JP5823762B2 - Thickness detection device and grinding machine - Google Patents

Description

  The present invention relates to a thickness detector for detecting the thickness of a workpiece such as a semiconductor wafer and a grinding machine equipped with the thickness detector.

  For example, in a semiconductor device manufacturing process, devices such as ICs and LSIs are formed in a plurality of regions partitioned by streets (division lines) formed in a lattice shape on the surface of a wafer having a substantially disk shape, Individual devices are manufactured by dividing each region in which devices are formed along a predetermined division line. When manufacturing individual devices in this manner, the back surface is generally ground to a predetermined thickness by grinding with a grinder before dividing the wafer into individual devices.

  In order to grind the back surface of the wafer to a predetermined thickness, it is necessary to grind while measuring the thickness of the wafer held on the holding surface of the chuck table of the grinding machine. As a method for detecting the thickness of the wafer, the first contact needle for measurement for detecting the surface height is brought into contact with the holding surface of the chuck table holding the wafer to obtain the height position HI of the holding surface of the chuck table. Next, H2−HI is calculated while detecting the height position H2 of the upper surface of the wafer by bringing the second contact needle into contact with the ground surface (upper surface) of the wafer held on the holding surface of the chuck table. We are seeking the thickness T of the wafer. (For example, refer to Patent Document 1).

Japanese Patent No. 2993821

In the above-described method for detecting the wafer thickness, the wafer thickness is obtained based on the difference between the height position of the wafer held on the chuck table holding surface and the height position of the chuck table holding surface. Since the thickness of the protective tape attached to protect the device formed on the surface changes depending on the pressing force of the grinding wheel, the wafer is set by measuring the wafer thickness after peeling the protective tape from the wafer surface. There is a problem that the finished thickness is not finished.
Further, in the method of detecting the thickness of the wafer described above, since the contact needle for measurement is brought into contact with the surface to be ground of the wafer, there is a problem that the surface to be ground becomes ring-shaped and the quality of the wafer is deteriorated. is there.

  In order to solve the above problem, the present applicant can accurately detect the thickness of the workpiece even if the workpiece has a protective tape attached to the surface opposite to the workpiece surface, Japanese Patent Application No. 2010-161007 proposes a non-contact type thickness detection device and a grinding machine equipped with a thickness detection device that do not damage the work surface of the work piece. The present invention irradiates light having a predetermined wavelength region having transparency with respect to a workpiece held and processed by a chuck table, and generates a spectral interference waveform from reflected light reflected from the upper and lower surfaces of the workpiece. The waveform analysis is performed based on the spectral interference waveform and the theoretical waveform function, and the optical path length of the reflected light reflected from the upper surface of the workpiece and the optical path length of the reflected light reflected from the lower surface of the workpiece are calculated. It is a thickness detection device for determining the thickness of a workpiece based on the optical path length difference.

  Thus, in the non-contact type thickness detecting apparatus described above, the detection light is irradiated perpendicularly to the upper surface of the workpiece, and therefore the reflected light reflected from the upper surface of the workpiece and the workpiece are transmitted. Since the amount of reflected light reflected on the lower surface is different, the spectral interference waveform required from the reflected light reflected on the upper and lower surfaces of the workpiece cannot be clarified, and the thickness of the workpiece is highly accurate. It is difficult to detect.

  The present invention has been made in view of the above facts, and the main technical problem thereof is a non-contact type thickness detecting device capable of accurately detecting the thickness of a workpiece and a grinding machine equipped with the thickness detecting device. It is to provide.

