Polishing apparatus and polishing method

Abstract

To provide a polishing device and polishing method which can correctly measure the film thickness of a workpiece used for manufacturing a semiconductor device during polishing of the workpiece.SOLUTION: A processing system is configured to determine the film thickness of a workpiece W on the basis of relative reflectance data calculated by the following calculation formula. The relative reflectance data=MD1 / [BD1 k]. Here, MD1 is first intensity measurement data indicating the intensity of reflection light from the workpiece W measured by a first spectrometer 27; BD1 is first base intensity data; and k is a change rate to second base intensity data of second intensity measurement data indicating the intensity of light of a light source measured by a second spectrometer 28 during polishing of the workpiece W.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a polishing apparatus and method for polishing workpieces used in the manufacture of semiconductor devices such as wafers, substrates, and panels, and in particular to a technique for determining the film thickness of the workpiece based on optical information contained in reflected light from the workpiece. [Background technology]

[0002] In the manufacturing process of semiconductor devices, various materials are repeatedly formed in the form of films on a silicon wafer to form a layered structure. In order to form this layered structure, technology for flattening the surface of the top layer is important. Chemical mechanical polishing (CMP) is used as one method of such flattening.

[0003] Chemical mechanical polishing (CMP) is performed by a polishing apparatus. This type of polishing apparatus generally includes a polishing table that supports a polishing pad, a polishing head that holds a wafer having a film, and a polishing liquid supply nozzle that supplies a polishing liquid (e.g., slurry) onto the polishing pad. The polishing apparatus supplies the polishing liquid onto the polishing pad from the polishing liquid supply nozzle while rotating the polishing head and the polishing table. The polishing head presses the surface of the wafer against the polishing pad, thereby polishing the film that forms the surface of the wafer with the polishing liquid present between the wafer and the polishing pad.

[0004] In order to measure the thickness of a non-metallic film such as an insulating film or a silicon layer (hereinafter simply referred to as film thickness), a polishing apparatus generally includes an optical film thickness measuring device. This optical film thickness measuring device is configured to guide light emitted from a light source to the surface of the wafer and determine the film thickness of the wafer by analyzing the spectrum of the light reflected from the wafer. The polishing apparatus can terminate polishing of the wafer or change the polishing conditions of the wafer based on the determined film thickness. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-194427 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the spectrum of the reflected light from the wafer may vary even under the same conditions (e.g., same film thickness, same measurement point). Such spectrum variation leads to unstable film thickness measurement results, preventing accurate monitoring of the film thickness during wafer polishing. A film thickness measurement device that measures the film thickness of a stationary wafer can obtain stable film thickness measurement results by repeatedly measuring the film thickness at the same measurement point and calculating the average of the multiple measured values ​​obtained. However, the optical film thickness measurement device described above cannot perform such processing because it dynamically measures the film thickness of the wafer while the wafer is rotating.

[0007] Therefore, the present invention provides a polishing apparatus and a polishing method that can accurately measure the film thickness of a workpiece used in the manufacture of semiconductor devices, such as a wafer, substrate, or panel, while the workpiece is being polished. [Means for solving the problem]

[0008] The present inventors have found that there are two reasons why the spectrum of reflected light from a workpiece is not stable.

[0009] The first reason is that the amount of light emitted by the light source changes each time it emits light. In particular, in a flash light source that emits light by discharging, the amount of light emitted each time it emits light is likely to change due to discharge fluctuations. Normally, during polishing of a workpiece, the light source flashes multiple times each time the polishing table rotates, irradiating multiple measurement points on the workpiece with light. There is a slight variation in the amount of light irradiated to these measurement points.

[0010] The second reason is that the optical path that the light takes through the fiber optic cable changes each time the light source emits light. The light source is connected to a fiber optic cable, and the light is guided through the fiber optic cable to the workpiece. A light source with a small irradiating diameter illuminates a different location on the end face of the fiber optic cable each time it emits light, and as a result, the light is guided to the workpiece through a different part in the fiber optic cable. Such differences in the optical path in the fiber optic cable cause spectral variations in the reflected light from the workpiece.

[0011] In one embodiment, a polishing apparatus for polishing a workpiece includes a polishing table supporting a polishing pad, a polishing head for pressing the workpiece against the polishing pad to polish the workpiece, a light source for emitting light, a light projecting fiber optic cable connected to the light source and directing the light to the workpiece, a light receiving fiber optic cable for receiving reflected light from the workpiece, a first spectrometer connected to the light receiving fiber optic cable, a second spectrometer directly connected to the light source, a storage device storing a program, and a processing system including a calculation device for executing calculations according to instructions included in the program, the storage device storing therein first base intensity data indicating a reference intensity of light measured by the first spectrometer before polishing the workpiece, second base intensity data indicating a reference intensity of the light of the light source measured by the second spectrometer before polishing the workpiece, and a calculation formula for calculating relative reflectance data, and the processing system is configured to determine a film thickness of the workpiece based on the relative reflectance data, the calculation formula being expressed as follows: The relative reflectance data = MD1 / [BD1 k] wherein MD1 is first intensity measurement data indicating the intensity of the reflected light from the workpiece measured by the first spectrometer, BD1 is the first base intensity data, and k is the rate of change of second intensity measurement data indicating the intensity of the light of the light source measured by the second spectrometer during polishing of the workpiece relative to the second base intensity data.

[0012] In one embodiment, each of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is data indicating a plurality of intensities of light at a plurality of wavelengths, and the rate of change k is a plurality of rates of change corresponding respectively to the plurality of wavelengths. In one aspect, the processing system is configured to determine the multiple rates of change k after performing interpolation on the first base intensity data, the first intensity measurement data, the second base intensity data, and the second intensity measurement data to match the multiple wavelengths of the first base intensity data and the first intensity measurement data with the multiple wavelengths of the second base intensity data and the second intensity measurement data. In one embodiment, the plurality of wavelengths of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is an integer number of wavelengths. In one embodiment, the rate of change k is a rate of change of the representative intensity value of the second intensity measurement data relative to the representative intensity value of the second base intensity data. In one embodiment, the first spectrometer and the second spectrometer are configured to simultaneously measure the intensity of the reflected light from the work piece and the intensity of the light from the light source. In one embodiment, the system further comprises a direct fiber optic cable directly connecting the light source to the second spectrometer.

