JP7185446B2 - Grinding device and grinding method for workpiece - Google Patents

Description

The present invention relates to a grinding apparatus and grinding method for workpieces such as semiconductor wafers.

In the manufacturing process of a semiconductor device, in order to obtain a device with a desired thickness, at the stage of a semiconductor wafer, which is an aggregate of many devices, the thickness is measured by contact thickness measurement means or non-contact thickness measurement means, Grinding the back surface of the wafer to thin it is performed.

In addition, in response to the remarkable reduction in thickness of devices in recent years, workpieces such as semiconductor wafers are being processed to be thinner, and for this reason, higher accuracy is required for thickness control in grinding.

In the contact-type thickness measuring means, there is a problem that the probe that contacts the surface to be processed (back surface) of the workpiece scratches the surface to be processed, and the scratches cause the bending strength of the workpiece to decrease. There is In particular, when the thickness of the workpiece after grinding is relatively thin, the depth of the scratch has a large effect, so the decrease in the bending strength becomes significant.
On the other hand, a non-contact thickness measuring means (see, for example, Patent Document 1) using measurement light (laser light) capable of measuring the thickness without contacting a probe or the like to the workpiece is used to measure the resistance of the workpiece. It is advantageous in that it does not reduce the bending strength.

JP 2009-050944 A

As a non-contact method for measuring the thickness of a workpiece, for example, the workpiece is irradiated with measurement light from an irradiation unit of a non-contact thickness measuring means, and the irradiated measurement light is emitted from above and below the workpiece. In order to measure the thickness of the workpiece from the time difference and the incident angle at which the light receiving part of the non-contact thickness measuring means receives the reflected light reflected at the interface (upper surface (back surface) and lower surface (surface)), the thickness is In order to measure it, it is necessary to know the refractive index of the workpiece.

However, since the refractive index differs depending on the material of the workpiece, there is a problem that the non-contact thickness measuring means cannot measure the thickness of the workpiece whose refractive index is unknown.
Therefore, in the case of grinding a workpiece such as a semiconductor wafer, there is a problem of making it possible to measure the thickness of the workpiece whose refractive index is unknown by non-contact thickness measuring means.

In order to solve the above problems, the present invention provides a work piece having a surface on which a device is formed in a region partitioned by a plurality of division lines formed in a grid pattern and whose back surface is ground by a grinding wheel. The grinding apparatus comprises holding means for holding the surface of the workpiece by a holding surface of a chuck table rotating on a vertical rotation axis, and a grinding wheel rotating on a rotation axis orthogonal to the holding surface. Grinding means for grinding a workpiece; contact-type thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece by bringing a probe into contact with the workpiece; and measuring light. toward the work piece, and from the time difference between the light reflected by the back surface of the work piece and the light transmitted through the work piece and reflected by the front surface of the irradiated measurement light, the work piece Non-contact thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece, the amount L removed by grinding the workpiece measured by the contact thickness measuring means, and the non-contact type The refractive index n of the workpiece is calculated from the amount L1 removed by grinding of the workpiece measured by the thickness measuring means and the refractive index n1 arbitrarily set in the non-contact thickness measuring means. =L1×n1/L, and replaces the refractive index n1 set in the non-contact thickness measuring means with the calculated refractive index n, wherein the refractive index is the refractive index A grinding apparatus for a workpiece, characterized in that the thickness of the workpiece is measured by the non-contact thickness measuring means replaced by the ratio n.

Further, the present invention for solving the above-mentioned problems provides a workpiece for grinding, with a grinding wheel, the back surface of a workpiece having a surface on which a device is formed in a region partitioned by a plurality of division lines formed in a grid pattern. A method of grinding a workpiece, comprising: a holding step of holding the surface of the workpiece with a holding surface of a chuck table that rotates on a vertical rotating shaft; and bringing a probe into contact with the workpiece. and a contact-type thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece, and irradiating the measuring light toward the workpiece, and the irradiated measuring light is emitted at the back surface of the workpiece Non-contact thickness measurement that measures the thickness of the workpiece and the amount removed by grinding the workpiece from the time difference between the reflected light and the light transmitted through the workpiece and reflected on the surface of the workpiece. A grinding step of grinding the workpiece to the finished thickness of the chip with a grinding wheel rotating on a rotating shaft orthogonal to the holding surface while measuring with a means, and the workpiece measured by the contact-type thickness measuring means. A removed amount L of the workpiece, a removed amount L1 of the workpiece measured by the non-contact thickness measuring means set to an arbitrary refractive index n1, and an arbitrary set to the non-contact thickness measuring means. From the refractive index n1, the refractive index n of the workpiece is calculated by the formula n=L1×n1/L, and the refractive index n1 arbitrarily set in the non-contact thickness measuring means is calculated. and a refractive index calculation step replacing the refractive index with the refractive index n, and measuring the thickness of the workpiece with the non-contact thickness measuring means in which the refractive index is replaced with the refractive index n. Grinding method.

