Method for inspecting spectrum of reflected light from workpiece, and polishing device

Abstract

To provide a technique for inspecting a spectrum of reflected light from workpiece such as a wafer, during polishing of the workpiece.SOLUTION: A method for inspecting a spectrum of reflected light from workpiece includes: irradiating a plurality of film thickness measurement points on workpiece W with light from an optical sensor head, for each time section during polishing of the workpiece W; generating a plurality of measurement spectra of reflected light from the plurality of film thickness measurement points; calculating a plurality of feature amounts of the plurality of measurement spectra; plotting a plurality of time during which the plurality of measurement spectra are generated, and a plurality of measurement data points MD specified from the plurality of feature amounts on a coordinate system, and thereby executing data mapping; determining a correction index value indicating the number of the plurality of measurement data points MD existing in a threshold value TR determined on the coordinate system for each time section; and determining whether or not the correction index value is within a correction index value correction management range.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a technique for measuring the film thickness of a workpiece such as a wafer, substrate, or panel based on the spectrum of light reflected from the workpiece, and more particularly to a technique for detecting anomalies in the spectrum of light reflected from the workpiece. [Background technology]

[0002] The semiconductor device manufacturing process includes various steps, such as polishing insulating films such as SiO2 and metal films such as copper and tungsten. Wafer polishing is performed using a polishing apparatus. A polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that presses the wafer against the polishing pad, and a slurry supply nozzle that supplies slurry onto the polishing pad. While the polishing table is rotating, slurry is supplied to the polishing pad on the polishing table, and the polishing head presses the wafer against the polishing pad. The wafer is brought into sliding contact with the polishing pad in the presence of the slurry. The wafer surface is planarized by a combination of the chemical action of the slurry and the mechanical action of the abrasive grains contained in the slurry and the polishing pad.

[0003] Wafer polishing is terminated when the thickness of the film (insulating film, metal film, silicon layer, etc.) that constitutes the surface of the wafer reaches a predetermined target value. A polishing apparatus generally includes an optical film thickness measurement system to measure the thickness of non-metallic films such as insulating films and silicon layers. This optical film thickness measurement system is configured to direct light from a light source to the wafer surface, measure the intensity of the light reflected from the wafer with a spectroscope, and analyze the spectrum of the reflected light to measure the film thickness of the wafer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2022-156879 Summary of the Invention [Problem to be solved by the invention]

[0005] The intensity of the light reflected from the wafer may change due to malfunction or aging of the light source or optical system, resulting in an abnormal spectrum being acquired. In another example, if a wafer of a different type than the target wafer to be polished is sent to the polishing apparatus, the spectrum of the light reflected from that wafer may be acquired as an abnormal spectrum. Such an abnormal spectrum may cause an erroneous film thickness measurement. Furthermore, if the wafer polishing operation is controlled based on the film thickness measurement obtained from the abnormal spectrum, the desired polishing result may not be obtained.

[0006] SUMMARY OF THE INVENTION The present invention therefore provides a technique for inspecting the spectrum of light reflected from a workpiece, such as a wafer, while the workpiece is being polished. [Means for solving the problem]

[0007] In one aspect, there is provided a method for inspecting a spectrum of reflected light from a workpiece, the method comprising: polishing the workpiece by pressing the workpiece against a polishing pad on a polishing table while rotating the polishing table; irradiating a plurality of film thickness measurement points on the workpiece with light from an optical sensor head for each time interval during polishing of the workpiece; generating a plurality of measurement spectra of the reflected light from the plurality of film thickness measurement points; calculating a plurality of feature quantities of the plurality of measurement spectra; performing data mapping by plotting, on a coordinate system, a plurality of times at which the plurality of measurement spectra were generated and a plurality of measurement data points identified from the plurality of feature quantities of the plurality of measurement spectra; determining, for each time interval, a correction index value representing the number of the plurality of measurement data points that exist within a threshold range defined on the coordinate system; and determining whether the correction index value is within a correction control range.

[0008] In one aspect, when the correction index value is within the correction management range, the plurality of feature quantities are corrected by moving the plurality of measurement data points on the coordinate system until the plurality of measurement data points fall within the threshold range. In one embodiment, an alarm signal is generated when the correction index value is less than the lower limit of the correction control range. In one aspect, the method further includes: polishing a reference workpiece by pressing the reference workpiece against the polishing pad while rotating the polishing table; irradiating light from the optical sensor head to multiple film thickness measurement points on the reference workpiece for each time period during polishing of the reference workpiece; generating multiple reference spectra of reflected light from the multiple film thickness measurement points; calculating multiple feature quantities of the multiple reference spectra; performing data mapping by plotting multiple times at which the multiple reference spectra were generated and multiple reference data points identified from the multiple feature quantities of the multiple reference spectra on the coordinate system; and creating the threshold range for each time period during polishing of the reference workpiece based on the multiple reference data points on the coordinate system. In one embodiment, the threshold range is a range within a predetermined Mahalanobis distance from a reference point of the plurality of reference data points. In one aspect, when the correction index value is greater than the upper limit of the correction management range, the plurality of reference data points are updated by adding the plurality of measurement data points to the plurality of reference data points, and the threshold range is updated based on the updated plurality of reference data points.

[0009] In one aspect, the method further includes selecting either a first set of threshold ranges or a second set of threshold ranges from the progression of the plurality of measurement data points over time as the workpiece is polished, the threshold range being one of the plurality of threshold ranges of the selected one of the first set and the second set, the first set of threshold ranges being predetermined from a plurality of reference data points obtained during polishing of a first reference workpiece, and the second set of threshold ranges being predetermined from a plurality of reference data points obtained during polishing of a second reference workpiece having a surface structure different from that of the first reference workpiece. In one embodiment, the reference workpieces are a first reference workpiece and a second reference workpiece, and the method further includes creating multiple threshold ranges corresponding to different time intervals by combining a first threshold range created from multiple reference data points obtained during polishing of the first reference workpiece and a second threshold range created from multiple reference data points obtained during polishing of the second reference workpiece. In one aspect, the optical sensor heads are a first optical sensor head and a second optical sensor head positioned at different positions within the polishing table, and the method further includes creating multiple threshold ranges corresponding to different time intervals by combining a first threshold range created from multiple reference data points obtained by light irradiation from the first optical sensor head during polishing of the reference workpiece and a second threshold range created from multiple reference data points obtained by light irradiation from the second optical sensor head during polishing of the reference workpiece. In one aspect, each of the plurality of feature quantities includes at least a k-th principal component (k is a natural number) obtained by performing principal component analysis on a data set including a plurality of intensities of the reflected light at a plurality of wavelengths of each measured spectrum. In one aspect, when the correction index value is less than the lower limit of the correction control range during a plurality of consecutive time intervals during polishing of the workpiece, a plurality of new threshold ranges corresponding to the plurality of consecutive time intervals are created from a plurality of measurement data points acquired during the plurality of consecutive time intervals.

[0010] In one aspect, a polishing apparatus for a workpiece is provided, comprising: a polishing table; a table motor for rotating the polishing table; a polishing head for pressing the workpiece against a polishing pad on the polishing table to polish the workpiece; an optical sensor head for irradiating light onto a plurality of film thickness measurement points on the workpiece for each time interval during polishing of the workpiece; and a processing system for generating a plurality of measurement spectra of reflected light from the plurality of film thickness measurement points, wherein the processing system is configured to calculate a plurality of feature quantities of the plurality of measurement spectra, perform data mapping by plotting a plurality of times at which the plurality of measurement spectra were generated and a plurality of measurement data points identified from the plurality of feature quantities of the plurality of measurement spectra on a coordinate system, determine a correction index value representing the number of the plurality of measurement data points that exist within a threshold range defined on the coordinate system for each time interval, and determine whether the correction index value is within a correction control range.

[0011] In one aspect, the processing system is configured to correct the plurality of feature quantities by moving the plurality of measurement data points on the coordinate system until the plurality of measurement data points fall within the threshold range when the correction index value is within the correction management range. In one aspect, the processing system is configured to generate an alarm signal when the correction index value is less than a lower limit of the correction control range. In one aspect, the processing system is configured to select either a first set of threshold ranges or a second set of threshold ranges from the progression of the plurality of measurement data points over time as the workpiece is polished, the threshold range being one of the plurality of threshold ranges of the selected one of the first set and the second set, the first set of threshold ranges being predetermined from reference data points obtained during polishing of a first reference workpiece, and the second set of threshold ranges being predetermined from reference data points obtained during polishing of a second reference workpiece having a surface structure different from that of the first reference workpiece.

