current value of a characteristic from the function; calculating a difference between the initial value and the current value; Stopping the polishing when the target difference has reached the target difference. The function may be a linear function. The selected spectral feature may comprise spectral peak, spectral valley, or spectral zero-crossing. The characteristics may include wavelength, width, or intensity. The selected spectral feature may comprise a spectral peak, and the characteristic may comprise a peak width. The spectra can be measured for visible light, and the wavelength range can have a width of 50 to 200 nanometers.

In another aspect, a method of controlling polishing includes: receiving a user input that selects a fixed wavelength range that is a subset of the wavelengths measured by the in-situ monitoring system; Receiving an identifier of the selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing; Polishing the substrate; Measuring a sequence of spectra of light from the substrate while the substrate is being polished; For each spectrum in the sequence of spectra, determining a value of a property of the selected spectral feature to search for a fixed wavelength range of each spectrum for the selected spectral feature and to generate a sequence of values; And determining at least one of an adjustment to a polishing endpoint or a polishing rate based on the sequence of values.

Implementations may include one or more of the following features. The in-situ monitoring system may measure the intensity of wavelengths including at least visible light, and the fixed wavelength range may have a width of 50 to 200 nanometers. The selected spectral feature may be a spectral peak, a spectral valley, or a spectral code transition point. The characteristic may be wavelength, width or intensity.

In another aspect, a method of controlling polishing includes: polishing a substrate having a first layer; Receiving an identifier of the selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing; Measuring a sequence of spectra of light from the substrate while the substrate is being polished; Determining a first value for a characteristic of the feature at a time when the first layer is exposed; Adding an offset to the first value to produce a second value; And monitoring the characteristic of the feature, and aborting the polishing when it is determined that the characteristic of the feature has reached the second value.

Implementations may include one or more of the following features. The characteristic may be position, width or intensity. The selected feature may be persisted with a location, width, or intensity evolving through a sequence of spectra. The feature may be a peak or a valley of the spectrum. The substrate may comprise a second layer overlying the first layer, the polishing may comprise polishing the second layer, and the exposure of the first layer may be detected with an in-situ monitoring system have. The first value may be determined at a time when the in-situ monitoring system detects the exposure of the first layer. Detecting the exposure of the first layer may be a separate process from monitoring the characteristics of the features. Detecting the exposure of the first layer may include monitoring the total reflection intensity from the substrate. Monitoring the total reflection intensity may include, for each spectrum in the sequence of spectra, integrating the spectrum over a wavelength range to produce a total reflection intensity. The in-situ monitoring system may include a motor torque or friction monitoring system. The first value can be determined instantaneously during the polishing of the first layer, for example at the beginning of polishing of the first layer. The first layer may be exposed before the polishing of the substrate begins. Monitoring the characteristics of the feature may comprise determining, for each spectrum from the sequence of spectra, a value of the property to generate a sequence of values. By fitting a linear function to a sequence of values and determining an end-point time at which the linear function equals a second value, it can be determined that the characteristic of the feature has reached the second value. The polishing-total thickness of the first layer can be received, and an offset value can be calculated from the polishing-total thickness. It calculates an offset value _{(ΔV) (D 2 - d} T) / may include calculating a (dD / dV), and the d _T is the target thickness, D ₁ is the first layer from the set-up substrate Polish-pre-thickness, D ₂ is the post-polishing thickness of the first layer from the set-up substrate, and dD / dV is the rate of change in thickness as a function of the properties. Calculating the offset value? V may include calculating? V =? V _D + (d ₁ -D ₁ ) / (dD / dV) + (D ₂ -d _T ) / (dD / dV) Wherein D ₁ is the polishing-total thickness, D ₁ is the polishing-total thickness of the first layer from the set-up substrate, and ΔV _D is the thickness of the first layer of the set- This is the difference in the value of the characteristic of the feature. The polishing-total thickness (d ₁ ) can be measured at an individual measuring station. The rate of change in thickness (dD / dV) as a function of the characteristic may be the rate of change in thickness near the end of polishing. The first layer may comprise polysilicon and / or dielectric material, for example, substantially pure polysilicon, a dielectric material, or a combination of polysilicon and dielectric material.

Implementations may optionally include one or more of the following advantages. By identifying the wavelength range for searching for the selected spectral feature characteristics, the accuracy in determining the endpoint detection or the rate of change of the polishing rate can be higher, for example, the possibility of the system to select an incorrect spectral feature during subsequent spectral measurements . By tracking spectral features within a wavelength range instead of tracking across the entire spectrum, spectral features can be more easily and more quickly identified. The processing resources required to identify the selected spectral features can be reduced.

The time it takes for semiconductor manufacturers to develop an algorithm for detecting the end point of a particular product substrate can be shortened. Spectral feature tracking can be applied for polishing operations that begin with polishing of the reflective layer, and wafer-to-wafer thickness uniformity (WTWU) can be improved. The initial thickness of the layer can be measured prior to polishing and the target feature value can be calculated from the initial thickness and the target thickness to provide a more accurate end point determination.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description, drawings, and claims.

Figure 1 shows a chemical mechanical polishing apparatus.
Figure 2 is an overhead view of a polishing pad showing locations where in-situ measurements are performed.
Figure 3A shows a spectrum obtained from in-situ measurements.
Figure 3B shows the evolution of the spectra obtained from the in-situ measurements as the polishing progresses.
4A shows an exemplary graph of the spectrum of light reflected from a substrate.
4B shows the graph of FIG. 4A passed through a high pass filter.
5A shows the spectrum of light reflected from the substrate.
Figure 5B shows a contour plot of the spectra obtained from in-situ measurements of light reflected from the substrate.
FIG. 6A shows an exemplary graph of the progress of polishing, measured in terms of characteristic differential versus time.
FIG. 6B shows an exemplary graph of the polishing progress, measured in terms of characteristic difference versus time, in which properties of two different features are measured to adjust the polishing rate of the substrate.
Figure 7a shows another spectrum of light obtained from in-situ measurements.
Figure 7b shows the spectrum of light obtained after the spectrum of Figure 7a.
Figure 7c shows another spectrum of light obtained after the spectrum of Figure 7a.
Figure 8 shows a method for selecting peaks for monitoring.
Figure 9 illustrates a method for obtaining target parameters for a selected peak.
Figure 10 shows a method for determining an end point.
11 shows a setting method for end point detection.
Figure 12 shows another method for determining an end point.
Figure 13 shows a graph showing the total reflected intensity as a function of time during polishing.
Figure 14 shows a graph showing the wavelength location of the spectral peak as a function of time during polishing.
Like reference numbers and designations in the various drawings indicate like elements.

One optical monitoring technique is to measure the spectra of light reflected from the substrate during polishing and to identify the matching reference spectra from the library. One potential problem with the spectral matching approach is that, for some types of substrates, there are significant substrate-to-substrate differences in the underlying die features, resulting in an apparently the same outer layer thickness Resulting in variations in the spectra reflected from the substrates. These variations increase the difficulty of proper spectral matching and reduce the reliability of optical monitoring.

One technique for eliminating this problem is to measure the spectra of light reflected from the substrates being polished and to identify changes in spectral feature characteristics. Tracking changes in the characteristics of the features of the spectrum, e.g., the wavelengths of the spectral peaks, may enable greater uniformity in polishing between substrates in a batch. By determining the target difference in the spectral feature characteristics, the end point can be called (i.e., called an end point) when the value of the characteristic has changed by the target amount.

The substrate may have a simple, or significantly more complex, layer stack, such as a single dielectric layer disposed on the semiconductor layer. For example, the substrate may comprise a first layer and a second layer disposed over the first layer. The first layer is a dielectric, such as oxide, or carbon-doped silicon dioxide, such as silicon dioxide, for example, (Applied Materials, Inc. of from) Black Diamond ^TM or (Novellus Systems, Inc. of from) Coral ^Lt; RTI ID = 0.0 > ^TM . ≪ / RTI > The second layer may be a barrier layer of a composition different from that of the first layer. For example, the barrier layer may be a metal or a metal nitride, such as tantalum nitride or titanium nitride. A material formed from one or more additional layers, e.g., a low-k capping material, such as tetraethylorthosilicate (TEOS), is selectively disposed between the first and second layers. Both the first and second layers are at least semi-transparent. The first layer and one or more additional layers (if present) together provide a layer stack below the second layer. However, in some embodiments, only a single layer comprising, for example, polysilicon and / or dielectric is polished (although additional layers may be present below the layer being polished).

The chemical mechanical polishing may be used to planarize the substrate until the second layer is exposed. For example, if an opaque conductive material is present, this conductive material may be polished until the second layer, e.g., the barrier layer, is exposed. Thereafter, the remaining portion of the second layer over the first layer is removed, and the substrate is polished until the first layer, e.g., the dielectric layer, is exposed. It is also often desired to polish the first layer, for example the dielectric layer, until the target thickness remains or until the target amount of material is removed.