In the grinding apparatus for a workpiece according to the present invention, an amount L removed by grinding the workpiece measured by the contact thickness measuring means and an amount L1 removed by grinding the workpiece measured by the non-contact thickness measuring means are measured. and the refractive index n1 arbitrarily set in the non-contact thickness measuring means, the refractive index n of the workpiece is calculated by the formula n=L1×n1/L, and is set in the non-contact thickness measuring means. and a refractive index calculating means for replacing the calculated refractive index n1 with the calculated refractive index n, and measuring the thickness of the workpiece with the non-contact thickness measuring means in which the refractive index is replaced with the refractive index n. , the non-contact thickness measuring means enables correct measurement of the thickness of a workpiece whose refractive index is unknown.

Further, a method for grinding a workpiece according to the present invention includes contact-type thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece by bringing a probe into contact with the workpiece; A workpiece is irradiated with measurement light, and the thickness of the workpiece is calculated from the time difference between the light reflected from the back surface of the workpiece and the light transmitted through the workpiece and reflected from the front surface of the workpiece. and a non-contact thickness measuring means for measuring the amount removed by grinding the workpiece, while measuring the workpiece with a grinding wheel rotating on a rotating shaft perpendicular to the holding surface, until the finished thickness of the chip. A grinding step of grinding, a removed amount L of the workpiece measured by the contact thickness measuring means, and a removed amount L1 of the workpiece measured by the non-contact thickness measuring means with an arbitrary refractive index n1 set. and the refractive index n1 arbitrarily set in the non-contact thickness measuring means, the refractive index n of the workpiece is calculated by the formula n=L1×n1/L, and the non-contact thickness measuring means arbitrarily and a refractive index calculation step of replacing the refractive index n1 set to Thus, even the thickness of a workpiece whose refractive index is unknown can be accurately measured by the non-contact thickness measuring means, and the workpiece can be ground to a desired thickness.

It is a perspective view which shows an example of the component of a grinding apparatus. It is sectional drawing which shows the state which is grinding the to-be-processed object in a grinding apparatus. Graph showing changes over time in the thickness (μm) of the workpiece measured by the non-contact thickness measuring means before replacing the refractive index and the thickness over time measured by the contact thickness measuring means It is a graph which shows transition. Graph showing changes over time in the thickness (μm) of the workpiece measured by the non-contact thickness measuring means after replacing the refractive index and over time in the thickness of the workpiece measured by the contact thickness measuring means It is a graph which shows transition.

The workpiece W shown in FIG. 1 is, for example, a semiconductor wafer having a circular outer shape and made of silicon or the like as a base material. It is partitioned in a grid pattern by the planned lines S, and devices D such as ICs are formed in each region partitioned in the grid pattern. The surface Wa is protected by, for example, affixed with a protective tape (not shown).
A back surface Wb of the workpiece W is a ground surface to be ground. It is assumed that the actual refractive index (refractive index n) of the workpiece W is not known in advance. The workpiece W may be made of gallium arsenide, sapphire, gallium nitride, silicon carbide, or the like, other than silicon.

The grinding apparatus 2 shown in FIG. 1 includes at least holding means 3 for sucking and holding a workpiece W on a holding surface 300a of a chuck table 30, and grinding means 4 for grinding the workpiece W with a rotating grinding wheel 441. ing.
The grinding performed by the grinding device 2 includes polishing of the workpiece W with a polishing pad made of non-woven fabric such as felt.

The chuck table 30 of the holding means 3 has, for example, a circular outer shape, and is provided with a holding portion 300 made of a porous member or the like for sucking and holding the workpiece W, and a frame 301 supporting the holding portion 300 . The holding portion 300 communicates with a suction source (not shown) such as a vacuum generator, and a suction force generated by suction by the suction source (not shown) is transmitted to a holding surface 300a that is an exposed surface of the holding portion 300. As a result, the chuck table 30 sucks and holds the workpiece W on the holding surface 300a.
A rotating shaft 321 whose axial direction is the vertical direction (Z-axis direction) is connected to the lower portion of the chuck table 30 , and a motor 320 is connected to the rotating shaft 321 . The chuck table 30 is rotatable about a vertical axis by a motor 320 and a rotary shaft 321 .
The chuck table 30 can be reciprocated in the X-axis direction by, for example, X-axis moving means (not shown).

