Holding table, holding method, and edge trimming method

Abstract

To provide a holding table of new structure, a holding method, and an edge trimming method pertaining to a holding table that holds a wafer.SOLUTION: Provided is a holding table composed of a wafer having a warp in bowl-shaped form on the surface side, a tape pasted to the reverse side of the wafer, and an annular frame to which the outer periphery of the tape is pasted and holding a wafer unit in which the wafer is located at an opening of the annular frame. The holding table comprises: a table body that holds the wafer via the tape and includes a holding face where a suction part connected to a suction source and holding the middle part of the wafer by suction is formed; and a frame fixing part that holds the annular frame on the outside of the table body by pulling it down from the holding face. The annular frame of the wafer unit is held by the frame fixing part and the warp of the wafer is corrected, and then the suction part is connected to the suction source and the wafer is held in place via the tape.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a holding table and a holding method for holding a wafer unit in which a wafer having a cup-shaped warp is fixed to an annular frame. [Background technology]

[0002] It has been known that the risk of wafer breakage increases when a chamfered portion on the outer periphery of a semiconductor wafer becomes sharp-edged during grinding, as disclosed in, for example, Patent Document 1. In order to reduce the risk of wafer breakage, edge trimming is known, which removes the outer periphery of the wafer before grinding.

[0003] In this edge trimming process, in order to process the outer periphery of the wafer held on a holding table, in Patent Document 1, the underside of the wafer is held by suction using suction grooves in an area adjacent to the outer periphery of the wafer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-024036 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the case of the conventional method of suction holding of a wafer using a holding table, if the wafer is warped into a bowl shape, a gap is formed between the suction groove and the underside of the wafer, making it impossible to hold the wafer by suction.

[0006] In view of the above problems, the present invention relates to a holding table for holding a wafer, and proposes a holding table, a holding method, and an edge trimming method having a novel configuration. [Means for solving the problem]

[0007] The problem to be solved by the present invention has been described above, and the means for solving this problem will now be described.

[0008] According to one aspect of the present invention, a holding table is provided which holds a wafer unit comprising a bowl-shaped wafer having a warp on its front side, a tape attached to the back side of the wafer, and an annular frame to which the outer periphery of the tape is attached, with the wafer placed in an opening of the annular frame, the holding table including a holding surface connected to a suction source and having a suction portion formed therein which suction-holds the central portion of the wafer, the holding surface holding the wafer via the tape, and a frame fixing portion outside the table body which pulls the annular frame down from the holding surface and holds it, the holding table using the frame fixing portion to hold the annular frame of the wafer unit and correct the warp of the wafer, and then connecting the suction portion to the suction source and holding the wafer via the tape.

[0009] According to one aspect of the present invention, there is provided a holding method for holding a wafer unit comprising a bowl-shaped wafer having a warp on its front surface, a tape affixed to the back surface of the wafer, and an annular frame to which the outer periphery of the tape is affixed, the wafer being placed in an opening of the annular frame, the holding method comprising: a preparation step of preparing a holding table including a table body connected to a suction source and including a holding surface formed with a suction portion that suction-holds the central portion of the wafer and holds the wafer via the tape, and a frame fixing portion outside the table body that pulls the annular frame down from the holding surface and holds it; a placement step of placing the wafer unit on the holding table; a frame fixing step of, after carrying out the placement step, holding the annular frame of the wafer unit with the frame fixing portion to pull the annular frame down from the holding surface and correct the warp of the wafer; and a suction holding step of, after carrying out the frame fixing step, connecting the suction portion to the suction source and holding the wafer via the tape.

[0010] According to another aspect of the present invention, there is provided an edge trimming method for forming a chamfered portion by cutting a peripheral portion on a front surface side of a wafer. Effect of the Invention

[0011] The present invention provides the following advantages. That is, according to one aspect of the present invention, the warpage of the wafer is corrected, and the wafer can be reliably held by suction during edge trimming. [Brief description of the drawings]

[0012] [Figure 1] FIG. 13 is a diagram showing an example of a wafer unit. [Diagram 2] 1A to 1C are diagrams for explaining wafer warpage. [Diagram 3] FIG. 1 is a diagram showing an example of an edge trimming device. [Figure 4] FIG. 4 is a perspective view showing an example of the configuration of a holding table. [Diagram 5] FIG. 4 is a partial cross-sectional side view showing an example of the configuration of a holding table. [Figure 6] FIG. [Figure 7] FIG. 4 is a diagram for explaining a frame fixing step. [Figure 8] FIG. [Figure 9] 1A to 1C are diagrams illustrating processing steps. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a wafer on which edge trimming is to be performed.