One polishing method is to polish the conductive layer on the first polishing pad until at least the second layer, e. G., The barrier layer, is exposed. Also, a portion of the thickness of the second layer may be removed, for example during an overpolishing step at the first polishing pad. Thereafter, the substrate is transferred to a second polishing pad, where the second layer, for example the barrier layer, is completely removed, and a portion of the lower first layer, for example the thickness of the low-k dielectric, is also removed . Also, if additional layers or layers are present between the first and second layers, such additional layers or layers may be removed in the same polishing operation at the second polishing pad.

However, when the substrate is transferred to the second polishing pad, the initial thickness of the second layer may not be known. As described above, if the initial thickness of the second layer is not known, problems may arise with optical endpoint detection techniques that track spectral feature characteristics selected in spectral measurements to determine an endpoint at the target thickness. However, this problem can be reduced if spectral feature tracking is triggered by other monitoring techniques that can reliably detect the removal of the second layer and the exposure of the underlying first layer or layer structure. In addition, the substrate-to-substrate uniformity of the thickness of the first layer can be improved by measuring the initial thickness of the first layer and by calculating the target feature value from the target thickness and initial thickness for the first layer.

Spectral features may include spectral peaks, spectral valleys, spectral inflection points, or spectral code transition points. The characteristics of the features may include wavelength, width, or intensity.

Figure 1 shows a polishing apparatus 20 that can be operated to polish a substrate 10. The polishing apparatus 20 includes a rotatable disk-shaped platen 24 on which a polishing pad 30 is located. The platen may be actuated to rotate about an axis 25. For example, the motor may rotate the drive shaft 22 to rotate the platen 24. [ The polishing pad 30 may be releasably secured to the platen 24 by, for example, an adhesive layer. When worn, the polishing pad 30 can be removed and replaced. The polishing pad 30 may be a double-layered polishing pad having an outer polishing layer 32 and a softer backing layer 34.

By including an opening (i.e., a hole extending through the pad) or a solid window, an optical access 36 through the polishing pad is provided. Although the solid window can be fixed to the polishing pad, in some embodiments, such a solid window can be supported on the platen 24 and protrude into the opening in the polishing pad. The polishing pad 30 is generally placed on the platen 24 so that the opening or window is placed on the optical head 53 located in the recess 26 of the platen 24. [ As a result, the optical head 53 has an optical path through the opening or window with respect to the substrate to be polished.

The window can be, for example, a rigid crystalline or glassy material, such as quartz or glass, or a more flexible plastic material such as silicon, polyurethane or a halogenated polymer (e.g., a fluoropolymer ), Or a combination of the foregoing materials. The window may be transparent to white light. If the upper surface of the solid window is a rigid crystalline or glassy material, this upper surface must be sufficiently recessed from the polishing surface to prevent scratching. If the upper surface is allowed to contact such a polishing surface in close proximity to the polishing surface, the upper surface of the window should be a more flexible plastic material. In some embodiments, the solid window is fixed within the polishing pad, and is a polyurethane window, or a window having a combination of quartz and polyurethane. The window may have a high transmittance, for example about 80% transmittance, for monochromatic light of a particular color, for example blue light or red light. The window may be sealed to the polishing pad 30 so that no liquid leaks through the boundary of the window and the polishing pad 30.

In one embodiment, the window comprises a rigid crystalline or glassy material covered with an outer layer of a more ductile plastic material. The upper surface of the softer material may be flush with the polishing surface. The lower surface of the rigid material may be coplanar with the lower surface of the polishing pad, or may be recessed with respect to the lower surface of the polishing pad. In particular, if the polishing pad comprises two layers, the solid window can be integrated into the polishing layer, and the lower layer can have openings aligned with the solid window.

The lower surface of the window may optionally include one or more recesses. The recess may be formed, for example, to accommodate the end of the fiber optic cable or the end of the eddy current sensor. The recess allows the end of the fiber optic cable or the end of the eddy current sensor to be positioned at a distance less than the window thickness from the substrate surface being polished. In embodiments in which the window comprises a crystalline or glass like portion of rigidity and the recess is formed in this portion by machining, the recesses are removed to remove the scratches caused by machining Polished. Alternatively, solvent and / or liquid polymer may be applied to the surfaces of the recess to remove scratches caused by machining. Removal of scratches, typically caused by machining, can reduce scattering and increase the transmission of light through the window.

The backing layer 34 of the polishing pad can be attached to its outer polishing layer 32, for example, by an adhesive. An opening that provides an optical access path 36 may be formed in the pad 30 by cutting or molding the pad 30 to include, for example, such an opening, and a window may be inserted into the opening, To the pad 30 by an adhesive. Alternatively, the liquid precursor of the window may be dispensed into the openings in the pad 30 and cured to form a window. Alternatively, a solid transparent element, such as a crystalline or glass-like portion as described above, can be placed in the liquid pad material and the liquid pad material can be cured to form the pad 30 around the transparent element. In either of the later two cases, a block of pad material can be formed, and a layer of polishing pad having a molded window can be scythe from the block.

The polishing apparatus 20 comprises a combined slurry / rinse arm 39. During polishing, the arm 39 may be actuated to dispense a slurry 38 comprising a liquid and a pH adjuster. Alternatively, the polishing apparatus includes a slurry port that can be operated to dispense the slurry on the polishing pad 30.

The polishing apparatus 20 includes a carrier head 70 that can be operated to hold the substrate 10 against the polishing pad 30. [ The carrier head 70 is suspended from the support structure 72, e.g., a carousel and is connected to the carrier head rotation motor 76 by a carrier drive shaft 74, Can be rotated about the axis 71. [0064] In addition, the carrier head 70 may oscillate laterally within the radial slot formed in the support structure 72. In operation, the platen is rotated about its central axis 25, and the carrier head is rotated about its central axis 71 and laterally transversely across the upper surface of the polishing pad do.

The polishing apparatus also includes an optical monitoring system that can be used to determine a polishing endpoint as described below. The optical monitoring system includes a light source 51 and a photodetector 52. Light passes from the light source 51 through the optical access path 36 in the polishing pad 30 and impinges on the substrate 10 and is reflected from the substrate 10 and again passes through the optical access path 36 , And then to the photodetector (52).

A bifurcated optical cable 54 may be used to transfer light from the light source 51 to the optical access path 36 and back to the optical detector 52 from the optical access path 36. This bifurcated optical cable 54 may include a "trunk" 55 and two "branches" 56 and 58.

As described above, the platen 24 includes a recess 26 in which the optical head 53 is located. The optical head 53 holds one end of the trunk 55 of the bifurcated fiber cable 54 and the cable is configured to transmit light to and from the substrate surface to be polished. The optical head 53 may include one or more lenses or windows that rest on the end of the bifurcated fiber cable 54. Alternatively, the optical head 53 may only hold the end of the trunk 55 close to the solid window in the polishing pad. The optical head 53 can be removed from the recess 26 as needed, for example, to perform preventive maintenance or corrective maintenance.

The platen includes a removable in-situ monitoring module 50. The in-situ monitoring module 50 may include one or more of the following: a light source 51, a light detector 52, and a light source 51 and a light detector 52, And one or more of a network for transmitting and receiving signals from the light source 51 and the photodetector 52. For example, the output of the detector 52 may be a digital electronic signal that is transmitted to a controller for the optical monitoring system via a rotating coupler in the drive shaft 22, e.g., a slip ring. Similarly, the light source may be turned on or off in response to control commands in the digital electronic signals transmitted from the controller to the module 50 via the rotary coupler.

The in-situ monitoring module 50 may also hold the respective ends of the branch portions 56 and 58 of the bifurcated optical fiber 54. The light source can be operated to transmit light, which is transmitted through the branch 56, exits the end of the trunk 55 located in the optical head 53, and impinges on the substrate being polished. Light reflected from the substrate is received at the end of the trunk 55 located in the optical head 53 and is transmitted to the photodetector 52 through the branch 58.

In one embodiment, the bifurcated fiber cable 54 is a bundle of optical fibers. These bundles include a first group of optical fibers and a second group of optical fibers. The optical fibers in the first group are connected to transmit light from the light source 51 to the substrate surface being polished. The optical fibers in the second group are coupled to receive the light reflected from the substrate surface being polished and to transfer the received light to the optical detector 52. The optical fibers may be arranged such that the optical fibers in the second group form an X-like shape, and the X-shaped configuration (as viewed in cross section of the bifurcated fiber cable 54) Is centered on the longitudinal axis of the optical fiber (54). Alternatively, other arrangements may be implemented. For example, the optical fibers in the second group may form V-shaped shapes that are mirror images of each other. Suitable bifurcated optical fibers are available from Verity Instruments, Inc. of Carrollton, Texas, USA.

