JP7537986B2 - Wafer grinding method - Google Patents

Description

The present invention relates to a method for grinding wafers.

In a wafer grinding method that uses an annular grinding wheel to grind a wafer such as a semiconductor wafer held on the holding surface of a chuck table, the grinding wheel and the chuck table are arranged in a horizontal direction parallel to the holding surface so that the rotational path of the grinding wheel passes through the center of the holding surface. The holding surface is a conical slope with its center as its apex, and the wafer is ground on the rotational path in which the bottom surface of the grinding wheel is parallel to the conical slope.

When the top surface of a wafer is ground, a depression (e.g., center depth 0.5 μm, diameter 20 mm to 30 mm) is formed in the center of the wafer because there is a portion of the wafer near the apex of the conical slope that does not conform to the holding surface. For this reason, as disclosed in Patent Document 1, the top surface of the chuck table is self-ground to form a holding surface in which the apex of the conical slope is flattened in advance, so that a depression is not formed in the center of the wafer that is ground while held on the holding surface.

JP 2019-136806 A

However, self-grinding the top surface of the chuck table as described above to form an appropriate holding surface that does not form a depression in the center of the wafer takes a lot of time because the shape of the holding surface to be formed is complex.
Therefore, a wafer grinding method for grinding a wafer has a problem of grinding the wafer held on the holding surface flatly so that no depression is formed in the center, without taking the time to form the holding surface.

The present invention provides a method for grinding a wafer using a grinding device including: holding means for rotating a chuck table, on which a wafer is held on a holding surface that is a conical slope having a vertex at its center, around an axis of the holding surface; grinding means for rotating an annular grinding wheel around an axis of the center of the grinding wheel to grind the wafer held on the holding surface; grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to a bottom surface of the grinding wheel; and slide feed means for relatively moving the holding means and the grinding means in a direction parallel to the bottom surface of the grinding wheel, the method comprising: a holding step for holding a wafer on the holding surface; a first grinding step for rotating the wafer on an axis of the center of the wafer and relatively moving the holding means and the grinding means closer to each other in a direction perpendicular to the bottom surface of the grinding wheel, and stopping the movement in the perpendicular direction after the grinding wheel passes through the center of the wafer and grinds the wafer to a predetermined thickness; Therefore, this is a wafer grinding method comprising: a load measuring step of measuring a load value at the end of the first grinding step; a slide movement setting step of selecting a slide movement amount and a slide movement speed in the second grinding step from a preset data table based on the load value measured in the load measuring step and the grit size of the grinding wheel; a second grinding step of grinding the wafer by moving the holding means and the grinding means relatively in a direction parallel to the bottom surface of the grinding wheel after the first grinding step, the load measuring step and the slide movement setting step, thereby moving the grinding wheel from the center of the top surface of the wafer toward the outer periphery by the slide movement amount at the slide movement speed selected in the slide movement setting step ; and a third grinding step of grinding the wafer while moving the holding means and the grinding means relatively away from each other in the perpendicular direction after the second grinding step.
The second grinding step in the above grinding method desirably involves relatively reciprocating the holding means and the grinding means in a direction parallel to the lower surface of the grinding wheel by the amount of slide movement .

The wafer grinding method of the present invention makes it possible to form a wafer of uniform thickness without forming a recess in the center of the wafer, thereby shortening the wafer grinding time.

FIG. 2 is a perspective view showing the entire grinding device. FIG. 4 is a cross-sectional view showing a grinding means and a holding means in a first grinding step. FIG. 11 is a graph showing the relationship between the height of the lower surface of the grinding wheel and grinding time. 4 is a plan view showing the positional relationship between a grinding wheel and a wafer during grinding in a first grinding step. FIG. FIG. 11 is a table showing an example of a data table showing a slide movement amount and a slide movement speed in relation to a grinding wheel grit size and a load during grinding. FIG. 11 is a graph showing the relationship between the load and the slide movement amount for each slide movement speed. 11 is a plan view showing the positional relationship between a grinding wheel and a wafer during grinding in a second grinding step. FIG. 11 is a plan view showing the positional relationship between a grinding wheel and a wafer during grinding in a second grinding step. FIG.

1 Configuration of the Grinding Apparatus The grinding apparatus 1 shown in Fig. 1 is a grinding apparatus that grinds a disk-shaped wafer 17 using a grinding means 3. The configuration of the grinding apparatus 1 will be described below.
As shown in FIG. 1, the grinding device 1 includes a base 10 extending in the Y-axis direction, and a column 11 standing on the +Y-direction side of the base 10 .

