Wafer processing method

Abstract

To suppress dropping of relatively large offcuts when grinding a wafer.SOLUTION: A wafer processing method for thinning a wafer having a chamfered portion on the outer periphery thereof to achieve a finished thickness includes a trimming step of cutting the wafer along the outer peripheral edge thereof by cutting a first cutting blade from the surface side of the wafer into the chamfered portion up to a first depth position whose depth from the surface is equal to or more than the finished thickness, thereby forming an annular terrace portion, and a grinding step of polishing the wafer from the backside thereof to thin the wafer until the thickness thereof reaches the finished thickness. The wafer processing method further includes a first ultrasonic vibration cutting step in which before performing the grinding step, while applying ultrasonic vibration to a second cutting blade having a smaller blade thickness than the first cutting blade, the second blade is cut from the surface side of the wafer along the outer peripheral edge thereof up to a second depth position whose depth from the surface exceeds the first depth position, thereby forming a first annular cut groove.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method for thinning a disk-shaped wafer having a chamfered portion on its outer periphery to a predetermined thickness. [Background technology]

[0002] In the device chip manufacturing process, a disk-shaped wafer is used, on which devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are formed in multiple regions defined by multiple intersecting dividing lines (streets). By dividing this wafer along the dividing lines, multiple device chips, each equipped with a device, are obtained. The device chips are installed in various electronic devices, such as mobile phones and personal computers.

[0003] In recent years, there has been a remarkable trend toward miniaturization of electronic devices, and the demand for thinner device chips has also increased. Therefore, before dividing the wafer, it is ground from the back side using a grinding machine to thin it to a specified finished thickness, and the thinned wafer is then divided. In this case, thin device chips are finally obtained.

[0004] The outer periphery of a disk-shaped wafer has a chamfered portion where the corners have been removed. Therefore, when the wafer is thinned, a sharp knife-edge-like shape appears on the outer periphery, making the wafer susceptible to damage. Therefore, before grinding the wafer from the back side, an edge trimming process is performed in which the outer periphery of the wafer is cut from the front side to a depth equal to or greater than the finishing thickness, thereby partially removing the chamfered portion (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-173961 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the wafer is thinned by grinding from the backside after edge trimming, the scraps that make up the annular terraces that protrude outward due to the edge trimming break off just before the grinding wheel reaches them, causing relatively large scraps to fall.The fallen scraps accumulate in a drainage ditch that drains the grinding water used in grinding, requiring the grinding machine to be stopped and the drainage ditch to be cleaned frequently.

[0007] The present invention has been made in view of the above problems, and has as its object to provide a wafer processing method that can prevent relatively large scraps from falling when grinding wafers that have been edge-trimmed. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a wafer processing method for grinding a circular disk-shaped wafer having a chamfered portion on its outer periphery from its backside to thin it to a finishing thickness, the method comprising: a trimming step in which a first cutting blade is inserted into the chamfered portion from the front side of the wafer to a first depth position from the front side that is equal to or greater than the finishing thickness, thereby cutting the wafer along the outer periphery to form an annular terrace portion; a protective member adhering step in which a protective member is adhered to the front side of the wafer after the trimming step; and a grinding step in which the wafer is ground from the backside to thin it to the finishing thickness after the protective member adhering step, wherein ultrasonic vibrations are applied to a second cutting blade having a blade thickness thinner than that of the first cutting blade before the grinding step is performed, while cutting the wafer from the front side of the wafer along the outer periphery to a second depth position from the front side that is greater than the first depth position. On the terrace The second cutting blade is inserted On the terrace Forming the first annular cutting groove (However, this does not include the case where the first annular cutting groove is formed on the inner peripheral edge of the terrace portion.) There is provided a wafer processing method further comprising a first ultrasonic vibration cutting step.

[0009] According to another aspect of the present invention, there is provided a wafer processing method for grinding a disc-shaped wafer having a chamfered portion on its outer periphery from its backside to thin it to a finishing thickness, the method comprising: a trimming step of cutting the wafer along its outer periphery with a first cutting blade from its front side into the chamfered portion to a first depth position from the front side that is equal to or greater than the finishing thickness, thereby forming an annular terrace portion; a protective member adhering step of adhering a protective member to the front side of the wafer after the trimming step; and a grinding step of grinding the wafer from its backside to thin it to the finishing thickness after the protective member adhering step, the method further comprising a first ultrasonic vibration cutting step of applying ultrasonic vibrations to a second cutting blade having a blade thickness thinner than that of the first cutting blade before performing the grinding step, while adhering the second cutting blade to the terrace portion from the front side of the wafer along the outer periphery to a second depth position that is greater than the first depth position from the front side, thereby forming a first annular cutting groove in the terrace portion.Before the grinding step is performed, ultrasonic vibration is applied to the second cutting blade while the wafer is being ground from the front surface side along the outer circumferential edge to a third depth position where the depth from the front surface exceeds the first depth position. On the terrace The second cutting blade is inserted On the terrace The method further includes a second ultrasonic vibration cutting step of forming a second annular cutting groove, and the first annular cutting groove and the second annular cutting groove are formed concentrically. A wafer processing method is provided, which comprises the steps of:

[0010] More preferably, the first annular cutting groove is formed more inward than the second annular cutting groove, and the second depth position is closer to the surface than the third depth position.

[0011] Also, preferably, the first ultrasonic vibration cutting step is performed after the trimming step. [Effects of the Invention]

[0012] In a wafer processing method according to one aspect of the present invention, before grinding the wafer from the backside, the wafer is cut along the outer periphery with a first cutting blade to form an annular terrace portion, and separately, the wafer is cut with a second cutting blade to form a first annular cutting groove. When forming the first annular cutting groove, ultrasonic vibration is applied to the second cutting blade, so that the wafer is finely broken near the formed first annular cutting groove, forming a fractured layer.

[0013] When a wafer having a terrace portion with a first annular cutting groove formed on its outer periphery is ground from the backside, the terrace portion is subdivided using the first annular cutting groove and the fractured layer as starting points for division, producing fine scraps. The fine scraps are easily washed away when they fall into a drainage ditch and are not likely to accumulate in the drainage ditch, eliminating the need for frequent cleaning of the drainage ditch.

[0014] Therefore, one aspect of the present invention provides a wafer processing method that can prevent relatively large scrap pieces from falling when grinding an edge-trimmed wafer. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective view showing a wafer. [Figure 2] FIG. 2 is a perspective view schematically showing a cutting device. [Figure 3] FIG. 2 is a cross-sectional view schematically showing a wafer being cut by a first cutting blade. [Figure 4] FIG. 3 is a cross-sectional view schematically showing a wafer being cut by a second cutting blade. [Figure 5] FIG. 3 is an exploded perspective view schematically showing a second cutting unit. [Figure 6] FIG. 4 is a cross-sectional view schematically showing a second cutting unit. [Figure 7] 1 is an enlarged cross-sectional view schematically showing a portion of a wafer in which a plurality of annular cut grooves are formed in a terrace portion. FIG. [Figure 8] FIG. 2 is a perspective view schematically showing a grinding device. [Figure 9] FIG. 2 is a cross-sectional view schematically showing a wafer to which a protective member is attached. [Figure 10] FIG. 2 is a cross-sectional view schematically showing a wafer being ground. [Figure 11] FIG. 10 is a cross-sectional view schematically showing the wafer being further ground. [Figure 12] 3 is a flowchart showing the flow of each step of a wafer processing method according to an embodiment. [Figure 13] 10 is a photograph showing scraps recovered by carrying out a wafer processing method according to an embodiment of the present invention and scraps recovered by carrying out a wafer processing method according to a comparative example, side by side. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. First, a wafer to be processed by a wafer processing method according to this embodiment will be described. FIG. 1 is a perspective view schematically showing a wafer 1.

