JP7801950B2 - Grinding method for workpiece - Google Patents

Description

The present invention relates to a method for grinding a workpiece to form a recess with a circular bottom by grinding one side of the workpiece.

Device chips such as ICs (Integrated Circuits) are essential components in various electronic devices, including mobile phones and personal computers. These chips are manufactured by dividing a disk-shaped workpiece, such as a wafer, with multiple devices formed on its surface, into individual regions containing individual devices.

The workpiece may be thinned prior to separation in order to produce smaller chips. One method for thinning the workpiece is to grind it using a grinding machine equipped with a chuck table that holds the workpiece and a grinding wheel with multiple grinding stones arranged discretely in an annular pattern. This grinding is generally performed in the following order:

First, the front side of the workpiece is held by the chuck table so that the back side of the workpiece is exposed. Next, while both the chuck table and a grinding wheel with an outer diameter longer than the radius of the workpiece are rotated, one of the multiple grinding stones is brought into contact with the center of the back side of the workpiece. Next, while both the grinding wheel and the chuck table are still rotating, the multiple grinding stones are brought closer to the surface of the workpiece.

This grinds the back side of the workpiece, thinning it. However, thinning the workpiece reduces its rigidity, which can make it difficult to handle in subsequent processes. Therefore, a method has been proposed in which the workpiece is ground so as to thin only the portions of the workpiece that overlap multiple devices (see, for example, Patent Document 1).

In this method, a grinding wheel with an outer diameter shorter than the radius of the workpiece is used to grind the back side of the workpiece as described above, leaving the outer periphery of the workpiece intact and forming a recess with a circular bottom on the back side of the workpiece. This prevents a decrease in the rigidity of the workpiece and makes it easier to handle in subsequent processes.

Japanese Patent Application Laid-Open No. 2007-19461

In the above-mentioned method, it is preferable that the recess be formed so that the center of the back surface of the workpiece coincides with the center of the bottom surface of the recess. To form a recess in this way, the front side of the workpiece must be held by the chuck table so that the line that serves as the axis of rotation of the chuck table passes through the center of the back surface of the workpiece.

For this reason, in grinding machines, the position of the workpiece is often adjusted before it is loaded onto the chuck table. However, even after such position adjustment, there is a risk that the center of the back surface of the workpiece may be positioned off the straight line that serves as the rotation axis of the chuck table when it is loaded onto the chuck table.

In light of this, the object of the present invention is to provide a method for grinding a workpiece that can form a recess so that the center of the back surface (one side) of the workpiece coincides with the center of the bottom surface of the recess, even if the workpiece is loaded into a position that is shifted from the desired position on the chuck table.

According to the present invention, there is provided a method for grinding a workpiece, in which one surface of the workpiece is ground to form a recess having a circular bottom, the method including: a pre-holding step of holding the other surface of the workpiece with a chuck table; a pre-grinding step of grinding the one surface of the workpiece to form a preliminary recess having a circular bottom with a shorter diameter than the bottom of the recess and that is shallower than the recess; a measuring step, after the pre-grinding step, of measuring a displacement vector from the center of the one surface of the workpiece to the center of the bottom of the preliminary recess; a holding step, after the measuring step, of moving the chuck table and the workpiece relatively so as to move the position of the workpiece held by the chuck table during the pre-holding step by the amount of the displacement vector, and then holding the other surface of the workpiece with the chuck table; and a grinding step, after the holding step, of grinding the one surface of the workpiece to form the recess.

Preferably, in the preliminary grinding step, the workpiece is ground using a first grinding wheel including a first grinding stone, and in the grinding step, the workpiece is ground using a second grinding wheel including a second grinding stone, and the abrasive grains included in the second grinding stone have an average grain size smaller than that of the abrasive grains included in the first grinding stone.

In this invention, a preliminary recess is formed on one side of the workpiece, and then the displacement vector from the center of one side of the workpiece to the center of the bottom of the preliminary recess is measured. Here, the line that serves as the rotation axis of the chuck table passes through the center of the bottom of the preliminary recess. Therefore, this displacement vector corresponds to the displacement vector from the center of one side of the workpiece to the line that serves as the rotation axis of the chuck table.

