JPH10217081A - Double-sided work method and device of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sharply shorten work time by driving a pair of rotary grinding wheels in rotation, and simultaneously performing grinding work on both surfaces of a wafer by inserting this wafer into a clearance between the mutual rotary grinding wheels while clamping the wafer from its diametrical directional outside by a thin clamp member. SOLUTION: A cylinder device is actuated, and a clamper 44 is advanced, and a wafer W is clamped from its diametrical directional outside by this clamper 44 and a carrier 36. A movable carriage of both wheel spindle stocks is advanced, and grinding wheels 24 are brought near to each other, and a clearance dimension between both grinding wheels 24 is made to coincide with a dimension corresponding to a target thickness dimension of the wafer W. A moving carriage of a wafer holding stand is advanced further still in this condition, and grinding work is simultaneously performed on only both the obverse and reverse of the wafer W by the grinding wheels 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for processing both surfaces of a wafer made of a semiconductor or the like.

[0002]

2. Description of the Related Art Generally, the surface of a wafer made of a semiconductor such as silicon needs to be finished to a smooth surface having high flatness. Conventionally, as a means for performing such finishing processing, first, the wafer surface is lapped to obtain high flatness, and the crushed layer generated on the wafer surface due to the lapping and the surface layer contaminated with abrasive grains are chemically etched. A method of removing the surface and then smoothing the surface by mirror polishing is generally used.

[0003]

Since the lapping process is carried out in a complete batch system, the time required for wafer setting and wafer reset is long, and the processing margin tends to vary from batch to batch. . Furthermore, the use of a wrapping agent has the disadvantage that workability and work environment deteriorate.

As a means for solving such a defect, it is conceivable to perform surface grinding on the surface of the wafer instead of lapping. For example, there is a method for grinding one surface of the wafer while holding the other surface by suction. If this is done, both sides of the wafer cannot be processed simultaneously, and a significant reduction in processing time cannot be expected. In addition, since grinding is performed in a state where the wafer is elastically deformed according to the suction side shape by suction of the wafer, after the grinding, if suction is stopped and stress is eliminated, a pattern is generated on the surface of the wafer, There is also a disadvantage that high flatness cannot be obtained.

Further, when a wafer is cut out with a thickness gradient in a previous step (step of cutting out from an ingot), the wafer is sucked and ground as it is, and a target plane set along a predetermined crystal orientation and a finishing plane are finished. There is also a drawback that good parallelism with the plane cannot be obtained. For example, as shown in FIG. 8A, when the shape of the wafer W cut out by the wire saw becomes a shape that becomes thicker toward the lower side in FIG. If the upper surface of the wafer W is ground horizontally by suction as described above, the parallelism between the ground surface 70 and a target plane CC set in advance along a predetermined crystal orientation may be shifted by an angle θ. become.

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a method and an apparatus capable of processing both sides of a wafer efficiently and with high precision.

[0007]

As a means for solving the above-mentioned problems, the present invention is a method for simultaneously grinding both surfaces of a wafer. In this state, a plurality of clamps are arranged with a gap smaller than the thickness of the wafer and rotationally drive these rotary whetstones, while being thinner than the wafer and having an inner peripheral surface substantially matching the outer peripheral surface of the wafer. The wafer is clamped from the outside in the radial direction by a member, and the wafer is passed through the gap between the rotating grindstones in this clamped state so that both surfaces of the wafer are simultaneously brought into contact with the outer peripheral surfaces of both rotating grindstones.

According to this method, by simultaneously grinding both surfaces of the wafer, the processing time can be greatly reduced. Also, unlike the method of grinding while holding the wafer by suction, it does not perform grinding while generating large stress on the wafer, so it is necessary to maintain a suitable processed surface even after processing and releasing the wafer. Can be. In addition, even if the wafer is cut out with a thickness gradient, it can be properly corrected on both sides of the wafer as long as it is clamped and passed between the two grindstones, and a good finish along a predetermined crystal orientation can be obtained. Face can be obtained.