[0017] The wafer 1 is a disk-shaped member made of a material such as silicon, and has a front surface 1a and a back surface 1b that are generally parallel to each other. A plurality of planned dividing lines 3 are set on the front surface 1a of the wafer 1, and are arranged in a grid pattern so that they intersect with each other. Devices 5, such as ICs and LSIs, are formed in each of the regions defined by the planned dividing lines 3 on the front surface 1a of the wafer 1. The region on the front surface 1a of the wafer 1 where the devices 5 are formed is called a device region 7. The outer region surrounding the device region 7 is called a peripheral excess region 9.

[0018] There are no limitations on the material, structure, size, etc. of the wafer 1. For example, the wafer 1 may be a substrate made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass (quartz glass, borosilicate glass, etc.), etc. There are also no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 5, and the wafer 1 may not have any devices 5 formed thereon.

[0019] If the wafer 1 has corners on its periphery, the wafer 1 is prone to chipping or cracking when it receives an impact at the corners. If these chips or cracks progress from the peripheral excess region 9 to the device region 7, the devices 5 will be damaged. Therefore, the outer periphery 1c of the wafer 1 is chamfered in advance to remove the corners and form a rounded chamfered portion. Figure 3 includes a cross-sectional view showing the chamfered portion of the wafer 1.

[0020] The wafer 1 is ground from the back surface 1b side to thin the wafer 1, and then divided along the planned division lines 3 to produce a plurality of thin chips (device chips) each equipped with a device 5. For example, a cutting device equipped with an annular cutting blade or a laser processing device equipped with a laser processing unit that irradiates the wafer 1 with a laser beam is used to divide the wafer 1. The device chips manufactured by these processing devices are mounted in various electronic devices such as mobile phones and personal computers.

[0021] Next, a cutting device that performs edge trimming and the formation of an annular cut groove with a fractured layer in the wafer processing method according to this embodiment will be described. Fig. 2 is a perspective view that schematically shows a cutting device 2. However, the edge trimming and the formation of an annular cut groove with a fractured layer do not necessarily need to be performed by the same cutting device.

[0022] The wafer 1 to be cut by the cutting device 2 is carried into the cutting device 2 in a state where it is integrated with, for example, an annular frame (not shown) having an opening with a diameter larger than that of the wafer 1 and tape attached to the annular frame so as to close the opening of the annular frame. When a frame unit is formed by integrating the wafer 1, the tape, and the annular frame by attaching tape to the surface side of the wafer 1, the wafer 1 can be handled via the annular frame, making it easier to handle the wafer 1.

[0023] The cutting device 2 includes a base 4 that supports each of the components. An opening 4a is formed in the front corner of the base 4, and within this opening 4a is provided a cassette support table 8 that is raised and lowered by a lifting mechanism (not shown). Cassettes 10, each of which contains a plurality of wafers 1 that are part of a frame unit, are mounted on the upper surface of the cassette support table 8. For ease of explanation, only the outline of the cassette 10 is shown in FIG. 1.

[0024] A rectangular opening 4b is formed on the side of the cassette support base 8 so that its longitudinal direction is along the X-axis direction (front-rear direction, processing feed direction). A ball screw type X-axis movement mechanism (not shown), a table cover 14 that covers the top of the X-axis movement mechanism, and a dustproof and drip-proof cover 16 are arranged inside opening 4b. The X-axis movement mechanism has 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.

[0025] A holding table 18 is disposed 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 the wafer 1 placed on the holding surface 18a exposed upward. The holding table 18 is connected to a rotation 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).

[0026] The holding table 18 includes a porous member 18c having the same diameter as the wafer 1, and a frame that covers the porous member 18c. A suction path (not shown) is formed inside the holding table 18, 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 path reaches the porous member 18c.

[0027] 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 the same diameter as the wafer 1 and is formed to be approximately 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 periphery of the holding table 18.

[0028] When the wafer 1 is held by 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, the suction source and the porous member 18c are connected via the suction path, and a negative pressure is applied to the wafer 1 via the tape attached to the back surface 1b of the wafer 1.

[0029] The cutting device 2 is provided with a transport unit (not shown) in an area adjacent to the opening 4b that transports the wafer 1 to the holding table 18 or the like. A temporary placement mechanism for temporarily placing the wafer 1 is provided in a position close to the side of the cassette support table 8. The temporary placement mechanism includes, for example, a pair of guide rails 12 that move toward and away from each other while maintaining a state parallel to the Y-axis direction (indexing feed direction). The pair of guide rails 12 sandwich the wafer 1 pulled out of the cassette 10 by the transport unit along the X-axis direction and align it to a predetermined position.

[0030] The wafer 1 aligned in a predetermined position is lifted up by the transport unit and transported to the holding table 18. At this time, the pair of guide rails 12 are moved away from each other, and the wafer 1 is passed between the pair of guide rails 12.

[0031] A first cutting unit 24a and a second cutting unit 24b that use an annular cutting blade to cut the wafer 1 are provided above the holding table 18. A gate-shaped support structure 20 for supporting the first cutting unit 24a and the second cutting unit 24b is disposed on the upper surface of the base 4 so as to straddle the opening 4b.

[0032] A first moving unit 22a that moves the first cutting unit 24a in the Y-axis and Z-axis directions, and a second moving unit 22b that moves the second cutting unit 24b in the Y-axis and Z-axis directions are provided on the upper front surface of the support structure 20. The first moving unit 22a includes a Y-axis moving plate 28a, and the second moving unit 22b includes a Y-axis moving plate 28b. The two Y-axis moving plates 28a, 28b are slidably mounted on a pair of Y-axis guide rails 26 that are arranged on the front surface of the support structure 20 along the Y-axis direction.

[0033] A nut portion (not shown) is provided on the back surface (rear surface) of Y-axis moving plate 28a, and a Y-axis ball screw 30a that is generally parallel to Y-axis guide rail 26 is screwed into this nut portion. In addition, a nut portion (not shown) is provided on the back surface (rear surface) of Y-axis moving plate 28b, and a Y-axis ball screw 30b that is generally parallel to Y-axis guide rail 26 is screwed into this nut portion.

[0034] A Y-axis pulse motor 32a is coupled to one end of the Y-axis ball screw 30a. When the Y-axis pulse motor 32a rotates the Y-axis ball screw 30a, the Y-axis moving plate 28a moves in the Y-axis direction along the Y-axis guide rail 26. Furthermore, a Y-axis pulse motor (not shown) is coupled to one end of the Y-axis ball screw 30b. When the Y-axis pulse motor rotates the Y-axis ball screw 30b, the Y-axis moving plate 28b moves in the Y-axis direction along the Y-axis guide rail 26.

[0035] A pair of Z-axis guide rails 34a are provided along the Z-axis direction on the surface (front surface) side of Y-axis moving plate 28a, and a pair of Z-axis guide rails 34b are provided along the Z-axis direction on the surface (front surface) side of Y-axis moving plate 28b. Furthermore, a Z-axis moving plate 36a is slidably attached to the pair of Z-axis guide rails 34a, and a Z-axis moving plate 36b is slidably attached to the pair of Z-axis guide rails 34b.

[0036] A nut (not shown) is provided on the back side (rear side) of Z-axis moving plate 36a, and Z-axis ball screw 38a, which is provided in a direction generally parallel to Z-axis guide rail 34a, is threadedly engaged with this nut. Z-axis pulse motor 40a is connected to one end of Z-axis ball screw 38a, and by rotating Z-axis ball screw 38a with Z-axis pulse motor 40a, Z-axis moving plate 36a moves in the Z-axis direction along Z-axis guide rail 34a.

