Wafer cutting method

Abstract

To provide a cutting method of a wafer, with which a wafer having a recessed part can be properly cut.SOLUTION: There is provided a cutting method of a wafer for cutting a wafer that includes a circular recessed part at a central part and also includes an annular projection part surrounding the recessed part at an outer circumferential part. The cutting method of a wafer includes: a tape sticking step of sticking an adhesive tape along the recessed part and the projection part; a holding step of sucking the adhesive tape stuck to the recessed part by a holding surface of a chuck table that has the holding surface with a smaller diameter than the recessed part, to hold the wafer by the chuck table via the adhesive tape; and a cutting step of separating the recessed part and the projection part by making a rotating cutting blade cut into the wafer in such a manner that the cutting blade reaches the adhesive tape stuck to the recessed part and rotating the chuck table, in a state in which the projection part is not fixed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for cutting a wafer. [Background technology]

[0002] In the device chip manufacturing process, a wafer is used that has a surface side with device regions, each of which has a device formed in a plurality of regions partitioned by a plurality of streets (planned division lines) arranged in a grid pattern. By dividing this wafer along the streets, a plurality of device chips, each of which has a device, are obtained. The device chips are mounted on various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, there is a demand for thinner device chips. Therefore, a process for thinning a wafer is sometimes performed before the wafer is divided. For example, a grinding device is used for thinning the wafer. The grinding device includes a chuck table for holding the workpiece and a grinding unit for grinding the workpiece, and a grinding wheel including a grinding stone is attached to the grinding unit. The grinding device grinds and thins the wafer by contacting the grinding stone with the back side of the wafer held by the chuck table.

[0004] When a wafer is thinned by grinding, its rigidity decreases, making it difficult to handle (transport, hold, etc.) afterwards. To address this issue, a method has been proposed in which only the area of ​​the back side of the wafer that overlaps with the device area is ground to thin it. When this method is used, a recess is formed in the center of the wafer, while the outer periphery of the wafer is not thinned and remains thick, remaining as an annular protrusion. As a result, the outer periphery (protrusion) of the wafer functions as a reinforcing part, and the loss of rigidity of the wafer after grinding is suppressed.

[0005] The thinned wafer is finally divided into a number of device chips. At that time, the annular convex portion remaining on the outer periphery of the wafer is removed in advance so as not to hinder the division. To remove the convex portion of the wafer, for example, a cutting device that cuts the workpiece with an annular cutting blade is used. By cutting the wafer into an annular shape with the cutting blade, the center (concave portion) and the outer periphery (convex portion) of the wafer are separated.

[0006] When a wafer having a recess is processed by a cutting device, the wafer is held by a dedicated chuck table mounted on the cutting device. Patent Document 1 discloses a chuck table having a raised portion (convex portion) that fits into the recess of the wafer. When the wafer is placed on this chuck table, the recess of the wafer is supported by the raised portion, and the outer periphery of the wafer is supported by spacers provided around the raised portion. This allows the wafer to be held by the chuck table in a flat state. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-98248 A Summary of the Invention [Problem to be solved by the invention]

[0008] In general, in order to properly process a wafer having a recessed portion using a cutting device, it is considered essential to hold the entire wafer on a chuck table. Typically, a chuck table having a protruding portion (rising portion) corresponding to the recessed portion of the wafer as described above is used. However, if there is a difference between the depth of the recessed portion of the wafer and the protruding amount (height) of the protruding portion of the chuck table, the wafer is not held flat but is curved, and local stress is applied especially near the boundary between the recessed portion and the outer periphery of the wafer. If the wafer is cut with a cutting blade in this state, processing defects such as chipping are likely to occur.