The grinding means 4 shown in FIG. 1 includes a rotary shaft 40 (see FIG. 2) whose axial direction is the Z-axis direction orthogonal to the holding surface 300a of the chuck table 30, a housing 41 that rotatably supports the rotary shaft 40, It comprises a motor 42 for rotationally driving a rotary shaft 40 , a mount 43 attached to the lower end of the rotary shaft 40 , and a grinding wheel 44 detachably connected to the mount 43 . The grinding wheel 44 includes a ring-shaped wheel base 440 and a plurality of ring-shaped grinding wheels 441 having a substantially rectangular parallelepiped outer shape and arranged on the lower surface of the wheel base 440 . The grinding wheel 441 is formed by bonding diamond abrasive grains or the like with an appropriate bonding agent.
The grinding means 4 can be moved up and down in the Z-axis direction by a grinding feeding means 7 having a ball screw mechanism or the like.

The grinding apparatus 2 includes contact-type thickness measuring means 5 for measuring the thickness of the workpiece W and the amount removed by grinding the workpiece W by bringing the probe 50 into contact with the workpiece W. As shown in FIG. The probe 50, which can move up and down, is located above the holding surface 300a of the chuck table 30 and contacts the back surface Wb of the workpiece W, which is the surface to be measured. The probe 50 is supported by an arm portion 51, and the arm portion 51 pushes the probe 50 against the holding surface 300a of the chuck table 30 by pressing force generated by a spring incorporated therein. can be pressed with an appropriate force.

The contact-type thickness measuring means 5 detects the height position of the back surface Wb of the workpiece W using the probe 50 . Further, the contact-type thickness measuring means 5 grasps in advance the height position of the holding surface 300a and the thickness of the workpiece W before grinding. The height position of the back surface Wb of the object W is grasped. Therefore, the contact thickness measuring means 5 measures the height position of the back surface Wb of the workpiece W before grinding held by the holding surface 300a and the height position of the back surface Wb of the workpiece W measured during the grinding process. The amount of the workpiece W removed by grinding (removed amount) can be measured from the difference between , and the thickness of the workpiece W being ground can be measured sequentially.

The contact-type thickness measuring means 5 further includes a separate probe for measuring the height of the holding surface 300a of the chuck table 30. The difference from the height of the holding surface 300a of the chuck table 30 detected by the probe may be measured as the thickness of the workpiece W.

The grinding device 2 includes a non-contact thickness measuring means 6 capable of measuring the thickness of the workpiece W being ground and the amount removed by grinding the workpiece W without contact.
The non-contact thickness measuring means 6 is, for example, a reflective displacement sensor that uses measuring light. A collimator lens (projection lens) (not shown) that converts the light into light, a light receiving lens (not shown) that captures the reflected light reflected by the workpiece W, a light receiving unit 61 including a CCD or the like for detecting the reflected light, and a light projecting lens A housing 62 in which the unit 60, a collimator lens, a light receiving lens, a light receiving unit 61, etc. are arranged and shielded from external light is provided. The configuration of the non-contact thickness measuring means 6 is not limited to this embodiment.

The grinding device 2 comprises, for example, control means 9 for controlling the entire device. The control means 9 includes a CPU that performs arithmetic processing according to a control program and storage means such as a memory. It is electrically connected to means 6 and the like. Under the control of the control means 9, the rotary motion of the chuck table 30 by the motor 320 and the rotating shaft 321, the grinding feeding motion of the grinding means 4 in the Z-axis direction by the grinding feeding means 7, and the like are controlled.

Each step of grinding a workpiece W using the grinding apparatus 2 shown in FIGS. 1 and 2 according to the present invention will be described below.

(1) Holding Step The workpiece W shown in FIG. 1 is placed on the holding surface 300a of the chuck table 30 so that the back surface Wb faces upward. A suction force generated by a suction source (not shown) is transmitted to the holding surface 300a, whereby the chuck table 30 sucks and holds the surface Wa of the workpiece W on the holding surface 300a, as shown in FIG.