[0013] In one aspect, a polishing apparatus for polishing a workpiece includes a polishing table that supports a polishing pad, a polishing head that presses the workpiece against the polishing pad to polish the workpiece, a light source that emits light, a light projecting fiber optic cable connected to the light source and directing the light to the workpiece, a light receiving fiber optic cable that receives reflected light from the workpiece, a first spectrometer connected to the light receiving fiber optic cable, a second spectrometer directly connected to the light source, a storage device that stores a program, and a processing system including an arithmetic unit that executes operations according to instructions included in the program, the storage device having stored therein a plurality of different first base intensity data indicating a reference intensity of light measured by the first spectrometer before polishing the workpiece, and a plurality of different second base intensity data indicating a reference intensity of light of the light source measured by the second spectrometer before polishing the workpiece. a first base intensity data storage unit configured to store second base intensity data, the plurality of different first base intensity data and the plurality of different second base intensity data being associated in a one-to-one correspondence, the processing system being configured to: acquire first intensity measurement data indicative of an intensity of the reflected light from the workpiece measured by the first spectrometer; acquire second intensity measurement data indicative of an intensity of the light of the light source measured by the second spectrometer while polishing the workpiece; select second base intensity data from the plurality of different second base intensity data that best matches the second intensity measurement data; determine first base intensity data associated with the selected second base intensity data; calculate relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data; and determine a film thickness of the workpiece based on the relative reflectance data.

[0014] In one embodiment, the first spectrometer and the second spectrometer are configured to simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source while the workpiece is being polished. In one embodiment, the polishing apparatus further includes a direct-connection optical fiber cable that directly connects the light source to the second spectrometer, and an end of the light-projecting optical fiber cable and an end of the direct-connection optical fiber cable are bundled together to form a trunk optical fiber cable, and the trunk optical fiber cable is connected to the light source.

[0015] In one aspect, a polishing method for polishing a workpiece includes: before polishing the workpiece, light emitted from a light source is guided to a first spectrometer through a light projecting optical fiber cable and a light receiving optical fiber cable, and an intensity of the light is measured by the first spectrometer to generate first base intensity data indicating a reference intensity of the light; before polishing the workpiece, an intensity of the light emitted from the light source is measured by a second spectrometer to generate second base intensity data indicating a reference intensity of the light, the second spectrometer is directly connected to the light source; and while rotating a polishing table, the workpiece is pressed against a polishing pad on the polishing table to polish the workpiece. a first intensity measurement data indicating an intensity of reflected light from the workpiece measured by the first spectrometer during polishing of the workpiece; a second intensity measurement data indicating an intensity of light from the light source measured by the second spectrometer during polishing of the workpiece; a rate of change of the second intensity measurement data relative to the second base intensity data; a first base intensity data is multiplied by the rate of change to calculate corrected first base intensity data; a second intensity measurement data is divided by the corrected first base intensity data to calculate relative reflectance data; and a film thickness of the workpiece is determined based on the relative reflectance data.

[0016] In one embodiment, each of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is data indicating a plurality of intensities of light at a plurality of wavelengths, and the rate of change k is a plurality of rates of change corresponding respectively to the plurality of wavelengths. In one embodiment, the method further includes, prior to calculating the multiple change rates, performing interpolation on the first base intensity data, the first intensity measurement data, the second base intensity data, and the second intensity measurement data to match the multiple wavelengths of the first base intensity data and the first intensity measurement data with the multiple wavelengths of the second base intensity data and the second intensity measurement data. In one embodiment, the plurality of wavelengths of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is an integer number of wavelengths. In one embodiment, the rate of change is a rate of change of a representative intensity value of the second intensity measurement data relative to a representative intensity value of the second base intensity data. In one embodiment, the first spectrometer and the second spectrometer simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source while the workpiece is being polished.

[0017] In one aspect, a polishing method for polishing a workpiece includes, before polishing the workpiece, guiding light repeatedly emitted from a light source through a light projecting optical fiber cable and a light receiving optical fiber cable to a first spectrometer, measuring an intensity of the light with the first spectrometer to generate a plurality of different first base intensity data indicating a reference intensity of the light, measuring an intensity of the light repeatedly emitted from the light source with a second spectrometer to generate a plurality of different second base intensity data indicating a reference intensity of the light, the second spectrometer is directly connected to the light source, and associates the plurality of different first base intensity data with the plurality of different second base intensity data in a one-to-one correspondence, and applying a polishing pad on the polishing table while rotating the polishing table. a polishing method for polishing the workpiece by pressing the workpiece against the workpiece; obtaining first intensity measurement data indicative of an intensity of the reflected light from the workpiece measured by the first spectrometer while the workpiece is being polished; obtaining second intensity measurement data indicative of an intensity of the light of the light source measured by the second spectrometer while the workpiece is being polished; selecting second base intensity data from the plurality of different second base intensity data that best matches the second intensity measurement data; determining first base intensity data associated with the selected second base intensity data; calculating relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data; and determining a film thickness of the workpiece based on the relative reflectance data.

[0018] In one embodiment, the first spectrometer and the second spectrometer simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source while the workpiece is being polished. Effect of the Invention

[0019] The second base intensity data is the original reference data, and the second intensity measurement data is the reference data during polishing. According to the present invention, the first base intensity data is corrected using the rate of change of the second intensity measurement data relative to the second base intensity data. Furthermore, the first intensity measurement data obtained during polishing of the workpiece is divided by the corrected first base intensity data to obtain relative reflectance data. By such a calculation, the variation in the amount of light from the light source is removed from the relative reflectance data. As a result, an accurate film thickness can be determined from the relative reflectance data.