[0009] Therefore, the convex portion of the chuck table is formed so that its protrusion amount matches the depth of the concave portion of the wafer as much as possible. However, there are variations in the thickness of the wafer, the depth of the concave portion of the wafer, the thickness of the tape (dicing tape) attached to the wafer, the dimensions of the chuck table, etc., and there is a limit to the accuracy of processing for forming the convex portion on the chuck table. Due to these various factors, it is difficult to strictly match the depth of the concave portion of the wafer and the protrusion amount of the convex portion of the chuck table, and in reality, an error of 10 μm or more often occurs between the two. As a result, the wafer having the concave portion is fixed to the chuck table in a slightly curved state, and the occurrence of processing defects may not be sufficiently suppressed.

[0010] In addition, the depth of the recessed portion of the wafer varies depending on the type of wafer (diameter, thickness, material, etc.). Therefore, whenever the type of wafer to be processed is changed, the amount of protrusion of the protruding portion of the chuck table must also be changed. This requires time and cost to prepare and replace the chuck table, and reduces the efficiency of wafer processing by the cutting device.

[0011] The present invention has been made in view of the above problems, and has an object to provide a wafer cutting method capable of appropriately cutting a wafer having a recessed portion. [Means for solving the problem]

[0012] According to one aspect of the present invention, there is provided a method for cutting a wafer having a circular recess in the center and an annular protrusion surrounding the recess on the outer periphery, the method comprising the steps of: applying an adhesive tape along the recess and the protrusion; The wafer is supported by an annular frame via the adhesive tape. a tape adhering step of adhering the wafer to the recessed portion by a holding surface of a chuck table having a diameter smaller than that of the recessed portion, thereby adhering the wafer to the chuck table via the adhesive tape; and the frameand a cutting step of cutting the wafer into the recess and the protrusion while the recess is not fixed, by rotating the chuck table and cutting a rotating cutting blade into the wafer so as to reach the adhesive tape affixed to the recess.

[0013] Preferably, In the holding step, the wafer is held by the chuck table so that a surface of the wafer is exposed, and in the cutting step, the cutting blade is caused to cut into the exposed surface side of the wafer. Effect of the Invention

[0014] In a method for cutting a wafer according to one aspect of the present invention, a cutting blade is cut into the wafer while the convex portion (periphery) of the wafer is not fixed, to separate the concave portion (center) and the convex portion (periphery). This reduces the stress on the wafer during cutting, and suppresses the occurrence of processing defects. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1(A) is a perspective view showing the front side of a wafer, and FIG. 1(B) is a perspective view showing the back side of the wafer. [Diagram 2] FIG. 2(A) is a perspective view showing a wafer to which an adhesive tape has been adhered, and FIG. 2(B) is a cross-sectional view showing the wafer to which the adhesive tape has been adhered. [Diagram 3] FIG. [Figure 4] 2 is a cross-sectional view showing a wafer held by a chuck table. [Diagram 5] FIG. 5(A) is a perspective view showing the wafer in a state where the cutting blade has made a cut, and FIG. 5(B) is a cross-sectional view showing the wafer in a state where the cutting blade has made a cut. [Figure 6] FIG. 2 is an enlarged cross-sectional view showing the outer periphery of the wafer. [Figure 7] FIG. 7(A) is a perspective view showing the wafer when the chuck table rotates, and FIG. 7(B) is a cross-sectional view showing the wafer when the chuck table rotates. [Figure 8] 1 is a graph showing the measurement results of chipping size. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a wafer that can be processed using the wafer cutting method according to this embodiment will be described. Fig. 1(A) is a perspective view showing the front side of a wafer 11, and Fig. 1(B) is a perspective view showing the back side of the wafer 11.

[0017] For example, the wafer 11 is a disk-shaped substrate made of a semiconductor such as silicon, and has a front surface 11a and a back surface 11b that are generally parallel to each other. The wafer 11 is divided into a plurality of rectangular regions by a plurality of streets (planned division lines) 13 arranged in a lattice shape so as to intersect with each other. Furthermore, devices 15 such as ICs (Integrated Circuits), LSIs (Large Scale Integration), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed on the front surface 11a side of the regions divided by the streets 13.

