KR20130098172A - Dynamically or adaptively tracking spectrum features for endpoint detection - Google Patents

Abstract

The 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 polished, a series of spectra of light from the substrate are measured. A series of values of the characteristics of the selected spectral feature is generated from the series of spectra. For at least some spectra from the series of spectra, an altered wavelength range is generated based on the position of the spectral feature within the previous wavelength range used for the previous spectra in the series of spectra, wherein the altered wavelength range is the selected spectral feature. And the value of the characteristic of the selected spectral feature is determined.

Description

DYNAMICALLY OR ADAPTIVELY TRACKING SPECTRUM FEATURES FOR ENDPOINT DETECTION

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

Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconducting, or insulating layers on a silicon wafer (hereinafter referred to as 'deposition' for convenience). One manufacturing step includes depositing a filler layer over a non-planar surface and planarizing the filler layer. In 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 trenches or holes in the insulating layer. After planarization, portions of the conductive layer remaining between the raised pattern of the insulating layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. In 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 in 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 located against the rotating polishing pad. The carrier head provides a controllable load onto the substrate, pushing 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, that is, whether the substrate layer has been planarized to the desired flatness or thickness, or when the desired amount of material has been removed. Slurry distribution, polishing pad conditions, relative speed between the polishing pad and the substrate, and variations in the 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. As such, the polishing endpoint cannot simply be determined as a function of polishing time.

In some systems, the substrate is monitored optically in-situ during polishing, for example through a window in the polishing pad. However, existing optical monitoring techniques may not meet the increasing demands of semiconductor device manufacturers.

Some optical endpoint detection systems track spectral feature characteristics selected in spectral measurements to determine the endpoint or to change the polishing rate. In the spectrum, spectral features similar to the selected spectral feature may make it difficult to track the selected spectral feature. The identification of the wavelength range for the optical endpoint detection system for searching for the selected spectral feature enables the optical endpoint detection system to accurately identify the selected spectral feature with reduced processing resources.

In some polishing processes, a second layer of a second material, such as a barrier layer, such as a nitride, such as tantalum nitride or titanium nitride, is removed from the substrate, such that another first material, such as a dielectric Exposing a first layer or layer structure comprising a material, 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 specifications to determine the endpoint or to change the polishing rate may have problems in the polishing process because the initial thickness of the second material is not well known. Can be. However, these problems are due to spectral features by other monitoring techniques that can reliably detect the removal of the second material and the exposure of the underlying layer or layer structure, for example by motor torque, eddy current, or optical intensity monitoring. If tracking is triggered, it can be avoided. In addition, there may be substrate-to-substrate variation (variation per substrate) in the thickness of the layer or layer structure. 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 values can be calculated from this initial thickness and the target thickness. have.

In one aspect, 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 polished, a sequence of spectra of light from the substrate is measured. A series of values of the characteristics of the selected spectral feature is generated from the series of spectra. Such generating comprises generating, for at least some of the spectra from the series of spectra, an altered wavelength range based on the position of the spectral features within the previous wavelength range used for the previous spectra in the series of spectra. Searching for the changed wavelength range for and determining a value of the characteristic of the selected spectral feature. One or more of the polishing endpoints or adjustments to the polishing rate are determined based on the series of values.

Implementations may include one or more of the following features. The wavelength range can have a fixed width. Generating an altered wavelength range includes centering the constant width at a location of a feature within the previous wavelength range. Generating the altered wavelength range includes determining a position of the characteristic within the previous wavelength range and adjusting the wavelength range such that the characteristic is located closer to the center of the altered wavelength range within the altered wavelength range. Generating an altered wavelength range comprises determining a wavelength value for the selected spectral feature for at least a portion of the spectrum in the series of spectra to produce a series of wavelength values, fitting a function to the series of wavelength values. Fitting 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. Generating an altered wavelength range can include centering the width of the wavelength range at an expected wavelength value. Such a method may include fitting one or more functions to a series of values and determining one or more of a polishing endpoint or adjustment to a polishing rate based on the function. Determining the polishing endpoint comprises: calculating an initial value of the characteristic from the function, calculating a current value of the characteristic from the function, and calculating a difference between the initial value and the current value, and Stopping polishing when the difference reaches the target difference. The function is a linear function. The selected spectral features may include spectral peaks, spectral valleys, or spectral zero-crossing. The characteristic may include wavelength, width, or intensity. The selected spectral feature may comprise a spectral peak, and the characteristic may comprise a peak width. The spectrum 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 user input to select a constant wavelength range that is a subset of wavelengths measured by an in-situ monitoring system; Receiving an identification of a selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing; Polishing the substrate; For each spectrum in the series of spectra, while the substrate is polished, measuring the series of spectra of light from the substrate; Searching for a wavelength range of each spectrum for the selected spectral feature, and determining a value of a characteristic of the selected spectral feature to generate a series of values; And determining one or more of a polishing endpoint or an adjustment to the polishing rate based on the series of values.

Implementations may include one or more of the following features. The in-situ monitoring system measures the intensity of wavelengths comprising at least visible light, and the predetermined wavelength range has a width of 50 to 200 nanometers. The selected spectral feature may be a spectral peak, spectral valley, or spectral zero-crossing. The property can be wavelength, width or intensity.

In another aspect, a method of controlling polishing includes: polishing a substrate having a first layer; Receiving an identification of a selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing; Measuring a series of spectra of light from the substrate while the substrate is polished; Determining a first value for a property of the feature at the time that the first layer is exposed; Adding an offset with respect to the first value to produce a second value; Monitoring the characteristic of the feature and stopping 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 can be position, width or intensity. The selected feature may be associated with an evolving position, width or intensity through a series of spectra. The feature may be a peak or valley of the spectrum. The substrate includes a second layer overlying the first layer, the polishing comprises polishing a second layer, and exposure of the first layer may be detected by an in-situ monitoring system. The first value may be determined at a time when the first in-situ monitoring technique detects exposure of the first layer. Detecting the exposure of the first layer may be a process separate from monitoring the characteristics of the feature. Detecting exposure of the first layer may include monitoring total reflection intensity from the substrate. Monitoring the total reflection intensity may include, for each spectrum in the series of spectra, integrating the spectrum over a wavelength range to produce an overall reflection intensity. The in-situ monitoring system may include a motor torque or friction monitoring system. The first value may be determined immediately during polishing of the first layer, for example at the start of polishing of the first layer. The first layer can be exposed before polishing of the substrate begins. Monitoring the characteristic of the feature may include, for each spectrum from the series of spectra, determining a value of the characteristic to produce a series of values. By fitting a linear function to a series of values and determining an endpoint time at which the linear function equals a second value, the characteristic of the feature may be determined to reach the second value. The pre-polish thickness of the first layer may be received and the offset value may be calculated from the pre-polish thickness. Calculating the offset value ΔV may include calculating (D ₂ -d _T ) / (dD / dV), where d _T is a target thickness and D ₁ is a set-up substrate and the thickness before the D ₂ is a three-polishing of the first layer from the polishing of the first layer up from the substrate, and after the thickness, and dD / dV is the rate of change in thickness as a function of the characteristics. Calculating the offset value ΔV may include calculating ΔV = ΔV _D + (d ₁ -D ₁ ) / (dD / dV) + (D ₂ -d _T ) / (dD / dV) Wherein d ₁ is the pre-polish thickness, D ₁ is the pre-polish thickness of the first layer from the set-up substrate, and ΔV _D is the pre-polish thickness of the first layer of the set-up substrate Is the difference in the value of the characteristic of the feature between and the thickness after polishing. The pre-polish thickness d ₁ may be measured in a separate metrology station. The rate of change of thickness (dD / dV) as a function of the above properties may be the rate of change of thickness near the polishing endpoint. The first layer may comprise polysilicon and / or dielectric material, for example, may be made of substantially pure polysilicon, may be made of dielectric material, or may be a combination of polysilicon and dielectric material.

Implementations may optionally include one or more of the following advantages. By the identification of the wavelength range to search for the selected spectral feature characteristics, the accuracy in determining endpoint detection or polishing rate variation may be increased, for example the system may have incorrect spectral features during subsequent spectral measurements. It is easy to lower the possibility of selecting. By tracking spectral features in the wavelength range instead of tracking over the entire spectrum, the spectral features can be identified more easily and more quickly. The processing resources needed to identify the selected spectral features can be reduced.

