JP2023177443A - Grinding method for work-piece - Google Patents

Abstract

To provide a grinding method for a work-piece that can form a concave part so that a center of a surface to be ground of the work-piece matches with a center of a bottom surface of the concave part, even if the work-piece is carried in a position shifted from a desired position on a chuck table.SOLUTION: A displacement vector up to a center of a bottom surface of a preliminary concave part when viewed from a center of a surface to be ground of a work-piece is measured, after forming the preliminary concave part in the work-piece. A straight line acting as a rotating shaft of a chuck table passes on the center of the bottom surface of the preliminary concave part. This makes the displacement vector correspond to a displacement vector up to the straight line acting as the rotating shaft of the chuck table when viewed from the center of the surface to be ground of the work-piece. The concave part is formed in the work-piece, by making the chuck table hold the work-piece again after moving the chuck table and the work-piece relatively so that a position of the work-piece moves by a distance corresponding to the displacement vector.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for grinding a workpiece, which forms a recessed portion having a circular bottom surface by grinding one side of the workpiece.

2. Description of the Related Art Device chips such as ICs (Integrated Circuits) are essential components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a disk-shaped workpiece, such as a wafer, on which a plurality of devices are formed on the front surface into regions each including individual devices.

This workpiece may be thinned prior to its division in order to reduce the size of manufactured chips. Examples of methods for thinning the workpiece include grinding using a grinding device that includes a chuck table that holds the workpiece and a grinding wheel that has a plurality of grinding wheels that are arranged discretely in an annular shape. . This grinding is generally performed in the following order.

First, the front side of the workpiece is held by a chuck table so that the back side of the workpiece is exposed. Next, while rotating both the grinding wheel and the chuck table, which have an outer diameter longer than the radius of the workpiece, one of the plurality of grinding wheels is brought into contact with the center of the back surface of the workpiece. Next, the plurality of grinding wheels are brought close to the surface of the workpiece while both the grinding wheel and the chuck table are kept rotating.

As a result, the back side of the workpiece is ground and the workpiece is thinned. However, if the workpiece is made thinner, the rigidity of the workpiece decreases, which may make it difficult to handle the workpiece in subsequent steps. Therefore, a method has been proposed in which a workpiece is ground so as to thin only the portion of the workpiece that overlaps with a plurality of devices (see, for example, Patent Document 1).

In this method, by grinding the back side of the workpiece as described above using a grinding wheel having an outer diameter shorter than the radius of the workpiece, the outer circumference of the workpiece remains and a circular shape is formed. A recess having a bottom surface of is formed on the back surface of the workpiece. This suppresses a decrease in the rigidity of the workpiece, making it easier to handle the workpiece in subsequent steps.

Japanese Patent Application Publication No. 2007-19461

In the method described above, it is preferable that the recess is formed such that the center of the back surface of the workpiece and the center of the bottom of the recess coincide. In order to form such a recess, it is necessary to hold the front side of the workpiece with the chuck table so that a straight line serving as the rotation axis of the chuck table passes through the center of the back side of the workpiece.

Therefore, in the grinding apparatus, the workpiece is often carried into the chuck table after the position of the workpiece has been adjusted. However, even if such position adjustment is performed, there is a risk that the center of the back surface of the workpiece may be placed at a position that deviates from the straight line that serves as the rotation axis of the chuck table when the workpiece is transferred to the chuck table. be.

In view of this point, an object of the present invention is to keep the center of the back surface (one surface) of the workpiece and the recess even when the workpiece is carried to a position shifted from the desired position on the chuck table. It is an object of the present invention to provide a method for grinding a workpiece that can form a recess so that the center of the bottom surface coincides with the center of the workpiece.

According to the present invention, there is provided a method for grinding a workpiece in which a concave portion having a circular bottom is formed by grinding one side of the workpiece, the method comprising: grinding the other side of the workpiece using a chuck table; a preliminary holding step of holding the surface side, and grinding the one surface side of the workpiece, so that the surface side of the workpiece has a circular bottom surface having a diameter shorter than the bottom surface of the recess, and is smaller than the recess. a preliminary grinding step of forming a shallow preliminary recess; and after the preliminary grinding step, a measuring step of measuring a displacement vector from the center of the one surface of the workpiece to the center of the bottom surface of the preliminary recess; After the measuring step, the chuck table and the workpiece are moved relative to each other so that the position of the workpiece held by the chuck table during the preliminary holding step is moved by the displacement vector. a holding step of holding the other surface side of the workpiece with the chuck table after the movement; and after the holding step, grinding the one surface side of the workpiece, thereby removing the concave portion. A method of grinding a workpiece is provided, comprising: a grinding step to form a workpiece.

Preferably, in the preliminary grinding step, a first grinding wheel including a first grinding wheel is used to grind the workpiece, and in the grinding step, a second grinding wheel including a second grinding wheel is used. The workpiece is ground by grinding, and the abrasive grains contained in the second grinding wheel have a smaller average particle size than the abrasive grains contained in the first grinding wheel.

