JP2017216400A - Processing method of wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a width of a device region to be narrowed and suppress deterioration of processing efficiency.SOLUTION: A processing method of a wafer, includes: a protective member adhesion step of adhering a protective member onto a front surface of the wafer; a holding step of holding the wafer on a holding surface of a chuck table through the protective member; a first grinding step of grinding a back surface of the wafer corresponding to a device region with a first grinding wheel after the holding step and forming a circular concave part onto the back surface of the wafer and forming an annular convex part surrounding the circular concave part; and a second grinding step of obliquely moving toward a center of the wafer from a top of the annular convex part while grinding and transferring a second grinding wheel having a grinding diameter smaller than that of the first grinding wheel toward the holding surface, and removing an inner peripheral edge part of the annular convex part after the execution of the first grinding step, and grinding a bottom surface of the circular concave part by the second grinding wheel after the second grinding wheel is ground and transmitted in an idling manner. In the second grinding step, the inner peripheral edge part is ground and cracking of the inner peripheral edge part occurred in the first grinding step is removed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wafer processing method.

  For example, with the spread of SiP (System in Package) and the like, there is a demand for a grinding technique capable of thinning a wafer with a high yield. As one of grinding techniques for thinning a wafer, a TAIKO grinding technique is known. In the TAIKO grinding technique, when grinding the back surface of a wafer having a device region on which a plurality of devices are formed on the surface, the outer peripheral edge portion of the back surface of the wafer is left, and the back surface of the wafer corresponding to the device region inside the outer peripheral edge portion. This is a technique for grinding and thinning only the inner part of the film (see Patent Document 1). By the TAIKO grinding technique, an annular convex portion that functions as a reinforcing portion is formed at the outer peripheral edge portion of the wafer. By forming the annular convex portion, even after the inner portion of the wafer is thinned, for example, warpage of the wafer and cracking of the wafer during conveyance are suppressed.

  Similar to general grinding techniques, in the TAIKO grinding technique, a wafer is coarsely ground with a first grinding wheel and then finish-ground with a second grinding wheel having a smaller grain size than the first grinding wheel. In rough grinding with the first grinding wheel, there is a possibility that chipping occurs at the inner peripheral edge portion of the annular convex portion. If the chip | tip which generate | occur | produced in the inner peripheral edge part of a cyclic | annular convex part is left unattended, a crack may generate | occur | produce in a wafer. Therefore, in the TAIKO grinding technique, the inside of the outer peripheral edge portion of the wafer is roughly ground with the first grinding wheel to form the annular convex portion, and then the inner peripheral edge portion of the annular convex portion is ground with the second grinding wheel. Thus, a grinding technique for removing chips has been devised (see Patent Document 2). By removing the chip, the bending strength of the wafer can be improved.

Japanese Patent No. 5390740 JP 2008-042081 A

  Generally, the amount of wear of the grinding wheel increases as the contact time or contact pressure between the grinding wheel and the object to be ground increases. Further, the second grinding wheel having a small abrasive particle size is more easily consumed than the first grinding wheel. Therefore, after the rough grinding by the first grinding wheel is performed, when the second grinding wheel is ground and fed by the same movement trajectory as the grinding feed movement trajectory in the first grinding wheel, the wafer is finish-ground. The second grinding wheel is greatly consumed so that the end of the second grinding wheel is rounded. When the end of the second grinding wheel is rounded, the boundary between the inner peripheral surface of the annular convex portion and the bottom surface of the inner portion corresponding to the device region inside the annular convex portion is not sufficiently ground in finish grinding. , It will be rounded. As a result, the device region to be thinned becomes narrow, and it is impossible to secure a sufficient number of device chips. On the other hand, if the grinding feed rate is lowered in order to suppress the consumption of the second grinding wheel, the grinding time is prolonged and the processing efficiency is lowered, and the manufacturing cost is increased.

  An object of the present invention is to provide a wafer processing method capable of removing chips generated on a wafer by rough grinding while suppressing consumption of the second grinding wheel and suppressing a decrease in processing efficiency. .

  The present invention relates to a wafer processing method for processing a wafer having a device region in which a plurality of devices are formed and an outer peripheral surplus region surrounding the device region on the surface, and a protective member is attached to the surface of the wafer A protective member adhering step, a holding step for holding the wafer on the holding surface of the chuck table via the protective member, and a back surface of the wafer corresponding to the device region after the holding step with a first grinding wheel Grinding to form a circular concave portion on the back surface of the wafer and forming an annular convex portion surrounding the circular concave portion, and after performing the first grinding step, a smaller grinding wheel than the first grinding wheel An inner peripheral edge portion of the annular convex portion by moving the second grinding wheel having a particle size obliquely from the apex of the annular convex portion toward the center of the wafer while being fed toward the holding surface. And a second grinding step of grinding the bottom surface of the circular concave portion with the second grinding wheel after removing and grinding and feeding the second grinding wheel in an idle state. The second grinding step Then, the wafer processing method characterized by grind | pulverizing this inner peripheral edge part and removing the chip | tip of this inner peripheral edge part which generate | occur | produced at this 1st grinding step is provided.

