Polishing method and polishing apparatus

Abstract

To provide a polishing method and a polishing device capable of correctly determining the position of a measuring point of the film thickness of a workpiece.SOLUTION: In the polishing method, a first image of a first region and a second image of a second region in the surface of the workpiece W are generated by the imaging device 24 at predetermined time intervals during polishing of the workpiece W. Calculating a rotation angle of the workpiece W per unit time based on a tilt angle of the pattern on the first image, a tilt angle of the pattern on the second image, and the predetermined time interval, and calculating a time difference between a measurement time at which the film thickness at the measurement point MP is measured and an imaging time at which the second image is generated; The coordinates of the measurement point on the surface of the workpiece W are determined based on the relative position between the measurement point MP and the center point of the workpiece W, the rotation angle of the workpiece W per unit time, and the time difference.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a technique for polishing a workpiece such as a wafer, substrate, or panel while measuring the film thickness of the workpiece, and more particularly to a technique for identifying a film thickness measurement point. [Background technology]

[0002] In chemical mechanical polishing (CMP), a workpiece (e.g., a wafer) is rotated by a polishing head while being pressed against a polishing pad mounted on a rotating polishing table to polish the surface of the workpiece. While the workpiece is being polished, a polishing liquid (e.g., a slurry) is supplied onto the polishing pad.

[0003] A film thickness sensor is installed inside the polishing table to measure the film thickness on the workpiece. The film thickness sensor measures the film thickness as it moves across the workpiece while it is being polished. Examples of film thickness sensors include optical sensors and eddy current sensors. The film thickness sensor measures the film thickness at multiple measurement points, tracing a different path each time it moves across the workpiece. Therefore, the measurement points are distributed over the entire surface of the workpiece. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2022-108789 Summary of the Invention [Problem to be solved by the invention]

[0005] The film thickness of a workpiece varies not only in the radial direction of the workpiece but also in the circumferential direction of the workpiece. In order to polish the workpiece so as to reduce the film thickness variation in the circumferential direction of the workpiece, it is necessary to measure the film thickness variation in the circumferential direction during polishing of the workpiece.

[0006] However, during polishing of a workpiece, the workpiece may not rotate integrally with the polishing head, but may rotate within the polishing head relative to the polishing head. As a result, the rotational speed of the workpiece does not necessarily match the rotational speed of the polishing head. As a result, it is not possible to identify the position of the measurement point in the circumferential direction of the workpiece, which makes it difficult to accurately control the film thickness in the circumferential direction of the workpiece.

[0007] Therefore, the present invention provides a polishing method and a polishing apparatus that can accurately determine the position of the measurement point for the film thickness of a workpiece. [Means for solving the problem]

[0008] In one aspect, a polishing method is provided, which includes polishing a workpiece having a patterned surface by pressing the workpiece against a polishing pad on the polishing table while rotating a polishing table to which a film thickness sensor and an imaging device are fixed, and generating a first image of a first region and a second image of a second region within the surface of the workpiece at predetermined time intervals while polishing the workpiece, measuring a film thickness at a measurement point on the surface of the workpiece while polishing the workpiece, calculating a rotation angle of the workpiece per unit time based on the tilt angle of the pattern on the first image, the tilt angle of the pattern on the second image, and the predetermined time interval, calculating a time difference between the measurement time when the film thickness at the measurement point was measured and the imaging time when the second image was generated, and determining the coordinates of the measurement point on the surface of the workpiece based on the relative position between the measurement point and a center point of the workpiece, the rotation angle of the workpiece per unit time, and the time difference.

[0009] In one embodiment, the second region includes a center point of the workpiece. In one aspect, determining the coordinates of the measurement point involves determining the tilt angle of a predefined coordinate system on the surface of the workpiece based on the tilt angle of the pattern on the second image, calculating the rotation angle of the coordinate system that rotates during the time difference by multiplying the rotation angle of the workpiece per unit time by the time difference, determining a coordinate system at the measurement time by rotating the coordinate system at the imaging time around the center point of the workpiece by the calculated rotation angle, and determining the coordinate of the measurement point on the coordinate system at the measurement time from the relative position between the measurement point and the center point of the workpiece. In one aspect, calculating the rotation angle of the workpiece per unit time involves calculating the difference in tilt angle of the pattern between the first image and the second image, and dividing the difference in tilt angle by the predetermined time interval to calculate the rotation angle of the workpiece per unit time. In one aspect, the polishing method further includes generating an image of the gap between the inner circumference of the retaining ring of the polishing head and the outer circumference of the workpiece using the imaging device while polishing the workpiece, calculating the dimensions of the gap from the image, and correcting the coordinates of the measurement point based on the dimensions of the gap.

[0010] In one aspect, a polishing apparatus is provided, comprising: a polishing table for supporting a polishing pad; a table motor for rotating the polishing table; a polishing head for pressing a workpiece having a patterned surface against the polishing pad on the polishing table to polish the workpiece; a film thickness sensor fixed to the polishing table for measuring a film thickness at a measurement point on the surface of the workpiece; an imaging device fixed to the polishing table for generating a first image of a first region and a second image of a second region on the surface of the workpiece at a predetermined time interval; and a processing control unit for determining coordinates of the measurement point on the surface of the workpiece, wherein the processing control unit is configured to calculate a rotation angle of the workpiece per unit time based on the tilt angle of the pattern on the first image, the tilt angle of the pattern on the second image, and the predetermined time interval; calculate a time difference between the measurement time at which the film thickness at the measurement point was measured and the imaging time at which the second image was generated; and determine the coordinates of the measurement point on the surface of the workpiece based on the relative position between the measurement point and a center point of the workpiece, the rotation angle of the workpiece per unit time, and the time difference.

