Grinding device

Abstract

To provide a polishing device that can eliminate the problem that a device chip is sometimes damaged.SOLUTION: A polishing device includes: a chuck table 52 having a rotatable holding surface; polishing means comprising a rotary shaft 32 that rotatably supports a polishing pad 35 that polishes a wafer W held on the holding surface of the chuck table 52; perpendicularly feeding means that processing-feeds the polishing means in a perpendicular direction relatively with respect to the holding surface of the chuck table 52; parallely feeding means that processing-feeds the polishing means in a parallel direction relatively with respect to the holding surface of the chuck table 52; and control means 100. A through-hole 14 extending from one end to the other end is formed at a shaft center of the rotary shaft 32 of the polishing means, and thickness measuring means 4 that measures a thickness of the wafer W is arranged at the one end of the through-hole 14. The polishing device makes the thickness measuring means 4 measure the thickness of the wafer W and generates mapping data concerning the thickness of the wafer W.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a polishing apparatus for polishing a wafer held on a holding surface of a chuck table. [Background technology]

[0002] Wafers, on whose surface multiple devices such as ICs and LSIs are formed and partitioned by planned dividing lines, have their back surfaces ground and thinned by a grinding machine, and then polished by a polishing machine to remove grinding marks.Then, the wafer is divided into individual device chips by a dicing machine and a laser processing machine, and these are used in electrical devices such as mobile phones and personal computers.

[0003] A polishing device for polishing the back surface of a wafer is generally composed of a chuck table for holding the wafer and a polishing means having a rotatable polishing pad for polishing the wafer held on the chuck table, and can polish the grinding surface of the wafer to a desired smooth state (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 08-099265 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when grinding marks caused by processing by a grinding device are removed by a polishing device and then the wafer is irradiated with a laser beam to divide the wafer into individual device chips, there is a problem that division may be insufficient and the device chips may be damaged due to improper processing by the laser beam.

[0006] As a result of extensive research by the inventors of the present invention into the cause of the above-mentioned problem, it was found that when the grinding marks are removed using a polishing device, the thickness of the wafer becomes uneven, and when a laser beam is irradiated to divide the wafer into individual device chips, the focal point of the laser beam cannot be positioned in an appropriate position, making it impossible to properly perform processing using the laser beam.

[0007] The present invention has been made in consideration of the above facts, and its main technical object is to provide a polishing apparatus that can solve the problem of insufficient division and damage to device chips caused by improper processing using a laser beam. [Means for solving the problem]

[0008] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a polishing apparatus including a chuck table having a rotatable holding surface, polishing means having a rotation shaft that rotatably supports a polishing pad that polishes a wafer held on the holding surface of the chuck table, vertical feed means for processing-feeding the polishing means relatively in a direction perpendicular to the holding surface of the chuck table, parallel feed means for processing-feeding the polishing means relatively in a direction parallel to the holding surface of the chuck table, and control means, wherein a through hole extending from one end to the other is formed around the axis of the rotation shaft of the polishing means, and a thickness measurement means for measuring the thickness of the wafer is disposed at one end of the through hole, and the control means measures the thickness of the wafer with the thickness measurement means at a position determined by the change in the distance between the center of rotation of the wafer held and rotated on the chuck table fed by the parallel feed means and the center of the other end of the through hole facing the wafer, and the rotation angle of the chuck table, and creates mapping data relating to the wafer thickness.

[0009] The thickness measuring means includes a light source that emits light in a wavelength range that is transparent to the wafer; Chuck table a condenser that irradiates the light emitted from the light source onto a wafer held by the condenser; and a light source disposed in an optical path between the light source and the condenser. Chuck tableand a thickness calculation means for calculating the spectral interference waveform generated by the image sensor and outputting thickness information. Furthermore, the control means preferably includes at least an optical branching unit that branches return light reflected from a wafer held by the optical branching unit from the optical path, a diffraction grating that separates the return light branched by the optical branching unit into wavelengths, an image sensor that detects the intensity of the light separated into wavelengths by the diffraction grating and generates a spectral interference waveform, and a thickness calculation means that calculates the spectral interference waveform generated by the image sensor and outputs thickness information. Furthermore, the control means preferably determines that the wafer is acceptable if the thickness variation is within a tolerance based on the mapping data, and determines that the wafer is unacceptable if the thickness variation is outside the tolerance. [Effects of the Invention]