  In the wafer processing method according to the present invention, in the second grinding step, when the inner peripheral edge portion is ground or when the bottom surface of the circular concave portion is ground, the second inner edge portion is ground after the second inner edge portion is ground. It is preferable to set the grinding feed speed faster when the grinding wheel is moved in an idle state.

  ADVANTAGE OF THE INVENTION According to this invention, the processing method of the wafer which can remove the chip | tip which generate | occur | produced in rough grinding while suppressing consumption of a 2nd grinding wheel and suppressing the fall of processing efficiency is provided.

FIG. 1 is a perspective view showing an example of a wafer according to the present embodiment. FIG. 2 is a flowchart showing an example of a wafer processing method according to this embodiment. FIG. 3 is a diagram illustrating an example of the protective member attaching step according to the present embodiment. FIG. 4 is a side view showing an example of a grinding apparatus according to the present embodiment. FIG. 5 is a functional block diagram showing an example of a grinding apparatus according to the present embodiment. FIG. 6 is a perspective view showing an example of the first grinding step according to the present embodiment. FIG. 7 is a side view showing an example of the first grinding step according to the present embodiment. FIG. 8 is a side view showing an example of the second grinding step according to the present embodiment. FIG. 9 is a side view showing an example of the second grinding step according to the present embodiment. FIG. 10 is a cross-sectional view showing a part of the wafer after the second grinding step according to this embodiment is completed. FIG. 11 is a diagram schematically illustrating an example of a moving speed profile in the grinding feed direction of the second grinding wheel in the second grinding step according to the present embodiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The components of the embodiments described below can be combined as appropriate. Some components may not be used.

  In the following description, an XYZ orthogonal coordinate system is set, and the positional relationship of each part will be described with reference to this XYZ orthogonal coordinate system. One direction in the horizontal plane is defined as the X-axis direction, a direction orthogonal to the X-axis direction in the horizontal plane is defined as the Y-axis direction, and a direction orthogonal to each of the X-axis direction and the Y-axis direction is defined as the Z-axis direction. An XY plane including the X axis and the Y axis is parallel to the horizontal plane. The Z-axis direction orthogonal to the XY plane is the vertical direction.

  FIG. 1 is a perspective view showing an example of a wafer 2 according to this embodiment. As shown in FIG. 1, the wafer 2 is a substantially disk-shaped member, and has a front surface 2A and a back surface 2B facing the opposite direction of the front surface 2A. The front surface 2A and the back surface 2B are substantially parallel. The wafer 2 has a substrate and a functional layer provided on the surface of the substrate. The surface 2A of the wafer 2 includes the surface of the functional layer. The back surface 2B of the wafer 2 includes the back surface of the substrate. The functional layer is a layer in which a device is formed. The substrate includes at least one of a silicon substrate, a sapphire substrate, a lithium tantalate substrate, a lithium niobate substrate, and a ceramic substrate.

  Further, the wafer 2 has a notch 21. The wafer 2 may be provided with an orientation flat.

  The surface 2A of the wafer 2 has a device area DA in which a plurality of devices 22 are formed and an outer peripheral surplus area SA surrounding the device area DA. The device area DA is a circular area including the center of the surface 2A of the wafer 2. The outer peripheral surplus area SA is an annular (annular) area defined around the device area SA. The device 22 is formed in each of a plurality of regions partitioned by the division lines 23 that intersect with each other.

  The devices 22 are arranged in a matrix on the surface 2A of the wafer 2. The division | segmentation scheduled line 23 is provided in a grid | lattice form. The device 22 is partitioned by a division planned line 23. The device 22 is formed in the device area DA of the wafer 2. The device 22 is not formed in the outer peripheral surplus area SA. By dividing the wafer 2 along the division line 23, a device chip such as an IC (Integrated Circuit) or an LSI (Large Scale Integration) is manufactured.

