Polishing method and polishing apparatus

Abstract

The present invention provides a polishing method that can improve the measurement accuracy of a sensor having a sensor head positioned within a polishing table. [Solution] A polishing method comprising: when the polishing pad 2 supported on the polishing table 3 is in its initial state, a sensor 30 having a sensor head 35 positioned within the polishing table 3 detects a reference sample on the polishing pad 2 and outputs a reference sensor signal value; pressing the substrate W against the polishing surface 2a of the polishing pad 2 to polish the substrate W; detecting the substrate W with the sensor 30 during polishing and outputting a monitoring sensor signal value; after the polishing of the substrate W is completed, the sensor 30 detects a reference sample on the polishing pad 2 and outputs a post-polishing sensor signal value; and moving the sensor head 35 so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized.

Description

Technical Field

[0001] The present invention relates to a polishing method and a polishing apparatus for polishing a substrate such as a wafer.

Background Art

[0002] In the manufacturing process of semiconductor devices, there is a process of polishing a wafer to planarize the surface of the wafer. As one of the apparatuses for polishing a wafer, a polishing apparatus that performs chemical mechanical polishing (CMP) is known. The polishing apparatus supplies a polishing liquid to the polishing surface of a polishing pad supported by a polishing table, presses a wafer against the polishing surface, and further relatively moves the wafer and the polishing table. As a result, the surface of the wafer is polished.

[0003] Generally, a polishing apparatus includes a film thickness measuring device for measuring the film thickness of the surface of a wafer during polishing. When the measured value of the film thickness reaches a predetermined target value (in other words, the polishing end point), the polishing apparatus ends the polishing. As an example of a film thickness measuring device, there is an optical film thickness measuring device. The optical film thickness measuring device irradiates light from an optical sensor head disposed in a polishing table onto the surface of a wafer, receives the reflected light from the wafer by the optical sensor head, and analyzes the spectrum of the reflected light to determine the film thickness of the wafer. The polishing apparatus ends the polishing of the wafer based on the determined film thickness.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As the wafer is polished, the polishing pad wears down, and its thickness gradually decreases. The thinner the polishing pad becomes, the closer the wafer surface pressed against the pad gets to the optical sensor head of the optical film thickness measuring device. Changes in the distance between the wafer surface and the optical sensor head affect the light reception conditions of the optical sensor head, which can result in a decrease in the accuracy of film thickness measurement. Thus, in sensors that have a sensor head positioned within a polishing table, and whose detection conditions for the object being measured are affected by the distance between the sensor head and the object being measured, wear on the polishing pad can reduce measurement accuracy.

[0006] Therefore, the present invention provides a polishing method and a polishing apparatus that can improve the measurement accuracy of a sensor having a sensor head arranged in a polishing table. [Means for solving the problem]

[0007] In one embodiment, a polishing method is provided in which, when a polishing pad supported on a polishing table is in its initial state, a sensor having a sensor head positioned within the polishing table detects a reference sample on the polishing pad and outputs a reference sensor signal value, a substrate is pressed against the polishing surface of the polishing pad to polish the substrate, the substrate is detected by the sensor during polishing and a monitoring sensor signal value is output, after polishing of the substrate is completed, the sensor detects the reference sample on the polishing pad and outputs a post-polishing sensor signal value, and the sensor head is moved so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value. In one embodiment, moving the sensor head is to move the sensor head along a direction perpendicular to the pad support surface of the polishing table that supports the polishing pad.

[0008] In one embodiment, the sensor is an optical film thickness measuring device that optically measures the film thickness of the substrate, the sensor head is an optical sensor head that irradiates the substrate with light and receives reflected light from the substrate, the monitoring sensor signal value is a sensor signal value representing the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad in the initial state, and the post-polishing sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad after the polishing of the substrate is completed. In one embodiment, the polishing method further includes generating a reference spectrum of reflected light from the reference sensor signal value and generating a post-polished spectrum of reflected light from the post-polished sensor signal value, and moving the sensor head so as to minimize the difference between the reference sensor signal value and the post-polished sensor signal value is equivalent to moving the optical sensor head so as to minimize the difference between the reference spectrum and the post-polished spectrum.

[0009] In one embodiment, the polishing method further includes obtaining a correlation between the sensor signal value output when the reference sample on the polishing pad is detected by the sensor and the distance from the reference sample to the sensor head, and moving the sensor head so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value means calculating the amount by which the sensor head should be moved based on the reference sensor signal value, the post-polishing sensor signal value and the correlation, and moving the sensor head by the amount by which it should be moved. In one embodiment, the polishing method further includes detecting the reference sample on the polishing pad in multiple positional relationships between the reference sample and the sensor head at different distances from the reference sample to the sensor head, outputting multiple sample sensor signal values, and constructing a sample library by associating the multiple sample sensor signal values ​​with the distance from the reference sample to the sensor head in each of the multiple positional relationships. Moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized involves determining from the sample library the sample sensor signal value with the smallest difference from the reference sensor signal value and the sample sensor signal value with the smallest difference from the post-polishing sensor signal value, calculating the amount the sensor head should move based on the distance from the reference sample to the sensor head associated with the sample sensor signal value with the smallest difference from the reference sensor signal value and the distance from the reference sample to the sensor head associated with the sample sensor signal value with the smallest difference from the post-polishing sensor signal value, and moving the sensor head by the amount to be moved. In one embodiment, the output of the reference sensor signal value by the sensor and the output of the post-polishing sensor signal value by the sensor are performed during the water polishing of the reference sample.

[0010] In one embodiment, a polishing apparatus is provided comprising: a polishing table supporting a polishing pad; a polishing head for polishing a substrate by pressing the substrate against the polishing surface of the polishing pad; a sensor having a sensor head positioned within the polishing table, which detects the substrate and outputs a monitoring sensor signal value; a sensor moving mechanism for moving the sensor head; and a control device for controlling the operation of the sensor moving mechanism, wherein the control device is configured to move the sensor head in the sensor moving mechanism so as to minimize the difference between a reference sensor signal value output when the sensor detects a reference sample located on the polishing pad in an initial state and a post-polishing sensor signal value output when the sensor detects the reference sample located on the polishing pad after the polishing of the substrate is completed. In one embodiment, the sensor movement mechanism is configured to move the sensor head along a direction perpendicular to the pad support surface of the polishing table that supports the polishing pad.

[0011] In one embodiment, the sensor is an optical film thickness measuring device that optically measures the film thickness of the substrate, the sensor head is an optical sensor head that irradiates the substrate with light and receives reflected light from the substrate, the monitoring sensor signal value is a sensor signal value representing the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad in the initial state, and the post-polishing sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad after the polishing of the substrate is completed. In one embodiment, the optical film thickness measuring device is configured to generate a reference spectrum of reflected light from the reference sensor signal value and a post-polished spectrum of reflected light from the post-polished sensor signal value, and the control device is configured to move the optical sensor head in the sensor moving mechanism so that the difference between the reference spectrum and the post-polished spectrum is minimized.

[0012] In one embodiment, the control device obtains a correlation between the sensor signal value output when the reference sample on the polishing pad is detected by the sensor and the distance from the reference sample to the sensor head, calculates the amount by which the sensor head should move based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation, and is configured to move the sensor head by the amount to be moved by the sensor moving mechanism. In one embodiment, the sensor is configured to detect the reference sample on the polishing pad and output multiple sample sensor signal values ​​in multiple positional relationships between the reference sample and the sensor head, where the distance from the reference sample to the sensor head is different. The control device constructs a sample library by associating the multiple sample sensor signal values ​​with the distance from the reference sample to the sensor head in each of the multiple positional relationships. From the sample library, the control device determines the sample sensor signal value with the smallest difference from the reference sensor signal value and the sample sensor signal value with the smallest difference from the post-polishing sensor signal value. Based on the distance from the reference sample to the sensor head associated with the sample sensor signal value with the smallest difference from the reference sensor signal value and the distance from the reference sample to the sensor head associated with the sample sensor signal value with the smallest difference from the post-polishing sensor signal value, the control device calculates the amount the sensor head should move and causes the sensor moving mechanism to move the sensor head by the amount to be moved. In one embodiment, the reference sensor signal value is the sensor signal value output when the sensor detects the reference sample during water polishing of the reference sample using the polishing pad in the initial state, and the post-polishing sensor signal value is the sensor signal value output when the sensor detects the reference sample during water polishing of the reference sample using the polishing pad after the polishing of the substrate is completed. [Effects of the Invention]