Generally, there is an optimum distance between the polishing pad window and the end of the trunk 55 of the bifurcated fiber cable 54 near the polishing pad window. This distance can be determined experimentally and is influenced by, for example, the reflectivity of the window, the shape of the light beam emitted from the bifurcated fiber cable, and the distance to the monitored substrate. In one embodiment, the bifurcated fiber cable is positioned so as to be as close as possible to the lower end of the window, while the end near the window does not actually contact the window. In this embodiment, the polishing apparatus 20 can be operated to adjust the distance between the end of the bifurcated fiber cable 54 and the lower surface of the polishing pad window, for example as part of the optical head 53 Which may include mechanisms. Alternatively, an end near the bifurcated fiber cable 54 is embedded within the window.

The light source 51 may be operated to emit white light. In one embodiment, the emitted white light comprises light having wavelengths of 200-800 nanometers. A suitable light source is a xenon lamp or a xenon-mercury lamp.

The photodetector 52 may be a spectrometer. A spectrometer is basically an optical instrument for measuring the properties of light, e.g. intensity, over a portion of the electromagnetic spectrum. A suitable spectrometer is a grating spectrometer. A typical output for a spectrometer is the intensity of light as a function of wavelength.

The light source 51 and the photodetector 52 are coupled to a computing device that can be controlled to control their operation and receive their signals. The computing device may include a microprocessor located near the polishing apparatus, for example a personal computer. In connection with the control, the computing device may, for example, synchronize the activation of the light source 51 with the rotation of the platen 24. As shown in FIG. 2, the computer may cause the light source 51 to emit a series of flashes that terminate immediately after the substrate 10 begins to pass over the in-situ monitoring module 50 Can be released. Each of the dots 201-211 represents a position where light from the in-situ monitoring module 50 collides with and reflects on the substrate 10. [ Alternatively, the computer may cause the light source 51 to initiate immediately before passing the substrate 10 onto the in-situ monitoring module 50 and successively to emit light that terminates immediately after passing.

As the polishing progresses, for example, spectra obtained from successive sweeps of the sensor in the platen across the substrate provide a sequence of spectra. In some embodiments, the light source 51 emits a series of flashes of light onto a plurality of portions of the substrate 10. For example, the light source may emit flashes of light onto the central portion of the substrate 10 and onto the outer portion of the substrate 10. [ Light reflected from the substrate 10 may be received by the photodetector 52 to determine a plurality of sequences of spectra from multiple portions of the substrate 10. As features can be identified in the spectra, each feature is associated with a portion of the substrate 10. These features may be used, for example, in determining the endpoint conditions for polishing the substrate 10. In some embodiments, the polishing rate for one or more portions of the substrate 10 can be varied by monitoring portions of the substrate 10.

In connection with receiving signals, the computing device may receive a signal carrying information describing, for example, the spectrum of the light received by the optical detector 52. Figure 3A shows examples of spectra measured from light emitted from a single flash of a light source and reflected from a substrate. Spectrum 302 is measured from light reflected from the product substrate. Spectrum 304 is measured from light reflected from a base silicon substrate (which is a wafer having only a silicon layer). The spectrum 306 is obtained from the light received by the optical head 53 when no substrate is placed on the optical head 53. Under these conditions, referred to herein as dark conditions, the received light is typically ambient light.

The computing device may process the aforementioned signal, or a portion of the signal, to determine an end point of the polishing step. Without being limited to any particular theory, the spectrum of light reflected from the substrate 10 evolves as the polishing progresses. Figure 3b provides an example of the evolution of the spectrum as the polishing of the film of interest proceeds. The different lines of the spectrum represent different times in the polishing. As can be seen, the spectral characteristics of the reflected light change as the film thickness changes, and certain spectra are caused by specific thicknesses of the film. As the polishing of the film progresses, peaks in the spectrum of reflected light (i.e., local maximum) are observed, the height of such peaks are typically varied and the peaks tend to become wider as material is removed. As well as widening, the wavelength at which a particular peak is located is typically increased as the polishing progresses. In some embodiments, the wavelength at which a particular peak is located is typically reduced as the polishing progresses. For example, peak 310 (1) represents the peak of the spectrum at a particular time during polishing, and peak 310 (2) represents the same peak at a later time during polishing. Peak 310 (2) is located at a longer wavelength and is wider than peak 310 (1).

Relative changes in the wavelength and / or width of the peak (e.g., measured at a fixed distance below the peak or at a mid-height between the peak and the valley closest thereto), the absolute wavelength of the peak And / or width, or both, to determine the endpoint for polishing according to empirical formulas. The optimum peaks (or peaks) for use in determining the end point depend on what materials are polished and on the pattern of such materials.

In some implementations, the change in peak wavelength can be used to determine the end point. For example, when the difference between the starting wavelength of the peak and the current wavelength of the peak reaches a target difference, the polishing apparatus 20 may stop polishing the substrate 10. Alternatively, features other than the peaks may be used to determine the difference in wavelength of the light reflected from the substrate 10. For example, when the wavelength, inflection point, or x- or y-axis intercept of the valley can be monitored by the photodetector 52 and the wavelength is changed by a predetermined amount, The polishing of the substrate 10 can be stopped.

In some embodiments, in addition to or instead of wavelength, the monitored characteristic is the intensity or width of the feature. The features can be shifted by about 40 nm to 120 nm, but other shifts are possible. For example, in the case of dielectric polishing in particular, the upper limit can be much larger.

FIG. 4A provides an example of a measured spectrum 400a of light reflected from the substrate 10. FIG. To reduce the overall slope of the spectrum, the optical monitoring system can pass the spectrum 400a through a high-pass filter, resulting in the spectrum 400b shown in FIG. 4b. For example, during processing of a plurality of substrates in a batch, there can be large spectral differences between the wafers. To reduce spectral fluctuations across substrates in the same batch, a high pass filter may be used to normalize the spectra. An exemplary high-pass filter may have a cutoff of 0.005 Hz and a filter order of 4. The high pass filter is also used to help filter the sensitivity to underlying fluctuations, as well as to "flatten" the appropriate signal to make feature tracking easier.

To allow the user to select which feature of the end point to track to determine the end point, a contour plot can be created and displayed to the user. Figure 5b provides an example of an outline plot 500b generated from a plurality of spectral measurements of light reflected from the substrate 10 during polishing and Figure 5a provides an example of the measured spectrum 500a from a particular point in the contour plot 500b ). ≪ / RTI > Contour plot 500b includes features such as peak region 502 and valley region 504 resulting from associated peaks 502 and valleys 504 on spectrum 500a. As time elapses, the substrate 10 is polished and the light reflected from the substrate is changed, as indicated by changes to the spectral features in the contour plot 500b.

The test substrate may be polished to produce a contour plot 500b and the light reflected from the test substrate may be measured by the photodetector 52 during polishing to determine a sequence of spectra of light reflected from the substrate 10 Can be generated. The sequence of spectra may be stored, for example, in a computer system, which may optionally be part of an optical monitoring system. The polishing of the setup substrate may start at time T1 and may continue past the estimated end time.

When the polishing of the test substrate is complete, the computer causes the operator of the polishing apparatus 20 to present the contour plot 500b, for example on a computer monitor. In some implementations, the computer may allocate red for higher intensity values in, for example, spectrums, assign blue for lower intensity values in the spectra, and intermediate for intensity values in the spectra By assigning the colors (orange to green), the contour-plot is color-coded. In other implementations, the computer may assign gray of the darkest shade for lower intensity values in the spectra, assign the gray of the brightest shade to higher intensity values in the spectra, Lt; / RTI > by assigning intermediate shades to intermediate intensity values in the gray scale contours. Alternatively, the computer may be configured to determine the highest z values for the higher intensity values in the spectra, the lowest z value for the lower intensity values in the spectra, and the median z values for the median values in the spectra, (3-D) contour plots. 3-D contour plots can be displayed, for example, in color, grayscale, or black and white. In some embodiments, the operator of the polishing apparatus 20 may interact with the 3-D contour plot to view other features of the spectra.

Contour plot 500b of reflected light produced by monitoring a test substrate during polishing may include spectral features such as, for example, peaks, valleys, spectral code transition points, and inflection points. The features may have characteristics such as wavelengths, widths, and / or intensities. As the polishing pad 30 removes material from the top surface of the setup substrate, as indicated by the contour plot 500b, the light reflected from the setup substrate may change over time, Also changes with the lapse of time.

Prior to polishing the device substrates, the operator of the polishing apparatus 20 can view the contour plot 500b and select feature characteristics for tracking during processing of the arrangement of substrates having die features similar to the setup substrate. For example, the wavelength of the peak 506 may be selected for tracking by the operator of the polishing apparatus 20. A potential advantage of the contour plot 500b, particularly a color-coded contour plot or a 3-D contour plot, is that such a graphical display makes it easier for the user to select the appropriate feature, Since features with linearly changing properties over time can be easily distinguished visually.