The time for semiconductor manufacturers to develop algorithms for detecting endpoints of particular product substrates can be shortened. Spectral feature tracking may be applied for polishing operations that begin with polishing of the reflective layer, and wafer-to-wafer thickness uniformity (WTWU) may be improved. The initial thickness of the layer can be measured prior to polishing, and the target feature can be calculated from the initial thickness and the target thickness, providing more accurate endpoint determination.

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

Figure 1 shows a chemical mechanical polishing apparatus.
FIG. 2 is a diagram illustrating positions at which in-situ measurement is performed, and is a plan view of a polishing pad.
3A shows the spectrum obtained from in-situ measurements.
3B is a graph showing an unfolded spectrum obtained from in-situ measurements as polishing progresses.
4A shows an exemplary graph of the spectrum of light reflected from the substrate.
4B shows the graph of FIG. 4A through a high pass filter.
5A shows the spectrum of light reflected from the substrate.
5B shows a contour plot of the spectrum obtained from in-situ measurements of light reflected from the substrate.
6A shows an exemplary graph of polishing progress, measured as time versus property difference.
6B shows an exemplary graph of polishing progress, measured as characteristic difference versus time, with the properties of two different features measured to adjust the polishing rate of the substrate.
7A shows another spectrum of light obtained from in-situ measurements.
FIG. 7B shows the spectrum of light obtained after the spectrum of FIG. 7A.
FIG. 7C shows another spectrum of light obtained after the spectrum of FIG. 7A.
8 shows a method for selecting a peak for monitoring.
9 shows a method for obtaining target parameters for a selected peak.
10 shows a method for endpoint determination.
11 shows a setting method for endpoint detection.
12 illustrates another method for endpoint determination.
13 shows a graph showing the total reflected intensity as a function of time during polishing.
14 shows a graph showing the wavelength location of spectral peaks 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 spectrum of light reflected from the substrate during polishing, and to identify a matching reference spectra from the library. One problem with the spectral matching approach is that, in the case of some types of substrates, there are significant substrate-to-substrate variations in the bottom die features, which consequently have the same outer layer thickness on the surface. This results in variations in the spectra reflected from the substrates. These fluctuations increase the difficulty of proper spectral matching and reduce the reliability of optical monitoring.

One technique to counteract this problem is to measure spectra of reflected light from the substrates being polished and to identify changes in spectral feature characteristics. Tracking changes in changes in the properties of the spectral features, for example changes in the wavelength of the spectral peaks, allows for greater uniformity in polishing between substrates in the batch. By determining the target deviation in the spectral feature characteristic, the endpoint can be called when the value of the characteristic has changed by the target amount.

The substrate may be as simple as a single dielectric layer disposed on the semiconductor layer, or may have a considerably more complicated layer stack. For example, the substrate can include a first layer and a second layer disposed over the first layer. The first layer may be a dielectric, for example oxides such as silicon dioxide, or carbon doped silicon dioxide, such as, for example, from Black Diamond ^™ (from Applied Materials, Inc.) or from Novellus Systems, Inc. ) May be a low-k material such as Coral ^™ . The second layer may be a barrier layer of a different composition than the first layer. For example, the barrier layer may be a metal or metal nitride, for example tantalum nitride or titanium nitride. One or two or more additional layers, for example, a material formed of a low-k capping material, such as tetraethyl orthosilicate (TEOS), is optionally disposed between the first and second layers. Both the first layer and the second layer 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 there may be additional layers under the layer being polished).

Chemical mechanical polishing can be used to planarize the substrate until the second layer is exposed. For example, if an opaque conductive material is present, the conductive material may be polished until the second layer, for example the barrier layer, is exposed. Subsequently, the portion of the second layer remaining above the first layer is removed and the substrate is polished until the first layer, eg, the dielectric layer, is exposed. In addition, it is often required 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 a second layer, for example a barrier layer, is exposed. In addition, part of the thickness of the second layer may be removed, for example, during an overpolishing step in the first polishing pad. Subsequently, the substrate is transferred to a second polishing pad, where the second layer, eg, barrier layer, is completely removed, and a portion of the thickness of the underlying first layer, eg, low-k dielectric, is also Removed. Also, if additional layers or layers are present between the first layer and the second layer, such additional layers or layers can be removed in the same polishing operation in the second polishing pad.

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

Spectral features may include spectral peaks, spectral valleys, spectral inflection points, or spectral zero-crossings. Features 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 disposed. The platen may be operated to rotate about axis 25. For example, a motor may rotate drive shaft 22 to rotate platen 24. The polishing pad 30 may be detachably secured to the platen 24, for example by an adhesive layer. When worn, the polishing pad 30 can be detached and replaced. The polishing pad 30 may be a two-layer polishing pad having an outer polishing layer 32 and a softer backing layer 34.

By providing an opening (ie, a hole extending through the pad) or a solid window, an optical access 36 through the polishing pad is provided. In some implementations the solid window may be supported on the platen 24 and may protrude into an opening in the polishing pad, but the solid window may be secured to the polishing pad. The polishing pad 30 is generally positioned on the platen 24 such that an opening or window is placed over the scientific head 53 located in the recess 26 of the platen 24. As a result, the optical head 53 has an optical path through an opening or window to the substrate to be polished.

The window may be, for example, a rigid crystalline or glassy material, for example quartz or glass, or a softer plastic material, for example silicone, polyurethane or a halogenated polymer (e.g., fluorine Low polymer), or a combination of the foregoing materials. The window may be transparent to white light. If the top surface of the solid window is a rigid crystalline or glassy material, the top surface must be sufficiently recessed from the polishing surface to prevent scratching. If the top surface is close to and comes into contact with the polishing surface, the top surface of the window should be a softer 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 transmission, for example about 80%, for monochromatic light of a particular color, for example blue light or red light. The window may be sealed against the polishing pad 30, so that no liquid leaks through the boundary between 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 softer plastic material. The top surface of the softer material may be coplanar with the polishing surface. The bottom surface of the rigid material may be coplanar or recessed with respect to the bottom 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 bottom layer can have an opening aligned with the solid window.

The bottom surface of the window may optionally include one or more recesses. The recess can be shaped to receive, for example, the end of the optical fiber cable or the end of the eddy current sensor. The recess allows the end of the optical fiber cable or the end of the eddy current sensor to be positioned at a distance from the substrate surface to be polished, the distance being less than the thickness of the window. In an embodiment where the window comprises a rigid crystalline portion or a glass like portion and the recess is formed in the portion by machining, the recess is polished to remove scratches caused by the machining. Instead, a solvent and / or liquid polymer can be applied to the surface of the recess to remove scratches caused by the processing. In general, the removal of scratches caused by processing can reduce scattering and improve the transmission of light through the window.

The backing layer 34 of the polishing pad can be attached to the outer polishing layer 32 by, for example, an adhesive. An opening providing the optical access path 36 may be formed in the pad 30 by, for example, cutting or molding the pad 30 to include the opening, and a window may be inserted into the opening, and For example, it may be fixed to the pad 30 by an adhesive. Instead, the liquid precursor of the window can be dispensed into an opening in the pad 30 and cured to form the window. Instead, a solid transparent element, such as the crystalline or glass like portion described above, may be located in the liquid pad material, and the liquid pad material may be cured to form the pad 30 around the transparent element. In either of the latter two cases, a block of pad material can be formed, and a layer of polishing pad having a molded window can be scythed from the block.

The polishing apparatus 20 includes a combined slurry / rinse arm 39. During polishing, the arm 39 can be operated to dispense a slurry 38 comprising a liquid and a pH adjuster. Instead, the polishing apparatus includes a slurry port that can be operated to dispense the slurry onto 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 a support structure 72, for example a carousel, and is connected to the carrier head rotating motor 76 by a carrier drive shaft 74, thus supporting the carrier. The head may be rotated about the axis 71. In addition, the carrier head 70 may oscillate laterally in a radial slot formed in the support structure 72. During operation, the platen is rotated about its central axis 25, and the carrier head is rotated about its central axis 71 and translated laterally across the top surface of the polishing pad. ).

The polishing apparatus also includes an optical monitoring system that can be used to determine the polishing endpoint as described below. The optical monitoring system includes a light source 51 and a light detector 52. Light impinges from the light source 51 through the optical access path 36 in the polishing pad 30, impinges on the substrate 10 and is reflected back from the substrate 10 through the optical access path 36, and Move to the photo detector 52.

A bifurcated optical cable 54 can be used to transfer light from the light source 51 to the optical access 36 and back from the optical access 36 to the photo detector 52. Two-pronged 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 an optical head 53 is disposed. The optical head 53 holds one end of the trunk 55 of the two-pronged fiber cable 54, which cable is configured to move light to and from the substrate to be polished. The optical head 53 may include one or more lenses or windows overlying the ends of the two-pronged fiber cable 54. Instead, the optical head 53 can only hold the end of the trunk 55 near the solid window in the polishing pad. The optical head 53 can be removed from the recess 26 as needed, for example, to perform protective or corrective maintenance.

