Wafer processing method

Abstract

To prevent a DAF and a protective member from adhering in a mark (a groove) for replacing a notch or the like.SOLUTION: A processing method of a wafer, for reducing a thickness into a finishing thickness by grinding the wafer in which a structure indicating a crystal orientation is formed at an outer periphery while having a bevelled part from a front surface to a back surface at the outer periphery, from the back surface side, includes steps of: removing the bevelled part at a depth of the finishing thickness or more from the front surface of the wafer by cutting the wafer along the outer periphery; making a cutting blade cut into a position adjacent to the structure, and cutting the wafer at the depth that is the finishing thickness ir more and less than the thickness of the wafer, from the front surface; forming a groove indicating a crystal direction of the wafer instead of the structure; distributing a protective member to the front surface of the wafer; and grinding the wafer from the back surface to reduce the thickness to the finishing thickness and removing a bottom part of the groove to expose the groove to the back surface of the wafer.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer having a chamfer on its outer periphery and thinning the wafer by grinding the wafer having a notch formed on its outer periphery.

Background Art

[0002] In the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, first, a plurality of planned division lines (streets) intersecting each other are set on the surface of a wafer made of a material such as a semiconductor. Then, devices such as ICs (Integrated Circuits) and LSIs (Large-scale Integration) are formed in each region partitioned by the planned division lines. Thereafter, when the wafer is thinned by grinding from the back side and divided along the planned division lines, individual device chips are formed.

[0003] Notches such as notches and orientation flats indicating the crystal orientation of the members constituting the wafer are formed on the outer periphery of the silicon wafer on which the devices are formed. And in various steps of the wafer processing process, this notch etc. are referred to and the processing position etc. are determined. Further, a chamfer is formed on the outer periphery of the wafer to prevent chipping of the end portion. On the outer periphery of the wafer having the chamfer formed, the cross-sectional shape of the wafer becomes an arc shape from the front surface to the back surface.

[0004] Here, when the wafer having a chamfer formed on its outer periphery is thinned by grinding from the back side, a knife edge shape composed of an arc surface and a flat grinding surface constituting the chamfer is generated on the outer periphery of the wafer, and chipping is likely to occur on the outer periphery of the wafer. Therefore, before grinding the wafer, edge trimming processing is performed in which an annular cutting blade is cut into the outer periphery of the wafer to remove the chamfer (see Patent Document 1). <​​However, when edge trimming is performed and the wafer is subsequently ground to thin it, notches and other cutouts are lost from the wafer, which creates a problem in that the crystal orientation of the wafer cannot be determined. Therefore, a method has been proposed to form grooves on the wafer as substitute marks for notches and other cutouts before they are lost (see Patent Documents 2 and 3). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2000-173961 [Patent Document 2] Japanese Patent Publication No. 2013-115187 [Patent Document 3] Japanese Patent Publication No. 2013-211409 [Overview of the project] [Problems that the invention aims to solve]

[0007] In recent years, technologies have been developed to package multiple device chips by stacking them in order to reduce the mounting area and increase integration. By pre-placing an adhesive film called a die attach film (DAF) on each device chip and attaching the device chips to each other via the DAF, a package can be formed. To obtain a device chip with a DAF, the DAF is attached to a wafer, and then the DAF is separated from the wafer. The DAF is then attached to the back surface of the wafer, which is the surface that has been ground and thinned.

[0008] Furthermore, a tape-like protective material is attached to the surface side of the wafer to protect devices and other elements formed on the wafer surface when the wafer is ground from the back side. Therefore, when DAF is attached to the back side of a wafer that has been thinned by grinding, the DAF may drip into grooves that serve as marks to replace notches, etc., and the DAF may stick to the protective material within the grooves. In this case, the protective material and the DAF adhere strongly, making it difficult to separate them, and excessive force may be applied to the wafer during separation, potentially causing damage.

[0009] This invention has been made in view of the above problems, and its objective is to provide a wafer processing method in which the DAF and protective member do not adhere to each other at marks (grooves) that replace notches, etc. [Means for solving the problem]

[0010] According to one aspect of the present invention, a wafer processing method for thinning a wafer having a chamfered portion extending from the front to the back surface and a structure indicating the crystal orientation formed on the outer circumference, by grinding the wafer from the back surface to a finished thickness, comprising: a chamfered portion removal step of removing the chamfered portion from the surface of the wafer to a depth greater than or equal to the finished thickness by cutting the wafer along its outer circumference; a groove forming step of cutting the wafer to a depth greater than or equal to the finished thickness and not exceeding the thickness of the wafer by inserting a cutting blade into a position adjacent to the structure, thereby forming a groove indicating the crystal orientation of the wafer in place of the structure; a protective member placement step of placing a protective member on the surface of the wafer after performing the chamfered portion removal step and the groove forming step; and a grinding step of thinning the wafer to the finished thickness by grinding the wafer from the back surface after performing the protective member placement step, and removing the bottom of the groove to expose the groove on the back surface of the wafer. In the chamfer removal step, the wafer is cut along its outer circumference with the cutting blade, The grinding step provides a wafer processing method in which the groove is exposed on the back surface of the wafer, thereby forming an opening on the back surface, and the entire circumference of the opening is surrounded by the back surface of the wafer.

[0012] Furthermore, preferably, in the groove-forming step, the cutting blade is made to cut into the surface of the structure at a position adjacent to it, from a direction perpendicular to the surface.

[0013] Preferably, the groove forming step is performed after the chamfer removal step. Alternatively, preferably, the groove forming step is performed before the chamfer removal step. Preferably, after the grinding step, the process further comprises a DAF attachment step of attaching a DAF to the back surface of the wafer. Even more preferably, after the DAF attachment step, the process further comprises a peeling step of peeling the protective member from the surface of the wafer. More preferably, the DAF attached to the back surface of the wafer in the DAF attachment step does not come into contact with the protective member in the groove. [Effects of the Invention]

[0014] In a wafer processing method according to one aspect of the present invention, before grinding the wafer, a cutting blade is made to cut into a groove indicating the crystal orientation in place of a structure such as a notch that indicates the crystal orientation. Then, the wafer is ground from the back side to thin it to the final thickness, and the bottom of the groove is removed to expose the groove on the back side of the wafer. This groove indicates the crystal orientation as a mark that replaces a structure such as a notch.