[0012] In one aspect, the processing system is configured to perform principal component analysis on a data set including multiple intensities of the reflected light at multiple wavelengths for each measured spectrum, and to determine features including at least a k-th principal component (k is a natural number) obtained from the principal component analysis. In one aspect, the processing system is configured to, when the correction index value is less than a lower limit of the correction control range during a plurality of consecutive time intervals during polishing of the workpiece, create a plurality of new threshold ranges corresponding to the plurality of consecutive time intervals from a plurality of measurement data points acquired during the plurality of consecutive time intervals. In one aspect, the processing system is configured to determine the threshold range, the range being within a predetermined Mahalanobis distance from a reference point of a plurality of reference data points obtained from polishing a reference workpiece. In one aspect, the processing system is configured to, when the correction index value is greater than an upper limit of the correction control range, update the plurality of reference data points by adding the plurality of measurement data points to the plurality of reference data points, and update the threshold range based on the updated plurality of reference data points. [Effects of the Invention]

[0013] The measurement data points are compared with the threshold range for each time interval during the workpiece polishing time, and the processing system can determine whether the measurement spectrum is normal based on the comparison results. Because a threshold range is defined for each time interval, polishing of the workpiece can be stopped when the measurement data points significantly deviate from the threshold range. As a result, over-polishing of the workpiece can be prevented. Subsequent damage to the workpiece due to an incorrect polishing process can also be prevented. The workpiece can be re-polished under different polishing conditions, or the workpiece can be removed from the polishing apparatus without re-polishing. As a result, the response time after detecting an abnormality can be shortened. If the abnormality in the measurement spectrum is due to the optical film thickness measurement device, the optical film thickness measurement device can be repaired. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Figure 2] FIG. 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measurement device. [Figure 3] FIG. 4 is a schematic diagram showing an example of a measured spectrum generated from light intensity measurement data. [Figure 4] FIG. 10 is a diagram showing an example of optical film thickness measurement points on a workpiece. [Figure 5] FIG. 1 illustrates one embodiment of data mapping. [Figure 6] FIG. 10 is a diagram showing a plurality of measurement data points MDN acquired when the polishing table has made its Nth rotation. [Figure 7] FIG. 10 is a diagram showing a plurality of measurement data points MDN+1 acquired when the polishing table is rotating for the N+1th time. [Figure 8] FIG. 10 is a diagram showing a plurality of measurement data points MDN+2 acquired when the polishing table is at its N+2th rotation. [Figure 9] FIG. 10 illustrates an embodiment in which the plurality of measurement data points MDN+2 is moved until the plurality of measurement data points MDN+2 falls within a threshold range TRN+2. [Figure 10]FIG. 10 is a diagram showing an example in which all or most of a plurality of measurement data points MDN+3 lie outside the threshold range TRN+3. [Figure 11] 11 is a flowchart of the embodiment described with reference to FIGS. [Figure 12] FIG. 1 illustrates an embodiment in which a first set and a second set of threshold ranges are provided. [Figure 13] 1 is a graph showing an example of measurement data points plotted on a coordinate system over time during polishing of a workpiece. [Figure 14] 14 is a flowchart of the embodiment described with reference to FIGS. 12 and 13. [Figure 15] 10 is a graph illustrating one embodiment of creating new threshold ranges during polishing of a workpiece. [Figure 16] FIG. 10 illustrates one embodiment of creating first and second threshold ranges from reference data points obtained during polishing of a first and second reference workpiece. [Figure 17] FIG. 2 is a top view showing an example of the positional relationship between an optical sensor head and a polishing head. [Figure 18] FIG. 10 illustrates an embodiment in which a first threshold range and a second threshold range are combined to create multiple threshold ranges corresponding to different time intervals. [Figure 19] FIG. 1 is a top view showing an embodiment of a polishing apparatus equipped with a first optical sensor head and a second optical sensor head. [Figure 20] A figure showing an example of multiple first threshold ranges created from multiple reference data points obtained by irradiating light from a first optical sensor head, and multiple second threshold ranges created from multiple reference data points obtained by irradiating light from a second optical sensor head. [Figure 21] FIG. 10 is a diagram showing a plurality of first threshold ranges and a plurality of second threshold ranges arranged along the time axis. [Figure 22] FIG. 10 is a diagram showing a plurality of first threshold ranges and a plurality of second threshold ranges moved along a feature axis. DETAILED DESCRIPTION OF THE INVENTION

[0015] Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating one embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 supporting a polishing pad 2, a polishing head 1 pressing a workpiece W against the polishing pad 2, a table motor 6 rotating the polishing table 3, a polishing liquid supply nozzle 5 for supplying a polishing liquid such as slurry onto the polishing pad 2, and an operation control unit 9 for controlling the operation of the polishing apparatus. The upper surface of the polishing pad 2 forms a polishing surface 2a for polishing the workpiece W. The workpiece W has a film on its surface that forms an interconnect structure. Examples of the workpiece W include wafers, substrates, wiring boards, and square substrates used in the manufacture of semiconductor devices. In one example, the workpiece W is a product wafer on which a multilayer or single-layer film is formed.

[0016] The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head rotating device 15. The polishing head rotating device 15 is configured to rotate the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The configuration of the polishing head rotating device 15 is not particularly limited, but in one example, the polishing head rotating device 15 includes an electric motor, a belt, a pulley, etc. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the direction indicated by the arrow. The polishing head 1, the polishing head rotating device 15, and the table motor 6 are connected to an operation control unit 9.

[0017] The workpiece W is polished as follows. The table motor 6 and polishing head rotating device 15 rotate the polishing table 3 and polishing head 1 in the directions indicated by the arrows in FIG. 1, while a polishing liquid is supplied from the polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While the workpiece W is rotated by the polishing head 1, the polishing head 1 presses the workpiece W against the polishing surface 2a of the polishing pad 2 with the polishing liquid present on the polishing pad 2. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad 2.

[0018] The operation control unit 9 includes a storage device 9a storing a program and an arithmetic unit 9b that executes calculations according to instructions included in the program. The operation control unit 9 is composed of at least one computer. The storage device 9a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic unit 9b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the operation control unit 9 is not limited to these examples.

[0019] The polishing apparatus is equipped with an optical film thickness measuring device 20 that measures the film thickness of the workpiece W. The optical film thickness measuring device 20 is equipped with a light source 22 that emits light, an optical sensor head 25 that irradiates the workpiece W with the light from the light source 22 and receives the light reflected from the workpiece W, a spectrometer 27 connected to the optical sensor head 25, and a processing system 30 that measures the film thickness of the workpiece W based on the spectrum of the light reflected from the workpiece W. The optical sensor head 25 is disposed within the polishing table 3 and rotates together with the polishing table 3.

[0020] The processing system 30 includes a storage device 30a that stores a program and an arithmetic device 30b that executes calculations according to instructions included in the program. The processing system 30 is composed of at least one computer. The storage device 30a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic device 30b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the processing system 30 is not limited to these examples.

[0021] Each of the operation control unit 9 and the processing system 30 may be configured with multiple computers. For example, each of the operation control unit 9 and the processing system 30 may be configured with a combination of an edge server and a cloud server. In one embodiment, the operation control unit 9 and the processing system 30 may be configured with a single computer.

[0022] 2 is a cross-sectional view showing the detailed configuration of the optical film thickness measurement device 20. The optical film thickness measurement device 20 includes a light-projecting fiber optic cable 31 connected to the light source 22 and a light-receiving fiber optic cable 32 connected to the spectrometer 27. The tip 31a of the light-projecting fiber optic cable 31 and the tip 32a of the light-receiving fiber optic cable 32 form the optical sensor head 25. That is, the light-projecting fiber optic cable 31 guides light emitted by the light source 22 to the workpiece W on the polishing pad 2, and the light-receiving fiber optic cable 32 receives the light reflected from the workpiece W and transmits it to the spectrometer 27.