[0018] The wafer 11 includes, on the front surface 11a side, a substantially circular device region 17A in which a plurality of devices 15 are formed, and an annular peripheral surplus region 17B surrounding the device region 17A. The peripheral surplus region 17B corresponds to an annular region of a predetermined width (e.g., about 2 mm) including the outer periphery of the front surface 11a. In Fig. 1(A), the boundary between the device region 17A and the peripheral surplus region 17B is indicated by a two-dot chain line.

[0019] There are no limitations on the material, shape, structure, size, etc. of the wafer 11. For example, the wafer 11 may be a substrate made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc. There are also no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 15.

[0020] A plurality of device chips, each including a device 15, are manufactured by dividing the wafer 11 into a lattice shape along the streets 13. Furthermore, a thinning process is performed on the wafer 11 before division, thereby obtaining thinned device chips.

[0021] For example, a grinding device is used to thin the wafer 11. The grinding device includes a chuck table (holding table) that holds the workpiece, and a grinding unit that performs grinding on the workpiece, and a grinding wheel including a grinding stone is attached to the grinding unit. When the wafer 11 is held by the chuck table and the grinding stone is brought into contact with the back surface 11b of the wafer 11 while rotating the chuck table and the grinding wheel, the back surface 11b of the wafer 11 is ground, and the wafer 11 is thinned.

[0022] However, if the entire back surface 11b side of the wafer 11 is ground, the entire wafer 11 is thinned and the rigidity of the wafer 11 is reduced, making it difficult to subsequently handle (transport, hold, etc.) the wafer 11. For this reason, the thinning process (grinding) is sometimes performed only on a partial region of the back surface 11b side of the wafer 11.

[0023] For example, only the central portion of the wafer 11 is ground and thinned. In this case, as shown in Fig. 1(B), a circular recess (groove) 19 is formed in the back surface 11b of the wafer 11. The recess 19 is provided at a position corresponding to the device region 17A. Specifically, the size (diameter) of the recess 19 is set to be approximately the same as the size (diameter) of the device region 17A, and the recess 19 is formed at a position overlapping with the device region 17A.

[0024] The recess 19 includes a circular bottom surface 19a that is generally parallel to the front surface 11a and back surface 11b of the wafer 11, and an annular side surface (inner wall) 19b that is generally parallel to the thickness direction of the wafer 11 and connected to the back surface 11b and bottom surface 19a. An annular protrusion (reinforcement) 21 that corresponds to an area that has not been subjected to the thinning process (grinding) remains on the outer periphery of the wafer 11. The protrusion 21 includes the outer periphery excess area 17B and surrounds the device area 17A and the recess 19.

[0025] By thinning only the central portion of the wafer 11, the outer periphery (the convex portion 21) of the wafer 11 remains thick. This prevents the rigidity of the wafer 11 from decreasing, and the wafer 11 is less likely to be deformed or damaged when it is handled. In other words, the convex portion 21 functions as a reinforcing region that reinforces the wafer 11.

[0026] Next, a specific example of a wafer cutting method for dividing a wafer 11 having recesses 19 into a plurality of device chips will be described. In this embodiment, first, an adhesive tape is attached to the wafer 11 (tape attachment step). Fig. 2(A) is a perspective view showing the wafer 11 to which an adhesive tape 23 is attached, and Fig. 2(B) is a cross-sectional view showing the wafer 11 to which the adhesive tape 23 is attached.

[0027] An adhesive tape 23 having a size large enough to cover the entire back surface 11b of the wafer 11 is attached to the back surface 11b of the wafer 11. For example, a circular adhesive tape 23 having a diameter larger than that of the wafer 11 is attached to cover the back surface 11b of the wafer 11. The adhesive tape 23 may be a flexible film including a circular base material and an adhesive layer (glue layer) provided on the base material. For example, the base material is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate, and the adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive. Alternatively, an ultraviolet-curing resin that is cured by irradiation with ultraviolet light may be used as the adhesive layer.