The platen includes a removable in-situ monitoring module 50. In-situ monitoring module 50 may include one or more of the following: light source 51, light detector 52, and light source 51 and light detector 52 and from light sources One or two or more of a network for receiving and transmitting signals to the 51 and the photo detector 52. For example, the output of the detector 52 may be a digital electronic signal that is delivered to a controller for an optical monitoring system via a rotary coupler in the drive shaft 22, eg, a slip ring. Similarly, the light source can 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 branched portions 56 and 58 of the bifurcated optical fiber 54. The light source can be activated to transmit light, which light is transported through the branches 56 and exits the end of the trunk 55 located in the optical head 53 and impinges on the substrate being polished. The light reflected from the substrate is received at the end of the trunk 55 located in the optical head 53 and sent through the branch 58 to the photo detector 52.

In one embodiment, the two-pronged fiber cable 54 is a bundle of optical fibers. The bundle includes a first group of optical fibers and a second group of optical fibers. Optical fibers in the first group are connected to transfer light from the light source 51 to the substrate to be polished. The optical fibers in the second group are connected to receive the light reflected from the substrate to be polished and to transfer the received light to the photo detector 52. The optical fibers may be aligned such that the optical fibers in the second group form an X-like shape, and the X-like shape is the length of the two-pronged fiber 54 (as seen in cross section of the two-fiber fiber cable 54). Centered on the direction axis. Alternatively, other arrangements can be implemented. For example, the optical fibers in the second group may form V-like shapes that are mirror images of each other. Suitable two-pronged fiber 54 is available from Verity Instruments Inc. of Carrollton, Texas, USA.

In general, there is an optimum distance between the polishing pad window and the end of the trunk 55 of the two-pronged fiber cable 54 near the polishing pad window. The distance can be determined empirically and is influenced, for example, by the reflectivity of the window, the shape of the light beam emitted from the two-pronged fiber cable, and the distance to the monitored substrate. In one embodiment, a two-pronged fiber cable is arranged so that the end near the window is as close as possible to the bottom of the window without actually touching the window. In this embodiment, the polishing apparatus 20 is operable to adjust the distance between the end of the two-pronged fiber cable 54 and the bottom surface of the polishing pad window, for example as part of the optical head 53. It may include a mechanism that can. Instead, the proximate end of the two-pronged fiber cable 54 is embedded in the window.

The light source 51 can be operated to emit white light. In one embodiment, the emitted white light comprises light having wavelengths of 200-800 nanometers. Suitable light sources are xenon lamps or xenon-mercury lamps.

The photo detector 52 may be a spectrometer. A spectrometer is basically an optical instrument for measuring the properties of light, for example intensity, over a portion of the electromagnetic spectrum. Suitable spectrometers are grating spectrometers. The output for a typical spectrometer is the intensity of light as a function of wavelength.

Light source 51 and photodetector 52 are connected to a computing device that can be operated to control the operation of light source 51 and photodetector 52 and to receive signals from light source 51 and photodetector 52. do. The computing device may include a microprocessor, for example a personal computer, disposed near the polishing apparatus. 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 generates a series of flashes starting with just before the substrate 10 passes over the in-situ monitoring module 50 and ending immediately after the light source 51. You can let this release. Each of the points 201-211 represents a location where light from the in-situ monitoring module 50 impinges and reflects on the substrate 10. Instead, the computer may cause the light source 51 to continuously emit light starting just before the substrate 10 passes over the in-situ monitoring module 50 and ending immediately after it passes.

The spectrum obtained as the polishing proceeds, for example from successive sweeps of the sensor in the platen 24 across the substrate, provides a series of spectra. In some implementations, the light source 51 emits a series of flashes of light onto the plurality of portions of the substrate 10. For example, the light source can emit flashes of light onto the central portion of the substrate 10 and the outer portion of the substrate 10. In order to determine a plurality of series of spectra from the plurality of portions of the substrate 10, light reflected from the substrate 10 may be received by the photo detector 52. Features may be identified in the spectrum where each feature is associated with a portion of the substrate 10. For example, features may be used in determining an endpoint condition for polishing of substrate 10. In some implementations, monitoring of the plurality of portions of the substrate 10 allows to change the polishing rate for one or more portions of the substrate 10.

In connection with receiving the signals, the computing device may, for example, receive a signal carrying information indicative of the spectrum of light received by the photo detector 52. 3A shows examples of spectra measured from light emitted from a single flash of light source and reflected from a substrate. Spectrum 302 is measured from the light reflected from the product substrate. Spectrum 304 is measured from light reflected from a base silicon substrate (which is a wafer with only a silicon layer). The spectrum 306 is obtained from the light received by the optical head 53 when no substrate is placed above 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 the end point of the polishing step. Without being limited to any particular theory, the spectrum of light reflected from the substrate 10 evolves as polishing proceeds. 3B provides an example of development of the spectrum as polishing of the film of interest proceeds. Different lines of the spectrum represent different times in polishing. As shown, the properties of the spectrum of the reflected light change as the film thickness changes, and special spectra are exhibited by the particular thicknesses of the film. As polishing of the film proceeds, peaks (ie, local maximums) in the spectrum of reflected light are observed, the height of such peaks typically changes, and the peaks tend to grow wider and wider as the material is removed. In addition to broadening, the wavelength at which a particular peak is located is typically increased as polishing progresses. In some implementations, the wavelength at which a particular peak is located is typically reduced as polishing progresses. For example, peaks 310 and 1 represent peaks in the spectrum at specific times during polishing, and peaks 310 and 2 represent the same peaks at later times during polishing. Peaks 310 and 2 are located at a wider and longer wavelength than the peaks 310 and 1.

The wavelength and / or width of the peak (e.g., measured at a distance below the peak or at the intermediate height between the peak and the valley closest to), the absolute wavelength and / or width of the peak, or both Relative changes can be used to determine endpoints for polishing according to empirical formulas. The optimal peak (or peaks) to use in determining the endpoint depends on which materials are polished and on the pattern of those materials.

In some implementations, a change in peak wavelength can be used to determine the endpoint. For example, when the difference between the start wavelength of the peak and the current wavelength of the peak reaches the target difference, the polishing apparatus 20 may stop polishing the substrate 10. Instead, features other than peaks may be used to determine the difference in the wavelength of the light reflected from the substrate 10. For example, the wavelength of the valley, the point of refraction, or the x- or y-axis intercept can be monitored by the photo detector 52, and when the wavelength has changed by a predetermined amount, the polishing apparatus 20 ) Can stop polishing the substrate 10.

In some implementations, the intensity or width of the feature in addition to or instead of the wavelength becomes a monitored characteristic. The features may be shifted on the order of 40 nm to 120 nm, but other shifts are possible, for example, in particular in the case of dielectric polishing, the upper limit may be much larger.

4A provides an example of a measured spectrum 400a of light reflected from the substrate 10. In order to reduce the overall slope of the spectrum, the optical monitoring system can pass the spectrum 400a through the high pass filter, resulting in the spectrum 400b shown in FIG. 4B. For example, large spectral differences may exist between wafers while processing a plurality of substrates in a batch. In order to reduce spectral variations across substrates in the same batch, a highpass filter can be used to normalize the spectrum. An exemplary high pass filter may have a cutoff of 0.005 Hz and a filter order of four. High pass filters are used to help filter out sensitivity to underlying variations, as well as to "flatten out" the legitimate signal to make feature tracking easier.

In order to allow the user to select which features of the end point to use for tracking to determine the end point, a contour plot can be generated and displayed to the user. 5B provides an example of a contour plot 500b generated from a plurality of spectral measurements of light reflected from the substrate 10 during polishing, and FIG. 5A shows measured spectra from a particular instant in contour plot 500b. An example of 500a is provided. 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. Over time, the substrate 10 is polished and the light reflected from the substrate changes as shown by the change to the spectral features in the contour plot 500b.

To produce the contour plot 500b, the test substrate can be polished and the light reflected from the test substrate can be measured by the photo detector 52 during polishing and thus a series of light reflected from the substrate 10. It is possible to generate a spectrum of. A series of spectra can be stored, for example, in a computer system, which can optionally be part of an optical monitoring system. Polishing of the setup substrate may begin at time T1 and continue past the estimated endpoint time.

