JP7147011B2 - WAFER, WAFER THINNING METHOD, AND WAFER THINNING APPARATUS - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor substrate, and more particularly to a wafer, a wafer thinning method, and a wafer thinning apparatus capable of improving the yield when thinning a semiconductor wafer.

Semiconductor manufacturing technology includes machining technology, lithography technology, thin film formation technology, etching technology, ion implantation technology, and cleaning technology. Semiconductor machining technology includes cutting (slicing), grinding, lapping, polishing, CMP (chemical mechanical polishing), and back grinding in each process of wafer manufacturing, wafer processing, chipping, and assembly. , dicing, etc.

Moreover, recently, the demand for applications such as thin cards and wireless tags is increasing, and the demand for high-density mounting is increasing. In order to meet these demands, ultra-thin wafers are required, and the demand for ultra-thin technology is increasing. In order to make the wafer extremely thin, various devices and methods have been devised in the grinding of the wafer. In addition, the diameter of wafers is increasing in order to improve productivity and reduce costs, but in order to achieve ultra-thin wafers with large diameters, polishing/grinding methods, finishing methods, processing equipment, and transport methods are required. etc., a lot of ingenuity is required.

Thinning of a semiconductor wafer is performed by back grinding to obtain a desired thickness by grinding the back surface of the semiconductor wafer. When the semiconductor wafer is simply ground from the back surface, the mechanical strength of the semiconductor wafer decreases. break easily. In addition, the semiconductor wafer tends to warp, and as a result, when the thickness is reduced, the defect rate of the semiconductor wafer due to cracks and warps increases sharply.

In order to prevent the defective rate of semiconductor wafers from increasing due to cracks and warpage due to back grinding, the back surface of the semiconductor wafer is ground leaving a few millimeters of the outer edge to thin the inside of the outer edge of the semiconductor wafer. layer. That is, it is known to form a recess inside the outer edge, and is described, for example, in Japanese Unexamined Patent Application Publication No. 2002-200014.

In addition, an annular step is formed on the peripheral edge of the front surface side of the chamfered wafer before thinning to prevent a knife edge. Patent Document 2 describes that the depth should correspond to the target thickness of the wafer after thinning.

JP 2007-335659 A Japanese Patent Application Laid-Open No. 2007-152906

The prior art described above is effective in reducing the transfer risk of thin wafers and in reducing warpage, and can reduce edge chipping. However, it has been difficult to improve the quality by mechanically polishing the wafer to prevent damage to the wafer due to the microcrack (fine scratches and cracks) layer caused by backgrinding.

It is an object of the present invention to solve the above-mentioned problems of the prior art, and to eliminate damage to the wafer end surface during the process of pressing a polishing tape against the edge of the wafer end surface, and the wafer breakage due to the handling work after the wafer shape processing. to improve productivity and profitability.

In order to achieve the above object, the present invention provides a wafer thinning method for processing a wafer to a desired thickness by back grinding, wherein the edge portion of the outer periphery of the wafer is processed as a chamfered portion, and the chamfered portion is chamfered. The upper part is removed from the upper surface of the wafer to the target thickness (T) to be thinned horizontally from the outer periphery to the inner periphery of the wafer, the length of the machining allowance removed from the outer periphery is L, and the angle of the chamfered portion with respect to the horizontal After processing the wafer into a shape that satisfies L = T/tan φ + α with φ and a margin α, the contact angle with the polishing tape that polishes the outermost peripheral portion of the wafer after processing the wafer into the above shape and the angle φ is determined to be equal to

Further, the present invention is a wafer thinning method for processing a wafer to a desired thickness by back grinding, wherein the edge portion of the outer periphery of the wafer is processed as a chamfered portion, and the upper portion of the chamfered portion is the wafer. From the upper surface to the target thickness (T) to be thinned, the wafer is horizontally removed from the outer periphery toward the inner periphery, and the machining allowance length removed from the outer circumference is L, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α , and the angle φ is determined to be equal to the angle of the portion of the inner surface of the wafer transfer cassette that contacts the outer periphery of the wafer.

Further, the present invention provides a wafer thinning apparatus for processing a wafer to a desired thickness by back grinding, a chamfering apparatus for processing an edge portion of the outer periphery of the wafer as a chamfered portion, and a whetstone that horizontally cuts and removes the upper part of the chamfered portion that has been chamfered in advance to a target thickness (T) from the outer periphery toward the inner periphery of the wafer, and the removed machining allowance length is L, The wafer is processed into a shape of L=T/tan φ+α where φ is the angle of the portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer, and the wafer is processed into the above shape. The contact angle with the polishing tape that polishes the outermost periphery of the wafer is determined to be equal to the angle φ.