[0028] The adhesive tape 23 is applied along the contour of the back surface 11b side of the wafer 11. That is, as shown in Fig. 2(B), the adhesive tape 23 is applied along (following) the bottom surface 19a and the side surface 19b of the recess 19 and the back surface (lower surface) of the protrusion 21. Note that Fig. 2(B) illustrates a case in which there is a small gap (space) between the bottom surface 19a and the side surface 19b and the adhesive tape 23 at the outer periphery of the recess 19, but the adhesive tape 23 may be applied so as to be in close contact with the bottom surface 19a and the side surface 19b.

[0029] An annular frame 25 made of metal such as SUS (stainless steel) is attached to the outer periphery of the adhesive tape 23. A circular opening 25a is provided in the center of the frame 25, penetrating the frame 25 in the thickness direction. The diameter of the opening 25a is larger than the diameter of the wafer 11. The center of the adhesive tape 23 is attached to the back surface 11b side of the wafer 11 arranged inside the opening 25a, and the outer periphery of the adhesive tape 23 is attached to the frame 25. As a result, the wafer 11 is supported by the frame 25 via the adhesive tape 23, and a frame unit (work set) is formed in which the wafer 11, the adhesive tape 23, and the frame 25 are integrated.

[0030] The wafer 11 with the adhesive tape 23 attached thereto is cut by a cutting device. Fig. 3 is a perspective view showing the cutting device 2. In Fig. 3, the X-axis direction (processing feed direction, first horizontal direction) and the Y-axis direction (indexing feed direction, second horizontal direction) are perpendicular to each other. The Z-axis direction (vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction. The cutting device 2 includes a chuck table (holding table) 4 that holds the wafer 11, and a cutting unit 10 that cuts the wafer 11 held by the chuck table 4.

[0031] The upper surface of the chuck table 4 is a flat surface that is generally parallel to the horizontal direction (XY plane direction) and constitutes a circular holding surface 4a (see FIG. 4) that holds the wafer 11. In addition, the chuck table 4 is connected to a ball screw type moving mechanism (not shown) that moves the chuck table 4 along the X-axis direction, and a rotational drive source (not shown) such as a motor that rotates the chuck table 4 around a rotation axis that is generally parallel to the Z-axis direction.

[0032] A cutting unit 10 is disposed above the chuck table 4. The cutting unit 10 includes a cylindrical housing 12, and the housing 12 accommodates a columnar spindle 14 (see FIG. 4) disposed along the Y-axis direction. A tip end (one end) of the spindle 14 is exposed to the outside of the housing 12, and a base end (the other end) of the spindle 14 is connected to a rotation drive source such as a motor.

[0033] An annular cutting blade 16 is attached to the tip of the spindle 14. The cutting blade 16 rotates at a predetermined rotational speed around a rotation axis roughly parallel to the Y-axis direction by power transmitted from a rotation drive source via the spindle 14.

[0034] As the cutting blade 16, for example, a hub-type cutting blade (hub blade) is used. The hub blade is composed of an annular base made of metal or the like and an annular cutting edge formed along the outer periphery of the base, which is integrated together. The cutting edge of the hub blade is composed of an electroformed grinding stone in which abrasive grains made of diamond or the like are fixed by a binder such as a nickel plating layer. However, a washer-type cutting blade (washer blade) can also be used as the cutting blade 16. A washer blade is composed only of an annular cutting edge in which abrasive grains are fixed by a binder made of metal, ceramics, resin, or the like.

[0035] The cutting blade 16 attached to the cutting unit 10 is covered by a blade cover 18 fixed to the housing 12. The blade cover 18 includes a pair of connection parts 20 connected to a tube (not shown) through which a liquid (cutting fluid) such as pure water is supplied, and a pair of nozzles 22 connected to the pair of connection parts 20 and disposed on both sides (front and back sides) of the cutting blade 16. Each of the pair of nozzles 22 has a supply port (not shown) formed therein that opens toward the cutting blade 16.

[0036] When cutting fluid is supplied to the connection portion 20, the cutting fluid flows into the pair of nozzles 22, and is supplied from the supply ports of the pair of nozzles 22 toward both surfaces (front and back surfaces) of the cutting blade 16. This cutting fluid cools the wafer 11 and the cutting blade 16, and washes away chips (cutting chips) generated by the cutting process.