[0013] The sensor detects a reference sample located on the polishing pad in the initial state and outputs a reference sensor signal value, and detects a reference sample located on the polishing pad after the polishing of the substrate is completed and outputs a post-polishing sensor signal value. By moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized, the distance between the sensor head and the substrate can be maintained at a reference distance. As a result, the measurement accuracy of the sensor having the sensor head disposed in the polishing table can be improved.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram showing an embodiment of a polishing apparatus. [Figure 2] It is a cross-sectional view showing an embodiment of a polishing apparatus provided with an optical film thickness measuring device as a sensor. [Figure 3] It is a diagram showing an example of a monitoring spectrum generated by a data processing unit. [Figure 4] It is a top view showing the positional relationship between the substrate and the polishing table during polishing. [Figure 5] It is a diagram for explaining how the light reception condition of the reflected light from the substrate received by the optical sensor head changes due to the wear of the polishing pad. [Figure 6] It is a schematic diagram showing an embodiment of a sensor moving mechanism. [Figure 7] It is a diagram showing an example of a reference spectrum and a post-polishing spectrum. [Figure 8] It is a diagram showing an example of a plurality of sample spectra stored in a sample library. [Figure 9] It is a flowchart for explaining an embodiment of a method for polishing a substrate. [Figure 10] It is a flowchart for explaining an embodiment of a method for polishing a substrate. [Figure 11] It is a flowchart for explaining an embodiment of a method for moving an optical sensor head so that the difference between the reference spectrum and the post-polishing spectrum is minimized. [Figure 12]A flowchart for explaining another embodiment of a method of moving an optical sensor head such that the difference between a reference spectrum and a post-polishing spectrum is minimized. [Figure 13] A flowchart for explaining yet another embodiment of a method of moving an optical sensor head such that the difference between a reference spectrum and a post-polishing spectrum is minimized. [Figure 14] A schematic diagram showing another embodiment of an optical sensor head. [Figure 15] FIG. 9 is a diagram for explaining how the light reception conditions of reflected light from a substrate received by an optical sensor head change due to wear of a polishing pad in an obliquely arranged optical sensor head shown in FIG. 14.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of a polishing apparatus 1. The polishing apparatus 1 shown in FIG. 1 is an apparatus for chemically and mechanically polishing a substrate such as a wafer. The polishing apparatus 1 includes a polishing pad 2 having a polishing surface 2a, a polishing table 3 for supporting the polishing pad 2, a polishing head 10 for polishing the substrate W by pressing the substrate W against the polishing surface 2a of the polishing pad 2, a liquid supply nozzle 20 for supplying a liquid such as a polishing liquid (for example, a slurry containing abrasive grains) onto the polishing pad 2, a sensor 30 for detecting the substrate W and outputting a sensor signal value, and a control device 50 for controlling the operations of these components. The sensor 30 has a sensor head disposed within the polishing table 3.

[0016] In this embodiment, the sensor 30 is an optical film thickness measuring device that optically measures the film thickness of the substrate W. Figure 2 is a cross-sectional view showing one embodiment of a polishing apparatus 1 equipped with an optical film thickness measuring device as the sensor 30. The polishing pad 2 is supported on the pad support surface 3a of the polishing table 3. In this embodiment, the pad support surface 3a is made up of the flat upper surface of the polishing table 3. The upper surface of the polishing pad 2 constitutes the polishing surface 2a for polishing the substrate W. The polishing pad 2 has a thickness. The thickness of the polishing pad 2 refers to the distance from the upper surface (polishing surface 2a) of the polishing pad 2 to the lower surface (contact surface with the pad support surface 3a of the polishing table 3). Through holes 2b are formed in the polishing pad 2. Holes 3b are formed in the upper surface of the polishing table 3. The through holes 2b and holes 3b are in communication. As will be described later, the through holes 2b allow light for film thickness measurement to pass through.

[0017] The polishing table 3 is connected to the table motor 6 via the table shaft 5. The table motor 6 is configured to rotate the polishing table 3. The polishing table 3 is rotated around its axis by the table motor 6. The polishing pad 2 rotates together with the polishing table 3. For example, the polishing table 3 rotates in the direction indicated by the arrow in Figure 2.

[0018] The polishing head 10 is connected to a polishing head motor (not shown) via a polishing head shaft 12. The polishing head motor is configured to rotate the polishing head 10. The polishing head 10 is rotated around its axis by the polishing head motor. The polishing head 10 rotates together with the polishing head shaft 12. For example, the polishing head 10 rotates in the direction indicated by the arrow in Figure 2.

[0019] The lower surface of the polishing head 10 is configured to hold the substrate W. A vacuum source (not shown) for vacuum-suctioning the substrate W is connected to the lower surface of the polishing head 10. The substrate W is held by suction to the lower surface of the polishing head 10 by the vacuum source. In other words, the lower surface of the polishing head 10 constitutes a substrate holding surface for holding the substrate W.

[0020] Furthermore, an airbag (not shown) is provided on the underside of the polishing head 10 to press the substrate W toward the polishing surface 2a of the polishing pad 2. The airbag generates pressure to press the held substrate W. A gas supply line (not shown) is connected to the airbag, and the pressure is adjusted by the amount of gas supplied. The airbag presses the substrate W from its back side. The polishing head 10 uses the airbag to press the substrate W toward the polishing surface 2a of the polishing pad 2.

[0021] The polishing head 10 is connected to a polishing head lifting mechanism (not shown) via a polishing head shaft 12. The polishing head lifting mechanism is configured to move the polishing head 10 up and down (up and down). The polishing head 10 moves up and down relative to the polishing pad 2 by the polishing head lifting mechanism. The polishing head 10 moves up and down together with the polishing head shaft 12. The polishing head lifting mechanism lowers the polishing head 10, which holds the substrate W, toward the polishing pad 2, thereby bringing the surface of the substrate W (in other words, the surface to be polished) into contact with the polishing surface 2a of the polishing pad 2. The polishing head lifting mechanism may further lower the polishing head 10 to press the surface of the substrate W toward the polishing surface 2a of the polishing pad 2.

[0022] The control unit 50 consists of at least one computer. The control unit 50 includes a storage device 50a in which a program is stored, and an arithmetic unit 50b that performs calculations according to the instructions contained in the program. The storage device 50a includes a main memory such as RAM and an auxiliary storage device such as a hard disk drive (HDD) or solid-state drive (SSD). Examples of the arithmetic unit 50b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the control unit 50 is not limited to these examples.

[0023] Polishing of the substrate W is performed as follows: The polishing head 10 holds the substrate W with its surface (the surface to be polished) facing the polishing pad 2. While the polishing table 3 is rotated by the table motor 6, polishing liquid is supplied from the liquid supply nozzle 20 onto the polishing surface 2a of the polishing pad 2. In this state, the polishing head 10 is rotated by the polishing head motor and lowered by the polishing head lifting mechanism. As a result, the surface of the substrate W comes into contact with the polishing surface 2a of the polishing pad 2. Furthermore, the polishing head 10 presses the substrate W toward the polishing pad 2. The surface of the substrate 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 surface 2a.

[0024] The optical film thickness measuring device 30 includes a light source 31 that emits light, an optical sensor head 35 that irradiates the substrate W with light from the light source 31 and receives reflected light from the substrate W, a spectrometer 37 that generates intensity measurement data of the reflected light from the substrate W, and a data processing unit 39 that determines the thickness of the film on the substrate W based on the intensity measurement data of the reflected light from the substrate W. The optical film thickness measuring device 30 is configured to detect the intensity of the reflected light from the substrate W and output a monitoring sensor signal value, which is a sensor signal value representing the intensity of the reflected light.

[0025] The optical sensor head 35 is positioned inside the hole 3b of the polishing table 3. The optical sensor head 35 is positioned below the polishing surface 2a of the polishing pad 2. In this embodiment, the optical sensor head 35 is positioned below the pad support surface 3a of the polishing table 3. In one embodiment, the optical sensor head 35 may be positioned inside the through hole 2b, as long as it is below the polishing surface 2a of the polishing pad 2.

[0026] The through-hole 2b and the hole 3b are filled with a liquid (e.g., pure water) as a light-transmitting medium. In other words, the space between the surface of the substrate W to be polished and the optical sensor head 35 is filled with liquid. Light irradiated from the optical sensor head 35 onto the surface of the substrate W and reflected light from the surface of the substrate W pass through the liquid. This liquid is supplied by a liquid supply line (not shown) connected to the hole 3b and discharged by a liquid discharge line (not shown) connected to the hole 3b.

[0027] In one embodiment, the light-transmitting medium may be air instead of a liquid. Alternatively, a transparent window (not shown) may be provided instead of the light-transmitting liquid. The transparent window may be provided inside the through-hole 2b or inside the hole 3b, provided that it is located below the polishing surface 2a of the polishing pad 2 and above the optical sensor head 35. In this case, the transparent window is provided so as to block at least one of the through-hole 2b and the hole 3b. In another embodiment, a transparent window (not shown) that blocks the through-hole 2b or hole 3b filled with liquid (e.g., pure water) may be provided.

[0028] The optical sensor head 35 is connected to the light source 31 and the spectrometer 37. The spectrometer 37 is connected to the data processing unit 39. The light source 31, the optical sensor head 35, and the spectrometer 37 are mounted on the polishing table 3 and rotate together with the polishing table 3 and the polishing pad 2. The light source 31 is connected to the control device 50, and the operation of the light source 31 is controlled by the control device 50. The data processing unit 39 is connected to the control device 50. The data processing unit 39, like the control device 50, consists of at least one computer equipped with a storage device that stores a program and an arithmetic unit that performs calculations according to the instructions contained in the program.