A grinding feed means 4 that supports the grinding means 3 so that it can be raised and lowered is disposed on the side surface on the -Y direction side of the column 11. The grinding means 3 includes a spindle 30 having a rotation axis 35 in the Z-axis direction, a housing 31 that rotatably supports the spindle 30, a spindle motor 32 that rotates and drives the spindle 30 around the axis center in the Z-axis direction, a mount 33 connected to the lower end of the spindle 30, and a grinding wheel 34 that is detachably attached to the lower surface of the mount 33.

The grinding wheel 34 includes a wheel base 341 and a grinding stone 340 provided on the underside of the wheel base 341. The grinding stone 340 is formed, for example, in a circular ring shape, and the underside 342 of the grinding stone 340 is the grinding surface that comes into contact with the wafer 17.

By rotating the spindle 30 using the spindle motor 32, the mount 33 connected to the spindle 30 and the grinding wheel 34 attached to the underside of the mount 33 rotate together.

The grinding feed means 4 includes a ball screw 40 having a rotating shaft 45 in the Z-axis direction, a pair of guide rails 41 arranged parallel to the ball screw 40, a Z-axis motor 42 that rotates the ball screw 40 around the rotating shaft 45, a lift plate 43 whose internal nut is screwed onto the ball screw 40 and whose side is in sliding contact with the guide rail 41, and a holder 44 connected to the lift plate 43 and supporting the grinding means 3.

When the ball screw 40 is driven by the Z-axis motor 42 and rotates around the rotation shaft 45, the lift plate 43 is guided by the guide rail 41 and moves up and down in the Z-axis direction, and the grinding means 3 held by the holder 44 moves in the Z-axis direction.

A scale 470 is provided on the side surface of the guide rail 41 facing the -Y direction, and a reading unit 471 is provided on the side surface of the lift plate 43 facing the +X direction. The reading unit 471 has, for example, an optical recognition mechanism that reads the value of the scale marks formed on the scale 470, and can recognize the height position of the grinding means 3 by recognizing the marks on the scale 470.

The holding means 2 is disposed on the base 10. The holding means 2 includes a chuck table 20 that holds the wafer 17. The chuck table 20 includes a suction portion 21 and a frame 22 that supports the suction portion 21. The upper surface of the suction portion 21 is a holding surface 210 that holds the wafer 17, and the holding surface 210 has a conical slope shape with its center 2100 as its apex.

The chuck table 20 is connected to a suction source 26. When the suction source 26 is activated, the suction force generated is transmitted to the holding surface 210. By activating the suction source 26 with the wafer 17 placed on the holding surface 210, the wafer 17 can be suction-held on the holding surface 210.

The holding means 2 also includes a rotating means 24 having a motor or the like. By using the rotating means 24, the chuck table 20 can be rotated around the center 2100 of the holding surface 210 as an axis.

The chuck table 20 is rotatably supported by the table base 23. Three through holes 230 that penetrate the table base 23 in the Z-axis direction are formed at equally spaced positions on the same circumference of the table base 23. A support shaft 29 passes through each through hole 230, and the table base 23 is supported by the support shaft 29.

An internal base 100 is disposed inside the base 10. A slide feed means 5 for moving the chuck table 20 in the horizontal direction is disposed on the internal base 100.
The slide feed means 5 includes a ball screw 50 having a rotation shaft 55 in the Y-axis direction, a Y-axis motor 52 that rotates the ball screw 50 around the rotation shaft 55, a pair of guide rails 51 arranged parallel to the ball screw 50, and a slide plate 53 whose bottom nut is screwed onto the ball screw 50 and moves along the guide rails 51 in the Y-axis direction.

Three support shafts 29 are erected on the slide plate 53. A load sensor 290 is also provided between the slide plate 53 and the support shafts 29. The load sensor 290 detects the load acting on the chuck table 20 and can measure its magnitude.

When the ball screw 50 is rotated using the Y-axis motor 52, the slide plate 53 is guided by the guide rail 51 and moves horizontally in the Y-axis direction, and the chuck table 20 supported by the slide plate 53 via the support shaft 29 and table base 23 moves integrally with the slide plate 53 in the Y-axis direction.

A thickness measuring means 18 for measuring the thickness of the wafer 17 is disposed adjacent to the chuck table 20. The thickness measuring means 18 has, for example, a contact-type height gauge, and can measure the thickness of the wafer 17 by contacting the height gauge with the upper surface 170 of the wafer 17 and the upper surface 220 of the frame 22 and measuring the difference in height between the two.

