Polishing apparatus and polishing method

Abstract

The present invention relates to a polishing apparatus for polishing a substrate such as a wafer. A polishing apparatus (1) comprises: a polishing table (3) which supports a polishing pad (2); a polishing head (10) which presses a substrate (W) against a polishing surface (2a) of the polishing pad (2); an optical film thickness measurement device (30) which determines the film thickness measurement value of the substrate (W); and an operation control unit (60). The optical film thickness measurement device (30) comprises: a light-projecting unit (32) which irradiates the substrate (W) with light; a light-receiving unit (33) which receives reflected light from the substrate (W); and a first light amount sensor (41) and a second light amount sensor (42) which are disposed adjacent to the light-receiving unit (33) and which detect a light amount of the reflected light from the substrate (W). The operation control unit (60) is configured to determine, on the basis of a first light amount detected by the first light amount sensor (41) and a second light amount detected by the second light amount sensor (42), position correction amounts that are for the light-projecting unit (32) and the light-receiving unit (33) and correspond to the wear amount of the polishing pad (2).

Description

Polishing apparatus and polishing method

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

[0002] The manufacturing process of semiconductor devices includes a process of polishing wafers to flatten their surfaces. One known wafer polishing device is a polishing apparatus that performs chemical mechanical polishing (CMP). The polishing apparatus presses the wafer against the polishing surface while supplying a polishing liquid to the polishing surface of a polishing pad supported on a polishing table, and then moves the wafer and the polishing table relative to each other. This process polishes the wafer surface.

[0003] Generally, a polishing apparatus is equipped with a film thickness measurement device for measuring the film thickness on the surface of a wafer during polishing. The polishing apparatus terminates polishing when the measured film thickness reaches a predetermined target value (in other words, the polishing endpoint). One example of a film thickness measurement device is an optical film thickness measurement device. An optical film thickness measurement device projects light from its light-emitting unit onto a measurement point on the wafer surface and receives reflected light from the wafer surface using a light-receiving unit. The measured film thickness is determined based on this reflected light.

[0004] The optical film thickness measuring device is configured to irradiate the wafer surface with light from an optical sensor head disposed within the polishing table, receive the light reflected from the wafer with the optical sensor head, and determine the film thickness of the wafer by analyzing the spectrum of the reflected light. The polishing device terminates polishing of the wafer based on the determined film thickness.

[0005] Patent No. 5167010 JP 2024-94186 A

[0006] As the polishing pad is polished, it wears down and its thickness gradually decreases. The more the polishing pad thickness decreases, the closer the wafer surface pressed against the polishing pad gets to the light-emitting and light-receiving parts of the optical film thickness measurement device. If the distance between the measurement point on the wafer surface and the light-emitting and light-receiving parts changes, it affects the conditions under which the light-receiving part receives the light reflected from the wafer, which can result in a decrease in the accuracy of film thickness measurement.

[0007] In sensors that have a sensor head placed inside the polishing table and whose detection conditions for the object to be measured by the sensor head are affected by the distance between the sensor head and the object to be measured, measurement accuracy may decrease due to wear of the polishing pad.

[0008] Therefore, the present invention provides a polishing apparatus and a polishing method that can improve the measurement accuracy of the film thickness of a substrate.

[0009] Furthermore, the present invention provides a polishing method and a polishing apparatus that can improve the measurement accuracy of a sensor having a sensor head disposed in the polishing table.

[0010] In one aspect, there is provided a polishing apparatus comprising: a polishing table having a pad support surface that supports a polishing pad; a polishing head that presses a substrate against the polishing surface of the polishing pad; an optical film thickness measurement device that irradiates the substrate with light, receives light reflected from the substrate, and determines a film thickness measurement value of the substrate based on the reflected light; and an operation control unit, wherein the optical film thickness measurement device comprises a light projecting unit that irradiates the substrate with light, a light receiving unit that receives the light reflected from the substrate, and a first light intensity sensor and a second light intensity sensor that are disposed adjacent to the light receiving unit and detect the amount of light reflected from the substrate, and the operation control unit is configured to determine a position correction amount of the light projecting unit and the light receiving unit that corresponds to the amount of wear of the polishing pad, based on a first light intensity detected by the first light intensity sensor and a second light intensity detected by the second light intensity sensor.

[0011] In one aspect, the first light amount sensor and the second light amount sensor are arranged at different positions in a direction perpendicular to the pad support surface. In one aspect, the light projecting unit and the light receiving unit are inclined with respect to the pad support surface. In one aspect, the light receiving unit is located between the first light amount sensor and the second light amount sensor. In one aspect, the operation control unit is configured to determine the position correction amount based on a correlation between a difference between the first light amount and the second light amount, which is acquired in advance, and an amount of wear of the polishing pad.

[0012] In one aspect, the polishing apparatus further includes a sensor moving mechanism that moves the light-emitting unit and the light-receiving unit in the direction perpendicular to the pad support surface, and the operation control unit is configured to issue a command to the sensor moving mechanism to move the light-emitting unit and the light-receiving unit by the position correction amount. In one aspect, the light-emitting unit and the light-receiving unit are disposed in a hole formed inside the polishing table, and the sensor moving mechanism is configured to move the light-emitting unit and the light-receiving unit within the hole relative to the polishing table. In one aspect, the first and second light amounts are detected when the first and second light amounts are covered by the substrate pressed against the polishing surface. In one aspect, the first and second light amounts are detected during polishing of the substrate. In one aspect, the first and second light amounts are detected during idling operation when polishing of the substrate is not progressing and when the substrate is pressed against the polishing surface with a pressing force applied during polishing of the substrate.

[0013] In one aspect, there is provided a polishing method including pressing a substrate against a polishing surface of a polishing pad supported on a pad support surface of a polishing table, irradiating the substrate with light from a light-projecting unit of an optical film thickness measurement device that determines a film thickness measurement value of the substrate, receiving light reflected from the substrate by a light-receiving unit of the optical film thickness measurement device, detecting the amount of light reflected from the substrate by a first light intensity sensor and a second light intensity sensor arranged adjacent to the light-receiving unit, and determining a position correction amount of the light-projecting unit and the light-receiving unit corresponding to an amount of wear of the polishing pad based on a first light intensity detected by the first light intensity sensor and a first light intensity detected by the second light intensity sensor.

[0014] In one aspect, the first light quantity sensor and the second light quantity sensor are arranged at different positions in a direction perpendicular to the pad support surface. In one aspect, irradiating the substrate with light means irradiating the light obliquely with respect to the surface of the substrate to be polished, and receiving the reflected light from the substrate means receiving the reflected light that is obliquely reflected by the surface of the substrate to be polished. In one aspect, the light receiving unit is located between the first light quantity sensor and the second light quantity sensor. In one aspect, determining the position correction amount based on the first light quantity and the second light quantity means determining the position correction amount based on a correlation between a difference between the first light quantity and the second light quantity, which has been acquired in advance, and the amount of wear on the polishing pad.

[0015] In one aspect, the polishing method further includes moving the light-projecting unit and the light-receiving unit by the position correction amount along the direction perpendicular to the pad support surface. In one aspect, the light-projecting unit and the light-receiving unit are moved relative to the polishing table within a hole formed inside the polishing table. In one aspect, the detection of the first light amount and the second light amount is performed when the first light amount sensor and the second light amount sensor are covered by the substrate pressed against the polishing surface. In one aspect, pressing the substrate against the polishing surface involves rotating the polishing table and pressing the substrate against the polishing surface with the polishing head to polish the substrate, and the detection of the first light amount and the second light amount is performed while the substrate is being polished. In one aspect, pressing the substrate against the polishing surface means pressing the substrate against the polishing surface with a pressing force applied during polishing of the substrate while the polishing table is stopped during idling operation in which polishing of the substrate is not progressing, and the detection of the first light amount and the second light amount is performed during the idling operation.

[0016] In one aspect, a polishing method is provided, which includes: when a polishing pad supported on a polishing table is in an initial state, a sensor having a sensor head arranged in 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; during polishing of the substrate, the sensor detects the substrate and outputs a monitoring sensor signal value; 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 moving the sensor head so as to minimize a difference between the reference sensor signal value and the post-polishing sensor signal value. In one aspect, moving the sensor head means moving the sensor head along a direction perpendicular to a pad support surface of the polishing table that supports the polishing pad.

[0017] In one aspect, the sensor is an optical film thickness measurement 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 that represents the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value that represents 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 that represents the intensity of reflected light from the reference sample located on the polishing pad after polishing of the substrate is completed. In one aspect, the polishing method further includes generating a reference spectrum of reflected light from the reference sensor signal value and generating a post-polishing spectrum of reflected light from the post-polishing sensor signal value, and moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized by moving the optical sensor head so that the difference between the reference spectrum and the post-polishing spectrum is minimized.

[0018] In one aspect, the polishing method further includes obtaining a correlation between the sensor signal value output by the sensor when the reference sample on the polishing pad is detected and the distance from the reference sample to the sensor head, and moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized by calculating the amount 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 it should be moved. In one aspect, the polishing method further includes using the sensor to detect 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, outputting multiple sample sensor signal values, and storing the multiple sample sensor signal values ​​in association with the distance from the reference sample to the sensor head at the multiple positional relationships, thereby constructing a sample library. 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 that is smallest in difference from the reference sensor signal value and the sample sensor signal value that is smallest in difference from the post-polishing sensor signal value, calculating the amount by which the sensor head should be moved based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that is smallest in 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 is smallest in difference from the post-polishing sensor signal value, and moving the sensor head by the amount by which the sensor head should be moved. In one aspect, the output of the reference sensor signal value by the sensor and the output of the post-polishing sensor signal value by the sensor occur during water polishing of the reference sample.

[0019] In one aspect, a polishing apparatus is provided, comprising: a polishing table supporting a polishing pad; a polishing head that polishes a substrate by pressing the substrate against the polishing surface of the polishing pad; a sensor having a sensor head disposed in the polishing table and detecting the substrate and outputting a monitoring sensor signal value; a sensor moving mechanism that moves the sensor head; and a control device that controls the operation of the sensor moving mechanism, wherein the control device is configured to cause the sensor moving mechanism to move the sensor head so as to minimize a difference between a reference sensor signal value output by the sensor when a reference sample located on the polishing pad in an initial state is detected by the sensor and a post-polishing sensor signal value output by the sensor when the reference sample located on the polishing pad after polishing of the substrate is detected by the sensor. In one aspect, the sensor moving mechanism is configured to move the sensor head in a direction perpendicular to a pad support surface of the polishing table that supports the polishing pad.

[0020] In one aspect, the sensor is an optical film thickness measurement 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 that represents the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value that represents 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 that represents the intensity of reflected light from the reference sample located on the polishing pad after polishing of the substrate is completed. In one aspect, the optical film thickness measurement device is configured to generate a reference spectrum of reflected light from the reference sensor signal value and generate a post-polishing spectrum of reflected light from the post-polishing sensor signal value, and the control device is configured to cause the sensor moving mechanism to move the optical sensor head so as to minimize the difference between the reference spectrum and the post-polishing spectrum.

[0021] In one aspect, the control device is configured to obtain a correlation between the sensor signal value output by the sensor when the reference sample on the polishing pad is detected and the distance from the reference sample to the sensor head, calculate the amount the sensor head should move based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation, and cause the sensor moving mechanism to move the sensor head by the amount it should move. In one aspect, the sensor is configured to detect 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 output multiple sample sensor signal values. The control device is configured to construct a sample library by storing the multiple sample sensor signal values ​​in association with the distance from the reference sample to the sensor head at each of the multiple positional relationships, determine from the sample library the sample sensor signal value that is smallest in difference from the reference sensor signal value and the sample sensor signal value that is smallest in difference from the post-polishing sensor signal value, calculate the amount by which the sensor head should be moved based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that is smallest in 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 is smallest in difference from the post-polishing sensor signal value, and cause the sensor moving mechanism to move the sensor head by the amount by which it should be moved. In one aspect, the 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 the initial state, and the post-polishing 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 after polishing of the substrate is completed.

[0022] The operation control unit is configured to determine the position correction amount of the light-emitting unit and the light-receiving unit corresponding to the amount of wear of the polishing pad based on the first light amount detected by the first light amount sensor and the second light amount detected by the second light amount sensor. As a result, the polishing apparatus can improve the measurement accuracy of the film thickness of the substrate.

[0023] Furthermore, the sensor detects a reference sample located on the polishing pad in an initial state and outputs a reference sensor signal value, and detects the reference sample located on the polishing pad after 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 the reference distance. As a result, the measurement accuracy of the sensor having the sensor head disposed in the polishing table can be improved.

[0024] 6A is a schematic diagram showing an embodiment of a polishing apparatus; FIG. 6B is a diagram explaining the change in the light-receiving sensor head reflected light from the substrate W due to wear of the polishing pad; FIG. 6A is a diagram explaining the change in the light-receiving sensor head reflected light from the substrate W due to wear of the polishing pad; FIG. 6B ...C is a flowchart showing an example of a polishing method using the polishing apparatus shown in FIG. 6A; FIG. 6D is a flowchart showing another example of a polishing method using the polishing apparatus shown in FIG. 6B; FIG. 6E is a schematic diagram showing an optical film thickness measurement device according to another embodiment of the polishing apparatus; FIG. 6F is a schematic diagram showing another embodiment of the polishing apparatus; FIG. 6G is a schematic diagram showing an optical film thickness measurement device according to another embodiment of the polishing apparatus; FIG. 6H is a schematic diagram showing an embodiment of the polishing apparatus; FIG. 6I is a cross-sectional view showing an embodiment of the polishing apparatus equipped with an optical film thickness measurement device as a sensor; FIG. 6I is a diagram showing an example of a monitoring spectrum generated by a data processing unit; FIG. 6I is a top view showing the change in the light-receiving sensor head reflected light from the substrate due to wear of the polishing pad; FIG. 1 is a schematic diagram showing an embodiment of a sensor moving mechanism; FIG. 2 is a diagram showing an example of a reference spectrum and a post-polishing spectrum; FIG. 3 is a diagram showing an example of a plurality of sample spectra stored in a sample library; FIG. 4 is a flowchart illustrating an embodiment of a method for polishing a substrate; FIG. 5 is a flowchart illustrating an embodiment of a method for polishing a substrate; FIG. 6 is a flowchart illustrating an embodiment of a method for moving an optical sensor head so as to minimize the difference between the reference spectrum and the post-polishing spectrum; FIG. 7 is a flowchart illustrating another embodiment of a method for moving an optical sensor head so as to minimize the difference between the reference spectrum and the post-polishing spectrum; FIG. 8 is a schematic diagram showing another embodiment of an optical sensor head.25A and 25B are diagrams illustrating how the light receiving conditions of the optical sensor head, which is disposed obliquely as shown in FIG. 24, change due to wear of the polishing pad.