In order to solve the main technical problem, according to the present invention, in a thickness detection apparatus for detecting the thickness of a workpiece held on a chuck table,
A light emitter having a predetermined wavelength region that is transparent to the workpiece, and a light collector that collects light emitted by the light emitter and irradiates the workpiece held on the chuck table. A detection light irradiation means provided;
A condensing lens that collects the reflected light reflected by the upper and lower surfaces of the work piece irradiated by the detection light irradiation means and held by the chuck table;
A diffraction grating that diffracts interference of reflected light collected by the condenser lens;
An image sensor for detecting light intensity in a predetermined wavelength range of reflected light diffracted by the diffraction grating;
A spectral interference waveform is obtained based on a detection signal from the image sensor, a waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function, and the optical path length of the reflected light reflected from the upper surface of the workpiece and the target are analyzed. Control means for obtaining the thickness of the workpiece based on the optical path length difference with the optical path length of the reflected light reflected from the lower surface of the workpiece,
The detection light irradiation means includes a polarization filter that guides the P-polarized light in the light emitted from the light emitter to the condenser, and the workpiece to be processed is held by the chuck table. It is configured to irradiate the upper surface of the object with a predetermined incident angle ,
The predetermined incident angle is set so that the return light ratio from the upper surface of the workpiece matches the return light ratio from the lower surface,
A thickness detecting device is provided.

According to the present invention, there is provided a chuck table having a holding surface for holding a workpiece, a grinding means for grinding the workpiece held on the chuck table, and a workpiece held on the chuck table. In a grinding machine comprising a thickness detection device for detecting thickness,
The thickness detector is configured to irradiate a work piece held on the chuck table by collecting a light emitter having a predetermined wavelength region that is transparent to the work piece, and light emitted from the light emitter. A detection light irradiation means comprising a condenser
A condensing lens that collects the reflected light reflected by the upper and lower surfaces of the work piece irradiated by the detection light irradiation means and held by the chuck table;
A diffraction grating that diffracts interference of reflected light collected by the condenser lens;
An image sensor for detecting light intensity in a predetermined wavelength range of reflected light diffracted by the diffraction grating;
A spectral interference waveform is obtained based on a detection signal from the image sensor, a waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function, and the optical path length of the reflected light reflected from the upper surface of the workpiece and the target are analyzed. Control means for obtaining the thickness of the workpiece based on the optical path length difference with the optical path length of the reflected light reflected from the lower surface of the workpiece,
The detection light irradiation means includes a polarization filter that guides the P-polarized light in the light emitted from the light emitter to the condenser, and the workpiece to be processed is held by the chuck table. It is configured to irradiate the upper surface of the object with a predetermined incident angle ,
The predetermined incident angle is set so that the return light ratio from the upper surface of the workpiece matches the return light ratio from the lower surface,
A grinding machine is provided.

The workpiece is made of a silicon substrate, and the predetermined incident angle is set to 60 degrees.

In the thickness detection apparatus and the grinding machine according to the present invention, the detection light irradiation means includes a polarization filter that guides the P-polarized light in the light emitted from the light emitter to the condenser, and chucks the P-polarized light polarized by the polarization filter. The upper surface of the workpiece held on the table is irradiated with a predetermined incident angle, and the predetermined incident angle is determined by the ratio of the return light from the upper surface of the workpiece and the return light from the lower surface. Since the ratio is set to match, the amount of reflected light reflected from the upper surface of the workpiece held on the chuck table and the amount of reflected light reflected from the lower surface of the workpiece are made substantially uniform. Can do. Therefore, the spectral interference waveform obtained from the reflected light reflected from the upper and lower surfaces of the workpiece held on the chuck table becomes clear, and the thickness of the workpiece can be detected with high accuracy. It can be accurately ground down to a thickness of several μm.
Moreover, since the thickness detection apparatus according to the present invention is a non-contact type, the surface to be ground of the workpiece is not damaged.