Further, in this method, prior to the above-mentioned grinding, a tapered surface substantially matching the chamfered surface previously formed on the front and back edges of the wafer is formed on the inner peripheral surface of each clamp member. Accordingly, the movement of the wafer in the thickness direction of the wafer can also be restricted by the inner peripheral surface, and the falling off of the wafer from the clamp member can be more reliably prevented.

The present invention is also an apparatus for holding a wafer when simultaneously grinding both surfaces of the wafer, wherein the inner peripheral surface is thinner than the wafer and substantially coincides with the outer peripheral surface of the wafer. A plurality of clamp members, and clamp driving means for changing the relative positions of the clamp members so that these clamp members switch between a clamp state in which the wafer is clamped from the radial outside and a release state in which the wafer is released. It is provided with.

If the wafer is clamped and held by such a wafer holding device, it is possible to process the both surfaces of the wafer by passing the wafer through a gap between a pair of rotating grindstones in the held state.

Also in this wafer holding device, it is more preferable to form a tapered surface on the inner peripheral surface of each clamp member which substantially matches a processed surface formed by chamfering edges on both front and back sides of the wafer. .

[0013] If the inner peripheral surface of each clamp member is made of a material having a larger coefficient of friction with the wafer than the material of the clamp member body, the rotation of the wafer during processing is regulated to realize more precise processing. it can.

In this case, separately from the clamp member main body, a ring-shaped material is formed from a material having a large coefficient of friction with the wafer, and this is combined with the clamp member main body by means such as welding or bonding. However, if the inner peripheral surface of each clamp member is coated with a material having a higher coefficient of friction with the wafer than the material of the clamp member main body, the rotation of the wafer can be regulated with a simpler configuration.

When a non-circular portion is formed in a part of the outer periphery of the wafer, a rotation restricting portion for restricting the rotation of the wafer by contacting the outer peripheral surface of the non-circular portion is provided on at least one clamp member. By providing on the inner peripheral surface,
The rotation of the wafer can be more reliably prevented by using the non-circular portion.

The present invention also relates to an apparatus for simultaneously grinding both surfaces of a wafer, comprising a pair of rotary grindstones arranged with a gap smaller than the thickness of the wafer while the rotation axes are parallel to each other. A grindstone driving unit for rotating and driving these rotating grindstones, any one of the wafer holding devices, and moving the wafer held by the wafer holding device and the pair of rotating grindstones relative to each other so that the wafers held by the wafer holding device are rotated with each other. And a wafer feeding means for passing through the gap.

In this apparatus, if there is provided a grindstone feeding means for moving the rotating grindstones in opposite directions to change the gap size between the rotating grindstones, the wafer thickness dimension after processing can be freely set by the change in the gap dimension. Can be adjusted.

[0018]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG.

The wafer processing apparatus shown in FIGS. 2 to 4 has a bed 10. A grindstone table 12 is disposed on both left and right wings of the bed 10, and a wafer holding table 14 is disposed in the center of the back of both grindstone tables 12.

Each grindstone table 12 includes a fixed table 16 and a movable table 1.
8 is provided. The fixed base 16 extends in the left-right direction (the X-axis direction in FIGS. 2 and 4; hereinafter, simply referred to as “X-axis direction”) of the entire processing apparatus, and is fixed on the bed 10. The movable table 18 is supported on the fixed table 16 so as to be slidable in the X-axis direction, and is slid in the X-axis direction by a grinding wheel feed motor 28 and a feed screw mechanism (not shown).

