JP7474082B2 - Wafer grinding method - Google Patents

Description

The present invention relates to a grinding method for grinding semiconductor wafers, etc.

A grinding device for grinding semiconductor wafers comprises a chuck table that holds a wafer on a holding surface and rotates around the center of the holding surface, and a grinding means that rotates an annular grinding wheel around its center and grinds the wafer held on the holding surface. The holding surface is formed into an extremely gentle conical slope with its center at its apex, which is so gentle that it cannot be seen with the naked eye. Then, with the holding surface, which is an extremely gentle conical slope, tilted by the tilt adjustment means so that it is parallel to the underside of the grinding wheel, the grinding wheel passes through the center of the holding surface and grinds the wafer in the range from the outer periphery of the holding surface to the center on the grinding wheel's rotation trajectory.

For example, a vitrified bonded grinding wheel with air holes is moved toward the holding surface at a predetermined grinding feed rate, and the grinding wheel is pressed against the wafer held on the holding surface, applying a load of, for example, 60 N, while grinding the top surface of the wafer, which is the surface to be ground. As a result, the grinding wheel passing through the center of the wafer held on the holding surface during grinding is compressed just before the center due to the resistance from the wafer that resists the grinding load, and after passing the center, the grinding load is eliminated, and the resistance from the wafer is eliminated, causing the wheel to expand. As a result, the center of the wafer in the area of the grinding wheel's rotation trajectory comes into contact with the wheel more frequently, and is ground more than other parts, which may result in a depression, which is a cylindrical space with a diameter of 2 mm to 4 mm.

For this reason, as disclosed in, for example, Patent Document 1, there is an invention in which the top surface of the chuck table is ground to form an appropriate holding surface that does not form cylindrical depressions in the wafer (self-grinding).

JP 2019-136806 A

However, there is a problem in that forming an appropriate holding surface by self-grinding the upper surface of the chuck table as described above takes time because the shape of the holding surface to be formed is complex.
Therefore, in a wafer grinding method in which a wafer held on a holding surface is ground with a grinding wheel, there is a problem of not requiring a time-consuming process of forming the holding surface by self-grinding, and also of not forming a cylindrical depression in the center of the wafer after grinding while held by the holding surface.

The wafer is ground in a radial area of the holding surface parallel to the lower surface of the grinding wheel by using a grinding device including: holding means for holding a wafer on a holding surface that is a conical slope with the center at the apex and that can rotate about the center of the holding surface; grinding means for mounting an annular grinding wheel so that the grinding wheel can rotate about the center of the grinding wheel and for grinding the wafer held on the holding surface with the grinding wheel; horizontal movement means for relatively moving the holding means and the grinding means in a horizontal direction parallel to the lower surface of the grinding wheel; and grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to the holding surface. a grinding method for a wafer, the method comprising : a diameter measuring step of measuring a diameter of a cylindrical recess formed in the center of a test wafer held on a holding surface by grinding the test wafer with the grinding wheel whose rotation locus passes through the center of the holding surface; a step of removing the test wafer from the holding surface; a holding step of holding the wafer on the holding surface by aligning the center of the holding surface with the center of the wafer; and a step of moving the grinding wheel by using the horizontal moving means to move the grinding wheel, the diameter being a preset distance equal to the measured diameter measured in the diameter measuring step, the grinding wheel being moved to a predetermined distance equal to the measured diameter measured in the diameter measuring step, the cylindrical recess formed in the center of the test wafer held on the holding surface by the grinding wheel whose rotation locus passes through the center of the holding surface; a first positioning step of positioning the wafer with respect to the grinding wheel such that the distance between the outer or inner circumference of the rotational path and the center of the holding surface is half of the measured diameter by shifting the rotational path of the grinding wheel by a preset distance from the center of the holding surface so that the rotational path does not pass through the center of rotation of the wafer held on the holding surface ; and after the first positioning step, the grinding wheel is fed by the grinding feed means in a direction approaching the holding surface to grind the wafer to a thickness that is a preset value (e.g., 1 μm to 3 μm) thicker than a preset finishing thickness. a first grinding step of forming a cylindrical convex portion having a diameter smaller than the blade width in a central portion of the wafer where the grinding wheel does not pass, a second positioning step of using the horizontal movement means to position the wafer with respect to the grinding wheel so that the rotation locus of the grinding wheel passes through the center of the holding surface after the first grinding step, and a second grinding step of using the grinding feed means to move the grinding wheel in a direction approaching the holding surface after the second positioning step, thereby removing the cylindrical convex portion and grinding the wafer to the preset finishing thickness.

