JP5443180B2 - Thickness detection device and grinding machine - Google Patents

Description

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

  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. The wafer is generally formed to have a predetermined thickness by grinding the back surface with a grinder before dividing into individual devices.

  As a method for detecting the thickness of the wafer, the height position HI of the holding surface of the chuck table is obtained by bringing the first contact needle for measurement for detecting the surface height into contact with the holding surface of the chuck table holding the wafer. 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 surface to be ground (upper surface) held on the holding surface of the chuck table. The thickness T of the wafer is obtained. (For example, refer to Patent Document 1).

Patent No. 2993821

Thus, in the above-described method for detecting the thickness of the wafer, the thickness of the wafer is obtained based on the difference between the height position of the wafer held on the holding surface of the chuck table and the height position of the holding surface of the chuck table. Therefore, the thickness of the protective tape attached to protect the device formed on the surface of the wafer is changed by the pressing force of the grinding wheel, so that the thickness of the wafer is measured after peeling the protective tape from the surface of the wafer. Then, there is a problem that the wafer is not finished to the set thickness.
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.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is that the thickness of the workpiece is accurately measured even when the workpiece has a protective tape attached to the surface opposite to the workpiece. Another object of the present invention is to provide a thickness detecting device and a grinding machine equipped with the thickness detecting device that can detect the surface of the workpiece and does not damage the processing surface of the workpiece.

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 emitting source that emits light with a predetermined wavelength region that is transparent to the workpiece;
First light branching means for guiding light from the light emitting source to the first path and for guiding reflected light that travels backward through the first path to the second path;
A collimation lens that forms light guided to the first path into parallel light;
Second light branching means for dividing light formed into parallel light by the collimation lens into a third path and a fourth path;
An objective lens that is disposed in the third path and guides the light guided to the third path to a workpiece held by the chuck table;
Parallel light disposed between the second light branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens so that light from the objective lens is reflected. A condenser lens that generates pseudo-parallel light;
A reflecting mirror that is disposed in the fourth path and reflects parallel light guided to the fourth path and reverses the reflected light to the fourth path;
Reflected by the reflecting mirror, the fourth path, the second light branching unit, the collimation lens, and the first path are reversed to be guided from the first light branching unit to the second path. The reflected light is reflected by the upper and lower surfaces of the workpiece held on the chuck table, and the objective lens, the condenser lens, the second light branching unit, the collimation lens, and the first path are reversed. A diffraction grating for diffracting interference with the reflected light guided from the first light branching means to the second path;
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 an optical path length to the reflection mirror in the fourth path is calculated. The first optical path length difference (d1) with the optical path length to the upper surface of the workpiece held by the chuck table in the third path is obtained, and the optical path length to the reflecting mirror in the fourth path A second optical path length difference (d2) from the optical path length to the lower surface of the workpiece held on the chuck table in the third path is obtained, and the first optical path length difference (d1) and the second optical path length difference are obtained. And a control means for obtaining the thickness (T) of the workpiece based on the optical path length difference (d2).
The control means is based on the optical path length difference (d3) between the actual thickness (T) before processing the workpiece, the first optical path length difference (d1), and the second optical path length difference (d2). A refractive index detection step for obtaining a refractive index (r = d3 / T) of the workpiece, the refractive index (r), the first optical path length difference (d1) during processing of the workpiece, and the first A thickness detection step of obtaining a thickness (T = d3 / r) of the workpiece based on an optical path length difference (d3) from an optical path length difference (d2) of 2;
A thickness detecting device is provided.

  In the refractive index detection step, the first optical path length difference (d1) and the second optical path length are irradiated by irradiating the upper surface of the workpiece with detection light before processing the workpiece held on the chuck table. The optical path length to the reflection mirror in the fourth path by detecting the difference (d2) and the optical path length difference (d3) and irradiating the upper surface of the protective member attached to the lower surface of the workpiece with the detection light. And the optical path length difference (d4) between the optical path length to the upper surface of the protective member in the third path and subtracting the optical path length difference (d4) from the first optical path length difference (d1). The actual thickness (T = d1−d4) is obtained, and the refractive index (r = d3 / T) of the workpiece is obtained by dividing the optical path length difference (d3) by the actual thickness (T).