When polishing of the test substrate is completed, the computer provides a representation of the contour plot 500b to the drivers of the polishing apparatus 20, for example, on a computer monitor. In some implementations, for example, assigning red for higher intensity values in the spectrum, blue for lower intensity values in the spectrum, and intermediate colors (orange to orange) for intermediate intensity values in the spectrum. Green color), the computer color-codes the contour-plot. In other implementations, assign the darkest shade of gray for lower intensity values in the spectrum, and assign the brightest shade of gray for higher intensity values in the spectrum, and the middle intensity values in the spectrum. By assigning an intermediate shade to, the computer generates a grayscale contour plot. Instead, the computer outlines the 3-D contour with the largest z values for higher intensity values in the spectrum, the smallest z values for lower intensity values in the spectrum, and the intermediate z values for intermediate values in the spectrum. Plot 500b may be generated. 3-D outline plots can be displayed, for example, in color, grayscale, or black and white. In some implementations, the driver of the polishing apparatus 20 can interact with the 3-D contour plot to view other features of the spectrum.

The contour plot 500b of the reflected light generated from the monitoring of the test substrate during polishing may include spectral features such as, for example, peaks, valleys, spectral zero-crossing points, and refraction points. The features may have characteristics such as wavelengths, widths, and / or intensities. As shown by the contour plot 500b, as the polishing pad 30 removes material from the top surface of the setup substrate, the light reflected from the setup substrate may change over time, thus feature The characteristics change over time.

Prior to polishing the device substrates, the operator of the polishing apparatus 20 can see the contour plot 500b and select feature characteristics for tracking during processing of the placement of the substrates having die features similar to the setup substrate. have. For example, the wavelength of peak 506 may be selected for tracking by the driver of polishing apparatus 20. A potential advantage of the contour plot 500b, in particular of the color-coded contour plot or of the 3-D contour plot, is that such a graphical display allows the user to easily select the appropriate feature, For example, features with properties that change linearly with time are visually discernible.

In order to select an endpoint criterion, the properties of the selected feature can be calculated by linear interpolation based on the pre-polish and post-polish thicknesses of the test substrate. For example, the thicknesses D1 and D2 of the layers on the test substrate may be before-polishing (eg, the thickness of the test substrate before the time T1 when polishing is started) and after polishing (eg For example, the thickness of the test substrate after the time T2 at the end of the polishing) can be measured, respectively, and the values of the characteristic can be measured at the time T 'when the target thickness D' is obtained. have. T 'can be calculated from T' = T1 + (T2-T1) * (D2-D ') / (D2-D1), and the value V' can be determined from the spectrum measured at time T '. have. The target difference δV for the characteristic of the selected feature, such as a specific change in the wavelength of the peak 506, can be determined from V'-Vl, where V1 is the initial characteristic value (at time T1). Accordingly, the target difference δV is to be 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 the polishing is expected to be completed. Can be. The driver of the polishing apparatus 20 may input a target difference 604 (eg, δV) for the feature characteristics that are changed into the computer associated with the polishing apparatus 20.

In order to determine the value V ', which later determines the value of the points 602, robust line fitting may be used to fit the line 508 into the measured data. Points 602 may be determined by subtracting the value of line 508 at time T1 from the value of line 508 at time T '.

Based on the correlation between the amount of material removed from the setup substrate and the target difference in feature properties during polishing, a feature such as spectral peak 506 may be selected. In order to find feature properties that have a good correlation between the amount of material removed from the setup substrate and the target difference in feature properties, the operator of polishing apparatus 20 may select other features and / or feature properties.

In other implementations, the endpoint determination logic determines the spectral feature and endpoint measure for tracking.

Referring now to polishing of the device substrate, FIG. 6A is an exemplary graph 600a of other values 602a-d of feature characteristics tracked during polishing of the device substrate 10. Substrate 10 may be part of an arrangement of substrates to be polished if the driver of polishing apparatus 20 has selected a feature characteristic, such as the peak or valley wavelength, to track from the contour plot 500b of the setup substrate. have.

As the substrate 10 is polished, the photo detector 52 measures the spectrum of light reflected from the substrate 10. The endpoint determination logic uses the spectrum of light to determine a series of values for feature side measurements. As the material is removed from the surface of the substrate 10, the values of the selected feature characteristic may change. The difference between the series of values of the feature characteristic and the initial value V1 of the feature characteristic is used to determine other values 602a-d.

As the substrate 10 is polished, endpoint determination logic can determine the current value of the feature characteristic being tracked. In some implementations, the endpoint can be called when the current value of the feature has changed from the initial value by the target difference 604. In some implementations, for example, line 606 is fitted with other values 602a-d using certain line fitting. The function of line 606 may be determined based on other values 602a-d to predict the polishing end time. In some implementations, the function is a linear function of time versus property difference. As new difference values are calculated, the function of line 606, eg, slope and intersections, may change during polishing of substrate 10. In some implementations, the time for line 606 to reach the target difference 604 provides an estimated endpoint time 608. As the function of line 606 changes to accommodate the new difference values, the estimated endpoint time 608 may change.

In some implementations, a function of line 606 can be used to determine the amount of material removed from substrate 10 and a change in the current value determined by such a function can be used to reach a target difference. Determine when and when the endpoint needs to be called. Line 606 tracks the amount of material removed. Instead, when removing a particular thickness of material from the substrate 10, the amount and material of the material to be removed from the top surface of the substrate 10 should be requested using a change in the current value determined by the function. You can decide. For example, the driver may set the target difference to be the wavelength change of the selected feature 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, prior to polishing the substrate 10, the difference in the characteristic values of the selected features is zero. When 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 feature may change. For example, during polishing, the wavelength of the selected feature characteristic can be shifted to a higher or lower wavelength. With the noise effects excluded, the wavelength of the feature, and hence the wavelength difference, tends to change monotonously, often linearly. At time T ', the endpoint determination logic determines that the identified feature characteristic has changed by the target difference δV, and that the endpoint can be called. For example, when the wavelength of the feature has changed by a target difference of 50 nanometers, an endpoint is called and the polishing pad 30 stops polishing the substrate 10.

When processing a batch of substrates, the optical monitoring system 50 can, for example, track the same spectral feature 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 (substrate-to-substrate) over a batch based on the fundamental variation of the substrates. In some implementations, to minimize variability across multiple substrates, a fitted function or selected feature characteristic value for the value of feature characteristic changes may be changed by an endpoint metric (EM), instead of a target difference. At this point, the endpoint determination logic may call the endpoint. The endpoint determination logic may use the expected initial value (EIV) determined from the setup board. At time T1, when the feature characteristic 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 impact of the actual initial value on the endpoint determination, taking into account variations in substrates across the batch, the endpoint determination logic may use an initial value weight (IVW). Substrate variation can include, for example, substrate thickness or the thickness of underlying structures. Initial value weights may be correlated with substrate variations to increase uniformity between substrate and substrate processing. The endpoint metric is for example EM = IVW * (AIV-EIV) + (δV), for example by multiplying the initial value weight by the difference between the actual initial value and the expected initial value and adding the target difference. Can be determined as

In some implementations, the weighted combination is used to determine the endpoint. For example, endpoint determination logic may calculate the initial value of the characteristic from the function, the current value of the characteristic from the function, and the 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 and second differences.

6B is an exemplary graph 600b of characteristic measurement differences versus time taken from two portions of the substrate 10. For example, the optical monitoring system 50 may be a central feature of the substrate 10 and one feature positioned towards the edge portion of the substrate 10 to determine how much material has been removed from the substrate 10. You can track other features located toward. When testing the setup substrate, the operator of the polishing apparatus 20 may identify two features, for example, to track the corresponding portions of the setup substrate. 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 other types of die features on the setup substrate. As the substrate 10 is polished, the photo detector 52 can measure a series of spectra of reflected light from the two portions of the substrate 10 corresponding to selected features of the setup substrate. A series of values associated with the characteristics of the two features can be determined by the endpoint determination logic. By subtracting the initial characteristic value from the current characteristic value as the polishing time elapses, a series of first difference values 610a-b can be calculated for the feature characteristic in the first portion of the substrate. Similarly, a series of second difference values 612a-b may be calculated for the feature characteristic in the second portion of the substrate 10.