In this invention, the chuck table and the workpiece are moved relative to each other so that the position of the workpiece is moved by the amount of the displacement vector, and then the other side of the workpiece is held by the chuck table again, after which a recess is formed on one side of the workpiece. In this case, the workpiece is ground with the line that serves as the rotation axis of the chuck table passing through the center of one side of the workpiece. As a result, a recess can be formed so that the center of one side of the workpiece and the center of the bottom of the recess coincide.

FIG. 1 is a cross-sectional view schematically showing an example of a grinding apparatus. FIG. 2 is a flow chart that schematically shows an example of a method for grinding a workpiece. FIG. 3A is a cross-sectional view that schematically shows the state of the pre-holding step, and FIG. 3B is a top view that schematically shows the workpiece after the pre-holding step. FIG. 4A is a cross-sectional view that schematically shows the state of the pre-grinding step, and FIG. 4B is a top view that schematically shows the workpiece after the pre-grinding step. FIG. 5A is a cross-sectional view that schematically shows the state of the measurement step, and FIG. 5B is a top view that schematically shows the workpiece after the measurement step. FIG. 6A is a cross-sectional view that schematically shows the state of the holding step, and FIG. 6B is a top view that schematically shows the workpiece after the holding step. FIG. 7A is a cross-sectional view that schematically shows the state of the grinding step, and FIG. 7B is a top view that schematically shows the workpiece after the grinding step.

Embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is a cross-sectional view showing a schematic example of a grinding device. The grinding device 2 shown in Figure 1 has a chuck table 4. This chuck table 4 has a disk-shaped frame 4a made of, for example, ceramics.

A recess with a circular bottom is formed in the upper part of the frame 4a, and a disk-shaped porous plate 4b made of porous ceramics or the like is fixed in this recess. The upper surface of the porous plate 4b and the upper surface of the frame 4a surrounding the porous plate 4b are configured in a shape equivalent to the side of a cone, and function as a holding surface for holding the workpiece.

The underside of the porous plate 4b is connected to a suction source (not shown) such as an ejector via a flow path 4c formed inside the frame 4a. Therefore, when the suction source is operated with a workpiece placed on the holding surface of the chuck table 4, the workpiece is sucked into and held by the chuck table 4.

Furthermore, the chuck table 4 is connected to a rotation mechanism (not shown). This rotation mechanism includes, for example, a pulley and a motor. When this rotation mechanism operates, the chuck table 4 rotates around a rotation axis that is a straight line passing through the center of the holding surface of the chuck table 4 and the center of the bottom surface of the cone.

The chuck table 4 is also connected to a horizontal movement mechanism (not shown). This horizontal movement mechanism includes, for example, a ball screw and a motor. Alternatively, the horizontal movement mechanism includes, for example, a turntable and a motor. When this horizontal movement mechanism operates, the chuck table 4 moves horizontally.

The chuck table 4 is also connected to a tilt adjustment mechanism (not shown). This tilt adjustment mechanism includes, for example, one fixed shaft and two movable shafts that are arranged at approximately equal angular intervals along the circumferential direction of the chuck table 4 to support the chuck table 4. When the tilt adjustment mechanism operates, at least one of the two movable shafts raises and lowers the chuck table 4. As a result, the tilt of the rotation axis of the chuck table 4 is adjusted.

In the grinding device 2, a grinding wheel 6 is mounted at a position higher than the chuck table 4. This grinding wheel 6 includes an annular wheel base 6a made of a metal such as stainless steel or aluminum. An annular recess is formed on the underside of the wheel base 6a, and multiple grinding stones 6b are fixed in this recess at approximately equal angular intervals along the circumferential direction of the wheel base 6a.

Each of the multiple grinding wheels 6b contains a binder such as vitrified or resinoid, and abrasive grains such as diamond dispersed in the binder. The lower surfaces of the multiple grinding wheels 6b are positioned on approximately the same plane and function as grinding surfaces for grinding the workpiece.

The grinding wheel 6 is also connected to a rotation mechanism (not shown). This rotation mechanism includes, for example, a spindle and a motor. When this rotation mechanism operates, the grinding wheel 6 rotates around a vertical line as its axis of rotation. As the grinding wheel 6 rotates, the multiple grinding stones 6b trace a circular path. The grinding wheel 6 is designed so that the outer diameter of this path is shorter than the radius of the holding surface of the chuck table 4.

The grinding wheel 6 is also connected to a vertical movement mechanism (not shown). This vertical movement mechanism includes, for example, a ball screw and a motor. When this vertical movement mechanism operates, the grinding wheel 6 moves vertically.