[0023] The spectrometer 27 is connected to a processing system 30. The light-emitting fiber optic cable 31, the light-receiving fiber optic cable 32, the light source 22, and the spectrometer 27 are attached to the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The optical sensor head 25, which is composed of the tip 31a of the light-emitting fiber optic cable 31 and the tip 32a of the light-receiving fiber optic cable 32, is positioned facing the surface of the workpiece W on the polishing pad 2.

[0024] The optical sensor head 25 is positioned at a position where it crosses the surface of the workpiece W on the polishing pad 2 every time the polishing table 3 and polishing pad 2 make one rotation. The polishing pad 2 has a through hole 2b located above the optical sensor head 25. The optical sensor head 25 irradiates light onto the workpiece W through the through hole 2b every time the polishing table 3 makes one rotation, and receives reflected light from the workpiece W through the through hole 2b.

[0025] In one embodiment, a flow of pure water may be formed in the through hole 2b of the polishing pad 2 to prevent the polishing liquid and polishing debris from contacting the optical sensor head 25. Light is guided from the optical sensor head 25 through the pure water to the workpiece W, and the reflected light from the workpiece W passes through the pure water and is received by the optical sensor head 25. In another embodiment, a transparent window (not shown) may be fitted in the through hole 2b of the polishing pad 2. The transparent window is made of a material (e.g., transparent resin) that allows light to pass through. In this case, light is guided from the optical sensor head 25 to the workpiece W through the transparent window, and the reflected light from the workpiece W passes through the transparent window and is received by the optical sensor head 25.

[0026] The light source 22 is a flash light source that emits light repeatedly at short time intervals. An example of the light source 22 is a xenon flash lamp. The light source 22 is electrically connected to the operation control unit 9 and emits light in response to a trigger signal sent from the operation control unit 9. More specifically, while the optical sensor head 25 traverses the surface of the workpiece W on the polishing pad 2, the light source 22 receives multiple trigger signals and emits light multiple times. Therefore, each time the polishing table 3 rotates once, light is irradiated onto multiple film thickness measurement points on the workpiece W.

[0027] The light emitted by the light source 22 is transmitted to the optical sensor head 25. That is, the light is transmitted to the optical sensor head 25 through the light-emitting fiber optic cable 31 and emitted from the optical sensor head 25. The light passes through the through hole 2b of the polishing pad 2 and is incident on the workpiece W on the polishing pad 2. The light reflected from the workpiece W passes through the through hole 2b of the polishing pad 2 again and is received by the optical sensor head 25. The light reflected from the workpiece W is transmitted to the spectrometer 27 through the light-receiving fiber optic cable 32.

[0028] The spectrometer 27 is configured to separate the reflected light according to wavelength and measure the intensity of the reflected light at each wavelength over a predetermined wavelength range. That is, the spectrometer 27 separates the reflected light from the workpiece W according to wavelength and measures the intensity of the reflected light at each wavelength over a predetermined wavelength range to generate light intensity measurement data. The intensity of the reflected light at each wavelength may also be expressed as a relative value such as reflectance or relative reflectance. The light intensity measurement data is sent to the processing system 30.

[0029] The processing system 30 generates a spectrum of reflected light as shown in FIG. 3 from the light intensity measurement data. In the following description, the spectrum of reflected light from the workpiece W is referred to as the measured spectrum. The measured spectrum of reflected light from the workpiece W contains information about the film thickness of the workpiece W. In other words, the measured spectrum of reflected light varies depending on the film thickness of the workpiece W. The processing system 30 is configured to determine the film thickness of the workpiece W based on the measured spectrum of reflected light. For example, the processing system 30 determines a reference spectrum from a reference spectrum library that has a shape that is closest to the measured spectrum of reflected light, and determines the film thickness associated with this determined reference spectrum. In another example, the processing system 30 calculates a feature of the measured spectrum of reflected light, determines a reference feature from a reference feature library that is closest to the feature, and determines the film thickness associated with this determined reference feature. In another example, the processing system 30 performs a Fourier transform on the measured spectrum of reflected light and determines the film thickness from the resulting frequency spectrum.

[0030] FIG. 4 is a diagram showing an example of multiple film thickness measurement points on the workpiece W. As described above, during polishing of the workpiece W, the optical sensor head 25 irradiates the surface of the workpiece W with light multiple times while moving across the surface of the workpiece W with each rotation of the polishing table 3. Therefore, as shown in FIG. 4, multiple film thickness measurement points M irradiated with light from the optical sensor head 25 are arranged in a radial direction on the surface of the workpiece W. With each rotation of the polishing table 3, the optical sensor head 25 receives reflected light from the multiple film thickness measurement points M, and the processing system 30 generates multiple measurement spectra of the reflected light from the multiple film thickness measurement points M. Furthermore, the processing system 30 determines multiple film thicknesses at the multiple film thickness measurement points M from the multiple measurement spectra of the reflected light.

[0031] The film thickness of the workpiece W varies depending on the measurement spectrum of the reflected light. Therefore, in order for the optical film thickness measurement device 20 to correctly measure the film thickness of the workpiece W, it is necessary to acquire an accurate measurement spectrum that reflects the film thickness. However, the measurement spectrum may change due to failure or deterioration over time of optical elements such as the light source 22 and the optical fiber cables 31 and 32.

[0032] Therefore, the processing system 30 inspects the measured spectrum of the reflected light from the workpiece W, as described below. First, a reference workpiece having the same surface structure as the workpiece W is polished by the polishing apparatus shown in FIGS. 1 and 2. The reference workpiece is polished under the same polishing conditions as the workpiece W. The polishing conditions include the rotation speed of the polishing table 3, the rotation speed of the polishing head 1, the supply flow rate of the polishing liquid, the pressing pressure of the polishing head 1 against the workpiece W, etc.

[0033] The processing system 30 generates a spectrum of reflected light from the reference workpiece according to the method described with reference to Figures 1 to 4. In the following description, the spectrum of reflected light from the reference workpiece will be referred to as a reference spectrum. As described with reference to Figure 4, each time the polishing table 3 rotates once, light is irradiated onto multiple film thickness measurement points on the reference workpiece, and multiple reference spectra of reflected light from the multiple film thickness measurement points are generated.

[0034] The processing system 30 calculates a feature amount for each of the multiple reference spectra. The feature amount is an index representing the feature of each reference spectrum. More specifically, since each reference spectrum represents the intensity of reflected light at each wavelength as shown in FIG. 3, the feature amount is an index representing the feature of the intensity of reflected light at each wavelength of the reference spectrum.

[0035] In this embodiment, the processing system 30 performs principal component analysis on a data set including multiple intensities of reflected light at multiple wavelengths of each reference spectrum, and determines a feature quantity including at least the k-th principal component (k is a natural number) obtained from the principal component analysis. An example of a formula for calculating the k-th principal component is as follows: kth principal component = w k1 X1+w k2 X2+w k2 X3+... where Xn (n is a natural number) represents the intensity of reflected light at wavelength λn of the reference spectrum, and w kn is the weighting factor for the intensity Xn.

[0036] The processing system 30 calculates at least one feature for each reference spectrum. For example, the processing system 30 calculates the k-th principal component as a feature for each reference spectrum. In another example, the processing system 30 may calculate the k-th principal component and the k+1-th principal component as features for each reference spectrum. In this embodiment, the feature is the k-th principal component (k is a natural number) obtained by principal component analysis of the dataset. However, in other embodiments, the feature may be a statistical value of the dataset (e.g., mean, standard deviation, variance, etc.).

[0037] The optical sensor head 25 irradiates light onto multiple film thickness measurement points on the reference workpiece and receives reflected light from the multiple film thickness measurement points for each time interval during the polishing time of the reference workpiece. In one embodiment, the time interval is the time it takes for the polishing table 3 to make L rotations (L is a natural number). That is, for each L rotations of the polishing table 3, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the reference workpiece and receives reflected light from the multiple film thickness measurement points. For each L rotations of the polishing table 3, the processing system 30 generates multiple reference spectra of the reflected light from the multiple film thickness measurement points on the reference workpiece and calculates multiple feature quantities from the multiple reference spectra. Therefore, multiple feature quantities are acquired for each L rotations of the polishing table 3. In other embodiments, the time interval may be defined in terms of time. For example, the time interval may be defined in seconds (e.g., 0.5 seconds, 1 second, or 1.5 seconds).