A cover 27 is disposed around the chuck table 20, and the cover 27 is connected to the bellows 28 so that it can expand and contract. When the chuck table 20 moves horizontally in the Y-axis direction, the cover 27 moves in the Y-axis direction together with the chuck table 20, causing the bellows 28 to expand and contract.

The grinding device 1 is equipped with a control means 9 that controls various operations of the grinding device 1. The control means 9 can refer to a storage unit 90 that has a storage element such as a memory.

2. Wafer grinding method (holding process)
A method for grinding the wafer 17 using the grinding apparatus 1 will be described. First, the wafer 17 is placed on the holding surface 210 of the chuck table 20 shown in Fig. 1 so that the center 1700 of the upper surface 170 and the center 2100 of the holding surface 210 are horizontally aligned. Then, the suction source 26 is operated to transmit the generated suction force to the holding surface 210, thereby suction-holding the wafer 17 on the holding surface 210.

(First grinding process)
Next, the wafer 17 held on the chuck table 20 is moved in the +Y direction using the slide feed means 5 to move the wafer 17 below the grinding wheel 340. At this time, the horizontal positional relationship between the two is adjusted so that the lower surface 342 of the grinding wheel 340 passes through the center 1700 of the wafer 17 as shown in FIG.

The chuck table 20 is rotated around the center 2100 of the holding surface 210 by using the rotating means 24, thereby rotating the wafer 17 around its center 1700. Furthermore, the grinding wheel 340 is rotated around the rotating shaft 35 by using the spindle motor 32.

Then, while the wafer 17 and grinding wheel 340 are rotating, the grinding wheel 340 is lowered in the -Z direction, which is perpendicular to the lower surface 342, using the grinding feed means 4 shown in FIG. 1. This brings the grinding wheel 340 and the wafer 17 held on the chuck table 20 closer together.

Hereinafter, the height position of the lower surface 342 of the grinding wheel 340 when the grinding wheel 340 descends toward the upper surface 170 of the wafer 17 during grinding of the wafer 17 will be described with reference to the graph shown in FIG.
First, the grinding wheel 340 is lowered in the −Z direction at a preparatory speed 70 to position the height of the lower surface 342 of the grinding wheel 340 at the air-cut height 60. Here, the air-cut height 60 is the height immediately before the lower surface 342 of the grinding wheel 340 comes into contact with the upper surface 170 of the wafer 17.

Thereafter, the grinding wheel 340 is lowered in the −Z direction from the air-cut height 60 to the first grinding height 61 at the first grinding speed 71 over the air-cut time 80 .
As a result, the grinding wheel 340 approaches the upper surface 170 of the wafer 17 while rotating above the upper surface 170 without contacting the upper surface 170 .
Here, the first grinding height 61 is the height of the lower surface 342 of the grinding wheel 340 when the lower surface 342 of the grinding wheel 340 comes into contact with the upper surface 170 of the wafer 17. When the grinding wheel 340 is positioned at the first grinding height 61, the lower surface 342 of the grinding wheel 340 comes into contact with the upper surface 170 of the wafer 17.

Figure 4 shows the state in which the lower surface 342 of the grinding wheel 340 is in contact with the upper surface 170 of the wafer 17. The arc-shaped grinding region 12 shown in Figure 4 is the region in which the upper surface 170 of the wafer 17 and the lower surface 342 of the grinding wheel 340 are in contact. As the wafer 17 and the grinding wheel 340 rotate while the upper surface 170 of the wafer 17 and the lower surface 342 of the grinding wheel 340 are in contact in the grinding region 12 corresponding to the radius of the wafer, the lower surface 342 of the grinding wheel 340 comes into contact with the entire upper surface 170 of the wafer 17, and the entire upper surface 170 of the wafer 17 is ground.

With the lower surface 342 of the grinding wheel 340 positioned at the first grinding height 61 and in contact with the upper surface 170 of the wafer 17, the grinding wheel 340 is further lowered in the -Z direction at the first grinding speed 71. As a result, the upper surface 170 of the wafer 17 is ground.
As shown in FIG. 3, the lower surface 342 of the grinding wheel 340 descends from the first grinding height 61 to the second grinding height 62 over the first grinding time 81 .

Then, with the lower surface 342 of the grinding wheel 340 positioned at the second grinding height 62, the grinding wheel 340 is lowered in the -Z direction at a second grinding speed 72 that is slower than the first grinding speed 71. This causes the upper surface 170 of the wafer 17 to be ground more slowly than when the grinding wheel 340 was lowering at the first grinding speed 71.