[0011] In one embodiment, the second region includes a center point of the workpiece. In one aspect, the processing control unit is configured to determine the tilt angle of a predefined coordinate system on the surface of the workpiece based on the tilt angle of the pattern on the second image, calculate the rotation angle of the coordinate system that rotates during the time difference by multiplying the rotation angle of the workpiece per unit time by the time difference, determine the coordinate system at the measurement time by rotating the coordinate system at the imaging time around the center point of the workpiece by the calculated rotation angle, and determine the coordinate of the measurement point on the coordinate system at the measurement time from the relative position between the measurement point and the center point of the workpiece. In one aspect, the processing control unit is configured to calculate a difference in tilt angle of the pattern between the first image and the second image, and calculate the rotation angle of the workpiece per unit time by dividing the difference in tilt angle by the predetermined time interval. In one aspect, the processing control unit is configured to generate an image of the gap between the inner circumference of the retaining ring of the polishing head and the outer circumference of the workpiece using the imaging device while the workpiece is being polished, calculate the dimensions of the gap from the image, and correct the coordinates of the measurement point based on the dimensions of the gap. [Effects of the Invention]

[0012] The rotation angle per unit time of the workpiece can be calculated from the two images of the first and second regions of the workpiece, and the coordinates of the film thickness measurement point on the workpiece can be determined based on this rotation angle per unit time. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a polishing apparatus. [Figure 2] FIG. 2 is a schematic diagram illustrating an embodiment of an imaging device fixed to a polishing table. [Figure 3] FIG. 2 is a cross-sectional view showing one embodiment of a polishing head. [Figure 4] FIG. 2 is a top view showing the positional relationship between the polishing table and the workpiece held by the polishing head. [Figure 5] 3A and 3B are schematic diagrams showing examples of a first image and a second image generated by an imaging device. [Figure 6] FIG. 2 is a schematic diagram showing an example of a coordinate system defined on the surface of a workpiece. [Figure 7] 1 is a schematic diagram showing an example of image generation by an imaging device and film thickness measurement by a film thickness sensor. FIG. [Figure 8] 10A and 10B are schematic diagrams showing another example of image generation by an imaging device and film thickness measurement by a film thickness sensor. [Figure 9] FIG. 10 is a schematic diagram showing yet another example of image generation by an imaging device and film thickness measurement by a film thickness sensor. [Figure 10] FIG. 10 is a top view showing another embodiment of the film thickness sensor. [Figure 11]11 is a schematic diagram showing an example of image generation by the imaging device shown in FIG. 10 and film thickness measurement by a film thickness sensor. FIG. [Figure 12] 11 is a schematic diagram showing another example of image generation by the imaging device shown in FIG. 10 and film thickness measurement by the film thickness sensor. FIG. [Figure 13] 10A and 10B are diagrams illustrating an embodiment of the operation of the imaging device and the processing control unit. [Figure 14] FIG. 10 is a schematic diagram showing an example of an image of a gap between a retaining ring and a workpiece, generated by an imaging device. [Figure 15] 10A and 10B are diagrams illustrating an embodiment of a process for correcting the coordinates of film thickness measurement points based on the dimensions of the gap. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing one embodiment of a polishing apparatus. As shown in Fig. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head 1 that presses a workpiece W against the polishing pad 2, a table motor 6 that rotates the polishing table 3, and a polishing liquid supply nozzle 5 that supplies a polishing liquid (e.g., a slurry containing abrasive grains) onto the polishing pad 2. The surface of the polishing pad 2 forms a polishing surface 2a that polishes the workpiece W.

[0015] Specific examples of the workpiece W include wafers, wiring substrates, square substrates, etc. used in the manufacture of semiconductor devices. The workpiece W has a surface on which a pattern is formed. Specific examples of the pattern include cells for forming wiring, scribe lines (dicing lines), etc.

[0016] The polishing table 3 is connected to a table motor 6, which is configured to rotate the polishing table 3 and the polishing pad 2 together. The polishing head 1 is fixed to the end of a polishing head shaft 11, which is rotatably supported by a head arm 15. The head arm 15 is rotatably supported by a support shaft 16.

[0017] The polishing head shaft 11 is connected to a vertical movement mechanism 18 disposed within the head arm 15. The vertical movement mechanism 18 is configured to move the polishing head shaft 11 up and down in its axial direction. The vertical movement of the polishing head shaft 11 by the vertical movement mechanism 18 can move the workpiece W held by the polishing head 1 toward or away from the polishing pad 2 on the polishing table 3. The configuration of the vertical movement mechanism 18 is not particularly limited, but in one example, the vertical movement mechanism 18 includes a servo motor, a ball screw mechanism, or the like.

[0018] The polishing head shaft 11 is connected to a polishing head rotating device 20 disposed within the head arm 15. The polishing head rotating device 20 is configured to rotate the polishing head shaft 11 and the polishing head 1 around their respective axes. The configuration of the polishing head rotating device 20 is not particularly limited, but in one example, the polishing head rotating device 20 includes an electric motor, a belt, a pulley, etc.