[0025] Embodiments of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing one embodiment of a polishing apparatus. 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, a polishing table 3 that supports the polishing pad 2, a polishing head 10 that holds a substrate W and presses it against the polishing pad 2, a polishing liquid supply nozzle 20 that supplies a polishing liquid (e.g., a slurry containing abrasive grains) onto the polishing pad 2, an optical film thickness measurement device 30 that measures the film thickness on the surface of the substrate W, and an operation control unit 60 that controls the operation of these components.

[0026] The polishing pad 2 is supported on a pad support surface 3a of the polishing table 3. In this embodiment, the pad support surface 3a is formed from the flat upper surface of the polishing table 3. The upper surface of the polishing pad 2 forms a polishing surface 2a for polishing the substrate W. The polishing pad 2 has a thickness. Hereinafter, 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) is referred to as the thickness of the polishing pad 2. A through hole 2b is formed in the polishing pad 2. A hole 3b is formed in the upper surface of the polishing table 3. The through hole 2b and the hole 3b are connected. As will be described later, the through hole 2b allows light to pass through for film thickness measurement.

[0027] The polishing table 3 is connected to a table motor 6 via a table shaft 5. The table motor 6 is configured to rotate the polishing table 3. The polishing table 3 is rotated about its axis by the table motor 6. The polishing pad 2 rotates integrally with the polishing table 3. For example, the polishing table 3 is rotated in the direction indicated by the arrow in FIG. 1 .

[0028] 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 about its axis by the polishing head motor. The polishing head 10 rotates integrally with the polishing head shaft 12. For example, the polishing head 10 is rotated in the direction indicated by the arrow in FIG. 1 .

[0029] The lower surface of the polishing head 10 is configured to hold the substrate W. A vacuum source (not shown) that vacuum-sucks the substrate W is connected to the lower surface of the polishing head 10. The substrate W is suction-held on the lower surface of the polishing head 10 by the vacuum source. In other words, the lower surface of the polishing head 10 forms a wafer-holding surface that holds the substrate W.

[0030] Furthermore, an air bag (not shown) is provided on the underside of the polishing head 10 to press the substrate W against the polishing surface 2a of the polishing pad 2. The air bag generates pressure to press the held substrate W. A gas supply line (not shown) is connected to the air bag, and the pressure is adjusted by the amount of gas supplied. The air bag presses the substrate W from its rear side. The polishing head 10 presses the substrate W against the polishing surface 2a of the polishing pad 2 by using the air bag.

[0031] 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 lift and lower (move up and down) the polishing head 10. The polishing head 10 is moved up and down relative to the polishing pad 2 by the polishing head lifting mechanism. The polishing head 10 moves up and down integrally with the polishing head shaft 12. The polishing head lifting mechanism lowers the polishing head 10 holding 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 against the polishing surface 2a of the polishing pad 2.

[0032] The operation control unit 60 is composed of at least one computer. The operation control unit 60 includes a storage device 60a in which a program is stored, and an arithmetic unit 60b that executes calculations according to instructions included in the program. The storage device 60a includes a main storage device such as RAM, and an auxiliary storage device such as a hard disk drive (HDD) or a solid-state drive (SSD). Examples of the arithmetic unit 60b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the operation control unit 60 is not limited to these examples.

[0033] The substrate W is polished as follows. The polishing head 10 holds the substrate W with its surface (surface to be polished) facing the polishing pad 2. While the polishing table 3 is rotated by the table motor 6, a polishing liquid is supplied from the polishing liquid supply nozzle 20 onto the polishing surface 2a of the polishing pad 2. In this state, the polishing head 10 is lowered by the polishing head lifting mechanism while being rotated by the polishing head motor. 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 against 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.

[0034] The optical film thickness measurement device 30 includes a light source 31, a light-projecting unit 32, a light-receiving unit 33, a spectroscope 37, and a spectral processing unit 39. The light-receiving unit 33 is provided in a light-receiving sensor head 35 (described later). The light-projecting unit 32 and the light-receiving unit 33 are disposed inside the polishing table 3. The light source 31, the light-projecting unit 32, the light-receiving unit 33, and the spectroscope 37 are attached to the polishing table 3 and rotate integrally with the polishing table 3 and the polishing pad 2. The light-projecting unit 32 is optically connected to the light source 31. The light-receiving unit 33 is optically connected to the spectroscope 37. The light source 31 is connected to an operation control unit 60. The spectroscope 37 is connected to the spectral processing unit 39, which is connected to the operation control unit 60. The spectral processing unit 39, like the operation control unit 60, is composed of at least one computer including a storage device storing a program and an arithmetic unit that executes calculations according to instructions included in the program.

[0035] As an example, the light-projecting unit 32 and the light-receiving unit 33 are each formed of an optical fiber cable. One end (tip) of the light-projecting unit 32 and one end (tip) of the light-receiving unit 33 are directed upward and face the substrate W held by the polishing head 10. One end of the light-projecting unit 32 and one end of the light-receiving unit 33 are inclined in directions approaching each other. The other end of the light-projecting unit 32 is optically connected to the light source 31, and the other end of the light-receiving unit 33 is optically connected to the spectroscope 37.

[0036] The light source 31 may be a light-emitting diode (LED), a halogen lamp, a xenon lamp, or the like. The light projecting unit 32 guides light from the light source 31 to irradiate the surface of the substrate W, and the light receiving unit 33 receives light reflected from the surface of the substrate W. The spectroscope 37 is configured to resolve the reflected light received by the light receiving unit 33 according to wavelength and measure the intensity of the reflected light over a predetermined wavelength range.

[0037] The spectral processing unit 39 generates a spectrum of reflected light representing the intensity of reflected light for each wavelength from the light intensity data obtained by the spectrometer 37, and determines the film thickness of the substrate W based on the spectrum of the reflected light. A known technique is used to determine the film thickness of the substrate W based on the spectrum. For example, the spectral processing unit 39 determines a reference spectrum from a reference spectrum library whose shape is closest to the spectrum of the reflected light, and determines the film thickness associated with the determined reference spectrum. In another example, the spectral processing unit 39 performs a Fourier transform on the spectrum of the reflected light and determines the film thickness from the obtained frequency spectrum. The measured film thickness value obtained by the spectral processing unit 39 is sent to the operation control unit 60. The operation control unit 60 determines that the polishing endpoint has been reached when the measured film thickness value reaches a predetermined target value.

[0038] The light-projecting unit 32 and the light-receiving unit 33 are disposed inside the hole 3b of the polishing table 3. The light-projecting unit 32 and the light-receiving unit 33 may be disposed below the polishing surface 2a of the polishing pad 2. In other words, one end of the light-projecting unit 32 and one end of the light-receiving unit 33 may be disposed below the polishing surface 2a of the polishing pad 2. As shown in FIG. 1 , one end of the light-projecting unit 32 and one end of the light-receiving unit 33 are disposed below the pad support surface 3a of the polishing table 3. In one embodiment, one end of the light-projecting unit 32 and one end of the light-receiving unit 33 may be disposed inside the through-hole 2b as long as they are below the polishing surface 2a of the polishing pad 2.

[0039] Through-hole 2b and hole 3b are filled with a liquid (e.g., pure water) as a medium that transmits light. In other words, the space between the surface of the substrate W to be polished and the tips of light-projecting unit 32 and light-receiving unit 33 is filled with liquid. Therefore, light incident on the surface of the substrate W from light-projecting unit 32 and light reflected from the surface of the substrate W to light-receiving unit 33 passes through the liquid. This liquid is supplied by a liquid supply line (not shown) connected to hole 3b and discharged by a liquid discharge line (not shown) connected to hole 3b.

[0040] The light-transmitting medium may be air instead of a liquid. A transparent window (not shown) may be provided instead of a light-transmitting liquid. The window may be provided inside the through-hole 2b or the hole 3b, as long as it is located below the polishing surface 2a of the polishing pad 2 and above the tips of the light-emitting unit 32 and the light-receiving unit 33. In this case, the window is provided so as to cover at least one of the through-hole 2b and the hole 3b.

[0041] FIG. 2 is a top view showing the positional relationship between the substrate W and the polishing table 3 during polishing. The light-projecting unit 32 and the light-receiving sensor head 35, including the light-receiving unit 33, cross (i.e., pass through) the substrate W along the trajectory shown by the dashed line in FIG. 2 each time the polishing table 3 rotates. The light-projecting unit 32 and the light-receiving sensor head 35 are disposed at a predetermined distance from the center O of the polishing table 3 in the radial direction of the polishing table 3. The center of the substrate W is disposed at a predetermined distance from the center O of the polishing table 3 in the radial direction of the polishing table 3. In FIG. 2, the distance from the center O of the polishing table 3 to the light-projecting unit 32 and the light-receiving 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 FIG. 2, the light-projecting unit 32 and the light-receiving sensor head 35 cross the center of the substrate W as the polishing table 3 rotates.

[0042] 2 shows an example of an arrangement in which the light projecting unit 32 and the light receiving sensor head 35 cross the center of the substrate W, but the arrangement of the light projecting unit 32 and the light receiving sensor head 35 is not limited to this. The light projecting unit 32 and the light receiving sensor head 35 only need to cross the surface of the substrate W. The operation control unit 60 is electrically connected to the table motor 6 (see FIG. 1). The operation control unit 60 receives information regarding the rotation of the polishing table 3 from the table motor 6. The operation control unit 60 determines that the light projecting unit 32 and the light receiving sensor head 35 are moving below the substrate W when the polishing table 3 is within a predetermined rotation angle range.

[0043] The light projecting unit 32 intermittently irradiates the surface of the substrate W with light at predetermined time intervals while moving below the substrate W. Specifically, the operation control unit 60 controls the light source 31 to cause the light source 31 to emit light intermittently at predetermined time intervals. The light from the light source 31 is irradiated intermittently at predetermined time intervals onto the surface of the substrate W via the light projecting unit 32. As a result, the light is irradiated onto a plurality of measurement points on the surface of the substrate W, and the film thickness at each measurement point is measured.

[0044] The light-projecting unit 32 and the light-receiving unit 33 of the light-receiving sensor head 35 may measure the film thickness by continuing to irradiate the surface of the substrate W with light while moving below the substrate W. In other words, the light-projecting unit 32 may continuously irradiate the surface of the substrate W with light. In this case, the operation control unit 60 controls the light source 31 to maintain emission of light while the light-projecting unit 32 moves below the substrate W. The light from the light source 31 continues to be irradiated onto the surface of the substrate W via the light-projecting unit 32. The spectroscope 37 measures the intensity of the reflected light at predetermined time intervals. As a result, the spectrum processing unit 39 generates a spectrum of the reflected light representing the intensity of the reflected light for each wavelength from the light intensity data obtained by the spectroscope 37 at predetermined time intervals, and determines the film thickness at each measurement point on the substrate W based on the spectrum of the reflected light.

[0045] 3 is an enlarged view of the optical film thickness measurement device 30 shown in FIG. 3. As shown in FIG. 3, the light-projecting unit 32 and the light-receiving unit 33 of the light-receiving sensor head 35 are inclined with respect to the pad support surface 3a of the polishing table 3. That is, the tip of the light-projecting unit 32, which is made up of a light-projecting optical fiber, and the tip of the light-receiving unit 33, which is made up of a light-receiving optical fiber, are inclined at a predetermined angle with respect to the surface of the substrate W. The tip of the light-receiving unit 33, which is made up of a light-receiving optical fiber, is inclined at an angle that allows it to receive reflected light. The light-projecting unit 32 is configured to irradiate light obliquely onto the surface of the substrate W (the surface to be polished), and the light-receiving unit 33 is configured to receive light reflected obliquely from the surface of the substrate W.

[0046] It is preferable that the light receiving unit 33 receives light at an angle substantially equal to the angle of reflection of the light on the surface of the substrate W. In other words, it is preferable that the tip of the light receiving unit 33 made of a light-receiving optical fiber is inclined so that the reflected light enters substantially perpendicularly to the tip of the light receiving unit 33. In this case, as shown in Fig. 3, the tip of the light projecting unit 32 made of a light-projecting optical fiber and the tip of the light receiving unit made of a light-receiving optical fiber 33 are inclined at the same angle in directions approaching each other.

[0047] As shown in FIG. 3 , the light-receiving sensor head 35 has a first light intensity sensor 41 and a second light intensity sensor 42 arranged adjacent to the light-receiving unit 33. The first light intensity sensor 41 and the second light intensity sensor 42 are configured to detect the intensity of light reflected from the substrate W. One end (tip) of the first light intensity sensor 41 and one end (tip) of the second light intensity sensor 42 are directed obliquely upward and face the substrate W held by the polishing head 10. The first light intensity sensor 41 and the second light intensity sensor 42 are inclined with respect to the pad support surface 3 a of the polishing table 3. The first light intensity sensor 41 and the second light intensity sensor 42 are arranged at different positions in a direction perpendicular to the pad support surface 3 a of the polishing table 3. The tip of the first light intensity sensor 41 and the tip of the second light intensity sensor 42 are inclined at a predetermined angle with respect to the surface of the substrate W. The tip of the first light intensity sensor 41 and the tip of the second light intensity sensor 42 are arranged at an angle that allows them to receive reflected light.

[0048] In this embodiment, the first light intensity sensor 41, the second light intensity sensor 42, and the light receiving unit 33 have the same inclination angle with respect to the surface of the substrate W (and the pad support surface 3 a). The tip of the first light intensity sensor 41, the tip of the second light intensity sensor 42, and the tip of the light-receiving optical fiber 33 are located in a plane perpendicular to the path of the light reflected from the substrate W. As an example, the tips of the first light intensity sensor 41 and the second light intensity sensor 42 are formed by optical fiber cables. As another example, the first light intensity sensor 41 and the second light intensity sensor 42 may be formed by light-receiving elements arranged at the tip of the light-receiving sensor head 35.

[0049] In this embodiment, the tip of the light-projecting unit 32 has a light-projecting surface large enough to enable the light-receiving unit 33, the first light intensity sensor 41, and the second light intensity sensor 42 to receive light reflected from the substrate W. For example, as shown in Fig. 3, the light-projecting surface of the light-projecting unit 32 made up of a light-projecting optical fiber is larger than the light-receiving surface of the light-receiving unit 33 made up of a light-receiving optical fiber.