In order to select an endpoint criterion, the characteristics of the selected feature may be calculated by linear interpolation based on the polishing-pre-thickness and post-polishing thickness of the test substrate. For example, the thickness (D1) and thickness (D2) of the layer on the test substrate can be determined by the thickness of the test substrate before polishing (e.g., the thickness of the test substrate before time T1 when polishing begins) The thickness of the test substrate after the time T2 when the polishing is finished) and the values of the characteristics at the time T 'when the target thickness D' is achieved are measured . T 'can be calculated from T' = T 1 + (T 2 -T 1) * (D 2 -D ') / D 2 -D 1 and the value of the characteristic V' can be calculated from the spectrum measured at time T ' Can be determined. A target difference [Delta] V for a feature of a selected feature, such as a specific change in wavelength of the peak 506, can be determined from V'-Vl, where V1 is the initial characteristic value (at time T1) to be. Accordingly, the target difference DELTA V is changed from the initial value V1 of the characteristic before polishing at time T1 to the value V 'of the characteristic at time T' at which polish is expected to be completed Lt; / RTI > The operator of the polishing apparatus 20 may enter, within the computer associated with the polishing apparatus 20, a target difference 604 (e.g., delta V) whose feature characteristics are to be changed.

As a result, the line 508 can be fitted to the measured data using robust line fitting to determine a value V 'that determines the value of the points 602. Subtracting the value of line 508 at time T1 from the value of line 508 at time T 'may be used to determine dots 602. [

A feature such as spectral peak 506 may be selected based on the correlation between the amount of material removed from the setup substrate during polishing and the target difference in the feature characteristics. The operator of the polishing apparatus 20 may select other features and / or feature characteristics to find a feature characteristic that has a good correlation between the amount of material removed from the setup substrate and the target difference in characteristics.

In other implementations, the endpoint determination logic determines a spectral feature and an endpoint criterion for tracking.

Now, referring to the polishing of the device substrate, FIG. 6A is an exemplary graph 600a of feature property differences 602a-d that are tracked during polishing of the device substrate 10. The substrate 10 may be part of the arrangement of the substrates to be polished wherein the operator of the polishing apparatus 20 has selected to track feature characteristics such as peak or valley wavelengths from the contour plot 500b of the setup substrate.

As the substrate 10 is polished, the photodetector 52 measures the spectra of light reflected from the substrate 10. The endpoint determination logic uses the spectra of the light to determine a sequence of values for the feature property. As the material is removed from the surface of the substrate 10, the values of the selected feature characteristics may be changed. The difference values 602a-d are determined using the difference between the sequence of values of the feature's property and the initial value V1 of the feature's property.

As the substrate 10 is polished, the endpoint determination logic can determine the current value of the feature being tracked. In some implementations, when the current value of the feature has changed by the target difference 604 from the initial value, the end point may be called. In some implementations, line 606 is fitted to difference values 602a-d, e.g., using robust line fitting. To predict the polishing endpoint time, the function of line 606 may be determined based on the difference values 602a-d. In some implementations, the function is a linear function of the time to characteristic difference. As new difference values are calculated, the function of the line 606, e.g., the slope and the intersection points, can be changed during polishing of the substrate 10. In some implementations, the time at which line 606 reaches target difference 604 provides an estimated endpoint time 608. [ As the function of line 606 changes to accommodate the new difference values, the estimated end time 608 may be changed.

In some embodiments, the function of the line 606 is used to determine the amount of material removed from the substrate 10, and the change in the current value determined by this function determines when the target difference has been reached It is used to determine when an endpoint needs to be called. Line 606 tracks the amount of material removed. Alternatively, when removing a specific thickness of material from the substrate 10, the amount of material removed from the top surface of the substrate 10 and the end point should be recalled, using a change in the current value determined by the function Can be determined. For example, the operator may set the target difference to the wavelength of the selected feature being changed by 50 nanometers. For example, a change in the wavelength of the selected peak can be used to determine how much material has been removed from the top layer of the substrate 10 and when the endpoint should be called.

At time T1, before polishing the substrate 10, the feature value difference of the selected feature is zero. As the polishing pad 30 begins to polish the substrate 10, as the material is polished from the top surface of the substrate 10, the characteristic values of the identified features may change. For example, during polishing, the wavelength of the selected feature characteristic may move to a higher or lower wavelength. Excluding noise effects, the wavelength of the feature, and hence the wavelength difference, tends to change monotonically and often linearly. At time T ', the end point determination logic determines that the identified feature characteristic has changed by the target difference (? V), and the end point can be called. For example, when the wavelength of the feature has been changed by a target difference of 50 nanometers, the end point is called, and the polishing pad 30 stops polishing the substrate 10.

When processing the placement of substrates, the optical monitoring system 50 may track the same spectral feature, for example across all substrates. The spectral feature may be associated with the same die feature on the substrates. The starting wavelength of the spectral feature can vary from substrate to substrate across the placement based on variation of the bottom of the substrates. In some implementations, when a function fitted to values of a selected feature property or feature property is changed by an endpoint metric (EM) instead of a target difference, in order to minimize variability across multiple substrates, The decision logic can call the end point. The endpoint determination logic may use the expected initial value (EIV) determined from the setup substrate. At time T1, when the feature characteristic being tracked on the substrate 10 is identified, the endpoint determination logic determines the actual initial value AIV for the substrate being processed. In order to reduce the effect of the actual initial value on the end point determination, taking into account variations in the substrates across the placement, the end point decision logic may use an initial value weight (IVW). Substrate variation can include, for example, substrate thickness or thickness of underlying structures. The initial value weights may be correlated with substrate variations to increase uniformity between the substrate and substrate processing. The endpoint metric may be determined by, for example, EM = IVW * (AIV - EIV) + (? V), for example by multiplying the difference between the actual initial value and the expected initial value by the initial value weight, have.

In some embodiments, a weighted combination is used to determine the endpoint. For example, the endpoint determination logic may calculate an initial value of a characteristic from a function, calculate a current value of the characteristic from the function, and calculate a first difference between the initial value and the current value. The endpoint determination logic may calculate a second difference between the initial value and the target value and generate a weighted combination of the first difference and the second difference.

6B is an exemplary graph 600b of characteristic measurement differences versus time, taken from two portions of the substrate 10. FIG. For example, the optical monitoring system 50 may include one feature located on the edge portion side of the substrate 10 and one feature located on the center portion side of the substrate 10 to determine how much material has been removed from the substrate 10. [ Other features being located can be tracked. When testing the setup substrate, the operator of the polishing apparatus 20 may identify two features, e.g., two, corresponding to the other portions of the setup substrate for tracking. In some implementations, the spectral features correspond to the same type of die features on the setup substrate. In other implementations, the spectral features are associated with different types of die features on the setup substrate. When the substrate 10 is being polished, the photodetector 52 may measure a sequence of spectra of light reflected from two portions of the substrate 10 corresponding to selected features of the setup substrate. A sequence of values associated with the characteristics of the two features may be determined by the endpoint determination logic. By subtracting the initial characteristic value from the current characteristic value as the polishing time elapses, a sequence of first difference values 610a-b can be calculated for the feature characteristic in the first portion of the substrate 10. [ Similarly, a sequence of second difference values 612a-b may be calculated for the feature characteristics in the second portion of the substrate 10.

The first line 614 may be fitted to the first difference values 610a-b and the second line 616 may be fitted to the second difference values 612a-b. The first line 614 and the second line 616 correspond to a first function and a second function, respectively, to determine an adjustment or estimated polishing end time 618 for the polishing rate 620 of the substrate 10, Lt; / RTI >

During polishing, an endpoint calculation based on the target difference 622, using a first function for the first portion of the substrate 10 and a second function for the second portion of the substrate, . If the estimated endpoint times for the first portion of the substrate and the second portion of the substrate are different (e.g., the first portion will reach the target thickness before the second portion), the first function and the second function An adjustment to the polishing rate 620 may be made such that it has the same end time 618. [ In some embodiments, the polishing rates of both the first portion and the second portion of the substrate are adjusted to reach the end point at both portions simultaneously. Alternatively, the polishing rate of the first portion or the second portion may be adjusted.

The polishing rates can be adjusted, for example, by increasing or decreasing the pressure in the corresponding region of the carrier head 70. [ The change in the polishing rate is directly proportional to the change in pressure, and can be assumed, for example, to be a simple Prestonian model. For example, when the first area of the substrate 10 is scheduled to reach the target thickness at time TA and the system sets the target time TT, The carrier head pressure may be multiplied by TT / TA to provide carrier head pressure after time T3. Additionally, polish the substrates, taking into account the effects of the platen or head rotational speed, the second order effects of different head pressure combinations, the polishing temperature, the slurry flow, or other parameters affecting the polishing rate A control model can be developed. At subsequent times during the polishing process, rates may be adjusted again, as appropriate.