  Next, a method for processing the wafer 2 according to the present embodiment will be described. FIG. 2 is a flowchart showing an example of a processing method of the wafer 2 according to the present embodiment. As shown in FIG. 2, the processing method of the wafer 2 includes a protective member attaching step (SP1) for attaching a protective member to the surface 2A of the wafer 2, and the wafer 2 on the chuck table holding surface via the protective member. Holding step (SP2) to hold, and after the holding step, the back surface 2B of the wafer 2 corresponding to the device area DA is ground with a first grinding wheel to form a circular recess in the back surface 2B of the wafer 2 and surround the circular recess After performing the first grinding step (SP3) for forming the annular convex portion and the first grinding step, the second grinding wheel having a smaller grain size than the first grinding wheel is ground and fed toward the holding surface. While moving obliquely from the apex of the annular convex portion toward the center of the wafer 2 to remove the inner peripheral edge portion of the annular convex portion and further grinding and feeding the second grinding wheel in an empty state, the bottom surface of the circular concave portion It comprises a second grinding step of grinding the second grinding wheel (SP4), a.

  The protective member attaching step (SP1) will be described. FIG. 3 is a diagram illustrating an example of the protective member attaching step according to the present embodiment. The protective member attaching step is a step of attaching the protective member 3 to the surface 2A of the wafer 2. As shown in FIG. 3, a protective member 3 for protecting the device 22 is attached to the surface 2 </ b> A of the wafer 2. The protection member 3 is a sheet-like member. In the XY plane, the outer shape and dimensions of the surface 2A of the wafer 2 and the outer shape and dimensions of the protection member 3 are substantially equal. The protection member 3 has, for example, a base film containing polyolefin and an adhesive material applied to one side of the base film. The protective member 3 is attached to the surface 2A of the wafer 2 via an adhesive material.

  Next, the holding step (SP2) will be described. FIG. 4 is a side view showing an example of the grinding apparatus 4 according to the present embodiment. FIG. 5 is a functional block diagram showing an example of the grinding apparatus 4 according to the present embodiment. The holding step is a step of holding the wafer 2 on the holding surface 6 of the chuck table 5 of the grinding device 4 via the protective member 3. The holding step is performed after the protective member attaching step.

  As shown in FIG. 4, the grinding apparatus 4 includes a chuck table 5 having a holding surface 6 that holds the wafer 2, and a grinding unit 7 that grinds the wafer 2 held on the chuck table 5.

  The chuck table 5 holds the wafer 2 via the protective member 3. The chuck table 5 is configured such that the holding surface 6 of the chuck table 5 and the protective member 3 attached to the back surface 2B of the wafer 2 face each other, and the back surface 2B of the wafer 2 faces upward through the protective member 3. 2 is held.

  The holding surface 6 of the chuck table 5 is substantially parallel to the XY plane. The chuck table 5 holds the wafer 2 so that the back surface 2B of the wafer 2 and the XY plane are parallel to each other. The chuck table 5 holds the wafer 2 so that the center of the holding surface 6 in the XY plane matches the center of the back surface 2B of the wafer 2.

  The chuck table 5 detachably holds the wafer 2. The chuck table 5 includes a vacuum chuck mechanism. The holding surface 6 of the chuck table 5 is provided with a plurality of suction ports connected to a vacuum suction source. The wafer 2 is sucked and held on the chuck table 5 by operating the vacuum suction source in a state where the wafer 2 is placed on the holding surface 6 of the chuck table 5 via the protective member 3. When the operation of the vacuum suction source is stopped, the wafer 2 and the protection member 3 are released from the chuck table 5.

  The chuck table 5 can be rotated about a table rotation axis AX1 parallel to the Z axis by the operation of the table driving device.

  The grinding unit 7 grinds the wafer 2 held on the chuck table 5. The grinding unit 7 grinds the back surface 2 </ b> B of the wafer 2 to thin the wafer 2. The grinding unit 7 is movably supported by a support mechanism (not shown). The grinding unit 7 is movable in the X-axis direction, the Y-axis direction, and the Z-axis direction by the operation of the grinding unit driving device.

  The grinding unit 7 includes a spindle 9, a grinding wheel 11 connected to the lower end of the spindle 9 via a wheel mount 10, and a grinding wheel 8 provided on the lower surface of the grinding wheel 11.

  The grinding wheel 8 can face the back surface 2 </ b> B of the wafer 2 held on the chuck table 5. In the XY plane, the grinding wheel 8 is provided in an annular shape.

  The grinding wheel 11 can rotate around a grinding rotation axis AX2 parallel to the Z axis by the operation of the grinding unit driving device.

  The rotating diameter of the grinding wheel 8 is smaller than the device area DA. In the present embodiment, the rotating diameter of the grinding wheel 8 is about half of the diameter of the wafer 2.