[0020] Further, according to the present invention, the second base intensity data that best matches the second intensity measurement data is selected from a plurality of different second base intensity data. The plurality of different second base intensity data are data that differ due to differences in the optical paths of light traveling in the optical fiber cable. The second base intensity data that best matches the second intensity measurement data is data that reflects such differences in the optical paths. Therefore, the first base intensity data associated with the selected second base intensity data is also data that reflects the differences in the optical paths. By dividing the first intensity measurement data by the first base intensity data, it is possible to calculate relative reflectance data from which the differences in the optical paths in the optical fiber cable have been removed. As a result, it is possible to determine an accurate film thickness from the relative reflectance data. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Diagram 2] FIG. 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measurement device. [Diagram 3] FIG. 4 is a diagram showing a spectrum generated from first intensity measurement data. [Figure 4] FIG. 13 is a diagram showing a spectrum generated from corrected first base intensity data. [Diagram 5] FIG. 1 shows a spectrum generated from relative reflectance data. [Figure 6]1 is a flow chart illustrating one embodiment of a polishing method for polishing a workpiece. [Figure 7] 4 is a graph showing the intensity and wavelength of light measured by a first spectrometer and a second spectrometer. [Figure 8] 11 is a graph showing a state in which the wavelength of the light intensity measured by the first spectroscope and the wavelength of the light intensity measured by the second spectroscope are made to match each other by interpolation. [Figure 9] 1 is a schematic diagram showing the position of the light incident spot on the end face of the trunk optical fiber cable and the optical paths of light within the light projecting optical fiber cable and the directly connected optical fiber cable; [Figure 10] 1 is a flow chart illustrating one embodiment of a polishing method for polishing a workpiece. [Figure 11] FIG. 13 is a schematic diagram showing another embodiment of the polishing apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing 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 having a film 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 a 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 constitutes a polishing surface 2a for polishing the workpiece W. Examples of the workpiece W include wafers, substrates, and panels used in the manufacture of semiconductor devices.

[0023] The polishing head 1 is connected to a head shaft 10, which is connected to a polishing head motor (not shown). The polishing head motor rotates the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, which 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 motor, and the table motor 6 are connected to an operation control unit 9.

[0024] The workpiece W is polished as follows. While the polishing table 3 and polishing head 1 are rotated in the direction shown by the arrow in Fig. 1, a polishing liquid is supplied from a 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 workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1 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 the polishing pad 2.

[0025] The operation control unit 9 includes a storage device 9a in which a program is stored, and a processing device 9b that executes calculations according to instructions included in the program. The operation control unit 9 includes 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 processing device 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.

[0026] The polishing apparatus includes an optical film thickness measuring device 20 for measuring the thickness of a film on the workpiece W. The optical film thickness measuring device 20 includes a light source 22 for emitting light, an optical sensor head 25 for irradiating the workpiece W with the light from the light source 22 and receiving the reflected light from the workpiece W, a first spectrometer 27 connected to the optical sensor head 25, a second spectrometer 28 directly connected to the light source 22, and a processing system 30 for determining the thickness of the film on the workpiece W based on the relative reflectance data of the reflected light from the workpiece W. The optical sensor head 25 is disposed in the polishing table 3 and rotates together with the polishing table 3. A plurality of optical sensor heads 25 connected to the first spectrometer 27 and the light source 22 may be provided.

[0027] The processing system 30 includes a storage device 30a in which a program is stored, 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.

[0028] Each of the operation control unit 9 and the processing system 30 may be composed of a plurality of computers. For example, each of the operation control unit 9 and the processing system 30 may be composed of 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 composed of a single computer.

[0029] 2 is a cross-sectional view showing a detailed configuration of the optical film thickness measuring device 20. The optical film thickness measuring device 20 includes a light projecting optical fiber cable 31 connected to the light source 22, a light receiving optical fiber cable 32 connected to the first spectrometer 27, and a direct optical fiber cable 33 that directly connects the light source 22 and the second spectrometer 28. The tip 31a of the light projecting optical fiber cable 31 and the tip 32a of the light receiving optical fiber cable 32 constitute the optical sensor head 25. That is, the light projecting optical fiber cable 31 guides the light of the light source 22 to the workpiece W on the polishing pad 2, and the light receiving optical fiber cable 32 receives the reflected light from the workpiece W and transmits it to the first spectrometer 27. One end of the direct optical fiber cable 33 is connected to the light source 22, and the other end is connected to the second spectrometer 28.

[0030] The first spectrometer 27 and the second spectrometer 28 are connected to a processing system 30. The light projecting fiber optic cable 31, the light receiving fiber optic cable 32, the direct-connected fiber optic cable 33, the light source 22, the first spectrometer 27, and the second spectrometer 28 are attached to the polishing table 3 and rotate together 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 projecting fiber optic cable 31 and the tip 32a of the light receiving fiber optic cable 32, is disposed facing the surface of the workpiece W on the polishing pad 2. The position of the optical sensor head 25 is a position where it crosses the surface of the workpiece W on the polishing pad 2 every time the polishing table 3 and the polishing pad 2 rotate once. 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 rotates once, and receives reflected light from the workpiece W through the through hole 2b.

[0031] The light source 22 is a flash light source that repeatedly emits light 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 upon receiving 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 measurement points on the workpiece W.

[0032] The second spectrometer 28 is directly connected to the light source 22 by a direct-connection fiber optic cable 33. The direct-connection fiber optic cable 33 extends from the light source 22 to the second spectrometer 28. The second spectrometer 28 is not connected to the optical sensor head 25, and receives only light from the light source 22. An end of the light projecting fiber optic cable 31 and an end of the direct-connection fiber optic cable 33 are bundled together to form one trunk fiber optic cable 35. The trunk fiber optic cable 35 is connected to the light source 22. That is, the trunk fiber optic cable 35 branches into the light projecting fiber optic cable 31 and the direct-connection fiber optic cable 33. Therefore, the light emitted from the light source 22 branches into two beams of light, and the two branched beams are transmitted to the optical sensor head 25 and the second spectrometer 28 through the light projecting fiber optic cable 31 and the direct-connection fiber optic cable 33, respectively.

[0033] Incidentally, light projecting optical fiber cable 31 and direct connection optical fiber cable 33 may each be formed by bundling a plurality of thin fibers (unbranched optical fibers).

[0034] The light emitted by the light source 22 is transmitted to the optical sensor head 25 and the second spectrometer 28 at the same time. That is, the light is transmitted to the optical sensor head 25 through the light-projecting optical fiber 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 reflected light from the workpiece W is transmitted to the first spectrometer 27 through the light-receiving optical fiber cable 32. At the same time, the light of the light source 22 is not sent to the optical sensor head 25 but is transmitted to the second spectrometer 28 through the direct-connected optical fiber cable 33.

[0035] The first spectrometer 27 and the second spectrometer 28 are configured to separate the light according to wavelength and measure the intensity of the reflected light at each wavelength over a predetermined wavelength range. That is, the first 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 first intensity measurement data. At the same time, the second spectrometer 28 separates the light of the light source 22 according to wavelength and measures the intensity of the light at each wavelength over the wavelength range to generate second intensity measurement data. The intensity of the light emitted by the light source 22 is measured simultaneously by the first spectrometer 27 and the second spectrometer 28. The first intensity measurement data and the second intensity measurement data are sent to the processing system 30.