(2) Grinding step before refractive index replacement The chuck table 30 is moved in the -X direction to below the grinding means 4 by the X-axis moving means (not shown), and the workpiece is held by the grinding wheel 44 and the chuck table 30. Alignment with W is performed. Alignment is performed, for example, so that the center of rotation of the grinding wheel 441 is displaced from the center of rotation of the workpiece W by a predetermined distance in the horizontal direction, and the locus of rotation of the grinding wheel 441 passes through the center of rotation of the workpiece W. done.

After the grinding wheel 44 is aligned with the workpiece W, the rotating shaft 40 is rotated by the motor 42, and the grinding wheel 44 rotates at a predetermined rotational speed as shown in FIG. Rotate. Further, the grinding means 4 is fed in the -Z direction by the grinding feeding means 7, and the grinding wheel 441 is brought into contact with the back surface Wb of the workpiece W to perform the grinding process. Furthermore, during grinding, the workpiece W rotates as the chuck table 30 rotates about the axis in the Z-axis direction. conduct.

When the grinding wheel 441 starts grinding the workpiece W, the probe 50 is pressed against the rotating back surface Wb of the workpiece W with a predetermined pressing force, and the contact thickness measuring means 5 grinds the workpiece W. Measurement of removal amount and thickness by is started.
Further, the light projecting section 60 of the non-contact thickness measuring means 6 irradiates the workpiece W positioned below the housing 62 with the measurement light. The measurement light is converted into parallel light by a collimator lens and enters the workpiece W at a predetermined angle (for example, approximately perpendicular). A portion of the measurement light is reflected by the back surface Wb, which is the upper surface of the workpiece W, and the remaining measurement light is refracted by the workpiece W (refractive index n) and passes through the workpiece W to be processed. It is reflected by the surface Wa, which is the lower surface of the object W. Then, the light receiving lens catches the light reflected by the back surface Wb of the workpiece W and the light transmitted through the workpiece W and reflected by the front surface Wa of the workpiece W, and the time difference when the light receiving unit 61 receives the light is , the non-contact thickness measuring means 6 measures the thickness of the workpiece W. As shown in FIG.

The non-contact thickness measuring means 6 grasps the thickness of the workpiece W before grinding in advance, and compares the thickness of the workpiece W measured during grinding with the thickness of the workpiece W before grinding. The difference is sequentially calculated and measured as the amount removed by grinding the workpiece W. FIG.

(3) Refractive Index Calculation Step Assume that the removal amount L is the removal amount measured by the contact-type thickness measuring means 5 at an arbitrary time during grinding of the workpiece W (when the machining time t1 has elapsed from the start of the grinding process). The removal amount L measured by the contact-type thickness measuring means 5 is an accurate removal amount after the processing time t1 of the workpiece W has elapsed. A graph G1 indicated by a one-dot chain line in FIG. 3 is an example of a graph showing changes over time in the thickness (μm) of the workpiece W measured by the contact-type thickness measuring means 5 .

The amount of removal measured by the non-contact thickness measuring means 6 during grinding of the workpiece W at an arbitrary time (when the processing time t1 has elapsed from the start of the grinding process) is defined as the amount of removal L1. The non-contact thickness measuring means 6 has a refractive index n1 arbitrarily set in advance by the operator, that is, a refractive index n1 different from the actual refractive index n of the workpiece W that has not yet been recognized. In this state, the thickness of the workpiece W is measured, and the removal amount L1 is calculated from the measured thickness. A graph G2 indicated by a solid line in FIG. 3 is an example of a graph showing changes in the thickness (μm) of the workpiece W measured by the non-contact thickness measuring means 6 over time. Graphs G1 and G2 are graphs obtained from experiments actually conducted by the inventors of the present invention.

Here, when the feed speed of the processing condition setting of the grinding means 4 preset in the control means 9 in order to grind the workpiece W to a desired thickness is set as the speed V, an arbitrary refractive index n1 is set. In the non-contact thickness measuring means 6,
Feeding speed of grinding means 4 calculated by non-contact thickness measuring means 6 V1=V/n1 (Formula 1)
holds.
Removal amount L1=feed rate V1 of grinding means 4 calculated by non-contact thickness measuring means 6.times.machining time t1=(V/n1).times.t1 (formula 2)
holds.

On the other hand, assuming that the actual refractive index n of the workpiece W is set in the non-contact thickness measuring means 6, for example, the non-contact thickness measuring means 6:
Feeding speed of grinding means 4 calculated by non-contact thickness measuring means 6 V2=V/n (Formula 3)
holds.
Accurate removal amount L measured by contact-type thickness measuring means 5=Velocity V2×Processing time t1=(V/n)×t1 (Formula 4)
holds.