  The grinding unit 7 includes a first grinding unit 71 for rough grinding and a second grinding unit 72 for finish grinding. That is, in the present embodiment, the grinding device 4 has two grinding units 7, that is, a first grinding unit 71 and a second grinding unit 72.

  The grinding wheel 8 includes a first grinding wheel 81 and a second grinding wheel 82 having a smaller abrasive particle size than the first grinding wheel 81. In the present embodiment, the first grinding wheel 81 is provided in the first grinding unit 71. The second grinding wheel 82 is provided in the second grinding unit 72.

  The first grinding wheel 81 is a grinding wheel for rough grinding composed of a resin or vitrified bond having an abrasive grain size of # 320 to 600. The second grinding wheel 82 is a grinding wheel for finish grinding composed of a resin or vitrified bond having an abrasive grain size of # 2000 or more.

  In the cross section including the grinding rotation axis AX2, the grinding wheel 8 is rectangular. The grinding wheel 8 has an outer surface 8A facing outward in a radial direction with respect to the grinding rotation axis AX2, and a lower surface 8B. The lower surface 8B is substantially parallel to the XY plane. In the cross section including the grinding rotation axis AX2, a corner 8K is formed by the outer surface 8A and the lower surface 8B. When the grinding wheel 8 is not consumed, the outer surface 8A and the lower surface 8B are substantially orthogonal and the corner 8K is sharp in the cross section including the grinding rotation axis AX2.

  As shown in FIG. 5, the grinding device 4 includes a table driving device 12 that drives the chuck table 5, a grinding unit driving device 13 that drives the grinding unit 7, and a control unit 14 that controls the grinding device 4.

  The table driving device 12 includes a rotary actuator that generates power for rotating the chuck table 5 about the table rotation axis AX1. The table driving device 12 includes an X-axis actuator that generates power for moving the chuck table 5 in the X-axis direction and a Y-axis actuator that generates power for moving the chuck table 5 in the Y-axis direction. Have. The table driving device 12 is controlled by the control means 14. The chuck table 5 can be rotated about the table rotation axis AX <b> 1 by the operation of the table driving device 12. Further, the chuck table 5 can be moved in the X-axis direction and the Y-axis direction by the operation of the table driving device 12.

  The grinding unit driving device 13 has a rotary actuator that generates power for rotating the grinding wheel 11 about the grinding rotation axis AX2. The grinding unit driving device 13 includes an X-axis actuator that generates power for moving the grinding unit 7 in the X-axis direction, and a Y-axis actuator that generates power for moving the grinding unit 7 in the Y-axis direction. And a Z-axis actuator for moving the grinding unit 7 in the Z-axis direction. The grinding unit driving device 13 is controlled by the control means 14. The grinding wheel 11 of the grinding unit 7 can rotate around the grinding rotation axis AX2 by the operation of the grinding unit driving device 13. Further, the grinding unit 7 is movable in the X-axis direction, the Y-axis direction, and the Z-axis direction by the operation of the grinding unit driving device 13.

  The control means 14 includes an arithmetic processing unit 15 having a microprocessor such as a CPU (Central Processing Unit), a nonvolatile memory such as a ROM (Read Only Memory) or a storage, and a volatile memory such as a RAM (Random Access Memory). Including a storage device 16 and an input / output interface device 17. The arithmetic processing device 15 performs arithmetic processing in accordance with a computer program stored in the storage device 16 and outputs a control signal for controlling the grinding device 4 via the input / output interface device 17.

  Next, the first grinding step (SP3) will be described. FIG. 6 is a perspective view showing an example of the first grinding step according to the present embodiment. FIG. 7 is a side view showing an example of the first grinding step according to the present embodiment. In the first grinding step, the back surface 2B of the wafer 2 corresponding to the device area DA is ground with the first grinding wheel 81 of the first grinding unit 71 to form the circular recess 24 on the back surface 2B of the wafer 2, and the circular recess 24 Is a step of forming an annular convex portion 25 that surrounds. The first grinding step is performed after the holding step.

  As shown in FIGS. 6 and 7, after the wafer 2 is held on the chuck table 5 via the protective member 3, the chuck table 5 is rotated about the table rotation axis AX1 as indicated by an arrow R1, The grinding wheel 11 of one grinding unit 71 is rotated about the grinding rotation axis AX2 as indicated by the arrow R2. With the chuck table 5 and the grinding wheel 11 of the first grinding unit 71 rotating, the first grinding unit 71 is lowered (ground feed) in the −Z direction, whereby the first grinding wheel 81 and the wafer 2 are moved. The back surface 2B is brought into contact. Thereby, the back surface 2B of the wafer 2 is ground and the wafer 2 is thinned.