[0029] The optical film thickness measuring device 30 includes a light-emitting optical fiber cable 32 that guides light emitted from a light source 31 to the surface of the substrate W, and a light-receiving optical fiber cable 33 that receives reflected light from the substrate W and sends the reflected light to a spectrometer 37. The optical sensor head 35 is composed of the tip of the light-emitting optical fiber cable 32 and the tip of the light-receiving optical fiber cable 33. The light-emitting optical fiber cable 32 is an optical transmission unit that guides light emitted from the light source 31 to the surface of the substrate W. The light-receiving optical fiber cable 33 is an optical transmission unit that sends reflected light from the substrate W to the spectrometer 37. One end (tip) of the light-emitting optical fiber cable 32 and one end (tip) of the light-receiving optical fiber cable 33 are located inside the hole 3b of the polishing table 3 and face the substrate W held by the polishing head 10. The other end of the light-emitting optical fiber cable 32 is connected to the light source 31, and the other end of the light-receiving optical fiber cable 33 is connected to the spectrometer 37.

[0030] The light source 31 can be a light-emitting diode (LED), a halogen lamp, a xenon lamp, or the like. The optical sensor head 35 irradiates the surface of the substrate W with light from the light source 31 and receives the reflected light from the surface of the substrate W. The spectrometer 37 decomposes the reflected light received by the optical sensor head 35 according to its wavelength and outputs a monitoring sensor signal value representing the intensity of the reflected light over a predetermined wavelength range.

[0031] The data processing unit 39 is configured to generate a reflected light spectrum representing the intensity of reflected light at each wavelength from the monitoring sensor signal values ​​obtained by the spectrometer 37. Hereinafter, the spectrum generated from the monitoring sensor signal values ​​will be referred to as the monitoring spectrum. The monitoring spectrum of reflected light is represented as a line graph (i.e., a spectral waveform) showing the relationship between the wavelength and intensity of the reflected light. The intensity of the reflected light can also be expressed as a relative value such as reflectance or relative reflectance.

[0032] Figure 3 shows an example of a monitoring spectrum generated by the data processing unit 39. In Figure 3, the horizontal axis represents the wavelength of light reflected from the substrate W, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. Relative reflectance is an index value indicating the intensity of reflected light, and is the ratio of the light intensity to a predetermined reference intensity. By dividing the light intensity (measured intensity) at each wavelength by the predetermined reference intensity, unwanted noise such as variations in intensity inherent to the optical system and light source of the device can be removed from the measured intensity.

[0033] The reference intensity is the light intensity measured in advance for each wavelength, and the relative reflectance is calculated for each wavelength. Specifically, the relative reflectance is obtained by dividing the light intensity (measured intensity) at each wavelength by the corresponding reference intensity. The reference intensity can be obtained, for example, by directly measuring the light intensity emitted from the optical sensor head 35, or by irradiating a mirror with light from the optical sensor head 35 and measuring the intensity of the reflected light from the mirror. Alternatively, the reference intensity may be the intensity of reflected light from a silicon substrate measured by a spectrometer 37 when a silicon substrate without a film (bare substrate) is being water-polished on a polishing pad 2 in the presence of water, or when the silicon substrate (bare substrate) is placed on the polishing pad 2.

[0034] In actual polishing, the corrected measured intensity is obtained by subtracting the dark level (background intensity obtained under conditions where light is blocked) from the measured intensity, the corrected reference intensity is obtained by subtracting the dark level from the reference intensity, and then the relative reflectance is obtained by dividing the corrected measured intensity by the corrected reference intensity. Specifically, the relative reflectance R(λ) can be calculated using the following equation (1).

number

[0035] In the example shown in Figure 3, the monitoring spectrum of the reflected light is a spectral waveform showing the relationship between the relative reflectance and the wavelength of the reflected light. However, in one embodiment, the monitoring spectrum of the reflected light may be a spectral waveform showing the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

[0036] The data processing unit 39 determines the film thickness of the substrate W based on the monitoring spectrum of the reflected light. Known techniques are used to determine the film thickness of the substrate W based on the monitoring spectrum. For example, the data processing unit 39 determines a reference spectrum from a reference spectrum library that has the shape closest to the monitoring spectrum and determines the film thickness associated with this determined reference spectrum. In another example, the data processing unit 39 performs a Fourier transform on the monitoring spectrum and determines the film thickness from the resulting frequency spectrum. The film thickness measurement obtained by the data processing unit 39 is sent to the control device 50. The control device 50 determines that the polishing endpoint has been reached when the film thickness measurement reaches a predetermined target value.

[0037] Figure 4 is a top view showing the positional relationship between the substrate W and the polishing table 3 during polishing. The optical sensor head 35 crosses (in other words, passes over) the substrate W, tracing the trajectory shown by the dashed line in Figure 4, each time the polishing table 3 completes one rotation. The optical sensor head 35 is positioned at a predetermined distance from the center O of the polishing table 3 in the radial direction. The center of the substrate W is also positioned at a predetermined distance from the center O of the polishing table 3 in the radial direction. In Figure 4, the distance from the center O of the polishing table 3 to the optical sensor head 35 is equal to the distance from the center O of the polishing table 3 to the center of the substrate W. Therefore, in Figure 4, the optical sensor head 35 crosses the center of the substrate W as the polishing table 3 rotates.

[0038] Note that Figure 4 shows an example arrangement where the optical sensor head 35 crosses the center of the substrate W, but the arrangement of the optical sensor head 35 is not limited to this. The optical sensor head 35 only needs to cross the surface of the substrate W. The control device 50 is electrically connected to the table motor 6 (see Figure 2). The control device 50 receives information about the rotation of the polishing table 3 from the table motor 6. The control device 50 determines that the optical sensor head 35 is moving below the substrate W when the polishing table 3 is within a predetermined range of rotation angles.

[0039] As the optical sensor head 35 moves beneath the substrate W, it intermittently irradiates the surface of the substrate W with light at predetermined time intervals. Specifically, the control device 50 controls the light source 31, causing it to emit light intermittently at predetermined time intervals. The light from the light source 31 is intermittently irradiated onto the surface of the substrate W via the optical sensor head 35 at predetermined time intervals. As a result, light is irradiated onto multiple measurement points on the surface of the substrate W, and the film thickness at each measurement point is measured.

[0040] The optical sensor head 35 may maintain light irradiation on the surface of the substrate W while moving below the substrate W to measure the film thickness. In other words, the optical sensor head 35 may continuously irradiate the surface of the substrate W with light. In this case, the control device 50 controls the light source 31 to maintain emission while the optical sensor head 35 moves below the substrate W. The light from the light source 31 continues to irradiate the surface of the substrate W via the optical sensor head 35. The spectrometer 37 measures the intensity of the reflected light at predetermined time intervals and outputs a monitoring sensor signal value representing the intensity of the reflected light. As a result, the data processing unit 39 generates a monitoring spectrum of reflected light representing the intensity of reflected light for each wavelength from the monitoring sensor signal values ​​obtained by the spectrometer 37 at predetermined time intervals, and determines the film thickness at each measurement point on the substrate W based on the monitoring spectrum of reflected light.

[0041] Figure 5 illustrates how the light reception conditions for reflected light from the substrate W received by the optical sensor head 35 change as the polishing pad 2 wears down. The thickness of the polishing pad 2 gradually decreases as it wears down due to polishing of the substrate W. In other words, the thickness of the polishing pad 2 gradually decreases. As shown in Figure 5, as the thickness of the polishing pad 2 decreases, the position of the surface of the substrate W pressed against the polishing surface 2a of the polishing pad 2 changes in a direction that moves closer to the optical sensor head 35. In other words, the distance from the surface of the substrate W to the tip of the light-emitting optical fiber cable 32 and the tip of the light-receiving optical fiber cable 33 decreases as the polishing pad 2 wears down.

[0042] The intensity of reflected light from the surface of the substrate W received by the optical sensor head 35 depends on the distance from the surface of the substrate W to the optical sensor head 35. The smaller the distance from the surface of the substrate W to the optical sensor head 35, the greater the intensity of reflected light from the surface of the substrate W received by the optical sensor head 35. The larger the distance from the surface of the substrate W to the optical sensor head 35, the smaller the intensity of reflected light from the surface of the substrate W received by the optical sensor head 35. Therefore, as the polishing pad 2 wears down and the distance from the surface of the substrate W to the optical sensor head 35 decreases, the intensity of reflected light from the surface of the substrate W received by the optical sensor head 35 increases.

[0043] As described above, the data processing unit 39 determines the film thickness of the substrate W based on the monitoring spectrum of reflected light generated from the intensity of the reflected light received by the optical sensor head 35. Therefore, changes in the intensity of reflected light due to wear of the polishing pad 2 may affect the measurement accuracy of the film thickness of the substrate W.

[0044] Therefore, the polishing apparatus 1 is equipped with a sensor moving mechanism 40 for moving the optical sensor head 35, and by moving the optical sensor head 35 with the sensor moving mechanism 40, the distance from the surface of the substrate W to the optical sensor head 35 is kept constant even when the polishing pad 2 is worn down. Figure 6 is a schematic diagram showing one embodiment of the sensor moving mechanism 40. The sensor moving mechanism 40 is configured to move the optical sensor head 35 in a direction perpendicular to the pad support surface 3a of the polishing table 3 (i.e., in the thickness direction of the polishing pad 2). As shown in Figure 6, the sensor moving mechanism 40 includes a sensor support member 41 that supports the optical sensor head 35, a first gear 43 connected to the sensor support member 41, a second gear 46 that meshes with the first gear 43, and a motor 48 connected to the second gear 46. Examples of the motor 48 include a servo motor and a stepping motor. The sensor support member 41 is located inside the hole 3b of the polishing table 3.