[0036] The memory device 30a of the processing system 30 stores therein first base intensity data indicating a reference intensity of light measured in advance by the first spectrometer 27 before polishing the workpiece W, and second base intensity data indicating a reference intensity of light of the light source 22 measured in advance by the second spectrometer 28 before polishing the workpiece W. The first base intensity data and the second base intensity data are data acquired in advance before polishing the workpiece W, while the above-mentioned first intensity measurement data and second intensity measurement data are data acquired during polishing of the workpiece W.

[0037] Each of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data indicates a plurality of intensities of light at a plurality of wavelengths within the above-mentioned predetermined wavelength range. For example, the first intensity measurement data indicates a plurality of intensities of light reflected from the workpiece W at a plurality of wavelengths. The plurality of intensities of light indicated by the above-mentioned data may be relative intensities with respect to a dark level (background intensity obtained under conditions in which light is blocked) as a reference for light intensity. Specifically, the value obtained by subtracting the dark level from the measurement value of the light intensity at each wavelength may be the light intensity included in each data. For example, if the measurement value of the light intensity at wavelength λ is M(λ), the light intensity E(λ) at wavelength λ included in each data may be given by the following formula. E(λ)=M(λ)-D(λ) (1) Here, λ represents the wavelength, and D(λ) represents the dark level at the wavelength λ. However, the light intensity indicated by each piece of data is not limited to this example, and may be, for example, the measured values ​​of the light intensity obtained by the first spectroscope 27 and the second spectroscope 28 themselves.

[0038] The first intensity measurement data indicating the intensity of the reflected light from the workpiece W includes information on the film thickness of the workpiece W. In other words, the first intensity measurement data varies depending on the film thickness of the workpiece W. Therefore, as will be described later, the processing system 30 can determine the film thickness of the workpiece W by processing the first intensity measurement data.

[0039] In contrast, the first base intensity data indicates a reference intensity of light measured in advance for each wavelength. The first base intensity data is obtained, for example, by irradiating a mirror with light from the optical sensor head 25 and measuring the intensity of the reflected light from the mirror with the first spectrometer 27. Alternatively, the first base intensity data may be the intensity of the reflected light from a silicon wafer measured by the first spectrometer 27 when a silicon wafer without a film (bare wafer) is being water-polished or slurry-polished in the presence of water or slurry on the polishing pad 2, or when the silicon wafer (bare wafer) is placed on the polishing pad 2.

[0040] In this embodiment, the relative reflectance data is determined by dividing the first intensity measurement data by the first base intensity data. The relative reflectance data is an index showing the intensity of reflected light at each wavelength. By dividing the first intensity measurement data by the first base intensity data, unnecessary noise such as the intensity variations inherent to the optical system of the device and the light source 22 can be removed from the measured intensity.

[0041] Both the second base intensity data and the second intensity measurement data are measurement data of the light intensity of the light source 22 and are unrelated to the reflected light from the workpiece W. The second base intensity data is data indicating a reference intensity of the light of the light source 22, and the second intensity measurement data is data indicating the intensity of the light of the light source 22 while the workpiece W is being polished. In this embodiment, the second intensity measurement data and the second base intensity data are used as correction coefficients to eliminate variations in the relative reflectance data caused by changes in the amount of light from the light source 22 at each measurement point.

[0042] The second base intensity data is acquired at the same time as the first base intensity data described above, prior to polishing of the workpiece W. That is, the first spectrometer 27 measures the intensity of light transmitted from the optical sensor head 25 over a predetermined wavelength range, and simultaneously, the second spectrometer 28 measures the intensity of light from the light source 22 over the same wavelength range.

[0043] The second intensity measurement data is acquired at the same timing as the first intensity measurement data described above during polishing of the workpiece W. That is, the first spectrometer 27 measures the intensity of the reflected light from the workpiece W transmitted from the optical sensor head 25 over a predetermined wavelength range, and at the same time, the second spectrometer 28 measures the intensity of the light from the light source 22 over the same wavelength range.

[0044] The storage device 30a of the processing system 30 stores a formula for calculating the relative reflectance data, and the processing system 30 is configured to determine the film thickness of the workpiece W based on the relative reflectance data. The formula is expressed as follows: Relative reflectance data = MD1 / [BD1 k] (2) Here, MD1 is the first intensity measurement data indicating the intensity of reflected light from the workpiece W measured by the first spectrometer 27 during polishing of the workpiece W, BD1 is the above-mentioned first base intensity data indicating the reference intensity of light measured by the first spectrometer 27 before polishing of the workpiece W, and k is the rate of change of the second intensity measurement data indicating the intensity of light from the light source 22 measured by the second spectrometer 28 during polishing of the workpiece W relative to the second base intensity data.

[0045] The change in the second intensity measurement data relative to the second base intensity data does not depend on the change in the film thickness of the workpiece W, but only on the change in the amount of light from the light source 22. Therefore, by multiplying the first base intensity data by the rate of change k, the first base intensity data is corrected (i.e., the change in the amount of light from the light source 22 is reflected in the first base intensity data). Since the first intensity measurement data MD1 reflects the change in the amount of light from the light source 22, similar to the second intensity measurement data, the change in the amount of light from the light source 22 is removed (canceled) by dividing the first intensity measurement data MD1 by the corrected first base intensity data. As a result, the processing system 30 can determine an accurate film thickness from the relative reflectance data.

[0046] Fig. 3 shows a spectrum generated from the first intensity measurement data, Fig. 4 shows a spectrum generated from the corrected first base intensity data, and Fig. 5 shows a spectrum generated from the relative reflectance data obtained by dividing the first intensity measurement data by the corrected first base intensity data. The shape of the spectrum generated from the relative reflectance data changes according to the film thickness of the workpiece W. The processing system 30 generates a spectrum as shown in Fig. 5 from the relative reflectance data obtained by the above calculation formula, and determines the film thickness of the workpiece W based on this spectrum.

[0047] A known technique can be used to determine the film thickness of the workpiece W based on the spectrum. For example, the processing system 30 determines a reference spectrum from a reference spectrum library that is closest in shape to the spectrum, and determines the film thickness associated with the determined reference spectrum. In another example, the processing system 30 performs a Fourier transform on the spectrum and determines the film thickness from the resulting frequency spectrum.