  In the first grinding step, a part of the back surface 2 </ b> B of the wafer 2 held on the chuck table 5 via the protective member 3 is ground by the first grinding wheel 81 of the first grinding unit 71.

  In the first grinding step, the corresponding device area EA corresponding to the device area DA defined on the front surface 2 </ b> A of the back surface 2 </ b> B of the wafer 2 is ground by the first grinding wheel 81 of the first grinding unit 71.

  That is, in the present embodiment, on the surface 2A of the wafer 2, a device area DA in which a plurality of devices 22 are formed and an outer peripheral surplus area SA surrounding the device area SA are defined. On the back surface 2B of the wafer 2, a corresponding device area EA corresponding to the device area DA and a corresponding outer peripheral surplus area TA surrounding the corresponding device area EA are defined.

  The corresponding device area EA is a circular area including the center of the back surface 2B of the wafer 2. In the XY plane, the external shape and dimensions of the device area DA and the external shape and dimensions of the corresponding device area EA are substantially the same. In the XY plane, the position of the device area DA and the position of the corresponding device area EA are substantially the same.

  The corresponding outer peripheral surplus area TA is a ring-shaped (annular) area defined around the corresponding device area EA. In the XY plane, the outer shape and size of the outer peripheral surplus region SA and the outer shape and size of the corresponding outer peripheral surplus region TA are substantially the same. In the XY plane, the position of the outer peripheral surplus area SA and the position of the corresponding outer peripheral surplus area TA are substantially the same.

  As shown in FIGS. 6 and 7, in the first grinding step, the corresponding device area EA on the back surface 2 </ b> B of the wafer 2 is ground by the first grinding wheel 81 of the first grinding unit 71, and the corresponding back surface 2 </ b> B of the wafer 2 is handled. The outer peripheral surplus area TA is not ground. Thereby, as shown in FIG.6 and FIG.7, the circular recessed part 24 circular in XY plane is formed in the back surface 2B of the wafer 2. FIG. An annular convex portion 25 surrounding the circular concave portion 24 is formed around the circular concave portion 24.

  The circular recess 24 has a bottom surface 26 and an inner peripheral surface 27 connected to the outer edge of the bottom surface 26. In the XY plane, the bottom surface 26 is circular. The bottom surface 26 is substantially parallel to the XY plane. The inner peripheral surface 27 is formed to be orthogonal to the bottom surface 26.

  The annular protrusion 25 has an end face 28. The end surface 28 is a non-ground surface of the back surface 2B and is substantially parallel to the XY plane. In the XY plane, the end surface 28 has an annular shape (annular shape). The inner edge of the end surface 28 of the annular convex portion 25 is connected to the inner peripheral surface 27. The end surface 28 and the inner peripheral surface 27 are orthogonal to each other. A corner portion 29 is formed by the end surface 28 and the inner peripheral surface 27.

  In the following description, a part of the annular convex portion 25 including at least the corner portion 29 is appropriately referred to as an inner peripheral edge portion 30 of the annular convex portion 25. The inner peripheral edge part 30 may be a concept including a part of the inner peripheral surface 27 connected to the corner part 29 and a part of the end face 28 connected to the corner part 29.

  In the present embodiment, the corresponding device area EA on the back surface 2B of the wafer 2 is ground by the first grinding wheel 81 until the thickness of the wafer 2 in the device area DA reaches the first thickness T1. In addition, the thickness of the ring-shaped convex part 25 which is not grounded is thickness Tr larger than 1st thickness T1.

  Next, the second grinding step (SP4) will be described. 8 and 9 are side views showing an example of the second grinding step according to the present embodiment. FIG. 10 is a cross-sectional view showing a part of the wafer 2 after the second grinding step according to the present embodiment is completed.

  In the second grinding step, the second grinding wheel 82 having a smaller grain size than the first grinding wheel 81 is ground and fed toward the holding surface 6 of the chuck table 5, and the apex (corner portion 29) of the annular convex portion 25. Then, the inner peripheral edge portion 30 of the annular convex portion 25 is removed obliquely toward the center of the wafer 2, and the second grinding wheel 82 is ground and fed in an empty state, and then the bottom surface 26 of the circular concave portion 24 is moved. This is a step of grinding with the second grinding wheel 82. The second grinding step is performed after the first grinding step.