[0038] The processing system 30 associates multiple feature quantities with multiple times at which multiple reference spectra were generated. Because each feature quantity is calculated from the corresponding reference spectrum, each feature quantity can be associated with the time at which the corresponding reference spectrum was generated. The time at which a reference spectrum was generated is not particularly limited as long as it directly or indirectly indicates the time at which the reference spectrum was generated by the processing system 30. For example, the time at which a reference spectrum was generated may be represented by the time at which light for generating the reference spectrum was emitted from the light source 22, or the time at which the spectrometer 27 received the reflected light for generating the reference spectrum, or the time at which the processing system 30 received the light intensity measurement data for generating the reference spectrum, or may be a time linked to the time at which the reference spectrum was generated by the processing system 30.

[0039] The processing system 30 performs data mapping by plotting, on a coordinate system, the multiple times at which the multiple reference spectra were generated and the multiple reference data points identified from the multiple feature quantities corresponding to the multiple times. Figure 5 is a diagram showing one embodiment of data mapping. As shown in Figure 5, the coordinate system has a vertical axis representing the feature quantities of the reference spectra and a horizontal axis representing time.

[0040] The processing system 30 generates a plurality of reference spectra of reflected light from a plurality of film thickness measurement points on the reference workpiece for each time interval during the polishing time of the reference workpiece, and calculates a plurality of feature quantities of the plurality of reference spectra. In the embodiment described below, the time interval is the time it takes for the polishing table 3 to make one rotation. For each rotation of the polishing table 3, the processing system 30 plots the plurality of feature quantities of the plurality of reference spectra and a plurality of reference data points identified from the corresponding plurality of times on a coordinate system.

[0041] FD shown in Figure 5 N represents a plurality of reference data points acquired when the polishing table 3 has made an Nth rotation (N is a natural number), and FD N+1represents a number of reference data points acquired when the polishing table 3 rotates (N+1), and FD N+2 represents the plurality of reference data points acquired when the polishing table 3 is at the (N+2)th rotation. As can be seen from FIG. 5, the number of reference data points increases with the polishing time of the reference workpiece. In the following description, the reference data point FD N , F.D. N+1 , F.D. N+2 Each of these is sometimes simply referred to as a reference data point FD.

[0042] The processing system 30 determines a threshold range for each time interval. The threshold range is an allowable dispersion range of the multiple reference data points, determined on a coordinate system for each time interval. All or most of the multiple reference data points FD acquired for each time interval are within the corresponding threshold range. In one embodiment, a predetermined percentage (%) of the multiple reference data points FD are within the corresponding threshold range. The predetermined percentage (%) is, for example, within the range of 90 to 100%.

[0043] In the example shown in Figure 5, the threshold range TR N is a set of multiple reference data points FD N The threshold range TR N+1 is a set of multiple reference data points FD N+1 The threshold range TR N+2 is a set of multiple reference data points FD N+2 Similarly, the processing system 30 determines a plurality of threshold ranges corresponding to a plurality of time intervals. In the following description, the threshold range TR N , T.R. N+1 , T.R. N+2 Each of these is sometimes simply referred to as the threshold range TR.

[0044] In one embodiment, each threshold range TR is a range within a predetermined Mahalanobis distance from a reference point determined from a plurality of reference data points FD within the corresponding time interval, where the predetermined Mahalanobis distance is the distance at which a predetermined percentage of the plurality of reference data points FD fall within the corresponding threshold range TR.

[0045] In another embodiment, each threshold range TR is a range within a predetermined Euclidean distance from a reference point defined from the plurality of reference data points FD within the corresponding time interval. The predetermined Euclidean distance is a distance within which a predetermined percentage (%) of the plurality of reference data points FD fall within the corresponding threshold range TR. In yet another embodiment, each threshold range TR is a range defined based on a standard deviation or variance calculated from a normal distribution of the plurality of reference data points FD within the corresponding time interval.

[0046] An example of the reference point is the center of gravity of the multiple reference data points FD within the time interval corresponding to each threshold range TR. In one example, the center of gravity of the multiple reference data points FD may be determined by multiplying the distances of the multiple reference data points FD from the virtual center of gravity by different weighting coefficients according to the distances of the multiple reference data points FD. The processing system 30 stores multiple threshold ranges TR corresponding to multiple time intervals in the storage device 30a.

[0047] In the above embodiment, multiple threshold ranges TR were determined from reference data points obtained during polishing of one reference workpiece, but in one embodiment, multiple reference workpieces may be polished in the same manner, and multiple threshold ranges TR corresponding to multiple time intervals may be determined from reference data points obtained during polishing of these reference workpieces.

[0048] The processing system 30 uses a threshold range TR to inspect the measured spectrum of reflected light generated during polishing of the workpiece W. Polishing of the workpiece W and generation of the measured spectrum of reflected light from the workpiece W are performed in the same manner as for the reference workpiece. That is, the polishing table 3 is rotated by the table motor 6, and the workpiece W is polished by pressing the workpiece W against the polishing pad 2 on the polishing table 3 by the polishing head 1. The optical sensor head 25 irradiates light onto multiple film thickness measurement points on the workpiece W for each time interval during polishing of the workpiece W and receives reflected light from the multiple film thickness measurement points. In one example, the time interval corresponds to the time it takes for the polishing table 3 to make one rotation.

[0049] The processing system 30 generates multiple measurement spectra of reflected light from multiple film thickness measurement points and calculates multiple feature quantities for the multiple measurement spectra. The feature quantities for the measurement spectra are calculated in the same manner as the feature quantities for the reference spectra. That is, the processing system 30 calculates the k-th principal component (k is a natural number) by performing principal component analysis on a data set including multiple intensities of reflected light at multiple wavelengths for each measurement spectrum, and determines feature quantities that include at least the k-th principal component. The feature quantities for each measurement spectrum are the same type of index as the feature quantities for the reference spectrum. That is, if the feature quantity for the reference spectrum includes only the k-th principal component, the feature quantity for the measurement spectrum also includes only the k-th principal component. If the feature quantity for the reference spectrum includes the k-th principal component and the k+1-th principal component, the feature quantity for the measurement spectrum also includes the k-th principal component and the k+1-th principal component.

[0050] The processing system 30 performs data mapping by plotting the times at which the measured spectra were generated and the measured data points identified from the features on a coordinate system in the same manner as the data mapping performed for the reference spectra.

[0051] FIG. 6 shows a plurality of measurement data points MD acquired when the polishing table 3 is rotated N times. N 7 is a diagram showing a plurality of measurement data points MD obtained when the polishing table 3 is at the N+1th rotation. N+1 8 is a diagram showing a plurality of measurement data points MD obtained when the polishing table 3 is at the N+2th rotation. N+2 In the following description, the measurement data points MD N , M.D. N+1 , M.D. N+2 Each of the points MD may be simply referred to as a measurement data point MD. As shown in Figures 6 to 8, the processing system 30 plots multiple measurement data points MD on a coordinate system each time the polishing table 3 makes one rotation. The coordinate system has a vertical axis representing the feature amount and a horizontal axis representing time.

[0052] The processing system 30 determines a correction index value representing the number of measurement data points MD that are within a threshold range TR defined on the coordinate system for each time interval. This correction index value is an index indicating the degree to which the measurement data points MD are within the threshold range TR. Examples of correction index values ​​include the following: The number of measurement data points that lie within the threshold range The ratio of the number of multiple measurement data points that exist within the threshold range to the total number of multiple measurement data points The distance between the center of gravity of multiple measurement data points and the center of the threshold range

[0053] In the embodiment described below, the correction index value is the ratio of the number of the plurality of measurement data points MD that are within the threshold range TR to the total number of the plurality of measurement data points MD. In the example shown in FIG. 6, the processing system 30 N The threshold range TR corresponds to the time interval during which N Multiple measurement data points MD N The number of multiple measurement data points MD N The ratio of the number of the errors to the total number of errors is calculated, and the correction index value, which is the calculated ratio, is determined.

[0054] In this embodiment, the correction index value is the proportion of the multiple measurement data points MD that lie within the threshold range TR. For example, if the calculated correction index value is 100%, all of the multiple measurement data points MD lie within the threshold range TR. If the calculated correction index value is 50%, half of the multiple measurement data points MD lie within the threshold range TR. The processing system 30 determines whether the correction index value is within a predetermined correction control range. As will be described later, the correction control range is a numerical range for determining whether to correct the measurement spectrum, use the measurement spectrum for film thickness measurement without correction, or generate an alarm signal. For example, the correction control range is 20 to 80%.