[0037] A nut (not shown) is provided on the back side (rear side) of Z-axis moving plate 36b, and Z-axis ball screw 38b, which is provided in a direction generally parallel to Z-axis guide rail 34b, is threadedly engaged with this nut. Z-axis pulse motor 40b is connected to one end of Z-axis ball screw 38b, and by rotating Z-axis ball screw 38b with Z-axis pulse motor 40b, Z-axis moving plate 36b moves in the Z-axis direction along Z-axis guide rail 34b.

[0038] A first cutting unit 24a is provided below the Z-axis moving plate 36a. A camera unit 46a is provided adjacent to the first cutting unit 24a to photograph the wafer 1 held by suction on the holding table 18. A second cutting unit 24b is provided below the Z-axis moving plate 36b. A camera unit 46b is provided adjacent to the second cutting unit 24b to photograph the wafer 1 held by suction on the holding table 18.

[0039] The first moving unit 22a controls the positions of the first cutting unit 24a and the camera unit 46a in the Y-axis and Z-axis directions, and the second moving unit 22b controls the positions of the second cutting unit 24b and the camera unit 46b in the Y-axis and Z-axis directions. The positions of the first cutting unit 24a and the second cutting unit 24b are controlled independently.

[0040] An opening 4c is formed at a position opposite the opening 4b from the opening 4a. A cleaning unit 48 for cleaning the wafer 1 is disposed within the opening 4c, and the wafer 1 cut on the holding table 18 is cleaned by the cleaning unit 48. The wafer 1 cleaned by the cleaning unit 48 is stored back into the cassette 10. Each of the cutting units 24a and 24b will be described in more detail below.

[0041] 3 is a cross-sectional view schematically showing the wafer 1 being cut by the first cutting unit 24a. The first cutting unit 24a is used for trimming, which cuts the wafer 1 along the outer periphery 1c to remove a portion of the chamfered portion. Note that FIG. 3 does not include the clamp 18b of the holding table 18, the camera unit 46a, the annular frame, tape, etc.

[0042] The first cutting unit 24a includes a spindle 50a extending in the Y-axis direction and a rotation drive source (not shown) such as a motor connected to the base end of the spindle 50a. A circular first cutting blade 56a is fixed to the tip of the spindle 50a via a flange mechanism 52a.

[0043] The first cutting blade 56a is a cutting blade called a hub type, which has an annular base 58a made of a material such as aluminum and having a through-hole in the center, and a grinding stone portion 60a fixed to the outer periphery of the base 58a. However, the first cutting blade 56a is not limited to the hub type.

[0044] A grinding wheel 60a is fixed to the outer periphery of the base 58a. The grinding wheel 60a includes countless abrasive grains and a bonding material (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 bonding material is a nickel-plated layer, a resin bond, a vitrified bond, a metal bond, or the like. The thickness of the first cutting blade 56a used in the edge trimming process is determined, for example, according to the width of the terrace portion formed on the wafer 1. However, the method for determining the blade thickness is not limited to this. The blade thickness of the first cutting blade 56a is preferably, for example, 2 mm or more. However, the blade thickness is not limited to this.

[0045] The boss (not shown) of the flange mechanism 52a, which protrudes in the Y-axis direction, is inserted into the insertion hole of the base 58a, the first cutting blade 56a is brought into contact with the flange surface of the flange mechanism 52a, and the fixing nut 54a is tightened onto the tip of the boss. This fixes the first cutting blade 56a to the tip of the spindle 50a. The first cutting unit 24a also includes a pair of cutting fluid supply nozzles 62a arranged to sandwich the lower part of the first cutting blade 56a fixed to the tip of the spindle 50a.

[0046] When the rotation drive source is operated to rotate the spindle 50a, the first cutting blade 56a can be rotated, and the rotating first cutting blade 56a can be made to cut into the wafer 1 held by suction on the holding table 18, thereby cutting the wafer 1. At this time, cutting fluid such as pure water is sprayed from the cutting fluid supply nozzle 62a onto the wafer 1 and the first cutting blade 56a, and the cutting fluid removes processing chips and frictional heat generated by cutting.

[0047] FIG. 4 is a cross-sectional view schematically showing the wafer 1 being cut by the second cutting unit 24b. Note that FIG. 4 omits the clamp 18b of the holding table 18, the camera unit 46b, the annular frame, the tape, and the like. FIG. 5 is an exploded perspective view schematically showing the second cutting unit 24b, and FIG. 6 is a cross-sectional view schematically showing the second cutting unit 24b. The second cutting unit 24b is used to cut the wafer 1 along the outer periphery to form an annular cutting groove in the outer periphery excess region 9.

[0048] The second cutting unit 24b includes a spindle 50b extending in the Y-axis direction and a housing 51b that rotatably accommodates the base end of the spindle 50b. A rotational drive source (not shown), such as a motor, connected to the base end of the spindle 50b is accommodated inside the housing 51b. A circular second cutting blade 56b is fixed to the tip of the spindle 50b via a flange mechanism 52b. The second cutting unit 24b includes a pair of cutting fluid supply nozzles 62b that are disposed so as to sandwich the lower portion of the second cutting blade 56b fixed to the tip of the spindle 50b.

[0049] The second cutting blade 56b is a so-called washer-type cutting blade that consists of a grinding stone portion and does not have an annular base. However, the second cutting blade 56b is not limited to a washer-type. The grinding stone portion includes countless abrasive grains such as diamond and a binder that disperses and fixes the abrasive grains. For example, the abrasive grains are made of diamond, cubic boron nitride, or the like, and the binder is made of metal, ceramics, resin, or the like.

[0050] The blade thickness of the second cutting blade 56b used to form the annular cutting groove in the outer peripheral excess region 9 may be determined in accordance with the width of the annular cutting groove to be formed, and is preferably set to, for example, 300 μm. However, the blade thickness of the second cutting blade 56b is not limited to this.

[0051] The second cutting unit 24b includes an ultrasonic vibration imparting unit that imparts ultrasonic vibrations to the second cutting blade 56b along the radially outward direction thereof. The configuration of the second cutting unit 24b that imparts ultrasonic vibrations to the second cutting blade 56b while rotating it will be further described below.

[0052] 5 is an exploded perspective view showing the second cutting unit 24b. The second cutting blade 56b attached to the second cutting unit 24b has a first surface 57a and a second surface 57b that are generally parallel to each other, and a circular opening 57c is provided in the center of the second cutting blade 56b, penetrating the second cutting blade 56b in the thickness direction.

[0053] The tip (one end) of the spindle 50b is exposed from the housing 51b, and a thread (external thread) 53 is formed on the outer circumferential surface of the tip of the spindle 50b. A rotation drive source (not shown), such as a motor, is connected to the base end (the other end) of the spindle 50b. This rotation drive source rotates the spindle 50b around a rotation axis that is roughly parallel to the Y-axis direction.

[0054] A flange mechanism 52b, to which a second cutting blade 56b is attached, is fixed to the tip of the spindle 50b. The flange mechanism 52b has a rear flange 64 that supports the second cutting blade 56b from the rear side, and a front flange 66 that supports the second cutting blade 56b from the front side.

[0055] The rear flange 64 includes a disk-shaped flange portion 68 and a cylindrical support shaft (boss portion) 70 that protrudes from the center of a surface 68a of the flange portion 68. The flange portion 68 is provided with an opening 64a that penetrates the center of the flange portion 68 and the center of the support shaft 70. In addition, a threaded portion (male thread) 70a is formed on the outer peripheral surface of the tip portion of the support shaft 70.

[0056] The rear flange 64 of the flange mechanism 52b is attached to the spindle 50b so that the tip of the spindle 50b is inserted into the opening 64a. In this state, the annular fixing nut 72 is screwed onto the threaded portion 53 formed on the tip of the spindle 50b and tightened. This fixes the rear flange 64 of the flange mechanism 52b to the tip of the spindle 50b.

