Polishing Pad Thickness Measuring Device

Abstract

To provide a thickness measuring device of a polishing pad that can measure an abrasion of the polishing pad in terms of thickness and confirm the abrasion of the polishing pad by a direct method.SOLUTION: A thickness measuring device 10, which measures a thickness of a polishing pad 13 that is used in polishing an object to be polished such as a wafer W, comprises: a polishing pad holding plate 31, mounted with a polishing pad 32, which can move horizontally in a rotating and vertical direction; a sensor 14 for measuring a thickness of the polishing pad that is pressed against the polishing pad holding plate 31 at a nearly right angle through the polishing pad 32 so as to output an electric signal corresponding to a distance up to the polishing pad holding plate 31; and a control part 15 having measuring means 36 that measures a thickness of the polishing pad 32, on the basis of the electric signal outputted from the sensor 14 for measuring the thickness of the polishing pad.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thickness measuring device for a polishing pad, and more particularly to a thickness measuring device for a polishing pad used for determining the life of a polishing pad and the like.

Background Art

[0002] Conventionally, a polishing apparatus that polishes a polishing pad and a workpiece while applying a load between the polishing pad and the workpiece is known (see, for example, Patent Document 1).

[0003] As such a polishing apparatus, for example, a polishing apparatus that performs Chemical Mechanical Polish (hereinafter referred to as "CMP") used for planarizing the surface of a semiconductor device wafer or the like can be cited. CMP is a process of removing surface irregularities of a wafer by combining physical polishing with chemical actions (dissolution by an abrasive and a solution). By using an abrasive called slurry and applying pressure to the surface of the wafer with an appropriate polishing pad and causing relative movement, polishing is advanced to perform uniform polishing within the wafer surface.

[0004] In such a polishing apparatus, the polishing surface of the polishing pad becomes clogged and deteriorates over time. Therefore, it is maintained by periodically performing dressing so that good processing can be continued.

[0005] This dressing is performed by bringing the polishing surface of the polishing pad into contact with the dressing surface of the dressing and relatively moving the polishing pad and the dressing. As the dressing, for example, a tool in which abrasive grains such as diamond particles are distributed over the entire dressing surface having an annular or circular shape is used. The relative movement is performed, for example, by rotating both the polishing pad and the dressing.

[0006] The thickness of the polishing pad decreases due to wear during polishing of the workpiece such as a wafer and wear during dressing. Eventually, the desired polishing characteristics can no longer be obtained and the lifespan ends. Therefore, it is necessary to replace the polishing pad with a new one. Conventionally, the lifespan of the polishing pad has been determined based on the cumulative polishing time by the polishing pad, the cumulative dressing time, the number of workpieces polished, the number of dressing times, etc. When it was determined that the lifespan had ended (the limit of use), the polishing pad was replaced with a new one.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the lifespan of the polishing pad varies in terms of the wear progress of each polishing pad due to differences in the characteristics of each polishing pad (initial thickness, elastic modulus, hardness, etc.). In a method of determining the lifespan of the polishing pad by ignoring the characteristics of each polishing pad and based on the cumulative polishing time by the polishing pad, the cumulative dressing time, the number of workpieces polished, the number of dressing times, etc., there is a risk that in operation, polishing may be performed with a polishing pad in an over-worn state. Therefore, in order to prevent damage to the wafer, a method for accurately checking the wear of the polishing pad by a more direct method is required.

[0009] Therefore, in order to provide a polishing pad thickness measuring device that measures the wear of the polishing pad and enables the wear of the polishing pad to be confirmed by a direct method, a technical problem to be solved arises, and the present invention aims to solve this problem.

Means for Solving the Problems

[0010] The present invention is proposed to achieve the above object, and the invention described in claim 1 is a polishing pad thickness measuring device for measuring the thickness of a polishing pad used for polishing an object to be polished, comprising a polishing pad holding plate to which the polishing pad is attached and rotates integrally, and capable of horizontally moving in the vertical direction, and a polishing pad thickness measuring sensor capable of moving in the vertical direction. The polishing pad is formed of a non-conductive material, and the polishing pad holding plate is formed of a conductive material. The polishing pad thickness measuring sensor An eddy current displacement sensor, is pushed into the polishing pad holding plate through the polishing pad and moved to a predetermined position, and the thickness of the polishing pad for conversion corresponds to the distance to the polishing pad holding plate measurement and outputs a signal, providing a polishing pad thickness measuring device.