At the front end (end from the center of the processing apparatus) of each movable table 18, a grindstone holder 20 is formed. A grinding wheel rotating shaft 22 extending vertically is rotatably held by the grinding wheel holding unit 20, and a grinding wheel (rotary grinding wheel) 24 is fixed around the grinding wheel rotating shaft 22. When the two carriages 18 are slid in the opposite directions by the operation of the grinding wheel feed motor 28, the grinding wheels 24 come into contact with and separate from each other, so that the gap between the grinding wheels 24 can be arbitrarily adjusted. Has become. A rotation drive motor (grinding wheel driving means) 26 is connected to each of the grinding wheel rotation shafts 22, and the operation of the rotation drive motor 26 causes the grinding wheel 24 to rotate in a predetermined direction about the grinding wheel rotation shaft 22 (FIG. 1B). (In the direction of the arrow).

The wafer holding table 14 also includes a fixed table 30 and a moving table 32. The fixed base 30 extends in the front-rear direction (the Y-axis direction in FIGS. 2 and 4; hereinafter, simply referred to as “Y-axis direction”) of the entire processing apparatus, and is fixed on the bed 10. The movable table 32 is slidably supported on the fixed table 30 in the Y-axis direction, and is slid in the Y-axis direction by a wafer feed motor (wafer sending means) 33 and a feed screw mechanism (not shown). I have.

A pair of upper and lower support arms 34 extending in the Y-axis direction is fixed to the movable table 32, and a carrier (clamp member) 36 is provided between the front ends of the support arms 34.
Has been fixed. As shown in FIG. 1A, the carrier 36 has a plate shape thinner than the wafer W to be processed, and has an arc-shaped inner peripheral surface 36a having the same radius of curvature as the radius of the wafer W. Have. Further, since the taper surface tf is formed by chamfering the edges on both the front and back sides of the wafer W, the inner peripheral surface 36a is adjusted so that the taper surface tf and the inner peripheral surface 36a of the carrier 36 substantially match. It is formed in a V-groove shape.

In the present invention, the present invention can be applied to wafers of various materials that can be ground, such as silicon, regardless of the specific material of the wafer W.

At a position behind the carrier 36,
A cylinder device (clamp driving means) 38 is provided. The cylinder device 38 has a plurality of telescopic rods 39 that expand and contract in the X-axis direction by supplying hydraulic or pneumatic pressure to the cylinder body. A fixed plate 40 is fixed to the front ends of these telescopic rods 39. A clamper holding member 42 extends forward (in a direction approaching the carrier 36) from the fixing plate 40, and a clamper (clamp member) 44 is fixed to a front end of the clamper holding member 42.

The clamper 44 also has a thinner plate shape than the wafer W, similarly to the carrier 36.
Has an arc-shaped inner peripheral surface 44a having the same radius of curvature as the radius of. Further, in order to make the tapered surface tf of the wafer W substantially coincide with the inner peripheral surface 44a of the clamper 44, the inner peripheral surface 44a is also formed in a V-groove shape. When the clamper 44 is driven forward by the operation of the cylinder device 38, the inner peripheral surface 44a of the clamper 44 and the inner peripheral surface 36a of the carrier 36 substantially match the outer tapered surface tf of the wafer W. In this state, the wafer W can be clamped (two-dot chain line in FIG. 1), and by operating the wafer feed motor 33 in this clamped state, the wafer W is transferred integrally with the moving table 32 in the Y-axis direction. Has become.

Here, the arrangement positions of the carrier 36 and the clamper 44 in the X-axis direction are set at positions that match the intermediate positions of the two grinding wheels 24. Further, the axial dimension (vertical dimension in the illustrated example) of the two grinding wheels 24 is set to be equal to or larger than the diameter of the wafer W, and the entire area of both surfaces of the wafer W can be brought into contact with the two grinding wheels 24. The height position where the carrier 36 and the clamper 44 hold the wafer W is set so as to be as follows.

On the bed 10, a wafer supply table 46 is provided upright at a position halfway from a position where the carrier 36 and the clamper 44 are most retracted to a position between the two grinding wheels 24 as shown in FIG. . On the upper side of the wafer supply table 46, a suction portion 47 for suction-holding the wafer W is provided on one side surface (the right side surface in FIG. 3, the front side surface in FIG. 4).