The actual refractive index n of the workpiece W in the above (Equation 3) is not set in the non-contact thickness measuring means 6 at present, and is arbitrarily set in the non-contact thickness measuring means 6 by the operator. A refractive index n1 is set. Therefore, the refractive index calculation means 90 included in the control means 9 shown in FIG. 2 executes the arithmetic processing described below.
That is, from (Equation 2) and (Equation 4),
L1/(V/n1)=L/(V/n) (Formula 5)
holds. Then, by modifying the formula (5), the following formula for obtaining the actual refractive index n of the workpiece W is
n=(L1×n1)/L (Formula 6)
is derived.

When the refractive index calculation means 90 calculates the actual refractive index n of the workpiece W using the above (formula 6), the refractive index n set instead.
An example of calculation of a specific numerical value of the refractive index n is shown using (Equation 6) and graphs G1 and G2 shown in FIG. An arbitrary refractive index n1 set in the non-contact thickness measuring means 6 is, for example, refractive index n1=3.2. When the machining time t1 has elapsed, the removal amount L of the workpiece W measured by the contact-type thickness measuring means 5, which can be read from the graph G1, is 18.8171 μm. The removed amount L1 of the workpiece W measured by the thickness measuring means 6 is 22.78038 μm.
When calculating the actual refractive index n of the workpiece W by substituting each of the above numerical values into (Equation 6),
n=(22.78038*3.2)/18.8171=3.873987.
Then, the refractive index calculating means 90 replaces the refractive index n1=3.2 arbitrarily set in the non-contact thickness measuring means 6 with the calculated refractive index n=3.873987.

(4) Grinding step after refractive index replacement The thickness of the workpiece W is accurately measured by the non-contact thickness measuring means 6 in which the refractive index is replaced from the refractive index n1 to the actual refractive index n of the workpiece W. The workpiece W is ground to a desired thickness while being cut. After that, the grinding feed means 7 raises the grinding means 4 in the +Z direction, the grinding wheel 441 is separated from the workpiece W, and the grinding of the workpiece W is completed.

As described above, the grinding apparatus 2 for the workpiece W according to the present invention has the amount L removed by grinding the workpiece W measured by the contact thickness measuring means 5 and the amount L removed by grinding the workpiece W measured by the non-contact thickness measuring means 6. From the amount L1 removed by grinding the workpiece W and the refractive index n1 arbitrarily set in the non-contact thickness measuring means 6, the refractive index n of the workpiece W is calculated as follows: n=L1×n1/L and a refractive index calculating means 90 that replaces the refractive index n1 set in the non-contact thickness measuring means 6 with the calculated refractive index n, and the non-contact thickness in which the refractive index is replaced with the refractive index n By measuring the thickness of the workpiece W with the measuring means 6, the non-contact thickness measuring means 6 can accurately measure the thickness of the workpiece W whose refractive index is unknown.

Further, the grinding method of the workpiece W according to the present invention is a contact type grinding method in which the probe 50 is brought into contact with the workpiece W to measure the thickness of the workpiece W and the amount removed by grinding the workpiece W. A thickness measuring means 5 irradiates the workpiece W with measurement light, and the irradiated measurement light reflects light from the back surface Wb of the workpiece W and light transmitted through the workpiece W and reflected from the front surface Wa. While measuring the thickness of the workpiece W and the amount removed by grinding of the workpiece W from the time difference in receiving the light, the holding surface 300a of the chuck table 30 and the A grinding step of grinding the workpiece W to the finished thickness of the chip with a grinding wheel 441 rotating on an orthogonal rotating shaft 40, a removal amount L of the workpiece W measured by the contact thickness measuring means 5, and an arbitrary From the removed amount L1 of the workpiece W measured by the non-contact thickness measuring means 6 with the refractive index n1 set and the refractive index n1 arbitrarily set in the non-contact thickness measuring means 6, the workpiece a refractive index calculation step of calculating the refractive index n of W by the formula n=L1×n1/L and replacing the refractive index n1 arbitrarily set in the non-contact thickness measuring means 6 with the calculated refractive index n; By measuring the thickness of the workpiece W with the non-contact thickness measuring means 6 in which the refractive index is replaced by the refractive index n, the thickness of the workpiece W whose refractive index is unknown can also be measured in a non-contact manner. The thickness can be measured correctly by the thickness measuring means 6, and the workpiece W can be ground to a desired thickness.