[0019] The polishing apparatus further includes a process control unit 9 that controls the operation of each component of the polishing apparatus. The process control unit 9 is electrically connected to the polishing head 1, the table motor 6, the polishing head rotating device 20, the polishing liquid supply nozzle 5, and the vertical movement mechanism 18, and controls the operation of the polishing head 1, the table motor 6, the polishing head rotating device 20, the polishing liquid supply nozzle 5, and the vertical movement mechanism 18.

[0020] The process control unit 9 includes a storage device 9a storing a program and an arithmetic unit 9b that executes calculations according to instructions included in the program. The process control unit 9 is composed of at least one computer. The storage device 9a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the arithmetic unit 9b include a CPU (central processing unit) and a GPU (graphics processing unit). However, the specific configuration of the process control unit 9 is not limited to these examples. The process control unit 9 may also be composed of multiple computers.

[0021] The workpiece W is polished as follows. The process control unit 9 issues commands to the table motor 6, polishing head rotation device 20, and polishing liquid supply nozzle 5 to rotate the polishing table 3 and polishing head 1 in the directions indicated by the arrows in FIG. 1, while supplying polishing liquid from the polishing liquid supply nozzle 5 to the polishing surface 2a of the polishing pad 2 on the polishing table 3. While being rotated by the polishing head 1, the workpiece W is pressed against the polishing surface 2a of the polishing pad 2 by the polishing head 1, with the polishing liquid present between the polishing pad 2 and the workpiece W. The surface of the workpiece W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid and / or the polishing pad 2.

[0022] The polishing apparatus further includes a film thickness sensor 21 that measures the film thickness of the workpiece W on the polishing pad 2. The film thickness sensor 21 is fixed to the polishing table 3 and rotates integrally therewith. The film thickness sensor 21 is configured to measure the film thickness at a measurement point on the surface of the workpiece W each time it traverses the surface of the workpiece W. Specific examples of the film thickness sensor 21 include an optical film thickness sensor and an eddy current film thickness sensor, but the type of film thickness sensor 21 is not particularly limited as long as it can measure the film thickness of the workpiece W. The film thickness sensor 21 is electrically connected to the process control unit 9, and the measured film thickness is transmitted from the film thickness sensor 21 to the process control unit 9.

[0023] The polishing apparatus further includes an imaging device 24 that generates an image of the surface of the workpiece W on the polishing pad 2. The film thickness sensor 21 is fixed to the polishing table 3 and rotates integrally with the polishing table 3. The imaging device 24 is configured to generate multiple images of multiple regions within the surface of the workpiece W at predetermined time intervals while moving across the surface of the workpiece W.

[0024] FIG. 2 is a schematic diagram showing one embodiment of an imaging device 24 fixed to the polishing table 3. As shown in FIG. 2, the imaging device 24 is disposed within the polishing table 3. The polishing pad 2 has a through-hole 2b located above the imaging device 24. The through-hole 2b is covered with a transparent window 25 made of a transparent material such as transparent resin or glass. The imaging device 24 generates an image of an area within the surface of the workpiece W through the transparent window 25. The imaging device 24 is electrically connected to the processing control unit 9, and the image is transmitted from the imaging device 24 to the processing control unit 9 shown in FIG. 1.

[0025] Next, the polishing head 1 will be described. Fig. 3 is a cross-sectional view showing one embodiment of the polishing head 1. The polishing head 1 includes a carrier 31 fixed to the end of the polishing head shaft 11, an elastic membrane 34 attached to the lower part of the carrier 31, and a retainer ring 32 disposed below the carrier 31. The retainer ring 32 is disposed around the elastic membrane 34. The retainer ring 32 is an annular structure that holds the workpiece W to prevent it from flying out of the polishing head 1 while it is being polished.

[0026] The elastic membrane 34 includes a contact portion 35 having a contact surface 35a that can come into contact with the upper surface of the workpiece W, and inner wall portions 36a, 36b, 36c and an outer wall portion 36d that are connected to the contact portion 35. The contact portion 35 has substantially the same size and shape as the upper surface of the workpiece W. The inner wall portions 36a, 36b, 36c and the outer wall portion 36d are endless walls that are arranged concentrically.

[0027] A plurality of pressure chambers 38A, 38B, 38C, and 38D (four in this embodiment) are provided between the elastic membrane 34 and the carrier 31. The pressure chambers 38A, 38B, 38C, and 38D are formed by the contact portion 35, inner wall portions 36a, 36b, and 36c, and outer wall portion 36d of the elastic membrane 34. In this embodiment, the elastic membrane 34 forms four pressure chambers 38A to 38D, but in another embodiment, the elastic membrane 34 may form three pressure chambers, or may form five or more pressure chambers.

[0028] An annular membrane (rolling diaphragm) 40 is disposed between the carrier 31 and the retainer ring 32, and a pressure chamber 38E is formed inside this membrane 40. Gas transfer lines F1, F2, F3, F4, and F5 are connected to the pressure chambers 38A, 38B, 38C, 38D, and 38E, respectively. The gas transfer lines F1, F2, F3, F4, and F5 extend via a rotary joint 45 attached to the polishing head shaft 11.

[0029] The gas transfer lines F1, F2, F3, F4, and F5 are connected to a compressed gas supply source (not shown) that serves as a utility supply source provided in the factory where the polishing apparatus is installed. Compressed gas such as compressed air is supplied to the pressure chambers 38A, 38B, 38C, 38D, and 38E through the gas transfer lines F1, F2, F3, F4, and F5, respectively.