Further, the present invention provides a wafer thinning apparatus for processing a wafer to a desired thickness by back grinding, a chamfering apparatus for processing an edge portion of the outer circumference of the wafer as a chamfered portion, and a whetstone that horizontally cuts and removes the upper part of the chamfered portion that has been chamfered in advance to a target thickness (T) from the outer periphery toward the inner periphery of the wafer, and the removed machining allowance length is L, Assuming that the margin α and the angle φ of the portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer, it is processed into a shape that satisfies L=T/tanφ+α, and the angle φ is the inner surface of the wafer transfer cassette. is determined to be equal to the angle of the portion in contact with the outer peripheral portion of the wafer.

Furthermore, the present invention provides a wafer thinned to a desired thickness by back grinding, wherein the edge portion of the outer periphery of the wafer is processed as a chamfered portion, and the upper portion of the chamfered portion is thinned from the upper surface of the wafer. It is horizontally removed from the outer periphery to the inner periphery of the wafer up to the thickness (T), and L is the length of the machining allowance removed from the outer periphery, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, L = T /tan φ+α, and the angle φ is determined to be equal to the contact angle with the polishing tape that polishes the outer peripheral portion of the wafer.

Furthermore, the present invention provides a wafer thinned to a desired thickness by back grinding, wherein the edge portion of the outer periphery of the wafer is processed as a chamfered portion, and the upper portion of the chamfered portion is thinned from the upper surface of the wafer. It is horizontally removed from the outer periphery to the inner periphery of the wafer up to the thickness (T), and L is the length of the machining allowance removed from the outer periphery, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, L = T /tan φ+α, and the angle φ is determined to be equal to the angle of the portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer.

According to the present invention, the upper portion of the chamfered portion on the outer periphery of the wafer is horizontally removed from the outer periphery toward the inner periphery to the target thickness (T) for thinning, the machining allowance length is L, and the angle of the chamfered portion with respect to the horizontal is φ , and margin α, the wafer is processed into a shape that satisfies L = T / tan φ + α. Back grinding can be achieved without damaging the end face. Therefore, the productivity and profitability of thinned wafers can be improved.

FIG. 1 is a front view showing a main part according to one embodiment of the present invention; FIG. 1 is a plan view showing a main part according to one embodiment of the present invention; FIG. 2 is a sectional view showing the shape of a wafer W after chamfering according to one embodiment of the present invention; FIG. 2 is a cross-sectional view showing cutting by a trimming grindstone according to one embodiment of the present invention; A cross-sectional view showing the detailed shape of the outer peripheral portion of the wafer W according to one embodiment of the present invention. FIG. 2 is a side view showing a state of contact between a wafer W and a polishing tape according to one embodiment of the present invention; 1 is a diagram showing the configuration of a polishing apparatus according to one embodiment of the present invention; FIG. Cross-sectional views showing the back grinding process and the shape of the wafer W according to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings. The thinning of semiconductor wafers is performed by backgrinding, in which the semiconductor wafer is ground from the back surface to a desired thickness. Then, the peripheral edge is processed to prevent damage such as cracks and chips during handling.

In addition, when a chamfered wafer is thinned, the cross section of the peripheral edge sharpens to become thinner toward the outer peripheral side, changing into a knife-edge shape. Before thinning, cutting is performed in advance to prevent a knife edge.

First, the chamfering device will be described. FIG. 1 is a front view showing the main part of a chamfering device according to one embodiment of the present invention, and FIG. 2 is a plan view.

As shown in the figure, the chamfering device 50 comprises a wafer feeding unit 50A and a grinding unit 50B. A pair of Y-axis guide rails 52, 52 are laid at a predetermined interval on the horizontally arranged base plate 51 of the wafer feeding unit 50A. A Y-axis table 56 is slidably supported on the pair of Y-axis guide rails 52 , 52 via Y-axis linear guides 54 , 54 .

A nut member 58 is fixed to the lower surface of the Y-axis table 56 , and a Y-axis ball screw 60 is screwed into the nut member 58 . The Y-axis ball screw 60 is rotatably supported at both ends by bearing members 62, 62 disposed on the base plate 51 between the pair of Y-axis guide rails 52, 52, and has a Y-axis at one end. A shaft motor 64 is coupled.