  After the circular recess 24 and the annular protrusion 25 are formed on the wafer 2 by the first grinding step, the wafer 2 on which the circular recess 24 and the annular protrusion 25 are formed is held on the chuck table 5 via the protective member 3. In this state, the chuck table 5 is rotated about the table rotation axis AX1 as indicated by the arrow R1. Further, the grinding wheel 11 of the second grinding unit 72 having the second grinding wheel 82 is rotated around the grinding rotation axis AX2 as indicated by the arrow R2. Before the second grinding wheel 82 of the second grinding unit 72 and the wafer 2 come into contact with each other, the lower surface 8B of the second grinding wheel 82 disposed outside the grinding rotation axis AX2 in the radial direction with respect to the center of the wafer 2. The chuck table 5 holding the wafer 2 and the second grinding wheel 82 are aligned so that a part thereof faces the end face 28 of the annular convex portion 25 with a gap.

  In the following description, as shown by the solid line in FIG. 8, a part of the lower surface 8 </ b> B of the second grinding wheel 82 and the annular convex portion 25 arranged outside the grinding rotation axis AX <b> 2 in the radial direction with respect to the center of the wafer 2. A state in which the end face 28 of the first electrode 28 is opposed to each other with a gap is appropriately referred to as a first state.

  In the state where the chuck table 5 and the grinding wheel 11 of the second grinding unit 72 are rotating, the control means 14 moves the second grinding unit 72 from the first state toward the holding surface 6 of the chuck table 5 in the −Z direction. And is moved obliquely from the apex (corner portion 29) of the annular convex portion 25 toward the center of the wafer 2.

  In the following description, as indicated by an arrow C1 in FIG. 8, while the second grinding unit 72 in the first state is ground and fed in the −Z direction toward the holding surface 6 of the chuck table 5, the annular convex portion 25. The oblique movement from the apex (corner portion 29) toward the center of the wafer 2 is appropriately referred to as oblique processing feed.

  In this embodiment, an angle θ formed by an XY plane orthogonal to the grinding feed direction and a movement axis parallel to the movement direction of the second grinding wheel 82 indicated by an arrow C1 is appropriately set to the slope angle of the second grinding wheel 82. It is called θ. In the present embodiment, the slope angle θ satisfies the condition of 0 [°] <θ <90 [°]. Preferably, the slope angle θ satisfies a condition of 60 [°] ≦ θ ≦ 85 [°].

  The second grinding unit 72 is moved as indicated by the arrow C1 and the oblique processing feed is performed, so that the second grinding wheel 82 and the inner peripheral edge portion 30 of the annular convex portion 25 come into contact with each other. Thereby, the inner peripheral edge portion 30 of the annular convex portion 25 including the corner portion 29 is removed by the second grinding wheel 82. By removing the inner peripheral edge portion 30, an inclined surface 31 is formed between the inner peripheral surface 27 and the end surface 28 as shown in FIG. The inclined surface 31 is formed so as to be away from the holding surface 6 toward the outside in the radial direction with respect to the center of the wafer 2.

  There is a possibility that the inner peripheral edge portion 30 of the annular convex portion 25 formed in the first grinding step is chipped. In the present embodiment, the inner peripheral edge portion 30 is ground by the second grinding wheel 82 in the second grinding step. In the second grinding step, the inner peripheral edge portion 30 is ground by the second grinding wheel 82, whereby the chip of the inner peripheral edge portion 30 generated in the first grinding step is removed.

  In the present embodiment, the control unit 14 obliquely feeds the second grinding unit 72 so that a part of the inner peripheral surface 27 and a part of the end surface 28 remain. The second grinding wheel 82 obliquely processed and fed from the first state to form the inclined surface 31 makes a transition to the second state where it does not contact the wafer 2.

  The control means 14 obliquely feeds the second grinding unit 72 in the first state to shift to the second state, and then in the idle state where the second grinding wheel 82 is not brought into contact with the annular convex portion 25, the arrow C2 As shown in FIG.

  When the second grinding unit 72 is ground and fed in the −Z direction, the bottom surface 26 of the circular recess 24 and the second grinding wheel 82 come into contact with each other. The control means 14 rotates the chuck table 5 around the table rotation axis AX1 and rotates the grinding wheel 11 around the grinding rotation axis AX2 while the bottom surface 26 of the circular recess 24 and the second grinding wheel 82 are in contact with each other. Then, the bottom surface 26 of the circular recess 24 is ground with the second grinding wheel 82.

  In the present embodiment, the bottom surface 26 of the circular recess 24 is ground by the second grinding wheel 82 until the thickness of the wafer 2 in the device area DA becomes the second thickness T2 that is thinner than the first thickness T1. That is, after the second grinding wheel 82 and the bottom surface 26 of the circular recess 24 having the first thickness T1 are brought into contact, the second grinding wheel 82 is further ground and fed in the −Z direction.