A nozzle (not shown) is also provided near the grinding wheel 6. This nozzle is connected to a pump (not shown) that supplies grinding fluid such as water, and supplies the grinding fluid to the contact interface (machining point) between the workpiece and the multiple grinding wheels 6b when the workpiece is ground with the multiple grinding wheels 6b.

In the grinding device 2, a camera 8 is provided at a position higher than the chuck table 4 and spaced apart from the grinding wheel 6. This camera 8 includes, for example, a light source, an objective lens, and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and captures images of structures located below it.

Figure 2 is a flowchart showing a schematic example of a grinding method for a workpiece in which one surface of the workpiece is ground using a grinding device 2 to form a recess with a circular bottom. In this method, the other surface of the workpiece is first held by the chuck table 4 (pre-holding step: S1).

Figure 3(A) is a cross-sectional view showing the preliminary holding step (S1), and Figure 3(B) is a top view showing the workpiece after the preliminary holding step (S1). The workpiece 11 on which recesses are formed using this method is, for example, a wafer made of a semiconductor material such as silicon, with a radius longer than the outer diameter of the trajectory of the multiple grinding stones 6b when the grinding wheel 6 is rotated.

A number of devices are arranged in a matrix on the surface (other surface) 11a of the workpiece 11. In other words, the boundaries between the devices extend in a grid pattern. Furthermore, a protective member (not shown) made of resin or the like is preferably attached to the surface 11a of the workpiece 11. In this case, the impact applied to the surface 11a when grinding the back surface (one surface) 11b of the workpiece 11 can be reduced, thereby protecting the multiple devices.

In the preliminary holding step (S1), first, the workpiece 11 is loaded onto the chuck table 4 so that the back surface 11b of the workpiece 11 faces upward and the entire upper surface of the porous plate 4b is covered by the workpiece 11. Note that, at this stage, it is not necessary to perform high-precision position adjustment of the workpiece 11 prior to loading the workpiece 11.

For this reason, the center of the surface 11a of the workpiece 11 is often positioned at a position offset from the center of the holding surface of the chuck table 4, i.e., the point where the straight line that serves as the rotation axis of the chuck table 4 passes through. Next, the suction source that communicates with the underside of the porous plate 4b is activated. This causes the surface 11a of the workpiece 11 to be sucked and held by the chuck table 4.

After the preliminary holding step (S1), the back surface (one side) of the workpiece 11 is ground to form a preliminary recess with a circular bottom (preliminary grinding step: S2). Figure 4(A) is a cross-sectional view that schematically illustrates the preliminary grinding step (S2), and Figure 4(B) is a top view that schematically illustrates the workpiece 11 after the preliminary grinding step (S2).

In the preliminary grinding step (S2), first, the tilt of the chuck table 4 is adjusted so that the line segment connecting the highest point on the periphery of the holding surface of the chuck table 4 and the center of the holding surface is perpendicular to the vertical direction. Note that if the chuck table 4 is already tilted so that this line segment is already perpendicular to the vertical direction, this adjustment is not necessary.

Next, the chuck table 4 is moved horizontally so that, in a plan view, the trajectory of the multiple grinding stones 6b when the grinding wheel 6 is rotated overlaps with the center of the holding surface of the chuck table 4. Specifically, a portion of the trajectory slightly outside the inner periphery is positioned directly above the center of the holding surface of the chuck table 4 so that the diameter of the preliminary recess 11c is relatively small.

Next, both the chuck table 4 and the grinding wheel 6 are rotated. Next, while both the chuck table 4 and the grinding wheel 6 are still rotating, the grinding wheel 6 is lowered so that the grinding surfaces of the multiple grinding wheels 6b are pressed against the back surface 11b of the workpiece 11. As a result, the back surface 11b of the workpiece 11 is ground by the multiple grinding wheels 6b, forming a preliminary recess 11c with a circular bottom surface.

After the preliminary grinding step (S2), the displacement vector from the center of the back surface (one surface) 11b of the workpiece 11 to the center of the bottom surface of the preliminary recess 11c is measured (measurement step: S3). Figure 5(A) is a cross-sectional view that schematically illustrates the measurement step (S3), and Figure 5(B) is a top view that schematically illustrates the workpiece 11 after the measurement step (S3).