By driving the Y-axis motor 64, the Y-axis ball screw 60 rotates, and the Y-axis table 56 slides along the Y-axis guide rails 52, 52 in the horizontal direction (Y-axis direction) via the nut member 58. .

A pair of X-axis guide rails 66 , 66 are laid on the Y-axis table 56 so as to be orthogonal to the pair of Y-axis guide rails 52 , 52 . An X-axis table 70 is slidably supported on the pair of X-axis guide rails 66, 66 via X-axis linear guides 68, 68, .

A nut member 72 is fixed to the lower surface of the X-axis table 70 , and an X-axis ball screw 74 is screwed into the nut member 72 . The X-axis ball screw 74 is rotatably supported at both ends by bearing members 76, 76 arranged on the X-axis table 70 between a pair of X-axis guide rails 66, 66. An output shaft of an X-axis motor (not shown) is connected to the end.

Therefore, by driving the X-axis motor, the X-axis ball screw 74 rotates, and the X-axis table 70 slides in the horizontal direction (X-axis direction) along the X-axis guide rails 66 , 66 via the nut member 72 . do.

A Z-axis base 80 is erected vertically on the X-axis table 70, and a pair of Z-axis guide rails 82, 82 are laid on the Z-axis base 80 at a predetermined interval. A Z-axis table 86 is slidably supported by the pair of Z-axis guide rails 82 , 82 via Z-axis linear guides 84 , 84 .

A nut member 88 is fixed to the side surface of the Z-axis table 86 , and a Z-axis ball screw 90 is screwed into the nut member 88 . The Z-axis ball screw 90 is rotatably supported at its both ends by bearing members 92, 92 disposed on the Z-axis base 80 between a pair of Z-axis guide rails 82, 82, and its lower end is connected to the output shaft of the Z-axis motor 94 .

By driving the Z-axis motor 94, the Z-axis ball screw 90 rotates, and the Z-axis table 86 slides in the vertical direction (Z-axis direction) along the Z-axis guide rails 82, 82 via the nut member 88. . A θ-axis motor 96 is installed on the Z-axis table 86 .

An output shaft of the θ-axis motor 96 is connected to a θ-axis shaft 98 whose axis is the θ-axis (rotational axis θ) parallel to the Z-axis. ) 10 are horizontally connected. The wafer W is placed on the suction table 10 and held by vacuum suction.

In the wafer feeding unit 50A, the suction table 10 moves horizontally in the Y-axis direction in the drawing by driving the Y-axis motor 64, and moves horizontally in the X-axis direction in the drawing by driving the X-axis motor. By driving the Z-axis motor 94, it moves vertically in the Z-axis direction in the drawing, and by driving the .theta.-axis motor 96, it rotates around the .theta.-axis.

A mount 102 is installed on the base plate 51 of the grinding unit 50B. A peripheral motor 104 is installed on the frame 102, and the output shaft of the peripheral motor 104 is connected to a spindle 106 having a rotation axis CH parallel to the Z-axis. A grinding wheel 108 for chamfering the outer peripheral portion of the wafer W is detachably attached to the spindle 106 and rotated by driving the outer peripheral motor 104 . A nozzle 121 for discharging a coolant (grinding liquid) toward a processing point where the wafer W contacts the grindstone wheel 108 is provided.

In the chamfering apparatus 50 configured as described above, the wafer W is chamfered as follows. As a preparatory step before chamfering, the wafer W to be chamfered is placed on the suction table 10 and held by suction. Then, the outer peripheral motor 104 and the .theta.-axis motor 96 are driven to rotate both the grinding wheel 108 and the suction table 10 in the same direction at high speed. For example, the rotation speed of the grindstone wheel 108 is set to 3000 rpm, and the rotation speed of the suction table 10 is set so that the peripheral speed of the wafer W is 5 mm/sec.

Also, the Z-axis motor 94 is driven to adjust the height of the suction table 10 so that the height of the wafer W corresponds to the height of the grindstone wheel 108 . Further, the X-axis motor is driven to align the θ-axis (rotational axis θ), which is the rotational axis of the wafer W, with the rotational axis CH of the grindstone wheel 108 in the X-axis direction.

Next, as a chamfering step, the Y-axis motor 64 is driven to feed the wafer W toward the grindstone wheel 108 . Then, the speed is decelerated just before the outer peripheral portion of the wafer W comes into contact with the grindstone wheel 108, and then the wafer W is sent toward the grindstone wheel 108 at a low speed.