In some implementations, the computing device utilizes the wavelength range to easily identify the selected spectral feature in the measured spectrum of light reflected from the device substrate 10. The computing device searches for the wavelength range for the selected spectral feature, e.g., for intensity, width or wavelength, to distinguish these selected spectral features from other spectral features similar to the spectral feature selected in the measured spectrum.

7A shows an example of a spectrum 700a measured from light received by a photodetector 52. FIG. Spectrum 700a includes selected spectral features 702, e.g., spectral peaks. This selected spectral feature 702 may be selected by the endpoint decision logic to be tracked during the CMP of the substrate 10. The characteristics 704 (e.g., wavelength) of the selected spectral feature 702 may be identified by endpoint determination logic. When the characteristic 704 has been changed by the target difference, the end point determination logic calls the end point.

In some implementations, the endpoint determination logic determines the wavelength range 706 where the search for the selected spectral feature 702 is made. Wavelength range 706 may have a width of about 50 to about 200 nanometers. In some embodiments, the wavelength range 706 is predetermined, for example, by receiving a user input that selects a wavelength range, for example, by an operator, or by associating a wavelength range with the placement of substrates Is specified as a process parameter for the placement of the substrates by retrieving the wavelength range from the memory. In some implementations, the wavelength range 706 is based on historical data, e.g., the average or maximum distance between successive spectral measurements. In some implementations, the wavelength range 706 is based on information about the test substrate, e.g., twice the target difference? V.

FIG. 7B is an example of a spectrum 700b measured from light received by the photodetector 52. FIG. For example, the spectrum 700b is measured during the rotation of the platen 24 immediately after the spectrum 700a is taken. In some implementations, the endpoint determination logic determines the value (e.g., 520 nm) of the characteristic 704 in the previous spectrum 700a and adjusts the wavelength range 706 to adjust the wavelength range 708 To be closer to the characteristic 704.

In some implementations, the endpoint determination logic uses the function of line 606 to determine the expected current value of the characteristic 704. For example, the endpoint determination logic determines the expected current value of the characteristic 704 by determining the expected difference using the current polishing time and adding this expected difference to the initial value Vl of the characteristic 704 do. The end point determination logic can center the wavelength range 708 (i.e., center it) to the expected current value of the characteristic 704.

7C is another example of a spectrum 700c measured from the light received by the photodetector 52. FIG. For example, the spectrum 700c is measured during the rotation of the platen 24 immediately after the spectrum 700a is taken. In some implementations, the endpoint determination logic utilizes the previous value of the characteristic 704 for the center of the wavelength range 710.

For example, the endpoint determination logic determines the average variation between the values of the characteristics 704 determined during two consecutive passes of the optical head 53 under the substrate 10. The end point determination logic can set the width of the wavelength range 710 to be twice the average variation. In some implementations, the endpoint determination logic uses the standard deviation of the variations between the values of the features 704 in determining the width of the wavelength range 710. [

In some implementations, the width of the wavelength range 706 is the same for all spectral measurements. For example, the widths of the wavelength range 706, the wavelength range 708, and the wavelength range 710 are the same. In some implementations, the widths of the wavelength ranges are different. For example, when the characteristic 704 is estimated to have changed by 2 nanometers from a previous measurement of the characteristic, the width of the wavelength range 708 is 60 nanometers. When the characteristic 704 is estimated to have changed by 5 nanometers from a previous measurement of the characteristic, the width of the wavelength range 708 is 80 nanometers, which is a wavelength range greater than the range for smaller changes in the characteristic.

In some implementations, the wavelength range 706 is the same for all spectral measurements while polishing the substrate 10. For example, the wavelength range 706 is from 475 nanometers to 555 nanometers, and the endpoint determination logic determines wavelengths from 475 nanometers to 555 nanometers for all spectral measurements taken during polishing of the substrate 10. [ Lt; RTI ID = 0.0 > 702, < / RTI > but other wavelength ranges are possible. Wavelength range 706 may be selected by user input as a subset of the entire spectral range measured by the in-situ monitoring system.

In some implementations, the endpoint determination logic searches for the selected spectral feature 702 in the modified wavelength range for some spectral measurements and in the wavelength range used for the previous spectrum in the remaining spectra . For example, the endpoint determination logic may determine the wavelength range 708 for the spectrum measured during the first rotation of the platen 24 and the wavelength range 708 for the spectrum measured during the continuous rotation of the platen 24. [ ), The selected spectral features 702 were searched, and both measurements were made in the first region of the substrate 10. Subsequently, in this example, the end point determination logic searches for another selected spectral feature in the wavelength range 710 for the two spectra measured during the same platen rotations, Lt; RTI ID = 0.0 > 10 < / RTI >

In some implementations, the selected spectral feature 702 is a spectral valley or spectral code transition point. In some embodiments, characteristic 704 is the intensity or width of the peak or valley (e.g., the width measured at a fixed distance below the peak or at a mid-height between the peak and the nearest valley).

FIG. 8 illustrates a method 800 for selecting a target difference? V for use in determining an endpoint for a polishing process. The properties of the substrate having the same pattern as the product substrate are measured (step 802). In this specification, the substrate to be measured is referred to as a "setup" substrate. The setup substrate may simply be a substrate the same as or similar to the product substrate, or the setup substrate may be a substrate from the arrangement of product substrates. The properties to be measured may include the polishing-total thickness of the film of interest at a particular point of interest on the substrate. Typically, the thicknesses are measured at a plurality of locations. These positions are generally chosen such that die features of the same type are measured for each position. Measurements can be made at the measurement station. The in-situ optical monitoring system can measure the spectrum of light reflected from the substrate prior to polishing.

The setup substrate is polished according to the polishing step of interest, and spectra obtained during polishing are collected (step 804). Polishing and spectral collection can be performed in the polishing apparatus described above. The spectra are collected by the in-situ monitoring system during polishing. The substrate is overpolished, i. E. Polished past the estimated end point, so that the spectrum of light reflected from the substrate when the target thickness is achieved can be obtained.

The properties of the over-polished substrate are measured (step 806). These properties include the post-polishing thicknesses of the film of interest at the particular locations or locations used for the pre-polishing measurement.

A selected feature, such as a peak or valley, is selected to monitor during polishing (step 808), by examining the collected spectra using measured thicknesses and collected spectra. The feature may be selected by an operator of the polishing apparatus, or the selection of features may be automated (e.g., based on conventional peak-finding algorithms and experimental peak-selection formulas). For example, an operator of the polishing apparatus 20 may be presented with a contour plot 500b, and the operator may select a feature for tracking from the contour plot 500b as described above with reference to Fig. 5b. If it is expected that a particular area of the spectrum will include features desirable to be monitored during polishing (e.g., due to calculations of feature behavior based on past experience or theory), then only features in that area need to be considered have. Typically, a feature is selected that indicates the correlation between the amount of material removed from the top of the setup substrate as the substrate is polished.

Linear interpolation may be performed using the measured polishing-full film thickness and the post-polishing substrate thickness to determine the approximate time at which the target film thickness was achieved. This approximate time can be compared to spectral contour plots to determine the end point value of the selected feature property. The difference between the initial value and the end point value of the feature characteristic can be used as the target difference. In some implementations, the function is fitted to values of this feature property to normalize the values of the feature property. The difference between the end point value of the function and the initial value of the function can be used as the target difference. During polishing of the remaining substrates in the arrangement of the substrates, the same features are monitored.

Alternatively, the spectra are processed to increase accuracy and / or accuracy. The spectra may be processed, for example, to normalize these spectra to a common reference, to average these spectra, and / or to filter out noise from these spectra. In one implementation, a low pass filter is applied to the spectra to reduce or eliminate sharp spikes.

Typically, the spectral feature to monitor is chosen empirically for a particular endpoint decision logic such that the target thickness is achieved when the computer device calls the endpoint by applying a particular feature-based endpoint logic. The endpoint determination logic uses the target difference in the feature characteristics to determine when the endpoint should be called. The change in the characteristic can be measured with respect to the initial characteristic value of the feature when the polishing is started. Alternatively, the end point may be called for the expected initial value EIV and the actual initial value AIV, in addition to the target difference? V. To compensate for variations in the bottom of each substrate, the endpoint logic may multiply the starting value weight (SVW) by the difference between the actual initial value and the expected initial value. For example, the endpoint determination logic may terminate policing when the endpoint metric, EM = SVW * (AIV - EIV) + V,

In some implementations, the endpoint is determined using a weighted combination. For example, the endpoint determination logic may calculate an initial value of a characteristic from a function, calculate a current value of the characteristic from the function, and calculate a first difference between the initial value and the current value. The endpoint determination logic may calculate a second difference between the initial value and the target value and generate a weighted combination of the first difference and the second difference. When the weighted value reaches the target value, the end point can be called. The endpoint determination logic can determine when the endpoint should be called by comparing the monitored difference (or differences) to the target difference in the characteristics. If the monitored difference matches the target difference or exceeds the target difference, the endpoint is called. In one implementation, the monitored difference must match or exceed the target difference for some time period (e.g., two rotations of the platen) before the endpoint is called.