[0055] In the example shown in FIG. 6, the processing system 30 determines the threshold range TR N Multiple measurement data points MDN The number of multiple measurement data points MD N The correction index value, which is the ratio of the number of measurement data points MD to the total number of measurement data points MD, is determined to be greater than the upper limit of the correction control range. N All or most of the values ​​are in the threshold range TR N Therefore, when the correction index value is greater than the upper limit of the correction control range, the processing system 30 calculates the correction index value from the plurality of measurement data points MD N The multiple measurement spectra corresponding to the respective points are determined to be normal, and multiple film thicknesses at the multiple film thickness measurement points on the workpiece W are determined (estimated) from the multiple measurement spectra.

[0056] The measurement data points MD shown in Fig. 6 N indicates that the corresponding measured spectrum is normal. Therefore, the measured data point MD N is the threshold range TR N Specifically, when the correction index value is greater than the upper limit of the correction control range, the processing system 30 updates the plurality of measurement data points MD N multiple reference data points FD N (See Figure 5) to add multiple reference data points FD N and update the updated multiple reference data points FD N Based on the threshold range TR N Update the threshold range TR N The reference data point FD used to determine N As the number of s is increased, the processing system 30 can determine a more accurate threshold range TR.

[0057] In the example shown in FIG. 7, the processing system 30 determines the threshold range TR N+1 Multiple measurement data points MD N+1 The number of multiple measurement data points MD N+1 Therefore, the processing system 30 determines that the correction index value, which is a ratio of the number of measurement data points MD to the total number of measurement data points MD, is greater than the upper limit of the correction control range. N+1The measurement data points MD shown in FIG. 7 are determined to be normal, and the thicknesses of the workpiece W at the measurement points MD are determined (estimated) from the measurement data points MD. N+1 indicates that the corresponding measured spectrum is normal, so the measured data point MD N+1 Threshold Range TR N+1 can be used to update

[0058] In the example shown in FIG. 8, the processing system 30 determines the threshold range TR N+2 Multiple measurement data points MD N+2 The number of multiple measurement data points MD N+2 When the correction index value is within the correction control range, the processing system 30 determines that the correction index value, which is the ratio of the number of measurement data points MD to the total number of measurement data points MD, is within the correction control range. N+2 Threshold range TR N+2 Multiple measurement data points MD N+2 By moving the coordinate system, multiple measurement data points MD N+2 Correct multiple feature quantities identified from multiple measurement data points MD N+2 Examples of movement include translation, rotation, and shrinking.

[0059] In one embodiment, the processing system 30 processes a plurality of measurement data points MD N+2 In this embodiment, the corrected feature quantities are converted into a plurality of corrected measurement spectra by moving each measurement data point MD N+2 Since the feature amount is the k-th principal component obtained by principal component analysis, the k-th principal component can be restored to the format of the original data set. That is, the processing system 30 converts each corrected feature amount into a plurality of intensities of reflected light at a plurality of wavelengths, and creates a corrected measured spectrum from the converted plurality of intensities and the corresponding plurality of wavelengths. The corrected measured spectrum is a spectrum that is within a threshold range TR N+2 Since the corrected measurement spectrum is generated from measurement data points present within the film thickness range, the processing system 30 can determine the exact film thickness from the corrected measurement spectrum.

[0060] In this embodiment, the feature amount is the k-th principal component (k is a natural number) obtained by principal component analysis of the dataset, but in other embodiments, the feature amount may be a statistical value of the dataset (for example, mean, standard deviation, variance, etc.). When the feature amount is the average of multiple intensities included in the dataset, the multiple intensities are corrected by subtracting an intensity corresponding to the amount of movement of the measurement data point into the threshold range TR from each of the multiple intensities of reflected light at multiple wavelengths, and a corrected measurement spectrum is created from the corrected multiple intensities and the corresponding multiple wavelengths.

[0061] In one embodiment, the processing system 30 may calculate the film thickness of the workpiece W from the corrected feature without creating a corrected measurement spectrum. For example, the processing system 30 determines a reference feature that is closest to the corrected feature from a reference feature library, and then determines the film thickness associated with the determined reference feature. The reference feature library includes multiple reference features and multiple corresponding film thicknesses.

[0062] In the example shown in FIG. 10, the processing system 30 sets the threshold range TR N+3 Multiple measurement data points MD N+3 The number of multiple measurement data points MD N+3 The correction index value, which is the ratio of the number of measurement data points MD to the total number of measurement data points MD, is determined to be smaller than the lower limit of the correction control range. N+3 All or most of the values ​​are in the threshold range TR N+3 Therefore, when the correction index value is smaller than the lower limit of the correction control range, the processing system 30 calculates the correction index value by dividing the plurality of measurement data points MD N+3 An alarm signal is generated that indicates an abnormality in the measured spectrum corresponding to the measured value.

[0063] In one embodiment, the processing system 30 may send an alarm signal to the operation control unit 9, and upon receiving the alarm signal, the operation control unit 9 may issue a command to the polishing apparatus to terminate polishing of the workpiece W. The operation control unit 9 may issue a command to the polishing apparatus to perform regrinding of the workpiece W. In another embodiment, the processing system 30 may send the alarm signal to a host computer that manages the polishing apparatus. Sending the alarm signal to the host computer can prompt the manager to inspect or repair the polishing apparatus.

[0064] FIG. 11 is a flow chart of the embodiment described with reference to FIGS. In step S101, the reference workpiece is polished by pressing it against the polishing pad 2 on the polishing table 3 while rotating the polishing table 3. For each time interval during the polishing time of the reference workpiece, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the reference workpiece, and the processing system 30 generates multiple reference spectra of the reflected light from the multiple film thickness measurement points.

[0065] The multiple film thickness measurement points of the reference workpiece are distributed across the entire surface of the reference workpiece. The surface of the reference workpiece includes a mixture of device regions and scribe lines. The light reflected from the scribe lines is significantly different from the light reflected from the device regions and may be noise in the film thickness measurement. Therefore, in one embodiment, the processing system 30 may perform filtering on the multiple reference spectra generated during polishing of the reference workpiece to remove the potentially noisy reference spectra.

[0066] In step S102, the processing system 30 calculates a plurality of feature quantities for a plurality of reference spectra. At least one feature quantity is calculated for each reference spectrum. Examples of the feature quantity include the k-th principal component (k is a natural number) obtained by principal component analysis, an average, and other statistical values. In step S103, the processing system 30 performs data mapping by plotting, on a coordinate system, multiple reference data points FD identified from multiple times at which multiple reference spectra were generated and the corresponding multiple feature quantities (see FIG. 5).

[0067] In step S104, the processing system 30 determines a threshold range TR for each time interval within the polishing time of the reference workpiece based on the multiple reference data points FD on the coordinate system (see FIG. 5). In one embodiment, the time interval is the time it takes for the polishing table 3 to make one rotation. Multiple threshold ranges TR corresponding to the multiple time intervals are determined. In one embodiment, each threshold range TR is a range within a predetermined Mahalanobis distance from a reference point that is predetermined based on the multiple reference data points FD within the corresponding time interval.

[0068] In step S105, the workpiece W is polished by pressing it against the polishing pad 2 on the polishing table 3 while rotating the polishing table 3. During each time interval during polishing of the workpiece W, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the workpiece W, and the processing system 30 generates multiple measurement spectra of reflected light from the multiple film thickness measurement points. In one embodiment, the processing system 30 may filter the multiple measurement spectra generated during polishing of the workpiece W to remove measurement spectra that may be noise.

[0069] In step S106, the processing system 30 calculates a plurality of feature quantities of the plurality of measured spectra. The feature quantities of the measured spectra are calculated in the same manner as the feature quantities of the reference spectra calculated in step S102 above. In step S107, the processing system 30 performs data mapping by plotting, on a coordinate system, the multiple times at which the multiple measurement spectra were generated and the multiple measurement data points MD identified from the multiple feature quantities of the multiple measurement spectra (see Figures 6, 7, and 8).