In the measurement step (S3), first, the chuck table 4 is moved horizontally so that at least a portion of the outer periphery of the workpiece 11 and at least a portion of the outer periphery of the preliminary recess 11c are included in the range that can be captured by the camera 8. Next, by alternately repeating capturing images by the camera 8 and rotating the chuck table 4, an image including the outer periphery of the workpiece 11 and the outer periphery of the preliminary recess 11c is formed.

Next, using this image, the coordinates of three points on the outer periphery of the workpiece 11 (e.g., points P1, P2, and P3 shown in Figure 5(B)) and three points on the outer periphery of the preliminary recess 11c (e.g., points P4, P5, and P6 shown in Figure 5(B)) are determined in an XY coordinate plane perpendicular to the vertical direction. Next, based on these coordinates, the coordinate of the center C1 of the back surface 11b of the workpiece 11 and the coordinate of the center C2 of the bottom surface of the preliminary recess 11c are determined.

Specifically, when the coordinates of points P1 to P3 are ( _X1 , _Y1 ), ( _X2 , _Y2 ), and ( _X3 , _Y3 ), respectively, the coordinates ( _XC1 , _YC1 ) of the rear surface 11b of the workpiece 11 on the XY coordinate plane are calculated by the following formulas (1) and (2).

Similarly, when the coordinates of points P4 to P6 are (X ₄ , Y ₄ ), (X ₅ , Y ₅ ), and (X ₆ , Y ₆ ), respectively, the coordinates (X _C2 , Y _C2 ) of the bottom surface of the preliminary recess 11c in the XY coordinate plane are calculated by the following formulas (3) and (4).

Next, a displacement vector (ΔX, ΔY) is measured from the center C1 of the rear surface 11b of the workpiece 11 to the center C2 of the bottom surface of the preliminary recess 11c. Specifically, this displacement vector is calculated using the following formulas (5) and (6).

After the measurement step (S3), the chuck table 4 and the workpiece 11 are moved relative to each other so that the position of the workpiece 11 is moved by the displacement vector (ΔX, ΔY), and then the surface (other surface) 11a of the workpiece 11 is held by the chuck table 4 (holding step: S4). Figure 6(A) is a cross-sectional view that schematically illustrates the state of the holding step (S4), and Figure 6(B) is a top view that schematically illustrates the workpiece 11 after the holding step (S4).

In the holding step (S4), first, the operation of the suction source connected to the underside of the porous plate 4b is stopped. Next, the workpiece 11 is raised directly upward by the conveying mechanism (not shown) of the grinding device 2, and the workpiece 11 is removed from the chuck table 4. Next, the conveying mechanism holding the workpiece 11 is moved by the displacement vector (ΔX, ΔY).

Alternatively, the chuck table 4 is moved by the inverse vector (-ΔX, -ΔY) of the displacement vector (ΔX, ΔY). Next, the workpiece 11 is lowered directly downward by a transport mechanism (not shown) and loaded back onto the chuck table 4. Next, the suction source connected to the underside of the porous plate 4b is operated again. As a result, the front surface 11a of the workpiece 11 is sucked to the chuck table 4 and held there again.

After the holding step (S4), the back surface (one surface) 11b of the workpiece 11 is ground to form a recess with a circular bottom (grinding step: S5). Figure 7(A) is a cross-sectional view that schematically illustrates the grinding step (S5), and Figure 7(B) is a top view that schematically illustrates the workpiece 11 after the grinding step (S5).

In the grinding step (S5), first, the chuck table 4 is moved horizontally so that, in a plan view, the trajectory of the multiple grinding stones 6b when the grinding wheel 6 is rotated overlaps with the center of the holding surface of the chuck table 4. Specifically, a portion slightly inside the outer periphery of the trajectory is positioned directly above the center of the holding surface of the chuck table 4 so that the diameter of the recess 11d becomes relatively large.

Next, both the chuck table 4 and the grinding wheel 6 are rotated. Next, while both the chuck table 4 and the grinding wheel 6 are still rotating, the grinding wheel 6 is lowered so that the grinding surfaces of the multiple grinding wheels 6b are pressed against the back surface 11b of the workpiece 11. As a result, first, the portion of the back surface 11b of the workpiece 11 that is located slightly outside the side surface of the preliminary recess 11c is ground by the multiple grinding wheels 6b.