[0015] Here, the grooves are formed by cutting the wafer with a cutting blade to a depth greater than or equal to the finished thickness from the surface, but not exceeding the thickness of the wafer. Therefore, when the grooves formed by this method are exposed on the back surface of the wafer, the area of ​​the opening formed on the back surface becomes relatively small. Consequently, when DAF is attached to the back side of the ground and thinned wafer, the DAF does not fall significantly into the opening. Therefore, the protective material attached to the surface side of the wafer and the DAF attached to the back side do not come into contact and stick together.

[0016] Therefore, according to one aspect of the present invention, a wafer processing method is provided in which the DAF and the protective member do not adhere to each other at marks (grooves) that replace notches or the like. [Brief explanation of the drawing]

[0017] [Figure 1] It is a perspective view schematically showing a wafer. [Figure 2] It is a perspective view schematically showing a cutting device. [Figure 3] It is a cross-sectional view schematically showing a chamfer removal step. [Figure 4] It is a perspective view schematically showing a groove formation step. [Figure 5] It is a plan view schematically showing a groove formation position. [Figure 6] FIG. 6(A) is a side view schematically showing a groove formation step, FIG. 6(B) is a side view schematically showing a protective member disposition step, FIG. 6(C) is a side view schematically showing a wafer on which a grinding step has been performed, and FIG. 6(D) is a side view schematically showing a DAF sticking step. [Figure 7] It is a perspective view schematically showing a grinding device. [Figure 8] It is a cross-sectional view schematically showing a grinding step. [Figure 9] It is a plan view schematically showing the back side of a wafer on which a groove is formed and which is ground from the back side. [Figure 10] It is a flowchart showing the flow of each step of a wafer processing method.

Embodiments for Carrying Out the Invention

[0018] Referring to the accompanying drawings, embodiments according to one aspect of the present invention will be described. First, a wafer that is an object to be processed by the wafer processing method according to the present embodiment will be described. FIG. 1 is a perspective view of a wafer 1. The wafer 1 is a disc-shaped wafer made of a material such as Si (silicon), SiC (silicon carbide), GaN (gallium nitride), GaAs (gallium arsenide), or other semiconductors.

[0019] The surface 1a of wafer 1 is divided by multiple intersecting division lines 3. Devices 5, such as ICs and LSIs, are formed in each region of the surface 1a of wafer 1 that is divided by the division lines 3. The region on the surface 1a of wafer 1 where multiple devices 5 are formed is the device formation region 7, and the surrounding region is the outer peripheral surplus region 9. When wafer 1 is thinned by grinding from the back surface 1b and divided along the division lines 3, individual device chips are formed.

[0020] A technology has been developed to package multiple formed device chips by stacking them. By pre-placing an adhesive film called a die attach film (DAF) on each device chip and attaching the device chips to each other via the DAF, a package can be formed. To obtain a device chip with a DAF, the DAF is attached to wafer 1, and then both wafer 1 and the DAF are separated. The DAF is then attached to the back surface 1b of the wafer 1, which is the ground surface that has been thinned by grinding.

[0021] Incidentally, in order to prevent chipping or cracking at the edges of wafer 1, a chamfered portion (see Figure 3) is formed on the outer circumference 1c of wafer 1, where the corners are beveled off. The cross-sectional shape of the chamfered portion is, for example, an arc shape extending from the surface 1a to the back surface 1b. In addition, a notch called a notch 11 is formed on the outer circumference 1c of wafer 1, indicating the crystal orientation of the material constituting wafer 1.

[0022] The electrical properties of semiconductor elements such as transistors that constitute multiple devices 5 formed on wafer 1 may change depending on the relationship between the channel direction and the crystal orientation of the semiconductor material. Also, the ease of dividing wafer 1 may change depending on the relationship between the planned division line 3 and the crystal orientation of the semiconductor material constituting wafer 1. Therefore, the notch 11 is referenced when setting the planned division line 3 on wafer 1, when forming devices 5, and when dividing wafer 1.

[0023] If a wafer 1 with a chamfered edge 1c is thinned by grinding it from the back surface 1b side, a knife-edge shape will be created in the cross-sectional shape of the wafer 1 at the outer edge 1c, formed by the chamfered edge and the grinding surface. As a result, chipping is likely to occur on the outer edge 1c of the thinned wafer 1. Therefore, before grinding the wafer 1, a process called edge trimming is performed on the wafer 1, in which the outer edge 1c of the wafer 1 is cut to remove the chamfered edge.

[0024] Next, a cutting apparatus that can be used for the chamfer removal step (edge ​​trimming) and groove formation step in the wafer processing method according to this embodiment will be described. Figure 2 is a schematic perspective view of the cutting apparatus 2. However, the chamfer removal step and the groove formation step do not need to be performed with the same cutting apparatus.

[0025] The wafer 1 to be cut by the cutting device 2 is brought into the cutting device 2 in an integrated state with, for example, an annular frame (not shown) having an opening with a diameter larger than the diameter of the wafer 1, and a tape (not shown) attached to the annular frame so as to close the opening of the annular frame. By attaching the tape to the wafer 1, the wafer 1, the tape, and the annular frame are integrated to form a frame unit, the wafer 1 can be handled via the annular frame, making it easier to handle the wafer 1. Note that the annular frame and tape are omitted in each figure.

[0026] The cutting apparatus 2 includes a base 4 that supports each component. An opening 4a is formed in the front corner of the base 4, and a cassette support base 8, which moves up and down by a lifting mechanism (not shown), is provided inside this opening 4a. A cassette 10, each containing a plurality of wafers 1 that have become part of a frame unit, is mounted on the upper surface of the cassette support base 8. For the sake of explanation, only the outline of the cassette 10 is shown in Figure 2.