a grinding device for grinding a wafer in a radial region of the holding surface parallel to a lower surface of the grinding wheel using a grinding device comprising: holding means for holding a wafer on a holding surface that is a conical slope having a vertex at the center and that can rotate about an axis of the holding surface; grinding means for mounting the grinding wheel so that the grinding wheel is rotatable about the center of the grinding wheel and for grinding the wafer held on the holding surface with the grinding wheel; horizontal movement means for relatively moving the holding means and the grinding means in a horizontal direction parallel to a lower surface of the grinding wheel; and grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to the holding surface, the method comprising the steps of: holding a wafer on the holding surface by aligning the center of the holding surface with the center of the wafer; a first grinding step of, after the first positioning step, feeding the grinding wheel in a direction approaching the holding surface by the grinding feed means to grind the wafer to a thickness that is thicker than a predetermined finishing thickness by a predetermined value, thereby forming a cylindrical convex portion having a diameter smaller than the cutting width in a central portion of the wafer that is not passed by the grinding wheel; a second positioning step of, after the first grinding step, using the horizontal movement means to position the wafer relative to the grinding wheel so that the rotational locus of the grinding wheel passes through the center of the holding surface; and a second grinding step of, after the second positioning step, moving the grinding wheel in a direction approaching the holding surface by the grinding feed means to remove the cylindrical convex portion and grind the wafer to the predetermined finishing thickness .

The method for grinding a wafer according to the present invention includes a holding step in which the center of the holding surface is aligned with the center of the wafer to hold the wafer on the holding surface, a first positioning step in which the horizontal movement means is used to position the wafer relative to the grinding wheel by shifting the rotational trajectory of the grinding wheel, which is defined by the radial blade width of the grinding wheel, a preset distance from the center of the holding surface so that the rotational trajectory of the grinding wheel does not pass through the center of the holding surface, and a first grinding step in which, after the first positioning step, the grinding wheel is fed by the grinding feed means in a direction approaching the holding surface to grind the wafer to a thickness that is a preset value (1 μm to 3 μm) thicker than a preset finishing thickness, thereby forming a cylindrical protrusion with a diameter smaller than the blade width of the grinding wheel in the central portion of the wafer where the grinding wheel does not pass. Then, after the first grinding step, a second positioning step is performed in which the horizontal movement means is used to position the wafer relative to the grinding wheel so that the rotational trajectory of the grinding wheel passes through the center of the holding surface, and after the second positioning step, the grinding wheel is moved in a direction approaching the holding surface by the grinding feed means to eliminate the cylindrical convex portion and grind the wafer to a preset finishing thickness. By performing this step, in the second grinding step, the center of the wafer is more likely to come into contact with the grinding wheel, and the cylindrical convex portion formed on the grinding surface of the wafer in the first grinding step is ground away more than the other parts of the grinding surface of the wafer, making it possible to make the wafer after the second grinding step into a wafer of uniform thickness that does not have the cylindrical concave portion that was previously formed in the center of the wafer.

FIG. 2 is a perspective view showing an example of a grinding device. 11A to 11C are cross-sectional views for explaining a holding step, a first positioning step, and a first grinding step. FIG. 11 is a plan view for explaining a holding step, a first positioning step, and a first grinding step. 10 is a cross-sectional view illustrating a case in which the wafer is positioned relative to the grinding wheel in the first positioning step by shifting the distance between the outer periphery of the rotational trajectory and the center of the holding surface to half the blade width of the grinding wheel. FIG. This is a plan view explaining the case where, in the first positioning step, the wafer is positioned relative to the grinding wheel by shifting it so that the distance between the outer periphery of the rotational trajectory and the center of the holding surface is half the blade width of the grinding wheel. 4 is a graph showing the relationship between the grinding time and the height of the grinding means in the wafer grinding method according to the present invention. 11 is a cross-sectional view for explaining a second positioning step and a second grinding step. FIG. FIG. 11 is a plan view for explaining a second positioning step and a second grinding step. 11 is a cross-sectional view for explaining a diameter measurement process using a test wafer. FIG. 10 is a cross-sectional view illustrating a cylindrical recess formed in the center of a test wafer in a diameter measurement process. FIG. 11 is a cross-sectional view illustrating a case where a first positioning step is performed using the measured diameter of a cylindrical recess measured in the diameter measuring step. FIG. 13 is a plan view illustrating a case where the first positioning step is performed using the measured diameter of the cylindrical recess measured in the diameter measuring step. FIG.

The grinding apparatus 1 shown in FIG. 1 is an apparatus that uses a grinding means 16 to grind a wafer 80 that is suction-held on a holding means 30 such as a chuck table, and the front (-Y direction side) on an apparatus base 10 of the grinding apparatus 1 is an attachment/detachment area where the wafer 80 is attached to and detached from the holding means 30, and the rear (+Y direction side) on the apparatus base 10 is a processing area where the wafer 80 held on the holding means 30 is ground by the grinding means 16.
The grinding device according to the present invention is not limited to a grinding device having a single-axis grinding means 16 such as the grinding device 1, but may be a two-axis grinding device having a rough grinding means and a finish grinding means and capable of positioning the wafer 80 below the rough grinding means or the finish grinding means using a rotating turntable.

