JP2005335014A - Wafer grinding method and grinding wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To have no harmful effect on a wafer and a device by preventing micro vibration of a grinding wheel caused by impact force and grinding resistance when starting to grind with the grinding wheel, from being transmitted to the wafer in the case of grinding the wafer using the grinding wheel. <P>SOLUTION: A cushioning material 220 is interposed between a wheel mount 210 and a wheel base 230a, and the wafer W1 is held on the chuck table 14a. The chuck table 14a is rotated to rotate the wafer W1, and the wheel mount 210 is rotated and fed for grinding to bring a grinding wheel part 230b of the grinding wheel 230 into contact with the wafer W1 to perform grinding. Impact force when the grinding wheel part 230b and the wafer W1 come in contact, and the micro vibration of the grinding wheel part 230b caused by grinding resistance, are absorbed by the cushioning material 220. A phenomenon causing grinding distortion such as a crack on a ground surface W1b is thereby suppressed to prevent a lowering of anti-bending strength of the device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for grinding a wafer capable of producing a high-quality wafer or device with high productivity and a grinding wheel used therefor.

  A wafer on which a plurality of devices such as integrated circuits are formed on the surface side is divided into individual devices by a dicing apparatus or the like and used for various electronic devices.

  Before the wafer is divided into individual devices, the back surface is ground so that the back surface is smoothed and finished to a desired thickness. In addition, a groove having a depth corresponding to the finished thickness of the device is formed on the street of the wafer, and the groove formed by grinding the back surface of the wafer is exposed from the back surface of the wafer so that the wafer is individually A technique called dicing (DBG) that divides into devices has also been put into practical use. In either case, it is essential to grind the back surface of the wafer (see, for example, Patent Document 1).

JP 2003-007653 A

  However, when the rotating grinding wheel is fed by grinding and reaches the predetermined pressing force upon contact with the wafer to start grinding, a strong impact force is transmitted to the wafer at the moment of the start. Further, during grinding, slight vibration is generated in the grinding wheel due to grinding resistance, and the wafer is finely beaten along with this. Due to these phenomena, grinding distortion such as cracks occurs on the ground surface of the wafer, and there is a problem that the bending strength of the device constituting the wafer is lowered.

  In addition, a groove having a depth corresponding to the finished thickness of the device is formed on the street of the wafer, and the groove formed by grinding the back surface of the wafer is exposed from the back surface of the wafer so that the wafer is individually In a technique called dicing (DBG) that divides into devices, the grinding feed rate is slowed down carefully so as not to divide into individual devices until the grooves are exposed from the back surface of the wafer. Grinding must be performed, and there is a problem that productivity is low. Furthermore, in pre-dicing, grinding is continued to form a desired thickness even after being divided into individual devices, so that the grinding wheel generates slight vibrations due to grinding resistance, and the devices are struck finely accordingly. There is also a problem that the device is damaged.

  Therefore, the problem to be solved by the present invention is to prevent the impact strength at the start of grinding by the grinding wheel and the slight vibration of the grinding wheel from being transmitted to the wafer, thereby preventing the bending strength and the damage of the wafer and the device from being reduced. That is.

  According to the present invention, a chuck table including a holding unit that holds a wafer and a holding unit base that can rotate while supporting the holding unit, and a grindstone unit that grinds the wafer held by the chuck table are fixed to a wheel base. A grinding method for a wafer using a grinding apparatus comprising at least a grinding wheel configured, a wheel mount that supports the wheel base, and a grinding feed means for grinding and feeding the wheel mount. In the meantime, the shock absorber mounting process for interposing the shock absorber in the wheel base or the chuck table, the wafer holding process for holding the wafer in the chuck table, the wafer is rotated by rotating the chuck table, and the wheel mount is rotated. And the wheel mount is fed by grinding. At least composed of a performing grinding step a grinding stone portion of a stone in contact with the wafer.