[0037] A ball screw type moving mechanism (not shown) is connected to the cutting unit 10. The moving mechanism moves the cutting unit 10 along the Y-axis direction and the Z-axis direction. The moving mechanism adjusts the position of the cutting blade 16 in the indexing feed direction, the cutting depth of the cutting blade 16 into the wafer 11, etc.

[0038] When the wafer 11 is processed by the cutting device 2, first, the wafer 11 is held by the chuck table 4 via the adhesive tape 23 (holding step). FIG. 4 is a cross-sectional view showing the wafer 11 held by the chuck table 4.

[0039] The chuck table 4 has a cylindrical frame (main body) 6 made of metal such as SUS, glass, ceramics, resin, etc. A cylindrical recess (groove) 6b is formed on the top surface 6a side of the center of the frame 6, and a disk-shaped holding member 8 is fitted into the recess 6b. The holding member 8 is a member made of a porous material such as porous ceramics, and includes holes (flow paths) therein that communicate from the top surface to the bottom surface of the holding member 8.

[0040] The holding member 8 is connected to a suction source (not shown) such as an ejector via a flow path (not shown), a valve (not shown), and the like formed inside the frame 6. In addition, the upper surface of the holding member 8 forms a circular suction surface 8a that sucks the wafer 11. The upper surface 6a of the frame 6 and the suction surface 8a of the holding member 8 are disposed on approximately the same plane and form the holding surface 4a of the chuck table 4.

[0041] The wafer 11 is placed on the chuck table 4 so that the front surface 11a side is exposed upward. The chuck table 4 is configured so that the holding surface 4a can hold the bottom surface 19a of the recess 19 of the wafer 11. Specifically, the diameter of the holding surface 4a is smaller than the diameter of the recess 19. When the wafer 11 is placed on the chuck table 4, the holding surface 4a side of the chuck table 4 is fitted into the recess 19. As a result, the bottom surface 19a of the recess 19 is supported by the holding surface 4a via the adhesive tape 23.

[0042] When the negative pressure (suction force) of the suction source is applied to the holding member 8 with the wafer 11 placed on the chuck table 4, the area of ​​the adhesive tape 23 attached to the bottom surface 19a of the recess 19 is sucked to the suction surface 8a. As a result, the wafer 11 is sucked and held by the chuck table 4 via the adhesive tape 23.

[0043] If the wafer 11 is placed on the holding surface 4a with no suction force acting on the suction surface 8a, the weight of the convex portion 21 of the wafer 11 may cause the wafer 11 to bend upwardly. However, if suction force is applied to the suction surface 8a, the bottom surface 19a of the concave portion 19 is supported flat along the holding surface 4a. As a result, the curvature of the wafer 11 is corrected, and the wafer 11 as a whole becomes generally flat.

[0044] Here, no members (part of the chuck table 4, other holding members, etc.) for holding the wafer 11, the adhesive tape 23, or the frame 25 are provided in an area radially outward of the outer periphery of the holding surface 4a of the chuck table 4. Therefore, when the wafer 11 is held by the chuck table 4, the protrusion 21 of the wafer 11, the outer periphery of the adhesive tape 23, and the frame 25 are not fixed and are in a floating state.

[0045] However, the cutting device 2 may include a plurality of clamps (not shown) that are provided around the chuck table 4 and grip and fix the frame 25. In this case, the frame 25 is not gripped by the clamps and is in a released state during the holding step and the cutting step described below.

[0046] Next, the wafer 11 is cut by the cutting blade 16 to separate the concave portion 19 and the convex portion 21 of the wafer 11 (cutting step). In the cutting step, the chuck table 4 is rotated while the cutting blade 16 is cutting into the wafer 11, thereby cutting the wafer 11 into a ring shape. Note that in the cutting step, the convex portion 21 of the wafer 11, the outer periphery of the adhesive tape 23, and the frame 25 are not fixed and are maintained in a floating state (see FIG. 4).