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 includes a light source that emits light having a predetermined wavelength region that is transmissive to a workpiece;
First light branching means for guiding light from the light emitting source to the first path and for guiding reflected light that travels backward through the first path to the second path;
A collimation lens that forms light guided to the first path into parallel light;
Second light branching means for dividing light formed into parallel light by the collimation lens into a third path and a fourth path;
An objective lens that is disposed in the third path and guides the light guided to the third path to a workpiece held by the chuck table;
Parallel light disposed between the second light branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens so that light from the objective lens is reflected. A condenser lens that generates pseudo-parallel light;
A reflecting mirror that is disposed in the fourth path and reflects parallel light guided to the fourth path and reverses the reflected light to the fourth path;
Reflected by the reflecting mirror, the fourth path, the second light branching unit, the collimation lens, and the first path are reversed to be guided from the first light branching unit to the second path. The reflected light is reflected by the upper and lower surfaces of the workpiece held on the chuck table, and the objective lens, the condenser lens, the second light branching unit, the collimation lens, and the first path are reversed. A diffraction grating for diffracting interference with the reflected light guided from the first light branching means to the second path;
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 an optical path length to the reflection mirror in the fourth path is calculated. The first optical path length difference (d1) with the optical path length to the upper surface of the workpiece held by the chuck table in the third path is obtained, and the optical path length to the reflecting mirror in the fourth path A second optical path length difference (d2) from the optical path length to the lower surface of the workpiece held on the chuck table in the third path is obtained, and the first optical path length difference (d1) and the second optical path length difference are obtained. And a control means for obtaining the thickness (T) of the workpiece based on the optical path length difference (d2).
The control means irradiates the upper surface of the workpiece with detection light before processing the workpiece held on the chuck table to thereby detect the first optical path length difference (d1) and the second optical path length difference ( d2) and the optical path length difference (d3), and the optical path length to the reflection mirror in the fourth path by irradiating the upper surface of the protective member attached to the lower surface of the workpiece with the detection light An optical path length difference (d4) from the optical path length to the upper surface of the protection member in the third path is obtained, and the optical path length difference (d4) is subtracted from the first optical path length difference (d1). Is obtained, and the refractive index for obtaining the refractive index (r = d3 / T) of the workpiece is obtained by dividing the optical path length difference (d3) by the actual thickness (T). An optical path length difference (d3) between the refractive index (r) and the first optical path length difference (d1) and the second optical path length difference (d2) when processing the workpiece; ) To detect the thickness of the workpiece (T = d3 / r) based on
A grinding machine is provided.

  The thickness detection apparatus according to the present invention is configured as described above, and detects the thickness (T) at the time of processing the workpiece based on the optical path length difference of the reflected light reflected from the upper surface and the lower surface of the workpiece. The thickness (T) of the workpiece can be accurately detected without being affected by the change in the thickness of the protective tape attached to the workpiece. In addition, the thickness detection apparatus according to the present invention obtains the refractive index (r) of the workpiece, and obtains the thickness (T) during machining of the workpiece in consideration of the refractive index (r). Even if the refractive index varies depending on the material, the accurate thickness (T) of the workpiece can be detected. Furthermore, 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.