A support column 48 is erected at an appropriate position on the bed 10, and a dressing device 50 is supported on an upper end of the support column 48. The dressing device 50 includes a fixed table 52 and a lifting table 54. The fixed table 52 is fixed to the support column 48. The lifting table 54 slides on the fixed table 52 in the vertical direction (the Z-axis direction in FIG. 4). It is supported so that it can move up and down.

The grindstone holding rod 56 extends downward from the lifting table 54.
The dressing grindstone 58 is fixed to the lower end of the grindstone holding rod 56. The dressing grindstone 58 has both ends in the X-axis direction protruding from both side surfaces of the grindstone holding rod 56.
The supporting position of the entire dressing device 50 is set so that the side surfaces of the dressing device 4 can be simultaneously contacted (see FIG. 2). Also,
A dress feed motor 60 is provided on the top of the fixed base 52, and the lift table 54, the grindstone holding rod 56, and the dressing grindstone 58 are vertically reciprocated by the dress feed motor 60 and a feed screw mechanism (not shown). It is designed to be driven.

According to this apparatus, both sides of the wafer W can be processed, for example, by the following method.

As an initial state, the moving table 18 of the grindstone table 12, the moving table 32 of the wafer holding table 14, and the clamper 44 are all retracted. That is, the grinding wheels 24 are largely separated from each other, and the carrier 36 and the clamper 44 are attached to the suction section 4.
7 and the clamper 44 is largely separated rearward from the carrier 36. In addition, the dressing device 5
The 0 dressing grindstone 58 is retracted to a position above the two grinding grindstones 24.

The movable table 32 is advanced by operating the wafer feed motor 33, and the arc-shaped inner peripheral surface 36 of the carrier 36 is
It stops at the position where the center of a has passed the center of the suction part 47.

The wafer W cut out by a slicing device (not shown) is transported, and is sucked by the suction portion 47.

The cylinder device 38 is operated to advance the clamper 44, and the clamper 44 and the carrier 3 are moved forward.
6 clamps the wafer W from the outside in the diameter direction (the state shown by the two-dot chain line in FIG. 1A). After this clamping, the suction by the suction section 47 is stopped.

The operation of each of the rotary drive motors 26 drives the grinding wheel 24 to rotate.
Is moved forward so that the grinding wheels 24 approach each other, and the gap between the two grinding wheels 24 matches the size corresponding to the target thickness dimension of the wafer W (<current thickness dimension).

In this state, the moving table 32 of the wafer holding table 14 is further advanced. Here, since the carrier 36 and the clamper 44, which are clamping members, are thinner than the wafer W, the carrier 36 and the clamper 44 pass between the grinding wheels 24 without contacting the two grinding wheels 24, and the wafer W Grinding wheel 2 only on both sides
4 (the state shown in FIG. 1B). Thereby, both surfaces of the wafer W are simultaneously ground. Wafer W after processing
Are appropriately collected by an unillustrated collecting means. If the sharpness of the grinding wheel 24 becomes dull, the dressing device 50
The two grindstones 24 are appropriately dressed using the dressing grindstone 58.

As described above, in this method and apparatus, the wafer W is clamped by the thin clamping members (the carrier 36 and the clamper 44) from the outside in the diameter direction, and the grinding whetstones 24 approaching each other are kept in this clamped state. Since the wafer W is passed between them, both surfaces of the wafer W can be ground at one time, thereby greatly reducing the processing time.

In addition, the wafer W is held only by lightly holding it between the carrier 36 and the clamper 44, and a large stress is generated on the wafer W during processing as in the method of grinding while holding one surface of the wafer W by suction. I will not let you
There is no inconvenience that defects occur on the surface of the wafer W after processing.

Even when the wafer W is cut out with a thickness gradient (that is, when both surfaces of the wafer W are mutually inclined), it is preferable to pass the wafer W between the grinding wheels 24. Shape correction can be performed, and a surface with high flatness can be easily obtained.