Further, a new workpiece W is ground by the grinding device 2 in which the refractive index of the non-contact thickness measuring means 6 is replaced with the refractive index n (n=3.873987). A graph G4 indicated by a one-dot chain line in FIG. 4 is an example of a graph showing changes over time in the thickness (μm) of the workpiece W measured by the contact-type thickness measuring means 5 . A graph G5 indicated by a solid line is an example of a graph showing changes in the thickness (μm) of the workpiece W measured by the non-contact thickness measuring means 6 over time. Graphs G4 and G5 are graphs obtained from experiments actually conducted by the inventors of the present invention.

As shown in FIG. 4, when grinding a new workpiece W, the thickness of the workpiece W measured by the non-contact thickness measuring means 6 and the thickness of the workpiece W measured by the contact thickness measuring means 5 The thickness of the workpiece W substantially matched from the start to the end of grinding, and while the thickness of the workpiece W was correctly measured by the non-contact thickness measuring means 6, the workpiece W could be ground to the desired thickness.

It goes without saying that each step of the method for grinding a workpiece according to the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea. Moreover, each component of the grinding apparatus 2 illustrated in the attached drawings is not limited to this, and can be changed as appropriate within the range in which the effects of the present invention can be exhibited.

W: work piece Wa: front surface S: line to be divided D: device Wb: back surface 2: grinding device
3: Holding means 30: Chuck table 300: Holding part 300a: Holding surface 301: Frame body 320: Motor 321: Rotating shaft
4: Grinding Means 40: Rotating Axis 41: Housing 42: Motor 43: Mount 44: Grinding Wheel 440: Wheel Base 441: Grinding Wheel 5: Contact Thickness Measuring Means 50: Probe 51: Arm 6: Non-Contact Thickness Measuring Means 60: Light Projecting Part 61: Light Receiving Part 62: Housing 9: Control Means 90: Refractive Index Calculating Means

Claims (2)

A grinding apparatus for a workpiece that grinds the back surface of the workpiece having a surface on which a device is formed in a region partitioned by a plurality of division lines formed in a grid pattern with a grinding wheel,
holding means for holding the surface of the workpiece with a holding surface of a chuck table that rotates about a vertical rotation axis;
Grinding means for grinding the workpiece with a grinding wheel rotating on a rotating shaft orthogonal to the holding surface;
contact thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece by contacting the probe with the workpiece;
The measurement light is irradiated toward the workpiece, and the measurement light is reflected from the back surface of the workpiece and the light transmitted through the workpiece and reflected from the front surface. non-contact thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece;
The amount L removed by grinding the workpiece measured by the contact-type thickness measuring means, the amount L1 removed by grinding the workpiece measured by the non-contact thickness measuring means, and the non-contact thickness measuring means , from the arbitrarily set refractive index n1, the refractive index n of the workpiece is calculated by the formula n=L1×n1/L, and the refractive index set in the non-contact thickness measuring means and refractive index calculation means for replacing the calculated refractive index n with n1,
A grinding apparatus for a workpiece, wherein the thickness of the workpiece is measured by the non-contact thickness measuring means in which the refractive index is replaced by the refractive index n. A method of grinding a workpiece having a surface on which a device is formed in a region partitioned by a plurality of division lines formed in a grid pattern, wherein the back surface of the workpiece is ground with a grinding wheel,
a holding step of holding the surface of the workpiece with a holding surface of a chuck table that rotates about a vertical rotating shaft;
Contact thickness measuring means for measuring the thickness of the workpiece and the amount removed by grinding the workpiece by bringing a probe into contact with the workpiece, and irradiating the workpiece with measurement light. Then, the thickness of the workpiece and the grinding of the workpiece are determined from the time difference between the light reflected by the back surface of the workpiece and the light transmitted through the workpiece and reflected by the front surface of the workpiece. A grinding step of grinding the workpiece to the finished thickness of the chip with a grinding wheel rotating on a rotating shaft perpendicular to the holding surface while measuring with a non-contact thickness measuring means that measures the amount removed by When,
A removed amount L1 of the workpiece measured by the contact thickness measuring means, a removed amount L1 of the workpiece measured by the non-contact thickness measuring means having an arbitrary refractive index n1, and the non-contact thickness measuring means. From the refractive index n1 arbitrarily set in the contact thickness measuring means, the refractive index n of the workpiece is calculated by the formula n=L1×n1/L, and the non-contact thickness measuring means arbitrarily a refractive index calculation step of replacing the set refractive index n1 with the calculated refractive index n,
A method of grinding a workpiece, wherein the thickness of the workpiece is measured by the non-contact thickness measuring means in which the refractive index is replaced by the refractive index n.

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