[0050] Fig. 4 is an enlarged perspective view of the light-receiving sensor head 35 shown in Fig. 3. As shown in Fig. 4, the light-receiving sensor head 35 has a head housing 45 at its end, and the end of the light-receiving unit 33, the end of the first light amount sensor 41, and the end of the second light amount sensor 42 are supported by the head housing 45. The relative positional relationship between the light-receiving unit 33, the first light amount sensor 41, and the second light amount sensor 42 is fixed by the head housing 45. In this embodiment, the light-receiving unit 33 is located between the first light amount sensor 41 and the second light amount sensor 42.

[0051] In this specification, the amount of light reflected from the substrate W detected by the first light amount sensor 41 is referred to as the "first light amount," and the amount of light reflected from the substrate W detected by the second light amount sensor 42 is referred to as the "second light amount." The first light amount sensor 41 and the second light amount sensor 42 are connected to the operation control unit 60. The first light amount detected by the first light amount sensor 41 and the second light amount detected by the second light amount sensor 42 are sent to the operation control unit 60.

[0052] 5 is a diagram illustrating how the reflected light from the substrate W received by the light-receiving sensor head 35 changes due to wear of the polishing pad 2. The thickness of the polishing pad 2 gradually becomes thinner as it is worn away by polishing the substrate W. In other words, the thickness of the polishing pad 2 gradually decreases. As shown in FIG. 5, as the thickness of the polishing pad 2 decreases, the position of the surface of the substrate W pressed against the polishing pad 2 changes in a direction closer to the light-projecting unit 32 and the light-receiving sensor head 35. In other words, the distance from the surface of the substrate W to the tip of the light-projecting optical fiber 32 and the tip of the light-receiving sensor head 35 decreases as the polishing pad 2 wears.

[0053] As described above, the light projecting optical fiber 32 projects light obliquely onto the surface of the substrate W. Therefore, when the distance from the surface of the substrate W to the tip of the light projecting optical fiber 32 and the tip of the light receiving sensor head 35 becomes short, the position of the light reflected from the substrate W shifts relative to the light receiving sensor head 35. This prevents the light receiving unit 33 from properly receiving the light reflected from the substrate W, and as a result, there is a risk that the film thickness of the substrate W cannot be measured accurately.

[0054] Therefore, in this embodiment, position correction amounts for the light-projecting unit 32 and the light-receiving sensor head 35 are determined corresponding to the amount of wear of the polishing pad 2. Fig. 6A is a diagram illustrating the amount of reflected light detected by the light-receiving sensor head 35 before the polishing pad 2 shown in Fig. 5 is worn, and Fig. 6B is a diagram illustrating the amount of reflected light detected by the light-receiving sensor head 35 after the polishing pad 2 shown in Fig. 5 is worn. As shown in Figs. 6A and 6B, the amount of reflected light from the substrate W is greatest at the center in a plane perpendicular to the path of the reflected light and decreases with increasing distance from the center.

[0055] 6A and 6B , the light-receiving position R1 represents the range in which the light-receiving unit 33 receives reflected light from the substrate W, the light-receiving position R2 represents the range in which the first light intensity sensor 41 receives reflected light from the substrate W, and the light-receiving position R3 represents the range in which the second light intensity sensor 42 receives reflected light from the substrate W. As shown in FIG. 6A , before the polishing pad 2 is worn out, the light-receiving unit 33 receives the central portion of the reflected light from the substrate W. At such light-receiving position R1, the light-receiving unit 33 can receive a sufficient amount of reflected light to accurately measure the film thickness of the substrate W. Before the polishing pad 2 is worn out, the first light amount detected by the first light intensity sensor 41 and the second light amount detected by the second light intensity sensor 42 are equal.

[0056] As shown in FIG. 6B , after the polishing pad 2 is worn, the light receiving unit 33 receives a portion of the reflected light from the substrate W that is shifted from the center. At this light receiving position R1, the light receiving unit 33 cannot receive a sufficient amount of reflected light to accurately measure the film thickness of the substrate W. After the polishing pad 2 is worn, the first light amount detected by the first light amount sensor 41 and the second light amount detected by the second light amount sensor are different. As described above, the first light amount sensor 41 and the second light amount sensor 42 are disposed at different positions in the direction perpendicular to the pad support surface 3 a of the polishing table 3 (i.e., the thickness direction of the polishing pad 2). Therefore, as the polishing pad 2 is worn, the amount of reflected light received by the first light amount sensor 41 and the second light amount sensor 42 changes. In the example of FIG. 6B , the first light amount detected at the light receiving position R2 is greater than the second light amount detected at the light receiving position R3. In this way, the relationship between the first light amount and the second light amount changes with wear of the polishing pad 2. However, the arrangement of the first light amount sensor 41 and the second light amount sensor 42 is not particularly limited to this embodiment as long as the positional relationship causes a change in the detected light amount with wear of the polishing pad 2.

[0057] The operation control unit 60 is configured to determine position correction amounts for the light-projecting unit 32 and the light-receiving sensor head 35 (including the light-receiving unit 33, the first light quantity sensor 41, and the second light quantity sensor 42) corresponding to the amount of wear of the polishing pad 2, based on the first light quantity detected by the first light quantity sensor 41 and the second light quantity detected by the second light quantity sensor 42. A correlation between the difference between the first light quantity and the second light quantity, which has been acquired in advance, and the amount of wear of the polishing pad 2 is stored in the storage device 60a of the operation control unit 60. The operation control unit 60 calculates the difference between the first light quantity detected by the first light quantity sensor 41 and the second light quantity detected by the second light quantity sensor 42. The operation control unit 60 determines position correction amounts for the light-projecting unit 32 and the light-receiving sensor head 35 based on the calculated difference between the first light quantity and the second light quantity, and the correlation between the difference between the first light quantity and the second light quantity and the amount of wear of the polishing pad 2.

[0058] The first light amount and the second light amount are detected when the first light amount sensor 41 and the second light amount sensor 42 are covered by the substrate W pressed against the polishing surface 2 a of the polishing pad 2. The operation control unit 60 determines that the first light amount sensor 41 and the second light amount sensor 42 are covered by the substrate W on the polishing pad 2 based on the rotation angle of the polishing table 3 and the relative position between the polishing table 3 and the polishing head 10.

[0059] In one embodiment, the first light amount and the second light amount are detected during polishing of the substrate W. The operation control unit 60 determines the position correction amounts of the light projector 32 and the light receiving sensor head 35 based on the first light amount and the second light amount detected during polishing of the substrate W. The determination of the position correction amounts of the light projector 32 and the light receiving sensor head 35 may be performed every time a substrate W is polished, or every time a predetermined number of substrates W are polished.

[0060] In another embodiment, the first light amount and the second light amount are detected during idling operation in which polishing of the substrate W is not progressing and the substrate W is pressed against the polishing surface 2 a of the polishing pad 2 with a pressing force applied during polishing of the substrate W. During idling operation of the substrate W, the supply of polishing liquid to the polishing surface 2 a and the rotation of the polishing table 3 are stopped, and polishing of the substrate W does not progress. The pressing force applied during polishing of the substrate W is determined in advance based on, for example, a polishing recipe for polishing the substrate W held by the polishing head 10.

[0061] The operation control unit 60 determines the position correction amounts of the light projecting unit 32 and the light receiving sensor head 35 based on the first light amount and the second light amount detected during idling operation. The determination of the position correction amounts of the light projecting unit 32 and the light receiving sensor head 35 may be performed every time a substrate W is polished during idling operation, or may be performed during idling operation after a predetermined number of substrates W have been polished.

[0062] 3 , the polishing apparatus 1 further includes a sensor moving mechanism 50 that moves the light-receiving sensor head 35, which includes the light-projecting unit 32 and the light-receiving unit 33, in a direction perpendicular to the pad support surface 3 a of the polishing table 3 (i.e., in the thickness direction of the polishing pad 2). The sensor moving mechanism 50 includes a sensor support member 51 that supports the light-projecting unit 32 and the light-receiving sensor head 35, a first gear 53 connected to the sensor support member 51, a second gear 56 that meshes with the first gear 53, and a motor 58 connected to the second gear 56. Examples of the motor 58 include a servo motor and a stepping motor. The sensor support member 51 is disposed inside the hole 3 b in the polishing table 3.

[0063] At least a portion of the light-projecting unit 32 and the light-receiving sensor head 35 is supported by a sensor support member 51. The relative positions of the light-projecting unit 32 and the light-receiving sensor head 35 are fixed by the sensor support member 51. In this embodiment, the sensor support member 51 is attached to the inner surface of the polishing table 3, which defines the hole 3b, via a sealing member (not shown) so as to be movable relative to the polishing table 3. This prevents liquid filling the hole 3b from leaking between the sensor support member 51 and the inner surface of the polishing table 3 and adhering to the first gear 53, the second gear 56, the motor 58, etc. In one embodiment, instead of the sealing member, a cover may be provided to prevent liquid from adhering to the first gear 53, the second gear 56, the motor 58, etc.

[0064] The first gear 53 is connected to a screw 54. The screw 54 is threaded into a threaded hole 51a provided in the sensor support member 51. The second gear 56 is connected to a rotation shaft 58a of a motor 58. When the motor 58 is driven, the second gear 56 rotates via the rotation shaft 58a. When the second gear 56 rotates, the first gear 53 rotates in conjunction with the second gear 56. The rotation of the second gear 53 rotates the screw 54, and the sensor support member 51, and the light-projecting unit 32 and the light-receiving sensor head 35 (including the light-receiving unit 33, the first light quantity sensor 41, and the second light quantity sensor 42) supported by the sensor support member 51 are moved together in a direction perpendicular to the pad support surface 3a. In this way, the sensor moving mechanism 50 moves the light-projecting unit 32 and the light-receiving sensor head 35 within the hole 3b relative to the polishing table 3.

[0065] The specific configuration of the sensor moving mechanism 50 is not particularly limited to this embodiment as long as it can move the light projecting unit 32 and the light receiving sensor head 35 in a direction perpendicular to the pad support surface 3 a. For example, the screw 54 may be directly connected to the rotation shaft 58 a of the motor 58. The sensor moving mechanism 50 is connected to an operation control unit 60, and the operation of the sensor moving mechanism 50 is controlled by the operation control unit 60.

[0066] The operation control unit 60 is configured to issue a command to the sensor moving mechanism 50 to move the light projecting unit 32 and the light receiving sensor head 35 by the position correction amount determined as described above. The operation control unit 60 of this embodiment has the function of a motor driver that controls the rotation amount of the motor 58 of the sensor moving mechanism 50. A storage device 60a of the operation control unit 60 stores a correlation between the movement amount of the light projecting unit 32 and the light receiving sensor head 35 and the rotation amount of the motor 58, which has been acquired in advance. The operation control unit 60 controls the rotation amount of the motor 58 based on the correlation between the movement amount of the light projecting unit 32 and the light receiving sensor head 35 and the rotation amount of the motor 58, so as to move the light projecting unit 32 and the light receiving sensor head 35 by the determined position correction amount.

[0067] In one embodiment, the operation control unit 60 may be configured to issue a command to the sensor moving mechanism 50 to move the light projecting unit 32 and the light receiving sensor head 35 by the determined position correction amount when the determined position correction amount exceeds a predetermined threshold. The predetermined threshold is a value corresponding to the amount of wear of the polishing pad 2 that exceeds the range in which the light receiving unit 33 can properly receive reflected light from the substrate W, and is determined in advance by experiment or the like.

[0068] In one embodiment, the operation control unit 60 may directly control the amount of rotation of the motor 58 for correcting the positions of the light projecting unit 32 and the light receiving sensor head 35, based on the first light amount detected by the first light amount sensor 41 and the second light amount detected by the second light amount sensor 42. In this case, the storage device 60a of the operation control unit 60 may store a correlation between the difference between the first light amount and the second light amount, which has been acquired in advance, and the amount of rotation of the motor 58 for correcting the positions of the light projecting unit 32 and the light receiving sensor head 35. In this case, the operation control unit 60 still indirectly determines the amount of position correction of the light projecting unit 32 and the light receiving sensor head 35.

[0069] 7 is a flowchart showing an example of a polishing method using the polishing apparatus 1 shown in FIG. 1. In step S101, the polishing apparatus 1 starts polishing the substrate W. Specifically, the operation control unit 60 issues commands to the table motor 6, the polishing head motor, and the polishing liquid supply nozzle 20 to rotate the polishing table 3 and the polishing head 10 while supplying the polishing liquid onto the polishing surface 2 a of the polishing pad 2. The operation control unit 60 then issues a command to the polishing head lifting mechanism to lower the polishing head 10 and to the polishing head 10 to press the substrate W against the polishing pad 2. As a result, 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 2 a.

[0070] In step S102, while the substrate W is being polished, the optical film thickness measuring device 30 measures the film thickness on the surface of the substrate W. In step S103, the first light intensity sensor 41 and the second light intensity sensor 42 detect a first light intensity and a second light intensity of light reflected from the substrate W when the substrate W is irradiated with light from the light projector 32 during film thickness measurement. In step S104, the operation control unit 60 determines a position correction amount for the light receiving sensor head 35 including the light projector 32 and the light receiver 33 based on the first light intensity and the second light intensity. In step S105, the operation control unit 60 issues a command to the sensor moving mechanism 50 to move the light projector 32 and the light receiving sensor head 35 by the position correction amount.

[0071] In step S106, the optical film thickness measuring device 30 measures the film thickness on the surface of the substrate W. In step S107, the operation control unit 60 determines the polishing endpoint based on the measured film thickness of the substrate W. In step S108, the polishing apparatus 1 ends polishing of the substrate W. Specifically, the operation control unit 60 issues a command to the polishing head 10 to stop pressing the substrate W against the polishing pad 2, and issues a command to the polishing head lifting mechanism to lift the polishing head 10. Furthermore, the operation control unit 60 issues commands to the table motor 6, the polishing head motor, and the polishing liquid supply nozzle 20 to stop rotation of the polishing table 3 and the polishing head and to stop supply of the polishing liquid onto the polishing surface 2 a.

[0072] The timing at which step S103 is performed is not particularly limited as long as the first light quantity sensor 41 and the second light quantity sensor 42 are covered by the substrate W pressed against the polishing surface 2 a of the polishing pad 2 during polishing of the substrate W. Furthermore, step S105 may be performed after the substrate W has been polished.

[0073] 8 is a flowchart showing another example of a polishing method using the polishing apparatus 1 shown in Fig. 1. In step S201, the operation control unit 60 issues a command to the polishing head 10 while the substrate W is idling, causing the polishing head 10 to press the substrate W against the polishing surface 2a of the polishing pad 2 with the pressing force applied during polishing of the substrate W. While the substrate W is idling, the supply of polishing liquid to the polishing surface 2a and the rotation of the polishing table 3 are stopped, and polishing of the substrate W does not proceed.