The first line 614 can be fitted with respect to the first difference values 610a-b and the second line 616 can be fitted with respect to the second difference values 612a-b. In order to determine an estimated polishing endpoint time 618 or an adjustment to the polishing rate 620 of the substrate 10, the first line 614 and the second line 616 are each a first function and a second function, respectively. Can be determined by

During polishing, using the first function for the first portion of the substrate 10 and using the second function for the second portion of the substrate, the endpoint calculation based on the target difference 622 is time TC. Is done on. If the estimated endpoint times for the first portion of the substrate and the second portion of the substrate are different (eg, if the first portion will reach the target thickness prior to the second portion), then the first function and the second function The polishing rate 620 may be adjusted such that Ds may have the same endpoint time 618. In some implementations, the polishing rates of both the first and second portions of the substrate are adjusted so that an endpoint is reached at both portions simultaneously. Instead, the polishing rate of the first portion or the second portion can 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 polishing rate is directly proportional to the change in pressure, for example it can be assumed to be a simple Prestonian model. For example, when the first area of the substrate 10 is planned to reach the target thickness at time TA, and when the system sets the target time TT, the carrier head in the corresponding area before time T3. The pressure may be multiplied by TT / TA, thus providing the carrier head pressure after time T3. In addition, a control model can be developed for polishing substrates, taking into account the influence of platen or head rotational speed, secondary effects of other head pressure combinations, polishing temperature, slurry flow, or other parameters affecting the polishing rate. . In subsequent times during the polishing process, the rates may be adjusted again, as appropriate.

In some implementations, the computing device uses a wavelength range to readily identify selected spectral features in the measured spectrum of light reflected from the device substrate 10. To distinguish the selected spectral feature from other spectral features similar to the selected spectral feature in the measured spectrum, for example from intensity, width or wavelength, the computing device searches for a wavelength range for the selected spectral feature.

7A shows an example of the spectrum 700a measured from the light received by the photo detector 52. Spectrum 700a includes a selected spectral feature 702, for example a spectral peak. This selected spectral feature 702 may be selected by endpoint determination logic for tracking during CMP of the substrate 10. The characteristic 704 (eg, wavelength) of the selected spectral feature 702 may be identified by endpoint determination logic. When the characteristic 704 has changed by the target difference, the endpoint determination logic calls the endpoint.

In some implementations, the endpoint determination logic determines the wavelength range 706 in which 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 implementations, the wavelength range 706 is determined and, for example, specified by the driver, for example, by the user receiving a user input to select the wavelength range, or the wavelength range is determined with the placement of the substrates. It is specified as a process parameter for the placement of the substrates by bringing the wavelength range from the associating memory. In some implementations, the wavelength range 706 is based on historical data, eg, average or maximum distance between successive spectral measurements. In some implementations, the wavelength range 706 is based on information about the test substrate, eg, twice the target difference δV.

7B is an example of a spectrum 700b measured from the light received by the photo detector 52. For example, the spectrum 700b is measured immediately after the spectrum 700a is taken during the rotation of the platen 24. In some implementations, the endpoint determination logic determines the value of the characteristic 704 in the previous spectrum 700a (eg, 520 nm) and adjusts the wavelength range 706 to adjust the wavelength range 708. The center is located 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 characteristic 704. For example, the endpoint determination logic may use the current polishing time to determine the expected present value of the feature 704 and determine the expected difference by adding the expected difference to the initial value V1 of the feature 704. . The endpoint determination logic may center the wavelength range 708 on the expected current value of the characteristic 704.

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

For example, endpoint determination logic determines the average variation between the values of the characteristic 704 determined during two consecutive passes of the optical head 53 under the substrate 10. The endpoint determination logic may set the width of the wavelength range 710 to twice the average variation. In some implementations, the endpoint determination logic uses the standard deviation of the variation between the values of the characteristic 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 wavelength range 706, the wavelength range 708, and the width of 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 the previous measurement of the characteristic, the width of the wavelength range 708 is 80 nanometers, and this 80 nanometer wavelength range is in the case of smaller changes in the characteristic. It is a wavelength range larger than the wavelength range.

In some implementations, the wavelength range 706 is the same for all spectral measurements during polishing of the substrate 10. For example, the wavelength range 706 is 457 nanometers to 555 nanometers, and the endpoint determination logic is selected within wavelengths of 457 nanometers to 555 nanometers for all spectral measurements taken during polishing of the substrate 10. While searching for spectral feature 702, other wavelength ranges are possible. The wavelength range 706 can be selected by user input as a subset of the full spectral range measured by the in-situ monitoring system.

In some implementations, the endpoint determination logic searches for the selected spectral feature 702 within the modified wavelength range of some of the spectral measurements and within the wavelength range used for the previous spectrum in the rest of the spectrum. For example, the endpoint determination logic may include the wavelength range 706 for the spectrum measured during the first rotation of the platen 24 and the wavelength range for the spectrum measured during the continuous rotation of the platen 24. Searching for the selected spectral feature 702 in 708, where both measurements are taken in the first region of the substrate 10. Continuing in such an example, the endpoint determination logic searches for another selected spectral feature in the wavelength range 710 for the two spectra measured during the same platen rotations, where both measurements are different from the first region 10. Is taken in the second zone.

In some implementations, the selected spectral feature 702 is a spectral valley or spectral zero-crossing point. In some implementations, characteristic 704 is the width or intensity of the peak or valley (eg, the width measured at a distance below or below the peak, measured at an intermediate height between the peak and the nearest valley).

8 shows a method 800 of selecting a target difference δV for use in determining an endpoint for a polishing process. 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 "set-up" substrate. The set-up substrate may simply be the same or similar substrate as the product substrate, or the set-up substrate may be one substrate from the batch of product substrates. Properties measured may include the pre-polish thickness of the film of interest at the particular location of interest of the substrate. Typically, the thickness is measured at multiple locations. The locations are generally selected so that the same type of die feature is measured for each location. The measurement can be performed at the metrology station. The in-situ optical monitoring system can measure the spectrum of light reflected from the substrate prior to polishing.

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

Properties of the overpolished substrate are measured (step 806). Properties include the post-polish thickness of the film of interest at the particular location or locations used for the pre-polish measurement.

By examining the collected spectra, the measured thicknesses and the collected spectra are used to select particular features such as peaks or valleys for monitoring during polishing (step 808. Features are selected by the operator of the polishing apparatus). Or selection of the feature (eg, based on conventional peak-search algorithms and empirical peak-selection formulas) can be automated, for example, contour plots to the driver of the polishing apparatus 20. 500b may be presented and the driver may select a feature for tracking from the contour plot 500b as described above with reference to Figure 5b (eg, calculation of feature behavior based on theory or past). Experience has shown that if a particular area of the spectrum is expected to contain the desired features for monitoring during polishing, The feature that indicates a correlation between the amount of material removed from the upper end of the up substrate is selected - it is necessary to consider only the features typically, three as the substrate is polished.

In order to determine the approximate time that the target film thickness has been achieved, linear interpolation can be performed using the measured pre-polish film thickness and the post-polish substrate thickness. To determine the endpoint value of the selected feature characteristic, rough time can be compared against the spectral contour plot. The difference between the initial value and the endpoint value of the feature characteristic can be used as the target difference. In some implementations, a function is fitted to the values of the feature property to normalize the values of the feature property. The difference between the endpoint value of the function and the initial value of the function can be used as the target difference. The same feature is monitored during polishing of the remaining substrates during placement of the substrates.

Optionally, the spectrum is processed to increase accuracy and / or precision. The spectrum can be processed, for example, to normalize the spectrum to a common reference, to average the spectrum, and / or to filter noise from the spectrum. In one implementation, a lowpass filter is applied over the spectrum to reduce or eliminate abrupt spikes.

Typically, spectral features for monitoring are empirically selected for particular endpoint determination logic, such that a target thickness is achieved when the computer device calls the endpoint by applying special feature-based endpoint logic. The endpoint determination logic uses the target difference in the feature properties to determine when the endpoint should be called. The change in property can be measured with respect to the initial property value of the feature when polishing begins. Instead, the endpoint may be called for the expected initial value EIV and the actual initial value AIV, in addition to the target difference δV. To compensate for the basic variations of substrate to substrate, the endpoint logic can multiply the difference between the actual initial value and the expected initial value by the starting value weight SVW. For example, when the endpoint metric is EM = SVW * (AIV-EIV) + δV, the endpoint determination logic can end the polishing.

In some implementations, the weighted combination is used to determine the endpoint. For example, endpoint determination logic may calculate the initial value of the characteristic from the function, the current value of the characteristic from the function, and the 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 and second differences. The endpoint can be called when the weighted value reaches the target value. The endpoint determination logic can determine when the endpoint should be called by comparing the monitored difference (or differences) with the target difference of the characteristic. If the monitored difference matches 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 (eg, two rotations of the platen) before the endpoint is called.