[0014] The back surface Wb of the wafer W is fixed to an annular frame F via a tape T, and the wafer W is handled as a wafer unit U. The material of the wafer W is, for example, silicon, sapphire, SiC, GaAs, or the like.

[0015] Devices D are formed in a regular arrangement on the surface Wa of the wafer W. On the surface Wa of the wafer W, mutually orthogonal streets S (planned division lines) are set in a lattice pattern, and the devices D are located in areas defined by each street S. Division starting points are formed by performing processing such as laser processing, plasma etching, and cutting along the streets S, and the wafer is broken at the division starting points to be separated into individual chips.

[0016] There are no limitations on the material, shape, structure, size, etc. of the wafer. For example, the wafer may include a base material formed of other semiconductors, ceramics, resin, etc. Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices. In addition, the wafer does not necessarily have to have any devices formed thereon.

[0017] 2 is a side cross-sectional view of a wafer unit U, in which the wafer W is warped into a bowl shape. Specifically, the wafer W is warped such that the front surface Wa is concave and the back surface Wb is convex, and the back surface Wb is attached to a tape T.

[0018] FIG. 3 is a diagram showing an example of an edge trimming device for performing edge trimming. The edge trimming device 1 is a device capable of edge trimming by a first cutting means 61 or a second cutting means 62 equipped with a cutting blade 63 for cutting the wafer W held on the holding table 30. The first cutting means 61 and the second cutting means 62 are disposed so as to face each other in the Y-axis direction. Note that the edge trimming device 1 is not limited to a type capable of dual-cutting (simultaneous cutting on two axes) the wafer W.

[0019] A cutting feed means 13 for moving the holding table 30 in the X-axis direction is disposed on the base 10 of the edge trimming device 1. The cutting feed means 13 is composed of a ball screw 13a having an axis extending in the X-axis direction, a pair of guide rails 13b disposed parallel to the ball screw 13a, a motor 13c for rotating the ball screw 13a, and a movable plate 13d whose internal nut is screwed into the ball screw 13a and whose bottom is in sliding contact with the guide rails 13b. When the motor 13c rotates the ball screw 13a, the movable plate 13d moves in the X-axis direction while being guided by the guide rails 13b, and the holding table 30 disposed on the movable plate 13d is cut and fed in the X-axis direction with the movement of the movable plate 13d.

[0020] A gate-type column 14 is erected on the rear side (-X direction side) of the base 10 so as to straddle the movement path of the holding table 30. On the front side of the gate-type column 14, for example, a first horizontal movement means 15 is disposed for reciprocating the first cutting means 61 in the Y-axis direction perpendicular to the X-axis direction and the Z-axis direction.

[0021] The first horizontal movement means 15 includes, for example, a ball screw 15a having an axis extending in the Y-axis direction, a pair of guide rails 15b arranged parallel to the ball screw 15a, a motor (not shown) connected to one end of the ball screw 15a, and a movable plate 15c whose internal nut is screwed into the ball screw 15a and whose side is in sliding contact with the guide rail 15b. When the motor (not shown) rotates the ball screw 15a, the movable plate 15c moves in the Y-axis direction while being guided by the guide rail 15b, and the first cutting means 61 arranged on the movable plate 15c via the first cutting feed means 17 is horizontally moved (indexed feed) in the Y-axis direction.

[0022] The first cutting feed means 17 can reciprocate the first cutting means 61 in the Z-axis direction, and includes a ball screw 17a having an axis extending in the Z-axis direction, a pair of guide rails 17b arranged parallel to the ball screw 17a, a motor 17c connected to the ball screw 17a, and a support member 17d that supports the first cutting means 61, has an internal nut that screws into the ball screw 17a, and has a side that slides against the guide rails 17b. When the motor 17c rotates the ball screw 17a, the support member 17d moves in the Z-axis direction while being guided by the pair of guide rails 17b, and accordingly, the first cutting means 61 is cut and fed in the Z-axis direction.

[0023] On the front surface of the gate-type column 14 shown in FIG. 1, for example, a second horizontal moving means 16 for reciprocating the second cutting means 62 in the Y-axis direction is disposed. The second horizontal movement means 16 includes, for example, a ball screw 16a having an axis extending in the Y-axis direction, a pair of guide rails 15b arranged parallel to the ball screw 16a, a motor 16c connected to the ball screw 16a, and a movable plate 16d whose internal nut is screwed onto the ball screw 16a and whose side is in sliding contact with the guide rail 15b. When the motor 16c rotates the ball screw 16a, the movable plate 16d is guided by the guide rail 15b and moves in the Y-axis direction, and the second cutting means 62 arranged on the movable plate 16d via the second cutting feed means 18 is horizontally moved (indexed feed) in the Y-axis direction.