[0070] In step S108, the processing system 30 determines a correction index value representing the number of measurement data points present within a threshold range TR defined on the coordinate system for each time interval, and determines whether the correction index value is within the correction control range. In one example, the correction index value is the ratio of the number of measurement data points present within each threshold range TR to the total number of measurement data points. In another example, the correction index value is the actual number of measurement data points present within each threshold range TR.

[0071] In step S109, if the correction index value is within the correction control range, the processing system 30 corrects the plurality of feature quantities corresponding to the plurality of measurement data points MD by moving the plurality of measurement data points MD on the coordinate system until the plurality of measurement data points MD fall within the corresponding threshold range TR (see FIG. 9 ). In one embodiment, the processing system 30 generates a plurality of corrected measurement spectra by converting the corrected plurality of feature quantities into a plurality of measurement spectra. The processing system 30 determines (estimates) a plurality of film thicknesses at the plurality of film thickness measurement points on the workpiece W from the plurality of corrected measurement spectra. In another embodiment, the processing system 30 determines (estimates) a plurality of film thicknesses at the plurality of film thickness measurement points on the workpiece W from the corrected plurality of feature quantities without generating a corrected measurement spectrum.

[0072] In step S110, if the correction index value is greater than the upper limit of the correction management range, the processing system 30 determines (estimates) multiple film thicknesses at multiple film thickness measurement points on the workpiece W from the measurement spectrum without correcting multiple feature quantities corresponding to multiple measurement data points MD. In step S111, if the correction index value is smaller than the lower limit of the correction control range, the processing system 30 generates an alarm signal. The processing system 30 may send the alarm signal to the operation control unit 9 to stop polishing the workpiece W.

[0073] The change in the spectrum of reflected light over polishing time shows different trends depending on the surface structure of the workpiece W. In particular, the spectrum of reflected light from the workpiece W can be affected not only by the top layer of the workpiece W but also by the underlying layers. As a result, the change in the measurement data points identified from the feature amounts and time over polishing time can vary depending on the surface structure of the workpiece W. In order to correctly inspect the spectrum of reflected light from the workpiece W, it is necessary to select an appropriate threshold range based on differences in the surface structure of the workpiece W.

[0074] 12, the processing system 30 has a first set and a second set of threshold ranges determined from reference data points obtained during polishing of a plurality of reference workpieces having different surface structures. Details of this embodiment that are not specifically described are the same as those of the previously described embodiment, and therefore, a redundant description thereof will be omitted.

[0075] A first set of threshold ranges is generated from reference data points obtained during polishing of a first reference workpiece, and a second set of threshold ranges is generated from reference data points obtained during polishing of a second reference workpiece. The first and second reference workpieces are polished under the same polishing conditions as workpiece W. The first and second sets of threshold ranges are generated in a manner similar to the embodiment described with reference to FIG. 5.

[0076] The first reference workpiece and the second reference workpiece have different surface structures. As a result, the trend of the first set of threshold ranges TR1 with polishing time is different from the trend of the second set of threshold ranges TR2 with polishing time, as shown in Figure 12. In the example shown in Figure 12, the first set of threshold ranges TR1 shows a downward trend with polishing time, while the second set of threshold ranges TR2 shows an upward trend with polishing time. The first set of threshold ranges TR1 and the second set of threshold ranges TR2 are stored in a memory device 30a of the processing system 30.

[0077] FIG. 13 is a graph showing an example of the temporal progression of measurement data points MD plotted on a coordinate system during polishing of a workpiece W. The processing system 30 selects either the first set of threshold ranges TR1 or the second set of threshold ranges TR2 shown in FIG. 12 based on the trend of progression of the measurement data points MD over the polishing time of the workpiece W. In the example shown in FIG. 13, the measurement data points MD show an upward trend over the polishing time. Therefore, the processing system 30 selects the second set of threshold ranges TR2. After the second set is selected, the processing system 30 determines a correction index value representing the number of measurement data points MD that exist within the threshold range TR2 defined on the coordinate system for each time interval, as in the above-described embodiment, and determines whether the correction index value is within the correction control range.

[0078] In one embodiment, the processing system 30 may have three or more sets of threshold ranges obtained from reference data points obtained during polishing of three or more reference workpieces having different surface structures. The processing system 30 may select one of the three or more sets based on a trend of the plurality of measurement data points over time as the workpiece W is polished.

[0079] FIG. 14 is a flow chart of the embodiment described with reference to FIGS. In step S201, a first reference workpiece is pressed against the polishing pad 2 on the polishing table 3 while the polishing table 3 is rotated, and the first reference workpiece is polished. For each time period during polishing of the first reference workpiece, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the first reference workpiece, and the processing system 30 generates multiple reference spectra of reflected light from the multiple film thickness measurement points. Similarly, a second reference workpiece is pressed against the polishing pad 2 on the polishing table 3 while the polishing table 3 is rotated, and the second reference workpiece is polished. For each time period during polishing of the second reference workpiece, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the second reference workpiece, and the processing system 30 generates multiple reference spectra of reflected light from the multiple film thickness measurement points.

[0080] In step S202, the processing system 30 calculates a plurality of features of a plurality of reference spectra obtained from polishing the first reference workpiece and a plurality of features of a plurality of reference spectra obtained from polishing the second reference workpiece. In step S203, the processing system 30 performs data mapping by plotting, on a coordinate system, the multiple times at which the multiple reference spectra obtained from polishing the first reference workpiece were generated and the multiple reference data points FD identified from the corresponding multiple feature quantities (see FIG. 12). Similarly, the processing system 30 performs data mapping by plotting, on a coordinate system, the multiple times at which the multiple reference spectra obtained from polishing the second reference workpiece were generated and the multiple reference data points FD identified from the corresponding multiple feature quantities (see FIG. 12).

[0081] In step S204, the processing system 30 determines a first set of multiple threshold ranges TR1 defined for each time interval within the polishing time of the first reference workpiece based on the multiple reference data points FD on the coordinate system (see FIG. 12). Similarly, the processing system 30 determines a second set of multiple threshold ranges TR2 defined for each time interval within the polishing time of the second reference workpiece based on the multiple reference data points FD on the coordinate system (see FIG. 12).

[0082] In step S205, the workpiece W is polished by pressing it against the polishing pad 2 on the polishing table 3 while rotating the polishing table 3. During each time interval during polishing of the workpiece W, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the workpiece W, and the processing system 30 generates multiple measurement spectra of the reflected light from the multiple film thickness measurement points.

[0083] In step S206, the processing system 30 calculates a plurality of feature quantities of the plurality of measured spectra. In step S207, the processing system 30 performs data mapping by plotting, on a coordinate system, the multiple times at which the multiple measurement spectra were generated and the multiple measurement data points MD identified from the multiple feature quantities of the multiple measurement spectra (see FIG. 13). In step S208, the processing system 30 selects either a first set of multiple threshold ranges TR1 or a second set of multiple threshold ranges TR2 based on the progression of the multiple measurement data points MD over the polishing time of the workpiece W.

[0084] In step S209, the processing system 30 determines a correction index value representing the number of measurement data points MD that exist within the selected first set of threshold ranges TR1 or second set of threshold ranges TR2, and determines whether the correction index value is within a predetermined correction control range. In step S210, if the correction index value is within the correction control range, the processing system 30 corrects the plurality of feature quantities corresponding to the plurality of measurement data points MD by moving the plurality of measurement data points MD on the coordinate system until the plurality of measurement data points MD fall within the corresponding threshold range TR1 or TR2 (see FIG. 9 ). In one embodiment, the processing system 30 generates a plurality of corrected measurement spectra by converting the corrected plurality of feature quantities into a plurality of measurement spectra. The processing system 30 determines (estimates) a plurality of film thicknesses at the plurality of film thickness measurement points on the workpiece W from the plurality of corrected measurement spectra. In another embodiment, the processing system 30 determines (estimates) a plurality of film thicknesses at the plurality of film thickness measurement points on the workpiece W from the corrected plurality of feature quantities without generating a corrected measurement spectrum.

[0085] In step S211, if the correction index value is greater than the upper limit of the correction control range, the processing system 30 determines (estimates) multiple film thicknesses at multiple film thickness measurement points on the workpiece W from the measurement spectrum without correcting multiple feature quantities corresponding to multiple measurement data points MD. In step S212, if the correction index value is smaller than the lower limit of the correction control range, the processing system 30 generates an alarm signal. The processing system 30 may send the alarm signal to the operation control unit 9 to stop polishing the workpiece W.