1 is a perspective view of a grinding machine configured in accordance with the present invention. FIG. 2 is a block configuration diagram of a thickness detection device installed in the grinding machine shown in FIG. 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 of the optical path length difference which shows the optical path length difference to the upper surface of a workpiece calculated by the control means which comprises the thickness detection apparatus shown in FIG. 2, the optical path length difference to the lower surface of a workpiece, and the thickness of a workpiece . FIG. 2 is an explanatory view showing a method of actually measuring the thickness of a workpiece held on a chuck table constituting the grinding machine 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 apparatus 1 shown in FIG. 1 includes an apparatus housing generally indicated by 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. The grinding wheel 5 is attached to the lower surface of the wheel mount 44. The grinding wheel 5 is composed of an annular grinding wheel base 51 and a plurality of segments made up of grinding wheels 52 mounted on the lower surface of the grinding wheel base 51, and the grinding wheel 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 apparatus 1 includes a grinding unit feed mechanism 6 that moves the grinding unit 3 in the vertical direction (a 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 10 is formed with a notch 111 representing a crystal orientation on the outer peripheral portion, and a protective tape 12 as a protective member is attached to the surface of the wafer 10, and the protective tape 12 side is the chuck table 71. Is held on the upper surface (holding surface). 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 apparatus 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 device 8 in the illustrated embodiment includes a light source 81 that emits light having a predetermined wavelength region that is transmissive to a wafer 11 as a workpiece, and the light from the light source 81 is first. The first light branching means 82 that guides the reflected light that travels back to the first path 8a to the second path 8b and forms the light guided to the first path 8a into parallel light. A collimation lens 83 and second light branching means 84 that divides the light formed by the collimation lens 83 into parallel light into a third path 8c and a fourth path 8d are provided.

  As the light emitting source 81, for example, an LED, SLD, LD, halogen power source, ASE power source, or supercontinuum power source that emits light having a wavelength of 820 to 870 nm can be used. The first optical branching unit 82 may be a polarization maintaining fiber coupler, a polarization maintaining fiber circulator, a single mode fiber coupler, a single mode fiber coupler circulator, or the like. In the illustrated embodiment, the second light branching means 84 is constituted by a beam splitter 841 and a direction changing mirror 842. The path from the light emitting source 81 to the first light branching means 82 and the first path 8a are constituted by optical fibers.

  In the third path 8c, the objective lens 85 that guides the light guided to the third path 8c to the wafer 11 as a workpiece held by the chuck table 71, the objective lens 85, and the second lens 8c. A condensing lens 86 is disposed between the light branching means 84. The condensing lens 86 condenses the parallel light guided from the second light branching means 84 to the third path 8c, positions the condensing point in the objective lens 85, and quasi-parallels the light from the objective lens 85. Generate into light. In this way, the condenser lens 86 is disposed between the objective lens 85 and the second light branching means 84 to generate light from the objective lens 85 as pseudo-parallel light, thereby being held on the chuck table 71. When the reflected light reflected by the wafer 11 goes back through the objective lens 85, the condensing lens 86, the second light branching means 84, and the collimation lens 83, it can be converged on the optical fiber constituting the first path 6a. .

  The fourth path 8d is provided with a reflection mirror 87 that reflects the parallel light guided to the fourth path 6d and reverses the reflected light to the fourth path 6d. The reflection mirror 87 is attached to the lens case 850 of the objective lens 85 in the illustrated embodiment.

  In the second path 8b, a collimation lens 88, a diffraction grating 89, a condenser lens 90, and a line image sensor 91 are disposed. The collimation lens 88 is reflected by the reflection mirror 87 and travels backward from the first light branching means 82 to the second path 8d, the second light branching means 84, the collimation lens 83, and the first path 6a. The reflected light guided to 8b is reflected by the upper and lower surfaces of the wafer 11 held on the chuck table 71, and is reflected by the objective lens 85, the condensing lens 86, the second light branching means 84, the collimation lens 83, and the first path. The reflected light guided backward from 8a to the second path 8b from the first light branching means 82 is formed into parallel light. The diffraction grating 89 diffracts the interference of the both reflected lights formed in the parallel light by the collimation lens 88 and sends a diffraction signal corresponding to each wavelength to the line image sensor 91 via the condenser lens 90. The line image sensor 91 detects the light intensity at each wavelength of the reflected light diffracted by the diffraction grating 89 and sends a detection signal to the control means 10.