[0074] In step S202, the light-projecting unit 32 of the optical film thickness measuring device 30 irradiates the surface of the substrate W with light, and the first light intensity sensor 41 and the second light intensity sensor 42 detect the first and second light intensities of the light reflected from the substrate W. In step S203, the operation control unit 60 determines a position correction amount for the light-receiving sensor head 35 including the light-projecting unit 32 and the light-receiving unit 33 based on the first and second light intensities. In step S204, the operation control unit 60 issues a command to the sensor moving mechanism 50 to move the light-projecting unit 32 and the light-receiving sensor head 35 by the position correction amount.

[0075] Steps S205 to S208 are the same as steps S101 and S106 to S108 shown in FIG. 7, so a duplicated description will be omitted.

[0076] 1 to 8, the position correction amounts of the light-projecting unit 32 and the light-receiving sensor head 35 corresponding to the amount of wear of the polishing pad 2 are determined based on the first light amount and the second light amount. By moving the light-projecting unit 32 and the light-receiving sensor head 35 by the position correction amounts, the light reflected from the substrate W can be properly received by the light-receiving unit 33 even if the polishing pad 2 is worn.

[0077] 9 is a schematic diagram showing an optical film thickness measurement device 30 according to another embodiment of the polishing apparatus 1. The configuration and operation of this embodiment, which are not specifically described, are the same as those of the above-described embodiment, and therefore, redundant description thereof will be omitted. In this embodiment, the polishing apparatus 1 is provided with a distance measurement device 70 that measures the distance to the substrate W, instead of the first light intensity sensor 41 and the second light intensity sensor 42 of the optical film thickness measurement device 30. The polishing apparatus 1 of this embodiment differs from the above-described embodiment in that the position correction amount is determined based on the distance to the substrate W measured by the distance measurement device 70.

[0078] In this embodiment, the light-receiving unit 33 of the optical film thickness measurement device 30 is not provided in the light-receiving sensor head 35. The distance measurement device 70 is disposed inside the polishing table 3. The distance measurement device 70 is disposed between the light-projecting unit 32 and the light-receiving unit 33 of the optical film thickness measurement device 30, and is supported by the sensor support member 51 of the sensor moving mechanism 50. Specifically, the distance measurement device 70 is disposed inside the hole 3b of the polishing table 3, and is disposed below the pad support surface 3a of the polishing table 3. The distance measurement device 70 is configured to measure the distance between the distance measurement device 70 and the surface of the substrate W.

[0079] Examples of the distance measurement device 70 include an optical distance measurement device, a radio wave distance measurement device, an ultrasonic distance measurement device, and a camera equipped with an image sensor (e.g., a stereo camera). The distance measurement device 70 measures the distance between the distance measurement device 70 and the surface of the substrate W when the distance measurement device 70 is covered by the substrate W pressed against the polishing surface 2 a of the polishing pad 2. The operation control unit 60 determines that the distance measurement device 70 is covered by the substrate W on the polishing surface 2 a based on the rotation angle of the polishing table 3 and the relative position between the polishing table 3 and the polishing head 10.

[0080] The distance measurement device 70 is connected to the operation control unit 60, and the distance measured by the distance measurement device 70 between the distance measurement device 70 and the surface of the substrate W is sent to the operation control unit 60. The operation control unit 60 determines the position correction amounts of the light projector 32 and the light receiver 33 corresponding to the amount of wear of the polishing pad 2, based on the distance between the distance measurement device 70 and the substrate W measured by the distance measurement device 70. Specifically, the storage device 60a of the operation control unit 60 stores the distance between the distance measurement device 70 and the surface of the substrate measured in advance by the distance measurement device 70 before the wear of the polishing pad 2 (hereinafter referred to as the "initial distance"). The operation control unit 60 determines the position correction amounts of the light projector 32 and the light receiver 33 corresponding to the amount of wear of the polishing pad 2, based on the difference between the measured value of the distance between the distance measurement device 70 and the surface of the substrate W and the initial distance.

[0081] The operation control unit 60 is configured to issue a command to the sensor moving mechanism 50 to move the light-projecting unit 32 and the light-receiving unit 33 by the determined position correction amount. The sensor support member 51, and the light-projecting unit 32, the light-receiving unit 33, and the distance measuring device 70 supported by the sensor support member 51 are moved together in a direction perpendicular to the pad support surface 3 a.

[0082] In the polishing apparatus 1 of Figure 9, steps S103 and S104 described with reference to Figure 7 and steps S202 and S203 described with reference to Figure 8 can be replaced with a step of measuring the distance between the distance measuring device 70 and the surface of the substrate W using the distance measuring device 70, and a step of determining a position correction amount based on the distance between the distance measuring device 70 and the surface of the substrate W.

[0083] 10 is a schematic diagram showing yet another embodiment of the polishing apparatus 1. The configuration and operation of this embodiment, which are not particularly described, are the same as those of the embodiment described with reference to FIG. 9 , and therefore, redundant description will be omitted. In this embodiment, the polishing apparatus 1 includes, instead of the distance measurement device 70, a capacitance measurement device 80 that measures the capacitance between a capacitance sensor 82 disposed in the thickness direction of the polishing pad 2 and a conductive target 83. The polishing apparatus 1 of this embodiment differs from the embodiment described with reference to FIG. 9 in that the position correction amount is determined based on the capacitance between the capacitance sensor 82 and the conductive target 83 measured by the capacitance measurement device 80.

[0084] The capacitance measuring device 80 includes a capacitance sensor 82 arranged in the polishing table 3, a conductive target 83 arranged in a retainer ring 75 of the polishing head 10, a conductor 85 electrically connecting the capacitance sensor 82 and the conductor plate 83, and rotary connectors 88 and 87 attached to the conductor 85. The retainer ring 75 is an annular structure arranged along the outer periphery at the bottom of the polishing head 10. The retainer ring 75 has the function of holding the substrate W to prevent it from flying out of the polishing head 10 during polishing. The retainer ring 75 is made of an insulating material such as ceramic.

[0085] In this embodiment, the capacitance sensor 82 is disposed at the same height as the pad support surface 3 a of the polishing table 3. The capacitance sensor 82 is configured to detect the capacitance ε between the capacitance sensor 82 and the electrically connected conductive target 83. The capacitance sensor 82 is connected to the operation control unit 60, and the measured value of the capacitance ε between the capacitance sensor 82 and the conductive target 83 is sent to the operation control unit 60.

[0086] When measuring the capacitance, the capacitance sensor 82 and the conductive target 83 are positioned opposite each other with the polishing pad 2 in between. The capacitance sensor 82 measures the capacitance ε between itself and the conductive target 83 when the conductive target 83 is located below the capacitance sensor 82. The operation control unit 60 determines that the conductive target 83 is located below the capacitance sensor 82 based on the rotation angle of the polishing table 3 and the relative position of the polishing table 3 and the polishing head 10.

[0087] The capacitance sensor 82 and the conductive target 83 are electrically connected by a conductor 85 via a rotary connector 87 on the capacitance sensor 82 side and a rotary connector 88 on the conductive target 83 side. Examples of the rotary connectors 87, 88 include slip rings. The capacitance measuring device 80 is configured to measure the capacitance ε between the capacitance sensor 82 and the conductive target 83 by passing a current through the capacitance sensor 82 and the conductive target 83 from a power source (not shown) through the conductor 85.

[0088] The operation control unit 60 is configured to determine a distance d1 between the pad support surface 3a of the polishing table 3 and the retaining ring 75 based on the capacitance ε between the capacitance sensor 82 and the conductive target 83 measured by the capacitance measurement device 80. The storage device 60a of the operation control unit 60 stores a correlation between the capacitance ε between the capacitance sensor 82 and the conductive target 83, which has been acquired in advance, and the distance d1 between the pad support surface 3a of the polishing table 3 and the retaining ring 75. The operation control unit 60 determines the distance d1 between the pad support surface 3a and the retaining ring 75 based on the capacitance ε between the capacitance sensor 82 and the conductive target 83 measured by the capacitance sensor 82, and the correlation between the capacitance ε and the distance d1.

[0089] To prevent the substrate W from flying out of the polishing head 10 during polishing, the pressing force of the polishing pad 10 against the polishing pad 2 is adjusted so that it is greater in the area where the retaining ring 75 is located than in the area where the substrate W is located. The polishing pad 2, which is made of an elastic material, changes in thickness depending on the pressing force. Therefore, the distance d1 between the pad support surface 3a and the retaining ring 75 is smaller than the distance d2 between the pad support surface 3a and the substrate W. The correlation between the distance d1 and the distance d2 can be calculated from the elastic modulus of the polishing pad 2, the area of ​​the lower surface of the retaining ring 75, the area of ​​the substrate W, the amount of gas supplied to the airbag of the polishing head 10, and other factors. The correlation between the distance d1 and the distance d2 is stored in the storage device 60a of the operation control unit 60. The operation control unit 60 determines the distance d2 between the pad support surface 3a and the substrate W from the determined distance d1 based on the correlation between the distance d1 and the distance d2.

[0090] Based on the determined distance d2, the operation control unit 60 determines the position correction amounts of the light projecting unit 32 and the light receiving unit 33 corresponding to the amount of wear of the polishing pad 2. Specifically, the storage device 60a of the operation control unit 60 stores a distance d2 (hereinafter referred to as the "initial distance") that was determined in advance in a similar manner before the polishing pad 2 was worn. The operation control unit 60 determines the position correction amounts of the light projecting unit 32 and the light receiving unit 33 corresponding to the amount of wear of the polishing pad 2 from the difference between the determined distance d2 and the initial distance.

[0091] The operation control unit 60 is configured to issue a command to the sensor moving mechanism 50 to move the light-projecting unit 32 and the light-receiving unit 33 by the determined position correction amount. The sensor support member 51, and the light-projecting unit 32, the light-receiving unit 33, and the distance measuring device 70 supported by the sensor support member 51 are moved together in a direction perpendicular to the pad support surface 3 a.

[0092] In the polishing apparatus 1 of Figure 10, steps S103 and S104 described with reference to Figure 7 and steps S202 and S203 described with reference to Figure 8 can be replaced with a step of measuring the capacitance between the capacitance sensor 82 and the conductor target 83 using the capacitance measuring device 80, and a step of determining a position correction amount based on the capacitance between the capacitance sensor 82 and the conductor target 83.

[0093] Embodiments of the present invention will be described below with reference to the drawings. FIG. 11 is a schematic diagram illustrating one embodiment of a polishing apparatus 101. The polishing apparatus 101 shown in FIG. 11 is an apparatus for chemically and mechanically polishing a substrate such as a wafer. The polishing apparatus 101 includes a polishing pad 102 having a polishing surface 102a, a polishing table 103 supporting the polishing pad 102, a polishing head 110 that polishes the substrate W by pressing the substrate W against the polishing surface 102a of the polishing pad 102, a liquid supply nozzle 120 that supplies a liquid such as a polishing liquid (e.g., a slurry containing abrasive grains) onto the polishing pad 102, a sensor 130 that detects the substrate W and outputs a sensor signal value, and a control device 150 that controls the operation of these components. The sensor 130 has a sensor head disposed within the polishing table 103.

[0094] In this embodiment, the sensor 130 is an optical film thickness measuring device that optically measures the film thickness of the substrate W. FIG. 12 is a cross-sectional view showing an embodiment of a polishing apparatus 101 equipped with an optical film thickness measuring device as the sensor 130. The polishing pad 102 is supported on a pad support surface 103a of the polishing table 103. In this embodiment, the pad support surface 103a is formed by the flat upper surface of the polishing table 103. The upper surface of the polishing pad 102 forms a polishing surface 102a for polishing the substrate W. The polishing pad 102 has a thickness. The thickness of the polishing pad 102 refers to the distance from the upper surface (polishing surface 102a) of the polishing pad 102 to the lower surface (contact surface with the pad support surface 103a of the polishing table 103). A through hole 102b is formed in the polishing pad 102. A hole 103b is formed in the upper surface of the polishing table 103. The through hole 102b and the hole 103b are connected to each other. As will be described later, the through-hole 102b allows light to pass through for film thickness measurement.

[0095] The polishing table 103 is connected to a table motor 106 via a table shaft 105. The table motor 106 is configured to rotate the polishing table 103. The polishing table 103 is rotated about its axis by the table motor 106. The polishing pad 102 rotates integrally with the polishing table 103. For example, the polishing table 103 is rotated in the direction indicated by the arrow in FIG. 12 .

[0096] The polishing head 110 is connected to a polishing head motor (not shown) via a polishing head shaft 112. The polishing head motor is configured to rotate the polishing head 110. The polishing head 110 is rotated about its axis by the polishing head motor. The polishing head 110 rotates integrally with the polishing head shaft 112. For example, the polishing head 110 is rotated in the direction indicated by the arrow in FIG. 12 .

[0097] The lower surface of the polishing head 110 is configured to hold the substrate W. A vacuum source (not shown) that vacuum-sucks the substrate W is connected to the lower surface of the polishing head 110. The substrate W is suction-held on the lower surface of the polishing head 110 by the vacuum source. In other words, the lower surface of the polishing head 110 forms a substrate holding surface that holds the substrate W.

[0098] Furthermore, an air bag (not shown) is provided on the underside of the polishing head 110 to press the substrate W against the polishing surface 102a of the polishing pad 102. The air bag generates pressure to press the held substrate W. A gas supply line (not shown) is connected to the air bag, and the pressure is adjusted by the amount of gas supplied. The air bag presses the substrate W from its rear side. The polishing head 110 presses the substrate W against the polishing surface 102a of the polishing pad 102 by using the air bag.

[0099] The polishing head 110 is connected to a polishing head lifting mechanism (not shown) via a polishing head shaft 112. The polishing head lifting mechanism is configured to lift and lower (move up and down) the polishing head 110. The polishing head 110 is moved up and down relative to the polishing pad 102 by the polishing head lifting mechanism. The polishing head 110 moves up and down integrally with the polishing head shaft 112. The polishing head lifting mechanism lowers the polishing head 110 holding the substrate W toward the polishing pad 102, thereby bringing the surface of the substrate W (in other words, the surface to be polished) into contact with the polishing surface 102a of the polishing pad 102. The polishing head lifting mechanism may further lower the polishing head 110 to press the surface of the substrate W against the polishing surface 102a of the polishing pad 102.