[0086] 12-14, multiple sets of threshold ranges are used that are prepared in advance. In one embodiment, the processing system 30 may generate a new set of thresholds from measured spectra obtained during polishing of the workpiece W. For example, in the early stages of polishing the workpiece W, the processing system 30 may have only a first set of threshold ranges TR1 shown in FIG. 12, and generate a second set of threshold ranges TR2 shown in FIG. 12 from measured spectra obtained during polishing of the workpiece W.

[0087] If the measurement data points MD over the polishing time of the workpiece show an upward trend as shown in Figure 13, the measurement data points MD are outside the first set of threshold ranges TR1 of Figure 12. Therefore, the processing system 30 generates an alarm signal and commands the polishing apparatus to stop polishing the workpiece. However, the upward trend shown in Figure 13 is due to a workpiece of a different type than the workpiece that was originally intended to be polished, and is not due to a malfunction of the polishing apparatus.

[0088] Therefore, in this embodiment, when the correction index value is smaller than the lower limit of the correction control range during multiple consecutive time intervals during polishing of the workpiece W, the processing system 30 creates multiple new threshold ranges on the coordinate system corresponding to the multiple consecutive time intervals from multiple measurement data points acquired during these multiple consecutive time intervals.

[0089] For example, as shown in FIG. 15, a plurality of measurement data points MD obtained at successive time intervals during polishing of a workpiece W may be N ,MD N+1 ,MD N+2 ,MD N+3 is within the preset threshold range TR1 N ,TR1 N+1 ,TR1 N+2 ,TR1 N+3 If so, the processing system 30 calculates the number of measurement data points MD N ,MD N+1 ,MD N+2 ,MD N+3 ...to the new threshold range TR2 N ,TR2 N+1 ,TR2 N+2 ,TR2 N+3 In one embodiment, the plurality of consecutive time intervals are the initial time of polishing the workpiece W. When the next workpiece is polished, the newly created threshold range TR2 N ,TR2 N+1 ,TR2 N+2 ,TR2 N+3The processing system 30 can then correctly inspect the measured spectrum using the newly created threshold ranges.

[0090] Next, yet another embodiment for creating threshold ranges will be described with reference to Figures 16 to 18. In this example, a first reference workpiece and a second reference workpiece having the same surface structure are used to create first and second threshold ranges for each time interval during polishing of the first and second reference workpieces.

[0091] As shown in FIG. 16, a first reference workpiece is polished by the polishing apparatus, and a plurality of reference data points FD (FD N ,FD N+1 ,FD N+2 ...), a plurality of first threshold ranges TR1 (TR1 N ,TR1 N+1 ,TR1 N+2 Similarly, a second reference workpiece is polished by the polishing apparatus, and a plurality of reference data points FD (FD N ,FD N+1 ,FD N+2 ...), a plurality of second threshold ranges TR2 (TR2 N ,TR2 N+1 ,TR2 N+2 Create a new one.

[0092] 17 is a top view showing an example of the positional relationship between the optical sensor head 25 and the polishing head 1. As shown in Fig. 17, during polishing of the first reference workpiece W1, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the surface of the first reference workpiece W1 while moving across the surface of the first reference workpiece W1 in accordance with the rotation of the polishing table 3. Similarly, during polishing of the second reference workpiece W2, the optical sensor head 25 irradiates light onto multiple film thickness measurement points on the surface of the second reference workpiece W2 while moving across the surface of the second reference workpiece W2 in accordance with the rotation of the polishing table 3.

[0093] The relative position of the optical sensor head 25 with respect to the first reference workpiece W1 at the start of polishing of the first reference workpiece W1 may be different from the relative position of the optical sensor head 25 with respect to the second reference workpiece W2 at the start of polishing of the second reference workpiece W2. That is, the time when the optical sensor head 25 first crosses the surface of the first reference workpiece W1 may be different from the time when the optical sensor head 25 first crosses the surface of the second reference workpiece W2. For this reason, as shown in FIG. 16, the positions of the multiple threshold ranges TR1 on the time axis may be different from the positions of the multiple threshold ranges TR2 on the time axis.

[0094] Therefore, the processing system 30 sets a plurality of first threshold ranges TR1 (TR1 N ,TR1 N+1 ,TR1 N+2 ...), and a plurality of second threshold ranges TR2 (TR2 N ,TR2 N+1 ,TR2 N+2 By combining the thresholds (TR1, . . .), multiple threshold ranges (TR1, . . . ) corresponding to different time intervals can be created, as shown in Figure 18. N ,TR2 N ,TR1 N+1 ,TR2 N+1 ,TR1 N+2 ,TR2 N+2 More specifically, a plurality of first threshold ranges TR1 (TR1 N ,TR1 N+1 ,TR1 N+2...), and a plurality of second threshold ranges TR2 (TR2 N ,TR2 N+1 ,TR2 N+2 By arranging the threshold ranges TR1 and TR2 along the time axis, the first threshold range TR1 and the plurality of second threshold ranges TR2 are combined.

[0095] The multiple threshold ranges obtained in this way reflect the differences in the initial positions of the optical sensor head 25, so the processing system 30 can correctly inspect the measured spectrum using the threshold ranges shown in FIG.

[0096] In this embodiment, two reference workpieces are used to create multiple threshold ranges corresponding to different time intervals, but three or more reference workpieces may be used to create multiple threshold ranges corresponding to different time intervals.

[0097] 19 is a top view showing one embodiment of a polishing apparatus equipped with a first optical sensor head 25A and a second optical sensor head 25B. Each of the optical sensor heads 25A and 25B is optically coupled to the light source 22 and the spectroscope 27 shown in FIG. 2. The optical sensor heads 25A and 25B are disposed at different positions in the circumferential direction of the polishing table 3. The optical sensor heads 25A and 25B are at the same distance from the center of the polishing table 3. The other configurations of the polishing apparatus are the same as those of the embodiment described with reference to FIGS. 1 and 2, so redundant description will be omitted.

[0098] As shown in FIG. 19, while the workpiece W is being polished, the optical sensor heads 25A and 25B rotate together with the polishing table 3, while the optical sensor heads 25A and 25B move across the surface of the workpiece W alternately (ie, at different times).

[0099] The threshold range is created based on reference data points obtained during polishing of the reference workpiece Wr. During polishing of the reference workpiece Wr, the optical sensor heads 25A, 25B rotate together with the polishing table 3 while moving alternately (i.e., at different times) across the surface of the reference workpiece Wr.

[0100] FIG. 20 shows a plurality of reference data points FD (FD) obtained by irradiating light from the first optical sensor head 25A during polishing of the reference workpiece Wr. N ,FD N+1 ,FD N+2 Multiple first threshold ranges TR1 (TR1 N ,TR1 N+1 ,TR1 N+2 ), and a plurality of reference data points FD (FD N ,FD N+1 ,FD N+2 Multiple second threshold ranges TR2 (TR2 N ,TR2 N+1 ,TR2 N+2 FIG. 10 is a diagram showing an example of...

[0101] 20, the positions of the multiple threshold ranges TR1 on the time axis differ from the positions of the multiple threshold ranges TR2 on the time axis due to differences in the positions of the optical sensor heads 25A and 25B. In addition, the positions of the multiple threshold ranges TR1 on the feature axis differ from the positions of the multiple threshold ranges TR2 on the feature axis due to individual differences between the optical sensor heads 25A and 25B.

[0102] Therefore, the processing system 30 sets a plurality of first threshold ranges TR1 (TR1 N ,TR1 N+1 ,TR1 N+2 ...), and a plurality of second threshold ranges TR2 (TR2 N ,TR2 N+1 ,TR2 N+2 By combining the threshold ranges (TR1 N,TR2 N ,TR1 N+1 ,TR2 N+1 ,TR1 N+2 ,TR2 N+2 21, the processing system 30 arranges a plurality of first threshold ranges TR1 and a plurality of second threshold ranges TR2 along the time axis, and further, as shown in FIG. 22, the processing system 30 moves at least one of the plurality of first threshold ranges TR1 and the plurality of second threshold ranges TR2 along the feature axis, thereby aligning the plurality of first threshold ranges TR1 and the plurality of second threshold ranges TR2.