[0011] According to this configuration, the polishing pad thickness measuring sensor is pressed against the polishing pad holding plate substantially perpendicularly so as to sandwich the polishing pad attached to the polishing pad holding plate, and the distance from the polishing pad thickness measuring sensor to the polishing pad holding plate is measured as the thickness of the polishing pad. In this way, when the distance between the polishing pad thickness measuring sensor and the polishing pad holding plate is measured as the thickness of the polishing pad, the thickness of the polishing pad at the measurement time can be directly and accurately known.

[0013] further Using an eddy current displacement sensor, the distance to the polishing pad holding plate to which the polishing pad is attached is measured from above the polishing pad. The eddy current displacement sensor measures the distance based on the change in the magnetic field affected by the induced current generated in the polishing pad holding plate, which is a conductor. However, the non-conductive polishing pad does not affect the sensor magnetic field. Therefore, when the eddy current displacement sensor measures the distance from above the polishing pad to the polishing pad holding plate, the distance to the polishing pad holding plate can be accurately obtained as the thickness of the polishing pad.

[0014] Claim 2 The invention described in to 1 is, in the configuration described in claim the measurement A polishing pad thickness measuring device further includes a control unit having a measuring means for measuring the thickness of the polishing pad based on a signal, and a determining means for determining the life of the polishing pad from the measured thickness of the polishing pad.

[0015] According to this configuration, when determining the life of the polishing pad from the thickness of the polishing pad, the life at the measurement time can be directly and accurately known.

Effect of the Invention

[0016] According to the invention, the polishing pad holding plate is pressed against the polishing pad thickness measuring sensor so as to sandwich the polishing pad attached to the polishing pad holding plate, and the thickness of the polishing pad is measured. Therefore, the distance from the polishing pad thickness measuring sensor to the polishing pad holding plate can be obtained as the thickness of the polishing pad. Accordingly, the thickness of the polishing pad at the measurement time can be directly and accurately known. Further, it is possible to directly determine whether the polishing pad is at the end of its useful life or not, etc., and to quickly perform necessary processing. Thereby, damage to the wafer and the like can be prevented.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0018] The present invention provides a polishing pad thickness measuring device for measuring the thickness of a polishing pad used for polishing an object to be polished, in order to achieve the object of measuring the wear of the polishing pad by thickness and enabling the wear of the polishing pad to be confirmed by a direct method. The polishing pad thickness measuring device includes a polishing pad holding plate that is attached to the polishing pad and rotates integrally, and is horizontally movable in the vertical direction, and a polishing pad thickness measuring sensor that is pressed against the polishing pad holding plate at a substantially right angle through the polishing pad and outputs an electrical signal corresponding to the distance to the polishing pad holding plate. A control unit having a measuring means for measuring the thickness of the polishing pad based on the electrical signal from the polishing pad thickness measuring sensor is realized by including the above components.

Example

[0019] Hereinafter, an example according to an embodiment of the present invention will be described in detail based on the accompanying drawings. In the following examples, when referring to the shape, positional relationship, etc. of components, etc., unless otherwise specified or considered to be clearly not so in principle, those substantially similar or similar in shape, etc. are included.

[0020] Also, the drawings may be exaggerated by enlarging characteristic parts to make the characteristics easier to understand, and the dimensional ratios of components are not necessarily the same as the actual ones.

[0021] Also, expressions indicating directions such as up and down, left and right, etc. are not absolute. They are appropriate when the posture in which each part of the polishing pad thickness measuring device of the present invention is depicted, but should be interpreted as being changed according to the change in posture when the posture changes.

[0022] FIG. 1 is a side view schematically showing the configuration of a polishing device 11 equipped with a polishing pad thickness measuring device 10 according to the present invention, and FIG. 2 is a side view schematically showing the polishing pad thickness measuring device 10.

[0023] In FIG. 1, the polishing apparatus 11 is a CMP apparatus for performing planar processing on the surface of a semiconductor substrate in semiconductor manufacturing. The polishing apparatus 11 includes a rotary chuck table 12 capable of holding a wafer W, which is an example of an object to be polished, a polishing head 13 that supports a polishing pad 32 and is disposed above the rotary chuck table 12, a sensor 14 for measuring the thickness of the polishing pad disposed juxtaposed to the rotary chuck table 12, a control unit 15 for controlling the overall operation of the polishing apparatus 11 according to a predetermined procedure, and the like.