The perspective view of the grinding machine equipped with the thickness detection apparatus comprised according to this invention. FIG. 2 is a block configuration diagram of a thickness detection device installed in the grinding machine shown in FIG. The graph which shows the angle dependence of the return light ratio from the upper surface of a silicon substrate in the P polarized light irradiated to the silicon substrate. The graph which shows the angle dependence of the return light ratio from the lower surface of a silicon substrate in the P polarized light irradiated to the silicon substrate. The graph which shows the angle dependence of the return light ratio from the upper surface of a silicon substrate in the S polarized light irradiated to the silicon substrate. The graph which shows the angle dependence of the return light ratio from the lower surface of a silicon substrate in the S polarized light irradiated to the silicon substrate. Explanatory drawing which shows the spectral interference waveform calculated | required by the control means which comprises the thickness detection apparatus shown in FIG. Explanatory drawing which shows the relationship between the optical path length difference from the upper surface of a to-be-processed object calculated | required by the control means which comprises the thickness detection apparatus shown in FIG. FIG. 2 is an explanatory diagram of a grinding process performed by the grinding machine shown in FIG.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a thickness detecting device and a grinding machine equipped with the thickness detecting device configured according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a perspective view of a grinding machine equipped with a thickness detecting device constructed according to the present invention. A grinding machine 1 shown in FIG. 1 includes an apparatus housing denoted as a whole by reference numeral 2. This device housing 2 has a rectangular parallelepiped main portion 21 that extends elongated and an upright wall 22 that is provided at the rear end portion (upper right end in FIG. 1) of the main portion 21 and extends upward. A pair of guide rails 221 and 221 extending in the vertical direction are provided on the front surface of the upright wall 22. A grinding unit 3 as grinding means is mounted on the pair of guide rails 221 and 221 so as to be movable in the vertical direction.

  The grinding unit 3 includes a moving base 31 and a spindle unit 4 mounted on the moving base 31. The movable base 31 is provided with a pair of legs 311 and 311 extending in the vertical direction on both sides of the rear surface. The pair of legs 311 and 311 is slidably engaged with the pair of guide rails 221 and 221. Guided grooves 312 and 312 are formed. As described above, a support portion 313 protruding forward is provided on the front surface of the movable base 31 slidably mounted on the pair of guide rails 221 and 221 provided on the upright wall 22. A spindle unit 4 as a grinding means is attached to the support portion 313.

  The spindle unit 4 as grinding means includes a spindle housing 41 mounted on a support portion 313, a rotating spindle 42 rotatably disposed on the spindle housing 41, and a drive source for driving the rotating spindle 42 to rotate. As a servo motor 43. One end (lower end in FIG. 1) of the rotary spindle 42 rotatably supported by the spindle housing 41 is disposed so as to protrude from the lower end of the spindle housing 41, and a wheel mount is mounted on one end (lower end in FIG. 1). 44 is provided. Then, the grinding wheel 5 is attached to the lower surface of the wheel mount 44. The grinding wheel 5 includes an annular grindstone base 51 and a plurality of segments made of a grinding grindstone 52 mounted on the lower surface of the grindstone base 51, and the grindstone base 51 is wheeled by fastening screws 53. Mounted on the mount 44. The servo motor 43 is controlled by the control means 10 described later.

  The illustrated grinding machine 1 includes a grinding unit feed mechanism 6 that moves the grinding unit 3 in the vertical direction (direction perpendicular to a holding surface of a chuck table described later) along the pair of guide rails 221 and 221. ing. The grinding unit feed mechanism 6 includes a male screw rod 61 disposed on the front side of the upright wall 22 and extending substantially vertically. The male threaded rod 61 is rotatably supported by bearing members 62 and 63 whose upper end and lower end are attached to the upright wall 22. The upper bearing member 62 is provided with a pulse motor 64 as a drive source for rotationally driving the male screw rod 61, and the output shaft of the pulse motor 64 is connected to the male screw rod 61 by transmission. A connecting portion (not shown) that protrudes rearward from the center portion in the width direction is also formed on the rear surface of the movable base 31, and a through female screw hole (not shown) that extends in the vertical direction is formed in this connecting portion. The male screw rod 61 is screwed into the female screw hole. Accordingly, when the pulse motor 64 is rotated forward, the moving base 31, that is, the polishing unit 3 is lowered or advanced, and when the pulse motor 64 is reversed, the movable base 31, that is, the grinding unit 3 is raised or retracted. The pulse motor 64 is controlled by the control means 10 described later.