[0057] An annular front flange (pressing flange) 66 made of metal or the like is attached to the rear flange 64. The front flange 66 has a first surface (front surface) 66a and a second surface (back surface) 66b (see FIG. 6) that are generally parallel to each other. A circular opening 66c is provided in the center of the front flange 66, penetrating the front flange 66 in the thickness direction.

[0058] When the support shaft 70 of the rear flange 64 is inserted into the opening 57c of the second cutting blade 56b and the opening 66c of the front flange 66, in that order, the second cutting blade 56b and the front flange 66 are attached to the rear flange 64. In this state, when a fixing nut 74 is tightened onto a threaded portion 70a formed on the support shaft 70, the second cutting blade 56b and the front flange 66 are fixed to the flange mechanism 52b. As a result, the second cutting blade 56b is sandwiched between the rear flange 64 and the front flange 66 and fixed to the tip of the spindle 50b.

[0059] With the second cutting blade 56b attached to the tip of the spindle 50b, when the spindle 50b is rotated by a rotary drive source connected to the spindle 50b, the second cutting blade 56b rotates at a predetermined number of rotations around a rotation axis roughly parallel to the Y-axis direction.

[0060] 6 is a cross-sectional view showing the second cutting unit 24b equipped with the second cutting blade 56b. An annular protrusion 68b protruding from a surface 68a is provided along the outer periphery of the flange portion 68 of the rear flange 64. A plurality of through holes (slits) 68c penetrating the flange portion 68 in the thickness direction are provided in the region inside the protrusion 68b of the flange portion 68. For example, four arc-shaped through holes 68c are formed in the flange portion 68 at approximately equal intervals along the circumferential direction of the flange portion 68 (see FIG. 5).

[0061] Meanwhile, an annular protrusion 66d protruding from the second surface 66b is provided along the outer periphery of the front flange 66. Furthermore, a plurality of through holes (slits) 66e penetrating the front flange 66 in the thickness direction are provided in the region inside the protrusion 66d of the front flange 66. For example, four arc-shaped through holes 66e are formed in the front flange 66 at approximately equal intervals along the circumferential direction of the front flange 66 (see FIG. 5).

[0062] An annular support member 76a that supports the first surface 57a of the second cutting blade 56b is provided on the tip surface of the protruding portion 68b of the flange portion 68. An annular support member 76b that supports the second surface 57b of the second cutting blade 56b is provided on the tip surface of the protruding portion 66d of the front flange 66. The support members 76a and 76b are made of a synthetic resin or the like, and contact the second cutting blade 56b to hold it therebetween. The support members 76a and 76b are preferably made of a material having a hardness of 40 or more as measured by a durometer type D.

[0063] A vibrator 78a is provided inside the protruding portion 68b of the flange portion 68. Furthermore, a vibrator 78b is provided inside the protruding portion 66d of the front flange 66. For example, the vibrators 78a and 78b are fixed to the rear flange 64 and the front flange 66, respectively, with an adhesive. The vibrators 78a and 78b constitute a vibration imparting unit 78 that vibrates the second cutting blade 56b at a frequency that belongs to the ultrasonic band.

[0064] When the second cutting blade 56b and the front flange 66 are attached to the rear flange 64, the second cutting blade 56b is sandwiched and fixed between the support members 76a and 76b. The second cutting blade 56b is positioned so that the first surface 57a faces the vibrator 78a and the second surface 57b faces the vibrator 78b.

[0065] The vibrator 78a includes an annular piezoelectric element 80a provided along the circumferential direction of the flange portion 68 of the rear flange 64, a pair of electrodes 82a provided to sandwich the piezoelectric element 80a, and an insulator 84a covering the piezoelectric element 80a and the pair of electrodes 82a. Similarly, the vibrator 78b includes an annular piezoelectric element 80b provided along the circumferential direction of the front flange 66, a pair of electrodes 82b provided to sandwich the piezoelectric element 80b, and an insulator 84b covering the piezoelectric element 80b and the pair of electrodes 82b. For example, the piezoelectric elements 80a and 80b are made of piezoelectric ceramics such as barium titanate, lead zirconate titanate, or lithium tantalate.

[0066] Furthermore, wirings 86a and 86b are provided inside flange mechanism 52b. One end of each of wirings 86a and 86b branches into two and is exposed on the side surface of support shaft 70. One electrode 82a of vibrator 78a is connected to wiring 86a via lead wire 88a. The other electrode 82a of vibrator 78a is connected to wiring 86b via lead wire 88b.

[0067] Connection electrodes 90a and 90b exposed at the opening 66c are provided on the front flange 66. One electrode 82b of the vibrator 78b is connected to a wiring 86a via a lead wire 88c and the connection electrode 90a. The other electrode 82b of the vibrator 78b is connected to a wiring 86b via a lead wire 88d and the connection electrode 90b.

[0068] Furthermore, the second cutting unit 24b includes a voltage supply unit 92 that supplies AC voltage to the vibrators 78a and 78b that constitute the vibration imparting unit 78. The voltage supply unit 92 includes a power receiving section (power receiving unit) 94 provided on the back side (housing 51b side) of the rear flange 64, and a power feeding section (power feeding unit) 100 that is disposed on the front side (flange mechanism 52b side) of the housing 51b and faces the power receiving section 94.

[0069] The power receiving unit 94 includes an annular core 96 provided on the rear surface side of the rear flange 64. An annular recess 96a is formed on the front surface side (the power supply unit 100 side) of the core 96, and an annular coil (power receiving coil) 98 is provided inside this recess 96a. One end of the coil 98 is connected to the wiring 86a, and the other end of the coil 98 is connected to the wiring 86b.

[0070] The power supply unit 100 includes an annular core 102. For example, the core 102 is fixed to the surface side of the housing 51b with bolts (not shown). An annular recess 102a is formed on the surface side (the power receiving unit 94 side) of the core 102, and an annular coil (power supply coil) 104 is provided inside this recess 102a. The coil 104 is connected to an AC power supply 108 via wires 106a and 106b. A frequency converter 110 that controls the frequency of the AC voltage supplied from the AC power supply 108 is also connected to the AC power supply 108.

[0071] The power receiving unit 94 and the power supply unit 100 constitute a rotary transformer that transmits the AC voltage supplied from the AC power source 108 to the vibration imparting unit 78. When the wafer 1 is processed by the second cutting blade 56b, the AC voltage is applied to the coil 104 of the power supply unit 100 by the AC power source 108. At this time, the frequency of the AC voltage is controlled by the frequency converter 110.

[0072] The AC voltage applied to the coil 104 is supplied to the pair of electrodes 82a of the vibrator 78a and the pair of electrodes 82b of the vibrator 78b via the coil 98 of the power receiving unit 94, the wiring 86a, 86b, and the lead wires 88a, 88b, 88c, and 88d. This causes the piezoelectric element 80a of the vibrator 78a to vibrate in the radial direction together with the rear flange 64. Furthermore, the piezoelectric element 80b of the vibrator 78b to vibrate in the radial direction together with the front flange 66.

[0073] As a result, the second cutting blade 56b sandwiched between the rear flange 64 and the front flange 66 vibrates in the radial direction of the second cutting blade 56b. The frequency of the AC voltage supplied from the AC power supply 108 is controlled by the frequency converter 110 so that the second cutting blade 56b vibrates at a frequency that belongs to the ultrasonic band.

[0074] Here, a plurality of through holes 68c are provided in the flange portion 68 of the rear flange 64, and a plurality of through holes 66e are provided in the front flange 66 (see FIG. 5). This reduces the rigidity of the flange portion 68 and the front flange 66 in the radial direction, making the flange portion 68 and the front flange 66 more likely to vibrate in the radial direction. As a result, the second cutting blade 56b also more likely to vibrate in the radial direction.