  The control means 10 obtains the spectral interference waveform from the detection signal from the image sensor 81, executes waveform analysis based on the spectral interference waveform and the theoretical waveform function, and the optical path length to the reflection mirror 87 in the fourth path 8d. And the first optical path length difference (d1) between the optical path length to the upper surface of the wafer 11 held by the chuck table 71 in the third path 8c, and the optical path length to the reflecting mirror in the fourth path 8d A second optical path length difference (d2) from the optical path length to the lower surface of the wafer 11 held by the chuck table 71 in the third path 8c is obtained, and the first optical path length difference (d1) and the second optical path length difference are obtained. The thickness (T) of the wafer 11 is obtained based on the optical path length difference (d2). That is, the control means 10 obtains a spectral interference waveform as shown in FIG. 3 based on the detection signal from the image sensor 91. In FIG. 3, the horizontal axis indicates the wavelength of the reflected light, and the vertical axis indicates the light intensity.

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 optical path length from the beam splitter 841 of the second optical branch means 84 to the reflecting mirror 87 in the fourth path 8d is (L1), and the beam splitter 841 of the second optical branch means 84 in the third path 8c. The optical path length from the wafer 11 held on the chuck table 71 to the upper surface of the wafer 11 is (L2), and the wafer 11 held on the chuck table 71 from the beam splitter 841 of the second optical branching means 84 in the third path 8c. The optical path length to the lower surface of the optical path is (L3), the difference between the optical path length (L1) and the optical path length (L2) is the first optical path length difference (d1 = L1-L2), and the optical path length (L1) and the optical path length The difference from (L3) is the second optical path length difference (d2 = L1-L3).

  Next, the control means 10 executes waveform analysis based on the spectral interference waveform and the 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 first optical path length difference (d1 = L1−L2) and second optical path length difference (d2 = L1−L3), and W (λi) is a window function.
The above Equation 1 is the closest wave period (high correlation) in comparison between the theoretical waveform of cos and the spectral interference waveform (I (λ _n )), that is, the spectral interference waveform and the theoretical waveform function. An optical path length difference (d) having a high correlation coefficient is obtained. In addition, 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. The correlation coefficient with the function obtains the first optical path length difference (d1 = L1-L2) and the second optical path length difference (d2 = L1-L3). 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 performs the calculation based on the above-described Equation 1, Equation 2, and Equation 3, so that the signal intensity has the first optical path length difference (d1 = L1-L2) and the second optical path as shown in FIG. The length difference (d2 = L1-L3) is obtained. In FIG. 4, the horizontal axis indicates the optical path length difference (d), and the vertical axis indicates the signal intensity. In the example shown in FIG. 4, the signal intensity is high at the position where the optical path length difference (d) is 620 μm and the optical path length difference (d) is 500 μm. The signal intensity (A) at the position where the optical path length difference (d) is 620 μm represents the upper surface position of the wafer 11 at the position of the first optical path length difference (d1 = L1−L2). The signal intensity (B) at the position where the optical path length difference (d) is 500 μm represents the position of the lower surface of the wafer 11 at the position of the second optical path length difference (d2 = L1−L3). The optical path length difference (d3 = d1-d2) between the first optical path length difference (d1 = L1-L2) and the second optical path length difference (d2 = L1-L3) corresponds to the thickness (T0) of the wafer 11. To do.

  As described above, the thickness of the wafer 11 obtained by the optical path length difference (d3 = d1-d2) between the first optical path length difference (d1 = L1-L2) and the second optical path length difference (d2 = L1-L3). (T0) is different from the actual thickness of the wafer 11. That is, since the refractive index of the wafer 11 which is a workpiece is larger than that in the air, the optical path length of the reflected light reflected by the lower surface of the wafer 11 becomes long. Therefore, as described above, the wafer 11 obtained by the optical path length difference (d3 = d1-d2) between the first optical path length difference (d1 = L1-L2) and the second optical path length difference (d2 = L1-L3). The thickness (T0) of the wafer becomes thicker than the actual thickness of the wafer 11. Therefore, in the present invention, the thickness (T) of the wafer 11 is obtained in consideration of the refractive index of the wafer 11 that is a workpiece.