[0030] The pressure regulators Ra1 to Ra5 ​​are connected to the gas transfer lines F1, F2, F3, F4, and F5, respectively. The pressure regulators Ra1 to Ra5 ​​can independently change the pressures in the pressure chambers 38A to 38E. Therefore, the polishing head 1 can independently adjust the polishing pressures for the four corresponding regions of the workpiece W, namely, the center, inner middle, outer middle, and edge regions, and the pressing force of the retaining ring 32 against the polishing surface 2a of the polishing pad 2. For example, the polishing head 1 can press different regions of the surface of the workpiece W against the polishing surface 2a of the polishing pad 2 with different pressing forces. Therefore, the polishing head 1 can control the film thickness profile of the workpiece W to achieve a target film thickness profile.

[0031] FIG. 4 is a top view showing the positional relationship between the polishing table 3 and the workpiece W held by the polishing head 1. The polishing pad 2, the carrier 31 of the polishing head 1, and the elastic membrane 34 are not shown in FIG. 4. The workpiece W is rotated by the polishing head 1, but the workpiece W may rotate within the polishing head 1 relative to the polishing head 1. Therefore, the rotational speed of the workpiece W may not match the rotational speed of the polishing head 1. In the example shown in FIG. 4, the workpiece W rotates around the center point CP of the workpiece W within the retaining ring 32, as indicated by the arrow. The film thickness sensor 21 and the imaging device 24 are located at the same radial distance from the center TP of the polishing table 3. Therefore, the film thickness sensor 21 and the imaging device 24 move along the same path J.

[0032] 4, the radial distance of the film thickness sensor 21 and the imaging device 24 from the center TP of the polishing table 3 is the same as the radial distance of the center of the retaining ring 32 (the center of the polishing head 1) from the center TP of the polishing table 3. Therefore, the film thickness sensor 21 and the imaging device 24 cross the center point CP of the workpiece W every time the polishing table 3 rotates once.

[0033] The film thickness sensor 21 is located at a distance from the imaging device 24. In the embodiment shown in Fig. 4, the imaging device 24 is located in front of the film thickness sensor 21 in the rotation direction of the polishing table 3. Therefore, the imaging device 24 generates an image of the surface of the workpiece W, and then the film thickness sensor 21 measures the film thickness at a predetermined measurement point on the surface of the workpiece W.

[0034] The polishing apparatus is equipped with an angle detector 50 that detects the rotation angle of the polishing table 3. In the embodiment shown in FIG. 4, the angle detector 50 has a sensor target 52 arranged adjacent to the polishing table 3 and a proximity sensor 51 fixed to the polishing table 3 and detecting the sensor target 52. The sensor target 52 is fixed to a fixed member (not shown), and the position of the sensor target 52 is fixed. The proximity sensor 51 rotates integrally with the polishing table 3. Every time the polishing table 3 rotates once, the proximity sensor 51 detects the sensor target 52.

[0035] Because the sensor target 52 is stationary, the rotation angle of the polishing table 3 is uniquely determined at the time when the proximity sensor 51 detects the sensor target 52. Therefore, the angle detector 50, which is a combination of the proximity sensor 51 and the sensor target 52, can detect the rotation angle of the polishing table 3. The angle detector 50 is configured to transmit an angle detection signal to the processing control unit 9 when the proximity sensor 51 detects the sensor target 52.

[0036] The process control unit 9 can determine other rotation angles of the polishing table 3 from the rotation speed of the polishing table 3 and the time when the proximity sensor 51 detects the sensor target 52. For example, the rotation angle of the polishing table 3 at a time when a predetermined time has elapsed since the proximity sensor 51 detected the sensor target 52 can be calculated from the rotation angle of the polishing table 3 at the time when the proximity sensor 51 detected the sensor target 52, the rotation speed of the polishing table 3, and the predetermined time.

[0037] In one embodiment, the sensor target 52 may be fixed to the polishing table 3, and the proximity sensor 51 may be fixed to the above-mentioned fixed member (not shown). In this case, the sensor target 52 rotates integrally with the polishing table 3, and the proximity sensor 51 is stationary. In another embodiment, the angle detector 50 that detects the rotation angle of the polishing table 3 may be a rotary encoder built into or connected to the table motor 6.

[0038] 4, the imaging device 24 is configured to generate a first image of a first region C1 and a second image of a second region C2 within the surface of the workpiece W at predetermined time intervals. More specifically, when the imaging device 24 is positioned below the workpiece W, the processing control unit 9 instructs the imaging device 24 to generate images of the surface of the workpiece W multiple times at predetermined time intervals. As a result, the imaging device 24 generates a first image of the first region C1 and a second image of the second region C2 within the surface of the workpiece W at predetermined time intervals. In one embodiment, the second region C2 includes the center point CP of the workpiece W. The first and second images are transmitted from the imaging device 24 to the processing control unit 9.

[0039] The timing for generating the first image of the first region C1 and the second image of the second region C2 is determined based on the rotation angle of the polishing table 3 detected by the angle detector 50. That is, when the rotation angle of the polishing table 3 reaches a predetermined angle, the processing control unit 9 issues a command to the imaging device 24 to generate multiple images of the surface of the workpiece W at predetermined time intervals, and as a result, a first image of the first region C1 and a second image of the second region C2 within the surface of the workpiece W are generated.

[0040] FIG. 5 is a schematic diagram showing an example of a first image PI1 and a second image PI2 generated by the imaging device 24. As shown in FIG. 5, a pattern is formed on the surface of the workpiece W. Specific examples of the pattern include a wiring pattern, a cell, a scribe line, and a dicing line. There is a time difference t2-t1 between the imaging time t1 at which the first image PI1 is generated and the imaging time t2 at which the second image PI2 is generated. This time difference t2-t1 corresponds to the above-mentioned predetermined time interval when the imaging device 24 generates the first image PI1 and the second image PI2 of the surface of the workpiece W.