When the grinding surfaces of the multiple grinding wheels 6b come into contact with the bottom surface of the preliminary recess 11c, the back surface 11b of the workpiece 11 is ground until the area of the workpiece 11 overlapping the multiple devices reaches the specified finishing thickness. As a result, the back surface 11b of the workpiece 11 is ground by the multiple grinding wheels 6b, forming a recess 11d that has a circular bottom surface with a larger diameter than the bottom surface of the preliminary recess 11c and is deeper than the preliminary recess 11c.

In the method shown in Figure 2, a preliminary recess 11c is formed on the back surface 11b of the workpiece 11, and then the displacement vector (ΔX, ΔY) from the center of the back surface 11b of the workpiece 11 to the center of the bottom surface of the preliminary recess 11c is measured. Here, the line that serves as the rotation axis of the chuck table 4 passes through the center of the bottom surface of the preliminary recess 11c. Therefore, this displacement vector (ΔX, ΔY) corresponds to the displacement vector (ΔX, ΔY) from the center of the back surface 11b of the workpiece 11 to the line that serves as the rotation axis of the chuck table 4.

In this method, the chuck table 4 and workpiece 11 are moved relative to each other so that the position of the workpiece 11 is moved by the displacement vector (ΔX, ΔY), and the chuck table 4 then holds the front surface 11a of the workpiece 11 again, after which a recess 11d is formed on the back surface 11b of the workpiece 11. In this case, the workpiece 11 is ground with the line that serves as the rotation axis of the chuck table 4 passing through the center of the back surface 11b of the workpiece 11. As a result, the recess 11d can be formed so that the center of the back surface 11b of the workpiece 11 coincides with the center of the bottom surface of the recess 11d.

Note that the above-described method is one aspect of the present invention, and the content of the present invention is not limited to the above. For example, in the present invention, the grinding wheel (first grinding wheel) used in the preliminary grinding step (S2) may be different from the grinding wheel (second grinding wheel) used in the grinding step (S5). Specifically, the second grinding wheel may have a larger outer diameter than the first grinding wheel.

Also, the first grinding wheel may be a grinding wheel for rough grinding, and the second grinding wheel may be a grinding wheel for finish grinding. The grinding stone (second grinding stone) included in the grinding wheel for finish grinding generally contains abrasive grains with a smaller average particle size than the grinding stone (first grinding stone) included in the grinding wheel for rough grinding.

Furthermore, the present invention does not limit the movement mechanism that moves the chuck table 4 and the grinding wheel 6 relative to each other. For example, the present invention may be implemented in a grinding device that includes a vertical movement mechanism that moves the chuck table 4 vertically and a horizontal movement mechanism that moves the grinding wheel 6 horizontally.

In addition, the structures and methods of the above-described embodiments may be modified as appropriate without departing from the scope of the present invention.

2: Grinding device 4: Chuck table (4a: frame, 4b: porous plate, 4c: flow path)
6: Grinding wheel (6a: wheel base, 6b: grinding stone)
8: Camera 11: Workpiece (11a: front surface, 11b: back surface, 11c: preliminary recess, 11d: recess)

Claims (2)

A method for grinding a workpiece to form a recess having a circular bottom surface by grinding one surface of the workpiece, comprising:
a pre-holding step of holding the other surface of the workpiece by a chuck table;
a preliminary grinding step of grinding the one surface side of the workpiece to form a preliminary recess having a circular bottom surface with a diameter shorter than that of the bottom surface of the recess and shallower than the recess;
a measuring step of measuring a displacement vector from a center of the one surface of the workpiece to a center of the bottom surface of the preliminary recessed portion after the preliminary grinding step;
a holding step of relatively moving the chuck table and the workpiece so as to move the position of the workpiece held by the chuck table during the preliminary holding step by an amount equal to the displacement vector, and then holding the other surface side of the workpiece by the chuck table after the measuring step;
a grinding step of grinding the one surface side of the workpiece to form the recessed portion after the holding step;
A method for grinding a workpiece, comprising: In the preliminary grinding step, the one surface side of the workpiece is ground using a first grinding wheel including a first grinding stone;
In the grinding step, the one surface side of the workpiece is ground using a second grinding wheel including a second grinding stone;
2. The method for grinding a workpiece according to claim 1, wherein the abrasive grains contained in the second grinding wheel have an average grain size smaller than that of the abrasive grains contained in the first grinding wheel.