  An example of the buffer member is a rubber sheet, and the rubber sheet has a JIS standard HS hardness of, for example, greater than 20 and less than 80. The grinding feed rate of the wheel mount is preferably 0.1 μm / second to 15 μm / second, the rotational speed of the chuck table is preferably 10 rpm to 400 rpm, and the rotational speed of the grinding wheel is preferably 1000 rpm to 7200 rpm.

  When a plurality of devices are formed on the surface of the wafer and divided into streets, a protective member is attached to the surface, the protective member side is held by the chuck table in the wafer holding process, and the wafer is used in the grinding process. The back side of is ground. In addition, when a plurality of devices are formed on the front surface of the wafer and are divided into streets, and grooves having a predetermined depth are formed on the streets, the grooves formed on the front surface of the wafer are exposed from the back surface in the grinding process. Grind the backside until it comes out. An example of the wafer is a silicon wafer.

  Further, the present invention is a grinding wheel used for carrying out the above-described wafer grinding method, and includes a wheel base and a grinding wheel portion, and a cushioning material is disposed on a side of the wheel base that is mounted on the wheel mount.

  Further, the present invention is a grinding wheel used for carrying out the above-described wafer grinding method, and includes a wheel base and a grinding wheel portion, and the wheel base is configured to sandwich a cushioning material.

  In the wafer grinding method according to the present invention, a shock absorber is interposed between the grinding wheel and the wheel base, the wheel base constituting the grinding wheel or the chuck table, and the wheel mount on which the grinding wheel is mounted is ground. Since the wafer that has been fed and held on the chuck table is ground, the impact force at the moment when the grindstone portion constituting the grinding grindstone contacts the wafer is absorbed by the buffer material. Further, the vibration of the grinding wheel due to the grinding resistance generated during grinding is also absorbed by the buffer material, and the action of finely hitting the wafer is alleviated. Therefore, a phenomenon in which grinding distortion such as a crack on the ground surface of the wafer is reduced can be reduced, and a decrease in the bending strength or breakage of the wafer or device can be prevented.

  In addition, the grinding wheel according to the present invention includes a wheel base and a grindstone portion, and is configured such that a buffer material is disposed on a side of the wheel base that is mounted on the wheel mount, or the wheel base sandwiches the buffer material. Therefore, it can be used for carrying out the above-described wafer grinding method, which is useful for reducing the bending strength of the device and preventing damage.

  A grinding apparatus 1 shown in FIG. 1 shows an example of an apparatus used for carrying out the present invention. In the cassette mounting regions 10a and 10b, a wafer cassette 100a for storing a wafer to be ground and a wafer after grinding are shown. Are placed on the wafer cassette 100b.

  A loading / unloading means 11 for loading / unloading wafers to / from the wafer cassettes 100a, 100b is disposed in the vicinity of the cassette mounting areas 10a, 10b. The wafer carried out from the wafer cassette 100a by the carry-in / out means 11 is placed on the alignment table 12, where the wafer is aligned at a fixed position.

  A first transfer means 13a is disposed in the vicinity of the alignment table 12, and the wafers aligned on the alignment table 12 are transferred to the three chuck tables 14a, 14b, and 14c by the first transfer means 13a. It is conveyed to either. Each chuck table includes a holding unit 140 that holds a wafer, and a holding unit base 141 that supports the holding unit 140 and can rotate. Further, the three chuck tables 14 a, 14 b, and 14 c move as the turn table 15 rotates.

  In the grinding apparatus 1 of FIG. 1, a first grinding feed means 17 and a second grinding feed means 18 are disposed on a wall portion 16 rising from one end portion. The first grinding feed means 17 includes a pair of guide rails 170 arranged in the vertical direction, a ball screw 171 arranged in parallel to the guide rail 170, a motor 172 connected to the tip of the ball screw 171, and a guide The elevating unit 173 is slidably engaged with the rail 170 and has an inner nut screwed into the ball screw 171. The elevating unit 173 is moved up and down as the ball screw 171 is rotated by being driven by the motor 172. It has a configuration. Similarly, the second grinding feed means 18 includes a pair of guide rails 180 arranged in the vertical direction, a ball screw 181 arranged in parallel with the guide rail 180, and a motor 182 connected to the tip of the ball screw 181. And an elevating part 183 slidably engaged with the guide rail 180 and having an internal nut screwed into the ball screw 181. The elevating part 183 is driven by the motor 182 to rotate the ball screw 181. Is configured to move up and down.