[0010] The polishing apparatus of the present invention includes a chuck table having a rotatable holding surface, polishing means having a rotary shaft for rotatably supporting a polishing pad for polishing a wafer held on the holding surface of the chuck table, vertical feed means for relatively feeding the polishing means in a direction perpendicular to the holding surface of the chuck table, parallel feed means for relatively feeding the polishing means in a direction parallel to the holding surface of the chuck table, and control means, wherein a through hole extending from one end to the other end is formed at the axis of the rotary shaft of the polishing means, and thickness measurement means for measuring the thickness of the wafer is disposed at one end of the through hole, and the control means controls the distance between the center of rotation of the wafer held and rotated on the chuck table and fed by the parallel feed means and the center of the other end of the through hole facing the wafer. The thickness of the wafer is measured by the thickness measuring means at a position determined by the change in the distance and the rotation angle of the chuck table, and mapping data relating to the wafer thickness is created. This makes it possible to grasp the variation in thickness of the wafer W after polishing has been performed, and if the thickness variation is within the tolerance, it is possible to approve transport to the next process where laser processing will be performed, or if the thickness variation is outside the tolerance, it is possible to instruct reprocessing. This makes it possible to prevent wafers with uneven thickness from being divided, and to perform the dividing process only on wafers with a uniform thickness that can be divided appropriately, thereby ensuring that the wafer can be divided into individual device chips, and eliminating the problem of insufficient division areas potentially damaging the device chips. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an overall perspective view of a polishing apparatus. [Figure 2] 2 is a block diagram showing an optical system of a thickness measuring means of the polishing apparatus shown in FIG. 1. FIG. [Figure 3] FIG. 2 is a conceptual diagram of mapping data stored in a table. [Figure 4] 10 is a flowchart executed by a determination unit. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a polishing apparatus constructed based on the present invention will be described in detail with reference to the accompanying drawings.

[0013] 1 shows a perspective view of a polishing apparatus 1 of this embodiment. The polishing apparatus 1 includes a substantially rectangular parallelepiped housing 2, which houses a polishing means 3 for polishing a wafer W as a workpiece, a thickness measuring means 4 for measuring the thickness of the wafer W, a holding means 5 for holding the wafer W, a first cassette 6 arranged on the front side in the drawing for accommodating wafers W before polishing, a second cassette 7 arranged on the other side of the first cassette 6 in the X-axis direction in the drawing for accommodating wafers W after polishing, a temporary placement means 8 arranged adjacent to the first cassette 6 in the Y-axis direction in the drawing for aligning the centers of the wafers W, and a holding means 5 for holding the wafers W in the Y-axis direction in the second cassette 7. The apparatus includes a cleaning means 9 disposed adjacent to the first cassette 6, a first transport means 10 that transports the wafers W stored in the first cassette 6 to the temporary storage means 8 and transports the wafers W cleaned by the cleaning means 9 to the second cassette 7, a second transport means 11 that transports the wafers W placed on the temporary storage means 8 and centered onto the chuck table 52 of the holding means 5 positioned at the load / unload position (the front side in the drawing), a third transport means 12 that transports the polished wafers W from the chuck table 52 positioned at the load / unload position to the cleaning means 9, and a control means 100. The wafers W stored in the first cassette 6 have grinding marks on their back surfaces that were formed during a grinding process performed before the wafers were loaded into the polishing apparatus 1, and the polishing apparatus 1 of this embodiment removes these grinding marks by polishing.

[0014] The polishing means 3 is mounted on a pair of guide rails 22, 22 extending in the vertical direction on the inner surface of a support wall 21 erected on the rear end side of the device housing 2 so as to be movable in the vertical direction. The polishing means 3 includes a unit housing 31, a wheel mount 33 disposed at the lower end of a rotary shaft 32 rotatably supported by the unit housing 31, a polishing wheel 34 mounted on the wheel mount 33 and having a polishing pad 35 affixed to its underside, an electric motor 36 mounted on the upper end of the unit housing 31 for rotating the wheel mount 33, and a movable base 38 supporting the unit housing 31 via a support member 37. The movable base 38 is provided with guided grooves that slidably fit onto the guide rails 22, 22, and supports the polishing means 3 so as to be movable in the vertical direction. In addition, a through hole 14 (shown by a dashed line) is formed at the axis of the rotating shaft 32, penetrating the rotating shaft 32 and extending from one end (upper end) to the other end (lower end), and an opening (not shown) is formed on the underside of the polishing pad 35 arranged on the polishing wheel 34 at a position corresponding to the lower end of the through hole 14.