FIG. 9 illustrates a method 901 for selecting target values of characteristics associated with a selected spectral feature, for a particular target thickness and specific endpoint determination logic. The setup substrate is measured and polished as described above in steps 802-806 (step 903). In particular, spectra are collected and the time at which each collected spectrum is measured is stored.

The polishing rate of the polishing apparatus for a particular setup substrate is calculated (step 905). For example, using PR = (D2-D1) / PT, the average polishing rate (RR) is calculated using the polishing-front thickness D1, post-polishing thickness D2 and actual polishing time PT Can be calculated.

An endpoint time is calculated for a particular setup substrate (step 907), providing a calibration point for determining target values of the characteristics of the selected feature, as described below. The end point time can be calculated based on the calculated polishing rate PR, the pre-polishing start thickness ST of the film of interest, and the target thickness TT of the film of interest. Assuming that the polishing rate is constant through the polishing process, the endpoint time can be calculated as a simple linear interpolation. For example, ET = (ST-TT) / PR.

Optionally, the calculated end time can be evaluated by polishing another substrate during placement of the patterned substrates, stopping polishing at the calculated end time, and measuring the thickness of the film of interest. If the thickness is within a satisfactory range of the target thickness, the calculated endpoint time is satisfactory. Otherwise, the calculated endpoint time can be recalculated.

Target characteristic values for the selected feature are recorded from the spectrum collected from the setup substrate at the calculated end point time (step 909). If the parameters of interest involve changes in the position or width of the selected feature, such information can be determined by examining the spectra collected during the time period before the calculated end time. The difference between the initial values of the properties and the target values is recorded as the target differences for the feature. In some implementations, a single target difference is recorded.

10 illustrates a method 1000 of utilizing peak-based endpoint determination logic to determine an endpoint of a polishing step. The other of the arrangements of patterned substrates is polished using the above-described polishing apparatus (step 1002).

The identifier of the selected spectral feature, the wavelength range, and the characteristics of the selected spectral feature are received (step 1004). For example, the endpoint determination logic receives such an identifier from the computer along with processing parameters for the substrate. In some implementations, the processing parameters are based on information determined during processing of the setup substrate.

First, the substrate is polished and the light reflected from the substrate is measured to produce a spectrum, and the property value of the selected spectral feature is determined in the wavelength range of the measured spectrum. In each rotation of the platen, the following steps are performed.

One or more spectra of light reflected from the surface of the substrate being polished are measured to obtain one or more current spectra for the current platen rotation (step 1006). The one or more spectra measured for the current platen revolution are optionally processed to increase accuracy and / or accuracy as described above with respect to FIG. If only one spectrum is measured, this one spectrum is used as the current spectrum. If more than one current spectrum is measured for platen rotation, they are grouped, averaged within each group, and the averages are designated as current spectra. The spectra can be grouped by a radial distance from the center of the substrate.

As an example, a first current spectrum may be obtained from the spectra measured at points 202 and 210 (FIG. 2) and a second current spectrum may be obtained from the spectra measured at points 203 and 209 , Third current spectra can be obtained from the measured spectra at points 204 and 208, and so on. The characteristic values of the selected spectral peak can be determined for each current spectrum, and the polishing can be individually monitored within each region of the substrate. Alternatively, the worst-case values for the characteristics of the selected spectral peak may be determined from the current spectra and used by the endpoint decision logic.

During each rotation of the platen, additional spectra or spectra are added to the sequence of spectra for the current substrate. As the polishing progresses, the spectrum of at least some of the spectra in the sequence changes due to the material being removed from the substrate during polishing.

As described above with reference to Figures 7A-C, modified wavelength ranges for the current spectra are generated (step 1008). For example, the endpoint logic determines the modified wavelength ranges for the current spectra based on previous characteristic values. Modified wavelength ranges may be centered on previous characteristic values. In some embodiments, the modified wavelength ranges are determined based on expected property values such that the center of the wavelength ranges matches the expected property values, for example.

In some implementations, some of the wavelength ranges for current spectra are determined using other methods. For example, the wavelength range for the spectrum measured from the light reflected in the edge region of the substrate is determined by centering the wavelength range on the characteristic value from the previous spectrum measured in the same edge region of the substrate. Subsequently, in this example, the wavelength range for the spectrum measured from the light reflected within the central region of the substrate is determined by centering the wavelength range at the expected characteristic value for this central region.

In some implementations, the widths of the wavelength ranges for current spectra are the same. In some implementations, some of the widths of the wavelength ranges for current spectra are different.

Identifying the wavelength range for searching for the selected spectral feature characteristics can further increase the accuracy of the determination of the polish rate change or the detection of the end point such that the system may select an incorrect spectral feature during subsequent spectral measurements The probability is lower. Tracking the spectral features within the wavelength range instead of tracking across the entire spectrum makes it easier and faster to identify the spectral features. The processing resources required to identify the selected spectral features can be reduced.

The current property values for the selected peak are extracted from the modified wavelength ranges (step 1010), and the current property values are compared to the target property values using the endpoint determination logic described above in connection with FIG. 8 1012). For example, a sequence of values for a current feature property is determined from a sequence of spectra, and a function is fitted to a sequence of such values. The function can be, for example, a linear function, which can approximate the amount of material removed from the substrate during polishing based on the difference between the current and the initial property values.

As long as the endpoint determination logic determines that the endpoint condition is not met ("no" branch of step 1014), polishing is allowed to continue and steps 1006, 1008, 1010, 1012, and 1014 are repeated as appropriate . For example, the endpoint determination logic determines, based on such a function, that the target difference for the feature characteristics has not yet been reached.

In some embodiments, when the spectra of the light reflected from the plurality of portions of the substrate are measured, the endpoint determination logic may be implemented in one or more of the substrates so that the polishing of the plurality of portions may be completed more closely at the same time or at the same time. It may be determined that the polishing rate of two or more portions needs to be adjusted.

If the endpoint determination logic determines that the endpoint condition is met ("Yes" branch of step 1014), the endpoint is called and the polishing is stopped (step 1016).

To eliminate or reduce the effect of unwanted light reflections, the spectra can be normalized. The light reflections that media other than the film or films of interest contribute contribute to light reflections from the polishing pad window and from the base silicon layer of the substrate. Contributions from the window can be estimated by measuring the spectrum of light received by the in-situ monitoring system under dark conditions (i.e., no substrates are placed on the in-situ monitoring system). The contributions from the silicon layer can be estimated by measuring the spectrum of the light reflection of the bare silicon substrate. In general, these contributions are obtained before the polishing step is initiated. The raw spectra to be measured are normalized as follows:

Normalized spectrum = (A - Dark) / (Si - Dark),

Where A is the original spectrum, Dark is the spectrum obtained under dark conditions, and Si is the spectrum obtained from the bare silicon substrate.

In the described embodiment, a change in wavelength peak within the spectrum is used to perform endpoint detection. Also, a change in the wavelength valley in the spectrum (i.e., local minimum) can be used instead of or in combination with the peak. Further, when detecting the end point, a change of a plurality of peaks (or valleys) may be used. For example, each peak can be monitored individually, and an endpoint can be called when the majority of the changes in the peaks meet the endpoint condition. In other implementations, a change in inflection point or spectral code conversion point may be used to determine endpoint detection.

In some implementations, after the algorithm setup process 1100 (FIG. 11), the triggered feature tracking technique 1200 (FIG. 12) is used to polish one or more substrate (s).

First, the characteristics of the feature of interest in the spectrum are selected (step 1102) for use in tracking the polishing of the first layer, for example, using one of the techniques described above. For example, the feature may be a peak or a valley, and the characteristic may be the intensity of the peak or valley, or the width or position in frequency or wavelength. If the characteristics of the feature of interest can be applied to a wide variety of product substrates of different patterns, such features and characteristics can be preselected by the equipment manufacturer.

Also, the polishing rate (dD / dt) near the polishing end point is determined (step 1104). For example, a plurality of setup substrates may be polished according to a polishing process to be used for polishing product substrates, but at different polishing times near the expected end point polishing time. The setup substrates may have the same pattern as the product substrate. For each set-up substrate, the thickness before and after polishing of the layer can be measured, the amount removed can be calculated from the difference, and the amount removed and the associated polishing time for that set- / RTI > A positive linear function to be removed as a function of time can be fitted to the data set; The slope of this linear function provides the polishing rate.