  The elevating part 173 constituting the first grinding feed means 17 supports a spindle housing 190 disposed in the vertical direction, and the spindle housing 190 supports the spindle 200 so as to be rotatable. A wheel mount 210 is fixed to the tip of the spindle 200, and a motor 200a for driving the spindle 200 is connected to the other tip. Similarly, the elevating part 183 constituting the second grinding feed means 18 supports a spindle housing 191 disposed in the vertical direction, and the spindle housing 191 supports the spindle 201 so as to be rotatable. A wheel mount 211 is fixed to the tip of the spindle 201, and a motor 201a for driving the spindle 201 is connected to the other tip.

  A plurality of through holes 210a (211a) are formed in the wheel mount 210 (211), for example, as shown in FIG. A grinding wheel 230 (231) is fixed and supported on the wheel mount 210 (211) with a buffer material 220 (221) interposed (buffer material mounting step). The grinding wheel 230 (231) is configured by a grinding wheel portion 230b (231b) being fixed to the lower surface of a ring-shaped wheel base 230a (231a), and the wheel base 230a (231a) has a plurality of screw holes. 230c (231c) is formed. The buffer material 220 (221) has, for example, a thickness of about 5 mm, a JIS standard HS hardness of more than 20 and less than 80, and a plurality of through holes 220a (221a) are formed. As the buffer material 220 (221), for example, a rubber sheet can be used. Screws 240 (241) are inserted into the through holes 210a (211a) of the wheel mount 210 (211) and the through holes 220a (221a) of the cushioning material 220 (221), and screw holes 230c (231c) of the wheel base 230a (231a) are inserted. As shown in FIG. 3, the grinding wheel 230 (231) is fixed to the wheel mount 210 (211) via the cushioning material 220 (221), as shown in FIG. In addition, the buffer material 220 (221) is disposed on the side of the wheel base 230a (231a) on which the wheel mount 210 (211) is mounted, and the buffer material 220 (221) is previously integrated with the grinding wheel 230 (231). It may be.

  Next, a wafer grinding method will be described. For example, as shown in FIG. 4, when grinding the back surface W1b of the wafer W1 partitioned by the street S and having the plurality of devices D formed on the front surface W1a, the device is protected on the front surface W1a, for example, as shown in FIG. The wafer W1 is stored in the wafer cassette 100a shown in FIG. 1 in a state where the protective member P is attached and the front and back sides are reversed, and the wafer W1 is unloaded from the wafer cassette 100a by the loading / unloading means 11. Place on the alignment table 12. Then, after the wafer W1 is aligned at a certain position, it is transferred to, for example, the chuck table 14a by the first transfer means 13a. In the chuck table 14a, the protection member P attached to the wafer W1 is held by the holding unit 140, and the back surface W1b is exposed (wafer holding process).

  Next, the rotation of the turntable 15 positions the wafer W directly below the grinding wheel 230 (position of the chuck table 14c in FIG. 1). Then, as shown in FIG. 6, the chuck table 14a rotates at a rotational speed of, for example, 10 rpm to 400 rpm, and the first grinding feed means 17 (see FIG. 1) while the grindstone portion 230b rotates as the spindle 200 rotates. The wheel mount 210 is ground and fed, and the grindstone portion 230b is lowered, the rotating grindstone portion 230b comes into contact with the back surface W1b of the wafer W1, and the back surface W1b is ground (grinding step). Here, for example, rough grinding is performed. The grinding feed speed of the wheel mount 210 is, for example, about 0.1 μm / second to 15 μm / second, and the rotational speed of the grinding wheel 230b is, for example, 1000 rpm to 7200 rpm.