1 is, for example, a circular as-sliced wafer formed by thinly slicing a cylindrical silicon ingot with a wire saw or the like. The surface of the wafer 80 facing downward in FIG. 1 is a front surface 801, and the surface opposite to the front surface 801 in the Z-axis direction (vertical direction) is a ground surface 802. For example, the front surface 801 may be protected by a protective member (not shown) attached thereto.
It should be noted that the wafer 80 is not limited to the as-sliced wafer.

The holding means 30, which has a circular outer shape in a plan view, includes, for example, an adsorption part 300 made of a porous member or the like that adsorbs the wafer 80, and a frame 301 that supports the adsorption part 300. The adsorption part 300 of the holding means 30 communicates with a suction source 37 (see FIG. 2 ) such as an ejector mechanism or a vacuum generator, and the suction force generated by the suction source 37 is transmitted to a holding surface 302 that is composed of an exposed surface of the adsorption part 300 and an upper surface of the frame 301, thereby enabling the holding means 30 to adsorb and hold the wafer 80 on the holding surface 302.
The holding surface 302 forms a very gently sloping cone with its apex at the center of rotation 3022 of the holding means 30, the slope of which is so gentle that it cannot be discerned by the naked eye.

The holding means 30 is surrounded by a cover 39 and can rotate about a rotation axis whose axis direction is the Z-axis direction (vertical direction) and passes through the center 3022 of the holding surface 302. The horizontal movement means 13 is disposed below the cover 39 and a bellows cover 390 that is connected to the cover 39 and expands and contracts in the Y-axis direction, and can move back and forth in the Y-axis direction on the device base 10.

The horizontal movement means 13, which moves the holding means 30 and the grinding means 16 relatively in the horizontal direction (Y-axis direction) parallel to the underside of the grinding wheel 1644 of the grinding means 16, is equipped with a ball screw 130 having an axis in the Y-axis direction, a pair of guide rails 131 arranged parallel to the ball screw 130, a motor 132 connected to one end of the ball screw 130 and rotating the ball screw 130, and a movable plate 133 whose internal nut screws into the ball screw 130 and whose bottom is in sliding contact with the guide rail 131.When the motor 132 rotates the ball screw 130, the movable plate 133 is guided by the guide rail 131 and moves linearly in the Y-axis direction, and the holding means 30 arranged on the movable plate 133 via a table base 35 can be moved in the Y-axis direction.
The horizontal moving means 13 may be a turntable.

The holding means 30 is disposed on the movable plate 133 via a table base 35. The tilt of the table base 35 can be adjusted by a plurality of tilt adjustment means 34 disposed at equal intervals in the circumferential direction of the holding means 30. By adjusting the tilt of the table base 35, the tilt of the holding surface 302 of the holding means 30 relative to the lower surface of the grinding wheel 1644 of the grinding means 16 can be adjusted.
In this embodiment, the inclination adjustment means 34 includes, for example, two lifting units 340 arranged at an interval of 120 degrees in the circumferential direction of the holding means 30, and a fixed column unit 341 arranged at an interval of 120 degrees in the circumferential direction from the lifting units 340. The two lifting units 340 are, for example, electric cylinders or air cylinders that can move up and down in the Z-axis direction.

In the processing area, a column 11 is erected, and a grinding feed means 17 is disposed on the front surface of the column 11 on the -Y direction side, which moves the holding means 30 and the grinding means 16 relatively in a direction perpendicular to the holding surface 302 (Z-axis direction). The grinding feed means 17 includes a ball screw 170 whose axial direction is the Z-axis direction, a pair of guide rails 171 disposed parallel to the ball screw 170, a lifting motor 172 connected to the upper end of the ball screw 170 and rotating the ball screw 170, and a lifting plate 173 whose internal nut is screwed into the ball screw 170 and whose side is in sliding contact with the guide rail 171. When the lifting motor 172 rotates the ball screw 170, the lifting plate 173 is guided by the guide rail 171 and moves back and forth in the Z-axis direction, and the grinding means 16 fixed to the lifting plate 173 is fed for grinding in the Z-axis direction.

For example, the grinding device 1 is equipped with height position detection means 12 that detects the height position of the grinding means 16 that moves up and down by the grinding feed means 17. The height position detection means 12 is equipped with a scale 120 that extends in the Z-axis direction along a pair of guide rails 171, and a reading unit 123 that is fixed to the lift plate 173, moves together with the lift plate 173 along the scale 120, and optically reads the graduations of the scale 120.

The grinding means 16, which grinds the wafer 80 held on the holding surface 302 of the holding means 30, includes a rotating shaft 160 whose axial direction is the Z-axis direction, a housing 161 that rotatably supports the rotating shaft 160, a motor 162 that rotates the rotating shaft 160, an annular mount 163 connected to the lower end of the rotating shaft 160, a grinding wheel 164 that is detachably attached to the lower surface of the mount 163, and a holder 165 that supports the housing 161 and is fixed to the lift plate 173 of the grinding feed means 17.