[0075] Next, a grinding device used to thin the wafer 1 in the wafer processing method according to this embodiment will be described. Fig. 8 is a perspective view schematically showing a grinding device 112. An opening 114a is provided in the upper surface of a base 114 of the grinding device 112. An X-axis moving table 118 is provided within the opening 114a, on the upper surface of which a holding table 116 that holds the wafer 1 by suction is placed.

[0076] The X-axis moving table 118 can be moved in the X-axis direction by an X-axis moving mechanism (not shown). The X-axis moving table 118 is positioned between a loading / unloading area 120 where the wafer 1 is loaded / unloaded onto the holding table 116 by the X-axis moving mechanism, and a processing area 122 where the wafer 1 held by suction on the holding table 116 is ground.

[0077] A porous member having an upper surface with the same diameter as the wafer 1 is disposed on the upper surface of the holding table 116, and the upper surface of the porous member serves as holding surface 116a for holding the wafer 1. The holding table 116 has an internal suction path (not shown) with one end connected to the porous member and the other end connected to a suction source (not shown). When the suction source is activated, a negative pressure acts on the wafer 1 placed on holding surface 116a, and the wafer 1 is held by suction on the holding table 116. The holding table 116 can also rotate around an axis perpendicular to holding surface 116a.

[0078] A grinding unit 124 that grinds the wafer 1 is disposed above the processing region 122. A support part 126 is erected on the rear side of the base 114, and this support part 126 supports the grinding unit 124. A pair of Z-axis guide rails 128 extending in the Z-axis direction are provided on the front surface of the support part 126, and a Z-axis moving plate 130 is slidably attached to each Z-axis guide rail 128.

[0079] A nut portion (not shown) is provided on the back surface (rear surface) of Z-axis moving plate 130, and Z-axis ball screw 132, which is parallel to Z-axis guide rail 128, is threadedly engaged with this nut portion. Z-axis pulse motor 134 is connected to one end of Z-axis ball screw 132. When Z-axis pulse motor 134 rotates Z-axis ball screw 132, Z-axis moving plate 130 moves in the Z-axis direction along Z-axis guide rail 128.

[0080] A grinding unit 124 that grinds the wafer 1 is fixed to the lower front side of the Z-axis moving plate 130. When the Z-axis moving plate 130 is moved in the Z-axis direction, the grinding unit 124 moves in the Z-axis direction.

[0081] The grinding unit 124 has a spindle 138 along the Z-axis direction, a housing 136 that rotatably accommodates the upper end of the spindle 138, and a disk-shaped wheel mount 140 fixed to the lower end of the spindle 138. The housing 136 accommodates a rotational drive source such as a motor that is connected to the upper end of the spindle 138 and rotates the spindle 138 about the Z-axis direction.

[0082] An annular grinding wheel 142 is fixed to the underside of the wheel mount 140. On the underside of the grinding wheel 142, a grinding stone 144 is arranged in an annular shape, with abrasive grains made of diamond or the like dispersed and fixed in a binder.

[0083] When the spindle 138 is rotated to rotate the grinding wheel 142, the grinding stone 144 rotates on a circular orbit. Then, the grinding unit 124 is lowered to bring the rotating grinding stone 144 into contact with the surface to be ground of the wafer 1, thereby grinding the wafer 1. The grinding device 112 has a thickness measuring device (not shown) and proceeds with grinding while monitoring the thickness of the wafer 1, and when the thickness of the wafer 1 reaches a predetermined finish thickness, the lowering of the grinding unit 124 is stopped and grinding is completed.

[0084] When the wafer 1 is ground with the grinding wheel 144, processing debris and frictional heat are generated from the wafer 1 and the grinding wheel 144. The grinding device 112 is equipped with a grinding water supply nozzle 146 (see FIG. 10 etc.), and while the wafer 1 is being ground with the grinding wheel 144, grinding water 148 such as pure water is supplied to the wafer 1 etc. from the grinding water supply nozzle 146. The processing debris and frictional heat are removed by the grinding water 148.

[0085] The grinding device 112 has a drain groove 114b in the opening 114a through which used grinding water flows, and the grinding water 148 takes in processing chips and frictional heat before flowing out into the drain groove 114b. A drain outlet 114c is formed in the bottom surface of the drain groove 114b, and the used grinding water that has flowed into the drain groove 114b is discharged from the drain outlet 114c.

[0086] Because a chamfer is formed on the outer periphery 1c of the wafer 1, if the wafer 1 is thinned to the finishing thickness as is, the chamfer will partially remain, creating a knife-edge shape and making the wafer 1 susceptible to damage. Therefore, before grinding the wafer 1 from the back surface 1b side, an edge trimming process is performed in which the outer periphery of the wafer 1 is cut from the front surface 1a side to a depth equal to or greater than the finishing thickness, thereby partially removing the chamfer.

[0087] However, when the wafer 1 is subsequently ground from the back surface 1b side by the grinding device 112 to thin it, scraps remaining on the outer periphery of the wafer 1 break off just before the grinding wheel 144 reaches the terrace portion 13 (see FIG. 7, etc.) formed by the edge trimming process, and relatively large scraps fall. The large scraps that fall accumulate in the drain groove 114b for draining grinding water or clog the drain outlet 114c, so in the past, the drain groove 114b of the grinding device 112 and the like had to be cleaned frequently.

[0088] Therefore, in the wafer processing method according to this embodiment, before grinding the wafer 1 from the back surface 1b side, an annular cut groove with a fractured layer is formed near the terrace portion 13 formed by the edge trimming process. When the wafer 1 is ground from the back surface 1b side in this state, the annular cut groove and fractured layer act as starting points for dividing the terrace portion, resulting in the generation of fine scraps. When the fine scraps fall into the drain groove 114b, they are easily washed away and do not accumulate, making them less likely to clog the drain outlet 114c. This eliminates the need to frequently clean the drain groove 114b.

[0089] The wafer processing method according to this embodiment will be described below. Fig. 12 is a flowchart showing the flow of each step of the wafer processing method according to this embodiment, in which a disk-shaped wafer 1 having a chamfered portion on its outer periphery 1c is ground from the back surface 1b side to thin it to a finish thickness.

[0090] In the wafer processing method according to this embodiment, first, a trimming step S10 is performed in which the wafer 1 is cut along its outer periphery to form an annular terrace portion on the chamfered portion. The trimming step S10 is performed by a cutting device 2 shown in FIG.

[0091] First, a cassette 10 containing a frame unit in which a wafer 1, a tape, and an annular frame are integrated is carried to the cassette support table 8. Then, the wafer 1 (frame unit) is pulled out of the cassette 10 and placed on the holding surface 18a of the holding table 18, and the wafer 1 is suction-held by the holding table 18 via the tape. At this time, the front surface 1a of the wafer 1 is exposed upward.

[0092] The edge trimming process of the wafer 1 is performed by the first cutting unit 24a. Figure 3 is a cross-sectional view that shows a schematic view of the wafer 1 that is edge trimmed. First, the camera unit 46a photographs the wafer 1 to detect the position of the outer periphery 1c of the wafer 1. Then, the positions of the first cutting unit 24a and the holding table 18 are adjusted so that the grinding stone portion 60a of the first cutting blade 56a is positioned above the outer periphery 1c of the wafer 1.

[0093] Next, the spindle 50a is rotated to rotate the first cutting blade 56a, and the first cutting unit 24a is lowered until the bottom end of the grindstone 60a reaches a first depth position 13a (see FIG. 7) that is greater than or equal to the finishing thickness from the surface 1a of the wafer 1. For example, if the thickness of the wafer 1 is 700 μm, the first depth position 13a is preferably about 300 μm below the surface 1a of the wafer 1.