  After the rough grinding is completed, the wafer W1 is positioned immediately below the grinding wheel 231 (position of the chuck table 14b in FIG. 1) by the rotation of the turntable 15. Then, as shown in FIG. 6, while the chuck table 14a is rotated, the wheel mount 211 is ground and fed by the second grinding feed means 18 (see FIG. 1) while the grindstone 231b is rotated along with the rotation of the spindle 201. Then, the grindstone portion 231b is lowered, the rotating grindstone portion 231b contacts the back surface W1b of the wafer W1, and the back surface W1b is ground (grinding step). Here, finish grinding is performed.

  In both cases of rough grinding and finish grinding, since the buffer material 220 (221) is disposed between the grinding wheel 230 (231) and the wheel mount 210 (211), the rough grinding and finish grinding are started. In other words, due to the action of the buffer material 220 (221), the impact force when the grindstone portion 230b (231b) contacts the back surface of the wafer W1 is reduced, and the impact force is not transmitted to the wafer W1. Further, grinding resistance is generated by contact between the grindstone portion 230b (231b) and the wafer W1, and fine vibration is generated in the grindstone portion 230b (231b). This fine vibration is also absorbed by the buffer material 220 (221) and is applied to the wafer W1. Is less likely to be transmitted, so that the wafer W1 is finely struck. Therefore, it becomes difficult for grinding distortion such as cracks to occur on the ground surface (back surface W1b) of the wafer W1, and it is possible to prevent the bending strength of the individual devices D constituting the wafer W1 from being lowered or damaged.

  As shown in FIG. 7, a groove G having a depth corresponding to the finished thickness of the device D is formed in the street S in the wafer W2 in which a plurality of devices D are formed on the surface W2a. In a technique called pre-dicing (DBG) in which the groove G formed by grinding the back surface W2b of the wafer W2 is exposed from the back surface W2b of the wafer W to divide the wafer W into individual devices D As shown in FIG. 7, the object to be ground is a wafer W2 in which grooves G are formed in advance on the surface street. Also in this case, rough grinding or finish grinding is performed as shown in FIG. In the finish grinding, the groove G is exposed from the back surface W2b side by grinding and is divided into individual devices D, and is formed to a predetermined thickness.

  In the case of the pre-dicing, it is necessary not to be divided into individual devices until the groove G is exposed from the back surface W2b of the wafer W2, but the slight vibration caused by the impact force or grinding resistance on the wafer W2 is buffered. Since it is absorbed by the material 220 (221) and is not transmitted to the wafer W2, it can be divided into devices without lowering the bending strength and without damaging even if the grinding feed speed is not reduced. Therefore, it is possible to prevent a decrease in productivity.

  In the above example, as shown in FIGS. 2 and 3, the case where the cushioning material 220 (221) is interposed between the wheel mount 210 (211) and the grinding wheel 230 (231) has been described. For example, as shown in FIG. 8, it is good also as a structure which interposes the buffer material 232b inside the wheel base 232a which comprises the grinding wheel 232, and clamps the buffer material 232b by the wheel base 232a.

  Further, as shown in FIG. 9, in the chuck table 14 d that holds the wafer, a buffer material 222 may be interposed inside the holding portion base 143. In either case, the shock absorber absorbs the impact force when the grindstone comes into contact with the wafer, and the shock absorber absorbs the slight vibration of the grindstone during grinding, so there is grinding distortion such as cracks on the grinding surface of the wafer. It is difficult to occur, and it is possible to prevent the bending strength of the individual devices constituting the wafer from being lowered or damaged.

  The wafer W1 (W2) thus ground is positioned in the vicinity of the second transfer means 13b by the rotation of the turntable 15, and is transferred to the cleaning means 25 by the second transfer means 13b, where the grinding debris is removed. After that, it is accommodated in the wafer cassette 100b by the loading / unloading means 11.

  In the above description, the grinding device 1 having two grinding wheels has been described as an example. However, the present invention can be applied to a device having only one grinding stone or three or more grinding wheels. Any number of chuck tables may be used.