[0027] A rectangular opening 4b is formed on the side of the cassette support base 8, with its longitudinal direction aligned with the X-axis direction (front-to-back direction, machining feed direction). Inside the opening 4b are a ball screw type X-axis movement mechanism (not shown), a table cover 14 covering the top of the X-axis movement mechanism, and a dustproof and waterproof cover 16. The X-axis movement mechanism includes an X-axis movement table (not shown) covered by the table cover 14, and moves this X-axis movement table in the X-axis direction.

[0028] A holding table 18 is positioned on the upper surface of the X-axis moving table so as to be exposed from the table cover 14. The holding table 18 has the function of suction-holding a wafer 1 placed on its upper-exposed holding surface 18a. The holding table 18 is connected to a rotational drive source (not shown), such as a motor, and rotates around a rotation axis that is roughly parallel to the Z-axis direction (vertical direction).

[0029] The holding table 18 comprises a porous member 18c having the same diameter as the wafer 1, and a frame covering the porous member 18c. Inside the holding table 18, a suction passage (not shown) is formed, one end of which is connected to a suction source (not shown), such as an ejector, provided outside the holding table 18. The other end of the suction passage reaches the porous member 18c.

[0030] The upper surface of the porous member 18c is exposed on the holding surface 18a of the holding table 18. The upper surface of the porous member 18c has a diameter equivalent to that of the wafer 1 and is formed to be roughly parallel to the X-axis and Y-axis directions. Furthermore, a plurality of clamps 18b for fixing an annular frame that supports the wafer 1 are provided around the holding table 18.

[0031] When holding the wafer 1 on the holding table 18, first, the frame unit including the wafer 1 is placed on the holding surface 18a of the holding table 18. Then, a suction source and a porous member 18c are connected via a suction passage, and negative pressure is applied to the wafer 1 via tape attached to the back surface 1b of the wafer 1. The annular frame is also fixed with a clamp 18b.

[0032] The cutting apparatus 2 includes a transport unit (not shown) in the area adjacent to the opening 4b for transporting the wafer 1 to the holding table 18, etc. A temporary placement mechanism for temporarily placing the wafer 1 is provided in a position close to the side of the cassette support base 8. The temporary placement mechanism includes, for example, a pair of guide rails 12 that move closer to and further away from each other while maintaining a state parallel to the Y-axis direction (indexing feed direction). The pair of guide rails 12 grip the wafer 1 pulled out from the cassette 10 by the transport unit along the X-axis direction and align it to a predetermined position.

[0033] The wafer 1, positioned in the predetermined location, is lifted by the transport unit and transported to the holding table 18. At this time, the pair of guide rails 12 are separated from each other, and the wafer 1 is passed between the pair of guide rails 12.

[0034] Above the holding table 18, a first cutting unit 24a and a second cutting unit 24b are provided, which cut the wafer 1 with an annular cutting blade. On the upper surface of the base 4, a gate-shaped support portion 20 for supporting the first cutting unit 24a and the second cutting unit 24b is positioned so as to straddle the opening 4b.

[0035] The upper front of the support section 20 is provided with a first moving unit 22a for moving the first cutting unit 24a in the Y-axis direction and the Z-axis direction, and a second moving unit 22b for moving the second cutting unit 24b in the Y-axis direction and the Z-axis direction. The first moving unit 22a is equipped with a Y-axis moving plate 28a, and the second moving unit 22b is equipped with a Y-axis moving plate 28b. The two Y-axis moving plates 28a and 28b are slidably mounted on a pair of Y-axis guide rails 26 arranged along the Y-axis direction on the front of the support section 20.

[0036] A nut portion (not shown) is provided on the back side (rear side) of the Y-axis moving plate 28a, and a Y-axis ball screw 30a, which is generally parallel to the Y-axis guide rail 26, is screwed into this nut portion. Similarly, a nut portion (not shown) is provided on the back side (rear side) of the Y-axis moving plate 28b, and a Y-axis ball screw 30b, which is generally parallel to the Y-axis guide rail 26, is screwed into this nut portion.

[0037] A Y-axis pulse motor 32a is connected to one end of the Y-axis ball screw 30a. By rotating the Y-axis ball screw 30a with the Y-axis pulse motor 32a, the Y-axis moving plate 28a moves in the Y-axis direction along the Y-axis guide rail 26. Additionally, a Y-axis pulse motor (not shown) is connected to one end of the Y-axis ball screw 30b. By rotating the Y-axis ball screw 30b with this Y-axis pulse motor, the Y-axis moving plate 28b moves in the Y-axis direction along the Y-axis guide rail 26.

[0038] A pair of Z-axis guide rails 34a are provided on the front surface of the Y-axis moving plate 28a, along the Z-axis direction, and a pair of Z-axis guide rails 34b are provided on the front surface of the Y-axis moving plate 28b, along the Z-axis direction. A pair of Z-axis moving plates 36a are slidably attached to the pair of Z-axis guide rails 34a, and a pair of Z-axis moving plates 36b are slidably attached to the pair of Z-axis guide rails 34b.

[0039] A nut portion (not shown) is provided on the back side (rear side) of the Z-axis moving plate 36a, and a Z-axis ball screw 38a is screwed into this nut portion, positioned to be approximately parallel to the Z-axis guide rail 34a. A Z-axis pulse motor 40a is connected to one end of the Z-axis ball screw 38a, and by rotating the Z-axis ball screw 38a with the Z-axis pulse motor 40a, the Z-axis moving plate 36a moves in the Z-axis direction along the Z-axis guide rail 34a.

[0040] A nut portion (not shown) is provided on the back side (rear side) of the Z-axis moving plate 36b, and a Z-axis ball screw 38b, which is positioned to be roughly parallel to the Z-axis guide rail 34b, is screwed into this nut portion. A Z-axis pulse motor 40b is connected to one end of the Z-axis ball screw 38b, and by rotating the Z-axis ball screw 38b with the Z-axis pulse motor 40b, the Z-axis moving plate 36b moves in the Z-axis direction along the Z-axis guide rail 34b.

[0041] A first cutting unit 24a is provided below the Z-axis moving plate 36a. A camera unit 46a for photographing the wafer 1 held by the holding table 18 is provided adjacent to the first cutting unit 24a. A second cutting unit 24b is provided below the Z-axis moving plate 36b. A camera unit 46b for photographing the wafer 1 held by the holding table 18 is provided adjacent to the second cutting unit 24b.