  A chuck table mechanism 7 is disposed in the main portion 21 of the housing 2. The chuck table mechanism 7 includes a chuck table 71, a cover member 72 that covers the periphery of the chuck table 71, and bellows means 73 and 74 disposed before and after the cover member 72. The chuck table 71 is configured to be rotated by a rotation driving unit (not shown), and is configured to suck and hold the wafer 11 as a workpiece on its upper surface (holding surface) by operating a suction unit (not shown). Has been. In the illustrated embodiment, the wafer 11 is made of a silicon wafer, and a protective tape 12 as a protective member is attached to the surface of the wafer 11, and the protective tape 12 side is held on the upper surface (holding surface) of the chuck table 71. Is done. Further, the chuck table 71 is moved between a workpiece placement area 70a shown in FIG. 1 and a grinding area 70b facing the grinding wheel 5 constituting the spindle unit 4 by a chuck table moving means (not shown). The bellows means 73 and 74 can be formed from any suitable material such as campus cloth. The front end of the bellows means 73 is fixed to the front wall of the main portion 21, and the rear end is fixed to the front end surface of the cover member 72. The front end of the bellows means 74 is fixed to the rear end surface of the cover member 72, and the rear end is fixed to the front surface of the upright wall 22 of the apparatus housing 2. When the chuck table 71 is moved in the direction indicated by the arrow 71a, the bellows means 73 is expanded and the bellows means 74 is contracted. When the chuck table 71 is moved in the direction indicated by the arrow 71b, the bellows means 73 is By being contracted, the bellows means 74 is extended.

  The illustrated grinding machine 1 includes a thickness detecting device 8 for detecting the thickness of the workpiece held on the chuck table 71. The thickness detecting device 8 is supported by a support means 80 rotatably disposed on the cover member 72 so as to be turned with a predetermined radius. Hereinafter, the thickness detection apparatus 8 will be described with reference to FIG.

  The thickness detection apparatus 8 in the illustrated embodiment includes a detection light irradiation means 81 for irradiating detection light to a wafer 11 as a workpiece held on a chuck table 71. The detection light irradiation means 81 includes a light emission source 811 that emits light having a predetermined wavelength region that is disposed in the detection light irradiation path 80a and is transmissive to the wafer 11 as a workpiece, and the light emission source 811. In the light emitted from the light source 811 that is disposed between the light source 811 and the light collector 812. The light collector 811 collects the light emitted from the light source and irradiates the wafer 11 held on the chuck table 71. And a polarizing filter 813 made of a bias holding fiber that guides the P-polarized light to the condenser 812. The detection light irradiation means 81 configured in this way is configured to irradiate the upper surface of the wafer 11 held by the chuck table 71 with a predetermined incident angle α with the P-polarized light polarized by the polarization filter 813. Yes. As the light emission source 811, for example, an LED, an SLD, an LD, a halogen power source, an ASE power source, or a supercontinuum power source that emits light having a wavelength of 820 to 870 nm can be used. In addition, in the illustrated embodiment, the polarizing filter 813 that guides the P-polarized light in the light emitted from the light source 811 to the condenser 812 has been described using the polarization holding fiber, but a polarizing plate may be used. . The incident angle α when the P-polarized light polarized by the polarizing filter 813 is condensed by the condenser 812 and applied to the upper surface of the wafer 11 held on the chuck table 71 is the wafer 11 as the workpiece. Is preferably set to 60 degrees.

  Here, the angle dependence of the ratio of the return light from the upper surface of the silicon substrate in the P-polarized light irradiated to the silicon substrate and the angle dependence of the ratio of the return light from the lower surface of the silicon substrate in the P-polarized light irradiated to the silicon substrate are shown. 3 and FIG. FIG. 3 shows the angle dependence of the return light ratio from the upper surface of the silicon substrate in the P-polarized light irradiated on the silicon substrate, and FIG. 4 shows the return light ratio from the lower surface of the silicon substrate in the P-polarized light irradiated on the silicon substrate. Angle dependence is shown. As shown in FIG. 3, the ratio of the return light from the top surface of the silicon substrate in the P-polarized light irradiated to the silicon substrate decreases as the incident angle α increases from zero (0) degrees, and decreases when the incident angle α is 60 degrees. .1 and increases rapidly after the incident angle α reaches a minimum of 75 degrees. On the other hand, as shown in FIG. 4, the ratio of the return light from the lower surface of the silicon substrate in the P-polarized light irradiated to the silicon substrate increases as the incident angle α increases from zero (0) degree, and the incident angle α becomes 60 degrees. After the incident angle α reaches a maximum of 75 degrees, it decreases rapidly. In this way, when the P-polarized light is irradiated onto the silicon substrate, the ratio of the return light from the upper surface matches the ratio of the return light from the lower surface at an incident angle α of 60 degrees. Therefore, by setting the incident angle α to 60 degrees, the amount of reflected light reflected from the upper surface of the wafer 11 as a workpiece held on the chuck table 71 and the amount of reflected light reflected from the lower surface of the wafer 11 are set. Can be made substantially uniform.