The grinding wheel 164 includes a wheel base 1643 and a grinding wheel 1644 arranged in a ring shape on the bottom surface of the wheel base 1643. In this embodiment, the grinding wheel 1644 is, for example, a vitrified bond grinding wheel in a continuous arrangement in which diamond abrasive grains or the like are fixed with a vitrified bond having air holes and formed into a single ring shape. The blade width of the ring-shaped grinding wheel 1644 is set to, for example, 3 mm. The grinding wheel may be a segmented grinding wheel in which multiple grinding wheel chips of approximately rectangular parallelepiped shape are arranged in a ring shape with a predetermined interval between the grinding wheel chips on the underside of the wheel base 1643, and the bond for fixing the abrasive grains is not limited to a vitrified bond and may be a resin bond.

Inside the rotating shaft 160 shown in FIG. 1, a flow passage (not shown) that is connected to a grinding water supply source and serves as a passage for grinding water is provided, penetrating the axial direction (Z-axis direction) of the rotating shaft 160, and the flow passage (not shown) further passes through the mount 163 and opens at the bottom surface of the wheel base 1643 so that the grinding water can be sprayed toward the grinding wheel 1644.

A thickness measuring means 38 that measures the thickness of the wafer 80 in a contact manner is disposed adjacent to the grinding means 16 when the grinding means 16 has been lowered to the grinding position. Note that the thickness measuring means 38 may be of a non-contact type, or the grinding device 1 may not be provided with a thickness measuring means 38.

The grinding device 1 is equipped with a control means 9 capable of controlling each component of the grinding device 1 described above. The control means 9, which is composed of a CPU and storage elements such as memory, is electrically connected to, for example, the grinding feed means 17, the grinding means 16, and the horizontal movement means 13, and under the control of the control means 9, the grinding feed operation of the grinding means 16 by the grinding feed means 17, the rotation operation of the grinding wheel 164 in the grinding means 16, and the positioning operation of the holding means 30 relative to the grinding wheel 164 by the horizontal movement means 13 are controlled.

The lift motor 172 is, for example, a servo motor, and an encoder (not shown) of the lift motor 172 is connected to the control means 9 which also functions as a servo amplifier, and an operation signal is supplied from the output interface of the control means 9 to the lift motor 172, causing the rotating shaft 160 to rotate, and the number of rotations detected by the encoder (not shown) is output as an encoder signal to the input interface of the control means 9. Then, the control means 9 which receives the encoder signal can successively recognize the height position of the grinding means 16 which is fed for grinding by the grinding feed means 17, and can feedback control the grinding feed speed of the grinding means 16.
The control means 9 may receive height position information of the grinding means 16 detected by the height position detection means 12 and successively recognize the height position of the grinding means 16 based on the information.

The motor 132 of the horizontal movement means 13 is, for example, a servo motor, and an encoder (not shown) of the motor 132 is connected to the control means 9, which also functions as a servo amplifier, and when an operation signal is supplied from the control means 9 to the motor 132, the ball screw 130 rotates, and the number of rotations detected by the encoder (not shown) is output as an encoder signal to the control means 9. Then, upon receiving the encoder signal, the control means 9 sequentially recognizes the position in the Y-axis direction of the holding means 30, which is moved horizontally in the Y-axis direction by the horizontal movement means 13, and becomes able to control the positioning of the holding means 30 at a predetermined position.

The following describes each step of the method for grinding a wafer 80 according to the present invention using the grinding device 1 shown in Figure 1.

(1) Holding Step First, the wafer 80 is placed on the holding surface 302 with the grinding surface 802 facing upward so that the center 3022 of the holding surface 302 of the holding means 30 positioned in the attachment/detachment area coincides with the center 808 of the wafer 80. Then, the suction force generated by the suction source 37 (see FIG. 2) is transmitted to the holding surface 302, so that the wafer 80 is held by the holding means 30. In addition, the inclination of the table base 35 and the holding means 30 is adjusted by the inclination adjustment means 34 shown in FIG. 1 so that the holding surface 302, which is a gentle conical inclination, is parallel to the grinding surface (lower surface) of the grinding wheel 1644 of the grinding means 16 shown in FIG. 1, and the grinding surface 802, which is the upper surface of the wafer 80 that is suction-held following the holding surface 302, which is a conical inclination, becomes approximately parallel to the lower surface of the grinding wheel 1644.