[0015] The illustrated polishing apparatus 1 includes a vertical feed means 39 that raises and lowers a movable base 38 of the polishing means 3 along the guide rails 22. The vertical feed means 39 includes a pulse motor 39a, a male-threaded rod 39b that is disposed vertically parallel to the guide rails 22, 22, rotatably supported on the support wall 21, and rotated by the pulse motor 39a, and a female-threaded block (not shown) that is attached to the movable base 38 and threadedly engages with the male-threaded rod 39b. The polishing means 3 is moved in the Z-axis direction (vertical direction) by driving the male-threaded rod 39b forward and backward by the pulse motor 39a. Furthermore, an operation panel 13 is disposed on the front side of the apparatus housing 2 in which the first conveying means 10 is disposed, for issuing polishing instructions to the control means 100 and specifying polishing conditions. A display monitor 16 that displays processing information and the like is connected to the control means 100.

[0016] The holding means 5 includes a cover table 51 and a chuck table 52 disposed at the center of the cover table 51 and protruding upward. The chuck table 52 has a holding surface on which the wafer W is held, and the holding surface is made of a breathable material. The chuck table 52 is rotatably supported and rotated by a rotation drive source (not shown). A parallel feed means (not shown) is disposed within the device housing 2, which feeds the chuck table 52 for processing in the Y-axis direction indicated by the arrow Y, which is parallel to the horizontal plane, and moves the chuck table 52 between a carry-in / out position on the front side in the Y-axis direction and a polishing position directly below the polishing means 3.

[0017] A cleaning water supply nozzle 23 is disposed in front of the loading / unloading position of the chuck table 52, for supplying cleaning water to the back surface of the wafer W after polishing. A slurry supply nozzle 24 is disposed near the polishing position, and during polishing, a liquid slurry containing free abrasive grains is sprayed from the slurry supply nozzle 24 and supplied onto the wafer W being polished by the polishing pad 35. The material of the polishing pad 35 is not particularly limited, but it can be formed from a material that is compatible with the above-mentioned slurry and elastically deformable, such as a urethane foam or a felt (nonwoven fabric) sheet.

[0018] The thickness measuring means 4 is disposed so as to face an opening 32a on one end side of the through hole 14 formed in the rotation shaft 32. The thickness measuring means 4 is connected to the control means 100, and measures the thickness of the wafer W at a predetermined position on the wafer W, and creates mapping data relating to the thickness of the wafer W, which will be described later.

[0019] FIG. 2 shows a block diagram of the optical system that constitutes the thickness measurement means 4, and the thickness measurement means 4 will be described in more detail with reference to FIG.

[0020] As shown in FIG. 2, the optical system constituting the thickness measuring means 4 includes a light source 41 that emits light LB1 having a predetermined wavelength range that is transparent to the wafer W held on the chuck table 52, a first optical path 41a formed by an optical fiber for guiding the light LB1 from the light source 41 to a second optical path 41b formed by an optical fiber on the chuck table 52 side, and a collimation lens 41b for guiding the light LB1 from the light source 41 to a collimation lens 41c formed by an optical fiber on the chuck table 52 side, and guiding the return light LB2 that is reflected by the wafer W held on the chuck table 52 and travels backward. The optical path 41b includes an optical branching unit 42 that branches the light LB1 into the optical path on the lens 45 side, a collimation lens 43 onto which light LB1 guided to the second optical path 41b is irradiated, a condensing lens 44 that condenses the light LB1 irradiated from the collimation lens 43, a diffraction grating 46 that disperses the return light LB2 that has been branched from the optical branching unit 42 and collimated by the collimation lens 45 into light beams of different wavelengths, and an image sensor 47 that receives the return light LB2 dispersed by the diffraction grating 46, detects the light intensity of each wavelength, and generates a spectral interference waveform. The spectral interference waveform generated by the image sensor 47 is sent to the control means 100.