[0041] When the workpiece W is rotating, the tilt angle of the pattern appearing in the first image PI1 differs from the tilt angle of the pattern appearing in the second image PI2. The processing control unit 9 calculates the tilt angle θ1 of the pattern on the first image PI1 with respect to the reference line RL and the tilt angle θ2 of the pattern on the second image PI2 with respect to the reference line RL. The reference line RL is not particularly limited, but is, for example, a straight line extending parallel to one side of the image captured by the imaging device 24.

[0042] The process control unit 9 is configured to calculate the rotation angle of the workpiece W per unit time based on the tilt angle θ1 of the pattern on the first image PI1, the tilt angle θ2 of the pattern on the second image PI2, and the above-mentioned predetermined time interval (t2 - t1). More specifically, the process control unit 9 calculates the difference (θ2 - θ1) between the tilt angle θ1 of the pattern on the first image PI1 and the tilt angle θ2 of the pattern on the second image PI2, and divides the tilt angle difference (θ2 - θ1) by the time interval (t2 - t1) to calculate the rotation angle of the workpiece W per unit time. In this embodiment, two images PI1 and PI2 are used to calculate the rotation angle of the workpiece W per unit time, but in other embodiments, three or more images may be used to calculate the rotation angle of the workpiece W per unit time.

[0043] After the imaging device 24 generates the first image PI1 and the second image PI2, the film thickness sensor 21 measures the film thickness at a predetermined measurement point on the surface of the workpiece W. The position of the predetermined measurement point on the surface of the workpiece W is identified by coordinates on the coordinate system shown in FIG. 6. FIG. 6 is a schematic diagram showing an example of a coordinate system defined on the surface of the workpiece W. The workpiece W has a notch 60 on its edge portion. In this example, the Y axis of the coordinate system passes through the notch 60 and the center point CP of the workpiece W, and the X axis passes through the center point CP of the workpiece W and is perpendicular to the Y axis. This coordinate system is a Cartesian coordinate system. In the following description, the coordinate system defined on the surface of the workpiece W may be referred to as an XY coordinate system.

[0044] 6, a plurality of patterns 100 are formed on the surface of the workpiece W. These patterns 100 are arranged along the Y-axis and X-axis of the XY coordinate system. That is, the arrangement direction of the plurality of patterns 100 is parallel to the Y-axis and X-axis of the XY coordinate system.

[0045] 7 is a schematic diagram showing an example of image generation by the imaging device 24 and film thickness measurement by the film thickness sensor 21. As shown in FIG. 7, when the imaging device 24 is positioned directly below the center point CP of the workpiece W, the processing control unit 9 issues a command to the imaging device 24 to generate a second image PI2 of a second region (see symbol C2 in FIG. 4) including the center point CP (imaging time t2). The processing control unit 9 determines the tilt angle of the XY coordinate system defined on the surface of the workpiece W based on the tilt angle of the pattern on the second image PI2 (e.g., angle θ2 in FIG. 5). The tilt angle of the XY coordinate system at imaging time t2 matches the tilt angle of the pattern on the second image PI2.

[0046] When the film thickness sensor 21 is positioned below the workpiece W, the process control unit 9 issues a command to the film thickness sensor 21 to measure the film thickness at a measurement point MP on the surface of the workpiece W (measurement time t3). Although the coordinates of the measurement point MP on the coordinate system shown in FIG. 7 are unknown at this time, the relative position of the measurement point MP with respect to the center point CP of the workpiece W can be determined from the radial distance between the film thickness sensor 21 and the center TP of the polishing table 3 and the rotation angle of the polishing table 3 at measurement time t3. That is, during polishing of the workpiece W, the position of the center point CP of the workpiece W with respect to the polishing table 3 is fixed. Meanwhile, the film thickness sensor 21 moves relative to the center point CP of the workpiece W. The path J that the film thickness sensor 21 takes across the surface of the workpiece W is determined by the radial distance between the film thickness sensor 21 and the center TP of the polishing table 3. The process control unit 9 can uniquely determine the relative position of the film thickness sensor 21 with respect to the center point CP of the workpiece W based on the radial distance between the film thickness sensor 21 and the center TP of the polishing table 3 and the rotation angle of the polishing table 3.

[0047] In one example, the process control unit 9 calculates a measurement time t3, which is the time when a predetermined delay time has elapsed since the process control unit 9 received an angle detection signal sent from an angle detector 50 consisting of a proximity sensor 51 and a sensor target 52, and at the measurement time t3 issues a command to the film thickness sensor 21 to measure the film thickness at a measurement point MP on the surface of the workpiece W. The predetermined delay time is determined from the difference between the position of the film thickness sensor 21 and the position of the measurement point MP on the workpiece W when the process control unit 9 received the angle detection signal, and the rotation speed of the polishing table 3.

[0048] In another example, the process control unit 9 receives the rotation angle of the polishing table 3 sent from the angle detector 50, which is made up of a rotary encoder, and at measurement time t3, when the rotation angle of the polishing table 3 reaches a predetermined measurement angle, issues a command to the film thickness sensor 21 to measure the film thickness at the measurement point MP on the surface of the workpiece W. In this way, the relative position of the measurement point MP with respect to the center point CP of the workpiece W can be determined from the radial distance between the film thickness sensor 21 and the center TP of the polishing table 3 and the rotation angle of the polishing table 3 at measurement time t3.