(2) First positioning step Next, as shown in Figures 2 and 3, the holding means 30 holding the wafer 80 by suction is moved in the +Y direction by the horizontal movement means 13, and the wafer 80 is positioned relative to the grinding wheel 1644 by shifting the rotational trajectory of the grinding wheel 1644 by a predetermined distance from the center 3022 of the holding surface 302 so that the rotational trajectory formed by the radial blade width (e.g., 3 mm) of the grinding wheel 1644 does not pass through the center 3022 of the holding surface 302, i.e., the rotational center 808 of the wafer 80 held on the holding surface 302. That is, the center of rotation of the grinding wheel 1644 is shifted horizontally (in the +Y or -Y direction) a predetermined distance from the center 3022 of the holding surface 302 of the holding means 30 (i.e., the center 808 of the wafer 80), and while conventionally the grinding means 16 is positioned horizontally so that the center (midpoint) of the blade width of the grinding wheel 1644 coincides with the center 3022 of the holding surface 302 of the holding means 30, in this embodiment, for example, the center of the blade width of the grinding wheel 1644 is shifted by 2.8 mm from the center 3022 of the holding surface 302. 2 and 3, the wafer 80 may be positioned relative to the grinding wheel 1644 by shifting the rotation path from the center 3022 of the holding surface 302 so that the distance between the inner circumference of the rotation path of the grinding wheel 1644 and the center 3022 of the holding surface 302 shown in Figures 2 and 3 is 1.5 mm, which is half the blade width of 3 mm of the grinding wheel 1644. This positioning may be performed, for example, by first aligning the center 3022 of the holding surface 302 with the center of the blade width of the grinding wheel 1644 as in the conventional method, and then moving the holding means 30 in the Y-axis direction by the amount of the shift (offset amount).
2 and 3, each component of the grinding device 1 is shown in a simplified manner.

In the first positioning step, as shown in Figures 4 and 5, the holding means 30 holding the wafer 80 by suction is moved in the +Y direction by the horizontal moving means 13, and the rotational path of the grinding wheel 1644, which has a blade width of 3 mm in the radial direction, is shifted a preset distance from the center 3022 of the holding surface 302 so that the rotational path does not pass through the center 3022 of the holding surface 302, and the distance between the outer periphery of the rotational path of the grinding wheel 1644 and the center 3022 of the holding surface 302 is 1.5 mm, which is half the blade width of 3 mm.

(3) First Grinding Step Next, the grinding means 16 is fed at a predetermined grinding feed speed in the -Z direction in which the grinding wheel 1644 approaches the holding surface 302 by the grinding feed means 17 shown in simplified form in Fig. 2. Specifically, as shown in graph G in Fig. 6, for example, the grinding means 16 located at the origin height position is lowered at high speed. In addition, the height position of the grinding means 16 that has started to descend from the origin height position is constantly grasped by the control means 9.
Then, the grinding means 16 reaches the air-cut start position Z1 as shown in graph G of Fig. 6. In graph G of Fig. 6, the horizontal axis represents the grinding time T, and the vertical axis represents the height position H of the grinding means 16.

When the grinding means 16 reaches the air cut start position Z1, the grinding feed means 17 controls the air cut feed speed during the air cut from the air cut start position Z1 until the grinding surface of the grinding wheel 1644 contacts the ground surface 802 of the wafer 80 (the air cut from time T1 to time T2 shown in graph G in FIG. 6) under the control of the control means 9 to be slower than the descent speed before reaching the air cut start position Z1, for example, to be the same as the grinding feed speed during grinding processing. By performing the air cut, the grinding wheel 1644 does not plunge into the wafer 80 at a speed that would damage the wafer 80.

After that, when the grinding means 16 descends to height position Z2, the grinding surface of the grinding wheel 1644, which is rotated in a counterclockwise direction as viewed from the +Z direction side as shown in Figures 2 and 3, comes into contact with the grinding surface 802 of the wafer 80, and grinding of the grinding surface 802 begins. In addition, as the holding means 30 rotates at a predetermined rotational speed, for example, in a counterclockwise direction as viewed from the +Z direction side, the wafer 80 held on the holding surface 302 also rotates, so that the grinding wheel 1644 grinds the entire surface 802 of the wafer 80 to be ground. Since the wafer 80 is held by suction along the holding surface 302, which is a gentle conical slope of the holding means 30, as shown in FIG. 3, within the range indicated by the arrow R in the rotation trajectory of the grinding wheel 1644, that is, within the radial area of the holding surface 302 parallel to the lower surface of the grinding wheel 1644 when viewed from the holding surface 302 side, the grinding wheel 1644 abuts against the wafer 80, and grinds the wafer 80 while applying a pressing load of, for example, 60 N to the wafer 80. In addition, during the rotation trajectory of the grinding wheel 1644, the inner blade on the inner circumference side of the grinding wheel 1644 is mainly the processing point. During the grinding process, grinding water is supplied to the contact area between the grinding wheel 1644 and the grinding surface 802 of the wafer 80 to cool and clean the contact area.

For example, the height position of the grinding means 16 is detected using the height position detection means 12 shown in Fig. 1, and the control means 9 controls the grinding feed amount of the grinding means 16 by the grinding feed means 17 while lowering the grinding means 16 to the height position Z3 shown in graph G in Fig. 6, so that the wafer 80 is ground to a thickness 1 μm to 3 μm thicker than the finishing thickness preset in the control means 9 (first grinding from time T2 to time T3 shown in graph G in Fig. 6), and then a so-called spark-out process is performed. In addition, a cylindrical convex portion 807 shown in Figs. 7 and 8 having a diameter (e.g., 2.6 mm) smaller than the blade width of the grinding wheel 1644 (3 mm in this embodiment) is formed in the center portion of the wafer 80 through which the grinding wheel 1644 does not pass after grinding to a thickness 1 μm to 3 μm thicker than the finishing thickness.
That is, the cylindrical convex portion 807 is formed inside the rotation locus shown in Fig. 2. The grinding wheel 1644 may be shifted so that the cylindrical convex portion 807 is formed outside the rotation locus.