[0021] The light source 41 may be, for example, a halogen lamp that emits light with a wavelength of 400 to 1200 nm. The light branching unit 42 may be selected from, for example, a polarization-maintaining fiber coupler, a polarization-maintaining fiber circulator, a single-mode fiber coupler, a single-mode fiber coupler circulator, etc. The light source 41 is not limited to the halogen lamp described above, but may be selected depending on the material of the wafer W to be polished, and may be appropriately selected from well-known light sources that emit light with a wavelength that transmits through the wafer W. The light LB1 guided to the condenser lens 44 is condensed by the condenser lens 44 and guided to the through hole 14 of the rotation shaft 32, and a condensing point P is positioned on the surface of the wafer W held on the chuck table 52 at a position corresponding to the center of the other end (lower end) of the through hole 14.

[0022] The control means 100 is configured by a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) that stores the control program, etc., a readable / writable random access memory (RAM) that temporarily stores detected values, calculation results, etc., an input interface, and an output interface (details not shown in the drawings). The control means 100 is provided with a thickness calculation means 110 and a determination means 120. The thickness calculation means 110, for example, performs a Fourier transform on the spectral interference waveform generated when light LB1 irradiated from a light source 41 is reflected by the front surface and the back surface of a wafer W held on a chuck table 52, and the returned light LB2 is guided via a condenser lens 44, a collimation lens 43, a light branching unit 42, and a diffraction grating 46 to an image sensor 47, and outputs thickness information of the wafer W. The determining means 120 determines whether or not the variation in thickness of the wafer W is within the allowable range based on the mapping data (described in detail later) created by the thickness calculating means 110.

[0023] The polishing apparatus 1 of this embodiment has roughly the same configuration as described above, and the functions and actions of the polishing apparatus 1 will be described in more detail.

[0024] When polishing a wafer W using the polishing apparatus 1 of this embodiment, the first transport means 10 and the second transport means 11 are operated to transport the wafer W stored in the first cassette 6 to the chuck table 52 via the temporary storage means 8, and the wafer W is placed with its front side facing downward and its back side facing upward. Once the wafer W is placed on the chuck table 52, a suction means (not shown) is operated to generate a suction negative pressure on the holding surface of the chuck table 52, thereby suction-holding the wafer W. An appropriate protective film may be attached to the front side of the wafer W.

[0025] After the wafer holding step is completed, the chuck table 52 is moved to a polishing position directly below the polishing means 3 by the parallel feed means, and polishing is performed by supplying slurry to the back surface of the wafer W from the slurry supply nozzle 24. More specifically, first, the chuck table 52 is rotated in the direction indicated by arrow R1 in FIG. 1 by a rotary drive means (not shown), the electric motor 36 is operated to rotate the rotary shaft 32 of the polishing unit 3 in the direction indicated by arrow R2, and the vertical feed means 39 is operated to lower the polishing means 3 in the direction indicated by arrow R3. The polishing pad 35 is brought into contact with the back surface of the wafer W and pressed with a predetermined pressing load while supplying slurry from the slurry supply nozzle 24. Polishing is performed for a predetermined polishing time, and grinding marks caused by the previous grinding process are removed from the back surface of the wafer W to smooth it.

[0026] After the above-mentioned polishing process is performed, the chuck table 52 is moved to the carry-in / out position on the front side of FIG. 1 by the above-mentioned parallel feed means, and cleaning water is sprayed from the cleaning water supply nozzle 23 onto the back surface of the rotating wafer W to clean the back surface of the wafer W.

[0027] After the wafer W has been cleaned by the cleaning water supply nozzle 23, the chuck table 52 is again moved toward the polishing position directly below the polishing means 3. Incidentally, the calculation means 110 stores a table 112 in which a plurality of predetermined positions are defined based on the shape data of the wafer W displayed on the display means 16 in Fig. 2, by changes in the distance (Y0-Ym) between the center of rotation O of the wafer W held and rotated on the chuck table 52 fed by the parallel feed means and the center of the other end of the through hole 14 facing the wafer W, and by changes in the rotation angle (0°-360°) of the chuck table 52 with the direction connecting the center of rotation O and the notch Wn as the reference (0°) (see Fig. 3). Then, the chuck table 52 is moved parallel to the Y-axis direction by the parallel feed means, and the thickness of the wafer W is calculated at each predetermined position defined by the change in the position corresponding to the center of rotation O of the wafer W rotating at an appropriate speed and the center of the other end (lower end) of the through hole 14 of the rotating shaft 32 facing the wafer W, and the change in the rotation angle of the chuck table.Thickness information corresponding to all predetermined positions defined in the table 112 shown in Figure 3 is calculated and stored, thereby completing the mapping data.