[0042] The first moving unit 22a controls the Y-axis and Z-axis positions of the first cutting unit 24a and camera unit 46a, and the second moving unit 22b controls the Y-axis and Z-axis positions of the second cutting unit 24b and camera unit 46b. The positions of the first cutting unit 24a and the second cutting unit 24b are controlled independently.

[0043] An opening 4c is formed opposite to opening 4a relative to opening 4b. A cleaning unit 48 for cleaning wafer 1 is located inside opening 4c, and wafer 1 cut on the holding table 18 is cleaned by the cleaning unit 48. After being cleaned by the cleaning unit 48, wafer 1 is stored back in the cassette 10.

[0044] Here, the cutting units 24a and 24b will be explained further. Figure 3 is a schematic cross-sectional view showing the edge trimming process (chamfer removal step S10) performed by the cutting units 24a and 24b. Figure 4 is a schematic perspective view showing the groove formation step S20, described later, performed using the cutting units 24a and 24b. The chamfer removal step S10 and the groove formation step S20 may be performed by either the first cutting unit 24a or the second cutting unit 24b, respectively.

[0045] Each cutting unit 24a, 24b comprises spindles 50a, 50b aligned with the Y-axis direction, and spindle housings 51a, 51b that rotatably house the base ends of the spindles 50a, 50b. The spindle housings 51a, 51b house a rotational drive source (not shown) such as a motor connected to the spindles 50a, 50b. Annular cutting blades 56a, 56b are fixed to the tips of the spindles 50a, 50b by flange mechanisms 52a, 52b and fixing nuts 54a, 54b.

[0046] The cutting blades 56a and 56b are hub-type cutting blades, which include annular bases 58a and 58b formed from a material such as aluminum and having a through hole in the center, and cutting edges (grinding wheels) 60a and 60b fixed to the outer circumference of the bases 58a and 58b. However, the cutting blades 56a and 56b are not limited to the hub type.

[0047] The cutting edges (grinding wheel sections) 60a and 60b contain countless abrasive grains and a binder (bond) that disperses and fixes the abrasive grains. For example, the abrasive grains are made of materials such as diamond or cubic boron nitride (cBN), and the binder is a nickel plating layer, resin bond, vitrified bond, metal bond, etc.

[0048] The cutting blade thickness of the cutting blades 56a and 56b used in the chamfer removal step S10 is determined, for example, according to the width of the chamfer formed on the outer circumference 1c of the wafer 1. The cutting blade thickness of the cutting blades 56a and 56b is preferably, for example, 2 mm or more. However, the blade thickness is not limited to this. In addition, the cutting blade thickness of the cutting blades 56a and 56b used in the groove formation step S20 is determined according to the width of the groove 15 (see Figure 9, etc.) formed in the wafer 1, which will be described later.

[0049] When the rotation drive source is activated and the spindles 50a and 50b are rotated, the cutting blades 56a and 56b can be rotated, and when the rotating cutting blades 56a and 56b are made to cut into the wafer 1 which is held by suction on the holding table 18, the wafer 1 can be cut. At this time, a cutting fluid such as pure water is sprayed onto the wafer 1 and the cutting blades 56a and 56b, and the processing debris and frictional heat generated by cutting are removed by the cutting fluid.

[0050] Next, a grinding apparatus that can be used in the grinding step S40 in the wafer processing method according to this embodiment will be described. Figure 7 is a schematic perspective view of the grinding apparatus 62, and Figure 8 is a schematic cross-sectional view of the wafer 1 being ground by the grinding apparatus 62. An opening 64a is provided on the upper surface of the base 64 of the grinding apparatus 62. Inside the opening 64a is an X-axis moving table 58 on which a holding table 66 for suction holding of the wafer 1 rests.

[0051] The X-axis moving table 58 is movable in the X-axis direction by an X-axis direction moving mechanism (not shown). The X-axis moving table 58 is positioned in an loading / unloading area 70 where wafers 1 are loaded and unloaded on the holding table 66 by the X-axis direction moving mechanism, and in a processing area 72 where wafers 1 held by the holding table 66 are ground.

[0052] A porous member having an upper surface diameter equal to that of the wafer 1 is disposed on the upper surface of the holding table 66, and the upper surface of the porous member becomes the holding surface 66a for holding the wafer 1. The holding table 66 has a suction passage (not shown) inside, one end of which is connected to the porous member and the other end of which is connected to a suction source (not shown). When the suction source is activated, negative pressure is applied to the wafer 1 placed on the holding surface 66a, and the wafer 1 is held in place by the holding table 66 through suction. The holding table 66 can also rotate around an axis perpendicular to the holding surface 66a.

[0053] A grinding unit 74 for grinding the wafer 1 is positioned above the processing area 72. A support section 76 is erected on the rear side of the base 64, and the grinding unit 74 is supported by this support section 76. A pair of Z-axis guide rails 78 extending in the Z-axis direction are provided on the front of the support section 76, and a Z-axis moving plate 80 is slidably attached to each Z-axis guide rail 78.

[0054] A nut (not shown) is provided on the back (rear) side of the Z-axis moving plate 80, and a Z-axis ball screw 82 parallel to the Z-axis guide rail 78 is screwed into this nut. A Z-axis pulse motor 84 is connected to one end of the Z-axis ball screw 82. When the Z-axis ball screw 82 is rotated by the Z-axis pulse motor 84, the Z-axis moving plate 80 moves in the Z-axis direction along the Z-axis guide rail 78.

[0055] A grinding unit 74, which performs grinding of the wafer 1, is fixed to the lower front side of the Z-axis moving plate 80. When the Z-axis moving plate 80 is moved in the Z-axis direction, the grinding unit 74 moves in the Z-axis direction.

[0056] The grinding unit 74 includes a spindle 88 aligned with the Z-axis direction, a spindle housing 86 that rotatably houses the upper end of the spindle 88, and a disc-shaped wheel mount 90 fixed to the lower end of the spindle 88. The spindle housing 86 houses a rotational drive source, such as a motor, which is connected to the upper end of the spindle 88 and rotates the spindle 88 around the Z-axis direction.