[0094] With the first cutting blade 56a cutting into the chamfered portion from the front surface 1a side of the wafer 1, the holding table 18 is rotated 360° or more around the table rotation axis perpendicular to the holding surface 18a. As a result, the wafer 1 is cut along the outer periphery, the chamfered portion is partially removed, and an annular terrace portion 13 (see FIG. 4, etc.) is formed on the wafer 1.

[0095] Next, in the cutting device 2, a first ultrasonic vibration cutting step S21 is performed in which the second cutting unit 24b cuts the wafer 1 to form a first annular cutting groove. Figure 4 is a cross-sectional view schematically showing the first ultrasonic vibration cutting step S21. In the first ultrasonic vibration cutting step S21, a second cutting blade 56b, which is thinner than the first cutting blade 56a, is inserted from the front surface 1a side into a position where the terrace portion 13 of the wafer 1 is to be formed.

[0096] In the first ultrasonic vibration cutting step S21, first, the positions of the second cutting unit 24b and the holding table 18 are adjusted to position the second cutting blade 56b above a predetermined position on the terrace portion 13. Then, while rotating the second cutting blade 56b, the vibration imparting unit 78 (see FIG. 6) vibrates the second cutting blade 56b in the radial direction of the second cutting blade 56b.

[0097] At this time, the vibration imparting unit 78 vibrates the second cutting blade 56b at a frequency belonging to the ultrasonic band. For example, the vibration frequency of the second cutting blade 56b is set to 20 kHz or higher. When the vibration imparting unit 78 imparts vibration to the second cutting blade 56b, the second cutting blade 56b vibrates so that its diameter increases or decreases. The amount of fluctuation in the diameter of the second cutting blade 56b (the difference between the maximum and minimum diameters) is, for example, about 5 μm.

[0098] In this state, the second cutting unit 24b is lowered until the lower end of the second cutting blade 56b reaches a second depth position 17a (see FIG. 7) that is deeper than the first depth position 13a from the surface 1a of the wafer 1. For example, the second depth position 17a is preferably about 500 μm below the surface 1a of the wafer 1.

[0099] With the second cutting blade 56b cutting into the terrace portion 13 from the front surface 1a side of the wafer 1, the holding table 18 is rotated 360° or more around the table rotation axis perpendicular to the holding surface 18a. As a result, the wafer 1 is cut along the outer periphery, and a first annular cutting groove 15a is formed in the annular terrace portion 13.

[0100] At this time, the vibration of the second cutting blade 56b at a frequency belonging to the ultrasonic band (ultrasonic vibration) causes the abrasive grains exposed from the lower end of the second cutting blade 56b to collide with the wafer 1 at a period corresponding to the ultrasonic vibration, which causes the wafer 1 to fracture, forming a fractured layer (not shown) around the first annular cutting groove 15a.

[0101] In the wafer processing method according to this embodiment, it is preferable to form an additional annular cut groove by the second cutting blade 56b in addition to the first annular cut groove 15a in the terrace portion 13 formed on the outer periphery 1c of the wafer 1. Next, a second ultrasonic vibration cutting step S22 for forming the second annular cut groove 15b (see FIG. 7) will be described.

[0102] In the second ultrasonic vibration cutting step S22, first, the position of the second cutting unit 24b in the Y direction is adjusted to position the second cutting blade 56b above a predetermined position radially outward of the wafer 1 relative to the first annular cutting groove 15a formed in the terrace portion 13. Then, similar to the first ultrasonic vibration cutting step S21, the second cutting blade 56b is rotated while the vibration imparting unit 78 (see FIG. 6) vibrates the second cutting blade 56b in the radial direction of the second cutting blade 56b.

[0103] In this state, the second cutting unit 24b is lowered until the lower end of the second cutting blade 56b reaches a third depth position 17b (see FIG. 7), which is deeper from the surface 1a of the wafer 1 than the second depth position 17a. That is, the second depth position 17a is closer to the surface 1a than the third depth position 17b. For example, the third depth position 17b is preferably about 550 μm below the surface 1a of the wafer 1.

[0104] With the second cutting blade 56b cutting into the terrace portion 13 from the front surface 1a side of the wafer 1, the holding table 18 is rotated 360° or more around the table rotation axis perpendicular to the holding surface 18a. As a result, the wafer 1 is cut along the outer periphery, and a second annular cut groove 15b is formed in the annular terrace portion 13. At this time, the wafer 1 is also fractured around the second annular cut groove 15b, and a fractured layer (not shown) is formed around the first annular cut groove 15a.

[0105] The annular cut groove may further be formed in the terrace portion 13 of the wafer 1. Fig. 7 is an enlarged cross-sectional view schematically showing the vicinity of the outer periphery 1c of the wafer 1 in which a first annular cut groove 15a, a second annular cut groove 15b, and a third annular cut groove 15c are formed in the terrace portion 13.

[0106] Here, as an example, the third annular cut groove 15c is formed so that its lower end reaches a fourth depth position 17c that is deeper from the surface 1a of the wafer 1 than the third depth position 17b at which the lower end of the second annular cut groove 15b is located. For example, the fourth depth position 17c is preferably located about 600 μm below the surface 1a of the wafer 1. However, the depth position of the lower end of the third annular cut groove 15c is not limited to this.

[0107] Since each annular cut groove is formed by rotating the holding table 18 at the same position, the first annular cut groove 15a, the second annular cut groove 15b, and the third annular cut groove 15c are formed concentrically around the rotation axis of the holding table 18. When a plurality of annular cut grooves 15a, 15b, and 15c are formed in the terrace portion 13 formed on the outer periphery 1c of the wafer 1 in this manner, it is preferable that the outermost annular cut grooves have their lower ends reach deeper positions.

[0108] In addition, up to this point, the first cutting blade 56a used in edge trimming is a hub-type cutting blade, and the second cutting blade 56b used in cutting with ultrasonic vibration is a washer-type cutting blade. However, the first cutting blade 56a and the second cutting blade 56b are not limited to this.

[0109] That is, a washer-type first cutting blade 56a may be used in the trimming step S10. Also, a hub-type second cutting blade 56b may be used in the first ultrasonic vibration cutting step S21 and the second ultrasonic vibration cutting step S22. When the second cutting blade 56b is a hub-type, for example, a vibration imparting unit is incorporated into a base supporting the grinding wheel portion.

[0110] After the trimming step S10, the first ultrasonic vibration cutting step S21, and the second ultrasonic vibration cutting step S22, a protective member attachment step S30 is performed in which a protective member is attached to the front surface 1a of the wafer 1 in preparation for grinding the wafer 1. Fig. 9 is a cross-sectional view schematically showing the wafer 1 placed on the holding table 116 of the grinding device 112 with the protective member 17 attached to the front surface 1a and the back surface 1b facing upward.

[0111] The protective member 17 is a disk-shaped member having the same diameter as the wafer 1, and is made of a material such as resin. When the protective member 17 is attached to the front surface 1a of the wafer 1, the front surface 1a does not come into direct contact with the holding table 116 when the wafer 1 is ground from the back surface 1b side. Therefore, the front surface 1a of the wafer 1 is not damaged. The wafer 1 with the protective member 17 attached to its front surface 1a side is placed on the holding table 116 and held by suction to the holding table 116.

[0112] After the protective member attaching step S30, a grinding step S40 is performed in which the wafer 1 is ground from the back surface 1b to thin it down to a finish thickness. Fig. 10 is a cross-sectional view showing a schematic early stage of the grinding step S40, and Fig. 11 is a cross-sectional view showing a schematic final stage of the grinding step S40.