[0024] The rotary chuck table 12 has a chuck surface 12a on its upper surface for sucking and holding the wafer W by negative pressure. Further, the rotary chuck table 12 is connected to a table motor 16 disposed below it via a table shaft 12b and is rotatable about the table shaft 12b by the driving force of the table motor 16. Above the rotary chuck table 12, a polishing liquid supply nozzle (not shown) is installed, and polishing liquid (e.g., slurry) is supplied onto the polishing surface of the wafer W by this polishing liquid supply nozzle.

[0025] The polishing head 13 is detachably attached to the lower end of a polishing head shaft 17. The polishing head shaft 17 is moved up and down integrally with the polishing head 13 in a substantially horizontal state with respect to the head arm 19 by an actuator 18. By the vertical movement of the polishing head shaft 17, the entire polishing head 13 can be raised and lowered in a substantially horizontal state with respect to the head arm 19 and positioned at a predetermined position. The polishing head 13 is supported by the head arm 19 via the polishing head shaft 17 and the actuator 18. The polishing head shaft 17 extends through the head arm 19.

[0026] The actuator 18 can move the polishing head 13 and the polishing head shaft 17 relative to the head arm 19. The direction of movement of the polishing head 13 by the actuator 18 is perpendicular (vertical direction) to the chuck surface 12a.

[0027] The actuator 18 that moves the polishing head shaft 17 and the polishing head 13 in the vertical direction is fixed to the support base 20. The support base 20 is fixed to the upper surface of the head arm 19. The actuator 18 includes a bearing 21 that rotatably supports the polishing head shaft 17, a bridge 22 that holds this bearing 21, a ball screw mechanism 23 connected to this bridge 22, and a servo motor 24 fixed on the support base 20.

[0028] The ball screw mechanism 23 includes a screw shaft 23a connected to the servo motor 24 and a nut 23b that the screw shaft 23a is screwed into. The nut 23b is held by the bridge 22.

[0029] The polishing head shaft 17 is integrally movable up and down with the bearing 21 and the bridge 22. That is, when the servo motor 24 is driven, the bridge 22 moves up and down via the ball screw mechanism 23, and thereby the polishing head shaft 17 and the polishing head 13 move up and down in a substantially horizontal state. The polishing head 13 is connected to the head arm 19 via the polishing head shaft 17, the actuator 18, and the support base 20.

[0030] The polishing head shaft 17 is supported by a ball spline bearing 25 so as to be movable in its axial direction. A pulley 26 is fixed to the outer peripheral portion of the ball spline bearing 25.

[0031] A polishing head rotation motor 27 is fixed to the head arm 19, and the pulley 26 is connected to a pulley 28 attached to the polishing head rotation motor 27 via a belt 29. Therefore, when the polishing head rotation motor 27 is rotationally driven, the ball spline bearing 25 and the polishing head shaft 17 rotate integrally via the pulley 28, the belt 29, and the pulley 26, and the polishing head 13 rotates around the polishing head shaft 17. Note that the pulleys 26, 28, the belt 29, and the ball spline bearing 25 are arranged inside the head arm 19.

[0032] The head arm 19 is supported by a pivot shaft 30 supported by a frame (not shown).

[0033] The polishing head 13 can detachably hold a disc-shaped polishing pad 32 having substantially the same outer diameter as that of the polishing pad holding plate 31 via the disc-shaped polishing pad holding plate 31 on its lower surface. The polishing pad holding plate 31 is formed of a conductor material (for example, stainless steel or the like), and the polishing pad 32 is formed of a non-conductor material (for example, polyester fiber or the like).

[0034] The head arm 19 is configured to be pivotable about the pivot shaft 30. The polishing head 13 holding the polishing pad 32 on its lower surface can be switched and moved to a position above the chuck surface 12a of the rotary chuck table 12 and a position above the sensor 14 for measuring the thickness of the polishing pad by the pivoting of the head arm 19.