[0047] First, the rotating cutting blade 16 is caused to cut into the wafer 11. Fig. 5(A) is a perspective view showing the wafer 11 in a state where the cutting blade 16 has made a cut, and Fig. 5(B) is a cross-sectional view showing the wafer 11 in a state where the cutting blade 16 has made a cut. When the cutting blade 16 is caused to cut into the wafer 11, the chuck table 4 is placed below the cutting unit 10. Then, the positions of the chuck table 4 and the cutting unit 10 are adjusted so that the cutting blade 16 overlaps with the outer periphery of the recess 19 of the wafer 11.

[0048] Next, while rotating the cutting blade 16, the cutting unit 10 is lowered toward the chuck table 4. This causes the cutting blade 16 to cut into the front surface 11a side of the wafer 11. The cutting unit 10 then descends until the lower end of the cutting blade 16 reaches the adhesive tape 23 attached to the bottom surface 19a of the recess 19. The difference in height between the front surface 11a of the wafer 11 and the lower end of the cutting blade 16 at this time corresponds to the cutting depth of the cutting blade 16 into the wafer 11.

[0049] 6 is an enlarged cross-sectional view showing the outer periphery of the wafer 11. The outer periphery of the wafer 11 includes regions A to D that overlap with the recess 19 of the wafer 11. Region A is a region that overlaps with the suction surface 8a of the holding member 8, region B is a region that overlaps with the upper surface 6a of the frame 6, and regions C and D are regions that do not overlap with the holding surface 4a. Region C is a region that overlaps with a region where the bottom surface 19a of the recess 19 is in contact with the adhesive tape 23. Region D is a region that overlaps with a region where the bottom surface 19a of the recess 19 is not in contact with the adhesive tape 23 (gaps between the bottom surface 19a and the side surfaces 19b and the adhesive tape 23).

[0050] For example, the cutting blade 16 cuts into the region B of the wafer 11. This makes it possible to cut the region of the wafer 11 that is securely supported by the frame 6 while securing a large device region 17A in the center of the wafer 11. However, the cutting blade 16 can also cut into the region A, region C, or region D.

[0051] Next, the chuck table 4 is rotated while keeping the cutting blade 16 rotating. Fig. 7(A) is a perspective view showing the wafer 11 when the chuck table 4 is rotating, and Fig. 7(B) is a cross-sectional view showing the wafer 11 when the chuck table 4 is rotating.

[0052] When the chuck table 4 is rotated once while the cutting blade 16 is cutting into the wafer 11, the wafer 11 is cut into an annular shape. As a result, an annular kerf (cut) 11c is formed in the vicinity of the boundary between the device region 17A and the peripheral excess region 17B, extending from the surface 11a of the wafer 11 to the bottom surface 19a of the recess 19. As a result, the central portion (recess 19) and the peripheral portion (protrusion 21) of the wafer 11 are separated.

[0053] In addition, when cutting the wafer 11 with the cutting blade 16, if the convex portion 21 of the wafer 11 is fixed at a specific position, the wafer 11 may be unintentionally curved due to an error in the positional relationship between the holding surface 4a of the chuck table 4 and the fixed position of the convex portion 21. In this case, stress acts on the wafer 11, and processing defects such as chipping (chipping) are likely to occur when the cutting blade 16 cuts into the wafer 11.

[0054] On the other hand, in this embodiment, when the cutting step is performed, the convex portion 21 of the wafer 11, the outer periphery of the adhesive tape 23, and the frame 25 are not fixed and are maintained in a floating state. Therefore, unintended curvature of the wafer 11 that may occur when the convex portion 21 is fixed at a specific position is avoided. Also, when the cutting blade 16 contacts the wafer 11, the convex portion 21 can be slightly displaced according to the load applied to the wafer 11. This reduces the stress of the wafer 11 compared to when the convex portion 21 is fixed. As a result, the occurrence of processing defects when cutting the wafer 11 with the cutting blade 16 is suppressed.