During the grinding process of the wafer 17, the thickness of the wafer 17 is measured using the thickness measuring means 18. Then, when the wafer 17 is ground to a predetermined thickness, the descent of the grinding wheel 340 is stopped. The graph in FIG. 3 shows that the lower surface 342 of the grinding wheel 340 reaches the stop height 63 over the second grinding time 82 and stops at the stop height 63.

(Load measurement process)
Next, the load value acting on the chuck table 20 at the end of the first grinding step is measured using the load sensor 290 shown in FIG.
The measurement of the load by the load sensor 290 may be started simultaneously with the start of the first grinding step.

(Slide operation setting process)
Next, in the second grinding step described later, the chuck table 20 is slid in the Y-axis direction to grind the upper surface 170 of the wafer 17 at a position in the Y-axis direction different from the grinding position in the first grinding step, so that the sliding movement amount of the chuck table 20 is obtained. For this purpose, based on the measured load value and the grit of the grinding wheel 340, a sliding movement amount and a sliding speed are selected from a data table 91 shown in FIG. 5 that is preset and stored in the memory unit 90. This data table 91 specifies the relative sliding movement amount of the chuck table 20 with respect to the grinding wheel 340 in the relationship between the relative sliding speed of the chuck table 20 with respect to the grinding wheel 340 and the load applied to the chuck table 20 at the end of the first grinding step, and is used to obtain the conditions of the second grinding step described later. Here, the relative sliding speed of the chuck table 20 with respect to the grinding wheel 340 corresponds to the grit of the grinding wheel 340. Also, FIG. 6 shows the data table 91 of FIG. 5 in a graph.

For example, if the grinding wheel 34 shown in FIG. 1 is Poligrind-12 (manufactured by Disco), the grit size of the grinding stone 340 is #8000, so a slide speed of 0.2 mm/s is selected. Furthermore, if the measured load value is, for example, 100 N, a slide movement amount of 1.0 mm is selected.

(Second grinding process)
After the slide speed and slide movement amount are selected, while maintaining the stop height 6 of the grinding wheel 340 at the end of the second grinding time 82, the wafer 17 held on the chuck table 20 is ground by moving it in the +Y direction, which is a direction parallel to the lower surface 342 of the grinding wheel 340, by a slide movement amount of 1.0 mm at a slide speed of 0.2 mm/s using the slide feed means 5 shown in Fig. 1. Depending on the movement amount, the rotational orbit of the grinding wheel 340 may not pass through the center 1700 of the wafer 17, as shown in Fig. 7.

As shown in FIG. 7, the rotational orbit of the grinding wheel 340 shown in FIG. 2 passes through the center 1700 of the wafer 17, and the wafer 17 moves in the -Y direction, causing the grinding wheel 340 to move relatively from the center 1700 of the upper surface 170 of the wafer 17 toward the outer periphery. The time required for this movement is the slide movement time 83 shown in FIG. 3, and during this movement, the lower surface 342 of the grinding wheel 340 comes into contact with the upper surface 170 of the wafer 17, grinding the upper surface 170 of the wafer 17. At the end of the second grinding process, for example, as shown in FIG. 8, the rotational orbit of the grinding wheel 340 does not pass through the center 1700 of the upper surface 170 of the wafer 17.

(Third grinding process)
Next, the grinding wheel 340 is raised in the +Z direction using the grinding feed means 4, and the chuck table 20 and the grinding wheel 340 are relatively separated in a direction perpendicular to the lower surface 342 of the grinding wheel 340. As a result, the wafer 17 is ground while the lower surface 342 of the grinding wheel 340 is separated from the wafer 17 held on the chuck table 20.
As shown in the graph of FIG. 3, the lower surface 342 of the grinding wheel 340 is spaced from the wafer 17 over a space time 84 .

Then, the grinding wheel 340 is moved sufficiently away from the upper surface 170 of the wafer 17 at even higher speed using the grinding feed means 4, and the wafer 17 is then removed from the holding surface 210.

In the above-described method for grinding the wafer 17, since the portion other than the central portion is ground in the second grinding step, the upper surface 170 of the wafer 17 becomes flat as a whole, and a wafer of uniform thickness can be formed without forming a recess in the center of the wafer 17. This makes it possible to shorten the grinding time.
Since the greater the load during grinding, the deeper and wider the recess formed in the center of the upper surface 170 of the wafer 17 tends to be, as shown in data table 91 of FIG. 5, as the load increases, the relative sliding movement of the chuck table 20 with respect to the grinding wheel 340 also increases.