[0028] In this embodiment, thickness measurement is started from the inside of the outer edge region where the notch Wn is formed (the position indicated by Y0 in the figure) in the direction in which the notch Wn of the wafer W shown on the display means 16 in Figure 2 is formed. After the thickness is measured at the measurement start point (angle 0°, Y0), the thickness of the wafer W is calculated by the thickness calculation means 110 while rotating the wafer W, for example, every 36°, and by rotating the wafer W 360°, thickness information at each point (92, 92, 93, 93, 92, ... 92 μm) is stored in a predetermined position in the table 112 shown in Figure 3. Note that since the thickness at 0° and the thickness at 360° are measured at the same position, the thickness measurement at 360° may be omitted. Next, the chuck table 52 is translated by the parallel feed means, thereby moving the position where the light LB1 is irradiated by the thickness measurement means 4 toward the center of rotation O by a distance obtained by dividing the distance from the measurement start point to the center of rotation O by a predetermined interval. As described above, the thickness of the wafer W is measured every 36° while the wafer W is rotated 360° to measure the thickness of the wafer W. By repeating this process, thickness information for the entire wafer W is recorded on the table 112 shown in FIG. 3 , thereby completing the mapping data. In this embodiment, the position defined by Ym coincides with the center of rotation O of the wafer W. Since the position where the light LB1 is irradiated by the thickness measurement means 4 is the center of rotation O of the wafer W, the thickness of the wafer W does not change even if the thickness of the wafer W is measured multiple times during the 360° rotation. As described above, the control means 100 acquires information about the thickness of the wafer W at all positions defined on the table 112 by the thickness measurement means 4, resulting in the mapping data shown in FIG. 3 . In the above embodiment, the parallel feed means is operated in stages each time the wafer W is rotated 360°, and the position where the light LB1 is irradiated is brought closer to the center of rotation O. However, the present invention is not limited to this, and the thickness of the wafer W may be measured by gradually bringing the position where the light LB1 is irradiated closer to the center of rotation O each time the wafer W is rotated 360°, and the thickness information may be calculated in a so-called spiral manner.

[0029] The determination means 120 of the control means 100 of this embodiment determines that the product is acceptable if the thickness variation is within the tolerance, and determines that the product is unacceptable if the thickness variation is outside the tolerance, based on the mapping data stored in the table 112. Figure 4 shows a flowchart 122 executed by the determination means 120.

[0030] When implementing the flowchart 122, first, in step S1, all of the data in the mapping data described above is referenced, and the maximum value Max of the thickness information is read. In this embodiment, the maximum value Max in the mapping data stored in the table 112 is 93 μm. Next, proceeding to step S2, the minimum value Min in the mapping data 112 is read. In this embodiment, the minimum value Min in the mapping data is 85 μm. Next, proceeding to step S3, the difference D = Max - Min is calculated (D = 8 μm in this embodiment). Here, the control means 100 stores a tolerance T for thickness variation, and the determination means 120 reads the tolerance T (T = 5 μm in this embodiment), and in step S4, determines whether the difference D is within the tolerance T. In this embodiment, since it is determined that the difference D (8 μm) is not within the tolerance T (5 μm) (No), a "fail" is determined in step S6. If the difference D is less than the allowable value T (5 μm), the result is determined as "pass" in step S5, and the flowchart 122 ends (END). The determination results of steps S5 and S6 are displayed on the display means 16 as appropriate, and are also stored in the control means 100.

[0031] According to the above-described embodiment, by creating mapping data, it is possible to grasp the variation in thickness of the wafer W and evaluate the polishing process performed by the polishing apparatus 1. Furthermore, if the variation in thickness is within the tolerance, transport to the next process where laser processing is performed is permitted, and if the variation in thickness is outside the tolerance, reprocessing is instructed, and if reprocessing is not possible, disposal or the like is instructed. This prevents wafers with non-uniform thickness from being divided, and performs division only on wafers with uniform thicknesses that can be appropriately divided, making it possible to reliably divide the wafer into individual device chips, and eliminating the problem of insufficient division areas potentially damaging the device chips.