[0035] The sensor 14 for measuring the thickness of the polishing pad is fixed and mounted on the sensor holding base 33 in a state of protruding upward from the sensor holding base 33. The sensor holding base 33 is connected to a sensor lifting cylinder 34 via a rod 34a and can be reciprocated in the vertical direction by driving the sensor lifting cylinder 34. In this embodiment, an eddy current displacement sensor is used as the sensor 14 for measuring the thickness of the polishing pad. When an eddy current sensor is used for the sensor 14 for measuring the thickness of the polishing pad, when the sensor 14 for measuring the thickness of the polishing pad abuts on the polishing pad holding plate 31 with the polishing pad 32 interposed therebetween, the measuring means 36 in the control unit 15 measures the distance to the polishing pad holding plate 31 from the magnitude of the eddy current generated between the sensor 14 for measuring the thickness of the polishing pad and the polishing pad holding plate 31, and recognizes this distance as the thickness of the polishing pad 32.

[0036] The control unit 15 has a measuring means 36 that calculates an electrical signal from the sensor 14 for measuring the polishing pad thickness to measure the thickness of the polishing pad 32, and a determination means 37 that determines whether or not the thickness of the polishing pad 32 measured by the measuring means 36 has an appropriate thickness, that is, whether or not there is no problem with the polishing process even if use continues. In addition to this, it executes the overall operation control of the polishing apparatus 11 and the thickness measuring apparatus 10. The control unit 15 is composed of, for example, a microcomputer, and controls the polishing apparatus 11 and the thickness measuring apparatus 10 in a predetermined procedure while performing necessary arithmetic processing according to a program incorporated in the microcomputer. Therefore, the polishing pad thickness measuring sensor 14, the table motor 16, the actuator 18, the servo motor 24, the polishing head rotation motor 27, the sensor lifting cylinder 34, the upper position detection sensor 35a, the lower position detection sensor 35b, etc. are connected to the control unit 15.

[0037] The polishing of the wafer W is performed as follows. The polishing head 13 is raised to a predetermined reference height and separated from the rotary chuck table 12. In this state, the wafer W placed on the chuck surface 12a of the rotary chuck table 12 is vacuum-sucked and chucked on the chuck surface 12a. Next, the rotary chuck table 12 and the polishing head 13 are rotated relative to each other, and polishing liquid (slurry) is supplied onto the surface of the wafer W from a polishing liquid supply nozzle (not shown). In this state, the polishing head 13 is lowered to the predetermined reference height, and the polishing pad 32 is pressed against the surface of the wafer W to be processed. As a result, the surface of the wafer W is rubbed against the polishing surface of the polishing pad 32 in the presence of the polishing liquid, and the surface of the wafer W is polished.

[0038] In such a polishing apparatus 11, the polishing surface of the polishing pad 32 deteriorates due to clogging progressing over time. Therefore, dressing is periodically performed for maintenance so that good processing can be continued. Also, the thickness of the polishing pad 32 becomes thinner due to wear associated with the polishing of the wafer W and wear associated with dressing. Eventually, the desired polishing characteristics can no longer be obtained and the life is exhausted. For this reason, it is necessary to replace the polishing pad with a new one. Therefore, in the thickness measuring device 10, the thickness of the polishing pad 32 is detected, the life of the polishing pad 32 is determined from the thickness, and when it is determined that the life has expired (usage limit), it prompts to replace the polishing pad 32 with a new one. Note that the thickness of the polishing pad 32 is generally about 6 mm, and replacement is required when it wears down to about 2 mm.

[0039] In the thickness measuring device 10, the thickness of the polishing pad 32 is measured as follows. FIG. 3 is an operation explanatory diagram of the thickness measuring device 10, and the thickness measuring device 10 operates in the order of (a), (b), (c), and (d) of FIG. 3. Also, FIG. 4 is a timing chart of the thickness measuring device 10. Therefore, the measurement of the thickness of the polishing pad 32 will be described according to the operation diagrams (a) to (d) of FIG. 3 and together with the timing chart (steps Sa to Sd) of FIG. 4.

[0040] When measuring the thickness of the polishing pad 32, first, the head arm 19 is swung according to an instruction from the control unit 15, and the polishing head 13 is moved from a position above the chuck surface 12a of the rotary chuck table 12 to a position above the polishing pad thickness measuring sensor 14. FIG. 3(a) shows a state where the polishing head 13 has moved to a position above the polishing pad thickness measuring sensor 14. This state corresponds to the state of step Sa in FIG. 4, and there is a gap between the polishing pad thickness measuring sensor 14 and the polishing pad 32. Then, the signal of the upper position detection sensor 35a is OFF, and the signal of the lower position detection sensor 35b is ON.