During the spark out from time T3 to time T4 shown in graph G of Figure 6, the descent of the grinding means 16 by the grinding feed means 17 is stopped, and the height position of the grinding means 16 is held at height position Z3, for example, for a predetermined time. In this state, the rotating grinding wheel 1644 removes the remaining ground portions of the grinding surface 802 of the rotating wafer 80, thereby smoothing the grinding surface 802.
In the first grinding step, the thickness of the wafer 80 may be measured by the thickness measuring means 38 shown in FIG.

After the spark out is performed, the grinding means 16 is subjected to an escape cut (escape cut from time T4 to time T5 shown in graph G in FIG. 6) by the grinding feed means 17. In the escape cut, the grinding means 16 slowly rises to suppress adverse effects on the grinding surface 802 of the wafer 80. Here, during the grinding process, a pressing load of, for example, 60N is applied from the grinding means 16 to the wafer 80, the holding means 30 that holds the wafer 80, the table base 35, the tilt adjustment means 34, etc. in the -Z direction, and when the grinding means 16 slowly rises, the wafer 80, etc. are released from the pressing load. As a result, a so-called springback phenomenon occurs, and the grinding surface 802 of the wafer 80 also rises, so that the state in which the grinding surface 802 of the wafer 80 is in contact with the lower surface of the grinding wheel 1644 continues, for example. Then, for example, while the grinding surface 802 of the wafer 80 follows and comes into contact with the lower surface of the rising grinding wheel 1644, the grinding means 16 rises to a predetermined height position Z4 and stops.
During the escape cut, the rising speed of the grinding means 16 may be increased so that the ground surface 802 of the wafer 80 does not come into contact with the lower surface of the grinding wheel 1644 .

(4) Second Positioning Step After the first grinding step, the holding means 30 is moved in the -Y direction by the horizontal moving means 13, and the wafer 80 is positioned relative to the grinding wheel 1644 so that the rotational locus of the grinding wheel 1644 passes through the center 3022 of the holding surface 302. That is, the wafer 80 is positioned relative to the grinding wheel 1644 so that the rotational locus of the grinding wheel 1644 is located directly above the cylindrical convex portion 807 formed in the center portion of the wafer 80 in the first grinding step. For example, as shown in graph G of FIG. 6, in the second positioning step performed from time T5 to time T6, the height position Z4 of the grinding means 16 is fixed, and the wafer 80 may be positioned relative to the grinding wheel 1644 while grinding the cylindrical convex portion 807 in the horizontal direction by the rotating grinding wheel 1644 without the grinding wheel 1644 being separated from the grinding surface 802 of the wafer 80. Alternatively, as shown by the dotted line in graph G of Figure 6, the grinding wheel 1644 can be raised and retracted by the grinding feed means 17 to a height position Z5 slightly above the grinding surface 802 of the wafer 80 to separate the grinding wheel 1644 from the wafer 80, and then the horizontal movement means 13 can position the wafer 80 as described above, and the grinding means 16 can be lowered again by the grinding feed means 17 at a downward speed that is approximately the same as the grinding feed speed in the second grinding process.

(5) Second Grinding Step Next, the grinding means 16 is fed at a predetermined grinding feed speed in the -Z direction by the grinding feed means 17 shown in simplified form in Fig. 7 so that the grinding wheel 1644 approaches the holding surface 302. Then, the rotating grinding wheel 1644 comes into contact with the grinding surface 802 of the wafer 80, and the grinding surface 802 is ground together with the cylindrical protrusion 807. In addition, as the holding means 30 rotates at a predetermined rotation speed, the wafer 80 held on the holding surface 302 also rotates, and the grinding wheel 1644 grinds the entire surface of the grinding surface 802 of the wafer 80 while grinding water is being supplied.

For example, the height position of the grinding means 16 is detected using the height position detection means 12 shown in Fig. 1, and the control means 9 controls the grinding feed amount of the grinding means 16 by the grinding feed means 17 while the wafer 80 is second ground (second grinding shown from time T6 to time T7 shown in graph G in Fig. 6) to the finishing thickness preset in the control means 9, spark out is performed from time T7 to time T8, and escape cut is performed from time T8 to time T9, and the grinding means 16 is raised and retreated from the wafer 80, and the second grinding step is completed. After the second grinding step, the wafer 80 is a wafer of uniform thickness in which the cylindrical convex portion 807 formed in the first grinding step is ground at a higher rate than the other grinding surfaces 802 in the second grinding step, and the wafer 80 is not formed in the center 808 in the conventional manner.
The cylindrical protrusion 807 is formed to have a size corresponding to the diameter of the blade width.