Further, in this embodiment, the carrier 3
6 and the inner peripheral surfaces 36a, 44a of the clamper 44 are formed in a V-groove shape that matches the mountain-shaped tapered surface tf formed by chamfering the edge of the wafer W, so that the wafer W is clamped in the X-axis direction. It can also be regulated from both outer sides (upper and lower sides in FIGS. 1A and 1B). For this reason,
Even when an external force acts on the wafer W from the X-axis direction during the processing, if the external force is a value within an appropriate range, the wafer W is caused by the carrier 36 and the clamper 4 due to the external force.
4 can be prevented from dropping in the X-axis direction.

In the present invention, regardless of the clamping direction, for example, when the wafer W is held in an upright state as shown in FIG. 4, the wafer W may be clamped from above and below. When W is held in a horizontal state, it may be clamped from front, rear, left and right. Alternatively, three or more clamp members may be arranged radially around the wafer W, and these clamp members may approach the wafer W in the centripetal direction. This is the same in the following embodiments.

In this embodiment, both sides of the wafer W are processed by moving the wafer W. For example, both grinding wheels 24 are mounted on a table movable in a direction parallel to both sides of the wafer W. However, it is also possible to process both surfaces of the wafer W by moving these grinding wheels 24.

The second embodiment will be described with reference to FIGS.

In the first embodiment, the carrier 36
And when the clamping force by the clamper 44 is relatively weak,
When a circumferential external force acts on the wafer W at a position deviated from the center thereof, the wafer W is rotated (that is, the outer peripheral surface of the wafer W is moved by the carrier 36 and the clamper 4).
4 may slide in the circumferential direction with respect to the inner peripheral surfaces 36a and 44a), and good grinding may not be possible.

Therefore, in the second embodiment, the inner peripheral edges 36b, 44b of the carrier 36 and the clamper 44 are formed of a material having a larger coefficient of friction with the wafer W than the material of the carrier 36 and the clamper 44. In addition, the circumferential slip of the wafer W is regulated.

Specifically, the carrier 36 and the clamper 44
Is made of a metal material such as stainless steel, and the wafer W
Is made of, for example, silicon, the inner peripheral portion 36
As a material for b and 44b, a synthetic resin such as polyurethane is suitable. In this case, the inner peripheral edge 36b,
The ring constituting 44b may be separately formed and fixed to the carrier 36 and the clamper 44 by means such as welding or bonding, or the inner circumference of the carrier 36 and the clamper 44 shown in FIG. The surfaces 36a and 44a may be coated with the above polyurethane or the like later. In any case, the falling off of the wafer W can be more reliably prevented by forming the inner peripheral surface into a V-shaped groove as in the first embodiment.

As shown in FIGS. 6 (a), 6 (b) and 7, the third and fourth embodiments have an orientation flat surface f on a part of the outer periphery of the wafer W.
When a non-circular portion such as f is formed, it is also possible to use this to stop the wafer W from rotating.

In the example of FIG. 6, a rectangular notch 36c is formed in a part of the inner peripheral surface of the clamper 44, and a rectangular rotation restricting plate 61 having the same width as this is inserted into the notch 36c. The rotation restricting plate 61 is fixed to the fixing piece 62 on the clamper 44 side using a bolt 64 and a nut 65 at a position where the rotation restricting plate 61 contacts the flat surface ff of the wafer W. The rotation restricting plate 61 is brought into contact with the flat surface ff of the wafer W, so that the wafer W
Rotation is regulated.

On the other hand, in the example of FIG. 7, instead of the clamper 44 and the rotation restricting plate 61 being separate members as described above,
The tip of the clamper 44 is formed in a V-groove shape to restrict rotation.

The "non-arc portion" necessary for regulating the rotation of the wafer W is not limited to the flat surface ff as described above, but may be a notch or the like which is depressed inward in the wafer radial direction. In any case, the rotation of the wafer W during the processing is prevented by forming the restricting portion in contact with the non-arc portion on at least one clamp member (at least one of the carrier 36 and the clamper 44 in the example of FIG. 1). be able to.