[0041] Next, upon the instruction of the control unit 15, the transition from step Sa to step Sb in FIG. 4 is started. In the transition to step Sb, the sensor lifting cylinder 34 is driven, and the polishing pad thickness measuring sensor 14 is lifted toward the polishing head 13 by the driving of the sensor lifting cylinder 34. Further, when the polishing pad thickness measuring sensor 14 is lifted by a predetermined amount, the signal of the lower position detection sensor 35b is switched from ON to OFF. As the lifting of the polishing pad thickness measuring sensor 14 further proceeds and just before the polishing pad thickness measuring sensor 14 reaches step Sb, the signal of the lower position detection sensor 35b is switched from OFF to ON. Then, the driving of the sensor lifting cylinder 34 is stopped by the instruction of the control unit 15, and the polishing pad thickness measuring sensor 14 is stopped at its lifted position. FIG. 3(b) shows the state where the polishing pad thickness measuring sensor 14 is moved to the upper position. This state corresponds to the state of step Sb in FIG. 4, and there is still a gap between the polishing pad thickness measuring sensor 14 and the polishing pad 32.

[0042] Next, upon the instruction of the control unit 15, the transition from step Sb to step Sc in FIG. 4 is started. In the transition to step Sb, the servo motor 24 is driven, and the polishing head 13 starts to descend by the driving force of the servo motor 24. Then, during the descent, the lower surface of the polishing pad 32 and the upper surface of the polishing pad thickness measuring sensor 14 come into contact with each other. FIG. 3(c) shows the state where the polishing pad holding plate 31 gently contacts the upper surface of the polishing pad thickness measuring sensor 14 with the polishing pad 32 sandwiched therebetween. Further, as the polishing head 13 descends further, the polishing pad holding plate 31 of the polishing head 13 strongly presses against the upper surface of the polishing pad thickness measuring sensor 14 with the polishing pad 32 sandwiched therebetween. Note that the signal T in FIG. 4 is a signal of the thickness amount of the polishing pad 32 measured by the measuring means 36 based on the signal from the polishing pad thickness measuring sensor 14 at the end of the transition from step Sb to step Sc.

[0043] Subsequently, upon the instruction of the control unit 15, the transition from step Sc to step Sd in FIG. 4 is started. The transition from step Sc to step Sd is performed continuously following the transition from step Sb to step Sc. That is, even when the lower surface of the polishing pad 32 comes into contact with the upper surface of the polishing pad thickness measurement sensor 14, the servo motor 24 is driven without being stopped. Then, the polishing pad holding plate 31 of the polishing head 13 strongly presses the polishing pad 32 against the upper surface of the polishing pad thickness measurement sensor 14 with the polishing pad 32 sandwiched therebetween, and further presses down the polishing pad thickness measurement sensor 14 against the upward pushing force of the sensor lifting cylinder 34. As a result, the polishing head 13 is strongly pressed against the upper surface of the polishing pad thickness measurement sensor with the polishing pad 32 sandwiched between the polishing pad holding plate 31 and the polishing pad thickness measurement sensor 14.

[0044] In Fig. 3(d), the lower surface of the polishing pad holding plate 31 is strongly pressed against the upper surface of the polishing pad thickness measuring sensor 14 with the polishing pad 32 interposed therebetween, showing a state where the polishing head 13 has pushed down the polishing pad thickness measuring sensor 14. When the transition from step Sc to step Sd is about to end, the signal of the upper position detection sensor 35a switches from ON to OFF, and outputs to the control unit 15 that the polishing pad thickness measuring sensor 14 is in a state where the polishing head 13 has pushed it down to a predetermined position. Then, in the control unit 15, the measuring means 36 acquires the electrical signal from the polishing pad thickness measuring sensor 14 when the polishing head 13 is strongly pressed against the polishing pad thickness measuring sensor 14, converts the signal into the thickness amount of the polishing pad 32, and can know the thickness of the polishing pad 32 based on the electrical signal. Thereby, the measuring means 36 detects the thickness of the polishing pad 32. Further, from the thickness of the polishing pad 32 measured here, the determination means 37 determines the life of the polishing pad 32. When the replacement life has come, the control unit 15 prompts the replacement of the polishing pad 32. After the measurement, according to the instruction of the control unit 15, the servo motor 24 and the sensor lifting cylinder 34 are controlled, the polishing head 13 rises, the polishing pad thickness measuring sensor 14 descends, and returns to the position of Fig. 3(a). Thereafter, according to the instruction of the control unit 15, the head arm 19 is swung, the polishing head 13 is moved to a position above the chuck surface 12a of the rotary chuck table 12, and the polishing process is started again.