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

The polishing rate of the polishing apparatus for the particular set-up substrate is calculated (step 905). Using pre-polish thickness (D1) and post-polish thickness (D2), and actual polishing time (PT), for example using PR = (D2-D1) / PT, the average polishing rate (RR) Can be calculated.

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

Optionally, the calculated endpoint time can be evaluated by polishing another substrate in the batch of patterned substrates, by stopping polishing at the calculated endpoint time, and by measuring the thickness of the film of interest. If the thickness is within the satisfaction range of the target thickness, the calculated endpoint time is satisfied. Alternatively, the calculated endpoint time can be re-calculated.

Target characteristic values for the selected features are recorded from the spectra collected from the set-up substrate at the calculated endpoint time (step 909). If the parameters of interest include a change in the position or width of the selected features, such information can be determined by examining the spectra collected during the period of time preceding the calculated endpoint time. The difference between the initial values of the characteristics 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 using peak-based endpoint determination logic to determine an endpoint of a polishing step. Using the polishing apparatus described above, the other of the batches of patterned substrates is polished (step 1002).

An identification of the selected spectral feature, the wavelength range, and the properties of the selected spectral feature is received (step 1004). For example, endpoint determination logic receives an identification from a computer having processing parameters for the substrate. In some implementations, processing parameters are based on information determined during processing of the set-up substrate.

The substrate is initially polished, the light reflected from the substrate is measured to produce a spectrum, and the characteristic value of the selected spectral feature is determined within the wavelength range of the measured spectrum. In each rotation of the platen, the following steps are carried out.

One or more spectra of light reflected from the surface of the substrate to be polished are measured to obtain one or more current spectra for the current platen rotation (step 1006). One or more spectra measured for the current platen rotation are optionally processed to increase accuracy and / or precision as described above with respect to FIG. 8. If only one spectrum is measured, one spectrum is used as the current spectrum. If more than one current spectrum is measured for one platen rotation, the measured spectra are grouped, averaged within each group, and the mean is designated to be the current spectrum. Spectra can be grouped by radial distance from the center of the substrate.

By way of 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. , A third current spectrum may be obtained from the spectrum measured at points 204 and 208, and so forth. The characteristic values of the selected spectral peak can be determined for each current spectrum, and polishing can be monitored independently within each region of the substrate. Instead, worst-case values for the characteristics of the selected spectral peak can be determined from the current spectrum and used by the endpoint determination logic.

During each rotation of the platen, additional spectra or spectra are added to the series of spectra for the current substrate. As polishing proceeds, due to the material being removed from the substrate during polishing, the spectra of at least some of the series of spectra are varied.

As described above with reference to FIGS. 7A-C, altered wavelength ranges for the current spectrum are generated (step 1008). For example, the endpoint logic determines changed wavelength ranges for the current spectrum based on previous specific values. The altered wavelength range can be centered on the previous characteristic values. In some implementations, the altered wavelength ranges are determined based on the expected characteristic values, eg, the center of the wavelength ranges coincide with the expected characteristic values.

In some implementations, some of the wavelength ranges for the current spectrum 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 characteristic values from the previous spectrum measured in the same edge region of the substrate. As a continuing example, the wavelength range for the spectrum measured from the light reflected in the center region of the substrate is determined by centering the wavelength range on the expected characteristic value for the center region.

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

By identifying the wavelength range to search for the selected spectral feature characteristics, it is possible to increase the accuracy of the determination of the polishing rate change or the detection of the end point, for example the system may detect an incorrect spectral feature during subsequent spectral measurements. It is easy to choose. By tracking spectral features in the wavelength range instead of tracking over the entire spectrum, the spectral features can be identified more easily and more quickly. The processing resources needed to identify the selected spectral features can be reduced.

The current characteristic values for the selected peak are extracted from the changed wavelength ranges (step 1010), and the current characteristic values are compared against the target characteristic values using the endpoint determination logic described above in the description of FIG. (1002)). For example, a series of values for the current feature characteristic are determined from a series of spectra, and a function is fitted over the series of values. The function can be, for example, a linear function, which can estimate the amount of material removed from the substrate during polishing based on the difference between the current property value and the initial property value.

While the endpoint determination logic determines that the endpoint condition has not been met ("No" branch of step 1014), polishing is allowed to continue, and steps 1006, 1008, 1010, 1012 and 1014 are repeated if appropriate. do. For example, the endpoint determination logic determines that the target difference for the feature characteristic has not yet been reached based on the function.

In some implementations, when the spectrum of light reflected from the plurality of portions of the substrate is measured, the endpoint determination logic can determine that the polishing rate of one or more portions of the substrate is such that polishing of the plurality of portions can be completed simultaneously or nearly simultaneously. It may be determined that it needs to be adjusted.

When the endpoint determination logic determines that the endpoint condition has been met (“yes” branch of step 1014), the endpoint is called and polishing is stopped (step 1016).

In order to eliminate or reduce the effects of undesirable light reflections, the spectrum can be normalized. Light reflections constituted by a medium other than the film or films of interest include light reflections from the polishing pad window and from the base silicon layer of the substrate. By measuring the spectrum of light received by the in-situ monitoring system under dark conditions (ie, when the substrates are not placed over the in-situ monitoring system), contributions from the window can be estimated. By measuring the spectrum of reflected light of the bare silicon substrate, the contribution from the silicon layer can be estimated. Contributions are generally obtained prior to the start of the polishing step. The measured raw spectrum is normalized as follows:

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

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

In the described embodiment, the change of the wavelength peak in the spectrum is used to perform endpoint detection. Changes in the wavelength valleys (ie, local minimums) within the spectrum can also be used instead of or in combination with peaks. When detecting an endpoint, a change in multiple peaks (or valleys) may also be used. For example, each peak can be monitored individually, and the endpoint can be called when most of the changes in the peaks meet the endpoint condition. In other implementations, a change in spectral zero-crossing or refraction point can be used to determine endpoint detection.

In some implementations, following the algorithm set-up process 1100 (FIG. 11), one or more substrate (s) is polished using the triggered tracking technique 1200 (FIG. 12).

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

In addition, the polishing rate dD / dt near the polishing endpoint is determined (step 1104). For example, a plurality of set-up substrates may be polished depending on the polishing processing to be used for polishing of product substrates, but at other polishing times close to the expected endpoint polishing time. The set-up substrates can have the same pattern as the product substrate. For each set-up substrate, the pre-polishing and post-polishing layer thicknesses can be measured, and the amount of removal calculated from the difference, and the associated polishing time and removal amount for that set-up substrate, are stored to save the data set. to provide. A removed amount of linear function as a function of time can be fitted to the data set; The slope of the linear function provides the polishing rate.

The algorithm set-up process includes measuring the initial thickness D ₁ of the first layer of the set-up substrate (step 1106). The set-up substrate may have the same pattern as the product substrate. The first layer may be a dielectric, for example a low-k material, such as carbon doped silicon dioxide, such as Black Diamond ^™ (from Applied Materials, Inc.) or from Novellus Systems, Inc. ) Coral ^TM .

Optionally, depending on the composition of the first material, a dielectric material, such as a low-k capping material, such as tetraethyl orthosilicate, that is different from other materials, for example, both the first and second materials One or more additional layers of (TEOS) are 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, such as a barrier layer, such as a nitride, such as tantalum nitride or titanium nitride, is deposited over the first layer or layer stack (step 1108). . In addition, a conductive layer, for example a metal layer, for example copper, may be deposited over the second layer (and in the trenches provided by the pattern of the first layer) (step 1109).

In metrology systems other than optical monitoring systems used during polishing, such as optical metrology stations or profilometers using optical polarimeters, for example in-line or independent metrology systems, measurements may be performed. Could be. In some metrology techniques, eg in the case of a profilometer, the initial thickness of the first layer is measured before the second layer is deposited, while in the case of other metrology techniques, eg in a polarimeter, the measurement It may be carried out before or after the two layers are deposited.

The set-up substrate is then polished according to the polishing process of interest (step 1110). For example, at the first polishing station, using the first polishing pad, a portion of the conductive layer and the second layer can be polished and removed (step 1110a). Then, at the second polishing station, using the second polishing pad, the second layer and a portion of the first layer may be polished and removed (step 1110b). However, in the case of some embodiments, it should be noted that there is no conductive layer, for example, the second layer is the outermost layer when polishing begins.