[0052]

As described above, according to the present invention, a pair of rotary grindstones are driven to rotate, and the wafer is passed through the gap between the rotary grindstones while clamping the wafer from the radial outside by a thin clamp member. Since both sides of the wafer are simultaneously ground, there is an effect that the processing time can be greatly reduced as compared with the related art, and a wafer surface with high flatness can be obtained with high accuracy.

Further, prior to the above-mentioned grinding, a tapered surface substantially matching the chamfered surface previously formed on the front and back edges of the wafer is formed on the inner peripheral surface of each clamp member. The movement of the wafer in the thickness direction of the wafer can also be regulated by the peripheral surface, and the effect of more reliably preventing the wafer from falling off the clamp member can be obtained.

The present invention also relates to an apparatus for holding a wafer when simultaneously grinding both sides of the wafer, wherein the inner peripheral surface is thinner than the wafer and substantially coincides with the outer peripheral surface of the wafer. A plurality of clamp members, and clamp driving means for changing the relative positions of the clamp members so that these clamp members switch between a clamp state in which the wafer is clamped from the radial outside and a release state in which the wafer is released. Therefore, by clamping and holding the wafer with this apparatus, it is possible to obtain the effect of performing the above method and simultaneously grinding both surfaces of the wafer.

Here, according to the structure in which the inner peripheral surface of each clamp member is made of a material having a larger coefficient of friction with the wafer than the material of the clamp member main body, the rotation of the wafer during processing is regulated so as to achieve a higher accuracy. High processing can be performed.

In this case, if the inner peripheral surface of each clamp member is coated with a material having a higher coefficient of friction with the wafer than the material of the clamp member main body, the rotation of the wafer can be regulated with a simple configuration.

When a non-circular portion is formed on a part of the outer periphery of the wafer, a rotation restricting portion for restricting the rotation of the wafer by contacting the outer peripheral surface of the non-circular portion is provided on at least one clamp member. By providing on the inner peripheral surface,
By using the non-circular portion, the effect of more reliably preventing the rotation of the wafer can be obtained.

Also, a pair of rotating grindstones arranged with a gap smaller than the thickness of the wafer while the rotating shafts are parallel to each other, a grindstone driving means for rotating these rotating grindstones, In a processing apparatus comprising: a holding device; and a wafer feeding unit that relatively moves the wafer holding device and a pair of rotating grindstones to pass a wafer held by the wafer holding device through a gap between the rotating grindstones. According to the apparatus provided with the whetstone feeding means for changing the gap size between the rotary whetstones by moving them in opposite directions, the effect of freely adjusting the thickness of the processed wafer by the change in the gap size is obtained.

[Brief description of the drawings]

FIG. 1A is a cross-sectional plan view showing a state in which a clamper approaches a wafer W in a first embodiment of the present invention, and FIG. 1B is a view showing the state in which the wafer is clamped by the clamper and a carrier. FIG. 4 is a cross-sectional plan view showing a state where both sides are ground.

FIG. 2 is an overall plan view of the wafer processing apparatus according to the first embodiment of the present invention.

FIG. 3 is an overall front view of the wafer processing apparatus according to the first embodiment of the present invention.

FIG. 4 is an overall perspective view of the wafer processing apparatus according to the first embodiment of the present invention.

FIG. 5A is a sectional view taken along line AA of FIG. 5B, and FIG. 5B is a side view showing a state where a carrier and a clamper clamp a wafer in the second embodiment of the present invention. .

6A is a sectional view taken along line BB of FIG. 6B, and FIG. 6B is a side view showing a state where a carrier and a clamper clamp a wafer in the third embodiment of the present invention. .

FIG. 7 is a side view showing a state where a carrier and a clamper are clamping a wafer in a fourth embodiment of the present invention.