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

In the present invention, the chuck table and the workpiece are relatively moved so that the position of the workpiece is moved by the displacement vector, and then the chuck table moves the other side of the workpiece again. After holding, a recess is formed on one side of the workpiece. In this case, the workpiece is ground with a straight line serving as the rotation axis of the chuck table passing through the center of one surface of the workpiece. As a result, the recess can be formed such that the center of one surface of the workpiece coincides with the center of the bottom surface of the recess.

FIG. 1 is a cross-sectional view schematically showing an example of a grinding device. FIG. 2 is a flowchart schematically showing an example of a method for grinding a workpiece. FIG. 3(A) is a cross-sectional view schematically showing the preliminary holding step, and FIG. 3(B) is a top view schematically showing the workpiece after the preliminary holding step. FIG. 4(A) is a cross-sectional view schematically showing the preliminary grinding step, and FIG. 4(B) is a top view schematically showing the workpiece after the preliminary grinding step. FIG. 5(A) is a sectional view schematically showing the state of the measurement step, and FIG. 5(B) is a top view schematically showing the workpiece after the measurement step. FIG. 6(A) is a cross-sectional view schematically showing the state of the holding step, and FIG. 6(B) is a top view schematically showing the workpiece after the holding step. FIG. 7(A) is a cross-sectional view schematically showing the state of the grinding step, and FIG. 7(B) is a top view schematically showing the workpiece after the grinding step.

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

Further, a recessed portion having a circular bottom surface is formed in the upper part of the frame 4a, and a disc-shaped porous plate 4b made of porous ceramics or the like is fixed to this recessed portion. The upper surface of the porous plate 4b and the upper surface of the frame 4a surrounding the porous plate 4b are configured to have a shape corresponding to the side surface of a cone, and function as a holding surface for holding the workpiece.

Further, the lower surface side of the porous plate 4b communicates with a suction source (not shown) such as an ejector via a flow path 4c formed inside the frame 4a. Therefore, when the suction source operates with the workpiece placed on the holding surface of the chuck table 4, the workpiece is attracted to the chuck table 4 side and held.

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 with 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 as the rotation axis.

Further, the chuck table 4 is 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 a turntable, a motor, and the like. When this horizontal movement mechanism operates, the chuck table 4 moves in the horizontal direction.

Further, the chuck table 4 is 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 so as to support the chuck table 4. When the tilt adjustment mechanism operates, at least one of the two movable shafts moves the chuck table 4 up and down. As a result, the inclination of the rotation axis of the chuck table 4 is adjusted.

In the grinding device 2, a grinding wheel 6 is provided at a higher position than the chuck table 4. This grinding wheel 6 includes an annular wheel base 6a made of metal such as stainless steel or aluminum. Further, an annular recess is formed on the lower surface of the wheel base 6a, and a plurality of grinding wheels 6b are fixed to this recess at approximately equal angular intervals along the circumferential direction of the wheel base 6a. .

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

Furthermore, the grinding wheel 6 is 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 with a straight line along the vertical direction as the rotation axis. Furthermore, when the grinding wheel 6 rotates, the plurality of grinding wheels 6b draw an annular locus. Note that the grinding wheel 6 is designed such that the outer diameter of this trajectory is shorter than the radius of the holding surface of the chuck table 4.

Further, the grinding wheel 6 is 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 in the vertical direction.

Further, a nozzle (not shown) is provided near the grinding wheel 6. This nozzle is in communication with a pump (not shown) that supplies a grinding fluid such as water, and is connected to the contact interface between the workpiece and the plurality of grinding wheels 6b when the workpiece is ground by the plurality of grinding wheels 6b. Supply grinding fluid to (machining point).

In the grinding device 2, a camera 8 is provided at a position higher than the chuck table 4 and separated from the grinding wheel 6. This camera 8 includes, for example, a light source, an objective lens, and an image sensor such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and takes an image of a structure that exists below. .

FIG. 2 is a flowchart schematically showing an example of a method for grinding a workpiece in which a recess having a circular bottom surface is formed by grinding one side of the workpiece in the grinding device 2. In this method, first, the other side of the workpiece is held by the chuck table 4 (preliminary holding step: S1).

FIG. 3(A) is a sectional view schematically showing the preliminary holding step (S1), and FIG. 3(B) is a top view schematically showing the workpiece after the preliminary holding step (S1). It is. The workpiece 11 on which the recesses are formed by this method is made of a semiconductor material such as silicon, and has a radius larger than the outer diameter of the locus of the plurality of grinding wheels 6b when the grinding wheel 6 is rotated. It's a long wafer.

A plurality of devices are arranged in a matrix on the surface (other surface) 11a of the workpiece 11. That is, the boundaries of the plurality of devices extend in a grid pattern. Furthermore, it is preferable that a protective member (not shown) made of resin or the like be attached to the surface 11a of the workpiece 11. In this case, when grinding the back surface (one surface) 11b side of the workpiece 11, the impact applied to the front surface 11a side can be alleviated and the plurality of devices can be protected.

In the preliminary holding step (S1), first, the workpiece 11 is carried 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. do. Note that, here, it is not necessary to perform highly accurate position adjustment of the workpiece 11 prior to carrying in the workpiece 11.