[0024] The second cutting feed means 18 can reciprocate the second cutting means 62 in the Z-axis direction, and includes a ball screw 18a having an axis extending in the Z-axis direction, a pair of guide rails 18b arranged parallel to the ball screw 18a, a motor 18c connected to the ball screw 18a, and a support member 18d that supports the second cutting means 62, has an internal nut that screws into the ball screw 18a, and has a side that slides against the guide rails 18b. When the motor 18c rotates the ball screw 18a, the support member 18d moves in the Z-axis direction while being guided by the pair of guide rails 18b, and accordingly, the second cutting means 62 is cut and fed in the Z-axis direction.

[0025] As shown in FIGS. 4 and 5, the holding table 30 is configured to include a table body 31, a frame fixing portion 35 arranged on the outside of the table body 31, and a rotation mechanism 38 for rotating the table body 31.

[0026] The table body 31 is made of a disk-shaped member made of, for example, metal or ceramics. The upper surface of the table body 31 forms a holding surface 32 that is circular in plan view for holding a wafer. A suction part 33 that suction-holds the center of the wafer is formed on the holding surface 32.

[0027] In this embodiment, the suction unit 33 is configured to have a cross-shaped groove 33a with the center of the holding surface 32 as the intersection point, and a plurality of annular grooves 33b arranged so as to form concentric circles around the center of the holding surface 32. The suction unit 33 is not limited to a specific shape of the groove for suction, as long as it can generate negative pressure at least at the center of the holding surface 32 and suck the central part of the wafer through the tape. The suction unit may also be configured by providing a plurality of holes. The central part of the wafer may be, for example, a very narrow range corresponding to the center of the wafer, or a relatively wide range such as a circle with a radius half the radius of the wafer.

[0028] The suction unit 33 is connected to a suction source 37 through a valve 34, and by controlling the opening and closing of the valve 34, a negative pressure is generated on the holding surface 32, and the wafer is sucked and held via the tape, as will be described in detail later.

[0029] The frame fixing portion 35 is for pulling down and holding the annular frame F (FIG. 1) below the height of the holding surface 32 outside the table main body 31, and in this embodiment is configured with four clamp mechanisms 36 arranged at 90 degree intervals around the periphery of the table main body 31. Each clamp mechanism 36 is configured with a support member 36a for supporting the annular frame F from below, an actuator 36b fixed to the support member 36a, and a holding member 36c that is driven by the actuator 36b to rotate and hold the annular frame F.

[0030] The table body 31 can be rotated by a rotation mechanism 38 built into the base 30A of the holding table 30. As described in detail below, the cutting blade is rotated to position it at a predetermined cutting height, and the table body 31 is rotated 360 degrees to perform edge trimming, which removes the peripheral edge portions of the wafer.

[0031] Next, an embodiment of a holding method using the above configuration will be described. As shown in Figures 2 and 4, this embodiment is a method for holding a wafer unit U consisting of a wafer W having a bowl-shaped warp on the front side, a tape T attached to the back side Wb of the wafer W, and an annular frame F to which the outer periphery of the tape T is attached, in which the wafer W is placed in an opening Fa of the annular frame F, and includes the following steps.

[0032] <Preparation steps> As shown in Figures 4 and 5, this is a step of preparing a holding table 30 which is connected to a suction source 37, includes a holding surface 32 on which a suction portion 33 is formed for suction-holding the central portion Wc of the wafer W, and holds the wafer W via the tape T, and includes a frame fixing portion 35 on the outside of the table body 31 for pulling the annular frame F down from the holding surface 32 and holding it.

[0033] <Placement step> As shown in FIG. 6, this is a step in which the wafer unit U is placed on the holding table 30. The wafer W has a bowl-shaped warp on the front side and bulges downward in Figure 6, so when the tape T is placed on the holding surface 32, there is a concern that a gap H will be formed between the underside of the wafer W (tape T) and the holding surface 32.

[0034] <Frame fixing step> As shown in FIG. 7, after the placement step is performed, the annular frame F of the wafer unit U is held by the frame fixing portion 35, thereby pulling the annular frame F below the holding surface 32, thereby correcting the warpage of the wafer W.