[0057] An annular grinding wheel 92 is fixed to the lower surface of the wheel mount 90. An annular grinding wheel 94, in which abrasive grains made of diamond or the like are dispersed and fixed in a binder, is arranged on the lower surface of the grinding wheel 92.

[0058] When the spindle 88 is rotated, the grinding wheel 92 rotates, causing the grinding wheel 94 to rotate along an annular orbit. Then, when the grinding unit 74 is lowered and the rotating grinding wheel 94 comes into contact with the surface of the wafer 1 to be ground, the wafer 1 is ground. The grinding apparatus 62 has a thickness measuring instrument (not shown) and proceeds with grinding while monitoring the thickness of the wafer 1, and stops the descent of the grinding unit 74 when the thickness of the wafer 1 reaches a predetermined finish thickness, thereby ending the grinding.

[0059] When wafer 1 is ground with grinding wheel 94, processing debris and frictional heat are generated from wafer 1 and grinding wheel 94. The grinding apparatus 62 is equipped with a grinding water supply nozzle (not shown) and supplies grinding water such as pure water to wafer 1 and the other parts from the grinding water supply nozzle while wafer 1 is being ground with grinding wheel 94. Processing debris and frictional heat are removed by the grinding water.

[0060] When the wafer 1 is thinned by grinding with the grinding device 62, a protective member 17 (see Figure 8, etc.) is attached to the surface 1a of the wafer 1 in order to protect the surface 1a of the wafer 1. The protective member 17 is a disc-shaped member having the same diameter as the wafer 1 and is made of a material such as resin. More specifically, the protective member 17 is a tape-shaped member comprising an adhesive layer that applies adhesive force to the wafer 1 and a base layer that supports the adhesive layer.

[0061] When the protective member 17 is attached to the surface 1a of the wafer 1, the surface 1a does not come into direct contact with the holding table 66 when the wafer 1 is ground from the back side 1b. Therefore, no damage occurs to the surface 1a of the wafer 1. The wafer 1 with the protective member 17 attached to the surface 1a is placed on the holding table 66 and held in place by suction on the holding table 66.

[0062] On the back surface 1b of the wafer 1, which was the surface that was ground and thinned, a DAF (Digital Adhesive Film) is attached, which functions as an adhesive material for device chips formed by dividing the wafer 1. Figure 6(D) includes a schematic side view showing the DAF 21 attached to the back surface 1b of the wafer 1.

[0063] When wafer 1 is edge-trimmed and ground from the back side 1b, structures such as notches 11 that indicate the crystal orientation of wafer 1 are lost. As a result, it becomes impossible to determine the crystal orientation of the ground wafer 1. Conventionally, before edge trimming was performed, wafer 1 was cut with a cutting blade from the radially outer side near structures such as notches 11 to form groove-shaped marks that penetrate the wafer 1 vertically. These marks replaced structures such as notches 11 and indicated the crystal orientation of wafer 1.

[0064] However, when a mark is formed that penetrates the wafer 1 vertically, and the wafer 1 is thinned by grinding from the back surface 1b side, and the DAF 21 is attached to the back surface 1b side of the wafer 1, the DAF 21 hangs down into the groove-shaped mark. Then, the protective member 17 that was attached to the front surface 1a side of the wafer 1 for grinding and the DAF 21 come into contact with each other in the groove-shaped mark and stick together.

[0065] In this case, the attached protective member 17 and the DAF 21 had to be separated, and during this process, excessive force was applied to the thinned wafer 1, which sometimes caused the wafer 1 to break. Therefore, in the wafer processing method according to this embodiment, when the DAF 21 is attached to the back surface 1b side of the ground and thinned wafer 1, the DAF 21 and the protective member 17 are not brought into contact in the grooves indicating the crystal orientation.

[0066] The following describes the wafer processing method according to this embodiment. The wafer processing method according to this embodiment is a method for thinning a wafer 1, which has a chamfered portion extending from the surface 1a to the back surface 1b on its outer circumference 1c and a structure indicating the crystal orientation (such as a notch 11) formed on the outer circumference 1c, by grinding it from the back surface 1b side to the final thickness. Figure 10 is a flowchart showing the flow of each step of the wafer processing method according to this embodiment.

[0067] First, a chamfer removal step (S10) is performed in which the chamfered portion is removed from the surface 1a of the wafer 1 to a depth greater than or equal to the finished thickness by cutting along the outer circumference 1c of the wafer 1. In the chamfer removal step S10, the cutting apparatus 2 described in Figure 2 is preferably used. Figure 3 is a schematic cross-sectional view showing the chamfer removal step S10.

[0068] First, the wafer 1 is placed on the holding table 18, and the wafer 1 is held in place by suction using the holding table 18. At this time, the surface 1a side of the wafer 1 is exposed upwards, and the center of the holding surface 18a of the holding table 18 is aligned with the center of the wafer 1.

[0069] Then, the relative positions of the holding table 18 and the cutting units 24a and 24b are adjusted so that the cutting edges 60a and 60b of the cutting blades 56a and 56b are positioned tangent to one end of the outer circumference 1c of the wafer 1. In addition, the heights of the cutting units 24a and 24b are adjusted so that the lower ends of the cutting edges 60a and 60b are positioned at a height lower than the surface 1a and at a depth exceeding the finished thickness of the wafer 1.

[0070] Subsequently, the cutting blades 56a and 56b are rotated, and the holding table 18 is moved to cut into one end of the outer circumference 1c of the wafer 1 with the cutting blades 60a and 60b. Then, the holding table 18 is rotated around the Z-axis to cut the entire outer circumference 1c of the wafer 1 with the cutting blades 56a and 56b. As a result, the chamfered portion of the outer circumference 1c of the wafer 1 is partially removed. Figure 4 includes a schematic perspective view showing the wafer 1 with the chamfered portion of the outer circumference 1c removed. A terrace portion 9a is formed on the outer circumference 1c of the wafer 1.