[0113] When grinding the wafer 1, the holding table 116 that holds the wafer 1 by suction is moved to the processing area 122 (see FIG. 8), and the rotation of the spindle 138 and the rotation of the holding table 116 are started. Then, while supplying grinding water 148 to the wafer 1 from the grinding water supply nozzle 146, the grinding unit 124 is lowered, and the grinding wheel 144 moving on the circular orbit is brought into contact with the back surface 1b of the wafer 1, and grinding of the wafer 1 is started.

[0114] When the wafer 1 is ground from the back surface 1b side, the thickness of the wafer 1 gradually decreases, and the deepest third annular cut groove 15c is first exposed on the back surface 1b side. At this time, the wafer 1 is divided by the third annular cut groove 15c, generating scraps, which are then crushed starting from a fracture layer formed around the third annular cut groove 15c.

[0115] As grinding continues, the next deepest second annular cut groove 15b is exposed on the back surface 1b side. At this time, the wafer 1 is divided at the second annular cut groove 15b, generating scraps, and the scraps are crushed starting from the fracture layer formed around the second annular cut groove 15b. As grinding continues, the next deepest first annular cut groove 15a is exposed on the back surface 1b side. At this time, the wafer 1 is divided at the first annular cut groove 15a, generating scraps, and the scraps are crushed starting from the fracture layer formed around the first annular cut groove 15a.

[0116] 11, the grinding unit 124 is lowered until the wafer 1 has a finishing thickness, thereby completing the grinding of the wafer 1. Then, the grinding unit 124 is raised to return the holding table 116 to the carry-in / out area 120, and the suction holding of the wafer 1 by the holding table 116 is released, and the wafer 1 is carried out of the grinding device 112.

[0117] As described above, in the wafer processing method according to this embodiment, when the wafer 1 is thinned and the grinding wheel 144 reaches the terrace portion 13, the annular cutting groove and the crushed layer become the starting points for division, and the vicinity of the outer periphery 1c of the wafer 1 is subdivided. The subdivided scraps are easily washed away when they fall into the drainage groove 114b and are not likely to accumulate in the drainage groove 114b, so there is no need to clean the drainage groove 114b frequently.

[0118] If the depth relationship of the annular cutting grooves 15a, 15b, and 15c were reversed, the annular cutting groove exposed on the back surface 1b would first cut away the portion outside the annular cutting groove. However, since the portion cut away is before it is subdivided, the resulting scrap material would be relatively large. Therefore, it is preferable that the depth relationship is not reversed. However, even if the depth relationship is reversed, the resulting scrap material would be smaller than when no annular cutting grooves are formed at all, making it less likely to accumulate in the drain groove 114b. [Example]

[0119] Next, an example will be described in which edge trimming was performed on a disk-shaped wafer 1 having a chamfered portion on the outer periphery 1c, two annular cutting grooves 15a, 15b were formed in the formed terrace portion 13, and the wafer 1 was ground from the back surface 1b side, and the resulting scrap material was collected and observed. In the wafer processing method according to this example, the two annular cutting grooves 15a, 15b were formed using a second cutting blade 56b to which ultrasonic vibrations were applied.

[0120] First, multiple silicon wafers with a thickness of 700 μm and a diameter of 8 inches were prepared as wafers 1. No devices 5 were formed on the surfaces 1a of these wafers 1. These wafers 1 were loaded into a cutting device 2 and processed one by one according to the procedure described below. The cutting device 2 used for edge trimming of the wafers 1 was a "DFD6361" manufactured by Disco Corporation. First, the wafers 1 were loaded onto a holding table 18 and held by the holding table 18 under suction.

[0121] Then, a washer-type first cutting blade 56a manufactured by Disco Corporation and having a blade thickness of 2 mm or more was used to cut along the outer periphery 1c of the wafer 1. At this time, a region 2 mm wide from the outer periphery 1c of the wafer 1 and 300 μm deep from the surface 1a was removed, forming a terrace portion 13 along the outer periphery 1c on the wafer 1. At this time, the rotation speed of the first cutting blade 56a was set to 30,000 rpm, the rotation speed of the holding table 18 was set to 1 degree per second, and the holding table 18 was rotated 370 degrees.

[0122] Next, the wafer 1 was loaded into a "DAD3350" ultrasonic vibration cutting machine manufactured by Disco Corporation. Then, a hub-type second cutting blade 56b, "U09RA-SDC600-BB200-50" manufactured by Disco Corporation with a blade thickness of 300 μm, was used to cut the terrace portion 13 along the outer periphery 1c, forming a first annular cutting groove 15a in the wafer 1. At this time, the first annular cutting groove 15a was formed so as to be 500 μm away from the outer periphery 1c of the wafer 1, and the second cutting blade 56b was cut to a height position 550 μm lower than the surface 1a of the wafer 1.

[0123] At this time, the rotation speed of the second cutting blade 56b was set to 30,000 rpm, the rotation speed of the holding table 18 was set to 1 degree per second, and the holding table 18 was rotated 370 degrees. At this time, ultrasonic vibrations with a radial amplitude of 5 μm and a frequency of 41 kHz were applied to the second cutting blade 56b.

[0124] Furthermore, the second cutting blade 56b was used to cut the terrace portion 13 along the outer periphery 1c, forming a second annular cut groove 15b in the wafer 1. At this time, the second annular cut groove 15b was formed radially inward of the first annular cut groove 15a so that the distance from the first annular cut groove 15a was 500 μm. At this time, the second cutting blade 56b was cut into the wafer 1 to a height position 500 μm lower than the surface 1a of the wafer 1.

[0125] At this time, the rotation speed of the second cutting blade 56b was set to 30,000 rpm, the rotation speed of the holding table 18 was set to 1 degree per second, and the holding table 18 was rotated 370 degrees. Also at this time, ultrasonic vibrations with a radial amplitude of 5 μm and a frequency of 41 kHz were applied to the second cutting blade 56b.

[0126] Next, the wafer 1 having the terrace portion 13, the first annular cut groove 15a, and the second annular cut groove 15b formed thereon was loaded into a grinding machine 112 as shown in FIG. 8 and other figures, and ground according to the following procedure. In the wafer processing method according to this example, the attachment of a protective member to the front surface 1a of the wafer 1 was omitted. The grinding machine 112 used to grind the wafer 1 was a "DAG810" manufactured by Disco Corporation. First, the wafer 1 was loaded onto a holding table 116 with the back surface 1b facing upward, and was held by suction on the holding table 116.

[0127] The wafer 1 was ground from the back surface 1b side using a grinding wheel manufactured by Disco Corporation as the grinding wheel 142 equipped with the grinding stone 144. At this time, the rotation speed of the holding table 116 was set to 300 rpm, the rotation speed of the spindle 138 was set to 3500 rpm, and the lowering speed of the grinding unit 124 was set to 0.7 μm per second. The finished thickness of the wafer 1 was set to 300 μm, and the grinding unit 124 was lowered until the thickness of the wafer 1 reached the finished thickness.

[0128] When the wafer 1 is ground by the grinding device 112, scraps are generated from the wafer 1 and fall into the drainage groove 114b. In this example, after grinding of the wafer 1 was completed, the scraps that had fallen into the drainage groove 114b were collected and observed, and their sizes were measured.

[0129] For comparison, two annular cut grooves 15a, 15b were formed with the second cutting blade 56b without applying ultrasonic vibration to a terrace portion 13 similarly formed on another wafer 1 by edge trimming, and the wafer 1 was ground from the back surface 1b side, and the resulting scrap material was observed. The only difference between the wafer processing method according to the example and the wafer processing method according to the comparative example is whether or not ultrasonic vibration was applied to the second cutting blade 56b when forming the two annular cut grooves 15a, 15b.

[0130] Figure 13 is a photograph of the collected scraps placed on a mesh fabric. The left side of the photograph shows three of the scraps 19a collected when the wafer processing method of the example is carried out. The right side of the photograph shows one of the scraps 19b collected when the wafer processing method of the comparative example is carried out. As is clear from the photograph shown in Figure 13, scrap 19a is significantly smaller than scrap 19b.