[0045] In the polishing pad thickness measuring device 10 in the polishing device 11 according to the configuration of this embodiment, when measuring the thickness of the polishing pad 32 of the polishing head 13, the polishing pad holding plate 31 is pressed against the polishing pad thickness measuring sensor 14 so as to sandwich the polishing pad 32 to measure the thickness of the polishing pad 32. In this way, when measuring the distance between the polishing pad thickness measuring sensor 14 and the polishing pad holding plate 31 with the polishing pad 32 interposed therebetween, the distance between the polishing pad thickness measuring sensor 14 and the polishing pad holding plate 31 can be obtained as the thickness of the polishing pad 32 as a measured value. Thereby, the thickness of the polishing pad 32 at the measurement time point can be directly and accurately known.

[0046] In addition, since the polishing pad 32 is formed of a non-conductive material and the polishing pad holding plate 31 is formed of a conductive material, and an eddy current displacement sensor is used as the sensor 14 for measuring the polishing pad thickness, eddy currents are not generated on the non-conductive polishing pad 32, and eddy currents are generated only on the conductive polishing pad holding plate 31. Therefore, when measuring the distance from the top of the polishing pad 32 to the polishing pad holding plate 31, the distance to the polishing pad holding plate 31 can be accurately obtained as the thickness of the polishing pad 32 without being affected by the polishing pad 32.

[0047] In addition, since the control unit 15 includes a determination means 37 for determining the life of the polishing pad 32 from the measured thickness of the polishing pad 32, the life at the measurement time can be directly and accurately known.

[0048] Although the case where an eddy current sensor is used as the sensor 14 for measuring the polishing pad thickness has been described, a linear scale, a laser sensor, an ultrasonic sensor, a proximity sensor, etc. can be used as the sensor 14 for measuring the polishing pad thickness for the eddy current sensor.

[0049] In addition, the present invention can make various modifications without departing from the spirit of the present invention, and it is natural that the present invention extends to the modified ones.

Explanation of Signs

[0050] 10: Thickness measuring device 11: Polishing device 12: Rotating chuck table 12a: Chuck surface 12b: Table axis 13: Polishing head 14: Sensor for measuring polishing pad thickness 15: Control unit 16: Table motor 17: Polishing head axis 18: Actuator 19: Head Arm 20: Support Base 21: Bearing 22: Bridge 23: Ball Screw Mechanism 23a: Screw Shaft 23b: Nut 24: Servo Motor 25: Ball Spline Bearing 26: Pulley 27: Polishing Head Rotation Motor 28: Pulley 29: Belt 30: Swivel Axis 31: Polishing Pad Holding Plate 32: Polishing Pad 33: Sensor Holding Base 34: Sensor Lifting Cylinder 34a: Rod 35a: Upper Position Detection Sensor 35b: Lower Position Detection Sensor 36: Measuring Means 37: Determination Means Sa: Step Sb: Step Sc: Step Sd: Step T: Signal W: Wafer

Claims

1. A polishing pad thickness measuring device for measuring the thickness of a polishing pad used for polishing an object to be polished, comprising: a polishing pad holding plate to which the polishing pad is attached and which rotates integrally with the polishing pad and which is movable in the vertical direction; a sensor for measuring the thickness of the polishing pad, the sensor being movable in the vertical direction; Equipped with the polishing pad is formed of a non-conductive material; the polishing pad support plate is formed of a conductive material; The polishing pad thickness measuring sensor is an eddy current displacement sensor, which is pressed into the polishing pad holding plate via the polishing pad and moves to a predetermined position, and outputs a measurement signal corresponding to the distance to the polishing pad holding plate, which is converted into the thickness of the polishing pad.

2. a measuring means for measuring the thickness of the polishing pad based on the measurement signal from the polishing pad thickness measuring sensor; A control unit further includes a determination unit for determining a life span of the polishing pad from the measured thickness of the polishing pad.

2. The polishing pad thickness measuring device according to claim 1.

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