[0071] Furthermore, in the wafer processing method according to this embodiment, a groove forming step S20 is performed before or after the chamfer removal step S10 to form grooves that indicate the crystal orientation of the wafer 1 in place of structures such as notches 11. Figure 4 is a schematic perspective view showing the groove forming step S20. In the groove forming step S20, cutting blades 56a and 56b are made to cut into positions 13 adjacent to the structure, cutting the wafer 1 from the surface 1a to a depth greater than or equal to the finished thickness and not exceeding the thickness of the wafer 1.

[0072] In the groove forming step S20, the cutting blades 56a and 56b used in the chamfer removal step S10 may be used. If the thickness of the cutting blades 56a and 56b used in the chamfer removal step matches the length of the groove formed in the groove forming step S20, the same cutting blades 56a and 56b can be used in both steps. Furthermore, in this case, the chamfer removal step S10 and the groove forming step S20 can be performed by a cutting device 2 equipped with a single cutting unit.

[0073] Furthermore, in the groove forming step S20, different cutting blades 56a and 56b used in the chamfer removal step S10 may be used. In this case, cutting blades 56a and 56b with a thickness corresponding to the length of the groove formed in the groove forming step S20 are used in the groove forming step S20.

[0074] In groove formation step S20, the cutting blades 56a and 56b are positioned above the wafer 1 such that the lower ends of the cutting edges 60a and 60b overlap with a position 13 adjacent to a structure such as a notch 11. Here, the position 13 adjacent to a structure such as a notch 11 is a position where a groove indicating the crystal orientation of the wafer 1 is formed in place of the structure. For example, it is a position whose positional relationship with the structure is specified, and where, when a groove is formed, it can indicate the crystal orientation of the wafer 1.

[0075] Next, the cutting blades 56a and 56b are started to rotate, and the cutting units 24a and 24b are lowered to cut into the wafer 1 with the cutting edges 60a and 60b. That is, the cutting blades 56a and 56b are cut into the wafer 1 at a position 13 adjacent to a structure such as a notch 11, from a direction perpendicular to the surface 1a. At this time, the cutting units 24a and 24b are lowered so that the lower ends of the cutting edges 60a and 60b reach a height deeper than the surface 1a, exceeding the finished thickness of the wafer 1. After that, the cutting units 24a and 24b are raised.

[0076] Figure 5 is a schematic plan view of wafer 1 after the chamfer removal step S10 and groove formation step S20 have been performed. When groove formation step S20 is performed, a groove 15 is formed at position 13 on wafer 1. Immediately after groove formation step S20, the groove 15 does not penetrate to the back surface 1b side of wafer 1.

[0077] Figure 6(A) includes a schematic side view showing the cutting blades 56a and 56b that have cut into the wafer 1. As shown in Figure 6(A), the lower ends of the cutting edges 60a and 60b of the cutting blades 56a and 56b may reach a height position deeper than the terrace portion 9a formed on the outer circumference 1c of the wafer 1 in the chamfer removal step S10. Alternatively, the lower ends of the cutting edges 60a and 60b may reach a height position shallower than the terrace portion 9a formed on the outer circumference 1c of the wafer 1.

[0078] Furthermore, the height position reached by the lower ends of the cutting blades 56a and 56b in the groove forming step S20 should be determined based on the planned width of the groove 15 exposed on the back surface 1b side in the grinding step S40 described later. The lower the height position reached by the lower ends of the cutting blades 60a and 60b in the groove forming step S20, the wider the width of the groove 15 exposed on the back surface 1b side in the grinding step S40. The higher the height position, the narrower the width of the groove 15 exposed on the back surface 1b side in the grinding step S40. In other words, the width of the exposed groove 15 area can be adjusted in this way.

[0079] In step S20, instead of cutting the cutting blades 56a and 56b into the wafer 1 at position 13 from above, the groove 15 may be formed by cutting the wafer 1 with the cutting blades 56a and 56b from the radially outer side toward the inside. In this case, the wafer 1 is cut by the cutting blades 56a and 56b from the outer circumference 1c to a predetermined length radially inward to form a groove 15 that does not penetrate in the vertical direction.

[0080] However, when grooves 15 are formed by this method, cracks are likely to occur from the tip side (the radially inward end) of the grooves 15 when the wafer 1 with the grooves 15 is ground to a predetermined thickness as described later. If the cracks grow and reach the device 5 formed on the surface 1a of the wafer 1, the wafer 1 will eventually be divided and the manufactured device chips will be defective. For this reason, in groove formation step S20, it is preferable that the cutting blades 56a and 56b cut into the wafer 1 from above.

[0081] Furthermore, in the groove formation step S20, by appropriately selecting the cutting edge shapes of the cutting edges 60a and 60b of the cutting blades 56a and 56b, grooves 15 of a specific shape can be formed on the wafer 1. For example, if a cutting blade with a constant cutting edge thickness is used, grooves 15 with a length corresponding to the cutting edge thickness can be formed on the wafer 1. Alternatively, for example, if a cutting blade with a sharp cutting edge that becomes thinner towards the tip is used, shorter grooves 15 can be formed on the wafer 1.

[0082] The groove formation step S20 may be performed before the chamfer removal step S10. If the same cutting blades 56a and 56b are used consecutively in both steps, the condition of the cutting blades 56a and 56b can be confirmed in advance by performing the groove formation step S20 first and observing the grooves 15 formed on the wafer 1. In addition, the height of the cutting blades 56a and 56b can be confirmed from the length of the grooves 15. Therefore, the chamfer removal step S10 can be performed with the cutting blades 56a and 56b whose condition and height have been confirmed.

[0083] In particular, during the chamfer removal step S10, a larger area is cut by the cutting blades 56a and 56b compared to when the cutting blades cut into the wafer 1 during division. Therefore, the wear on the cutting edges 60a and 60b of the cutting blades 56a and 56b is relatively rapid, and the height of the lower end of the cutting edges 60a and 60b tends to change with wear. For this reason, it is important to check the condition and height of the cutting blades 56a and 56b.