During at least the removal of the second layer and possibly during the entire polishing operation at the second polishing station, the spectrum is collected using the techniques described above (step 1112). In addition, independent detection techniques are used to detect the clearing of the second layer and the exposure of the first layer (step 1114). For example, the exposure of the first layer can be detected by a sharp change in the overall torque or motor torque of the light reflected from the substrate. At the time T ₁ of clearing of the second layer, the value V ₁ of the characteristic of the feature of interest in the spectrum is detected and stored. The time T _{1 at} which clearing is detected may also be stored.

Polishing may stop at the default time after detection of clearing (step 1118). The default time is long enough that polishing can be stopped after exposure of the first layer. The default time is selected so that the post-polish thickness is close enough to the target thickness that the polishing rate can be considered to be linear between the post-polish thickness and the target thickness. At the time when polishing is stopped, the value V ₂ of the characteristic of the feature of interest in the spectrum can be detected and stored, and the time T _{2 at} which polishing was stopped can also be detected and stored.

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

The default target change ΔV _D of the value of the characteristic is calculated (step 1122). This default target change in value 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 of clearing of the second layer and the time at which the polishing is stopped, ie, ΔV _D = V ₁ -V ₂ .

The rate of change of thickness dD / dV as a function of the monitored property near the end of the polishing operation is calculated (step 1124). For example, assuming that the wavelength position of the peak is monitored, the rate of change can be expressed as an angstrom of per angstrom per removal material of the shift at the wavelength position of the peak. As another example, assuming that the frequency width of the peak is monitored, the rate of change can be expressed as an angstrom of Hertz per removal material of the shift in frequency of the width of the peak.

In one implementation, the rate of change of the value as a function of time (dV / dt) can simply be calculated from the values at the exposure time of the second layer and at the end of polishing, for example dV / dt = (D ₂ -D ₁ ) / (T ₂ -T ₁ ). In another embodiment, measured values as a function of time using data from near the end of polishing of the set-up substrate, eg, from the last 25% or less of the time between T ₁ and T _2. A line may be fitted for; The slope of the line gives the rate of change of the value (dV / dt) as a function of time. In either case, by dividing the polishing rate by the rate of change of the value, the rate of change of thickness (dD / dV) as a function of the monitored property is then calculated, i.e., dD / dV = (dD / dt) / (dV / dt). Once the rate of change (dD / dV) is calculated, the rate must remain constant for the product; There should be no need to recalculate dD / dV for other lots of the same product.

Once the set-up process is complete, the product substrates can be polished.

Optionally, the initial thickness d ₁ of the first layer of one or more substrates from many product substrates is measured (step 1202). The product substrate has at least the same layer structure as the set-up substrate, and optionally the same pattern as the set-up substrate. In some implementations, not all product substrates are measured. For example, one substrate from a lot can be measured, and such initial thickness is used for all other substrates from the lot. As another example, one substrate from a cassette can be measured, and such initial thickness is used for all other substrates from that cassette. In other implementations, all product substrates are measured. The thickness of the first layer of the product substrate may be performed before or after completion of the set-up process.

As noted above, the first layer may be a dielectric, such as a low-k material, such as carbon doped silicon dioxide, such as Black Diamond ^™ (from Applied Materials, Inc.) or (Novellus Systems). Coral ^™ ) from Inc., Inc. In an metrology system other than an optical monitoring system used during polishing, such as an optical metrology station or profilometer using an optical polarimeter, the measurement may be performed, for example, in an in-line or independent metrology system.

Optionally, depending on the composition of the first material, a layer of additional other material of one or more other materials different from both the first and second materials, a dielectric material, for example a low-k capping material, e.g. For example, one or more additional layers of tetraethyl orthosilicate (TEOS) 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 another second material, such as a barrier layer, such as a second layer of nitride, such as tantalum nitride or titanium nitride, is deposited over the first layer or layer stack of the product substrate. (Step 1204). In addition, a conductive layer, such as a metal layer, such as copper, may be deposited over the second layer of the product substrate (and in the trenches provided by the pattern of the first layer) (step 1205). However, in the case of some embodiments, it should be noted that there is no conductive layer, for example, the second layer is the outermost layer when polishing begins.

In some metrology techniques, eg in the case of a profilometer, the initial thickness of the first layer is measured before the second layer is deposited, while in the case of other metrology techniques, eg in a polarimeter, the measurement It may be carried out before or after the two layers are deposited. Deposition of the second layer and the conductive layer may be performed before or after completion of the set-up process.

For each product substrate to be polished, a target characteristic difference ΔV is calculated based on the initial thickness of the first layer (step 1206). Typically this is done before the start of polishing, but a calculation may be made after the start of polishing but before spectral feature tracking is initiated (step 1210). In particular, the stored initial thickness d ₁ of the product substrate is received together with the target thickness d _T , for example from a host computer. In addition, the start and end thicknesses D1 and D2 determined for the set-up substrate, the rate of change of the thickness as a function of the monitored property (dD / dV), and the default target change of value ΔV _D are received. Can be.

In one embodiment, the target characteristic deviation ΔV is calculated as follows:

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

In some implementations, pre-thickness will not be available. In this case, "(d ₁ -D ₁ ) / (dD / dV)" will be omitted from the above formula, i.e.

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

In-situ monitoring techniques are used to detect clearing of the second layer and exposure of the first layer (step 1210). For example, the exposure of the first layer can be detected by a sharp change in the overall torque or motor torque of the light reflected from the substrate. For example, FIG. 13 shows a graph of the total intensity of light received from a substrate as a function of time while polishing a metal layer to expose a 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 preset wavelength range or over all measured wavelengths. Alternatively, instead of full intensity, the intensity at a particular monochromatic wavelength may be used. As shown in FIG. 13, as the copper layer is cleared, the overall intensity drops, and when the barrier is fully exposed, the overall intensity level is off. Leveling off of the intensity can be detected and used as a trigger to initiate spectral feature tracking.

When starting with the detection of at least the clearance of the second layer (and potentially earlier, for example, from the start of polishing of the product substrate with the second polishing pad), the spectrum can be obtained using the in-situ monitoring techniques described above. Obtained during polishing (step 1212). The spectrum is analyzed using the techniques described above to determine the value of the characteristic of the feature being tracked. For example, FIG. 14 shows a graph indicating the wavelength location of spectral peaks as a function of time during polishing. At the time t ₁ of clearing of the second layer, the value v ₁ of the characteristic of the tracked feature in the spectrum is detected and determined.

The target value v _T for the characteristic can now be calculated (step 1214). The target value v _T can be calculated by adding the target characteristic difference ΔV to the value of the characteristic v ₁ at the time t ₁ of the clearing of the second layer, ie with v _T = v ₁ + ΔV Can be calculated.

When the characteristic of the tracked feature reaches the target value, polishing is stopped (step 1216). In particular, for example, at each platen rotation, for each measured spectrum, the value of the characteristic of the tracked feature is determined to produce a series of values. As described above with reference to FIG. 6A, a function, such as a linear function of time, may be fitted over a series of values. In some implementations, the function can be fitted to values in the time window. When the function is satisfied, the target value provides the endpoint time at which polishing stops. The value of the characteristic v ₁ at the time t ₁ of the clearing of the second layer is detected and also determined by fitting a function, for example a linear function, to part of the series of values near the time t ₁ . Can be.

Although the method described by FIGS. 12 and 13 involves the deposition and removal of a second layer, in some embodiments, there is no second layer, for example, the first layer becomes the outermost layer when polishing begins. . 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 can be applied with or without an overlapping second layer; The second layer is optional. In particular, the deposition step of the second layer and the exposure detection step of the first layer can be omitted. Such first layer may comprise polysilicon and / or dielectric material, for example, consisting of substantially pure polysilicon, made of a dielectric material, or a combination of polysilicon and dielectric material. The dielectric material may be an oxide, for example silicon oxide, or a nitride, for example silicon nitride, or a combination of dielectric materials.

For example, the initial thickness d ₁ of the first layer of one or more substrates from many product substrates is measured (eg, as described with respect to step 1202). The target characteristic deviation ΔV is calculated based on the initial thickness of the first layer (as described for step 1206). Polishing of the first layer of the product substrate is initiated, and a spectrum is obtained during polishing of the first layer using the in-situ monitoring technique described above. The value v ₁ of the property can be measured during polishing of the first layer, for example immediately after the initiation of polishing of the first layer or after some time, such as after a few seconds. Waiting a few seconds allows the signals from the monitoring system to stabilize, thus making the measurement of the value v ₁ more accurate. The target value v _T for the characteristic is calculated (as described for step 1214). For example, the target characteristic difference ΔV may be added to the value of the characteristic v ₁ , ie v _T = v ₁ + ΔV. When the characteristic of the tracked feature reaches a target value, polishing is interrupted (as described for step 1216). This approach allows for the removal of the target thickness while compensating per substrate variation at the absolute peak position due to the substrate-to-substrate difference of the underlying structure.