[0103] The multiple threshold ranges obtained in this manner reflect differences in the placement and individual differences of the optical sensor heads 25A and 25B, so the processing system 30 can correctly inspect the measured spectrum using the threshold ranges shown in Figure 22.

[0104] In this embodiment, two optical sensor heads 25A and 25B are used to create multiple threshold ranges corresponding to different time intervals, but three or more optical sensor heads may also be used to create multiple threshold ranges corresponding to different time intervals.

[0105] The processing system 30 operates according to instructions contained in a program electronically stored in the storage device 30a. The program for causing the processing system 30 to execute the steps according to the embodiments described with reference to Figures 1 to 22 is recorded on a computer-readable recording medium, which is a non-transitory tangible object, and provided to the processing system 30 via the recording medium. Alternatively, the program may be input to the processing system 30 via a communication network such as the Internet or a local area network.

[0106] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0107] 1 polishing head 2 polishing pads 2a Polished surface 3 Polishing table 5 Polishing liquid supply nozzle 6 Table Motor 9. Operation control section 10 Head shaft 15 Polishing head rotation device 20 Optical film thickness measuring device 22 Light source 25 Optical sensor head 27 Spectrometer 30 Processing System 31 Light-emitting fiber optic cable 32 Receiving optical fiber cable W Workpiece

Claims

1. 1. A method for inspecting a spectrum of reflected light from a workpiece, comprising: While rotating the polishing table, the workpiece is pressed against a polishing pad on the polishing table to polish the workpiece; irradiating a plurality of film thickness measurement points on the workpiece with light from an optical sensor head for each time interval during polishing of the workpiece; generating a plurality of measurement spectra of reflected light from the plurality of film thickness measurement points; calculating a plurality of feature quantities of the plurality of measured spectra; performing data mapping by plotting, on a coordinate system, a plurality of times at which the plurality of measurement spectra were generated and a plurality of measurement data points identified from the plurality of feature quantities of the plurality of measurement spectra; determining a correction index value representing the number of the plurality of measurement data points existing within a threshold range defined on the coordinate system for each time interval; A method for determining whether the correction index value is within a correction control range.

2. 2. The method according to claim 1, wherein, when the correction index value is within the correction control range, the plurality of feature quantities are corrected by moving the plurality of measurement data points on the coordinate system until the plurality of measurement data points fall within the threshold range.

3. The method of claim 1 , further comprising generating an alarm signal when the correction index value is less than a lower limit of the correction control range.

4. While rotating the polishing table, a reference workpiece is pressed against the polishing pad to polish the reference workpiece; irradiating a plurality of film thickness measurement points on the reference workpiece with light from the optical sensor head for each time interval during polishing of the reference workpiece; generating a plurality of reference spectra of reflected light from the plurality of film thickness measurement points; calculating a plurality of feature quantities of the plurality of reference spectra; performing data mapping by plotting, on the coordinate system, a plurality of times at which the plurality of reference spectra were generated and a plurality of reference data points identified from the plurality of feature quantities of the plurality of reference spectra; The method of claim 1 , further comprising creating the threshold range for each time interval during polishing of the reference workpiece based on the plurality of reference data points on the coordinate system.

5. The method of claim 4 , wherein the threshold range is a range within a predetermined Mahalanobis distance from a reference point of the plurality of reference data points.

6. 5. The method of claim 4, wherein when the correction index value is greater than an upper limit of the correction control range, the plurality of reference data points are updated by adding the plurality of measurement data points to the plurality of reference data points, and the threshold range is updated based on the updated plurality of reference data points.

7. The method further includes selecting either a first set of threshold ranges or a second set of threshold ranges from the progression of the plurality of measurement data points over time polishing the workpiece; the threshold range is one of a plurality of threshold ranges in a selected one of the first set and the second set; the first set of threshold ranges is predetermined from a plurality of reference data points obtained during polishing of a first reference workpiece; 5. The method of claim 4, wherein the second set of threshold ranges is predetermined from a plurality of reference data points obtained during polishing of a second reference workpiece having a different surface structure than the first reference workpiece.

8. the reference workpieces are a first reference workpiece and a second reference workpiece; 5. The method of claim 4, further comprising: creating a plurality of threshold ranges corresponding to different time intervals by combining a first threshold range created from a plurality of reference data points obtained during polishing of the first reference workpiece and a second threshold range created from a plurality of reference data points obtained during polishing of the second reference workpiece.

9. the optical sensor heads are a first optical sensor head and a second optical sensor head disposed at different positions within the polishing table; 5. The method of claim 4, further comprising: creating a plurality of threshold ranges corresponding to different time intervals by combining a first threshold range created from a plurality of reference data points obtained by irradiating light from the first optical sensor head during polishing of the reference workpiece and a second threshold range created from a plurality of reference data points obtained by irradiating light from the second optical sensor head during polishing of the reference workpiece.

10. 2. The method of claim 1, wherein each of the plurality of feature quantities includes at least a k-th principal component (k is a natural number) obtained by performing principal component analysis on a data set including a plurality of intensities of the reflected light at a plurality of wavelengths of each measured spectrum.

11. 2. The method of claim 1, wherein when the correction index value is less than a lower limit of the correction control range for a plurality of consecutive time intervals during polishing of the workpiece, a plurality of new threshold ranges corresponding to the plurality of consecutive time intervals are created from a plurality of measurement data points acquired during the plurality of consecutive time intervals.

12. 1. An apparatus for polishing a workpiece, comprising: A polishing table, a table motor for rotating the polishing table; a polishing head that presses the workpiece against a polishing pad on the polishing table to polish the workpiece; an optical sensor head that irradiates light onto a plurality of film thickness measurement points on the workpiece for each time interval during polishing of the workpiece; a processing system for generating a plurality of measurement spectra of the reflected light from the plurality of film thickness measurement points; The processing system includes: calculating a plurality of feature quantities of the plurality of measured spectra; performing data mapping by plotting, on a coordinate system, a plurality of times at which the plurality of measurement spectra were generated and a plurality of measurement data points identified from the plurality of feature quantities of the plurality of measurement spectra; determining a correction index value representing the number of the plurality of measurement data points existing within a threshold range defined on the coordinate system for each time interval; The polishing apparatus is configured to determine whether the correction index value is within a correction control range.

13. 13. The polishing apparatus according to claim 12, wherein the processing system is configured to correct the plurality of feature quantities by moving the plurality of measurement data points on the coordinate system until the plurality of measurement data points fall within the threshold range when the correction index value is within the correction control range.

14. 13. The polishing apparatus according to claim 12, wherein the processing system is configured to generate an alarm signal when the correction index value is smaller than a lower limit of the correction control range.

15. the processing system is configured to select either a first set of threshold ranges or a second set of threshold ranges from the progression of the plurality of measurement data points over time polishing the workpiece; the threshold range is one of a plurality of threshold ranges in a selected one of the first set and the second set; the first set of threshold ranges is predetermined from reference data points obtained during polishing of a first reference workpiece; 13. The polishing apparatus of claim 12, wherein the second set of multiple threshold ranges is predetermined from reference data points obtained during polishing of a second reference workpiece having a different surface structure than the first reference workpiece.

16. The processing system includes: performing a principal component analysis on a data set including a plurality of intensities of the reflected light at a plurality of wavelengths for each measured spectrum; 13. The polishing apparatus according to claim 12, wherein the apparatus is configured to determine a feature quantity including at least a k-th principal component (k is a natural number) obtained from the principal component analysis.

17. 13. The polishing apparatus of claim 12, wherein the processing system is configured to create a plurality of new threshold ranges corresponding to a plurality of consecutive time intervals from a plurality of measurement data points acquired during the plurality of consecutive time intervals when the correction index value is smaller than a lower limit of the correction control range during the plurality of consecutive time intervals during polishing of the workpiece.

18. 13. The polishing apparatus of claim 12, wherein the processing system is configured to determine the threshold range, the threshold range being a range within a predetermined Mahalanobis distance from a reference point of a plurality of reference data points obtained from polishing a reference workpiece.

19. 20. The polishing apparatus of claim 18, wherein the processing system is configured to, when the correction index value is greater than an upper limit of the correction control range, update the plurality of reference data points by adding the plurality of measurement data points to the plurality of reference data points, and update the threshold range based on the updated plurality of reference data points.

Images