[0045] At least a portion of the optical sensor head 35 is supported by a sensor support member 41. In this embodiment, the sensor support member 41 is attached to the inner surface of the polishing table 3, which forms the hole 3b, so as to be movable relative to the polishing table 3 via a sealing member (not shown). This prevents the liquid filling the hole 3b from leaking out between the sensor support member 41 and the inner surface of the polishing table 3 and adhering to the first gear 43, the second gear 46, the motor 48, etc. In one embodiment, instead of the sealing member, a cover may be provided to prevent the liquid from adhering to the first gear 43, the second gear 46, the motor 48, etc.

[0046] The first gear 43 is connected to a screw 44. The screw 44 is screwed into a screw hole 41a provided in the sensor support member 41. The second gear 46 is connected to the rotating shaft 48a of the motor 48. When the motor 48 is driven, the second gear 46 rotates via the rotating shaft 48a. As the second gear 46 rotates, the first gear 43 rotates in conjunction with the second gear 46. This rotation of the second gear 43 causes the screw 44 to rotate, thereby moving the sensor support member 41 and the optical sensor head 35 supported by the sensor support member 41 in a direction perpendicular to the pad support surface 3a. In this way, the sensor moving mechanism 40 moves the optical sensor head 35 relative to the polishing table 3 within the hole 3b.

[0047] The specific configuration of the sensor movement mechanism 40 is not particularly limited to this embodiment, as long as it can move the optical sensor head 35 in a direction perpendicular to the pad support surface 3a. For example, the screw 44 may be directly connected to the rotation shaft 48a of the motor 48 without going through the first gear 43 and the second gear 46. The sensor movement mechanism 40 is connected to a control device 50, and the operation of the sensor movement mechanism 40 is controlled by the control device 50.

[0048] The storage device 50a of the control device 50 stores the correlation between the number of rotations of the motor 48, which has been acquired in advance, and the amount of movement of the optical sensor head 35. The control device 50 can control the amount of movement of the optical sensor head 35 by controlling the operation of the sensor movement mechanism 40 based on this correlation.

[0049] The movement of the optical sensor head 35 by the sensor movement mechanism 40 is performed based on the sensor signal value obtained by measuring a reference sample on the polishing pad 2 before and after wear using the optical film thickness measuring device 30. Examples of reference samples include a silicon substrate without a film formed on it (bare substrate), a mirror, and a test substrate having the same configuration as the substrate W. The optical film thickness measuring device 30 is configured to detect the reference sample located on the polishing pad 2 in its initial state and output a reference sensor signal value. The polishing pad 2 in its initial state is the polishing pad 2 before it is worn down by polishing the substrate W. A new polishing pad 2 undergoes a break-in process (also called dressing or water polishing) before being used to polish the substrate W. The polishing pad 2 in its initial state is the polishing pad 2 after this break-in process has been performed and before it is used to polish the substrate W.

[0050] In this embodiment, during the water polishing of a reference sample using the polishing pad 2 in its initial state, the optical film thickness measuring device 30 detects the reference sample located on the polishing pad 2 and outputs a reference sensor signal value. The water polishing of the reference sample is performed with water supplied from the liquid supply nozzle 20 onto the polishing surface 2a of the polishing pad 2, instead of a polishing liquid (e.g., slurry), while the polishing head 10 holds the reference sample on the polishing surface 2a of the polishing pad 2. Unlike polishing liquids such as slurry, water has no etching function and does not contain abrasive particles. In addition, the polishing head 10 does not press the reference sample strongly against the polishing pad 2 during water polishing. Therefore, polishing of the reference sample does not progress during the water polishing of the reference sample.

[0051] In one embodiment, the reference sample may not be wet-polished, and the optical film thickness measuring device 30 may detect the reference sample placed on the polishing pad 2 in its initial state and output a reference sensor signal value. For example, the polishing head lifting mechanism may be used to lower the polishing head 10 holding the reference sample toward the polishing pad 2, bringing the reference sample into contact with the polishing surface 2a of the polishing pad 2 in its initial state. Alternatively, the reference sample may simply be placed on the polishing pad 2 in its initial state.

[0052] The optical film thickness measuring device 30 is configured to detect the intensity of reflected light from a reference sample located on the polishing pad 2 in its initial state and to output a reference sensor signal value, which is a sensor signal value representing the intensity of reflected light from the reference sample. The control device 50 determines that the optical sensor head 35 is moving below the reference sample when the polishing table 3 is within a predetermined range of rotation angles. When the optical sensor head 35 is positioned below the reference sample, it irradiates light onto the surface of the reference sample. Specifically, the control device 50 controls the light source 31 and causes the light source 31 to emit light when the optical sensor head 35 is positioned below the reference sample. The light from the light source 31 is irradiated onto the surface of the reference sample via the optical sensor head 35. The spectrometer 37 detects the intensity of reflected light from the reference sample and outputs a reference sensor signal value representing the intensity of reflected light.

[0053] In this embodiment, the data processing unit 39 of the optical film thickness measuring device 30 generates a reflected light spectrum representing the intensity of reflected light for each wavelength from the reference sensor signal value. Hereinafter, the spectrum generated from the reference sensor signal value will be referred to as the reference spectrum. The reference spectrum of reflected light obtained by the data processing unit 39 is sent to the control device 50 and stored in the storage device 50a.

[0054] After acquiring the reference spectrum, the polishing apparatus 1 finishes water polishing of the reference sample and starts polishing the substrate W. The polishing pad 2 gradually wears down as the substrate W is polished. After the polishing of the substrate W is completed, the control device 50 is configured to determine whether or not it is a predetermined sensor position adjustment timing. For example, the control device 50 determines that it is a predetermined sensor position adjustment timing when a predetermined number of substrates have been polished, or when the usage time of the polishing pad 2 reaches a predetermined time. At the sensor position adjustment timing, the optical film thickness measuring device 30 is configured to detect the reference sample located on the polishing pad 2 after the polishing of the substrate W is completed and to output a post-polishing sensor signal value.

[0055] In this embodiment, during the water polishing of a reference sample using the polishing pad 2 after the substrate W has been polished, the optical film thickness measuring device 30 detects the reference sample located on the polishing pad 2 and outputs a post-polishing sensor signal value. When the control device 50 determines that it is time to adjust the sensor position, water polishing of the reference sample is started. This reference sample is the same as the reference sample used to acquire the reference sensor signal value. In one embodiment, water polishing of the reference sample may not be performed, and the optical film thickness measuring device 30 may detect the reference sample placed on the polishing pad 2 after the substrate W has been polished and output a post-polishing sensor signal value.

[0056] The optical film thickness measuring device 30 is configured to detect the intensity of reflected light from a reference sample located on the polishing pad 2 after polishing of the substrate W, and to output a post-polishing sensor signal value, which is a sensor signal value representing the intensity of reflected light from the reference sample. The output of the post-polishing sensor signal value is performed under the same conditions as the output of the reference sensor signal value. The optical film thickness measuring device 30 may also output the post-polishing sensor signal value by detecting the intensity of reflected light from the same measurement point (for example, the center of the reference sample) as when the reference sensor signal value was output. In this embodiment, the data processing unit 39 of the optical film thickness measuring device 30 generates a reflected light spectrum representing the intensity of reflected light for each wavelength from the post-polishing sensor signal value. Hereinafter, the spectrum generated from the post-polishing sensor signal value will be referred to as the post-polishing spectrum. The post-polishing spectrum of reflected light obtained by the data processing unit 39 is sent to the control device 50 and stored in the storage device 50a.

[0057] Figure 7 shows an example of a reference spectrum and a post-polishing spectrum. As shown in Figure 7, the reference spectrum Sr of reflected light and the post-polishing spectrum Sa of reflected light are different. The distance from the surface of the reference sample located on the worn polishing pad 2 after polishing of the substrate W to the optical sensor head 35 is smaller than the distance from the surface of the reference sample located on the polishing pad 2 in its initial state to the optical sensor head 35. Therefore, the post-polishing sensor signal value is larger than the reference sensor signal value, and the post-polishing spectrum Sa has a higher relative reflectivity at each wavelength than the reference spectrum Sr.

[0058] In the example shown in Figure 7, the reference spectrum of the reflected light and the spectrum of the reflected light after polishing are spectral waveforms that show the relationship between the relative reflectance and the wavelength of the reflected light. However, the reference spectrum of the reflected light and the spectrum of the reflected light after polishing may also be spectral waveforms that show the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

[0059] The control device 50 is configured to move the optical sensor head 35 on the sensor moving mechanism 40 so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value. In this embodiment, the control device 50 is configured to move the optical sensor head 35 on the sensor moving mechanism 40 so as to minimize the difference between the reference spectrum Sr and the post-polishing spectrum Sa. When the optical sensor head 35 is moved away from the pad support surface 3a of the polishing table 3, the distance from the surface of the reference sample to the optical sensor head 35 increases, and the difference between the reference spectrum Sr and the post-polishing spectrum Sa decreases. Minimizing the difference between the reference spectrum Sr and the post-polishing spectrum Sa means that the difference between the wavelength and relative reflectance values ​​that constitute each data point in the reference spectrum Sr and the wavelength and relative reflectance values ​​that constitute each data point in the post-polishing spectrum Sa is minimized.