[0100] The control device 150 is composed of at least one computer. The control device 150 includes a storage device 150a in which a program is stored, and an arithmetic device 150b that executes calculations according to instructions included in the program. The storage device 150a includes a main storage device such as RAM, and an auxiliary storage device such as a hard disk drive (HDD) or a solid-state drive (SSD). Examples of the arithmetic device 150b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the control device 150 is not limited to these examples.

[0101] The polishing of the substrate W is performed as follows. The polishing head 110 holds the substrate W with its surface (surface to be polished) facing the polishing pad 102. While the polishing table 103 is rotated by the table motor 106, a polishing liquid is supplied from the liquid supply nozzle 120 onto the polishing surface 102a of the polishing pad 102. In this state, the polishing head 110 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 102a of the polishing pad 102. Furthermore, the polishing head 110 presses the substrate W against the polishing pad 102. 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 102a.

[0102] The optical film thickness measuring device 130 includes a light source 131 that emits light, an optical sensor head 135 that irradiates the substrate W with light from the light source 131 and receives reflected light from the substrate W, a spectroscope 137 that generates measurement data of the intensity of the reflected light from the substrate W, and a data processing unit 139 that determines the thickness of the film on the substrate W based on the measurement data of the intensity of the reflected light from the substrate W. The optical film thickness measuring device 130 is configured to detect the intensity of the reflected light from the substrate W, and output a monitoring sensor signal value that is a sensor signal value that represents the intensity of the reflected light.

[0103] The optical sensor head 135 is disposed inside the hole 103b of the polishing table 103. The optical sensor head 135 is disposed below the polishing surface 102a of the polishing pad 102. In this embodiment, the optical sensor head 135 is disposed below the pad support surface 103a of the polishing table 103. In one embodiment, the optical sensor head 135 may be disposed inside the through-hole 102b, as long as it is below the polishing surface 102a of the polishing pad 102.

[0104] The through-hole 102b and the hole 103b are filled with a liquid (e.g., pure water) as a medium that transmits light. In other words, the space between the surface of the substrate W to be polished and the optical sensor head 135 is filled with liquid. Light irradiated onto the surface of the substrate W from the optical sensor head 135 and light reflected 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 103b and discharged by a liquid discharge line (not shown) connected to the hole 103b.

[0105] In one embodiment, the light-transmitting medium may be air instead of a liquid. A transparent window (not shown) may be provided instead of a light-transmitting liquid. The transparent window may be provided inside the through-hole 102b or the hole 103b, as long as it is positioned below the polishing surface 102a of the polishing pad 102 and above the optical sensor head 135. In this case, the transparent window is provided so as to cover at least one of the through-hole 102b and the hole 103b. In another embodiment, a transparent window (not shown) may be provided to cover the through-hole 102b or the hole 103b filled with a liquid (e.g., pure water).

[0106] The optical sensor head 135 is connected to the light source 131 and the spectroscope 137. The spectroscope 137 is connected to a data processing unit 139. The light source 131, the optical sensor head 135, and the spectroscope 137 are attached to the polishing table 103 and rotate integrally with the polishing table 103 and the polishing pad 102. The light source 131 is connected to a control device 150, and the operation of the light source 131 is controlled by the control device 150. The data processing unit 139 is also connected to the control device 150. Like the control device 150, the data processing unit 139 is composed of at least one computer having a storage device in which a program is stored and an arithmetic unit that executes calculations in accordance with instructions included in the program.

[0107] The optical film thickness measuring device 130 includes a light-projecting fiber optic cable 132 that guides light emitted from a light source 131 to the surface of the substrate W, and a light-receiving fiber optic cable 133 that receives light reflected from the substrate W and sends the reflected light to a spectroscope 137. The optical sensor head 135 is composed of the tip of the light-projecting fiber optic cable 132 and the tip of the light-receiving fiber optic cable 133. The light-projecting fiber optic cable 132 is an optical transmission unit that guides the light emitted by the light source 131 to the surface of the substrate W. The light-receiving fiber optic cable 133 is an optical transmission unit that sends light reflected from the substrate W to the spectroscope 137. One end (tip) of the light-projecting fiber optic cable 132 and one end (tip) of the light-receiving fiber optic cable 133 are located inside the hole 103b of the polishing table 103 and face the substrate W held by the polishing head 110. The other end of the light-emitting optical fiber cable 132 is connected to the light source 131 , and the other end of the light-receiving optical fiber cable 133 is connected to a spectroscope 137 .

[0108] The light source 131 may be a light-emitting diode (LED), a halogen lamp, a xenon lamp, or the like. The optical sensor head 135 irradiates the surface of the substrate W with light from the light source 131 and receives light reflected from the surface of the substrate W. The spectroscope 137 separates the reflected light received by the optical sensor head 135 according to wavelength, and outputs a monitoring sensor signal value representing the intensity of the reflected light over a predetermined wavelength range.

[0109] The data processing unit 139 is configured to generate a reflected light spectrum representing the intensity of reflected light for each wavelength from the monitoring sensor signal values ​​obtained by the spectroscope 137. Hereinafter, the spectrum generated from the monitoring sensor signal values ​​will be referred to as the monitoring spectrum. The reflected light monitoring spectrum is expressed 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.

[0110] Fig. 13 is a diagram showing an example of a monitoring spectrum generated by the data processing unit 139. In Fig. 13, 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. The 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, unnecessary noise such as variations in intensity inherent to the optical system of the apparatus or the light source can be removed from the measured intensity.

[0111] 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 calculated 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 intensity of light emitted from the optical sensor head 135, or by irradiating a mirror with light from the optical sensor head 135 and measuring the intensity of the light reflected from the mirror. Alternatively, the reference intensity may be the intensity of reflected light from a silicon substrate (bare substrate) without a film formed thereon, measured by the spectrometer 137 when the silicon substrate (bare substrate) is being water-polished on the polishing pad 102 in the presence of water, or when the silicon substrate (bare substrate) is placed on the polishing pad 102.

[0112] 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, and the corrected reference intensity is obtained by subtracting the dark level from the reference intensity. The corrected measured intensity is then divided by the corrected reference intensity to obtain the relative reflectance. Specifically, the relative reflectance R(λ) can be obtained using the following equation (1): where λ is the wavelength of light reflected from the substrate, E(λ) is the intensity at wavelength λ, B(λ) is the reference intensity at wavelength λ, and D(λ) is the background intensity (dark level) at wavelength λ measured under light-blocking conditions.

[0113] In the example shown in Figure 13, the monitoring spectrum of the reflected light is a spectral waveform that shows the relationship between the relative reflectance and the wavelength of the reflected light, but in one embodiment, the monitoring spectrum of the reflected light may be a spectral waveform that shows the relationship between the intensity of the reflected light itself and the wavelength of the reflected light.

[0114] The data processing unit 139 determines the film thickness of the substrate W based on the monitoring spectrum of the reflected light. A known technique is used as a method for determining the film thickness of the substrate W based on the monitoring spectrum. For example, the data processing unit 139 determines a reference spectrum that has a shape closest to the monitoring spectrum from a reference spectrum library, and determines the film thickness associated with the determined reference spectrum. In another example, the data processing unit 139 performs a Fourier transform on the monitoring spectrum and determines the film thickness from the obtained frequency spectrum. The film thickness measurement value obtained by the data processing unit 139 is sent to the control unit 150. The control unit 150 determines that the polishing endpoint has been reached when the film thickness measurement value reaches a predetermined target value.

[0115] 14 is a top view showing the positional relationship between the substrate W and the polishing table 103 during polishing. The optical sensor head 135 crosses (in other words, passes over) the substrate W, tracing the trajectory shown by the dashed line in FIG. 14, every time the polishing table 103 makes one rotation. The optical sensor head 135 is disposed at a predetermined distance from the center O of the polishing table 103 in the radial direction of the polishing table 103. The center of the substrate W is disposed at a predetermined distance from the center O of the polishing table 103 in the radial direction of the polishing table 103. In FIG. 14, the distance from the center O of the polishing table 103 to the optical sensor head 135 is equal to the distance from the center O of the polishing table 103 to the center of the substrate W. Therefore, in FIG. 14, the optical sensor head 135 crosses the center of the substrate W as the polishing table 103 rotates.

[0116] 14 shows an example in which the optical sensor head 135 is disposed so as to cross the center of the substrate W, but the arrangement of the optical sensor head 135 is not limited to this. The optical sensor head 135 only needs to cross the surface of the substrate W. The control device 150 is electrically connected to the table motor 106 (see FIG. 12). The control device 150 receives information regarding the rotation of the polishing table 103 from the table motor 106. The control device 150 determines that the optical sensor head 135 is moving below the substrate W when the polishing table 103 is within a predetermined rotation angle range.

[0117] The optical sensor head 135 irradiates the surface of the substrate W with light intermittently at predetermined time intervals while moving below the substrate W. Specifically, the control device 150 controls the light source 131 to cause the light source 131 to emit light intermittently at predetermined time intervals. The light from the light source 131 is irradiated intermittently at predetermined time intervals onto the surface of the substrate W via the optical sensor head 135. As a result, the light is irradiated onto a plurality of measurement points on the surface of the substrate W, and the film thickness at each measurement point is measured.

[0118] The optical sensor head 135 may measure the film thickness by continuing to irradiate the surface of the substrate W with light while moving below the substrate W. In other words, the optical sensor head 135 may continuously irradiate the surface of the substrate W with light. In this case, the control device 150 controls the light source 131 to maintain light emission while the optical sensor head 135 moves below the substrate W. Light from the light source 131 continues to be irradiated onto the surface of the substrate W via the optical sensor head 135. The spectroscope 137 measures the intensity of the reflected light at predetermined time intervals and outputs monitoring sensor signal values ​​representing the intensity of the reflected light. As a result, the data processing unit 139 generates a monitoring spectrum of the reflected light representing the intensity of the reflected light for each wavelength from the monitoring sensor signal values ​​obtained by the spectroscope 137 at predetermined time intervals, and determines the film thickness at each measurement point on the substrate W based on the monitoring spectrum of the reflected light.

[0119] 15 is a diagram illustrating how the light receiving conditions of the optical sensor head 135 for receiving reflected light from the substrate W change due to wear of the polishing pad 102. The thickness of the polishing pad 102 gradually becomes thinner as it is worn away by polishing the substrate W. In other words, the thickness of the polishing pad 102 gradually decreases. As shown in FIG. 15, as the thickness of the polishing pad 102 becomes thinner, the position of the surface of the substrate W pressed against the polishing surface 102a of the polishing pad 102 changes in a direction approaching the optical sensor head 135. In other words, the distance from the surface of the substrate W to the tip of the light-emitting fiber optic cable 132 and the tip of the light-receiving fiber optic cable 133 becomes smaller as the polishing pad 102 wears.

[0120] The intensity of the light reflected from the surface of the substrate W received by the optical sensor head 135 depends on the distance from the surface of the substrate W to the optical sensor head 135. The shorter the distance from the surface of the substrate W to the optical sensor head 135, the greater the intensity of the light reflected from the surface of the substrate W received by the optical sensor head 135, and the greater the distance from the surface of the substrate W to the optical sensor head 135, the smaller the intensity of the light reflected from the surface of the substrate W received by the optical sensor head 135. Therefore, as the polishing pad 102 wears out and the distance from the surface of the substrate W to the optical sensor head 135 decreases, the intensity of the light reflected from the surface of the substrate W received by the optical sensor head 135 increases.

[0121] As described above, the data processing unit 139 determines the film thickness of the substrate W based on the monitoring spectrum of the reflected light generated from the intensity of the reflected light received by the optical sensor head 135. Therefore, a change in the intensity of the reflected light due to wear of the polishing pad 102 may affect the measurement accuracy of the film thickness of the substrate W.

[0122] Therefore, the polishing apparatus 101 is provided with a sensor moving mechanism 140 that moves the optical sensor head 135. By moving the optical sensor head 135 with the sensor moving mechanism 140, the distance from the surface of the substrate W to the optical sensor head 135 is maintained constant even when the polishing pad 102 is worn. FIG. 16 is a schematic diagram showing one embodiment of the sensor moving mechanism 140. The sensor moving mechanism 140 is configured to move the optical sensor head 135 in a direction perpendicular to the pad support surface 103a of the polishing table 103 (i.e., in the thickness direction of the polishing pad 102). As shown in FIG. 16, the sensor moving mechanism 140 includes a sensor support member 141 that supports the optical sensor head 135, a first gear 143 connected to the sensor support member 141, a second gear 146 that meshes with the first gear 143, and a motor 148 connected to the second gear 146. Examples of the motor 148 include a servo motor and a stepping motor. The sensor support member 141 is disposed inside the hole 103 b of the polishing table 103 .

[0123] At least a portion of the optical sensor head 135 is supported by a sensor support member 141. In this embodiment, the sensor support member 141 is attached to the inner surface of the polishing table 103, which defines the hole 103b, via a sealing member (not shown) so as to be movable relative to the polishing table 103. This prevents the liquid filling the hole 103b from leaking out from between the sensor support member 141 and the inner surface of the polishing table 103 and adhering to the first gear 143, the second gear 146, the motor 148, etc. In one embodiment, instead of the sealing member, a cover may be provided to prevent the liquid from adhering to the first gear 143, the second gear 146, the motor 148, etc.

[0124] The first gear 143 is connected to a screw 144. The screw 144 is threaded into a threaded hole 141a provided in the sensor support member 141. The second gear 146 is connected to a rotation shaft 148a of a motor 148. When the motor 148 is driven, the second gear 146 rotates via the rotation shaft 148a. When the second gear 146 rotates, the first gear 143 rotates in conjunction with the second gear 146. The rotation of the second gear 143 rotates the screw 144, and the sensor support member 141 and the optical sensor head 135 supported by the sensor support member 141 are moved in a direction perpendicular to the pad support surface 103a. In this way, the sensor moving mechanism 140 moves the optical sensor head 135 within the hole 103b relative to the polishing table 103.

[0125] The specific configuration of the sensor moving mechanism 140 is not particularly limited to this embodiment as long as it can move the optical sensor head 135 in a direction perpendicular to the pad support surface 103a. For example, the screw 144 may be directly connected to the rotation shaft 148a of the motor 148 without going through the first gear 143 and the second gear 146. The sensor moving mechanism 140 is connected to the control device 150, and the operation of the sensor moving mechanism 140 is controlled by the control device 150.

[0126] The storage device 150a of the control device 150 stores a correlation between the number of rotations of the motor 148, which has been acquired in advance, and the amount of movement of the optical sensor head 135. The control device 150 can control the amount of movement of the optical sensor head 135 by controlling the operation of the sensor movement mechanism 140 based on this correlation.