  That is, in the present invention, the refractive index of the wafer 11 is obtained before the wafer 11 as a workpiece is ground. In order to obtain the refractive index of the wafer 11, first, the actual thickness (T) of the wafer 11 is measured. The actual thickness (T) of the wafer 11 can be measured by the thickness detector 8. First, as shown in FIG. 5A, the upper surface of the wafer 11 held on the chuck table 71 is irradiated with detection light from the thickness detection device 8, and as described above, the first optical path length difference (d1 = L1−L2) (the upper surface position of the wafer 11) and the second optical path length difference (d2 = L1−L3) (the lower surface position of the wafer 11) and the optical path length difference (d3 = d1−d2) (the thickness of the wafer 11 (T0) )) Is detected. Next, as shown in FIG. 5B, a thickness detecting device is provided on the upper surface of the protective tape 12 attached to the wafer 11 through a notch 111 representing the crystal orientation formed on the wafer 11 held on the chuck table 71. 8 is irradiated with detection light, and the optical path length (L1) from the beam splitter 841 to the reflection mirror 87 of the second optical branching means 84 in the fourth path 8d, and the second path in the third path 8c. An optical path length difference (d4 = L1−L4) (upper surface position of the protective tape 12) from the optical path length (L4) from the beam splitter 841 of the optical branching means 84 to the upper surface of the protective tape 12 is obtained. By subtracting the optical path length difference (d4) (upper surface position of the protective tape 12) from the first optical path length difference (d1 = L1-L2) (upper surface position of the wafer 11) thus determined. The actual thickness (T = d1-d4) of the wafer 11 can be obtained. Then, the optical path length difference (d3 = d1−d2) (the thickness (T0) of the wafer 11) between the first optical path length difference (d1) and the second optical path length difference (d2) obtained as described above is used. The refractive index (r = d3 / T) of the wafer 11 is obtained by dividing by the actual thickness (T) of 11 (refractive index detection step). The control means 10 temporarily stores the refractive index (r = d3 / T) of the wafer 11 thus obtained in a built-in memory. The actual thickness (T) of the wafer 11 is measured by a measuring instrument such as a micrometer, and the measured value is input to the control means 10 to obtain the refractive index (r = d3 / T) of the wafer 11. Also good.

  In this way, the refractive index (r = d3 / T) of the wafer 11 is obtained, and the thickness (T) at the time of processing the wafer 11 is obtained in consideration of this refractive index (r). That is, by dividing the optical path length difference (d3) between the first optical path length difference (d1) and the second optical path length difference (d2) by the refractive index (r), the actual processing at the time of processing the wafer 11 is performed. (T = d3 / r) can be obtained (thickness detection step).

  As described above, the thickness detection device 8 in the illustrated embodiment detects the thickness (T) of the wafer 11 during processing based on the optical path length difference of the reflected light reflected from the upper surface and the lower surface of the wafer 11. The thickness (T) of the wafer 11 can be accurately detected without being affected by the change in the thickness of the protective tape 12 attached to the surface of the wafer 11. Further, the thickness detecting device 8 in the illustrated embodiment obtains the refractive index (r) of the wafer 11 as described above, and obtains the thickness (T) at the time of processing the wafer 11 in consideration of the refractive index (r). Therefore, even if the refractive index varies depending on the material of the wafer 11, the accurate thickness (T) of the wafer 11 can be detected.

The illustrated grinding machine 1 is configured as described above. Hereinafter, a grinding method for grinding a wafer to a predetermined thickness using the grinding machine 1 will be described.
A protective tape 12 is attached to the surface, and the wafer 11 is placed on a chuck table 71 positioned in a workpiece placement area 70a in the grinding machine 1 shown in FIG. Is held on the chuck table 71 by suction. Therefore, the back surface of the wafer 11 sucked and held on the chuck table 71 is the upper side. If the wafer 11 is sucked and held on the chuck table 71, the control means 10 executes the above-described refractive index detection step to obtain the refractive index (r) of the wafer 11, and a memory incorporating the obtained refractive index (r). Temporarily store in.