  In the present embodiment, when the bottom surface 26 of the circular recess 24 is ground with the second grinding wheel 82, the second grinding step is performed so that the second grinding wheel 82 and the inner peripheral surface 27 do not come into contact with each other.

  In the present embodiment, in the second grinding step, when the inner peripheral edge portion 30 is ground with the second grinding wheel 82 or when the bottom surface 26 of the circular recess 24 is ground with the second grinding wheel 82, the inner peripheral edge The grinding feed speed is set faster when the second grinding wheel 82 moves in an idle state after grinding the portion 30.

  FIG. 11 is a diagram schematically illustrating an example of a moving speed profile in the Z-axis direction that is the grinding feed direction of the second grinding wheel 82 in the second grinding step according to the present embodiment. In FIG. 11, the vertical axis represents the moving speed (grinding feed speed) of the second grinding wheel 82 in the Z-axis direction, and the horizontal axis represents the elapsed time from the start of the second grinding step.

  The time point t1 is a time point in the first state where the lower surface 8B of the second grinding wheel 82 and the end surface 28 of the annular convex portion 25 face each other with a gap as described with reference to FIG. The oblique machining feed is performed from time t1, and the second grinding wheel 82 and the inner peripheral edge portion 30 come into contact at time t2. The oblique machining feed is continued, the inner peripheral edge portion 30 is removed, and the inclined surface 31 is formed. At time t3, the second grinding wheel 82 that is being obliquely fed is separated from the annular convex portion 25. The time point t3 is a time point in the second state in which the second grinding wheel 82 that has been obliquely fed and the annular convex portion 25 are separated. The grinding feed speed of the second grinding wheel 82 when the inner peripheral edge portion 30 is ground using the second cutting wheel 82 is the speed V1.

  After the second state, the second grinding wheel 82 is ground and fed in the −Z direction toward the holding surface 6 in a non-contact state with respect to the annular convex portion 25, that is, in an idle state. The grinding feed speed of the second grinding wheel 82 when the second grinding wheel 82 moves in an idle state after grinding the inner peripheral edge portion 30 is the speed V2.

  The second grinding wheel 82 ground and fed in the idle state comes into contact with the bottom surface 26 of the circular recess 24 at time t4. In order to grind the bottom surface 26 of the circular recess 24 with the second grinding wheel 82, the second grinding wheel 82 is ground and fed in the −Z direction in contact with the bottom surface 26 of the circular recess 24. When the second cutting grindstone 82 is used to grind the bottom surface 26 of the circular recess 24, the grinding feed speed of the second grinding grindstone 82 is a speed V3.

  In the present embodiment, the grinding feed speed V2 of the second grinding wheel 82 when the second grinding wheel 82 moves in an idle state after grinding the inner peripheral edge portion 30 is the same as that when the inner peripheral edge portion 30 is ground. The speed is set to be higher than the grinding feed speed V1 of the second grinding wheel 82 and the grinding feed speed V3 of the second grinding wheel 82 when grinding the bottom surface 26 of the circular recess 24.

  As described above, according to the present embodiment, in the TAIKO grinding technique, when finish grinding is performed using the second grinding wheel 82, the inner circumference of the annular convex portion 25 is caused by the second grinding wheel 82 that is obliquely fed. The edge part 30 is removed. When rough grinding is performed using the first grinding wheel 81, there is a high possibility that the inner peripheral edge portion 30 of the annular convex portion 25 is chipped. On the other hand, for example, at the boundary between the inner peripheral surface 27 and the bottom surface 26 or the end surface 28, the possibility of chipping is low. In the present embodiment, in the finish grinding, by feeding the second grinding wheel 82 obliquely, it is possible to remove only the inner peripheral edge portion 30 that is likely to be chipped. Since the inner peripheral edge portion 30 is removed while minimizing the contact time or contact pressure between the second grinding wheel 82 and the annular convex portion 25, chipping occurs in a state where consumption of the second grinding wheel 82 is suppressed. Can be removed. Since the consumption of the second grinding wheel 82 is suppressed, the state in which the corner portion 8K of the second grinding wheel 82 is sharp is maintained for a long time. Since the corner 8K of the second grinding wheel 82 is kept round for a long time, the second grinding wheel 82 is removed from the inner peripheral edge 30 with the second grinding wheel 82. 2, when the bottom surface 26 of the circular recess 24 is ground with the second grinding wheel 82, the bottom surface 26 is bounded with the inner peripheral surface 27 by the second grinding wheel 82. It is ground enough to the vicinity. Thereby, it is suppressed that the device area | region DA thinned by 2nd thickness T2 becomes narrow. When the corner 8K of the second grinding wheel 82 is rounded, a portion DL that is not thinned to the second thickness T2 by the second grinding wheel 82 as shown in FIG. 10 becomes large. In the present embodiment, the consumption of the second grinding wheel 82 is suppressed, and the state in which the corner 8K is sharp is maintained for a long period of time, so the portion DL can be reduced. Since the portion DL can be reduced and the device area DA thinned to the second thickness T2 can be increased, a sufficient number of device chips can be secured.