[0035] Specifically, in each clamp mechanism 36, the actuator 36b rotates the pressing member 36c, causing the pressing member 36c to press the annular frame F from above, and the lower surface of the annular frame F is pressed against the support member 36a, thereby clamping the annular frame F between the pressing member 36c and the support member 36a. The height of the upper surface of the support member 36a is set lower than the height of the holding surface 32, and when the pressing member 36c presses the annular frame F from above, the annular frame F is pulled down so as to be lower than the holding surface 32 of the holding table 30.

[0036] By thus pulling down the annular frame F from the holding surface 32, the peripheral portion Td of the tape T attached to the bottom surface of the annular frame F also moves downward, and the tape T is pulled so as to spread, generating tension, which also pulls the back side of the wafer W outward from the center of the wafer W, correcting the warpage of the wafer W. This correction of the warpage makes the back side of the wafer W flat, and prevents the occurrence of a gap H (FIG. 6) between the bottom surface of the wafer W (tape T) and the holding surface 32, particularly at the peripheral portion Wd of the wafer W. This allows the wafer W to be securely held on the holding table 30.

[0037] <Suction holding step> 8, after the frame fixing step is performed, the suction unit 33 is connected to the suction source 37 to hold the wafer W via the tape T. At this time, the generation of a gap H (FIG. 6) between the lower surface of the wafer W (tape T) and the holding surface 32 due to warping of the wafer W is suppressed, so the negative pressure formed by the suction unit 33 does not escape through the gap H (FIG. 6), and the lower surface of the wafer W (tape T) can be reliably suction-held.

[0038] <Processing steps> As shown in Fig. 9, this is a step in which a chamfered portion We is formed by cutting the peripheral portion Wd on the front surface Wa of the wafer W. During this processing step, the wafer with its warpage corrected is securely held by suction, so that the flapping of the wafer can be suppressed and edge trimming with high processing accuracy can be performed.

[0039] As shown in FIG. 9, edge trimming involves, for example, rotating the cutting blade 63 of the first cutting means 61 to position it at a predetermined cutting height, and rotating the holding table 30 360 degrees to remove the peripheral edge portion of the wafer W and form a chamfered portion We. [Explanation of symbols]

[0040] 1 Edge trimming device 30 Holding Table 31 Table body 32 Holding surface 33 Suction part 33a Cruciform groove 33b Circular groove 34 Valve 35 Frame fixing part 36 Clamping mechanism 36a Support member 36b Actuator 36c Pressing member 37 Suction source 38 Rotation mechanism 63 Cutting Blade D Device F Annular frame Fa Aperture H gap S Street T-Tape Td Periphery U Wafer Unit W wafer Wa Surface Wb back side Wc central part Wd Periphery We chamfered part

Claims

1. A holding table includes a wafer unit including a cup-shaped wafer having a warp on the front side, a tape attached to the rear side of the wafer, and an annular frame to which an outer periphery of the tape is attached, the holding table holding the wafer unit in an opening of the annular frame, a table body connected to a suction source, the table body including a holding surface having a suction portion formed thereon for suction-holding a central portion of the wafer, and the table body holding the wafer via the tape; a frame fixing portion that holds the annular frame by pulling it down from the holding surface on the outside of the table body, a holding table which holds the annular frame of the wafer unit with the frame fixing portion to correct the warp of the wafer, and then connects the suction portion to the suction source to hold the wafer via the tape;

2. A holding method for holding a wafer unit including a wafer having a cup-shaped warp on the front side, a tape attached to the rear side of the wafer, and an annular frame to which an outer periphery of the tape is attached, the wafer unit being placed in an opening of the annular frame, the method comprising: a preparation step of preparing a holding table including a table body connected to a suction source, the table body including a holding surface having a suction portion formed thereon for suction-holding the central portion of the wafer, and for holding the wafer via the tape, and a frame fixing portion outside the table body for pulling down the annular frame from the holding surface and holding it; a placing step of placing the wafer unit on the holding table; a frame fixing step of, after carrying out the placing step, holding the annular frame of the wafer unit with the frame fixing part, thereby pulling the annular frame down from the holding surface and correcting the warp of the wafer; a suction holding step of connecting the suction unit to the suction source and holding the wafer via the tape after the frame fixing step is performed; A holding method comprising:

3. The wafer held by the holding method according to claim 2, and an edge trimming method for forming a chamfered portion by cutting the peripheral portion on the front surface side of the wafer.

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