There are many techniques for removing noise from the sequence of values. Although fitting a line to a sequence has been described above, a non-linear function may be fitted to the sequence, or a sequence may be smoothed using a lowpass median filter. (In this case, the filtered values can be compared directly against the target values for endpoint determination).

As used herein, the term substrate may include, for example, a product substrate (eg, comprising a plurality of memory or processor dies), a test substrate, a bare substrate, and a gating substrate. Can be. The substrate may be in various integrated circuit fabrication steps, for example, the substrate may be a bare wafer, or the substrate may include one or more deposited and / or patterned layers. The term substrate can include circular disks and rectangular sheets.

All functional operations and embodiments of the invention described herein include, but are not limited to, digital electronic circuitry, or computer software, firmware, or hardware, including the structural means described herein and their structural equivalents, or combinations thereof. Can be implemented. Embodiments of the present invention may include one or more computers for execution by, or for performing control of, an operation of a data processing device, eg, a programmable processor, a computer, or multiple processors or computers. It may be implemented as program products, ie as one or more computer programs tangibly embodied in an information carrier, for example in a machine-readable storage device or as a propagated signal. 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, and such a program may be standalone. It can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. The computer program does not necessarily correspond to a file. A program may be part of a file holding other programs or data, in a single file dedicated to that program, or in a plurality of coordinated files (eg, one or more modules, sub-programs, Or files that store portions of code). The computer program may be deployed to run on one computer or on multiple computers interconnected by a communication network and distributed over a plurality of sites or at one site.

The processes and logic flows described herein may be practiced by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. Processes and logic flows may also be executed by special purpose logic circuitry, eg, an FPGA (Field Programmable Gate Array) or an ASIC (Application-Custom Integrated Circuit), and the device may also be an FPGA (Field Programmable Gate Array). Or as an ASIC (Application-Custom Integrated Circuit).

The above described polishing apparatuses and methods can be applied in various polishing systems. The polishing pad, or carrier head, or both can be moved to provide relative motion between the polishing surface and the substrate. For example, the platen may orbit instead of rotation. The polishing pad may be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applied to linear polishing systems, eg, to linear polishing systems where the polishing pad is a reel-to-reel belt in which the polishing pad moves continuously or linearly. The polishing layer may be a standard type (eg polyurethane with or without fillers) polishing material, soft material, or a material to which the abrasive is fixed. Relative positioning terms were used; It will be appreciated that the polishing surface and the substrate may be held in a vertical orientation or in some other orientation.

Specific embodiments of the invention have been described. Other embodiments are included within the scope of the following claims. For example, the actions recited in the claims may be performed in a different order and still achieve the desired result.

Claims (26)

As a way to control polishing:
Polishing the 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;
Measuring a series of spectra of light from the substrate while the substrate is polished;
Generating a series of values of a characteristic of the selected spectral feature from the series of spectra, wherein the generating step comprises, for at least some of the spectra from the series of spectra, the previous wavelength used for the previous spectra in the series of spectra Generating a modified wavelength range based on the position of the spectral feature within the range, searching for the changed wavelength range for the selected spectral feature, and determining a value of a characteristic of the selected spectral feature; And
Determining one or more of an adjustment or polishing endpoint for a polishing rate based on the series of values; Containing
How to control polishing. The method of claim 1,
The wavelength range has a constant width
How to control polishing. 3. The method of claim 2,
Generating the modified wavelength range includes centering the constant width at a location of a feature within a previous wavelength range.
How to control polishing. The method of claim 1,
Generating the modified wavelength range includes adjusting the wavelength range such that the characteristic is located closer to the center of the modified wavelength range within the changed wavelength range and determining the position of the characteristic within the previous wavelength range. doing
How to control polishing. The method of claim 1,
Generating the altered wavelength range includes determining a wavelength value for the selected spectral feature for at least a portion of the spectrum in the series of spectra to produce a series of wavelength values, fitting a function to the series of wavelength values. And calculating an expected wavelength value for the selected spectral feature for subsequent spectral measurements from the function.
How to control polishing. The method of claim 5, wherein
Where the function is a linear function
How to control polishing. The method of claim 5, wherein
Generating the modified wavelength range includes centering the width of the wavelength range at an expected wavelength value.
How to control polishing. The method of claim 1,
The spectrum is measured for visible light and the wavelength range is 50 to 200 nanometers wide.
How to control polishing. As a way to control polishing:
Receiving a user input selecting a constant wavelength range that is a subset of the wavelengths measured by the in-situ monitoring system;
Receiving an identification of a selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing;
Polishing the substrate;
While the substrate is polished, measuring a series of spectra of light from the substrate;
For each spectrum in a series of spectra, searching for a wavelength range of each spectrum for the selected spectral feature, and determining a value of a characteristic of the selected spectral feature to produce a series of values; And
Determining one or more of an adjustment or polishing endpoint for the polishing rate based on the series of values.
How to control polishing. The method of claim 9,
The in-situ monitoring system measures the intensity of wavelengths comprising at least visible light, and wherein the predetermined wavelength range has a width of 50 to 200 nanometers
How to control polishing. As a way to control polishing:
Polishing a substrate having a first layer;
Receiving an identification of a selected spectral feature and a characteristic of the selected spectral feature for monitoring during polishing;
Measuring a series of spectra of light from the substrate while the substrate is polished;
Determining a first value for a property of the feature at the time that the first layer is exposed;
Adding an offset with respect to the first value to produce a second value; And
Monitoring the characteristic of the feature and stopping polishing when it is determined that the characteristic of the feature has reached the second value;
How to control polishing. The method of claim 11,
Said substrate comprising a second layer overlying said first layer, said polishing comprising polishing a second layer, and further comprising detecting an exposure of said first layer with an in-situ monitoring system. doing
How to control polishing. 13. The method of claim 12,
The first value is determined at a time when the first in-situ monitoring technique detects exposure of the first layer.
How to control polishing. 13. The method of claim 12,
Detecting the exposure of the first layer is a process separate from monitoring the characteristics of the feature.
How to control polishing. 15. The method of claim 14,
Detecting exposure of the first layer includes monitoring total reflection intensity from the substrate.
How to control polishing. 15. The method of claim 14,
Monitoring the total reflection intensity includes integrating the spectrum over a wavelength range to produce an overall reflection intensity for each spectrum in the series of spectra.
How to control polishing. 15. The method of claim 14,
The in-situ monitoring system includes a motor torque or friction monitoring system.
How to control polishing. The method of claim 11,
Wherein the first value is determined during polishing of the first layer
How to control polishing. The method of claim 11,
Monitoring the characteristic of the feature includes, for each spectrum from the series of spectra, determining a value of the characteristic to produce a series of values
How to control polishing. The method of claim 19,
By fitting a linear function to a series of values and determining an endpoint time at which the linear function is equal to a second value, the characteristic of the feature is determined to reach the second value.
How to control polishing. The method of claim 11,
Receiving the pre-polish thickness of the first layer and calculating the offset value from the pre-polish thickness
How to control polishing. 22. The method of claim 21,
Calculating the offset value ΔV includes calculating (D ₂ -d _T ) / (dD / dV), where d _T is the target thickness and D ₁ is from a set-up substrate. Is the pre-polish thickness of the first layer, D ₂ is the post-polish thickness of the first layer from the set-up substrate, and dD / dV is the rate of change of thickness as a function of property
How to control polishing. 22. The method of claim 21,
Calculating the offset value (ΔV)
ΔV = ΔV _D + (d ₁ -D ₁ ) / (dD / dV) + (D ₂ -d _T ) / (dD / dV),
D ₁ is the pre-polish thickness, d _T is the target thickness, D ₁ is the pre-polish thickness of the first layer from the set-up substrate, and D ₂ is the first from the set-up substrate Post-polished thickness of the layer, wherein ΔV _D is the difference in the value of the characteristic of the feature between the pre-polished thickness and the post-polished thickness of the first layer of the set-up substrate, and dD / dV is a function of the characteristic It is rate of change of thickness
How to control polishing. 24. The method of claim 23,
Measuring the thickness before polishing (d ₁ ) in a separate metrology station
How to control polishing. 24. The method of claim 23,
dD / dV is the rate of change of thickness near the polishing endpoint
How to control polishing. The method of claim 11,
The first layer comprises polysilicon and / or dielectric material
How to control polishing.

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