[0060] The control device 50 may move the optical sensor head 35 to the sensor moving mechanism 40 so as to minimize the difference between the reference spectrum Sr and the polished spectrum Sa across the entire wavelength range, or it may move the optical sensor head 35 to the sensor moving mechanism 40 so as to minimize the difference between the reference spectrum Sr and the polished spectrum Sa in a specific wavelength range. The control device 50 may also move the optical sensor head 35 to the sensor moving mechanism 40 so as to minimize the difference between the average value of the relative reflectances constituting the data points included in the reference spectrum Sr in a specific wavelength range and the average value of the relative reflectances constituting the data points included in the polished spectrum Sa in the same specific wavelength range.

[0061] In one embodiment, the control device 50 moves the optical sensor head 35 on the sensor moving mechanism 40 so that the difference between the reference spectrum Sr and the polished spectrum Sa is minimized, using the shape matching index of the reference spectrum Sr and the polished spectrum Sa. The shape matching index is an index for determining the degree of shape matching (similarity) between the reference spectrum Sr and the polished spectrum Sa. Examples of shape matching indices include, but are not limited to, the absolute mean, mean square, correlation coefficient, GoF (Good of Fitting) value, cosine similarity, Euclidean distance, standard Euclidean distance, Mahalanobis distance, Manhattan distance, or combinations thereof, as well as combinations of normalized values ​​of these variables.

[0062] In one embodiment, the control device 50 determines feature quantities representing the characteristics of the reference spectrum Sr and the post-polished spectrum Sa, and moves the optical sensor head 35 in the sensor movement mechanism 40 so that the difference between the feature quantities of the reference spectrum Sr and the feature quantities of the post-polished spectrum Sa is minimized. The feature quantities of the spectrum are, for example, a set of numbers indicating the positions of the peaks and troughs of the spectrum. The positions of the peaks and troughs of the sample spectrum can be determined from the intensity and wavelength of the spectrum.

[0063] The control device 50 moves the optical sensor head 35 by a predetermined amount (for example, 0.01 mm) on the sensor moving mechanism 40, so as to minimize the difference between the reference spectrum Sr of the reflected light and the polished spectrum Sa of the reflected light. Specifically, each time the optical sensor head 35 is moved by a predetermined amount, the control device 50 acquires the polished spectrum Sa of the reflected light and moves the optical sensor head 35 to the position where the difference between the reference spectrum Sr of the reflected light and the polished spectrum Sa of the reflected light is minimized.

[0064] The control device 50 may move the optical sensor head 35 in the sensor moving mechanism 40 so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value, using the correlation between the previously acquired sensor signal value and the distance from the reference sample to the optical sensor head 35. In this embodiment, the optical sensor head 35 is moved in the sensor moving mechanism 40 so as to minimize the difference between the reference spectrum Sr and the post-polishing spectrum Sa, using the correlation between the previously acquired reflected light spectrum and the distance from the reference sample to the optical sensor head 35. The correlation between the sensor signal value output when the reference sample on the polishing pad 2 is detected by the optical film thickness measuring device 30 (in this embodiment, the reflected light spectrum generated from the sensor signal value) and the distance from the reference sample to the optical sensor head 35 is acquired in advance and stored in the storage device 50a of the control device 50. The control device 50 is configured to calculate the amount by which the optical sensor head 35 should be moved based on the reference sensor signal value, the post-polishing sensor signal value, and the above correlation. In this embodiment, the control device 50 calculates the amount by which the optical sensor head 35 should move based on the reference spectrum Sr of the reflected light, the spectrum Sa of the reflected light after polishing, and the correlation described above.

[0065] Specifically, the control device 50 calculates the distance from the reference sample to the optical sensor head 35 (hereinafter referred to as the reference distance) when the reference sensor signal value (in this embodiment, the reference spectrum Sr) is acquired, based on the reference sensor signal value (in this embodiment, the reference spectrum Sr) and the correlation described above. The control device 50 calculates the distance from the reference sample to the optical sensor head 35 (hereinafter referred to as the post-polishing distance) when the post-polishing sensor signal value (in this embodiment, the post-polishing spectrum Sa) is acquired, based on the post-polishing sensor signal value (in this embodiment, the post-polishing spectrum Sa) and the correlation described above. The control device 50 calculates the amount by which the optical sensor head 35 should move by subtracting the post-polishing distance from the reference distance. The control device 50 gives a command to the sensor movement mechanism 40 to move the optical sensor head 35 by the calculated amount.

[0066] In this embodiment, the reference distance was calculated from the reference spectrum Sr and the correlation described above, but the method for obtaining the reference distance is not particularly limited. For example, the reference distance may be obtained from the known initial thickness of the polishing pad 2 and the known distance from the pad support surface 3a to the optical sensor head 35 before polishing the substrate W (e.g., the height setting value of the optical sensor head 35).

[0067] In one embodiment, the control device 50 may move the optical sensor head 35 to the sensor moving mechanism 40 so as to minimize the difference between the reference sensor signal value and the post-polished sensor signal value, using the correlation between the sensor signal value (or reflected light spectrum) and the difference between a previously acquired reference distance and the distance from the reference sample to the optical sensor head 35, instead of the correlation between the sensor signal value (or reflected light spectrum) and the distance from the reference sample to the optical sensor head 35. In this case, the control device 50 does not calculate the reference distance based on the reference sensor signal value (or reference spectrum Sr), but calculates the amount by which the optical sensor head 35 should be moved by calculating the difference between the reference distance when the post-polished sensor signal value (or post-polished spectrum Sa) was acquired and the distance from the reference sample to the optical sensor head 35, based on the post-polished sensor signal value (or post-polished spectrum Sa) and the above correlation.

[0068] In other embodiments, the control device 50 may move the optical sensor head 35 to the sensor moving mechanism 40 using a pre-constructed sample library so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value. In this embodiment, the optical sensor head 35 is moved to the sensor moving mechanism 40 using a pre-constructed sample library so as to minimize the difference between the reference spectrum Sr and the post-polishing spectrum Sa. The sample library includes multiple sensor signal values ​​(hereinafter referred to as sample sensor signal values) output by the optical film thickness measuring device 30 when a reference sample on the polishing pad 2 is detected at multiple positional relationships between the reference sample and the optical sensor head 35 at different distances from the reference sample to the optical sensor head 35. In this embodiment, the sample library includes multiple sample spectra, which are the spectra of multiple reflected light generated from the multiple sample sensor signal values.

[0069] The optical film thickness measuring device 30 detects the intensity of multiple reflected light from the reference sample located on the polishing pad 2 at multiple positional relationships between the reference sample and the optical sensor head 35, where the distance from the reference sample to the optical sensor head 35 is different, and outputs multiple sample sensor signal values ​​representing the intensity of reflected light from the reference sample. The output of the sample sensor signal values ​​is performed under the same conditions as the output of the reference sensor signal value and the post-polishing sensor signal value. The control device 50 constructs a sample library by storing the multiple sample sensor signal values, each associated with the distance from the reference sample to the optical sensor head 35 in the above-mentioned multiple positional relationships. In this embodiment, the data processing unit 39 of the optical film thickness measuring device 30 generates multiple sample spectra of reflected light representing the intensity of reflected light for each wavelength from the multiple sample sensor signal values. The control device 50 constructs a sample library by storing the multiple sample spectra, each associated with the distance from the reference sample to the optical sensor head 35 in the above-mentioned multiple positional relationships. The sample library is stored in the storage device 50a of the control device 50.

[0070] Figure 8 shows an example of multiple sample spectra stored in the sample library. The multiple (n) sample spectra Ss1 to Ssn are multiple sample spectra acquired at multiple positional relationships between the reference sample and the optical sensor head 35, where the distance from the reference sample to the optical sensor head 35 is D1 to Dn, respectively. For example, sample spectrum Ss1 is the sample spectrum acquired at the positional relationship between the reference sample and the optical sensor head 35 when the distance from the reference sample to the optical sensor head 35 is D1. Sample spectrum Ss2 is the sample spectrum acquired at the positional relationship between the reference sample and the optical sensor head 35 when the distance is D2, which is greater than the distance D1. Similarly, sample spectra Ss3 and beyond are sample spectra acquired at positional relationships between the reference sample and the optical sensor head 35 as the distance gradually increases from D3 onwards. These multiple sample spectra Ss1 to Ssn are each associated with the distances D1 to Dn from the reference sample to the optical sensor head 35 and stored in the sample library.