As a result, the outer peripheral portion of the wafer W is brought into sliding contact with the grindstone wheel 108, and as described below, the wafer W is ground by minute amounts and chamfered. In addition, the coolant is discharged from the nozzle 121 toward the machining point to cool the machining point and discharge the grinding debris and grinding powder (crushed and dropped abrasive grains) of the grindstone.

When the outer peripheral portion of the wafer W reaches the deepest portion of the grinding groove and a predetermined time elapses, the chamfering process is completed, and the wafer W is moved away from the grindstone wheel 108 to a position for recovering the wafer W. Let For chamfering and shape processing, the outer peripheral portion of the wafer is processed with a CBN or SD diamond grindstone.

FIG. 3 is a cross-sectional view showing the shape of the wafer W when the chamfering process is completed. FIG. 8 is a cross-sectional view showing the back grinding process and the shape of the wafer W. As shown in FIG. The cross-sectional shape of the edge portion of the wafer W is chamfered, and the chamfered portion W-1 has a slightly rounded shape.

The wafer W is placed on the suction table 10 and back-grinding is performed by grinding and thinning the back side of the wafer W with the back-grinding whetstone 21 as indicated by the dotted line in FIG. If left as it is, the edge portion W-10 will have a sharp shape due to the chamfering angle. Then, the mechanical strength becomes very weak and edge chipping occurs. In addition, the edge portion flutters due to the influence of grinding water and processing conditions, and chipping occurs, which causes wafer breakage.

In back grinding, both rough grinding and finish grinding are good for reducing edge chipping. Furthermore, edge trimming is effective in which a groove is formed in the outer peripheral edge portion of the wafer W in advance before the back grinding process.

However, simply grooving to a depth corresponding to the target thickness T of the wafer W after thinning may cause chipping in the vicinity of the final finished thickness and scratches on the external shape when the wafer W is stored in a cassette. It is difficult to reduce transport damage and damage when polishing edges using polishing tape.

In the edge trimming, the hatched portion in FIG. 3 is processed with the trimming grindstone 20 before back grinding to edge trim the end surface of the wafer W to remove damage. As the trimming whetstone 20, a vitrified whetstone, a resin whetstone of No. 3000 or higher, or the like is suitable. After the edge trimming, minute irregularities on the ground wafer W are polished and mirror-finished so as not to affect the performance of the surface.

FIG. 4 is a cross-sectional view showing cutting by the trimming grindstone 20. As shown in FIG. The upper portion of the chamfered portion W-1, which is the hatched portion in FIG. 3, is removed from the upper surface of the wafer W by 50 to 150 μm corresponding to the target thickness T, and smoothed horizontally in the Y direction. Next, by swinging in the Z direction, the rising portion W-2, which is a plane perpendicular to the cutting direction, is mirror-finished to prevent cracks from entering.

As a result, it is possible to improve the workability and promote the cavitation effect, thereby preventing clogging at the working point due to the difficulty of coolant entering and the difficulty of sludge being discharged. Therefore, the cleaning of the grinding surface and the discharge of grinding dust are facilitated, and the protruding amount of the grinding grains is stably ensured, thereby improving the processing quality.

FIG. 5 is a cross-sectional view showing the detailed shape of the outer peripheral portion of the wafer W. As shown in FIG. L is a machining allowance length required to avoid transport damage and damage by the polishing tape, and is removed from the outer circumference of the wafer W toward the inner circumference. Unless the value of L is appropriate, it becomes difficult to reduce damage in the process after chamfering and improve quality.

The inner surface of the transfer cassette (not shown) is normally in contact with the outer periphery of the wafer W at a predetermined angle. φ is a chamfered angle that is approximately equal to the contact angle with a holder such as a transport cassette or with a polishing tape in the subsequent polishing process. φ is necessary to prevent the corner W-3 of the edge of the wafer W from coming into point contact with the inner surface of a holder such as a transfer cassette or the polishing tape.

FIG. 6 is a side view showing the state of contact between the wafer W and the polishing tape 31. As shown in FIG. If the machining allowance length L to be processed is equal to or less than T/tanφ, the corner W-3 of the wafer W to be used collides with the inner surface of the transfer cassette and the polishing tape 31 in point contact, and the corner W- 3 is more likely to chip. The polishing tape 31 is fed from the feed bobbin 34 while being guided by guide rollers 38 and 39 . The polishing tape 31 contacts the outer peripheral portion of the wafer W and is taken up by the take-up bobbin 35 via the guide rollers 36 and 37 .