The wafer grinding method according to the present invention is not limited to the above embodiment, and may be implemented in various different forms within the scope of the technical concept. Furthermore, the configuration of the grinding device 1 shown in the attached drawings is not limited to this, and may be modified as appropriate within the scope of the effects of the present invention.

For example, in the above embodiment, the grinding wheel 164 and the holding means 30 rotate in the same direction, and the rotating grinding wheel 1644 enters the wafer 80 from the outer periphery and grinds toward the center 808, performing outer and inner grinding. However, for example, in the first grinding step and the second grinding step, the grinding wheel 164 and the holding means 30 may rotate in opposite directions, and the rotating grinding wheel 1644 may enter the wafer 80 from the center 808 and grind toward the outer periphery, performing inner and outer grinding.

The wafer grinding method according to the present invention may include a diameter measurement step of measuring the diameter of a cylindrical recess formed at the center 8062 of the test wafer 806 held on the holding surface 302 by grinding the test wafer 806 shown in FIG. 9 with a grinding wheel 1644 whose rotational trajectory passes through the center 3022 of the holding surface 302 of the holding means 30 before carrying out the holding step described above.

(Diameter measuring step carried out before holding step)
As shown in Fig. 9, first, the test wafer 806 is placed on the holding surface 302 with the grinding surface facing upward and held by suction so that the center 3022 of the holding surface 302 of the holding means 30 and the center 8062 of the test wafer 806 coincide with each other. The test wafer 806 may be the wafer 80 shown in Fig. 1 or a dummy wafer. The holding means 30 holding the test wafer 806 by suction is sent in the +Y direction, and the center of rotation of the grinding wheel 1644 is shifted in the horizontal direction (+Y direction) by a predetermined distance from the center 3022 of the holding surface 302 of the holding means 30 (i.e., the center 8062 of the test wafer 806), so that the rotation locus consisting of the blade width (e.g., 3 mm) in the radial direction of the grinding wheel 1644 passes through the center of rotation 8062 of the test wafer 806. That is, for example, the center 8062 of the test wafer 806 held on the holding surface 302 is aligned with the center (midpoint) of the cutting edge width of the grinding wheel 1644 in the Y-axis direction.

Next, the grinding means 16 is fed at a predetermined grinding feed speed in the -Z direction by the grinding feed means 17 shown in FIG. 9 so that the grinding wheel 1644 approaches the holding surface 302. For example, the grinding surface of the grinding wheel 1644, which is rotated in a counterclockwise direction as viewed from the +Z direction side shown in FIG. 9, comes into contact with the surface to be ground (upper surface) of the test wafer 806, and grinding of the surface to be ground begins. In addition, as the holding means 30 rotates at a predetermined rotation speed, for example, in a counterclockwise direction as viewed from the +Z direction side, the test wafer 806 held on the holding surface 302 also rotates, so that the grinding wheel 1644 grinds the entire surface to be ground of the test wafer 806. Then, in the center 8062 of the test wafer 806 that has been ground to a thickness that is 1 μm to 3 μm thicker than the finishing thickness, a cylindrical recess 8068 shown in FIG. 10 is formed due to the phenomenon described in the Background Art section.

Then, for example, an image of the ground surface of the test wafer 806 is captured by an imaging means (not shown) positioned above the holding means 30, and image analysis using the captured image showing the formed cylindrical recess 8068 is performed by, for example, the control means 9 of the grinding device 1 shown in FIG. 1 to measure the diameter of the cylindrical recess 8068. For example, the measured diameter of the cylindrical recess 8068 is approximately 3 mm. Information about the measured diameter of the cylindrical recess 8068, 3 mm, is then stored in the memory element of the control means 9.

(Holding step carried out after diameter measurement step)
In the attachment/detachment area of the grinding device 1, the test wafer 806 is removed from the holding surface 302 of the holding means 30, and instead, the wafer 80 which will become the product chip shown in Figure 1 is held on the holding surface 302 by aligning the center 3022 of the holding surface 302 with the center 808 of the wafer 80, as in the holding process described above.

(First positioning step using the measured diameter measured in the diameter measuring step)
11 and 12, the holding means 30 holding the wafer 80 by suction is sent in the +Y direction by the horizontal moving means 13, and in order to prevent the rotational locus consisting of the radial blade width (e.g., 3 mm) of the grinding wheel 1644 from passing through the center 3022 of the holding surface 302, the measured diameter of 3 mm measured in the diameter measurement step is used to shift the rotational locus by the measured diameter of 3 mm from the position where the center of the blade width of the rotational locus of the grinding wheel 1644 coincides with the center 3022 of the holding surface 302, and the wafer 80 is positioned relative to the grinding wheel 1644. As a result, for example, the distance between the inner circumference of the rotational locus of the grinding wheel 1644 and the center 3022 of the holding surface 302 becomes 1.5 mm, which is half of the measured diameter of 3 mm.
The wafer 80 may be positioned relative to the grinding wheel 1644 so that the distance between the outer periphery of the rotational path of the grinding wheel 1644 and the center 3022 of the holding surface 302 is 1.5 mm, which is half the measured diameter of 3 mm.