[0048] FIG. 6 is a flow chart illustrating one embodiment of a polishing method for polishing a workpiece W. In step 101, before polishing the workpiece W, light emitted from the light source 22 is guided to the first spectrometer 27 through the light-projecting fiber optic cable 31 and the light-receiving fiber optic cable 32, and the intensity of the light is measured by the first spectrometer 27 to generate first base intensity data indicating a reference intensity of the light. The processing system 30 acquires the first base intensity data from the first spectrometer 27 and stores it in the storage device 30a. In step 102, before polishing the workpiece W, the light emitted from the light source 22 is guided to the second spectrometer 28 through the direct-connected optical fiber cable 33, and the intensity of the light is measured by the second spectrometer 28 to generate second base intensity data indicating a reference intensity of the light of the light source 22. The processing system 30 acquires the second base intensity data from the second spectrometer 28 and stores it in the storage device 30a. The measurement of the light intensity by the first spectrometer 27 in the above step 101 and the measurement of the light intensity by the second spectrometer 28 in the above step 102 are performed simultaneously.

[0049] In step 103, while rotating the polishing table 3, the polishing head 1 presses the workpiece W against the polishing pad 2 to start polishing the workpiece W. In step 104 , while the workpiece W is being polished, the processing system 30 obtains first intensity measurement data indicative of the intensity of the reflected light from the workpiece W as measured by the first spectrometer 27 . In step 105, during polishing of the workpiece W, the processing system 30 obtains second intensity measurement data indicative of the intensity of light from the light source 22 measured by the second spectrometer 28. The measurement of the intensity of the reflected light by the first spectrometer 27 in step 104 and the measurement of the intensity of the light from the light source 22 by the second spectrometer 28 in step 105 are performed simultaneously.

[0050] In step 106, the processing system 30 determines a rate of change of the second intensity measurement data relative to the second base intensity data. In step 107, the processing system 30 calculates corrected first base intensity data by multiplying the first base intensity data by the rate of change. In step 108, the processing system 30 calculates the relative reflectance data by dividing the first intensity measurement data by the corrected first base intensity data. In step 109, processing system 30 determines the film thickness of workpiece W based on the relative reflectance data.

[0051] The change rate k used in the above calculation formula may be multiple change rates corresponding to multiple wavelengths, or may be one change rate determined for multiple wavelengths. The multiple change rates k(λ) corresponding to multiple wavelengths are given by the following formula: k(λ)=MV2(λ) / BV2(λ), λ=λLL~λHL (3) Here, λ represents the wavelength of light, k(λ) represents the rate of change at wavelength λ, MV2(λ) represents the light intensity at wavelength λ included in the second intensity measurement data, BV2(λ) represents the light intensity at wavelength λ included in the second base intensity data, λLL represents the lower limit of the wavelength range of the light intensity measured by the first spectrometer 27 and the second spectrometer 28, and λHL represents the upper limit of the wavelength range. The wavelength λ is any wavelength between the lower limit λLL and the upper limit λHL.

[0052] According to this embodiment, the rate of change is calculated for each wavelength, so that the first base intensity data can be corrected more accurately.

[0053] The above-mentioned calculation formula (2) can be expressed as follows using formula (3). R(λ)=MV1(λ) / [BV1(λ)·k(λ)], λ=λLL~λHL (4) Here, R(λ) represents the relative reflectance at wavelength λ, MV1(λ) represents the intensity of reflected light at wavelength λ contained in the first intensity measurement data MD1, and BV1(λ) represents the reference intensity of light at wavelength λ contained in the first base intensity data BD1.

[0054] MV1(λ), ​​BV1(λ), ​​MV2(λ), and BV2(λ) included in the above formulas (3) and (4) are the light intensities at wavelength λ measured by the first spectroscope 27 and the second spectroscope 28. Each of the first spectroscope 27 and the second spectroscope 28 is configured to resolve light according to wavelength and measure the light intensity at each wavelength. However, due to mechanical differences between the first spectroscope 27 and the second spectroscope 28, there may be a difference between the wavelength of the intensity measured by the first spectroscope 27 and the wavelength of the intensity measured by the second spectroscope 28. This point will be described with reference to FIG. 7.

[0055] FIG. 7 is a graph showing the light intensity and its wavelength measured by the first spectrometer 27 and the second spectrometer 28. The first spectrometer 27 measures the light intensities MV1(λ1), MV1(λ2), and MV1(λ3) at the wavelengths λ1, λ2, and λ3, and the second spectrometer 28 similarly measures the light intensities MV2(λ1), MV2(λ2), and MV2(λ3) at the wavelengths λ1, λ2, and λ3. However, as shown in FIG. 7, in reality, due to mechanical differences between the first spectrometer 27 and the second spectrometer 28, there are slight differences between the wavelengths λ1, λ2, and λ3 of the light intensity measured by the first spectrometer 27 and the wavelengths λ1, λ2, and λ3 of the light intensity measured by the second spectrometer 28. Such differences in wavelengths may adversely affect the accuracy of the relative reflectance data.

[0056] Thus, in one embodiment, the processing system 30 is configured to perform an interpolation on the first base intensity data, the first intensity measurement data, the second base intensity data, and the second intensity measurement data to match a plurality of wavelengths of the first base intensity data and the first intensity measurement data with a plurality of wavelengths of the second base intensity data and the second intensity measurement data. After performing the interpolation, the processing system 30 calculates a plurality of change rates k, and further calculates the relative reflectance data.

[0057] FIG. 8 is a graph showing a state in which the wavelengths λ1, λ2, λ3 of the light intensity measured by the first spectrometer 27 and the wavelengths λ1, λ2, λ3 of the light intensity measured by the second spectrometer 28 are matched by interpolation. In this example, the multiple wavelengths λ1, λ2, λ3 of the first intensity measurement data after interpolation and the multiple wavelengths λ1, λ2, λ3 of the second intensity measurement data after interpolation are multiple wavelengths consisting of integers. That is, the processing system 30 performs interpolation on the first intensity measurement data to calculate light intensities MV1(λ1), MV1(λ2), MV1(λ3) at multiple wavelengths λ1, λ2, λ3 consisting of integers, and further performs interpolation on the second intensity measurement data to calculate light intensities MV2(λ1), MV2(λ2), MV2(λ3) at multiple wavelengths λ1, λ2, λ3 consisting of integers. As a result, the wavelengths match between the first intensity measurement data and the second intensity measurement data.