The outermost peripheral portion W-4 of the wafer W needs to be sufficiently mirror-finished by the polishing tape 31, and fine irregularities are polished to give a slightly rounded shape. Therefore, α is a margin (preferably 0.1 to 0.5 mm),
It is processed into a shape that satisfies L=T/tan φ+α.
T is the target thickness of the wafer W to be used, and φ is a holder such as a transfer cassette, or a chamfering angle that is approximately equal to the contact angle with the polishing tape. possible damage can be avoided.

FIG. 7 is a diagram showing the configuration of a polishing apparatus. The polishing apparatus includes a wafer stage 3 that holds a wafer W, a wafer stage moving mechanism 4 that moves the wafer stage 3 in a parallel direction, an edge polishing unit 5 as a polishing tape portion that polishes the edge portion of the wafer W, A polishing movement mechanism 6 for moving the edge polishing unit 5 with respect to the edge portion of the wafer W held on the wafer stage 3 is provided.

The wafer stage moving mechanism 4 includes a spindle 11 that rotatably supports the cylindrical member 30, a movable part 12 that can move integrally with the spindle 11, and a support that movably supports the wafer stage 3 on a base 13. a platform 14; In addition, the movable part 12 is movable in the direction indicated by the arrow Y. As shown in FIG. Further, the cylindrical member 30 is configured to be rotatable around the β axis as a rotation axis.

The edge polishing unit 5 includes a polishing head portion 32 as an edge contact portion that abuts and presses a polishing tape (strip-shaped polishing member) 31 against the edge portion of the wafer W, and a polishing tape that feeds the polishing tape 31 to the polishing head portion 32 . A feeding mechanism 33 is provided.

The polishing tape feeding mechanism 33 includes a feeding bobbin 34 as a tape feeding section for feeding the polishing tape 31 to the polishing head section 32, and a winding bobbin as a tape winding section for winding the polishing tape 31 fed out to the polishing head section 32. 35 and a rotation mechanism (not shown) that rotates the winding bobbin 35 . As the polishing tape 31, a polishing tape is used in which abrasive grains of polishing particles are applied to a base film on one side serving as a polishing surface.

The polishing moving mechanism 6 includes a shaft base 41 having a cylindrical member 40 holding the edge polishing unit 5 composed of the polishing head portion 32 and the polishing tape feeding mechanism 33, a movable portion 42 movable integrally with the shaft base 41, and a movable portion. It has an axle base 43 that supports the part 42 and a movable part 44 that can move integrally with the axle base 43 .

As described above, not only is the outer peripheral edge portion of the wafer W pre-grooved to a depth corresponding to the target thickness T before the back grinding process, but also the outer shape of the wafer W stored in the cassette. Optimal edge trimming is performed in consideration of transport damage such as scratches in the surface, or damage when polishing the edge using a polishing tape. This can effectively prevent damage during back grinding and chipping near the final finished thickness.

When trimming the edge, by swinging the trimming wheel 20 in the Z direction, the abrasive grains are vibrated in the Z direction, and the original cutting ability and the vibration acceleration motion of the abrasive grains are added to improve the grinding performance. . As a result, low-damage processing in the Z direction can be achieved. In addition, cavitation of abrasive grains is promoted on the side parallel to the cutting direction, and no damage occurs on the surface of the rising portion W-2, which is the vertical surface. By distributing the poor lubrication to the abrasive grains and the processing load, the shape retention performance of the grindstone is improved, the quality of the workpiece can be stabilized, and the grindstone life can be improved.

W... Wafer, W-1... Chamfered portion, W-2... Rising portion, W-3... Corner portion, W-4... Outermost peripheral portion, W-10... Edge portion, φ... Chamfering angle, L... Machining length T... Target thickness α... Margin 3... Wafer stage 4... Wafer stage moving mechanism 5... Edge polishing unit 6... Polishing moving mechanism 10... Suction table 11, 41, 43... Axle , 12, 42, 44 Movable portion 13 Base 14 Support 20 Trimming whetstone 21 Back grinding whetstone 30 Cylindrical member 31 Polishing tape 32 Polishing head 33 Polishing tape feeding mechanism 34 Feeding bobbin 35 Winding bobbin 36, 37, 38, 39 Guide roller 40 Cylindrical member 50 Chamfering device 50A Wafer feeding unit 50B Grinding unit 51 Base plate 52 Y-axis guide rail 54 Y-axis linear guide 56 Y-axis table 58, 72, 88 Nut member 60 Y-axis ball screw 62 Bearing member 64 Y-axis motor 66 X-axis guide rail 68 X-axis linear guide 70 X-axis table 74 X-axis ball screw 76, 92 Bearing member 80 Z-axis base 82 Z-axis guide rail 84 Z-axis linear guide , 86 Z-axis table 90 Z-axis ball screw 94 Z-axis motor 96 θ-axis motor 98 θ-axis shaft 102 Base 104 Peripheral motor 106 Spindle 108 Grinding wheel 121 …nozzle