[0032] The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, when measuring the thickness of a predetermined position on the wafer W, the thickness calculation means 110 performs waveform analysis such as Fourier transform on the spectral interference waveform generated by the image sensor 47 to output thickness information. However, the present invention is not limited to this. For example, a thickness measurement means may be provided that compares a spectral interference waveform obtained based on the return light of the light irradiated through the through hole 14 with a reference waveform recorded in advance in a reference waveform recording unit to determine the thickness from the reference waveform that matches the waveform (see, for example, JP 2020-176999 A). Furthermore, a white light source and a diffraction grating obtained by dispersing white light by an acousto-optical conversion means may be provided. A first pinhole mask that passes light of some wavelengths, a chromatic aberration lens that focuses the light that has passed through the first pinhole mask and irradiates it onto the workpiece, a beam splitter that deflects the reflected light of the light that has been irradiated onto the workpiece, a second pinhole mask that passes the reflected light deflected by the beam splitter, a photodetector that outputs a photodetection signal of the reflected light that has passed through the second pinhole mask, and a thickness measurement means that determines the height position of the workpiece based on a control signal from the acousto-optic deflection means and the photodetection signal from the photodetector (see, for example, Japanese Patent Application Laid-Open No. 2008-209299), may be provided and arranged on the other end of the above-mentioned rotating shaft 32.

[0033] Furthermore, in the above-described embodiment, when the thickness of the wafer W is measured by the thickness measurement means 4, the rotation angle of the wafer W held and rotated on the chuck table 52 is set to be every 36°, but the present invention is not limited to this, and the rotation angle may be set to another angle, for example, every 5°, 10°, etc.

[0034] Furthermore, in the above-described embodiment, the thickness of the wafer W is measured after polishing of the wafer W is completed, but the present invention is not limited to this. For example, the thickness of the wafer may be measured while polishing of the wafer W is being performed by the polishing apparatus 1. In this case, it is preferable to fill the polishing pad with an abrasive in advance and perform dry polishing without supplying slurry from the slurry supply nozzle 24. [Explanation of symbols]

[0035] 1: Polishing device 2: Device housing 21:Supporting wall 22: Guide rail 23: Cleaning water supply nozzle 24: Slurry supply nozzle 3: Polishing means 31: Unit housing 32: Rotation axis 32a: opening 33: Wheel mount 34: Polishing wheel 35: Polishing pad 36: Electric motor 37: Support member 38: Mobile base 39: Polishing feed mechanism 4: Thickness measurement method 41:Light source 41a: First optical path 41b: Second optical path 42: Optical branching section 43: Collimation lens 44: Condenser lens 44 45: Collimation lens 46: Diffraction grating 47: Image sensor 5: Holding means 51: Cover table 52: Chuck table 6: First cassette 7: Second cassette 8: Temporary storage means 9: Cleaning method 10: First transport means 11: Second transport means 12: Third transport means 14:Through hole 100: Control means 110: Thickness calculation means 112: Table 120: Judgment means 122: Flowchart LB1: light LB2: Return light

Claims

1. A polishing apparatus comprising: a chuck table having a rotatable holding surface; polishing means having a rotary shaft for rotatably supporting a polishing pad for polishing a wafer held on the holding surface of the chuck table; vertical feed means for relatively feeding the polishing means in a direction perpendicular to the holding surface of the chuck table; parallel feed means for relatively feeding the polishing means in a direction parallel to the holding surface of the chuck table; and control means, a through hole extending from one end to the other end is formed at the axis of the rotation shaft of the polishing means, and a thickness measuring means for measuring the thickness of the wafer is disposed at one end of the through hole; The control means measures the thickness of the wafer with the thickness measuring means at a position determined by the change in the distance between the center of rotation of the wafer held and rotating on the chuck table fed by the parallel feed means and the center of the other end of the through hole facing the wafer, and the rotation angle of the chuck table, and creates mapping data relating to the wafer thickness.

2. The thickness measuring means is 2. The polishing apparatus according to claim 1, comprising at least: a light source that emits light in a wavelength range that is transparent to the wafer; a condenser that irradiates the light emitted by the light source onto the wafer held on the chuck table; a light branching unit that is disposed in an optical path between the light source and the condenser and branches return light reflected from the wafer held on the chuck table from the optical path; a diffraction grating that disperses the return light branched by the light branching unit into wavelengths; an image sensor that detects the intensity of the light dispersed into wavelengths by the diffraction grating and generates a spectral interference waveform; and thickness calculation means that calculates the spectral interference waveform generated by the image sensor and outputs thickness information.

3. 3. The polishing apparatus according to claim 1, wherein the control means determines that the product is acceptable if the thickness variation is within an allowable value based on the mapping data, and determines that the product is unacceptable if the thickness variation is outside the allowable value.

Images