[0071] The control device 50 is configured to determine, from a pre-built sample library, the sample sensor signal value with the smallest difference from the reference sensor signal value, and the sample sensor signal value with the smallest difference from the post-polished sensor signal value. The control device 50 is configured to calculate the amount by which the optical sensor head 35 should move, based on the distance from the reference sample to the optical sensor head 35 associated with the sample sensor signal value with the smallest difference from the reference sensor signal value, and the distance from the reference sample to the optical sensor head 35 associated with the sample sensor signal value with the smallest difference from the post-polished sensor signal value.

[0072] In this embodiment, the control device 50 determines, from a pre-constructed sample library, the sample spectrum that is closest in shape to the determined reference spectrum Sr, and the sample spectrum that is closest in shape to the post-polished spectrum Sa. Based on the distance from the reference sample associated with the sample spectrum that is closest in shape to the reference spectrum Sr to the optical sensor head 35, and the distance from the reference sample associated with the sample spectrum that is closest in shape to the post-polished spectrum Sa to the optical sensor head 35, the control device 50 calculates the amount by which the optical sensor head 35 should move.

[0073] In the example shown in Figure 8, the control device 50 determines the reference distance as D14, which is the distance from the reference sample to the optical sensor head 35 that is associated with the sample spectrum Ss14 that is closest in shape to the reference spectrum Sr from the sample library. In the example shown in Figure 8, the control device 50 determines the post-polishing distance as D4, which is the distance from the reference sample to the optical sensor head 35 that is associated with the sample spectrum Ss4 that is closest in shape to the post-polished spectrum Sa from the sample library. The method for determining the sample spectrum with the closest shape from the sample library can be the shape matching index described above, but the method is not particularly limited.

[0074] The control device 50 calculates the amount the optical sensor head 35 should move by subtracting the post-polishing distance from the reference distance. The control device 50 then commands the sensor movement mechanism 40 to move the optical sensor head 35 by the calculated amount. In the example shown in Figure 8, the control device 50 calculates the distance (D14-D4) by subtracting the post-polishing distance D4 from the reference distance D14, and then instructs the sensor movement mechanism 40 to move the optical sensor head 35 by that distance (D14-D4).

[0075] In one embodiment, multiple sample sensor signal values ​​(or multiple sample spectra) may be stored in the sample library associated with the difference between a previously acquired reference distance and the distance from the reference sample to the optical sensor head 35, instead of the distance from the reference sample to the optical sensor head 35. In this case, the control device 50 determines the sample sensor signal closest to the post-polished sensor signal (or the sample spectrum whose shape is closest to the post-polished spectrum Sa) without determining the reference distance based on the reference sensor signal (or reference spectrum Sr), and determines the difference between the reference distance associated with the determined sample sensor signal (or sample spectrum) and the distance from the reference sample to the optical sensor head 35 as the amount by which the optical sensor head 35 should move.

[0076] Figures 9 and 10 are flowcharts illustrating one embodiment of a method for polishing the substrate W. The operations shown in Figures 9 and 10 are performed by the polishing apparatus 1 described above. In step S101, the polishing apparatus 1 starts water polishing of the reference sample using the polishing pad 2 in its initial state. In one embodiment, the reference sample may be placed on the polishing pad 2 in its initial state without water polishing of the reference sample. For example, the polishing head lifting mechanism may be used to lower the polishing head 10 holding the reference sample toward the polishing pad 2, bringing the reference sample into contact with the polishing surface 2a of the polishing pad 2 in its initial state. Alternatively, the reference sample may simply be placed on the polishing pad 2 in its initial state. In step S102, the optical film thickness measuring device 30 detects a reference sample on the polishing pad 2 in its initial state and outputs a reference sensor signal value representing the intensity of reflected light from the reference sample. In step S103, the data processing unit 39 generates a reference spectrum of reflected light representing the intensity of reflected light for each wavelength from the reference sensor signal value. The reference spectrum is stored in the storage device 50a of the control device 50.

[0077] In step S104, the polishing apparatus 1 completes the water polishing of the reference sample. In step S105, the polishing apparatus 1 starts polishing the substrate W to be polished. In step S106, the optical film thickness measuring device 30 detects the substrate W and outputs a monitoring sensor signal value representing the intensity of reflected light from the substrate W. In step S107, the data processing unit 39 generates a monitoring spectrum of reflected light representing the intensity of reflected light for each wavelength from the monitoring sensor signal value, and determines the film thickness of the substrate W based on the monitoring spectrum.

[0078] In step S108, the control device 50 determines whether the determined film thickness has reached a predetermined target value. When the film thickness has reached the predetermined target value ("Yes" in step S108), the control device 50 determines that the polishing endpoint has been reached and terminates the polishing of the substrate W (step S109). When the film thickness has not reached the predetermined target value ("No" in step S108), the polishing device 1 continues polishing the substrate W, and the optical film thickness measuring device 30 detects the substrate W again and outputs a monitoring sensor signal value (returns to step S106). Subsequently, the operations of steps S106 to S108 are repeated until the control device 50 determines in step S108 that the film thickness has reached the predetermined target value.

[0079] In step S110, after the polishing of the substrate W is completed, the control device 50 determines whether it is the predetermined sensor position adjustment timing. The control device 50 determines that it is the predetermined sensor position adjustment timing when a predetermined number of substrates have been polished, or when the usage time of the polishing pad 2 reaches a predetermined time. When the control device 50 determines that it is the sensor position adjustment timing ("Yes" in step S110), the polishing apparatus 1 starts water polishing of the reference sample using the polishing pad 2 after the polishing of the substrate W is completed (step S111). In one embodiment, the reference sample may not be water polished, and the reference sample may be placed on the polishing pad 2 after the polishing of the substrate W is completed. For example, the polishing head lifting mechanism may be used to lower the polishing head 10 holding the reference sample toward the polishing pad 2, bringing the reference sample into contact with the polishing surface 2a of the polishing pad 2 after the polishing of the substrate W. Alternatively, the reference sample may simply be placed on the polishing pad 2 after the polishing of the substrate W is completed. The placement of the reference sample on the polishing pad 2 is performed in the same manner as in step S101.

[0080] When the control device 50 determines that it is not time to adjust the sensor position (No in step S110), the polishing device 1 starts polishing the next substrate W (returning to step S105). Subsequently, the operations of steps S105 to S110 are repeated until the control device 50 determines in step S110 that it is time to adjust the sensor position. In step S112, the optical film thickness measuring device 30 detects a reference sample on the polishing pad 2 after polishing of the substrate W and outputs a post-polishing sensor signal value representing the intensity of reflected light from the reference sample. In step S113, the data processing unit 39 generates a post-polished spectrum of reflected light, representing the intensity of reflected light for each wavelength, from the post-polished sensor signal value. The post-polished spectrum is stored in the storage device 50a of the control device 50.

[0081] In step S114, the control device 50 moves the optical sensor head 35 to the sensor moving mechanism 40 so that the difference between the reference spectrum and the spectrum after polishing is minimized. In one embodiment, instead of the reference spectrum and the spectrum after polishing, the control device 50 may move the optical sensor head 35 to the sensor moving mechanism 40 so that the difference between the reference sensor signal value output by the optical film thickness measuring device 30 and the sensor signal value after polishing is minimized. In this case, the operations in steps S103 and S113 are not performed. In step S115, the polishing apparatus 1 finishes the water polishing of the reference sample. Then, the polishing apparatus 1 starts polishing the next substrate W (returning to step S105).

[0082] According to this embodiment, by moving the optical sensor head 35 so as to minimize the difference between the reference spectrum and the spectrum after polishing, the distance from the surface of the reference sample to the optical sensor head 35 can be maintained at the reference distance. As a result, the accuracy of the measurement of film thickness by the optical film thickness measuring device 30 having an optical sensor head 35 positioned in the polishing table 3 can be improved.

[0083] Figure 11 is a flowchart illustrating one embodiment of a method for moving the optical sensor head 35 so that the difference between the reference spectrum and the spectrum after polishing is minimized. Steps S201 to S207 shown in Figure 11 correspond to step S114 in Figure 10. In step S201, the control device 50 calculates the difference between the reference spectrum and the spectrum after polishing. The calculated difference between the reference spectrum and the spectrum after polishing is stored in the storage device 50a of the control device 50.

[0084] In step S202, the control device 50 moves the optical sensor head 35 by a predetermined amount using the sensor moving mechanism 40. The sensor moving mechanism 40 moves the optical sensor head 35 away from the pad support surface 3a of the polishing table 3. Steps S203 and S204 are the same operations as steps S112 and S113 in Figure 10, and step S205 is the same operation as step S201. In step S201, the difference between the reference spectrum before moving the optical sensor head 35 and the spectrum after polishing is calculated, and in step S205, the difference between the reference spectrum after moving the optical sensor head 35 by a predetermined amount and the spectrum after polishing is calculated.

[0085] In step S206, the control device 50 determines whether the difference between the reference spectrum before moving the optical sensor head 35 and the spectrum after polishing is smaller than the difference between the reference spectrum after moving the optical sensor head 35 by a predetermined amount. If the difference between the reference spectrum before moving the optical sensor head 35 and the spectrum after polishing is smaller than the difference between the reference spectrum after moving the optical sensor head 35, it indicates that the difference between the reference distance and the optical sensor head 35 from the surface of the reference sample has increased due to the movement of the optical sensor head 35.