[0058] Similarly, the multiple wavelengths λ1, λ2, λ3 of the first base intensity data after interpolation and the multiple wavelengths λ1, λ2, λ3 of the second base intensity data after interpolation are multiple wavelengths consisting of integers. That is, the processing system 30 performs interpolation on the first base intensity data to calculate the light intensities BV1(λ1), BV1(λ2), BV1(λ3) at the multiple wavelengths λ1, λ2, λ3 consisting of integers, and further performs interpolation on the second base intensity data to calculate the light intensities BV2(λ1), BV2(λ2), BV2(λ3) at the multiple wavelengths λ1, λ2, λ3 consisting of integers. As a result, the wavelengths match between the first base intensity data and the second base intensity data.

[0059] In this way, all wavelengths within the wavelength range of the light intensity measured by the first spectroscope 27 and the second spectroscope 28 are the same.

[0060] In one embodiment, the rate of change k may be one rate of change determined for multiple wavelengths. In this case, the above-mentioned interpolation is not necessary. The processing system 30 determines a representative intensity value of the second base intensity data and a representative intensity value of the second intensity measurement data, and calculates the rate of change k of the representative intensity value of the second intensity measurement data relative to the representative intensity value of the second base intensity data. Examples of the representative intensity value include an average value, a maximum value, a maximum value, etc. of multiple intensities corresponding to multiple wavelengths.

[0061] According to the embodiment described so far, the processing system 30 can eliminate the variation in the light emission of the light source 22, but at the same time, can also eliminate the change in the light amount of the light source 22 over time. That is, both the variation in the light emission of the light source 22 and the change in the light amount of the light source 22 over time can be expressed as a change in the second intensity measurement data relative to the second base intensity data. Therefore, the processing system 30 can eliminate not only the variation in the light emission of the light source 22, but also the change in the light amount of the light source 22 over time by performing data processing using the above-mentioned calculation formula.

[0062] Next, another embodiment of the polishing apparatus will be described. The configuration and operation of this embodiment that are not specifically described are the same as those of the embodiment described with reference to Figures 1 and 2, so that duplicated descriptions will be omitted.

[0063] As shown in Fig. 2, the light source 22 is connected to the trunk optical fiber cable 35, and the light emitted by the light source 22 first enters the end face of the trunk optical fiber cable 35, and is then distributed to the light projecting optical fiber cable 31 and the direct-connected optical fiber cable 33. Fig. 9 is a schematic diagram showing the position of the incident spot of light on the end face 35a of the trunk optical fiber cable 35, and the optical paths of light within the light projecting optical fiber cable 31 and the direct-connected optical fiber cable 33. As shown in Fig. 9, the incident spot S of the light emitted by the light source 22 is smaller than the end face 35a of the trunk optical fiber cable 35, and the incident spot S is located within the end face 35a of the trunk optical fiber cable 35.

[0064] During polishing of the workpiece W, the light source 22 repeatedly emits light at short time intervals. The position of the light incident spot S on the end face 35a of the trunk optical fiber cable 35 is not constant, but changes every time the light source 22 emits light. The optical path P1 of the light traveling in the light projecting optical fiber cable 31 (i.e., the light spot position in the light projecting optical fiber cable 31) and the optical path P2 of the light traveling in the directly connected optical fiber cable 33 change depending on the position of the light incident spot S on the end face 35a of the trunk optical fiber cable 35. The dotted circle in FIG. 9 shows the change in the position of the light incident spot S and the corresponding change in the optical paths P1 and P2. Such a change in the optical paths P1 and P2 in the light projecting optical fiber cable 31 and the directly connected optical fiber cable 33 causes a change in the spectrum of the reflected light from the workpiece W.

[0065] Although the optical path P1 in the light projecting optical fiber cable 31 and the optical path P2 in the directly connected optical fiber cable 33 change, there is a one-to-one relationship between the positions of the optical paths P1, P2 in these optical fiber cables 31, 33. In other words, the position of the optical path P1 of the light traveling in the light projecting optical fiber cable 31 uniquely corresponds to the position of the optical path P2 of the light traveling in the directly connected optical fiber cable 33. The second intensity measurement data indicating the intensity of the light of the light source 22 measured by the second spectrometer 28 during polishing of the workpiece W changes depending on the optical path P2 of the light traveling in the directly connected optical fiber cable 33, that is, depending on the position of the incident spot S of the light on the end face 35a of the trunk optical fiber cable 35. Therefore, the first intensity measurement data indicating the intensity of the reflected light from the workpiece W measured by the first spectrometer 27 during polishing of the workpiece W also changes while maintaining a one-to-one relationship with the second intensity measurement data.

[0066] In this embodiment, before polishing the workpiece W, the light source 22 is repeatedly caused to emit light while measuring the light intensity by the first spectrometer 27 and the second spectrometer 28 to generate a plurality of first base intensity data and a plurality of second base intensity data. The second base intensity data is acquired at the same timing as the first base intensity data before polishing the workpiece W. That is, the first spectrometer 27 measures the intensity of light transmitted from the optical sensor head 25 over a predetermined wavelength range, and at the same time, the second spectrometer 28 measures the intensity of light from the light source 22 over the same wavelength range.

[0067] Each time the light source 22 emits light, the position of the light incident spot S changes within the end face 35a of the trunk optical fiber cable 35, so that a plurality of different first base intensity data and a plurality of different second base intensity data are generated. A reference library including the plurality of different first base intensity data and the plurality of different second base intensity data is stored in the storage device 30a of the processing system 30. The plurality of different first base intensity data and the plurality of different second base intensity data are associated in a one-to-one correspondence.

[0068] The processing system 30 acquires first intensity measurement data indicative of the intensity of reflected light from the workpiece W measured by the first spectrometer 27 during polishing of the workpiece W, and acquires second intensity measurement data indicative of the intensity of light from the light source 22 measured by the second spectrometer 28. The second intensity measurement data is acquired at the same time as the first intensity measurement data during polishing of the workpiece W. That is, the first spectrometer 27 measures the intensity of reflected light from the workpiece W over a predetermined wavelength range, and at the same time, the second spectrometer 28 measures the intensity of light from the light source 22 over the same wavelength range.

[0069] The processing system 30 selects the second base intensity data that best matches the second intensity measurement data from a plurality of different second base intensity data included in the reference library, and determines the first base intensity data associated with the selected second base intensity data. "Best match" includes not only most similarity but also perfect match. A method of selecting the second base intensity data that best matches the second intensity measurement data (i.e., a method of determining the similarity of the intensity data) can be a method such as curve fitting or reproduction discrimination.