[0127] The movement of the optical sensor head 135 by the sensor moving mechanism 140 is performed based on sensor signal values ​​obtained by measuring a reference sample on the polishing pad 102 before and after wear using the optical film thickness measuring device 130. Examples of reference samples include a silicon substrate (bare substrate) without a film formed thereon, a mirror, and a test substrate having a configuration similar to that of the substrate W. The optical film thickness measuring device 130 is configured to detect the reference sample located on the polishing pad 102 in its initial state and output a reference sensor signal value. The initial state polishing pad 102 refers to the polishing pad 102 before it is worn down by polishing a substrate W. Before a new polishing pad 102 is used to polish a substrate W, it is dressed or water-polished as a break-in process. The initial state polishing pad 102 refers to the polishing pad 102 after this break-in process and before it is used to polish a substrate W.

[0128] In this embodiment, during water polishing of a reference sample using the polishing pad 102 in its initial state, the optical film thickness measurement device 130 detects the reference sample positioned on the polishing pad 102 and outputs a reference sensor signal value. Water polishing of the reference sample is performed while the polishing head 110 holds the reference sample on the polishing surface 102a of the polishing pad 102, while water, instead of a polishing liquid (e.g., slurry), is supplied from the liquid supply nozzle 120 to the polishing surface 102a of the polishing pad 102. Unlike polishing liquids such as slurry, water does not have an etching function and does not contain abrasive particles. In addition, during water polishing, the polishing head 110 does not press the reference sample strongly against the polishing pad 102. Therefore, polishing of the reference sample does not progress during water polishing of the reference sample.

[0129] In one embodiment, the reference sample is not polished with water, and the optical film thickness measurement device 130 may detect the reference sample placed on the initial polishing pad 102 and output a reference sensor signal value. For example, the polishing head lift mechanism may lower the polishing head 110 holding the reference sample toward the polishing pad 102, so that the reference sample comes into contact with the polishing surface 102a of the initial polishing pad 102. Alternatively, the reference sample may simply be placed on the initial polishing pad 102.

[0130] The optical film thickness measuring device 130 is configured to detect the intensity of reflected light from a reference sample positioned on the polishing pad 102 in an initial state and 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 150 determines that the optical sensor head 135 is moving below the reference sample when the polishing table 103 is within a predetermined rotation angle range. The optical sensor head 135 irradiates light onto the surface of the reference sample when positioned below the reference sample. Specifically, the control device 150 controls the light source 131 to emit light when the optical sensor head 135 is positioned below the reference sample. The light from the light source 131 is irradiated onto the surface of the reference sample via the optical sensor head 135. The spectroscope 137 detects the intensity of reflected light from the reference sample and outputs a reference sensor signal value representing the intensity of the reflected light.

[0131] In this embodiment, the data processing unit 139 of the optical film thickness measurement system 130 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 139 is sent to the control device 150 and stored in the storage device 150a.

[0132] After acquiring the reference spectrum, the polishing apparatus 101 finishes water polishing of the reference sample and starts polishing the substrate W. The polishing pad 102 gradually wears down as the substrate W is polished. After polishing of the substrate W is completed, the control device 150 is configured to determine whether it is time to adjust the sensor position. For example, the control device 150 determines that it is time to adjust the sensor position when a predetermined number of substrates have been polished or when the polishing pad 102 has been in use for a predetermined time. At the time to adjust the sensor position, the optical film thickness measurement device 130 is configured to detect the reference sample located on the polishing pad 102 after polishing of the substrate W is completed and output a post-polishing sensor signal value.

[0133] In this embodiment, during water polishing of a reference sample using the polishing pad 102 after polishing of the substrate W is completed, the optical film thickness measurement device 130 detects the reference sample located on the polishing pad 102 and outputs a post-polishing sensor signal value. When the control device 150 determines that it is time to adjust the sensor position, water polishing of the reference sample begins. This reference sample is the same as the reference sample used to obtain the reference sensor signal value. In one embodiment, water polishing of the reference sample is not performed, and the optical film thickness measurement device 130 may detect the reference sample located on the polishing pad 102 after polishing of the substrate W is completed and output a post-polishing sensor signal value.

[0134] The optical film thickness measurement device 130 is configured to detect the intensity of reflected light from a reference sample positioned on the polishing pad 102 after polishing of the substrate W is completed, and output a post-polishing sensor signal value, which is a sensor signal value representing the intensity of reflected light from the reference sample. The post-polishing sensor signal value is output under the same conditions as the output of the reference sensor signal value. The optical film thickness measurement device 130 may detect the intensity of reflected light from the same measurement point (e.g., the center of the reference sample) as when the reference sensor signal value was output, and output the post-polishing sensor signal value. In this embodiment, the data processing unit 139 of the optical film thickness measurement device 130 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 is referred to as the post-polishing spectrum. The post-polishing spectrum of reflected light obtained by the data processing unit 139 is sent to the control device 150 and stored in the storage device 150a.

[0135] 17 is a diagram showing an example of a reference spectrum and a post-polishing spectrum. As shown in FIG. 17, 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 102 after polishing of the substrate W to the optical sensor head 135 is shorter than the distance from the surface of the reference sample located on the polishing pad 102 in its initial state to the optical sensor head 135. Therefore, the post-polishing sensor signal value is greater than the reference sensor signal value, and the post-polishing spectrum Sa has a greater relative reflectance at each wavelength than the reference spectrum Sr.

[0136] In the example shown in Figure 17, the reference spectrum of reflected light and the post-polishing spectrum of reflected light are spectral waveforms that indicate the relationship between the relative reflectance and the wavelength of the reflected light, but the reference spectrum of reflected light and the post-polishing spectrum of reflected light may also be spectral waveforms that indicate the relationship between the intensity of reflected light itself and the wavelength of the reflected light.

[0137] The control device 150 is configured to cause the sensor moving mechanism 140 to move the optical sensor head 135 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 150 is configured to cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum Sr and the post-polishing spectrum Sa. When the optical sensor head 135 is moved in a direction away from the pad support surface 103 a of the polishing table 103, the distance from the surface of the reference sample to the optical sensor head 135 increases, thereby reducing the difference between the reference spectrum Sr and the post-polishing spectrum Sa. Minimizing the difference between the reference spectrum Sr and the post-polishing spectrum Sa means minimizing the difference between the wavelength and relative reflectance values ​​constituting each data point included in the reference spectrum Sr and the wavelength and relative reflectance values ​​constituting each data point included in the post-polishing spectrum Sa.

[0138] The control device 150 may cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum Sr and the after-polishing spectrum Sa over the entire wavelength range, or may cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum Sr and the after-polishing spectrum Sa in a specific wavelength range. The control device 150 may cause the sensor moving mechanism 140 to move the optical sensor head 135 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 the specific wavelength range and the average value of the relative reflectances constituting the data points included in the after-polishing spectrum Sa in the same specific wavelength range.

[0139] In one embodiment, the control device 150 uses a shape match index between the reference spectrum Sr and the polished spectrum Sa to cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum Sr and the polished spectrum Sa. The shape match index is an index for determining the degree of shape match (similarity) between the reference spectrum Sr and the polished spectrum Sa. Examples of the shape match index include, but are not limited to, the absolute mean, the root mean square, a correlation coefficient, a Good of Fit (GoF) value, cosine similarity, Euclidean distance, standard Euclidean distance, Mahalanobis distance, Manhattan distance, or a combination thereof, as well as a combination of normalized / standardized values ​​of these variables.

[0140] In one embodiment, the control device 150 determines feature quantities that represent the characteristics of the reference spectrum Sr and the after-polishing spectrum Sa, and causes the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the feature quantities of the reference spectrum Sr and the after-polishing spectrum Sa. The feature quantities of a spectrum are, for example, a set of numerical values ​​that indicate the positions of peaks and valleys in the spectrum. The positions of peaks and valleys in the sample spectrum can be identified from the spectral intensity and wavelength.

[0141] The control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 by a predetermined amount (e.g., 0.01 mm) at a time, thereby moving the optical sensor head 135 so that the difference between the reference spectrum Sr of the reflected light and the post-polishing spectrum Sa of the reflected light is minimized. Specifically, the control device 150 acquires the post-polishing spectrum Sa of the reflected light each time the optical sensor head 135 is moved by the predetermined amount, and moves the optical sensor head 135 to a position where the difference between the reference spectrum Sr of the reflected light and the post-polishing spectrum Sa of the reflected light is minimized.

[0142] The control device 150 may use a correlation between a previously acquired sensor signal value and the distance from the reference sample to the optical sensor head 135 to cause the sensor moving mechanism 140 to move the optical sensor head 135 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 150 uses a correlation between a previously acquired reflected light spectrum and the distance from the reference sample to the optical sensor head 135 to cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum Sr and the post-polishing spectrum Sa. The correlation between the sensor signal value (in this embodiment, the spectrum of reflected light generated from the sensor signal value) output when the reference sample on the polishing pad 102 is detected by the optical film thickness measuring device 130 and the distance from the reference sample to the optical sensor head 135 is previously acquired and stored in the storage device 150a of the control device 150. The control device 150 is configured to calculate the amount of movement of the optical sensor head 135 based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation. In this embodiment, the control device 150 calculates the amount of movement of the optical sensor head 135 based on the reference spectrum Sr of the reflected light, the post-polishing spectrum Sa of the reflected light, and the correlation described above.

[0143] Specifically, the control device 150 calculates the distance (hereinafter referred to as the reference distance) from the reference sample to the optical sensor head 135 when the reference sensor signal value (in this embodiment, the reference spectrum Sr) was acquired, based on the reference sensor signal value (in this embodiment, the reference spectrum Sr) and the correlation. The control device 150 calculates the distance (hereinafter referred to as the post-polishing distance) from the reference sample to the optical sensor head 135 when the post-polishing sensor signal value (in this embodiment, the post-polishing spectrum Sa) was acquired, based on the post-polishing sensor signal value (in this embodiment, the post-polishing spectrum Sa) and the correlation. The control device 150 calculates the amount of movement of the optical sensor head 135 by subtracting the post-polishing distance from the reference distance. The control device 150 issues a command to the sensor moving mechanism 140 to move the optical sensor head 135 by the calculated amount of movement.

[0144] In this embodiment, the reference distance is 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 thickness of the polishing pad 102 in the initial state and the known distance from the pad support surface 103 a to the optical sensor head 135 before polishing the substrate W (e.g., the height setting value of the optical sensor head 135).

[0145] In one embodiment, the control device 150 may use a correlation between the sensor signal value (or the spectrum of reflected light) and the difference between a previously acquired reference distance and the distance from the reference sample to the optical sensor head 135, instead of the correlation between the sensor signal value (or the spectrum of reflected light) and the distance from the reference sample to the optical sensor head 135, to cause the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value. In this case, the control device 150 calculates the amount to be moved of the optical sensor head 135 by calculating the difference between the reference distance when the post-polishing sensor signal value (or the post-polishing spectrum Sa) was acquired and the distance from the reference sample to the optical sensor head 135, from the post-polishing sensor signal value (or the post-polishing spectrum Sa) and the correlation, without calculating the reference distance based on the reference sensor signal value (or the reference spectrum Sr).

[0146] In another embodiment, the control device 150 may use a pre-constructed sample library to cause the sensor moving mechanism 140 to move the optical sensor head 135 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 150 uses a pre-constructed sample library to cause the sensor moving mechanism 140 to move the optical sensor head 135 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 measurement device 130 when the reference sample on the polishing pad 102 is detected in multiple positional relationships between the reference sample and the optical sensor head 135, where the distances from the reference sample to the optical sensor head 135 are different. In this embodiment, the sample library includes multiple sample spectra, which are multiple reflected light spectra generated from the multiple sample sensor signal values.

[0147] The optical film thickness measurement device 130 detects the intensities of multiple reflected light beams from a reference sample positioned on the polishing pad 102 at multiple positional relationships between the reference sample and the optical sensor head 135, where the distance from the reference sample to the optical sensor head 135 varies, and outputs multiple sample sensor signal values ​​representing the intensities of the reflected light from the reference sample. The sample sensor signal values ​​are output under the same conditions as the output of the reference sensor signal values ​​and the post-polishing sensor signal values. The control device 150 constructs a sample library by storing the multiple sample sensor signal values ​​in association with the distances from the reference sample to the optical sensor head 135 at the multiple positional relationships. In this embodiment, the data processing unit 139 of the optical film thickness measurement device 130 generates multiple reflected light sample spectra representing the intensity of reflected light for each wavelength from the multiple sample sensor signal values. The control device 150 constructs a sample library by storing the multiple sample spectra in association with the distances from the reference sample to the optical sensor head 135 at the multiple positional relationships. The sample library is stored in the storage device 150a of the control device 150.

[0148] FIG. 18 shows an example of multiple sample spectra stored in a sample library. The multiple (n) sample spectra Ss1 to Ssn are sample spectra acquired at multiple positional relationships between the reference sample and the optical sensor head 135 when the distances from the reference sample to the optical sensor head 135 are D1 to Dn, respectively. For example, sample spectrum Ss1 is a sample spectrum acquired at a positional relationship between the reference sample and the optical sensor head 135 when the distance from the reference sample to the optical sensor head 135 is D1. Sample spectrum Ss2 is a sample spectrum acquired at a positional relationship between the reference sample and the optical sensor head 135 when the distance from the reference sample to the optical sensor head 135 is D2, which is greater than distance D1. Similarly, sample spectrum Ss3 and subsequent sample spectra are sample spectra acquired at positional relationships between the reference sample and the optical sensor head 135 where the distance gradually increases from distance D3 onward. These multiple sample spectra Ss1 to Ssn are stored in the sample library in association with the distances D1 to Dn from the reference sample to the optical sensor head 135, respectively.

[0149] The control device 150 is configured to determine, from a pre-established sample library, the sample sensor signal value that is the smallest difference from the reference sensor signal value and the sample sensor signal value that is the smallest difference from the post-polishing sensor signal value, and to calculate the amount by which the optical sensor head 135 should be moved based on the distance from the reference sample to the optical sensor head 135 associated with the sample sensor signal value that is the smallest difference from the reference sensor signal value and the distance from the reference sample to the optical sensor head 135 associated with the sample sensor signal value that is the smallest difference from the post-polishing sensor signal value.

[0150] In this embodiment, the control device 150 selects, from a pre-constructed sample library, the sample spectrum having the shape closest to the reference spectrum Sr and the sample spectrum having the shape closest to the after-polishing spectrum Sa. The control device 150 calculates the amount by which the optical sensor head 135 should be moved based on the distance from the reference sample associated with the sample spectrum having the shape closest to the reference spectrum Sr to the optical sensor head 135 and the distance from the reference sample associated with the sample spectrum having the shape closest to the after-polishing spectrum Sa to the optical sensor head 135.