  Next, the angle dependence of the return light ratio when the silicon substrate is irradiated with S-polarized light will be examined. FIG. 5 shows the angle dependence of the return light ratio from the top surface of the silicon substrate in the S-polarized light irradiated on the silicon substrate, and FIG. 6 shows the bottom surface of the silicon substrate in the S-polarized light irradiated on the silicon substrate. The angle dependence of the return light ratio is shown. As can be seen from FIGS. 5 and 6, the ratio of the return light from the upper surface of the silicon substrate in the S-polarized light irradiated to the silicon substrate matches the ratio of the return light from the lower surface of the silicon substrate in the S-polarized light irradiated to the silicon substrate. There is no incident angle α. Therefore, when S-polarized light is used, the amount of reflected light reflected from the upper surface of the wafer 11 as a workpiece held on the chuck table 71 and the amount of reflected light reflected from the lower surface of the wafer 11 are made uniform. Is impossible to do. Thus, S-polarized light is not suitable for use as detection light because there is no incident angle α in which the ratio of the return light from the upper surface of the silicon substrate and the ratio of the return light from the lower surface of the silicon substrate are the same. As described above, it is necessary to use P-polarized light.

  As shown in FIG. 2, a condensing lens 82 and a transmission means are provided in a light receiving path 80b for receiving reflected light reflected by the upper and lower surfaces of the wafer 11 irradiated by the detection light irradiation means 81 and held by the chuck table 71. 83, a collimation lens 84, a diffraction grating 85, and a line image sensor 86 are disposed. The condensing lens 82 condenses the reflected light reflected by the upper surface and the lower surface of the wafer 11 irradiated by the detection light irradiation means 81 and held by the chuck table 71. The transmission means 83 transmits reflected light collected by the condensing lens 82 toward the collimation lens 84, and is composed of a bias holding fiber or an optical fiber. The collimation lens 84 forms the reflected light transmitted by the transmission means 83 into parallel light and guides it to the diffraction grating 85. The diffraction grating 85 diffracts the interference of the two reflected lights formed into parallel light by the collimation lens 84 and sends a diffraction signal corresponding to each wavelength to the line image sensor 86. The line image sensor 86 detects the light intensity at each wavelength of the reflected light diffracted by the diffraction grating 85 and sends a detection signal to the control means 10.

  The control means 10 obtains a spectral interference waveform from the detection signal from the line image sensor 86, executes waveform analysis based on the spectral interference waveform and a theoretical waveform function, and detects the upper surface of the wafer 11 held on the chuck table 71 and The optical path length difference (d) of the reflected light reflected from the lower surface and guided to the light receiving path 80b is obtained, and the thickness (t) of the wafer 11 is obtained based on the optical path length difference (d). That is, the control means 10 obtains a spectral interference waveform as shown in FIG. 7 from the detection signal from the line image sensor 86. FIG. 7 shows a spectral interference waveform when the wafer thickness is 70 μm, the horizontal axis indicates the wavelength (nm) of the reflected light, and the vertical axis indicates the light intensity. The reflected light reflected by the upper and lower surfaces of the wafer 11 held on the chuck table 71 and guided to the light receiving path 80b has a detection light incident angle α set to 60 degrees as described above, and is reflected on the upper surface of the wafer 11. Since the reflected light quantity and the reflected light quantity reflected by the lower surface of the wafer 11 are substantially uniform, the spectral interference waveform becomes clear.

Hereinafter, an example of the waveform analysis performed by the control unit 10 based on the spectral interference waveform and the theoretical waveform function will be described.
The control means 10 executes waveform analysis based on the spectral interference waveform and a theoretical waveform function. This waveform analysis can be executed based on, for example, Fourier transformation theory or wavelet transformation theory. In the embodiment described below, examples using the Fourier transformation formulas shown in the following formulas 1, 2, and 3 are used. explain.