Then, the first grinding step to the second grinding step described above are carried out, and the wafer 80 after the second grinding step is made into a wafer of uniform thickness that does not have the cylindrical recess that was previously formed in the center 808.

80: Wafer 802: Grinding surface 801: Surface 807: Cylindrical protrusion 1: Grinding device 10: Device base 30: Holding means 300: Suction part 301: Frame 302: Holding surface
35: Table base 34: Tilt adjustment means 340: Lifting section 341: Fixed column section 38: Thickness measurement means 37: Suction source 13: Horizontal movement means 130: Ball screw 132: Motor 133: Movable plate 11: Column 17: Grinding feed means 170: Ball screw 172: Lifting motor 16: Grinding means 160: Rotating shaft 162: Motor 164: Grinding wheel 1643: Wheel base 1644: Grinding stone 9: Control means 806: Test wafer 8062: Center of test wafer 8068: Cylindrical recess

Claims (2)

A method for grinding a wafer, comprising: holding means for holding a wafer on a holding surface that is a conical slope having an apex at the center and that is rotatable about an axis of the holding surface; grinding means for mounting an annular grinding wheel so that the grinding wheel is rotatable about an axis of the center of the grinding wheel and for grinding the wafer held on the holding surface with the grinding wheel; horizontal movement means for relatively moving the holding means and the grinding means in a horizontal direction parallel to a lower surface of the grinding wheel; and grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to the holding surface, the method comprising:
a diameter measuring step of measuring a diameter of a cylindrical recess formed at the center of the test wafer by grinding the test wafer held on the holding surface with the grinding wheel whose rotation locus passes through the center of the holding surface;
removing the test wafer from the holding surface;
a holding step of aligning a center of the holding surface with a center of the wafer and holding the wafer on the holding surface;
a first positioning step of positioning the wafer with respect to the grinding wheel such that the measured diameter measured in the diameter measuring step is a preset distance, and the horizontal moving means is used to shift the rotational locus formed by the blade width in the radial direction of the grinding wheel from the center of the holding surface by the preset distance so that the rotational locus does not pass through the center of rotation of the wafer held on the holding surface, thereby positioning the wafer with respect to the grinding wheel such that the distance between the outer or inner circumference of the rotational locus and the center of the holding surface is half of the measured diameter ;
a first grinding step in which, after the first positioning step, the grinding wheel is fed by the grinding feed means in a direction approaching the holding surface to grind the wafer to a thickness that is a preset value thicker than a preset finish thickness, thereby forming a cylindrical convex portion having a diameter smaller than the cutting width in a central portion of the wafer where the grinding wheel does not pass;
a second positioning step of positioning the wafer with respect to the grinding wheel using the horizontal moving means such that the rotation locus of the grinding wheel passes through the center of the holding surface after the first grinding step;
and a second grinding step of, after the second positioning step, moving the grinding wheel with the grinding feed means in a direction approaching the holding surface to remove the cylindrical convex portion and grind the wafer to the preset finishing thickness. A method for grinding a wafer, comprising: holding means for holding a wafer on a holding surface that is a conical slope having an apex at the center and that is rotatable about an axis of the holding surface; grinding means for mounting an annular grinding wheel so that the grinding wheel is rotatable about an axis of the center of the grinding wheel and for grinding the wafer held on the holding surface with the grinding wheel; horizontal movement means for relatively moving the holding means and the grinding means in a horizontal direction parallel to a lower surface of the grinding wheel; and grinding feed means for relatively moving the holding means and the grinding means in a direction perpendicular to the holding surface, the method comprising:
a holding step of aligning a center of the holding surface with a center of the wafer and holding the wafer on the holding surface;
a first positioning step of positioning the wafer with respect to the grinding wheel by shifting the rotation path of the grinding wheel, which is defined by the blade width in the radial direction of the grinding wheel, from the center of the holding surface by the preset distance so that the rotation path does not pass through the center of rotation of the wafer held on the holding surface, so that the distance between the outer periphery or inner periphery of the rotation path and the center of the holding surface is half the blade width;
a first grinding step in which, after the first positioning step, the grinding wheel is fed by the grinding feed means in a direction approaching the holding surface to grind the wafer to a thickness that is a preset value thicker than a preset finish thickness, thereby forming a cylindrical convex portion having a diameter smaller than the cutting width in a central portion of the wafer where the grinding wheel does not pass;
a second positioning step of positioning the wafer with respect to the grinding wheel using the horizontal moving means such that the rotation locus of the grinding wheel passes through the center of the holding surface after the first grinding step;
and a second grinding step of, after the second positioning step, moving the grinding wheel with the grinding feed means in a direction approaching the holding surface to remove the cylindrical convex portion and grind the wafer to the preset finishing thickness .

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