  As shown in FIG. 10, a buffer material 221 is interposed between the wheel mount 211 and the grinding wheel 231, and a rubber sheet is used as the buffer material 221 to finish the back surface of the wafer W <b> 2 in which the groove G is formed on the surface. When grinding and dividing into individual devices by the tip dicing technique (hereinafter referred to as “when there is a cushioning material”), as shown in FIG. 11, grinding directly on the wheel mount 211 without interposing the cushioning material. In the case where the grindstone 231 is attached and the wafer W2 having the groove G formed on the surface thereof is subjected to finish grinding and divided into individual devices (hereinafter referred to as “the case without a buffer material”), the spindle 201 is respectively used. An experiment was conducted to measure the load current of the driving motor 201a (see FIG. 1). In addition, experiment was performed about the rubber sheet in the case with a buffering material, respectively, having the hardness of JIS standard HS10, 20, 30, 40, 50, 60, 70, 80, 90. The conditions other than the presence / absence of the rubber sheet are the same, and in FIG. 11, parts that are configured in the same manner as in FIG.

  In this experiment, the rotational speed of the spindle is 3200 rpm, the rotational speed of the chuck table 14a (14b, 14c) is 300 rpm, the grinding feed speed of the wheel mount 211 is 0.3 μm / second, the outer diameter is 300 mm, the thickness is 150 μm, The back surface of the silicon wafer having grooves G formed on the front streets was ground by 50 μm and divided into devices having a thickness of 100 μm by the tip dicing technique.

  When a rubber sheet having a hardness of JIS standard HS of 20, 30, 40, 50, 60, 70, 80 was used, the result shown in FIG. 12 was obtained as a change in load current value in the grinding process. In FIG. 12, the horizontal axis represents time, and the vertical axis represents the load current value of the motor 201a. When there is a buffer material, there is a slight difference in load current value depending on the JIS standard HS hardness value of the rubber sheet. However, when the JIS standard HS is 20 to 80, the unified results as shown in FIG. was gotten. On the other hand, when the JIS standard HS was 10 and 90, the result as shown in FIG. 12 was not obtained.

  In the graph of FIG. 12, the load current value suddenly increases for about 30 seconds from when the grindstone portion 231b shown in FIGS. 10 and 11 starts to contact the wafer W2 with and without the buffer material. (Transient state), and after that, although there is some up-and-down movement, it remains at an almost constant value (stable state). However, only when there is no cushioning material, the load current value increases momentarily at a time t1 before the transition to the stable state. This is considered to indicate the height of the impact force at the moment of contact between the grindstone portion 231b and the wafer W2. On the other hand, when there is a buffer material, there is no such rapid increase in load current value, and a smooth transition is made from a transient state to a stable state. This is considered because the shock absorbing material 221 absorbed the impact force at the moment of contact.

  In the stable state, the fluctuation of the load current value is smaller when the buffer material is present than when the buffer material is absent. This is considered to be because the buffer material 221 absorbs the slight vibration of the grindstone portion 231b generated due to the grinding resistance. Further, the load current value is larger in the case with the buffer material than in the case without the buffer material. This indicates that the adhesion between the grindstone 231b and the back surface W2b of the wafer W2 is high, and the grinding efficiency is good.

  In both cases with and without a buffer material, the load current value increases about 100 seconds after the load current value is almost stabilized. This is considered to be due to the fact that the wafer W2 is divided into individual devices, but the amount of increase is smaller when the buffer material is present, and the impact force on the device when divided is low. ing. Therefore, it is considered that when the cushioning material is present, the divided devices can be prevented from being damaged.

  Although not shown, when the grinding sound was measured with and without the cushioning material, the grinding sound without the cushioning material was 80 decibels, but with the cushioning material. In this case and when the JIS standard HS of the rubber sheet is 20 to 80, the grinding sound was 70 dB. Also from this, it is considered that the vibration was absorbed by the buffer material 221 and the damage to the wafer was reduced.