In the above equation, λ is a wavelength, d is the optical path length difference (d), and W (λ _n ) is a window function.
Equation 1 above shows that the wave period is closest (highly correlated) between the cos theoretical waveform and the spectral interference waveform I (λ _n ), that is, the phase relationship between the spectral interference waveform and the theoretical waveform function. The optical path length difference (d) having a high number is obtained. Further, the above formula 2 is obtained by comparing the theoretical waveform of sin and the spectral interference waveform I (λ _n ) with the closest wave period (high correlation), that is, the spectral interference waveform and the theoretical waveform function. The correlation coefficient determines the optical path length difference (d). Then, the above Equation 3 obtains the average value of the result of Equation 1 and the result of Equation 2.

  The control means 10 obtains an optical path length difference (d) with a high signal intensity as shown in FIG. 8 by executing calculations based on the above formulas 1, 2, and 3. In FIG. 8, the horizontal axis represents the optical path length difference (d), and the vertical axis represents the signal intensity. In the example shown in FIG. 8, a peak waveform with a high signal intensity appears at a position where the optical path length difference (d) is 70 μm. This optical path length difference (d) corresponds to the thickness (t) of the wafer 11. In the waveform analysis described above, since the spectral interference waveform that is the basis of the waveform analysis is clear as described above, the thickness (t) of the wafer 11 can be obtained with high accuracy.

Next, a grinding method for grinding a wafer to a predetermined thickness using the grinding machine 1 equipped with the thickness detecting device 8 configured as described above will be described with reference to FIGS. 1 and 9.
That is, the wafer 11 having the protective tape 12 attached to the surface places the protective tape 12 side on the chuck table 71 positioned in the workpiece placement area 70a in the grinding machine 1. Then, it is sucked and held on the chuck table 71 by operating a suction means (not shown). Accordingly, the back surface 11b of the wafer 11 sucked and held on the chuck table 71 is on the upper side. If the wafer 11 is sucked and held on the chuck table 71, the control means 10 operates a moving means (not shown) to move the chuck table 71 in the direction indicated by the arrow 71a in FIG. 9, the outer peripheral edges of the plurality of grinding wheels 52 of the grinding wheel 5 are positioned so as to pass through the center of rotation of the chuck table 71. Then, the thickness detection device 8 is positioned at a detection position above the wafer 11 held by the chuck table 71.

  As described above, when the wafer 11 held on the grinding wheel 5 and the chuck table 71 is set in a predetermined positional relationship and the thickness detection device 8 is positioned at the detection position, the control means 10 drives a rotation drive means (not shown). The chuck table 71 is rotated in the direction indicated by an arrow 71c in FIG. 9 at a rotational speed of, for example, 300 rpm, and the servo motor 43 is driven to rotate the grinding wheel 5 in the direction indicated by an arrow 5a at a rotational speed of, for example, 6000 rpm. . Then, the control means 10 drives the pulse motor 64 of the grinding unit feed mechanism 6 in the normal direction to lower the grinding wheel 5 (grind feed) and press the plurality of grinding wheels 52 onto the upper surface of the wafer 11 with a predetermined pressure. As a result, the upper surface of the wafer 11, that is, the surface to be ground is ground (grinding step). In this grinding step, the thickness (t) at the time of processing the wafer 11 is measured. When the thickness (t) of the wafer 11 measured by the thickness detector 8 reaches a predetermined value, the control means 10 drives the pulse motor 64 of the grinding unit feed mechanism 6 in the reverse direction to raise the grinding wheel 5.

As described above, in the above-described embodiment, the incident angle α of the detection light irradiated by the detection light irradiation unit 81 is set to 60 degrees, so that the wafer 11 made of the silicon substrate held on the chuck table 71 is The reflected light reflected from the upper and lower surfaces and guided to the light receiving path 80b is substantially uniform in the amount of reflected light reflected from the upper surface of the wafer 11 and the reflected light reflected from the lower surface of the wafer 11. Since the waveform becomes clear and the thickness (t) of the wafer can be detected with high accuracy, the wafer 11 can be accurately ground to a thickness of several μm.
In the embodiment described above, since the thickness (t) of the wafer 11 is measured by the non-contact type thickness detector 8, the surface to be ground of the wafer is not damaged.