  Further, in this embodiment, the grinding feed speed V2 of the second grinding wheel 82 when moving in the idle state is the grinding feed speed V1 of the second grinding wheel 82 when grinding the inner peripheral edge portion 30; The speed is set faster than the grinding feed speed V3 of the second grinding wheel 82 when grinding the bottom surface 26 of the circular recess 24. When grinding the inner peripheral edge portion 30 and the bottom surface 26, by reducing the grinding feed speed of the second grinding wheel 82, uneven wear of the wafer 2 is suppressed, and grinding can be performed with high quality. When the second grinding wheel 82 is moved without being in contact with the wafer 2, the processing time of the second grinding wheel 82 can be increased to prevent the grinding time from increasing and the processing efficiency from decreasing.

  Moreover, in this embodiment, the annular convex part 25 which functions as a reinforcement part is formed in the wafer 2 with a TAIKO grinding technique. By forming the annular convex portion 25, even after the device area DA of the wafer 2 is thinned, warpage of the wafer 2, cracking of the wafer 2 during transportation, and the like are suppressed. Therefore, when post-processing such as sputtering processing is performed on the wafer 2 after the grinding processing, the subsequent processing is performed with high accuracy.

  Moreover, in the post-processing of the wafer 2, an etching process may be performed in which an etching solution is supplied to the wafer 2 while rotating the wafer 2 with a spin coater. The inner peripheral edge portion 30 is ground by the second grinding wheel 82 that is obliquely fed, and the inclined surface 31 is formed between the inner peripheral surface 27 and the end surface 28, whereby the circular recess 24 is supplied in the spin coater. The etchant is smoothly discharged outside the circular recess 24 along the inclined surface 31.

  The present invention is not limited to the above embodiment. That is, various modifications can be made without departing from the scope of the present invention.

2 Wafer 2A Front surface 2B Back surface 3 Protection member 4 Grinding device 5 Chuck table 6 Holding surface 7 Grinding unit 8 Grinding wheel 8A Outer surface 8B Lower surface 8K Corner 9 Spindle 10 Wheel mount 11 Grinding wheel 12 Table drive device 13 Grinding unit drive device 14 Control Means 15 Arithmetic processing device 16 Storage device 17 Input / output interface device 21 Notch 22 Device 23 Scheduled division line 24 Circular concave portion 25 Annular convex portion 26 Bottom surface 27 Inner peripheral surface 28 End surface 29 Corner portion 30 Inner peripheral edge portion 31 Inclined surface 71 First Grinding unit 72 Second grinding unit 81 First grinding wheel 82 Second grinding wheel AX1 Table rotation axis AX2 Grinding rotation axis DA Device area EA Corresponding device area SA Peripheral surplus area TA Corresponding surplus area T1 First thickness T2 Second thickness Tr Thickness

Claims (2)

A wafer processing method of processing a wafer having a device region in which a plurality of devices are formed and a peripheral surplus region surrounding the device region on a surface thereof,
A protective member attaching step for attaching a protective member to the surface of the wafer;
A holding step for holding the wafer on the holding surface of the chuck table via the protective member;
After the holding step, the back surface of the wafer corresponding to the device region is ground with a first grinding wheel to form a circular concave portion on the back surface of the wafer and to form an annular convex portion surrounding the circular concave portion. Steps,
After performing the first grinding step, the second grinding wheel having a smaller grain size than that of the first grinding wheel is fed to the holding surface from the top of the annular convex portion to the center of the wafer while being fed to the holding surface. The inner peripheral edge portion of the annular convex portion is removed obliquely, and the second grinding wheel is ground and fed in an empty state, and then the bottom surface of the circular concave portion is moved with the second grinding wheel. A second grinding step for grinding,
In the second grinding step, the inner peripheral edge portion is ground to remove a chip in the inner peripheral edge portion generated in the first grinding step.   In the second grinding step, the second grinding wheel moves in an idle state after grinding the inner peripheral edge portion than when grinding the inner peripheral edge portion or grinding the bottom surface of the circular recess. The method of processing a wafer according to claim 1, wherein the grinding feed speed is set to be faster with respect to time.

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