Claims (6)

A wafer thinning method for processing a wafer to a desired thickness by back grinding, comprising:
processing the edge portion of the outer periphery of the wafer as a chamfered portion,
removing the upper part of the chamfer horizontally from the outer periphery to the inner periphery of the wafer to a target thickness (T) to be thinned from the upper surface of the wafer;
Assuming that the length of the machining allowance removed from the outer periphery is L, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, when processing into a shape that satisfies L = T / tan φ + α,
A method for thinning a wafer, wherein the angle φ is determined so as to be equal to a contact angle with a polishing tape that polishes the outermost peripheral portion of the wafer after the processing . A wafer thinning method for processing a wafer to a desired thickness by back grinding, comprising:
processing the edge portion of the outer periphery of the wafer as a chamfered portion,
removing the upper part of the chamfer horizontally from the outer periphery to the inner periphery of the wafer to a target thickness (T) to be thinned from the upper surface of the wafer;
Assuming that the length of the machining allowance removed from the outer periphery is L, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, the shape is processed to be L = T / tan φ + α,
A method of thinning a wafer, wherein the angle φ is determined to be equal to the angle of a portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer. In a wafer thinning device for processing a wafer to a desired thickness by back grinding,
a chamfering device that processes the edge portion of the outer periphery of the wafer as a chamfered portion;
a whetstone that cuts horizontally from the outer circumference toward the inner circumference of the wafer to remove the upper portion of the chamfered portion that has been chamfered in advance before the back grinding process to a target thickness (T);
L = T / tan φ + α, where L is the removed machining allowance length, α is the allowance α, and φ is the angle of the portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer. When doing
The apparatus for thinning a wafer, wherein the angle φ is determined so as to be equal to the angle of contact with a polishing tape for polishing the outermost peripheral portion of the wafer after the processing . In a wafer thinning device for processing a wafer to a desired thickness by back grinding,
a chamfering device that processes the edge portion of the outer periphery of the wafer as a chamfered portion;
a grindstone that cuts horizontally from the outer periphery toward the inner periphery of the wafer to remove the upper part of the chamfered portion that has been chamfered in advance before the back grinding process to a target thickness (T),
L = T / tan φ + α, where L is the length of the removed machining allowance, α is the allowance α, and φ is the angle of the portion of the inner surface of the wafer transfer cassette that contacts the outer peripheral portion of the wafer,
The wafer thinning apparatus is characterized in that the angle φ is determined so as to be equal to the angle of a portion of the inner surface of the wafer transfer cassette that contacts the outer periphery of the wafer. In a wafer thinned to a desired thickness by back grinding,
The edge portion of the outer periphery of the wafer is processed as a chamfered portion,
an upper portion of the chamfer is removed horizontally from the outer circumference toward the inner circumference of the wafer to a target thickness (T) to be thinned from the upper surface of the wafer;
Assuming that the length of the machining allowance removed from the outer periphery is L, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, the shape is processed so that L = T / tan φ + α,
The wafer, wherein the angle φ is determined to be equal to the contact angle with a polishing tape that polishes the outer periphery of the wafer. In a wafer thinned to a desired thickness by back grinding,
The edge portion of the outer periphery of the wafer is processed as a chamfered portion,
an upper portion of the chamfer is removed horizontally from the outer circumference toward the inner circumference of the wafer to a target thickness (T) to be thinned from the upper surface of the wafer;
Assuming that the length of the machining allowance removed from the outer periphery is L, the angle φ of the chamfered portion with respect to the horizontal, and the allowance α, the shape is processed so that L = T / tan φ + α,
The angle φ is determined to be equal to the angle of a portion of the inner surface of the transfer cassette for the wafer that contacts the outer periphery of the wafer.

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