The algorithm setup process involves measuring the initial thickness D ₁ of the first layer of the setup substrate (step 1106). The setup substrate may have the same pattern as the product substrate. A first dielectric layer is, for example, low -k materials such as carbon-doped silicon dioxide, for example, (Applied Materials, Inc. of from) Black Diamond ^TM or (Novellus Systems, Inc. of from) Coral ^TM Lt; / RTI >

Optionally, depending on the composition of the first material, other materials, such as dielectric materials, such as low-k capping materials, such as tetraethylorthosilicate (TEOS), different from both the first and second materials ) Is deposited over the first layer (step 1107). The first layer and one or more additional layers together provide a layer stack.

Next, a second layer of another second material, e.g., a barrier layer, such as a nitride, e.g., tantalum nitride or titanium nitride, is deposited over the first layer or stack of layers (step 1108). Also, a conductive layer, e.g., a metal layer, e.g., copper, may be deposited over the second layer (and within the trenches provided by the pattern of the first layer) (step 1109).

In a metrology system other than the optical monitoring system to be used during polishing, for example, in an in-line or individual metrology station, such as an optical metrology station using ellipsometry or a profilometer, . For some metrology techniques, for example profilometry, the initial thickness of the first layer is measured before the second layer is deposited, but for other measurement techniques, such as ellipsometry, Or before or after the second layer is deposited.

Thereafter, the setup substrate is polished according to the polishing process of interest (step 1110). For example, a portion of the conductive layer and the second layer may be polished and removed at a first polishing station using a first polishing pad (step 1110a). A portion of the second layer and the first layer may then be polished and removed at a second polishing station using a second polishing pad (step 1110b). However, for some implementations, it should be noted that there is no conductive layer, for example, the second layer is the outermost layer when polishing begins.

During the removal of at least the second layer, and possibly during the entire polishing operation at the second polishing station, spectra are collected using the techniques described above (step 1112). Also, using a separate detection technique, removal of the second layer and exposure of the first layer are detected (step 1114). For example, the exposure of the first layer may be detected by an overall intensity of light reflected from the substrate or a sudden change in motor torque. The value (V ₁ ) of the characteristic of the feature of interest of the spectrum at the time (T ₁ ) at which the second layer is removed is detected and stored. The time (T ₁ ) at which the removal is detected can also be stored.

Polishing may be aborted at default time after detecting removal (step 1118). The default time is long enough to allow polishing to cease after exposure of the first layer. The default time is selected so that the polishing-after thickness is close enough to the target thickness so that the polishing rate can be regarded as linear between the post-polishing thickness and the target thickness. The value (V ₂ ) of the characteristic of the feature of interest in the spectrum at the time polishing is stopped can be detected and stored, and the time (T ₂ ) at which polishing was stopped can also be stored.

For example, the post-polishing thickness (D ₂ ) of the first layer is measured (step 1120), using the same metrology system used to measure the initial thickness.

A default target change in the value of the characteristic [Delta] V _D is calculated (step 1122). The default target change of these values will be used in the endpoint detection algorithm for the product substrate. The default target change can be calculated from the difference between the value at the time when the second layer is removed and the value at the time polishing is stopped. That is,? V _D = V ₁ - V ₂ .

The rate of change of thickness (dD / dV) is calculated as a function of the monitored characteristic near the end of the polishing operation (step 1124). For example, assuming that the wavelength location of a peak is being monitored, the rate of change may be expressed as a material (in angstrom units) that is removed every shift (in angstrom units) at the wavelength location of the peak. As another example, assuming that the frequency width of the peak is being monitored, the rate of change can be expressed as a material (in angstrom units) that is removed per shift (hertz) at the frequency of the width of the peak.

In one embodiment, the rate of change of the value (dV / dt) as a function of time can be calculated simply from the value at the exposure time of the second layer and from the value at the end of the polishing, for example dV / dt = (D ₂ -D ₁ ) / (T ₂ -T ₁ ). In another implementation, using data from the end of polishing of the setup substrate (e.g., the last 25% or less of the time between T ₁ and T ₂ ), as a function of time, Can be fitted; The slope of the line provides the rate of change of the value (dV / dt) as a function of time. In either case, the rate of change in thickness (dD / dV) as a function of the monitored characteristic is then calculated by dividing the polishing rate by the rate of change in value. That is, dD / dV = (dD / dt) / (dV / dt). Once the rate of change (dD / dV) is calculated, the rate must remain constant for the product; It is not necessary to recalculate dD / dV for different lots of the same product.

Once the setup process is complete, product substrates can be polished.

Optionally, an initial thickness d ₁ of the first layer of at least one substrate from the lot of the product substrate is measured (step 1202). The product substrates have at least the same layer structure as the setup substrates, and optionally have the same pattern as the setup substrates. In some implementations, not all product substrates are measured. For example, one substrate can be measured from a lot, and an initial thickness can be used for all other substrates from the lot. As another example, one substrate can be measured from a cassette, and an initial thickness can be used for all other substrates from the cassette. In other embodiments, all product substrates are measured. The measurement of the thickness of the first layer of the product substrate may be carried out before or after the completion of the setup process.

As described above, the first dielectric layer is, for example, low -k material, for example, for the carbon-doped silicon dioxide, for example, (Applied Materials, Inc. of from) Black Diamond ^TM or (Novellus Systems, Inc. ≪ / RTI > Coral ^TM ). In metrology systems other than the optical monitoring system to be used during polishing, measurements can be carried out in-line or at individual metrology stations, such as optical metrology stations or profilometers using, for example, ellipsometry.

Optionally, depending on the composition of the first material, one or more of other materials, such as low-k capping material, such as tetraethyl orthosilicate (TEOS), that is different from both the first and second materials Additional layers are deposited over the first layer on the product substrate (step 1203). The first layer and one or more additional layers together provide a layer stack.

Next, a second layer of a different second material, e.g., a barrier layer, such as a nitride, e.g., tantalum nitride or titanium nitride, is deposited over the first or layer stack of the product substrate (step 1204) . Also, a conductive layer, e.g., a metal layer, e.g., copper, may be deposited over the second layer of the product substrate (and within the trenches provided by the pattern of the first layer) (step 1205). However, for some implementations, it should be noted that there is no conductive layer, for example, the second layer is the outermost layer when polishing begins.

For some metrology techniques, for example profilometry, the initial thickness of the first layer is measured before the second layer is deposited, but for other measurement techniques, such as ellipsometry, May be performed before or after the deposition. The deposition of the second layer and the conductive layer may be performed before or after the completion of the setup process.

For each product substrate to be polished, the target characteristic difference [Delta] V is calculated based on the initial thickness of the first layer (step 1206). Typically, this occurs before polishing begins, but it is also possible that the calculation occurs after the polishing has begun but before the spectral feature tracking is started (step 1210). In particular, the stored initial thickness d ₁ of the product substrate is received, for example from the host computer, with the target thickness d _T. In addition, a default target change (? V _D ) of the starting and ending thicknesses (D1 and D2), the rate of change of thickness as a function of the monitored characteristic (dD / dV) .

In one embodiment, the target characteristic difference [Delta] V is calculated as follows:

? V =? V _D + (d ₁ -D ₁ ) / (dD / dV) + (D ₂ -d _T ) / (dD / dV)

In some embodiments, pre-thickness will not be available. In this case, "(d ₁ - D ₁ ) / (dD / dV)" In other words, it becomes as follows:

_{ΔV = ΔV D + (D 2} - d T) / (dD / dV)

The product substrate is polished (step 1208). For example, a portion of the conductive layer and second layer may be polished and removed at a first polishing station using a first polishing pad (step 1208a). Thereafter, a portion of the second layer and the first layer may be polished and removed at a second polishing station using a second polishing pad (step 1208b). However, it should be noted that in some embodiments, there is no conductive layer, for example, the second layer is the outermost layer when polishing begins.

Using in-situ monitoring techniques, removal of the second layer and exposure of the first layer are detected (step 1210). For example, the exposure of the first layer at time tl can be detected by an abrupt change in motor torque or an overall intensity of light reflected from the substrate. For example, Figure 13 shows a graph of total intensity of light received from the substrate as a function of time while polishing the metal layer to expose the lower barrier layer. This overall intensity can be generated from the spectral signal obtained by the spectral monitoring system, for example by integrating the spectral intensity over a predetermined wavelength range or across all wavelengths being measured. Alternatively, intensity at a particular monochromatic wavelength may be used rather than full intensity. As shown in FIG. 13, as the copper layer is removed, the overall strength is lowered, and when the barrier layer is fully exposed, the overall strength is level off. Stabilization of intensity can be detected and used as a trigger to initiate spectral feature tracking.

(And potentially earlier than, for example, from the start of polishing of the product substrate by the second polishing pad) at least during the polishing using the in-situ monitoring techniques described above, (Step 1212). Spectra are analyzed using the techniques described above to determine the value of the property of the feature being tracked. For example, Figure 14 shows a graph of the wavelength position of the spectral peak as a function of time during polishing. At the time t ₁ , when the removal of the second layer is detected, the value v ₁ of the property of the tracked feature in the spectrum is determined.