[0151] 18 , the control device 150 determines, as the reference distance, a distance D14 from the reference sample associated with a sample spectrum Ss14 in the sample library whose shape is closest to the reference spectrum Sr to the optical sensor head 135. In the example shown in FIG. 18 , the control device 150 determines, as the post-polishing distance, a distance D4 from the reference sample associated with a sample spectrum Ss4 in the sample library whose shape is closest to the post-polishing spectrum Sa to the optical sensor head 135. The method for determining the sample spectrum in the sample library whose shape is closest can use the shape match index described above, but the method is not particularly limited.

[0152] The control device 150 calculates the amount of movement of the optical sensor head 135 by subtracting the post-polishing distance from the reference distance. The control device 150 issues a command to the sensor moving mechanism 140 to move the optical sensor head 135 by the calculated amount of movement. In the example shown in Fig. 18, the control device 150 calculates the distance (D14-D4) by subtracting the post-polishing distance D4 from the reference distance D14, and causes the sensor moving mechanism 140 to move the optical sensor head 135 by the distance (D14-D4).

[0153] In one embodiment, multiple sample sensor signal values ​​(or multiple sample spectra) may be stored in the sample library in association with the difference between a previously acquired reference distance and the distance from the reference sample to the optical sensor head 135, instead of the distance from the reference sample to the optical sensor head 135. In this case, the control device 150 determines the sample sensor signal (or the sample spectrum having a shape closest to the after-polishing spectrum Sa) that is closest to the after-polishing sensor signal, without determining the reference distance based on the reference sensor signal (or the reference spectrum Sr), and determines the difference between the reference distance associated with the determined sample sensor signal (or the sample spectrum) and the distance from the reference sample to the optical sensor head 135 as the amount by which the optical sensor head 135 should be moved.

[0154] 19 and 20 are flowcharts illustrating an embodiment of a method for polishing a substrate W. The operations illustrated in FIGS. 19 and 20 are performed by the polishing apparatus 101 described above. In step S1101, the polishing apparatus 101 starts water polishing of a reference sample using the polishing pad 102 in its initial state. In one embodiment, the reference sample may be placed on the polishing pad 102 in its initial state without water polishing the reference sample. For example, the polishing head lift mechanism may lower the polishing head 110 holding the reference sample toward the polishing pad 102, bringing the reference sample into contact with the polishing surface 102a of the polishing pad 102 in its initial state. Alternatively, the reference sample may simply be placed on the polishing pad 102 in its initial state. In step S1102, the optical film thickness measurement device 130 detects the reference sample on the polishing pad 102 in its initial state and outputs a reference sensor signal value representing the intensity of reflected light from the reference sample. In step S1103, the data processing unit 139 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 150 a of the control device 150 .

[0155] In step S1104, the polishing apparatus 101 finishes water polishing of the reference sample. In step S1105, the polishing apparatus 101 starts polishing the substrate W to be polished. In step S1106, the optical film thickness measurement device 130 detects the substrate W and outputs a monitoring sensor signal value representing the intensity of reflected light from the substrate W. In step S1107, the data processing unit 139 generates a monitoring spectrum of the reflected light representing the intensity of the 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.

[0156] In step S1108, the control device 150 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 S1108), the control device 150 determines that the polishing endpoint has been reached and terminates polishing of the substrate W (step S1109). When the film thickness has not reached the predetermined target value ("No" in step S1108), the control device 150 causes the polishing apparatus 101 to continue polishing the substrate W, and the optical film thickness measurement device 130 again detects the substrate W and outputs a monitoring sensor signal value (return to step S1106). Thereafter, the operations of steps S1106 to S1108 are repeated until the control device 150 determines in step S1108 that the film thickness has reached the predetermined target value.

[0157] In step S1110, after polishing of the substrate W is completed, the control device 150 determines whether it is time to adjust the sensor position. The control device 150 determines that it is time to adjust the sensor position when a predetermined number of substrates have been polished or when the usage time of the polishing pad 102 reaches a predetermined time. When the control device 150 determines that it is time to adjust the sensor position ("Yes" in step S1110), the polishing apparatus 101 starts water polishing of the reference sample using the polishing pad 102 after polishing of the substrate W (step S1111). In one embodiment, water polishing of the reference sample may not be performed, and the reference sample may be placed on the polishing pad 102 after polishing of the substrate W. For example, the polishing head lifting mechanism may lower the polishing head 110 holding the reference sample toward the polishing pad 102, so that the reference sample contacts the polishing surface 102a of the polishing pad 102 after polishing of the substrate W. Alternatively, the reference sample may simply be placed on the polishing pad 102 after polishing of the substrate W. The reference sample is placed on the polishing pad 102 in the same manner as in step S1101.

[0158] When the control device 150 determines that it is not time to adjust the sensor position ("No" in step S1110), the polishing apparatus 101 starts polishing the next substrate W (return to step S1105). Thereafter, steps S1105 to S1110 are repeated until the control device 150 determines that it is time to adjust the sensor position in step S1110. In step S1112, the optical film thickness measurement device 130 detects the reference sample on the polishing pad 102 after polishing the substrate W and outputs a post-polishing sensor signal value representing the intensity of reflected light from the reference sample. In step S1113, the data processing unit 139 generates a post-polishing spectrum of reflected light representing the intensity of reflected light for each wavelength from the post-polishing sensor signal value. The post-polishing spectrum is stored in the storage device 150a of the control device 150.

[0159] In step S1114, the control device 150 controls the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum. In one embodiment, the control device 150 may also control the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value output by the optical film thickness measurement device 130, instead of the reference spectrum and the post-polishing spectrum. In this case, the operations of steps S1103 and S1113 are not performed. In step S1115, the polishing apparatus 101 finishes water polishing of the reference sample. Thereafter, the polishing apparatus 101 starts polishing the next substrate W (return to step S1105).

[0160] According to this embodiment, by moving the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum, the distance from the surface of the reference sample to the optical sensor head 135 can be maintained at the reference distance. As a result, the accuracy of film thickness measurement by the optical film thickness measurement device 130 having the optical sensor head 135 arranged inside the polishing table 103 can be improved.

[0161] 21 is a flowchart illustrating one embodiment of a method for moving the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum. Steps S1201 to S1207 shown in FIG. 21 correspond to step S1114 in FIG. 20. In step S1201, the control device 150 calculates the difference between the reference spectrum and the post-polishing spectrum. The calculated difference between the reference spectrum and the post-polishing spectrum is stored in the storage device 150a of the control device 150.

[0162] In step S1202, the control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 a predetermined distance. The sensor moving mechanism 140 moves the optical sensor head 135 in a direction away from the pad support surface 103a of the polishing table 103. Steps S1203 and S1204 are the same as steps S1112 and S1113 in Fig. 20, and step S1205 is the same as step S1201. In step S1201, the difference between the reference spectrum before moving the optical sensor head 135 and the post-polishing spectrum is calculated, and in step S1205, the difference between the reference spectrum after moving the optical sensor head 135 a predetermined distance and the post-polishing spectrum is calculated.

[0163] In step S1206, the control device 150 determines whether the difference between the reference spectrum and the post-polishing spectrum before moving the optical sensor head 135 is smaller than the difference between the reference spectrum and the post-polishing spectrum after moving the optical sensor head 135 by a predetermined amount. If the difference between the reference spectrum and the post-polishing spectrum before moving the optical sensor head 135 is smaller than the difference between the reference spectrum and the post-polishing spectrum after moving the optical sensor head 135, this indicates that the difference between the reference distance and the optical sensor head 135 from the surface of the reference sample has increased due to the movement of the optical sensor head 135.

[0164] When the difference between the reference spectrum and the post-polishing spectrum before moving the optical sensor head 135 is smaller than the difference between the reference spectrum and the post-polishing spectrum after moving the optical sensor head 135 a predetermined distance ("Yes" in step S1206), the control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum. That is, the control device 150 moves the optical sensor head 135 to the position before moving the optical sensor head 135 in step S1202. The sensor moving mechanism 140 moves the optical sensor head 135 in a direction approaching the pad support surface 103a of the polishing table 103. This allows the distance from the surface of the reference sample to the optical sensor head 135 to be maintained at the reference distance.

[0165] When the difference between the reference spectrum and the post-polishing spectrum before moving the optical sensor head 135 is equal to or greater than the difference between the reference spectrum and the post-polishing spectrum after moving the optical sensor head 135 by the predetermined movement amount ("No" in step S1206), the control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 again by the predetermined movement amount (return to step S1202). The sensor moving mechanism 140 moves the optical sensor head 135 in a direction away from the pad support surface 103a of the polishing table 103. Thereafter, the operations of steps S1202 to S1206 are repeated until the control device 150 determines in step S1206 that the difference between the reference spectrum and the post-polishing spectrum before moving the optical sensor head 135 is smaller than the difference between the reference spectrum and the post-polishing spectrum after moving the optical sensor head 135 by the predetermined movement amount.

[0166] FIG. 22 is a flowchart illustrating another embodiment of a method for moving the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum. Steps S1301 and S1302 in FIG. 22 correspond to step S1114 in FIG. 20. In step S1301, the control device 150 calculates the amount of movement of the optical sensor head 135 based on the correlation between the previously acquired spectrum of reflected light and the distance from the reference sample to the optical sensor head 135. The correlation between the spectrum of reflected light generated from the sensor signal value output when the reference sample on the polishing pad 102 is detected by the optical film thickness measurement device 130 and the distance from the reference sample to the optical sensor head 135 is previously acquired and stored in the storage device 150a of the control device 150. The control device 150 calculates the amount of movement of the optical sensor head 135 based on the reference spectrum Sr of reflected light, the post-polishing spectrum Sa of reflected light, and the correlation.

[0167] Specifically, the control device 150 calculates, from the reference spectrum Sr and the above correlation, a reference distance, which is the distance from the reference sample to the optical sensor head 135 when the reference spectrum Sr was acquired. The control device 150 calculates, from the after-polishing spectrum Sa and the above correlation, a post-polishing distance, which is the distance from the reference sample to the optical sensor head 135 when the after-polishing spectrum Sa was acquired. The control device 150 calculates the amount by which the optical sensor head 135 should be moved by subtracting the after-polishing distance from the reference distance. In step S1302, the control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 by the calculated amount by which it should be moved. This allows the distance from the surface of the reference sample to the optical sensor head 135 to be maintained at the reference distance.

[0168] Figure 23 is a flowchart illustrating yet another embodiment of a method for moving the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum. Steps S1401 to S1403 shown in Figure 23 correspond to step S1114 in Figure 20. In this embodiment, the sample library described with reference to Figure 18 is pre-constructed in the storage device 150a of the control device 150. The sample library stores a plurality of sample spectra acquired in a plurality of positional relationships between the reference sample and the optical sensor head 135, where the distance from the reference sample to the optical sensor head 135 varies, in association with the distance from the reference sample to the optical sensor head 135 in each of the plurality of positional relationships.

[0169] In step S1401, the control device 150 determines, from the pre-constructed sample library, the sample spectrum whose shape is closest to the reference spectrum Sr and the sample spectrum whose shape is closest to the post-polishing spectrum Sa, as described with reference to FIG. 18 . In step S1402, the control device 150 calculates the amount of movement of the optical sensor head 135 based on the distance from the reference sample associated with the sample spectrum whose shape is closest to the reference spectrum Sr (i.e., the reference distance) to the optical sensor head 135 and the distance from the reference sample associated with the sample spectrum whose shape is closest to the post-polishing spectrum Sa (i.e., the post-polishing distance). Specifically, the control device 150 calculates the amount of movement of the optical sensor head 135 by subtracting the post-polishing distance from the reference distance. In step S1403, the control device 150 causes the sensor moving mechanism 140 to move the optical sensor head 135 by the calculated amount of movement. This allows the distance from the surface of the reference sample to be maintained at the reference distance.

[0170] FIG. 24 is a schematic diagram showing another embodiment of the optical sensor head 135. The configuration and operation of this embodiment, unless otherwise specifically described, are the same as those of the above-described embodiment. As shown in FIG. 24 , the optical sensor head 135 may be disposed at an angle. Specifically, the optical sensor head 135 may be composed of an obliquely disposed tip of a light-projecting optical fiber cable 132 and an obliquely disposed tip of a light-receiving optical fiber cable 133. The tips of the light-projecting optical fiber cable 132 and the light-receiving optical fiber cable 133 are inclined at the same angle toward each other. The optical sensor head 135 is configured to irradiate the surface of the substrate W with light at an angle and receive light reflected obliquely from the surface of the substrate W. It is preferable that the light-receiving optical fiber cable 133 receive light at an angle substantially equal to the angle of reflection of the light from the surface of the substrate W. In other words, it is preferable that the tip of the light-receiving optical fiber cable 133 is inclined so that the reflected light enters substantially perpendicular to the tip of the light-receiving optical fiber cable 133.

[0171] 25 is a diagram illustrating how the light receiving conditions of the optical sensor head 135, which is disposed at an angle as shown in FIG. 24, change as the polishing pad 102 wears. As shown in FIG. 25, as the polishing pad 102 wears, the light path between the light-projecting fiber optic cable 132 and the measurement point becomes shorter, 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 fiber optic cable 133 may not be able to properly receive the reflected light. As a result, the optical film thickness measurement device 130 may not be able to accurately measure the film thickness of the substrate W.

[0172] 24 , the screw hole 141 a provided in the sensor support member 141 of the sensor moving mechanism 140 is provided between the light-emitting optical fiber cable 132 and the light-receiving optical fiber cable 133, but the arrangement of the screw hole 141 a is not particularly limited to this embodiment. In the polishing apparatus 101 having the optical sensor head 135 shown in FIG. 24 , as in the embodiments described with reference to FIGS. 11 to 22 , the sensor moving mechanism 140 moves the optical sensor head 135 so as to minimize the difference between the reference spectrum and the post-polishing spectrum (or the reference sensor signal value and the post-polishing sensor signal value), thereby maintaining the distance from the surface of the reference sample to the optical sensor head 135 at the reference distance. As a result, the accuracy of film thickness measurement by the optical film thickness measurement device 130 having the optical sensor head 135 disposed within the polishing table 103 can be improved.

[0173] 11 to 25, the polishing apparatus 101 is provided with an optical film thickness measuring device as an example of the sensor 130, but the sensor 130 is not limited to the optical film thickness measuring device. Other examples of the sensor 130 include an eddy current film thickness measuring device, a proximity sensor, an acoustic sensor, and an imaging device.