[0070] The spectrum of the reflected light from the workpiece W is affected by the optical path in the light projecting optical fiber cable 31. Therefore, when calculating the relative reflectance from the first intensity measurement data and the first base intensity data, if the calculation is performed using the intensity data of light that has passed through different optical paths, the calculation is affected by the optical path, and accurate film thickness measurement cannot be performed. On the other hand, the first base intensity data and the second base intensity data, and the first intensity measurement data and the second intensity measurement data are intensity data of light that has passed through the same optical path, and therefore have a corresponding relationship. Therefore, from the multiple second base intensity data, second base intensity data that is thought to have passed through a similar optical path in the directly connected optical fiber cable 33 and has a similar spectrum to the second intensity measurement data is selected. Furthermore, first base intensity data corresponding to the selected second base intensity data (measured at the same time) is obtained. As a result, by calculating the relative reflectance between the first intensity measurement data and the obtained first base intensity data, the influence of the optical path is eliminated, and the film thickness measurement accuracy can be improved.

[0071] The processing system 30 calculates the relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data, and determines the film thickness of the workpiece W based on the relative reflectance data. By such division, the change in the position of the light incident spot S within the end face 35a of the trunk optical fiber cable 35 is removed from the relative reflectance data. As a result, the processing system 30 can accurately determine the film thickness from the relative reflectance data.

[0072] FIG. 10 is a flow chart illustrating one embodiment of a polishing method for polishing a workpiece W. In step 201, before polishing the workpiece W, light repeatedly emitted from the light source 22 is guided to the first spectrometer 27 through the light-projecting fiber optic cable 31 and the light-receiving fiber optic cable 32, and the intensity of the light is measured by the first spectrometer 27 to generate a plurality of different first base intensity data indicating a reference intensity of the light. The processing system 30 acquires the plurality of different first base intensity data from the first spectrometer 27 and stores it in the storage device 30a.

[0073] In step 202, before polishing the workpiece W, light repeatedly emitted from the light source 22 is guided to the second spectrometer 28 through the directly connected optical fiber cable 33, and the intensity of the light is measured by the second spectrometer 28 to generate a plurality of different second base intensity data indicating a reference intensity of the light of the light source 22. The processing system 30 acquires the plurality of different second base intensity data from the second spectrometer 28 and stores it in the storage device 30a. The measurement of the light intensity by the first spectrometer 27 in step 201 and the measurement of the light intensity by the second spectrometer 28 in step 202 are performed simultaneously.

[0074] In step 203, while rotating the polishing table 3, the polishing head 1 presses the workpiece W against the polishing pad 2 to start polishing the workpiece W. In step 204 , while the workpiece W is being polished, the processing system 30 obtains first intensity measurement data indicative of the intensity of the reflected light from the workpiece W as measured by the first spectrometer 27 . In step 205, during polishing of the workpiece W, the processing system 30 obtains second intensity measurement data indicative of the intensity of light from the light source 22 measured by the second spectrometer 28. The measurement of the intensity of the reflected light by the first spectrometer 27 in step 204 and the measurement of the intensity of the light from the light source 22 by the second spectrometer 28 in step 205 are performed simultaneously.

[0075] In step 206, the processing system 30 selects the second base intensity data from the plurality of different second base intensity data that most closely matches the second intensity measurement data. In step 207, the processing system 30 determines the first base intensity data associated with the selected second base intensity data. In step 208, the processing system 30 calculates the relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data. In step 209, processing system 30 determines the film thickness of workpiece W based on the relative reflectance data.

[0076] In the embodiments described so far, one optical sensor head 25 is provided, but the present invention is not limited to the above embodiments, and multiple optical sensor heads 25 may be provided in the polishing table 3. For example, as shown in FIG. 11, the light-receiving optical fiber cables 32 constituting the multiple optical sensor heads 25 may be connected to the first spectrometer 27 via an optical path switching device 40 such as an optical switch or a shutter. The positions of the multiple optical sensor heads 25 are not particularly limited, and for example, the multiple optical sensor heads 25 may be disposed at positions passing through the center and edge portions of the workpiece W. In the embodiment shown in FIG. 11, two optical sensor heads 25 are provided, but three or more optical sensor heads 25 may be provided.

[0077] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can 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 according to the technical idea defined by the claims. [Explanation of symbols]

[0078] 1 Polishing head 2 Polishing Pads 2a Polished surface 3 Polishing table 5 Polishing fluid supply nozzle 6 Table Motor 9. Operation control section 10 Head shaft 20 Optical film thickness measuring device 22 Light source 25 Optical sensor head 27 1st spectrometer 28 Second spectrometer 30 Processing System 31 Light-emitting fiber optic cable 32 Receiving optical fiber cable 33 Direct-connect fiber optic cable 35 Trunk Fiber Optic Cable 40 Optical path switching device W Workpiece

Claims

1. 1. A polishing apparatus for polishing a workpiece, comprising: a polishing table supporting a polishing pad; a polishing head that presses the workpiece against the polishing pad to polish the workpiece; A light source that emits light; a light projecting fiber optic cable coupled to the light source for directing the light to the work piece; a receiving fiber optic cable for receiving light reflected from the workpiece; a first spectrometer coupled to the receiving optical fiber cable; A second spectrometer directly connected to the light source; a processing system including a storage device storing a program and a computing device for performing operations according to instructions included in the program; the storage device stores therein first base intensity data indicating a reference intensity of light measured by the first spectrometer before polishing the workpiece, second base intensity data indicating a reference intensity of light of the light source measured by the second spectrometer before polishing the workpiece, and a calculation formula for calculating relative reflectance data; the processing system is configured to determine a film thickness of the workpiece based on the relative reflectance data; The calculation formula is expressed as follows: The relative reflectance data=MD1 / [BD1·k] wherein MD1 is first intensity measurement data indicating the intensity of the reflected light from the workpiece measured by the first spectrometer, BD1 is the first base intensity data, and k is the rate of change of second intensity measurement data indicating the intensity of the light of the light source measured by the second spectrometer during polishing of the workpiece relative to the second base intensity data.

2. each of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is data indicative of a plurality of intensities of light at a plurality of wavelengths; 2. The polishing apparatus according to claim 1, wherein the rate of change k is a plurality of rates of change corresponding respectively to the plurality of wavelengths.