[0049] As shown in FIG. 7, the film thickness sensor 21 is spaced apart from the imaging device 24 in the circumferential direction of the polishing table 3. Therefore, there is a time difference t3-t2 between the measurement time t3 at which the film thickness sensor 21 measures the film thickness at the measurement point MP and the imaging time t2 at which the imaging device 24 generates the second image PI2 (see FIG. 5) of the second region including the center point CP of the workpiece W. During this time difference t3-t2, the workpiece W rotates around its center point CP. The rotational speed of the workpiece W at this time is expressed by the rotation angle of the workpiece W per unit time described above. In the embodiment shown in FIG. 7, the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 is longer than the radius of the workpiece W, but the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 is not limited to this embodiment.

[0050] The process control unit 9 determines the coordinates of the measurement point MP on the surface of the workpiece W as follows: The process control unit 9 calculates the time difference t3-t2 between the measurement time t3 at which the film thickness at the measurement point MP was measured and the imaging time t2 at which the second image PI2 was generated, and determines the coordinates of the measurement point on the surface of the workpiece W based on the relative position between the measurement point MP and the center point CP of the workpiece W, the rotation angle of the workpiece W per unit time, and the time difference t3-t2.

[0051] During the time difference t3-t2, the workpiece W rotates around its center point CP. Therefore, the XY coordinate system defined on the surface of the workpiece W also rotates around the center point CP of the workpiece W during the time difference t3-t2. The processing control unit 9 calculates the rotation angle of the XY coordinate system that rotates during the time difference t3-t2 by multiplying the rotation angle of the workpiece W per unit time by the time difference t3-t2. Furthermore, as shown in FIG. 7, the processing control unit 9 determines the XY coordinate system at the measurement time t3 by rotating the XY coordinate system at the imaging time t2 around the center point CP of the workpiece W by the calculated rotation angle. The actual position of the measurement point MP on the surface of the workpiece W is identified by the coordinates of the measurement point MP on the XY coordinate system at the measurement time t3.

[0052] In this way, the processing control unit 9 can determine the coordinates of the measurement point MP (i.e., the actual position of the measurement point MP) that reflect the free rotation of the workpiece W within the retaining ring 32. The coordinates of the measurement point MP identify not only the radial position of the workpiece W but also the circumferential position of the workpiece W. Therefore, it is possible to obtain not only the film thickness profile of the workpiece W in the radial direction but also the film thickness profile of the workpiece W in the circumferential direction.

[0053] FIG. 8 is a schematic diagram showing another example of image generation by the imaging device 24 and film thickness measurement by the film thickness sensor 21. In this embodiment, the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 is shorter than the radius of the workpiece W. This is for the following reason: The rotational speed of the workpiece W freely rotating within the retaining ring 32 is substantially constant, but may fluctuate slightly. Therefore, it is desirable that the time difference t3-t2 between the measurement time t3 at which the film thickness at the measurement point MP is measured and the imaging time t2 at which the second image PI2 is generated be as short as possible. In other words, it is desirable that the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 be as short as possible.

[0054] 8, the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 is shorter than the radius of the workpiece W. In this arrangement, there is a time when both the film thickness sensor 21 and the imaging device 24 are located below the workpiece W. It is desirable that the imaging device 24 and the film thickness sensor 21 be adjacent to each other.

[0055] FIG. 9 is a schematic diagram showing yet another example of image generation by the imaging device 24 and film thickness measurement by the film thickness sensor 21. In this embodiment, the distance between the imaging device 24 and the film thickness sensor 21 in the circumferential direction of the polishing table 3 is shorter than the radius of the workpiece W, and the measurement time t3 at which the film thickness at the measurement point MP is measured is the same as the imaging time t2 at which the second image PI2 is generated. In other words, the film thickness sensor 21 measures the film thickness at the measurement point MP at the same time that the imaging device 24 generates the second image PI2. Therefore, the time difference t3-t2 is zero. In this example, the workpiece W does not rotate relative to the polishing head 1 between the imaging time t2 and the measurement time t3. Therefore, the tilt angle of the XY coordinate system at measurement time t3 is the same as the tilt angle of the XY coordinate system at imaging time t2. The coordinates of the measurement point MP are coordinates on the XY coordinate system at imaging time t2 (measurement time t3).

[0056] 10 is a top view showing another embodiment of the film thickness sensor 21. In this embodiment, the film thickness sensor 21 is disposed at a position that passes through the edge of the workpiece W. In other words, the radial distance of the film thickness sensor 21 from the center TP of the polishing table 3 is shorter than the distance from the center TP of the polishing table 3 to the center point TP of the image capturing device 24 and the workpiece W. The film thickness sensor 21 measures the film thickness at a measurement point on the edge while tracing a path K that is different from the path J of the image capturing device 24 and crossing the edge of the workpiece W.

[0057] 10 , the distance between the film thickness sensor 21 and the imaging device 24 is shorter than the radius of the workpiece W. Therefore, there is a time when both the film thickness sensor 21 and the imaging device 24 are located below the workpiece W. In one embodiment, the distance between the film thickness sensor 21 and the imaging device 24 may be longer than the radius of the workpiece W.