In the second grinding step of the above grinding method, the chuck table 20 and the grinding wheel 340 may be moved back and forth relative to each other in a direction parallel to the lower surface 342 of the grinding wheel 340 by a predetermined sliding movement amount. In this case, the wafer 17 is slidably ground by repeatedly positioning the lower surface 342 of the grinding wheel 340 at the center of the upper surface 170 of the wafer 17 and then moving the lower surface 342 of the grinding wheel 340 away from the center of the upper surface 170 of the wafer 17. This allows the amount of the wafer 17 to be ground to be increased, and the time required for the second grinding step to be shortened.

In the above grinding device 1, the holding means 2 is configured to slide in the Y-axis direction, but the grinding means 3 may be configured to move in the X-axis direction or the Y-axis direction. In other words, it is sufficient that the holding means 2 and the grinding means 3 are relatively movable in a direction parallel to the lower surface 342 of the grinding wheel 340. In addition, in the grinding device 1, the grinding means 3 is configured to move in the Z-axis direction, but the holding means 2 may be configured to move in the Z-axis direction. In other words, it is sufficient that the holding means 2 and the grinding means 3 are relatively movable in a direction perpendicular to the lower surface 342 of the grinding wheel 340.

1: Grinding device 10: Base 100: Inner base 11: Column 12: Grinding area 17: Wafer 170: Top surface 1700: Center 18: Thickness measuring means
2: Holding means 20: Chuck table 21: Suction portion 210: Holding surface 2100: Center 22: Frame 220: Upper surface 23: Table base 230: Through hole 24: Rotating means 26: Suction source 27: Cover 28: Bellows 29: Support shaft 290: Load sensor 3: Grinding means 30: Spindle 31: Housing 32: Spindle motor 33: Mount 34: Grinding wheel 340: Grinding stone 341: Wheel base 342: Lower surface 343: Side surface 35: Rotating shaft 4: Grinding feed means 40: Ball screw 41: Guide rail 42: Z-axis motor 43: Lift plate 44: Holder 45: Rotating shaft 470: Scale 471: Reading portion 5: Slide feed means 50: Ball screw 51: Guide rail 52: Y-axis motor 53: Slide plate 55: Rotating shaft 60: Air cut height 61: First grinding height 62: Second grinding height 63: Stop height 70: Preparation speed 71: First grinding speed 72: Second grinding speed 80: Air cut time 81: First grinding time 82: Second grinding time 83: Slide movement time 84: Separation time 9: Control means 90: Memory unit 91: Data table

Claims (2)

A method for grinding a wafer using a grinding device including: holding means for rotating a chuck table, on which a wafer is held by a holding surface that is a conical slope having a center as an apex, about an axis of the holding surface; grinding means for rotating an annular grinding wheel about an axis of the center of the grinding wheel to grind the wafer held on the holding surface; grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to a bottom surface of the grinding wheel; and slide feed means for relatively moving the holding means and the grinding means in a direction parallel to the bottom surface of the grinding wheel,
a holding step of holding a wafer on the holding surface;
a first grinding step of rotating the wafer around its center as an axis, moving the holding means and the grinding means relatively close to each other in a direction perpendicular to a lower surface of the grinding wheel, and stopping the movement in the perpendicular direction after the grinding wheel passes through the center of the wafer and grinds the wafer to a predetermined thickness;
a load measuring step of measuring a load value at the end of the first grinding step by a load sensor;
a slide operation setting step of selecting a slide movement amount and a slide movement speed in the second grinding step from a preset data table based on the load value measured in the load measuring step and the grit size of the grinding wheel;
a second grinding step of relatively moving the holding means and the grinding means in a direction parallel to a lower surface of the grinding wheel after the first grinding step , the load measuring step and the slide movement setting step , thereby moving the grinding wheel from the center of the upper surface of the wafer toward the outer periphery by the slide movement amount at the slide movement speed selected in the slide movement setting step, thereby grinding the wafer;
and a third grinding step of, after the second grinding step, moving the holding means and the grinding means relatively apart in the vertical direction to move the lower surface of the grinding wheel away from the wafer while grinding the wafer. 2. The method for grinding a wafer according to claim 1, wherein said second grinding step comprises reciprocating said holding means and said grinding means relatively in a direction parallel to the lower surface of said grinding wheel by the amount of said slide movement .

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