[0084] Furthermore, the groove formation step S20 may be performed after the chamfer removal step S10. When the chamfer removal step S10 is performed to form terrace portions 9a along the outer circumference 1c of the wafer 1, the accuracy of the alignment of the cutting blades 56a, 56b and the wafer 1 can be confirmed by detecting the position of the outer edge of the region surrounded by the terrace portions 9a on the surface 1a of the wafer 1. In addition, the alignment of the cutting blades 56a, 56b can be performed based on the position of the outer edge. Therefore, in the groove formation step S20, the groove 15 can be precisely formed at a predetermined position.

[0085] In the wafer processing method according to this embodiment, after performing the chamfer removal step S10 and the groove formation step S20, a protective member placement step S30 is performed in which a protective member 17 is placed on the surface 1a of the wafer 1. Figure 6(B) is a schematic side view showing the wafer 1 with the protective member 17 placed on the surface 1a side and the wafer inverted. The protective member 17 protects the surface 1a side of the wafer 1 in the grinding step S40 which will be described next.

[0086] Next, the grinding step S40, which is performed after the protective member placement step S30, will be described. In the grinding step S40, the wafer 1 is ground from the back surface 1b to thin it to the finished thickness. At this time, the bottom of the groove 15 is removed and the groove 15 is exposed on the back surface 1b of the wafer 1.

[0087] The grinding step S40 is performed by the grinding apparatus 62 shown in Figure 7. First, as shown in Figure 6(B), the surface 1a on which the protective member 17 is placed is turned downwards, and the back surface 1b, which will be the surface to be ground, is turned upwards. Then, in this state, the wafer 1 is placed on the holding surface 66a of the holding table 66, the wafer 1 is held by suction with the holding table 66, and the holding table 66 is moved to the processing area 72.

[0088] Next, the spindle 88 is rotated to rotate the grinding wheel 92, moving the grinding wheel 94 along an annular track. Then, the grinding unit 74 is started to descend, and grinding of the wafer 1 is started by bringing the bottom surface of the moving grinding wheel 94 into contact with the back surface 1b of the wafer 1. Figure 8 is a schematic cross-sectional view showing the grinding step S40.

[0089] In grinding step S40, the thickness of wafer 1 is monitored by a thickness measuring instrument (not shown), and when it is confirmed that the thickness of wafer 1 has reached a predetermined finish thickness, the descent of the grinding unit 74 is stopped, and the grinding of wafer 1 is completed. Figure 9 is a schematic plan view showing the back surface 1b of wafer 1 that has been thinned by grinding from the back surface 1b side.

[0090] The chamfered portion formed on the outer circumference 1c of wafer 1 is removed in the chamfered portion removal step S10, with the portion on the surface 1a side being removed, and the remaining portion being removed in the grinding step S40. In Figure 9, the position 1d, which was the outer circumference 1c of wafer 1 before the grinding step S40 was performed, is shown by a dashed line. Since no chamfered portion remains on wafer 1 after grinding, a knife edge shape does not occur in the cross-sectional shape of wafer 1, and there is no risk of damage to wafer 1 caused by a knife edge shape.

[0091] Furthermore, in grinding step S40, the bottom of the groove 15 is removed during the process of grinding the wafer 1 until it reaches the final thickness, and the groove 15 is exposed on the back surface 1b side of the wafer 1. Figure 6(C) is a schematic side view of the wafer 1 when grinding step S40 is completed.

[0092] On the back surface 1b of wafer 1, an opening 19b is formed due to the exposure of the groove 15. After grinding, structures such as the notch 11 that were formed on the outer circumference 1c of wafer 1 are removed, but since the groove 15 is exposed on both the front surface 1a and the back surface 1b of wafer 1, the crystal orientation of wafer 1 can be determined based on the groove 15.

[0093] Here, the groove 15 is formed in the groove formation step S20 by the cutting blades 56a and 56b cutting into the wafer 1 from the surface 1a side. Therefore, as shown in Figure 6(C), the opening 19b on the back surface 1b side of the groove 15 is smaller than the opening 19a on the surface 1a side of the groove 15. Furthermore, the size of the opening 19b on the back surface 1b side can be adjusted by the cutting depth of the cutting blades 56a and 56b in the groove formation step S20.

[0094] For example, if the depth of the cut in the groove formation step S20 is set to slightly exceed the finished thickness of the wafer 1, the opening 19b of the groove 15 formed on the back surface 1b of the wafer 1 when the grinding step S40 is completed will be extremely small. In other words, as will be described later, it is possible to adjust the size of the opening 19b so that the DAF does not drip into the groove 15 when the DAF is attached to the back surface 1b of the wafer 1.

[0095] For example, when using cutting blades 56a and 56b with a diameter of 49.4 mm in groove formation step S20, the blades reach a depth lower than the surface 1a of the wafer 1, with the finished thickness of the wafer 1 added to 20 μm. In this case, when the grinding step S40 is performed to thin the wafer 1 to the finished thickness, an opening 19b with a width of about 2 mm can be formed on the back surface 1b of the wafer 1. Since the width of the notch 11 is about 3 to 4 mm, performing the groove formation step S20 in this way makes the width of the opening 19b about the same as or slightly smaller than the notch 11.

[0096] After the grinding step S40 is completed, the wafer 1 is removed from the grinding apparatus 62 and the DAF is attached to the back surface 1b side (DAF attachment step S50). Figure 6(D) is a schematic side view showing the wafer 1 with the DAF 21 attached. At this time, if the opening 19b is sufficiently small, the DAF 21 will not fall into the groove 15 and come into contact with the protective member 17 disposed on the surface 1a side of the wafer 1.

[0097] After the DAF 21 is attached to the back surface 1b of wafer 1, the protective member 17 is peeled off from the front surface 1a of wafer 1 (peeling step S60). Then, wafer 1 is divided along the planned division line 3 (dividing step S70). When wafer 1 is divided along the planned division line 3, along with the DAF 21, individual device chips with DAF 21 attached are manufactured.

[0098] The wafer 1 may be divided, for example, using a cutting device equipped with an annular cutting blade. Alternatively, it may be divided using a laser processing device that can laser process the wafer 1 by irradiating it with a laser beam. When the wafer 1 is loaded into the cutting device or laser processing device, a dicing tape may be attached to the back surface 1b of the wafer 1 via a DAF 21, and the outer periphery of the dicing tape may be fixed to an annular frame to form a frame unit.