[0058] Fig. 11 is a schematic diagram showing an example of image generation by the imaging device 24 shown in Fig. 10 and film thickness measurement by the film thickness sensor 21. As shown in Fig. 11, when the imaging device 24 is located directly below the center point CP of the workpiece W, the process control unit 9 issues a command to the imaging device 24 to generate a second image PI2 of a second region (see symbol C2 in Fig. 4) including the center point CP (imaging time t2). Thereafter, when the film thickness sensor 21 is located below the edge portion of the workpiece W, the process control unit 9 issues a command to the film thickness sensor 21 to measure the film thickness at a measurement point MP on the edge portion of the workpiece W (measurement time t3).

[0059] The process control unit 9 calculates the rotation angle of the XY coordinate system that rotates during the time difference t3-t2 by multiplying the rotation angle of the workpiece W per unit time by the time difference t3-t2. Furthermore, as shown in Fig. 11, the process control unit 9 determines the XY coordinate system at measurement time t3 by rotating the XY coordinate system at imaging time t2 by the calculated rotation angle around the center point CP of the workpiece W. The actual position of measurement point MP on the surface of the workpiece W is identified by the coordinates of measurement point MP on the XY coordinate system at measurement time t3.

[0060] FIG. 12 is a schematic diagram showing another example of image generation by the imaging device 24 shown in FIG. 10 and film thickness measurement by the film thickness sensor 21. As shown in FIG. 12, the measurement time t3 at which the film thickness at the measurement point MP is measured is the same as the imaging time t2 at which the second image PI2 is generated. In other words, the film thickness sensor 21 measures the film thickness at the measurement point MP at the same time that the imaging device 24 generates the second image PI2. Therefore, the time difference t3-t2 is 0. In this example, the workpiece W does not rotate relative to the polishing head 1 between the imaging time t2 and the measurement time t3. Therefore, the tilt angle of the XY coordinate system at measurement time t3 is the same as the tilt angle of the XY coordinate system at imaging time t2. The coordinates of the measurement point MP are coordinates on the XY coordinate system at imaging time t2 (measurement time t3).

[0061] 13 is a diagram illustrating one embodiment of the operation of the imaging device 24 and the processing control unit 9. In this embodiment, the processing control unit 9 issues a command to the imaging device 24 when the imaging device 24 is at a predetermined gap imaging position GP to generate an image of the gap between the inner periphery of the retaining ring 32 and the outer periphery of the workpiece W. The gap imaging position GP is a position on the path J of the imaging device 24 and directly below the gap between the inner periphery of the retaining ring 32 and the outer periphery of the workpiece W. The gap imaging position GP is located behind the center point CP of the workpiece W in the rotation direction of the polishing table 3. The image of the gap is generated before the first image of the first region C1 and the second image of the second region C2 shown in FIG. 4.

[0062] 13, the workpiece W is pressed against the inner periphery of the retaining ring 32 due to friction with the polishing pad 2. As a result, at the gap imaging position GP, ​​a gap exists between the inner periphery of the retaining ring 32 and the outer periphery of the workpiece W. This gap has a dimension (size) along the path J of the imaging device 24. The direction in which the workpiece W is pressed against the inner periphery of the retaining ring 32 may vary during polishing of the workpiece W, but is generally along the path J of the imaging device 24.

[0063] 13, when the workpiece W is pressed against the inner periphery of the retaining ring 32, the center point CP of the workpiece W does not coincide with the center point of the retaining ring 32, i.e., the center point of the polishing head 1 shown in FIGS. 1 and 3. As a result, the origin of the XY coordinate system (see FIG. 6) defined on the surface of the workpiece W is slightly offset from the center of the polishing head 1. In order for the polishing head 1 to properly polish the target area of ​​the workpiece W, it is necessary to obtain the accurate position of the film thickness measurement point on the surface of the workpiece W.

[0064] Therefore, in this embodiment, the processing control unit 9 calculates the size of the gap from the image and corrects the coordinates of the film thickness measurement point on the XY coordinate system based on the gap size, as follows. FIG. 14 is a schematic diagram showing an example of an image 200 of the gap between the retaining ring 32 and the workpiece W, generated by the imaging device 24. The image 200 shows the gap G between the inner periphery of the retaining ring 32 and the outer periphery of the workpiece W. The processing control unit 9 receives the image 200 of the gap G from the imaging device 24 and calculates the size of the gap G from the image 200. As described above, the direction in which the workpiece W is pressed against the inner periphery of the retaining ring 32 may change during polishing of the workpiece W, but the size of the gap G in the image 200 is generally constant.

[0065] The process control unit 9 corrects the coordinates of the measurement point MP determined in each of the above-described embodiments by moving the coordinates of the measurement point MP in a predetermined correction direction by the dimension of the gap G. FIG. 15 is a diagram illustrating one embodiment of a process for correcting the coordinates of the film thickness measurement point MP based on the dimension of the gap G. The process control unit 9 calculates the correction amount by dividing the dimension of the gap G by 2, and corrects the coordinates of the measurement point MP by moving the measurement point MP in a predetermined correction direction CD by the correction amount. The predetermined correction direction CD is a direction in which the gap G between the inner circumference of the retaining ring 32 and the outer circumference of the workpiece W disappears. In one embodiment, the predetermined correction direction CD is a direction from the center point of the retaining ring 32 (or the polishing head 1) toward the gap imaging position GP.

[0066] The corrected coordinates of the measurement point MP accurately represent the actual position of the measurement point MP on the surface of the workpiece W. Therefore, the polishing head 1 can polish the film thickness of the workpiece W with an appropriate pressing force based on the corrected coordinates of the measurement point MP.