[0174] The eddy current 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 the eddy currents, and output a monitoring sensor signal value. The eddy current 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 film thickness measuring device is disposed within the polishing table 103. The conditions for detecting the thickness of the metal on the substrate W by the eddy current film thickness measuring device are affected by the distance between the sensor head and the substrate W. When the sensor 130 is an eddy current film thickness measuring device, the control device 150 is configured to move the sensor head of the eddy current film thickness measuring device before and after polishing the substrate W so as to minimize the difference between the reference sensor signal value output by the eddy current film thickness measuring device after detecting a reference sample and the post-polishing sensor signal value.

[0175] The proximity sensor is configured to detect a detection object, such as a substrate W, placed above the polishing pad 102 and output a monitoring sensor signal value according 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. A sensor head of the proximity sensor is disposed within the polishing table 103. The detection conditions for the detection object by the proximity sensor are affected by the distance between the sensor head and the detection object. When the sensor 130 is a proximity sensor, the control device 150 is configured to move the sensor head of the proximity sensor before and after polishing the substrate W so as to minimize the difference between a reference sensor signal value output by the proximity sensor upon detecting a reference sample as the detection object and the post-polishing sensor signal value.

[0176] Examples of acoustic sensors include an acoustic emission (AE) sensor and an ultrasonic sensor. 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 toward 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 disposed within the polishing table 103. The detection conditions for the polishing sound of the substrate W and the ultrasonic waves reflected from the substrate W by the acoustic sensor are affected 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 ultrasonic waves reflected 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, polishing abnormalities 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. When the sensor 130 is an acoustic sensor, the control device 150 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 after detecting the reference sample and the post-polishing sensor signal value is minimized before and after polishing of the substrate W.

[0177] 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 monitoring sensor signal values ​​representing the intensity of light from the substrate W, and generate an image of the substrate W from the monitoring sensor signal values. The sensor head of the imaging device is disposed within the polishing table 103. The detection conditions for the light from the substrate W by the imaging device are affected by the distance between the sensor head and the substrate W. Specifically, a change in the distance between the sensor head and the substrate W can cause the image to become out of focus. When the sensor 130 is an imaging device, the control device 150 is configured to move the sensor head of the imaging device before and after polishing the substrate W so as to minimize the difference between the reference sensor signal values ​​output by the imaging device after detecting the reference sample and the image of the substrate W generated from the post-polishing sensor signal values. For example, the control device 150 moves the sensor head of the imaging device so as to minimize the difference in focus between the image of the substrate W generated from the reference sensor signal values ​​and the image of the substrate W generated from the post-polishing sensor signal values.

[0178] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would naturally be possible for a person skilled in the art, and the technical concept of the present invention may also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0179] The present invention can be used in a polishing apparatus and a polishing method for polishing a substrate such as a wafer.

[0180] REFERENCE SIGNS LIST 1 Polishing apparatus 2 Polishing pad 2a Polishing surface 2b Through hole 3 Polishing table 3a Pad support surface 3b Hole 5 Table shaft 6 Table motor 10 Polishing head 12 Polishing head shaft 20 Polishing liquid supply nozzle 30 Optical film thickness measuring device 31 Light source 32 Light projecting unit (light projecting optical fiber) 33 Light receiving unit (light receiving optical fiber) 35 Light receiving sensor head 37 Spectrometer 39 Spectral processing unit 41 First light amount sensor 42 Second light amount sensor 45 Head housing 50 Sensor moving mechanism 51 Sensor support member 51a Screw hole 53 First gear 54 Screw 56 Second gear 58 Motor 58a Rotating shaft 60 Operation control unit 60a Storage device 60b Arithmetic unit 70 Distance measuring device 75 Retaining ring 80 Electrostatic capacitance measuring device 82 Electrostatic capacitance sensor 83 Conductor target 85 Conductive wire 87, 88 Rotary connector 101 Polishing device 102 Polishing pad 102a Polishing surface 102b Through hole 103 Polishing table 103a Pad support surface 103b Hole 105 Table shaft 106 Table motor 110 Polishing head 112 Polishing head shaft 120 Liquid supply nozzle 130 Sensor (optical film thickness measuring device) 131 Light source 132 Light-emitting optical fiber cable 133 Light-receiving optical fiber cable 135 Sensor head (optical sensor head) 137 Spectrometer 139 Data processing unit 140 Sensor moving mechanism 141 Sensor support member 141a Screw hole 143 First gear 144 Screw 146 Second gear 148 Motor 148a Rotating shaft 150 Control device 150a Storage device 150b Arithmetic device

Claims

1. A polishing apparatus comprising: a polishing table having a pad support surface that supports a polishing pad; a polishing head that presses a substrate against the polishing surface of the polishing pad; an optical film thickness measuring device that irradiates light onto the substrate, receives light reflected from the substrate, and determines a measured film thickness of the substrate based on the reflected light; and an operation control unit, wherein the optical film thickness measuring device comprises a light projecting unit that irradiates the substrate with light, a light receiving unit that receives the light reflected from the substrate, and a first light intensity sensor and a second light intensity sensor that are arranged adjacent to the light receiving unit and detect the amount of light reflected from the substrate, and the operation control unit is configured to determine a position correction amount for the light projecting unit and the light receiving unit that corresponds to the amount of wear of the polishing pad based on the first light intensity detected by the first light intensity sensor and the second light intensity detected by the second light intensity sensor.

2. The polishing apparatus according to claim 1, wherein the first light quantity sensor and the second light quantity sensor are disposed at different positions in a direction perpendicular to the pad support surface.

3. The polishing apparatus according to claim 1, wherein said light-emitting portion and said light-receiving portion are inclined with respect to said pad support surface.

4. The polishing apparatus according to claim 1, wherein the light receiving portion is located between the first light quantity sensor and the second light quantity sensor.

5. The polishing apparatus of claim 1, wherein the operation control unit is configured to determine the position correction amount based on the correlation between the difference between the first light amount and the second light amount obtained in advance and the amount of wear on the polishing pad.

6. A polishing apparatus as described in claim 1, further comprising a sensor moving mechanism that moves the light-emitting unit and the light-receiving unit in the direction perpendicular to the pad support surface, and the operation control unit is configured to issue a command to the sensor moving mechanism to move the light-emitting unit and the light-receiving unit by the position correction amount.

7. A polishing apparatus as described in claim 6, wherein the light-emitting unit and the light-receiving unit are arranged in a hole formed inside the polishing table, and the sensor moving mechanism is configured to move the light-emitting unit and the light-receiving unit within the hole relative to the polishing table.

8. A polishing apparatus according to claim 1, wherein the first light amount and the second light amount are detected when the first light amount sensor and the second light amount sensor are covered by the substrate pressed against the polishing surface.

9. The polishing apparatus of claim 8, wherein the first amount of light and the second amount of light are detected while the substrate is being polished.

10. A polishing apparatus as described in claim 8, wherein the first light amount and the second light amount are detected during idling operation in which polishing of the substrate is not progressing and when the substrate is pressed against the polishing surface with a pressing force applied during polishing of the substrate.

11. A polishing method comprising: pressing a substrate against the polishing surface of a polishing pad supported on the pad support surface of a polishing table; irradiating the substrate with light from a light-projecting unit of an optical film thickness measuring device that determines a film thickness measurement value of the substrate; receiving light reflected from the substrate by a light-receiving unit of the optical film thickness measuring device; detecting the amount of light reflected from the substrate by a first light intensity sensor and a second light intensity sensor arranged adjacent to the light-receiving unit; and determining a position correction amount of the light-projecting unit and the light-receiving unit corresponding to the amount of wear of the polishing pad based on a first light intensity detected by the first light intensity sensor and a first light intensity detected by the second light intensity sensor.

12. The polishing method according to claim 11, wherein the first light quantity sensor and the second light quantity sensor are disposed at different positions in a direction perpendicular to the pad support surface.

13. A polishing method as described in claim 11, wherein irradiating the substrate with light means irradiating the light at an angle with respect to the surface of the substrate to be polished, and receiving the reflected light from the substrate means receiving the reflected light that is reflected at an angle with respect to the surface of the substrate to be polished.

14. The polishing method according to claim 11, wherein the light receiving portion is located between the first light quantity sensor and the second light quantity sensor.

15. The polishing method described in claim 11, wherein determining the position correction amount based on the first light amount and the second light amount is determining the position correction amount based on the correlation between the difference between the first light amount and the second light amount, which has been obtained in advance, and the amount of wear on the polishing pad.

16. The polishing method according to claim 11, further comprising moving the light projecting unit and the light receiving unit by the position correction amount along the direction perpendicular to the pad support surface.

17. A polishing method according to claim 16, wherein the light projecting unit and the light receiving unit are moved relative to the polishing table within holes formed inside the polishing table.

18. A polishing method according to claim 11, wherein the detection of the first light amount and the second light amount is performed when the first light amount sensor and the second light amount sensor are covered by the substrate pressed against the polishing surface.

19. The polishing method according to claim 18, wherein pressing the substrate against the polishing surface comprises rotating the polishing table and pressing the substrate against the polishing surface with the polishing head to polish the substrate, and wherein the first light amount and the second light amount are detected while the substrate is being polished.

20. The polishing method described in claim 18, wherein pressing the substrate against the polishing surface comprises pressing the substrate against the polishing surface with a pressing force applied during polishing of the substrate while the polishing table is stopped from rotating during idling operation in which polishing of the substrate is not progressing, and wherein the detection of the first light amount and the second light amount is performed during the idling operation.

21. A polishing method comprising: when a polishing pad supported on a polishing table is in an initial state, a sensor having a sensor head arranged in 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; while the substrate is being polished, the sensor detects the substrate and outputs a monitoring sensor signal value; 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 moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized.

22. The polishing method according to claim 21, wherein moving the sensor head comprises moving the sensor head along a direction perpendicular to a pad support surface of the polishing table that supports the polishing pad.

23. The polishing method according to claim 21, wherein 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 that represents the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value that represents 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 that represents the intensity of reflected light from the reference sample located on the polishing pad after polishing of the substrate has been completed.

24. The polishing method of claim 23, further comprising: generating a reference spectrum of reflected light from the reference sensor signal value; and generating a post-polishing spectrum of reflected light from the post-polishing sensor signal value; and moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized by moving the optical sensor head so that the difference between the reference spectrum and the post-polishing spectrum is minimized.

25. The polishing method of claim 21, further comprising obtaining a correlation between a sensor signal value output by the sensor when the reference sample on the polishing pad is detected and a distance from the reference sample to the sensor head, and moving the sensor head so that the difference between the reference sensor signal value and the post-polishing sensor signal value is minimized by: 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.

26. The polishing method according to claim 21, further comprising: detecting the reference sample on the polishing pad by the sensor in a plurality of positional relationships between the reference sample and the sensor head, the distances from the reference sample to the sensor head being different, and outputting a plurality of sample sensor signal values; and constructing a sample library by storing the plurality of sample sensor signal values ​​in association with the distances from the reference sample to the sensor head in the plurality of positional relationships, respectively; and moving the sensor head so as to minimize the difference between the reference sensor signal value and the post-polishing sensor signal value comprises: determining, from the sample library, the sample sensor signal value that is the smallest in difference from the reference sensor signal value and the sample sensor signal value that is the smallest in difference from the post-polishing sensor signal value; calculating an amount by which the sensor head should be moved based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that is the smallest in 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 is the smallest in difference from the post-polishing sensor signal value; and moving the sensor head by the amount by which the sensor head should be moved.

27. The polishing method of claim 21, 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 occur during water polishing of the reference specimen.

28. A polishing apparatus comprising: a polishing table that supports a polishing pad; a polishing head that polishes a substrate by pressing the substrate against the polishing surface of the polishing pad; a sensor having a sensor head arranged within the polishing table that detects the substrate and outputs a monitoring sensor signal value; a sensor moving mechanism that moves the sensor head; and a control device that controls the operation of the sensor moving mechanism, wherein the control device is configured to cause the sensor moving mechanism to move the sensor head so as to minimize the difference between a reference sensor signal value output by the sensor when a reference sample located on the polishing pad in an initial state is detected by the sensor, and a post-polishing sensor signal value output by the sensor when the reference sample located on the polishing pad after polishing of the substrate is completed.

29. A polishing apparatus according to claim 28, wherein the sensor moving mechanism is configured to move the sensor head along a direction perpendicular to a pad support surface of the polishing table that supports the polishing pad.

30. A polishing apparatus as described in claim 28, wherein 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 that represents the intensity of reflected light from the substrate during polishing, the reference sensor signal value is a sensor signal value that represents 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 that represents the intensity of reflected light from the reference sample located on the polishing pad after polishing of the substrate is completed.

31. A polishing apparatus according to claim 30, wherein the optical film thickness measuring device is configured to generate a reference spectrum of reflected light from the reference sensor signal value and to generate a post-polishing spectrum of reflected light from the post-polishing sensor signal value, and the control device is configured to cause the sensor moving mechanism to move the optical sensor head so that the difference between the reference spectrum and the post-polishing spectrum is minimized.

32. The polishing apparatus of claim 28, wherein the control device is configured to: obtain a correlation between a sensor signal value output by the sensor when the reference sample on the polishing pad is detected and the distance from the reference sample to the sensor head; calculate an amount to which the sensor head should be moved based on the reference sensor signal value, the post-polishing sensor signal value, and the correlation; and cause the sensor moving mechanism to move the sensor head by the amount to which it should be moved.

33. The polishing apparatus described in claim 28, wherein the sensor is configured to detect the reference sample on the polishing pad at a plurality of positional relationships between the reference sample and the sensor head, each of which has a different distance from the reference sample to the sensor head, and output a plurality of sample sensor signal values; and the control device is configured to: construct a sample library by storing the plurality of sample sensor signal values ​​in association with the distance from the reference sample to the sensor head at the plurality of positional relationships; determine from the sample library the sample sensor signal value that is smallest in difference from the reference sensor signal value and the sample sensor signal value that is smallest in difference from the post-polishing sensor signal value; calculate the amount by which the sensor head should be moved based on the distance from the reference sample to the sensor head associated with the sample sensor signal value that is smallest in 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 is smallest in difference from the post-polishing sensor signal value; and cause the sensor moving mechanism to move the sensor head by the amount by which it should be moved.

34. A polishing apparatus as described in claim 28, wherein the reference sensor signal value is a sensor signal value output by the sensor when the reference sample is detected during water polishing of the reference sample using the polishing pad in the initial state, and the post-polishing sensor signal value is a sensor signal value output by the sensor when the reference sample is detected during water polishing of the reference sample using the polishing pad after polishing of the substrate has been completed.

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