[0099] Alternatively, as the DAF attachment step S50, the DAF 21 attached to one side of the dicing tape may be placed together with the dicing tape on the back side 1b of the wafer 1. In this case as well, a frame unit can be formed by fixing the outer periphery of the dicing tape to an annular frame.

[0100] Furthermore, if the protective member 17 can be peeled off from wafer 1 before the DAF 21 is attached to wafer 1, the DAF 21 will not come into contact with the protective member 17 even if it drips into the groove 15. However, it is difficult to peel off the protective member 17 before fixing wafer 1, which has been thinned and weakened in the grinding step S40, to dicing tape or the like. Therefore, it is necessary to attach the DAF 21 to wafer 1 before peeling off the protective member 17.

[0101] As explained above, according to the wafer processing method of this embodiment, the size of the opening 19b formed by exposing the groove 15 indicating the crystal orientation of the wafer 1 on the back surface 1b can be adjusted to a size that prevents the DAF 21 from falling off. Therefore, the DAF 21 attached to the back surface 1b of the wafer 1 does not come into contact with the protective member 17 through the groove 15.

[0102] It should be noted that the present invention is not limited to the embodiments described above and can be implemented with various modifications. For example, in the above embodiments, as shown in Figures 6(B), 6(C), 9, etc., the case in which the groove 15 formed on the wafer 1 is exposed on the side of the wafer 1 was described as an example. That is, in the groove formation step S20 described above, the cutting position 13 (see Figure 4, etc.) where the cutting blades 56a, 56b cut included a part of the area that was cut and removed in the chamfer removal step S10 of the wafer 1. However, one aspect of the present invention is not limited thereto.

[0103] In other words, the cutting positions 13 where the cutting blades 56a and 56b cut in the groove formation step S20 do not necessarily include any area that was cut and removed from the wafer 1 in the chamfer removal step S10. In this case, the grooves 15 formed in the wafer 1 in the groove formation step S20 are not exposed to the sides of the wafer 1, and the openings 19b of the grooves 15 formed on the back surface 1b of the wafer 1 in the grinding step S40 are surrounded all around by the back surface 1b of the wafer 1.

[0104] When the opening 19b of the groove 15 is seamlessly surrounded all around by the back surface 1b of the wafer 1, the DAF 21 attached to the back surface 1b is less likely to sag into the opening 19b. Therefore, contact between the DAF 21 and the protective member 17 is less likely to occur.

[0105] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the objectives of the present invention. [Explanation of Symbols]

[0106] 1 wafer 1a surface 1b back side 1c outer circumference 1d Position that was on the outer perimeter Planned division lines (3 divisions) 5 devices 7. Device Formation Area 9. Peripheral surplus region 9a Terrace section 11 Notches 13 positions 15 groove 17 Protective components 19a,19b opening 21 DAF 2 Cutting equipment 4.64 base 4a,4b,4c,64a opening 8 Cassette Support Stands 10 cassettes 12 Guide rails 14 Table Covers 16 Dustproof and splashproof cover 18,66 retention tables 18a,66a Holding surface 18b Clamp 18c Porous material 20,76 Support part 22a, 22b Mobile Unit 24a, 24b Cutting Unit 26, 34a, 34b, 78 Guide rails 28a, 28b, 36a, 36b, 80 Mobile Plate 30a, 30b, 38a, 38b, 82 ball screws 32a, 40a, 40b, 84 pulse motor 46a, 46b Camera Unit 48 Washing Unit 50a, 50b, 88 spindles 51a, 51b, 86 Spindle Housing 52a, 52b Flange mechanism 54a, 54b Fixing nuts 56a Cutting blade 58 X-axis moving table 58a,58b base 60a, 60b cutting blades 62 Grinding equipment 70 Loading / unloading area 72 Processing area 74 Grinding Unit 90 Wheel Mount 92 Grinding Wheel 94 Grinding Wheel

Claims

1. A wafer processing method for thinning a wafer to a finished thickness by grinding a wafer having a chamfered portion extending from the front to the back surface on its outer circumference and a structure indicating the crystal orientation formed on the outer circumference, from the back surface side, A chamfer removal step involves cutting the wafer along its outer circumference to remove the chamfer from the surface of the wafer to a depth greater than or equal to the finished thickness, A groove forming step in which a cutting blade is made to cut the wafer at a position adjacent to the structure to a depth greater than or equal to the finished thickness and not exceeding the thickness of the wafer, thereby forming grooves that indicate the crystal orientation of the wafer in place of the structure, After performing the chamfering removal step and the groove forming step, a protective member placement step is performed in which a protective member is placed on the surface of the wafer, After performing the protective member placement step, the wafer is ground from the back surface to thin it to the finished thickness, and the bottom of the groove is removed to expose the groove on the back surface of the wafer in a grinding step, Equipped with, In the chamfer removal step, the wafer is cut along its outer circumference with the cutting blade, A wafer processing method wherein, in the grinding step, the groove is exposed on the back surface of the wafer, thereby forming an opening on the back surface, and the entire circumference of the opening is surrounded by the back surface of the wafer.

2. The method for processing a wafer according to claim 1, characterized in that, in the groove forming step, the cutting blade is made to cut into the surface of the structure at a position adjacent to the structure from a direction perpendicular to the surface.

3. The wafer processing method according to claim 1 or 2, characterized in that the groove forming step is performed after the chamfer removal step.

4. The wafer processing method according to claim 1 or 2, characterized in that the groove forming step is performed before the chamfer removal step.

5. A wafer processing method according to any one of claims 1 to 4, further comprising a DAF attachment step of attaching a DAF to the back surface of the wafer after performing the grinding step.

6. The wafer processing method according to claim 5, further comprising a peeling step of peeling the protective member off the surface of the wafer after the DAF bonding step.

7. The wafer processing method according to claim 5 or 6, characterized in that the DAF attached to the back surface of the wafer in the DAF attachment step does not come into contact with the protective member in the groove.

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