[0067] The embodiment described with reference to FIGS. 13 to 15 can be applied to any of the embodiments described with reference to FIGS.

[0068] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0069] 1 polishing head 2 polishing pads 2a Polished surface 3 Polishing table 5 Polishing liquid supply nozzle 6 Table Motor 9 Processing control section 11 Grinding head shaft 15 Head Arm 16 Spindle 18 Vertical movement mechanism 20 Polishing head rotation device 21 Film Thickness Sensor 24 Imaging device 25 Transparent Window 31 Career 32 Retainer ring 34 Elastic membrane 35 Contact area 35a Contact surface 36a,36b,36c Inner wall 36d Exterior wall 38A, 38B, 38C, 38D, 38E Pressure chamber 40 membranes F1, F2, F3, F4, F5 gas transfer lines 45 rotary joint Ra1~Ra5 Pressure Regulators 50 Angle detector 51 Proximity Sensor 52 Sensor Target TP Polishing Table Center CP Workpiece center C1 1st area C2 2nd area PI1 First Image PI2 2nd image 60 notches 100 patterns GP gap imaging position G Gap 200 images

Claims

1. a polishing table having a film thickness sensor and an imaging device fixed thereto is rotated, and a workpiece having a patterned surface is pressed against a polishing pad on the polishing table to polish the workpiece; generating a first image of a first region and a second image of a second region within a surface of the workpiece at predetermined time intervals while the workpiece is being polished; measuring a film thickness at a measurement point on a surface of the workpiece while the workpiece is being polished; calculating a rotation angle of the workpiece per unit time based on the tilt angle of the pattern on the first image, the tilt angle of the pattern on the second image, and the predetermined time interval; Calculating the time difference between the measurement time when the film thickness at the measurement point was measured and the image capturing time when the second image was generated; a polishing method for determining coordinates of the measurement point on the surface of the workpiece based on the relative position of the measurement point and the center point of the workpiece, the rotation angle of the workpiece per unit time, and the time difference.

2. The polishing method of claim 1 , wherein the second region includes a center point of the workpiece.

3. Determining the coordinates of the measurement points comprises: determining a tilt angle of a predefined coordinate system on the surface of the workpiece based on the tilt angle of the pattern on the second image; calculating a rotation angle of the coordinate system that rotates during the time difference by multiplying the rotation angle of the workpiece per unit time by the time difference; determining a coordinate system at the measurement time by rotating the coordinate system at the imaging time around the center point of the workpiece by the calculated rotation angle; 2. The polishing method according to claim 1, wherein the coordinates of the measurement point on the coordinate system at the measurement time are determined from the relative positions of the measurement point and the center point of the workpiece.

4. 2. The polishing method according to claim 1, wherein calculating the rotation angle of the workpiece per unit time comprises calculating a difference in tilt angle of the pattern between the first image and the second image, and dividing the difference in tilt angle by the predetermined time interval to calculate the rotation angle of the workpiece per unit time.

5. generating an image of a gap between an inner periphery of a retaining ring of the polishing head and an outer periphery of the workpiece using the imaging device while the workpiece is being polished; calculating the size of the gap from the image; The polishing method according to claim 1 , further comprising correcting coordinates of the measurement points based on the size of the gap.

6. a polishing table for supporting the polishing pad; a table motor for rotating the polishing table; a polishing head that presses a workpiece having a patterned surface against a polishing pad on the polishing table to polish the workpiece; a film thickness sensor fixed to the polishing table for measuring a film thickness at a measurement point on the surface of the workpiece; an imaging device fixed to the polishing table for generating a first image of a first region and a second image of a second region within the surface of the workpiece at predetermined time intervals; a processing and control unit for determining coordinates of the measurement points on the surface of the workpiece; The processing control unit calculating a rotation angle of the workpiece per unit time based on the tilt angle of the pattern on the first image, the tilt angle of the pattern on the second image, and the predetermined time interval; Calculating the time difference between the measurement time when the film thickness at the measurement point was measured and the image capturing time when the second image was generated; a polishing apparatus configured to determine coordinates of the measurement point on the surface of the workpiece based on the relative position between the measurement point and a center point of the workpiece, the rotation angle of the workpiece per unit time, and the time difference.

7. 7. The polishing apparatus of claim 6, wherein the second region includes a center point of the workpiece.

8. The processing control unit determining a tilt angle of a predefined coordinate system on the surface of the workpiece based on the tilt angle of the pattern on the second image; calculating a rotation angle of the coordinate system that rotates during the time difference by multiplying the rotation angle of the workpiece per unit time by the time difference; determining a coordinate system at the measurement time by rotating the coordinate system at the imaging time around the center point of the workpiece by the calculated rotation angle; 7. The polishing apparatus according to claim 6, wherein the apparatus is configured to determine the coordinates of the measurement point on the coordinate system at the measurement time from the relative position of the measurement point and the center point of the workpiece.

9. 7. The polishing apparatus of claim 6, wherein the processing control unit is configured to calculate a difference in tilt angle of the pattern between the first image and the second image, and to calculate the rotation angle of the workpiece per unit time by dividing the difference in tilt angle by the predetermined time interval.

10. The processing control unit generating an image of a gap between an inner periphery of a retaining ring of the polishing head and an outer periphery of the workpiece using the imaging device while the workpiece is being polished; calculating the size of the gap from the image; 7. The polishing apparatus according to claim 6, wherein the coordinates of the measurement points are corrected based on the size of the gap.

Images