[0086] The control device 50 moves the optical sensor head 35 to the sensor moving mechanism 40 so that the difference between the reference spectrum and the polished spectrum is minimized when the difference between the reference spectrum and the polished spectrum before moving the optical sensor head 35 is smaller than the difference between the reference spectrum and the polished spectrum after moving the optical sensor head 35 by a predetermined amount ("Yes" in step S206). In other words, the optical sensor head 35 is moved to the position it was in before moving it in step S202. The sensor moving mechanism 40 moves the optical sensor head 35 in a direction that brings it closer to the pad support surface 3a of the polishing table 3. This makes it possible to maintain the distance from the surface of the reference sample to the optical sensor head 35 as the reference distance.

[0087] If the control device 50 determines in step S206 that the difference between the reference spectrum before moving the optical sensor head 35 and the spectrum after polishing is greater than or equal to the difference between the reference spectrum after moving the optical sensor head 35 by a predetermined amount ("No"), it moves the optical sensor head 35 again by a predetermined amount using the sensor moving mechanism 40 (returning to step S202). The sensor moving mechanism 40 moves the optical sensor head 35 away from the pad support surface 3a of the polishing table 3. Subsequently, in step S206, the operation of steps S202 to S206 is repeated until the control device 50 determines that the difference between the reference spectrum before moving the optical sensor head 35 and the spectrum after polishing is less than the difference between the reference spectrum after moving the optical sensor head 35 by a predetermined amount.

[0088] Figure 12 is a flowchart illustrating another embodiment of a method for moving the optical sensor head 35 so that the difference between the reference spectrum and the spectrum after polishing is minimized. Steps S301 and S302 shown in Figure 12 correspond to step S114 in Figure 10. In step S301, the control device 50 calculates the amount by which the optical sensor head 35 should move based on the correlation between the previously acquired reflected light spectrum and the distance from the reference sample to the optical sensor head 35. The correlation between the reflected light spectrum generated from the sensor signal value output when the reference sample on the polishing pad 2 is detected by the optical film thickness measuring device 30 and the distance from the reference sample to the optical sensor head 35 is acquired in advance and stored in the storage device 50a of the control device 50. The control device 50 calculates the amount by which the optical sensor head 35 should move based on the reference reflected light spectrum Sr, the reflected light spectrum Sa after polishing, and the above correlation.

[0089] Specifically, the control device 50 calculates the reference distance, which is the distance from the reference sample to the optical sensor head 35 when the reference spectrum Sr is obtained, based on the reference spectrum Sr and the correlation described above. The control device 50 calculates the post-polishing distance, which is the distance from the reference sample to the optical sensor head 35 when the post-polishing spectrum Sa is obtained, based on the post-polishing spectrum Sa and the correlation described above. The control device 50 calculates the amount the optical sensor head 35 should move by subtracting the post-polishing distance from the reference distance. In step S302, the control device 50 moves the optical sensor head 35 by the amount calculated by the sensor movement mechanism 40. This allows the distance from the surface of the reference sample to the optical sensor head 35 to be maintained at the reference distance.

[0090] Figure 13 is a flowchart illustrating yet another embodiment of the method for moving the optical sensor head 35 so that the difference between the reference spectrum and the spectrum after polishing is minimized. Steps S401 to S403 shown in Figure 13 correspond to step S114 in Figure 10. In this embodiment, the storage device 50a of the control device 50 has a sample library pre-built in it, as described with reference to Figure 8. The sample library stores multiple sample spectra acquired at multiple positional relationships between the reference sample and the optical sensor head 35, each at a different distance from the reference sample to the optical sensor head 35, and associates these spectra with the distance from the reference sample to the optical sensor head 35 in each of the multiple positional relationships.

[0091] In step S401, the control device 50, as explained with reference to Figure 8, determines from a pre-constructed sample library the sample spectrum that is closest in shape to the reference spectrum Sr, and the sample spectrum that is closest in shape to the post-polishing spectrum Sa. In step S402, the control device 50 calculates the amount by which the optical sensor head 35 should move, based on the distance from the reference sample to the optical sensor head 35 associated with the sample spectrum whose shape is closest to the reference spectrum Sr (i.e., the reference distance), and the distance from the reference sample to the optical sensor head 35 associated with the sample spectrum whose shape is closest to the post-polished spectrum Sa (i.e., the post-polished distance). Specifically, the control device 50 calculates the amount by which the optical sensor head 35 should move by subtracting the post-polished distance from the reference distance. In step S403, the control device 50 moves the optical sensor head 35 by the amount calculated by the sensor movement mechanism 40. This allows the distance from the surface of the reference sample to the optical sensor head 35 to be maintained at the reference distance.

[0092] Figure 14 is a schematic diagram showing another embodiment of the optical sensor head 35. The configuration and operation of this embodiment, unless otherwise described, are the same as those of the embodiment described above. As shown in Figure 14, the optical sensor head 35 may be positioned at an angle. Specifically, the optical sensor head 35 may consist of the tip of a light-emitting optical fiber cable 32 positioned at an angle and the tip of a light-receiving optical fiber cable 33 positioned at an angle. The tip of the light-emitting optical fiber cable 32 and the tip of the light-receiving optical fiber cable 33 are inclined at the same angle in the direction toward each other. The optical sensor head 35 is configured to irradiate light at an angle toward the surface of the substrate W and to receive reflected light that has been reflected at an angle toward the surface of the substrate W. It is preferable that the light-receiving optical fiber cable 33 receives light at an angle substantially equal to the angle of reflection of light at the surface of the substrate W. That is, it is preferable that the tip of the light-receiving optical fiber cable 33 is inclined so that the reflected light enters substantially perpendicular to the tip of the light-receiving optical fiber cable 33.

[0093] Figure 15 illustrates how the light reception conditions for reflected light from the substrate W received by the optical sensor head 35 change due to wear of the polishing pad 2, in the diagonally positioned optical sensor head 35 shown in Figure 14. As shown in Figure 15, when the polishing pad 2 wears down, the light path between the light-emitting optical fiber cable 32 and the measurement point shortens, and the position of the measurement point shifts in the in-plane direction of the substrate W. Furthermore, because the path of the reflected light changes due to the shift in the position of the measurement point, the light-receiving optical fiber cable 33 may not be able to properly receive the reflected light. As a result, the optical film thickness measuring device 30 may not be able to accurately measure the film thickness of the substrate W.

[0094] In the embodiment shown in Figure 14, the screw hole 41a provided in the sensor support member 41 of the sensor moving mechanism 40 is located between the light-emitting optical fiber cable 32 and the light-receiving optical fiber cable 33, but the arrangement of the screw hole 41a is not particularly limited to this embodiment. In the polishing apparatus 1 having the optical sensor head 35 shown in Figure 14, similar to the embodiments described with reference to Figures 1 to 12, the distance from the surface of the reference sample to the optical sensor head 35 can be maintained at the reference distance by moving the optical sensor head 35 with the sensor moving mechanism 40 so as to minimize the difference between the reference spectrum and the spectrum after polishing (or the reference sensor signal value and the sensor signal value after polishing). As a result, the accuracy of the film thickness measurement by the optical film thickness measuring device 30 having the optical sensor head 35 arranged in the polishing table 3 can be improved.

[0095] In the embodiments described with reference to Figures 1 to 15, the polishing apparatus 1 is equipped with an optical film thickness measuring device as an example of a sensor 30, but the sensor 30 is not limited to an optical film thickness measuring device. Other examples of the sensor 30 include, for example, an eddy current type film thickness measuring device, a proximity sensor, an acoustic sensor, an imaging device, and the like.

[0096] The eddy current type film thickness measuring device is configured to induce eddy currents in the metal formed on the substrate W, detect the thickness of the metal from the impedance caused by the magnetic field of these eddy currents, and output a monitoring sensor signal value. The eddy current type film thickness measuring device is configured to determine the thickness of the metal formed on the substrate W based on the monitoring sensor signal value. The sensor head of the eddy current type film thickness measuring device is located in the polishing table 3. The detection conditions for the thickness of the metal on the substrate W by the eddy current type film thickness measuring device are affected by the distance between the sensor head and the substrate W. When the sensor 30 is an eddy current type film thickness measuring device, the control device 50 is configured to move the sensor head of the eddy current type film thickness measuring device so that the difference between the reference sensor signal value output by the eddy current type film thickness measuring device detecting a reference sample and the sensor signal value after polishing is minimized before and after polishing the substrate W.

[0097] The proximity sensor is configured to detect a detection object, such as a substrate W, placed above the polishing pad 2, and to output a monitoring sensor signal value corresponding to the positional relationship between the detection object and the proximity sensor. The proximity sensor is configured to determine the distance between the detection object and the proximity sensor based on the monitoring sensor signal value. The sensor head of the proximity sensor is located within the polishing table 3. The detection conditions for the detection object by the proximity sensor are influenced by the distance between the sensor head and the detection object. When the sensor 30 is a proximity sensor, the control device 50 is configured to move the sensor head of the proximity sensor so that the difference between the reference sensor signal value output by the proximity sensor after detecting a reference sample as a detection object and the post-polishing sensor signal value is minimized before and after polishing the substrate W.