It is a perspective view which shows an example of a grinding device. It is a disassembled perspective view which shows an example of the assembly | attachment state of a shock absorbing material. It is a perspective view which shows the same assembly | attachment state. It is a perspective view which shows an example of a wafer. It is a front view which shows the wafer which stuck the protection member on the surface. It is explanatory drawing which shows an example of a grinding process. It is a perspective view which shows another example of a wafer. It is a perspective view which shows another example of the assembly | attachment state of a shock absorbing material. It is a perspective view which shows another example of the assembly | attachment state of a shock absorbing material. It is explanatory drawing which shows the content of an experiment in case there exists a buffering material. It is explanatory drawing which shows the content of an experiment in case there is no buffer material. It is a graph which shows an experimental result.

Explanation of symbols

1: Grinding apparatus 10a, 10b: Cassette mounting area 100a, 100b: Wafer cassette 11: Loading / unloading means 12: Positioning table 13a: First transfer means 13b: Second transfer means 14a, 14b, 14c: Chuck table 140: Holding part 141: Holding part base 14d: Chuc table 142: Holding part 143: Holding part base 15: Turntable 16: Wall part 17: First grinding feed means 170: Guide rail 171: Ball screw 172: Motor 173: Lifting part 18: Second grinding feed means 180: Guide rail 181: Ball screw 182: Motor 183: Lifting part 190, 191: Spindle housing 200, 201: Spindle 200a, 201a: Motor 210, 211: Wheel mount 210a (211a) : Through hole 20, 221: Buffer material 230, 231: Grinding wheel 230a, 231a: Wheel base 230b, 231b: Wheel portion 230c, 231c: Screw hole 222: Buffer material 232: Grinding wheel 232a: Wheel base 232b: Buffer material 240, 241 Screw 25: Cleaning means W1: Wafer W1a: Front side W1b: Back side S: Street D: Device W2: Wafer W2a: Front side W2b: Back side S: Street D: Device G: Groove

Claims (8)

A chuck table having a holding unit for holding a wafer, a holding unit base that can rotate while supporting the holding unit, and a grindstone unit for grinding the wafer held on the chuck table are fixed to a wheel base. A method of grinding a wafer using a grinding apparatus comprising at least a grinding wheel, a wheel mount for supporting the wheel base, and a grinding feed means for grinding and feeding the wheel mount,
A cushioning material mounting step in which a cushioning material is interposed between the wheel mount and the wheelbase, the wheelbase, or the chuck table;
A wafer holding step for holding the wafer on the chuck table;
At least a grinding step of rotating the chuck table to rotate the wafer, rotating the wheel mount and grinding and feeding the wheel mount to bring the grinding wheel portion of the grinding wheel into contact with the wafer to perform grinding. A method for grinding a configured wafer.   The wafer grinding method according to claim 1, wherein the buffer member is a rubber sheet, and the JIS standard HS hardness of the rubber sheet is larger than 20 and smaller than 80.   The grinding feed rate of the wheel mount is 0.1 μm / second to 15 μm / second, the rotational speed of the chuck table is 10 rpm to 400 rpm, and the rotational speed of the grinding wheel is 1000 rpm to 7200 rpm. 3. The method for grinding a wafer according to 2. On the surface of the wafer, a plurality of devices are formed divided into streets, and a protective member is attached to the surface,
In the wafer holding step, the protective member side is held by the chuck table,
The wafer grinding method according to claim 1, wherein the back surface of the wafer is ground in the grinding step. On the surface of the wafer, a plurality of devices are formed divided into streets, and grooves having a predetermined depth are formed in the streets,
4. The wafer grinding method according to claim 1, wherein in the grinding step, the back surface is ground until a groove formed on the front surface of the wafer is exposed from the back surface.   The wafer grinding method according to claim 1, wherein the wafer is a silicon wafer. A grinding wheel used in the wafer grinding method according to any one of claims 1 to 6,
A grinding wheel comprising a wheel base and a grindstone, and having a cushioning material disposed on a side of the wheel base that is mounted on a wheel mount. A grinding wheel used in the wafer grinding method according to any one of claims 1 to 6,
A grinding wheel comprising a wheel base and a grindstone, the wheel base sandwiching a cushioning material.

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