[0055] When the annular protrusion 21 separated from the wafer 11 is removed, a thinned device region 17A remains on the chuck table 4. Thereafter, the wafer 11 is cut along the streets 13 with, for example, a cutting blade 16 to divide the wafer 11, thereby obtaining a plurality of device chips each including a device 15.

[0056] As described above, in the wafer cutting method according to this embodiment, while the protrusions 21 of the wafer 11 are not fixed, the cutting blade 16 cuts into the wafer 11 to separate the recesses 19 and the protrusions 21. This reduces the stress on the wafer 11 during cutting, and suppresses the occurrence of processing defects.

[0057] The structures, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the scope of the object of the present invention.

[0058] (Example) Next, the results of evaluation of the wafers cut using the wafer cutting method according to the present invention will be described. In this example, a wafer 11 according to a comparative example, which was cut by the cutting blade 16 while being held by a conventional method, and a wafer 11 according to an example, which was cut by the cutting blade 16 while being held by the method according to the present invention, were observed and compared.

[0059] An 8-inch silicon wafer (thickness 0.725 mm) was used as the wafer 11. The wafer 11 was previously thinned (grinded) to form a recess 19 (see FIG. 1(B) and the like). The recess 19 was formed so that a ring-shaped protrusion (reinforcement) 21 with a width of 2.1 mm remained on the outer periphery of the wafer 11, and the thickness of the device region 17A of the wafer 11 was 0.1 mm. Four of the above wafers 11 were prepared, two of which were used as wafers according to the comparative example (wafers A1 and A2), and the remaining two were used as wafers according to the embodiment (wafers B1 and B2).

[0060] Next, adhesive tape 23 was attached to each of wafers A1, A2, B1, and B2 (see FIG. 2(A) and FIG. 2(B)). After that, each of wafers A1, A2, B1, and B2 was cut using cutting device 2 (see FIG. 3).

[0061] The wafers A1 and A2 according to the comparative example were held and cut by a conventional method. Specifically, the bottom surfaces 19a of the recesses 19 of the wafers A1 and A2 were held by the holding surface 4a of the chuck table 4 (see FIG. 4). In addition, an annular support member (spacer) for supporting the lower surface side of the protrusions 21 of the wafers A1 and A2 was installed outside the holding surface 4a of the chuck table 4, and the protrusions 21 were held by the upper surface (holding surface) of the support member.

[0062] The holding surface of the support member was positioned lower than the holding surface 4a of the chuck table 4, and the difference in height between the holding surface 4a and the holding surface of the support member was matched to the depth of the recess 19. The area of ​​the adhesive tape 23 attached to the lower surface side of the protrusion 21 was sucked and held by the holding surface of the support member. That is, the wafers A1 and A2 according to the comparative example were in a state in which the bottom surface 19a of the recess 19 and the protrusion 21 were held.

[0063] On the other hand, the wafers B1 and B2 according to the embodiment were held and cut by the method according to the present invention. Specifically, as shown in Fig. 4, the bottom surfaces 19a of the recesses 19 of the wafers B1 and B2 were held by the holding surface 4a of the chuck table 4, and the protrusions 21 of the wafers B1 and B2 were not held and were left floating.

[0064] Next, the wafers A1, A2, B1, and B2 were cut with a cutting blade. Specifically, the wafers A1, A2, B1, and B2 were first cut with the cutting blade 16 (see FIG. 5(A) and FIG. 5(B)). The cutting blade 16 was cut into the area overlapping with the frame 6 of the chuck table 4 (area B in FIG. 6). The rotation speed of the cutting blade 16 (the rotation speed of the spindle 14) was set to 30,000 rpm.

[0065] Thereafter, while maintaining the rotation of the cutting blade 16, the chuck table 4 was rotated once to cut the wafers A1, A2, B1, and B2 in an annular shape (see FIGS. 7(A) and 7(B)). When cutting the wafer A1 according to the comparative example and the wafer B1 according to the example, the rotation speed of the chuck table 4 was set to a low speed (3 deg / s). On the other hand, when cutting the wafer A2 according to the comparative example and the wafer B2 according to the example, the rotation speed of the chuck table 4 was set to a high speed (15 deg / s).