[0098] Examples of acoustic sensors include AE ​​(Acoustic Emission) sensors and ultrasonic sensors. The AE sensor is configured to detect the polishing sound of the substrate W and output a monitoring sensor signal value. The ultrasonic sensor is configured to emit ultrasonic waves towards the substrate W, detect the ultrasonic waves reflected from the substrate W, and output a monitoring sensor signal value. The sensor head of the acoustic sensor is located within the polishing table 3. The detection conditions for the polishing sound of the substrate W and the reflected ultrasonic waves from the substrate W by the acoustic sensor are influenced by the distance between the sensor head and the substrate W. The polishing sound of the substrate W detected by the AE sensor and the reflected ultrasonic waves from the substrate W detected by the ultrasonic sensor are correlated with the polishing state of the substrate W (e.g., the polishing endpoint of the substrate W, the polishing rate of the substrate W, the polishing abnormality of the substrate W, etc.). Therefore, the acoustic sensor is configured to determine the polishing state of the substrate W based on changes in the monitoring sensor signal value. If the sensor 30 is an acoustic sensor, the control device 50 is configured to move the sensor head of the acoustic sensor so that the difference between the reference sensor signal value output by the acoustic sensor detecting the reference sample and the sensor signal value after polishing is minimized before and after polishing the substrate W.

[0099] An example of an imaging device is a camera equipped with an image sensor such as a CMOS sensor or a CCD sensor. The imaging device is configured to detect the substrate W, output a monitoring sensor signal value representing the intensity of light from the substrate W, and generate an image of the substrate W from the monitoring sensor signal value. The sensor head of the imaging device is located within the polishing table 3. The detection conditions for light from the substrate W by the imaging device are affected by the distance between the sensor head and the substrate W. Specifically, if the distance between the sensor head and the substrate W changes, the image may not be in focus. If the sensor 30 is an imaging device, the control device 50 is configured to move the sensor head of the imaging device so that the difference between the reference sensor signal value output by the imaging device after detecting a reference sample and the image of the substrate W generated from the post-polishing sensor signal value is minimized before and after polishing the substrate W. For example, the control device 50 moves the sensor head of the imaging device so that the difference in the degree of focus between the image of the substrate W generated from the reference sensor signal value and the image of the substrate W generated from the post-polishing sensor signal value is minimized.

[0100] Each of the embodiments described above is intended to enable a person with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by a person skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of Symbols]

[0101] 1 Polishing equipment 2 polishing pads 2a Polished surface 2b through hole 3 Polishing Table 3a Pad support surface 3b hole 5 Table shaft 6 Table motors 10 polishing heads 12 Polished Head Shafts 20 liquid supply nozzles 30. Sensor (Optical film thickness measuring device) 31 Light source 32 Optical fiber cables for floodlighting 33 Optical fiber cable for receiving light 35. Sensor head (optical sensor head) 37 Spectrometer 39 Data Processing Unit 40 Sensor movement mechanism 41 Sensor support member 41a Screw hole 43 First gear 44 screws 46 Second gear 48 Motor 48a Rotation axis 50 Control device 50a storage device 50b Arithmetic unit

Claims

1. When the polishing pad supported on the polishing table is in its initial state, a sensor having a sensor head positioned within the polishing table detects a reference sample on the polishing pad and outputs a reference sensor signal value. The substrate is pressed against the polishing surface of the polishing pad and polished. During the polishing of the substrate, the sensor detects the substrate and outputs a monitoring sensor signal value. After the polishing of the substrate is completed, the sensor detects the reference sample on the polishing pad and outputs the post-polishing sensor signal value. A polishing method comprising moving the sensor head so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value.

2. The polishing method according to claim 1, wherein moving the sensor head is to move the sensor head along a direction perpendicular to the pad support surface of the polishing table that supports the polishing pad.

3. The sensor is an optical film thickness measuring device that optically measures the film thickness of the substrate. The sensor head is an optical sensor head that irradiates light onto the substrate and receives reflected light from the substrate. The monitoring sensor signal value is a sensor signal value representing the intensity of reflected light from the substrate during polishing. The aforementioned reference sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad in the initial state. The polishing method according to claim 1, wherein the post-polishing sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad after the completion of polishing the substrate.

4. A reference spectrum of reflected light is generated from the aforementioned reference sensor signal value. The process further includes generating a post-polished spectrum of reflected light from the post-polished sensor signal value, The polishing method according to claim 3, wherein moving the sensor head so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value is equivalent to moving the optical sensor head so as to minimize the difference between the reference spectrum and the post-polishing spectrum.

5. The sensor further includes obtaining a correlation between the sensor signal value output when the reference sample on the polishing pad is detected and the distance from the reference sample to the sensor head. Moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized is: Based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation, the amount the sensor head should move is calculated. The polishing method according to claim 1, wherein the sensor head is moved by the amount to be moved.

6. The sensor detects the reference sample on the polishing pad at multiple positional relationships between the reference sample and the sensor head, where the distance from the reference sample to the sensor head is different, and outputs multiple sample sensor signal values. The method further includes constructing a sample library by storing the plurality of sample sensor signal values ​​in relation to the distance from the reference sample to the sensor head in the plurality of positional relationships, Moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized is: From the aforementioned sample library, the sample sensor signal value with the smallest difference from the reference sensor signal value and the sample sensor signal value with the smallest difference from the post-polishing sensor signal value are determined. Based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that has the smallest difference from the reference sensor signal value, and the distance from the reference sample to the sensor head associated with the sample sensor signal value that has the smallest difference from the post-polishing sensor signal value, the amount by which the sensor head should move is calculated. The polishing method according to claim 1, wherein the sensor head is moved by the amount to be moved.

7. The polishing method according to claim 1, wherein the output of the reference sensor signal value by the sensor and the output of the post-polishing sensor signal value by the sensor are performed during the water polishing of the reference sample.

8. A polishing table that supports the polishing pad, A polishing head that polishes the substrate by pressing it against the polishing surface of the polishing pad, A sensor having a sensor head positioned within the polishing table, which detects the substrate and outputs a monitoring sensor signal value, A sensor movement mechanism for moving the sensor head, The system includes a control device that controls the operation of the sensor movement mechanism, Polishing apparatus, wherein the control device is configured to move the sensor head in the sensor moving mechanism so as to minimize the difference between the reference sensor signal value output when the sensor detects a reference sample located on the polishing pad in its initial state and the post-polishing sensor signal value output when the sensor detects the reference sample located on the polishing pad after the polishing of the substrate is completed.

9. The polishing apparatus according to claim 8, wherein the sensor moving mechanism is configured to move the sensor head along a direction perpendicular to the pad support surface of the polishing table that supports the polishing pad.

10. The sensor is an optical film thickness measuring device that optically measures the film thickness of the substrate. The sensor head is an optical sensor head that irradiates light onto the substrate and receives reflected light from the substrate. The monitoring sensor signal value is a sensor signal value representing the intensity of reflected light from the substrate during polishing. The aforementioned reference sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad in the initial state. The polishing apparatus according to claim 8, wherein the post-polishing sensor signal value is a sensor signal value representing the intensity of reflected light from the reference sample located on the polishing pad after the completion of polishing the substrate.

11. The aforementioned optical film thickness measuring device is A reference spectrum of reflected light is generated from the aforementioned reference sensor signal value. The system is configured to generate the post-polished spectrum of reflected light from the post-polished sensor signal value. The polishing apparatus according to claim 10, wherein the control device is configured to move the optical sensor head in the sensor moving mechanism so that the difference between the reference spectrum and the spectrum after polishing is minimized.

12. The control device is The sensor obtains the correlation between the sensor signal value output when the reference sample on the polishing pad is detected and the distance from the reference sample to the sensor head. Based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation, the amount the sensor head should move is calculated. The polishing apparatus according to claim 8, wherein the sensor moving mechanism is configured to move the sensor head by the amount to be moved.

13. The sensor is configured to detect the reference sample on the polishing pad and output multiple sample sensor signal values ​​in multiple positional relationships between the reference sample and the sensor head, where the distance from the reference sample to the sensor head is different. The control device is A sample library is constructed by storing the multiple sample sensor signal values ​​in relation to the distance from the reference sample to the sensor head in the multiple positional relationships. From the aforementioned sample library, the sample sensor signal value with the smallest difference from the reference sensor signal value and the sample sensor signal value with the smallest difference from the post-polishing sensor signal value are determined. Based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that has the smallest difference from the reference sensor signal value, and the distance from the reference sample to the sensor head associated with the sample sensor signal value that has the smallest difference from the post-polishing sensor signal value, the amount by which the sensor head should move is calculated. The polishing apparatus according to claim 8, wherein the sensor moving mechanism is configured to move the sensor head by the amount to be moved.

14. The aforementioned reference sensor signal value is the sensor signal value output when the reference sample is detected by the sensor during water polishing of the reference sample using the polishing pad in its initial state. The polishing apparatus according to claim 8, wherein the post-polishing sensor signal value is the sensor signal value output when the sensor detects the reference sample during water polishing of the reference sample using the polishing pad after the completion of polishing the substrate.

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