1: Grinding machine 2: Equipment housing 3: Grinding unit 31: Moving base 4: Spindle unit 41: Spindle housing 42: Rotating spindle 43: Servo motor 44: Wheel mount 5: Grinding wheel 51: Grinding wheel base 52: Grinding wheel 6: Grinding unit feed mechanism 64: Pulse motor 7: Chuck table mechanism 71: Chuck table 8: Thickness detection device 81: Detection light irradiation means 811: Light source 812: Condenser 813: Deflection holding fiber (polarization filter)
82: Condensing lens 83: Transmission means 84: Collimation lens 85: Diffraction grating 86: Line image sensor 10: Control means 11: Wafer

Claims (4)

In a thickness detector for detecting the thickness of a workpiece held on a chuck table,
A light emitter having a predetermined wavelength region that is transparent to the workpiece, and a light collector that collects light emitted by the light emitter and irradiates the workpiece held on the chuck table. A detection light irradiation means provided;
A condensing lens that collects the reflected light reflected by the upper and lower surfaces of the work piece irradiated by the detection light irradiation means and held by the chuck table;
A diffraction grating that diffracts interference of reflected light collected by the condenser lens;
An image sensor for detecting light intensity in a predetermined wavelength range of reflected light diffracted by the diffraction grating;
A spectral interference waveform is obtained based on a detection signal from the image sensor, a waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function, and the optical path length of the reflected light reflected from the upper surface of the workpiece and the target are analyzed. Control means for obtaining the thickness of the workpiece based on the optical path length difference with the optical path length of the reflected light reflected from the lower surface of the workpiece,
The detection light irradiation means includes a polarization filter that guides the P-polarized light in the light emitted from the light emitter to the condenser, and the workpiece to be processed is held by the chuck table. It is configured to irradiate the upper surface of the object with a predetermined incident angle ,
The predetermined incident angle is set so that the return light ratio from the upper surface of the workpiece matches the return light ratio from the lower surface,
A thickness detection apparatus characterized by the above. The thickness detection apparatus according to claim 1 , wherein the workpiece is made of a silicon substrate, and the predetermined incident angle is set to 60 degrees. A chuck table having a holding surface for holding a workpiece, a grinding means for grinding the workpiece held on the chuck table, and a thickness detection device for detecting the thickness of the workpiece held on the chuck table In a grinding machine comprising:
The thickness detector is configured to irradiate a work piece held on the chuck table by collecting a light emitter having a predetermined wavelength region that is transparent to the work piece, and light emitted from the light emitter. A detection light irradiation means comprising a condenser
A condensing lens that collects the reflected light reflected by the upper and lower surfaces of the work piece irradiated by the detection light irradiation means and held by the chuck table;
A diffraction grating that diffracts interference of reflected light collected by the condenser lens;
An image sensor for detecting light intensity in a predetermined wavelength range of reflected light diffracted by the diffraction grating;
A spectral interference waveform is obtained based on a detection signal from the image sensor, a waveform analysis is performed based on the spectral interference waveform and a theoretical waveform function, and the optical path length of the reflected light reflected from the upper surface of the workpiece and the target are analyzed. Control means for obtaining the thickness of the workpiece based on the optical path length difference with the optical path length of the reflected light reflected from the lower surface of the workpiece,
The detection light irradiation means includes a polarization filter that guides the P-polarized light in the light emitted from the light emitter to the condenser, and the workpiece to be processed is held by the chuck table. It is configured to irradiate the upper surface of the object with a predetermined incident angle ,
The predetermined incident angle is set so that the return light ratio from the upper surface of the workpiece matches the return light ratio from the lower surface,
A grinding machine characterized by that. The grinding machine according to claim 3 , wherein the workpiece is made of a silicon substrate, and the predetermined incident angle is set to 60 degrees.

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