  Next, the control means 10 operates a moving means (not shown) of the chuck table 71 holding the wafer 11, and moves the chuck table 71 in the direction indicated by the arrow 71a in FIG. As shown, 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 measurement position above the wafer 11 held on 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 detecting device 8 is positioned at the measurement position, the control means 10 drives a rotation driving means (not shown). The chuck table 71 is rotated in the direction indicated by the arrow 71a in FIG. 6 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 the 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 so as to lower the grinding wheel 5 (grind feed), so that a plurality of grinding wheels 52 are ground surfaces which are the upper surface (back surface) of the wafer 11. Is pressed at a predetermined pressure. As a result, the surface to be ground which is the wafer 11 is ground (grinding step).

  In the grinding step, the thickness (T) at the time of processing the wafer 11 in consideration of the refractive index (r) of the wafer 11 is measured. That is, when the wafer 11 is processed, the optical path length difference (d3) between the first optical path length difference (d1) and the second optical path length difference (d2) is divided by the refractive index (r) as described above. The actual thickness at (T = d3 / r) is measured. When the thickness (T) of the wafer 11 measured by the thickness detection device 8 reaches a predetermined value, the control means 10 drives the pulse motor 64 of the grinding unit feed mechanism 6 in reverse to raise the grinding wheel 5.

  As described above, since the thickness (T) of the wafer 11 is measured by the non-contact type thickness detector 8 in the grinding process, the surface to be ground of the wafer 11 is not damaged. The thickness (T) of the wafer 11 detected by the thickness detection device 8 detects the thickness (T) at the time of processing the wafer 11 based on the optical path length difference of the reflected light reflected from the upper surface and the lower surface of the wafer 11. Therefore, the wafer 11 can be ground to a predetermined thickness while accurately measuring the thickness (T) of the wafer 11 without being affected by a change in the thickness of the protective tape 12 adhered to the surface of the wafer 11. Further, the thickness detecting device 8 in the illustrated embodiment obtains the refractive index (r) of the wafer 11 as described above, and obtains the thickness (T) at the time of processing the wafer 11 in consideration of the refractive index (r). Therefore, even if the refractive index varies depending on the material of the wafer 11, the accurate thickness (T) of the wafer 11 can be detected.

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 detector 81: Light emission source 82: First light branching means 83: Collimation lens 84: Second light branching means 85: Objective lens 65
86: Condensing lens 87: Reflecting mirror 88: Collimation lens 89: Diffraction grating 90: Condensing lens 91: Line image sensor 10: Control means 11: Wafer

Claims (3)