Now, the target value v _T for the characteristic can be calculated (step 1214). The target value v _T can be calculated by adding the target characteristic difference? V to the value v ₁ of the characteristic at the removal time t ₁ of the second layer. That is, v _T = v ₁ +? V.

When the property of the tracked feature reaches the target value, polishing is stopped (step 1216). In particular, for each measured spectrum, for example in each platen revolution, the value of the property of the tracked feature is determined to produce a sequence of values. As described above with reference to Fig. 6A, a function, e.g., a linear function of time, may be fitted for a sequence of values. In some implementations, the function may be fitted to values within the time window. If the function is satisfied, the target value provides the end time point at which polishing is interrupted. The value v ₁ of the characteristic at time t ₁ at which removal of the second layer is detected can also be determined by fitting a function, e.g., a linear function, to a portion of the sequence of values near time t ₁ have.

Although the method described by Figures 12 and 13 involves deposition and removal of the second layer, in some embodiments there is no second layer, e.g., when the polishing begins, the first layer is the outermost layer Layer. For example, the process of measuring the initial thickness of the first layer prior to polishing and calculating the target feature value from the initial thickness and the target thickness may be applied in the presence or absence of the overlying second layer; The second layer is optional. In particular, the deposition step of the second layer and the step of detecting the exposure of the first layer may be omitted. Such a first layer may comprise polysilicon and / or dielectric material, for example, substantially pure polysilicon, a dielectric material, or a combination of polysilicon and dielectric material. The dielectric material may be an oxide, such as silicon oxide, or a nitride, such as silicon nitride, or a combination of dielectric materials.

For example, an initial thickness (d ₁ ) of a first layer of at least one substrate from a lot of product substrates is measured (e.g., as described for step 1202). (E.g., as described for step 1206), a target characteristic difference? V is calculated based on the initial thickness of the first layer. Polishing of the first layer of the product substrate is initiated and spectra are obtained during polishing of the first layer using the in-situ monitoring technique described above. The value of the characteristic v ₁ may be measured during the polishing of the first layer, for example immediately after the start of polishing of the first layer or shortly after the start of polishing of the first layer (e.g. after a few seconds) . A few seconds of waiting allows the signals from the monitoring system to be stabilized, thereby making the measurement of the value v ₁ more accurate. (E.g., as described for step 1214), a target value v _T for the characteristic may be calculated. For example, a target characteristic difference (ΔV) can be added to the value (v ₁₎ of the attribute. That is, v _T = v ₁ + ΔV. When the property of the tracked feature reaches the target value, the polishing is stopped (e.g., as described for step 1216). This approach enables removal to the target thickness, while compensating for substrate-to-substrate variations in absolute peak locations due to substrate-to-substrate differences within the substrate.

There are many techniques for removing noise from a sequence of values. Although fitting the line to the sequence has been described above, it is possible that the non-linear function is fitted to the sequence, or a sequence can be smooth using a lowpass median filter (in this case, Value can be directly compared with the target value to determine the end point).

As used herein, the term substrate may include, for example, a substrate (e.g., comprising a plurality of memory or processor dies), a test substrate, a bare substrate, and a gating substrate have. Such a substrate may be in various stages of integrated circuit fabrication, for example the substrate may be a bare wafer, or it may comprise one or more deposited and / or patterned layers. The term substrate may include circular disks and rectangular sheets.

All of the functional acts and embodiments of the present invention described herein may be embodied in the form of digital electronic circuitry, or computer software, firmware, or software, including the structural means disclosed herein, and structural equivalents thereof, It can be implemented in hardware. Embodiments of the invention may be embodied in one or more computer program products, that is, one or more computer programs embodied in the form of an information carrier, for example as a machine-readable storage device or a propagated signal , Which are intended to be executed by or in control of a data processing apparatus, e.g., a programmable processor, computer, or a plurality of processors or computers. A computer program (also known as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, ), Which may be deployed as a stand-alone program, or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program may be stored as part of a file that holds other programs or data, as a single file dedicated to the program, or as multiple coordinated files (e.g., one or more modules, sub-programs, Or files that store parts of the code). A computer program may be deployed to run on a single computer, or on a single site, or on multiple computers that are distributed across multiple sites and interconnected by a communications network.

The processes and logic flows described herein may be performed by one or more programmable processors executing one or more computer programs for performing functions by operating on input data to generate an output. Processes and logic flows may also be performed by a logic circuit, such as an FPGA (field programmable gate array) or ASIC (application specific integrated circuit), and the device may also be implemented as a logic circuit have.

The above-described polishing apparatuses and methods can be applied in various polishing systems. The polishing pad, or carrier head, or both, can move to provide relative motion between the polishing surface and the substrate. For example, the platen can orbit rather than rotate. The polishing pad may be a circular (or any other shape) pad fixed to the platen. Some aspects of the endpoint detection system can be applied to linear polishing systems, for example, where the polishing pad is a linear moving reel-to-reel belt. The polishing layer may be a standard (e.g., polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Relative positioning terms have been used; It should be understood that the polishing surface and substrate can be maintained in a vertical orientation or any other orientation.

Specific embodiments of the invention have been described. Other embodiments are within the scope of the following claims. For example, the operations described in the claims may be performed in a different order and still achieve desirable results.

Claims (12)

A computer-readable storage medium including instructions tangibly embodied in a machine-readable storage device,
The instructions cause the processor to:
Wherein the fixed wavelength range is a subset of the wavelengths measured by the in-situ monitoring system, wherein the fixed wavelength range is a subset of the wavelengths measured by the in-
Receiving an identification of a spectral feature selected for monitoring during polishing and a characteristic of the selected spectral feature,
Receive a sequence of spectra of light from the substrate while the substrate is being polished,
For each of the spectra in the sequence of the spectra, to search for a fixed wavelength range of each of the spectra for the selected spectral feature, and to determine a value of the property of the selected spectral feature to generate a sequence of values - each value from the sequence of values is the value of the characteristic of the associated spectrum in the sequence of the spectra, and
Determine at least one of an adjustment to the polishing rate or a polishing endpoint based on the sequence of values,
The selected spectral feature includes a spectral peak, a spectral valley, or a zero cross-crossing,
The characteristic may include wavelength, width, or intensity.
Computer readable storage medium. delete delete The method according to claim 1,
Wherein the fixed wavelength range has a width between 50 nm and 200 nm,
Computer readable storage medium. In a chemical mechanical polishing system,
A platen for supporting the polishing pad;
A carrier head for supporting the substrate in contact with the polishing pad;
An in-situ optical monitoring system configured to measure a sequence of spectra of light from the substrate while the substrate is being polished; And
Controller,
The controller comprising:
Wherein the fixed wavelength range is a subset of the wavelengths measured by the in-situ monitoring system,
Receive an identifier of a spectral feature selected for monitoring during polishing and a characteristic of the selected spectral feature,
Receiving a sequence of spectra of light from the in-situ monitoring system,
For each spectrum in the sequence of the spectra, a fixed wavelength range of each of the spectra for the selected spectral feature, and determining a value of a property of the selected spectral feature to generate a sequence of values, Is the value of the property of the associated spectrum in the sequence of said spectra, and
And to adjust at least one of an adjustment to the polishing rate or a polishing endpoint based on the sequence of values,
Wherein the selected spectral feature comprises a spectral peak, a spectral valley, or a spectral code conversion point,
The characteristic may include wavelength, width, or intensity.
Chemical mechanical polishing system. delete delete 6. The method of claim 5,
Wherein the in-situ monitoring system measures the intensity of wavelengths including at least visible light, and wherein the fixed wavelength range has a width between 50 nm and 200 nm,
Chemical mechanical polishing system. A method of controlling polishing, comprising:
Receiving a user input that selects a fixed wavelength range, wherein the fixed wavelength range is a subset of the wavelengths measured by the in-situ monitoring system;
Receiving an identifier of the selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing;
Polishing the substrate;
Measuring a sequence of spectra of light from the substrate with the in-situ monitoring system while the substrate is being polished;
Retrieving a fixed wavelength range of each of the spectra for the selected spectral feature in each spectrum in the sequence of spectra and determining a value of a property of the selected spectral feature to generate a sequence of values, Wherein each value from a sequence of values is a value of a property of an associated spectrum in the sequence of spectra; And
Determining at least one of an adjustment to the polishing rate or a polishing endpoint based on the sequence of values,
Wherein the selected spectral feature comprises a spectral peak, a spectral valley, or a spectral code conversion point,
The characteristic may include wavelength, width, or intensity.
Method for controlling polishing. delete delete 10. The method of claim 9,
Wherein the in-situ monitoring system measures the intensity of wavelengths including at least visible light, the fixed wavelength range being between 50 nm and 200 nm,
Method for controlling polishing.

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