FIG. 8A is a diagram showing a shape of a wafer cut by a wire saw, and FIG. 8B is a diagram showing a wafer shape obtained by a conventional grinding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Grinding wheel stand 14 Wafer holding table 24 Grinding grindstone (rotary grindstone) 26 Rotation drive motor (grindstone drive means) 28 Grindstone feed motor (grindstone sending means) 33 Wafer feed motor (wafer sending means) 36 Carrier (clamp member) 36a Carrier Inner peripheral surface 36b Inner peripheral edge of carrier 38 Cylinder device (clamp driving means) 44 Clamper (clamp member) 44a Inner peripheral surface of clamper 44b Inner peripheral edge of rotation 61 Rotation regulating plate W Wafer tf Wafer outer peripheral taper surface ff Wafer flat surface ( Outer peripheral surface of non-arc part)

Continued on the front page (72) Inventor: Fumihiko Hasegawa 150, Odakura Osaikura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture Inside the Shirakawa Plant, Shin-Etsu Semiconductor Co., Ltd. Semiconductor Corporation Shirakawa Factory

Claims (9)

[Claims] 1. A method for simultaneously grinding both surfaces of a wafer, wherein a pair of rotary whetstones are arranged with a gap smaller than the thickness of the wafer while their rotation axes are parallel to each other. While rotating the grindstone, the wafer is clamped from the outside in the radial direction by a plurality of clamp members having a thickness smaller than the wafer and having an inner peripheral surface substantially matching the outer peripheral surface of the wafer, and the clamped state is maintained. A double-sided processing method for a wafer, characterized in that a wafer is passed through the gap between the rotating whetstones so that both surfaces of the wafer are simultaneously brought into contact with the outer peripheral surfaces of the two whetstones. 2. A double-sided wafer processing method according to claim 1, wherein a tapered surface that substantially matches a chamfered surface that has been previously machined on both front and back edges of the wafer before the grinding is formed in each of the clamp members. A method for processing both sides of a wafer, wherein the method is formed on a peripheral surface. 3. An apparatus for holding a wafer when simultaneously grinding both surfaces of the wafer, the apparatus comprising a plurality of thinner wafers having an inner peripheral surface substantially matching the outer peripheral surface of the wafer. And clamp driving means for changing the relative positions of the clamp members so that the clamp members switch between a clamp state in which the wafer is clamped from the radial outside and a release state in which the wafer is released. A wafer holding device characterized by the above-mentioned. 4. A wafer holding device according to claim 3, wherein a tapered surface substantially matching a processed surface formed by chamfering both front and back edges of the wafer is formed on an inner peripheral surface of each clamp member. A wafer holding device characterized by the above-mentioned. 5. The wafer holding device according to claim 3, wherein the inner peripheral surface of each clamp member is made of a material having a larger coefficient of friction with the wafer than the material of the clamp member main body. apparatus. 6. The wafer holding device according to claim 5, wherein the inner peripheral surface of each clamp member is coated with a material having a higher coefficient of friction with the wafer than the material of the clamp member main body. 7. The wafer holding device according to claim 3, wherein the wafer is in contact with an outer peripheral surface of a non-circular portion formed on a part of an outer periphery of the wafer to regulate rotation of the wafer. A wafer holding device, wherein a portion is provided on an inner peripheral surface of at least one clamp member. 8. An apparatus for simultaneously grinding both surfaces of a wafer, comprising: a pair of rotating grindstones arranged with a gap smaller than the thickness of the wafer while rotating axes are parallel to each other; A grindstone driving means for rotating and driving a grindstone, the wafer holding device according to any one of claims 3 to 7, and a wafer held by the wafer holding device by relatively moving the wafer holding device and the pair of rotating grindstones. And a wafer feeding means for passing the wafer through a gap between the rotary whetstones. 9. The wafer double-side processing apparatus according to claim 8, further comprising a grinding wheel feeding means for moving the rotating grinding wheels in opposite directions to change a gap size between the rotating grinding wheels. Double-sided processing equipment.