In a thickness detector for detecting the thickness of a workpiece held on a chuck table,
A light emitting source that emits light with a predetermined wavelength region that is transparent to the workpiece;
First light branching means for guiding light from the light emitting source to the first path and for guiding reflected light that travels backward through the first path to the second path;
A collimation lens that forms light guided to the first path into parallel light;
Second light branching means for dividing light formed into parallel light by the collimation lens into a third path and a fourth path;
An objective lens that is disposed in the third path and guides the light guided to the third path to a workpiece held by the chuck table;
Parallel light disposed between the second light branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens so that light from the objective lens is reflected. A condenser lens that generates pseudo-parallel light;
A reflecting mirror that is disposed in the fourth path and reflects parallel light guided to the fourth path and reverses the reflected light to the fourth path;
Reflected by the reflecting mirror, the fourth path, the second light branching unit, the collimation lens, and the first path are reversed to be guided from the first light branching unit to the second path. The reflected light is reflected by the upper and lower surfaces of the workpiece held on the chuck table, and the objective lens, the condenser lens, the second light branching unit, the collimation lens, and the first path are reversed. A diffraction grating for diffracting interference with the reflected light guided from the first light branching means to the second path;
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 an optical path length to the reflection mirror in the fourth path is calculated. The first optical path length difference (d1) with the optical path length to the upper surface of the workpiece held by the chuck table in the third path is obtained, and the optical path length to the reflecting mirror in the fourth path A second optical path length difference (d2) from the optical path length to the lower surface of the workpiece held on the chuck table in the third path is obtained, and the first optical path length difference (d1) and the second optical path length difference are obtained. And a control means for determining the thickness (t) of the workpiece based on the optical path length difference (d2).
The control means is based on the optical path length difference (d3) between the actual thickness (T) before processing the workpiece, the first optical path length difference (d1), and the second optical path length difference (d2). A refractive index detection step for obtaining a refractive index (r = d3 / T) of the workpiece, the refractive index (r), the first optical path length difference (d1) during processing of the workpiece, and the first A thickness detection step of obtaining a thickness (t = d3 / r) of the workpiece based on the optical path length difference (d3) from the optical path length difference (d2) of 2;
A thickness detection apparatus characterized by the above.   The refractive index detecting step irradiates the upper surface of the workpiece with detection light before processing the workpiece held on the chuck table to thereby detect the first optical path length difference (d1) and the second optical path length. The optical path to the reflection mirror in the fourth path by detecting the difference (d2) and the optical path length difference (d3) and irradiating the upper surface of the protection member attached to the lower surface of the workpiece with the detection light The optical path length difference (d4) between the optical path length to the upper surface of the protective member in the third path is obtained, and the optical path length difference (d4) is subtracted from the first optical path length difference (d1). The actual thickness (T = d1-d4) of the workpiece is obtained, and the refractive index (r = d3 / T) of the workpiece is obtained by dividing the optical path length difference (d3) by the actual thickness (T). The thickness detection device according to claim 1. 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 includes a light source that emits light having a predetermined wavelength region that is transmissive to a workpiece;
First light branching means for guiding light from the light emitting source to the first path and for guiding reflected light that travels backward through the first path to the second path;
A collimation lens that forms light guided to the first path into parallel light;
Second light branching means for dividing light formed into parallel light by the collimation lens into a third path and a fourth path;
An objective lens that is disposed in the third path and guides the light guided to the third path to a workpiece held by the chuck table;
Parallel light disposed between the second light branching means and the objective lens is guided to the third path, and a focusing point is positioned on the objective lens so that light from the objective lens is reflected. A condenser lens that generates pseudo-parallel light;
A reflecting mirror that is disposed in the fourth path and reflects parallel light guided to the fourth path and reverses the reflected light to the fourth path;
Reflected by the reflecting mirror, the fourth path, the second light branching unit, the collimation lens, and the first path are reversed to be guided from the first light branching unit to the second path. The reflected light is reflected by the upper and lower surfaces of the workpiece held on the chuck table, and the objective lens, the condenser lens, the second light branching unit, the collimation lens, and the first path are reversed. A diffraction grating for diffracting interference with the reflected light guided from the first light branching means to the second path;
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 an optical path length to the reflection mirror in the fourth path is calculated. The first optical path length difference (d1) with the optical path length to the upper surface of the workpiece held by the chuck table in the third path is obtained, and the optical path length to the reflecting mirror in the fourth path A second optical path length difference (d2) from the optical path length to the lower surface of the workpiece held on the chuck table in the third path is obtained, and the first optical path length difference (d1) and the second optical path length difference are obtained. And a control means for determining the thickness (t) of the workpiece based on the optical path length difference (d2).
The control means irradiates the upper surface of the workpiece with detection light before processing the workpiece held on the chuck table to thereby detect the first optical path length difference (d1) and the second optical path length difference ( d2) and the optical path length difference (d3), and the optical path length to the reflection mirror in the fourth path by irradiating the upper surface of the protective member attached to the lower surface of the workpiece with the detection light An optical path length difference (d4) from the optical path length to the upper surface of the protection member in the third path is obtained, and the optical path length difference (d4) is subtracted from the first optical path length difference (d1). Is obtained, and the refractive index for obtaining the refractive index (r = d3 / T) of the workpiece is obtained by dividing the optical path length difference (d3) by the actual thickness (T). An optical path length difference (d3) between the refractive index (r) and the first optical path length difference (d1) and the second optical path length difference (d2) when processing the workpiece; ) To detect the thickness of the workpiece (t = d3 / r) based on
A grinding machine characterized by that.

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