3. 3. The polishing apparatus of claim 2, wherein the processing system is configured to calculate the multiple change rates k after performing interpolation on the first base intensity data, the first intensity measurement data, the second base intensity data, and the second intensity measurement data to match the multiple wavelengths of the first base intensity data and the first intensity measurement data with the multiple wavelengths of the second base intensity data and the second intensity measurement data.

4. 4. The polishing apparatus of claim 3, wherein the plurality of wavelengths of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data are a plurality of integer number of wavelengths.

5. 2. The polishing apparatus according to claim 1, wherein the rate of change k is a rate of change of the representative intensity value of the second intensity measurement data relative to the representative intensity value of the second base intensity data.

6. 6. The polishing apparatus according to claim 1, wherein the first spectrometer and the second spectrometer are configured to simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source.

7. 7. The polishing apparatus of claim 1, further comprising a direct optical fiber cable that directly couples the light source to the second spectrometer.

8. 1. A polishing apparatus for polishing a workpiece, comprising: a polishing table supporting a polishing pad; a polishing head that presses the workpiece against the polishing pad to polish the workpiece; A light source that emits light; a light projecting fiber optic cable coupled to the light source for directing the light to the work piece; a receiving fiber optic cable for receiving light reflected from the workpiece; a first spectrometer coupled to the receiving optical fiber cable; A second spectrometer directly connected to the light source; a processing system including a storage device storing a program and a computing device for performing operations according to instructions included in the program; the storage device stores therein a plurality of different first base intensity data indicating a reference intensity of light measured by the first spectrometer before polishing the workpiece, and a plurality of different second base intensity data indicating a reference intensity of light of the light source measured by the second spectrometer before polishing the workpiece; the plurality of different first base strength data and the plurality of different second base strength data are associated in a one-to-one correspondence; The processing system includes: obtaining first intensity measurement data indicative of the intensity of the reflected light from the workpiece as measured by the first spectrometer; obtaining second intensity measurement data indicative of the intensity of the light from the light source measured by the second spectrometer during polishing of the workpiece; selecting second base strength data from the plurality of different second base strength data that most closely matches the second strength measurement data; determining first base strength data associated with the selected second base strength data; calculating relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data; a polishing apparatus configured to determine a film thickness of the workpiece based on the relative reflectance data.

9. 9. The polishing apparatus of claim 8, wherein the first spectrometer and the second spectrometer are configured to simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light of the light source while the workpiece is being polished.

10. the polishing apparatus further comprising a direct optical fiber cable directly connecting the light source to the second spectrometer; an end of the light projecting optical fiber cable and an end of the direct connection optical fiber cable are bundled together to form a trunk optical fiber cable; 10. The polishing apparatus according to claim 8, wherein the trunk optical fiber cable is connected to the light source.

11. 1. A polishing method for polishing a workpiece, comprising: Prior to polishing the workpiece, light emitted from a light source is guided to a first spectrometer through a light projecting optical fiber cable and a light receiving optical fiber cable, and an intensity of the light is measured by the first spectrometer to generate first base intensity data indicating a reference intensity of the light; Before polishing the workpiece, an intensity of the light emitted from the light source is measured by a second spectrometer to generate second base intensity data indicating a reference intensity of the light, the second spectrometer being directly connected to the light source; While rotating a polishing table, the workpiece is pressed against a polishing pad on the polishing table to polish the workpiece; obtaining first intensity measurement data indicative of an intensity of reflected light from the workpiece as measured by the first spectrometer while polishing the workpiece; obtaining second intensity measurement data indicative of the intensity of the light of the light source measured by the second spectrometer during polishing of the workpiece; determining a rate of change of the second intensity measurement data relative to the second base intensity data; multiplying the first base intensity data by the rate of change to calculate corrected first base intensity data; calculating relative reflectance data by dividing the first intensity measurement data by the corrected first base intensity data; determining a film thickness of the workpiece based on the relative reflectance data.

12. each of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is data indicative of a plurality of intensities of light at a plurality of wavelengths; The polishing method according to claim 11 , wherein the rate of change k is a plurality of rates of change corresponding respectively to the plurality of wavelengths.

13. 13. The polishing method of claim 12, further comprising, prior to calculating the multiple change rates, performing an interpolation on the first base intensity data, the first intensity measurement data, the second base intensity data, and the second intensity measurement data to match the multiple wavelengths of the first base intensity data and the first intensity measurement data with the multiple wavelengths of the second base intensity data and the second intensity measurement data.

14. 14. The polishing method of claim 13, wherein the plurality of wavelengths of the first base intensity data, the second base intensity data, the first intensity measurement data, and the second intensity measurement data is a multiple of an integer number of wavelengths.

15. 12. The polishing method according to claim 11, wherein the rate of change is a rate of change of the representative intensity value of the second intensity measurement data relative to the representative intensity value of the second base intensity data.

16. 16. The polishing method of claim 11, wherein the first spectrometer and the second spectrometer simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source while the workpiece is being polished.

17. 1. A polishing method for polishing a workpiece, comprising: Before polishing the workpiece, light repeatedly emitted from a light source is guided to a first spectrometer through a light projecting optical fiber cable and a light receiving optical fiber cable, and an intensity of the light is measured by the first spectrometer, thereby generating a plurality of different first base intensity data indicating a reference intensity of the light; A second spectrometer is directly connected to the light source to measure the intensity of the light repeatedly emitted from the light source, thereby generating a plurality of different second base intensity data indicating a reference intensity of the light, Associating the plurality of different first base strength data with the plurality of different second base strength data in a one-to-one correspondence; While rotating a polishing table, the workpiece is pressed against a polishing pad on the polishing table to polish the workpiece; obtaining first intensity measurement data indicative of an intensity of reflected light from the workpiece measured by the first spectrometer while polishing the workpiece; obtaining second intensity measurement data indicative of the intensity of the light from the light source measured by the second spectrometer during polishing of the workpiece; selecting second base strength data from the plurality of different second base strength data that most closely matches the second strength measurement data; determining first base strength data associated with the selected second base strength data; calculating relative reflectance data by dividing the first intensity measurement data by the determined first base intensity data; determining a film thickness of the workpiece based on the relative reflectance data.

18. 20. The method of claim 17, wherein the first spectrometer and the second spectrometer simultaneously measure the intensity of the reflected light from the workpiece and the intensity of the light from the light source while the workpiece is being polished.

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