[0131] More specifically, when the sizes of the recovered scraps 19a and 19b were measured, it was confirmed that the average width of scrap 19a was approximately 75% smaller than that of scrap 19b. This is thought to be because, when ultrasonic vibrations were applied to second cutting blade 56b to form annular cutting grooves 15a and 15b, a fractured layer was formed at the bottom of the annular cutting grooves 15a and 15b. It is thought that, when wafer 1 was ground from the back surface 1b side, this fractured layer became the starting point for division, causing wafer 1 to be subdivided near terrace portion 13.

[0132] 13, scrap 19a is smaller than scrap 19b not only in width but also in length. This suggests that the fractured layer formed on wafer 1 promotes fragmentation of wafer 1 in the length direction. The above-described examples and comparative examples confirmed that forming annular cutting grooves 15a, 15b with second cutting blade 56b to which ultrasonic vibrations are applied results in fragmented small scraps being produced when wafer 1 is finally ground.

[0133] The present invention is not limited to the above-described embodiment and can be implemented with various modifications. For example, in the above-described embodiment, three annular grooves 15a, 15b, and 15c are formed in the terrace portion 13 of the wafer 1, but the wafer processing method according to one aspect of the present invention is not limited to this. Only the first annular groove 15a may be formed in the terrace portion 13, and the second ultrasonic vibration cutting step S22 may not be performed. Even in this case, the amount of scrap generated during grinding of the wafer 1 is smaller than in the conventional method.

[0134] In the above embodiment, the first ultrasonic vibration cutting step S21 is performed after the trimming step S10, but this aspect of the present invention is not limited to this. That is, the first ultrasonic vibration cutting step S21 and the like may be performed first to form one or more annular cut grooves 15a, 15b, 15c near the outer periphery 1c of the wafer 1, and then the trimming step S10 may be performed to form the terrace portion 13.

[0135] Even in this case, the annular cutting grooves 15a, 15b, and 15c are formed in the terrace portion 13 before the grinding step S40 is performed, thereby reducing the amount of scrap material generated in the grinding step S40. Before the terrace portion 13 is formed, the outer periphery 1c of the wafer 1 can be easily detected by the camera unit 46b disposed near the second cutting unit 24b.

[0136] However, when forming the annular cutting grooves 15a, 15b, 15c without forming the terrace portion 13, the second cutting blade 56b must be cut deep into the wafer 1 from the surface 1a, which requires a second cutting blade 56b with a long cutting edge.

[0137] The structures, methods, etc. according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of symbols]

[0138] 1 wafer 1a surface 1b back side 1c outer circumference 3 Planned division line 5 Devices 7 Device Area 9 Surplus outer area 13 Terrace 13a, 17a, 17b, 17c depth position 15a, 15b, 15c Circular cutting groove 17 Protective materials 19a, 19b Scrap wood 2 Cutting equipment 4 Foundation 4a,4b,4c opening 8 Cassette support stand 10 cassettes 12 Guide rail 14 Table Cover 16 Dustproof and water-resistant cover 18 Holding table 18a Holding surface 18b Clamp 18c Porous material 20 Support structure 22a, 22b Mobile unit 24a, 24b Cutting unit 26, 34a, 34b Guide rails 28a, 28b, 36a, 36b Moving plates 30a, 30b, 38a, 38b ball screws 32a, 40a, 40b Pulse motor 46a, 46b Camera unit 48 Cleaning Unit 50a,50b spindle 51b Housing 52a, 52b flange mechanism 53 Threaded section 54a Fixing nut 56a, 56b Cutting blade 57a 1st page 57b 2nd side 57c aperture 58a base 60a Grindstone section 62a, 62b Cutting fluid supply nozzle 64 Rear flange 64a aperture 66 Front flange 66a 1st page 66b 2nd side 66c aperture 66d Convex part 66e through hole 68 Flange 68a surface 68b Convex part 68c through hole 70 Support shaft 70a threaded part 72,74 Fixing nut 76a, 76b Support members 78 Vibration unit 78a,78b Oscillator 80a, 80b Piezoelectric body 82a,82b electrode 84a, 84b Insulator 86a, 86b wiring 88a, 88b, 88c, 88d lead wires 90a, 90b Connection electrodes 92 Voltage Supply Unit 94 Power receiving unit 96,102 cores 96a, 102a Recess 98,104 coils 100 Power supply unit 106a, 106b wiring 108 AC power supply 110 Frequency Converter 112 Grinding equipment 114 Foundation 114a aperture 114b Drain 114c Drain 116 Holding table 116a Holding surface 118 X-axis moving table 120 Loading / unloading area 122 Processing area 124 Grinding Unit 126 Support part 128 Z-axis guide rail 130 Z-axis moving plate 132 Z-axis ball screw 134 Z-axis pulse motor 136 Housing 138 Spindle 140 Wheel Mount 142 Grinding Wheel 144 Grinding Wheel 146 Grinding water supply nozzle 148 Grinding water

Claims

1. A wafer processing method for thinning a disk-shaped wafer having a chamfered outer periphery to a finish thickness by grinding the wafer from its back surface, comprising the steps of: a trimming step in which a first cutting blade is inserted into the chamfered portion from the front surface side of the wafer to a first depth position that is equal to or greater than the finishing thickness, thereby cutting the wafer along the outer periphery, thereby forming an annular terrace portion; a protective member attaching step of attaching a protective member to the front surface side of the wafer after the trimming step; a grinding step of grinding the wafer from the back surface to thin it to the finished thickness after the protective member attaching step, The wafer processing method further comprises a first ultrasonic vibration cutting step, before carrying out the grinding step, in which ultrasonic vibrations are applied to a second cutting blade having a blade thickness thinner than that of the first cutting blade, and the second cutting blade is caused to cut into the terrace portion from the surface side of the wafer along the outer peripheral edge to a second depth position whose depth from the surface exceeds the first depth position, thereby forming a first annular cutting groove in the terrace portion (except when the first annular cutting groove is formed on the inner peripheral edge of the terrace portion).

2. A wafer processing method for thinning a disk-shaped wafer having a chamfered outer periphery to a finish thickness by grinding the wafer from the backside, comprising: a trimming step in which a first cutting blade is inserted into the chamfered portion from the front surface side of the wafer to a first depth position that is equal to or greater than the finishing thickness, thereby cutting the wafer along the outer periphery, thereby forming an annular terrace portion; a protective member attaching step of attaching a protective member to the front surface side of the wafer after the trimming step; a grinding step of grinding the wafer from the back surface to thin it to the finished thickness after the protective member attaching step, a first ultrasonic vibration cutting step of, before the grinding step, applying ultrasonic vibration to a second cutting blade having a blade thickness thinner than that of the first cutting blade, cutting the second cutting blade into the terrace portion from the front surface side of the wafer along the outer peripheral edge to a second depth position whose depth from the surface exceeds the first depth position, thereby forming a first annular cutting groove in the terrace portion; a second ultrasonic vibration cutting step of, before the grinding step, cutting the second cutting blade into the terrace portion from the front surface side of the wafer along the outer circumferential edge to a third depth position whose depth from the front surface exceeds the first depth position while applying ultrasonic vibration to the second cutting blade, thereby forming a second annular cutting groove in the terrace portion; A wafer processing method, wherein the first annular cutting groove and the second annular cutting groove are formed concentrically.

3. The first annular cutting groove is formed more inward than the second annular cutting groove, 3. The wafer processing method according to claim 2, wherein the second depth position is closer to the surface than the third depth position.

4. 4. The wafer processing method according to claim 1, wherein the first ultrasonic vibration cutting step is performed after the trimming step.

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