[0066] Then, the eight main chippings (chippings) remaining on the bottom surface 19a of the wafers A1, A2, B1, and B2 after cutting were observed, and the chipping sizes were measured. Specifically, the length of the chipping that developed from the kerf 11c (see Fig. 7(A) and Fig. 7(B)) along the bottom surface 19a in the direction perpendicular to the kerf 11c (diameter direction of the wafer) was measured as the chipping size. In addition, the maximum value (maximum chipping size) and average value (average chipping size) of the chipping sizes were calculated from the measured sizes of the eight chippings.

[0067] 8 is a graph showing the measurement results of chipping size. Note that the dots (black circles), crosses, and white circles in the graph indicate the chipping size, maximum chipping size, and average chipping size, respectively.

[0068] 8, when comparing wafers A1 and B1 cut by setting the rotation speed of the chuck table 4 to a low speed (3 deg / s), the maximum chipping size was reduced from 55 μm to 30 μm and the average chipping size was reduced from 39 μm to 20 μm by cutting the wafers with the cutting method according to the present invention. Also, when comparing wafers A2 and B2 cut by setting the rotation speed of the chuck table 4 to a high speed (15 deg / s), the maximum chipping size was reduced from 88 μm to 29 μm and the average chipping size was reduced from 65 μm to 17 μm.

[0069] Conventionally, in order to cut a wafer 11 having recesses 19 without causing processing defects, it has been considered preferable to cut the wafer 11 while holding both the recesses 19 and the protrusions 21 of the wafer 11. However, from the above results, it has been confirmed that cutting the wafer 11 while the protrusions 21 are not fixed and are floating effectively reduces the stress on the wafer 11 and significantly reduces the size of chipping.

[0070] Furthermore, when the wafer 11 was held by the conventional method, as the rotation speed of the chuck table 4 increased, the processing time became shorter, but the chipping size tended to increase (see wafers A1 and A2). On the other hand, when the wafer 11 was cut with the protrusions 21 not fixed and floating, no increase in chipping size was observed even when the rotation speed of the chuck table 4 was increased (see wafers B1 and B2). This confirmed that the wafer cutting method according to the present invention is also extremely effective in increasing the processing feed speed. [Explanation of symbols]

[0071] 11 Wafers 11a surface 11b Back side 11c Calf (cut) 13th Street (Planned division line) 15 Devices 17A Device Area 17B Surplus outer area 19 Groove 19a Bottom 19b Side (inner wall) 21 Convex part (reinforcement part) 23 Adhesive Tape 25 Frames 25a opening 2 Cutting equipment 4 Chuck table (holding table) 4a Holding surface 6 Frame (main body) 6a Top side 6b Recess (groove) 8 Retaining member 8a Suction surface 10 Cutting unit 12. Housing 14 Spindle 16 Cutting blade 18 Blade Cover 20 Connection 22 Nozzle

Claims

1. A method for cutting a wafer, the method comprising the steps of: cutting a wafer having a circular recess in a central portion and an annular protrusion surrounding the recess in an outer periphery, the steps comprising: a tape adhering step of adhering an adhesive tape along the concave portion and the convex portion and supporting the wafer with an annular frame via the adhesive tape; a holding step of holding the wafer by the chuck table via the adhesive tape by sucking the adhesive tape attached to the recessed portion with a holding surface of a chuck table having a diameter smaller than that of the recessed portion; a cutting step of separating the concave portion and the convex portion by cutting a rotating cutting blade into the wafer so as to reach the adhesive tape affixed to the concave portion and rotating the chuck table while the convex portion and the frame are not fixed.

2. In the holding step, the wafer is held by the chuck table so that a surface of the wafer is exposed; 2. The method for cutting a wafer according to claim 1, wherein in the cutting step, the cutting blade is caused to cut into the exposed front surface side of the wafer.

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