Therefore, the center of the surface 11a of the workpiece 11 is often located at a position offset from the center of the holding surface of the chuck table 4, that is, the point through which a straight line serving as the rotation axis of the chuck table 4 passes. Next, a suction source communicating with the lower surface side of the porous plate 4b is operated. As a result, the surface 11a side of the workpiece 11 is attracted and held by the chuck table 4.

After the preliminary holding step (S1), a preliminary recess having a circular bottom surface is formed by grinding the back surface (one surface) of the workpiece 11 (preliminary grinding step: S2). FIG. 4(A) is a sectional view schematically showing the preliminary grinding step (S2), and FIG. 4(B) is a top view schematically showing the workpiece 11 after the preliminary grinding step (S2). It is a diagram.

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

Next, the chuck table 4 is moved in the horizontal direction so that the trajectory of the plurality of grinding wheels 6b when the grinding wheel 6 is rotated overlaps with the center of the holding surface of the chuck table 4 in plan view. Specifically, a portion slightly outside the inner periphery of the above trajectory 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 keeping both the chuck table 4 and the grinding wheel 6 rotating, the grinding wheel 6 is lowered so that the grinding surfaces of the plurality of grinding wheels 6b are pressed against the back surface 11b of the workpiece 11. As a result, the back surface 11b side of the workpiece 11 is ground by the plurality of grinding wheels 6b, and a preliminary recess 11c having a circular bottom surface is formed.

After the preliminary grinding step (S2), a 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). FIG. 5(A) is a sectional view schematically showing the state of the measurement step (S3), and FIG. 5(B) is a top view schematically showing the workpiece 11 after the measurement step (S3). be.

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

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

Specifically, when the respective coordinates of points P1 to P3 are (X ₁ , Y ₁ ), (X ₂ , Y ₂ ), and (X ₃ , Y ₃ ), the workpiece in the XY coordinate plane The coordinates (X _C1 , Y _C1 ) of the back surface 11b of No. 11 are calculated by the following equations (1) and (2).

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

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

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

In the holding step (S4), first, the operation of the suction source communicating with the lower surface side of the porous plate 4b is stopped. Next, the workpiece 11 is raised directly above by a transport mechanism (not shown) of the grinding device 2 and is carried out from the chuck table 4 . Next, the transport mechanism that holds 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 below by a transport mechanism (not shown) and is carried into the chuck table 4 again. Next, the suction source communicating with the lower surface side of the porous plate 4b is operated again. As a result, the surface 11a side of the workpiece 11 is attracted to the chuck table 4 and held again.

After the holding step (S4), a recessed portion having a circular bottom surface is formed by grinding the back surface (one surface) 11b side of the workpiece 11 (grinding step: S5). FIG. 7(A) is a cross-sectional view schematically showing the state of the grinding step (S5), and FIG. 7(B) is a top view schematically showing the workpiece 11 after the grinding step (S5). be.

In the grinding step (S5), first, the chuck table 4 is moved horizontally so that the locus of the plurality of grinding wheels 6b when the grinding wheel 6 is rotated overlaps the center of the holding surface of the chuck table 4 in plan view. move it to Specifically, a portion slightly inside the outer periphery of the above trajectory is positioned directly above the center of the holding surface of the chuck table 4 so that the diameter of the recessed portion 11d is relatively large.

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

When the grinding surfaces of the plurality of grinding wheels 6b come into contact with the bottom surface of the preliminary recess 11c, the back surface 11b side of the workpiece 11 is pressed until the area overlapping with the plurality of devices of the workpiece 11 reaches a predetermined finishing thickness. Grind. As a result, the back surface 11b side of the workpiece 11 is ground by the plurality of grinding wheels 6b, resulting in a recess having a circular bottom surface having a longer diameter than the bottom surface of the preliminary recess 11c and deeper than the preliminary recess 11c. 11d is formed.

In the method shown in FIG. 2, after forming the preliminary recess 11c on the back surface 11b side of the workpiece 11, a displacement vector ( ΔX, ΔY). Here, a straight line serving 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 straight line serving as the rotation axis of the chuck table 4.

In this method, the chuck table 4 and the workpiece 11 are relatively moved so that the position of the workpiece 11 is moved by the displacement vector (ΔX, ΔY), and then the chuck table 4 After the front surface 11a side of the workpiece 11 is held again, a recess 11d is formed on the back surface 11b side of the workpiece 11. In this case, the workpiece 11 is ground with a straight line serving as the rotational 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 such that the center of the back surface 11b of the workpiece 11 and the center of the bottom of the recess 11d coincide.

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

Further, the first grinding wheel may be a grinding wheel for rough grinding, and the second grinding hole may be a grinding wheel for finish grinding. In addition, the grinding wheel (second grinding wheel) included in the grinding wheel for finish grinding is generally a grinding wheel with a smaller average particle diameter than the grinding wheel (first grinding wheel) included in the grinding wheel for rough grinding. Contains grains.

Further, in the present invention, there is no restriction on the moving mechanism for relatively moving the chuck table 4 and the grinding wheel 6. For example, the present invention may be implemented in a grinding apparatus that includes a vertical movement mechanism that moves the chuck table 4 in the vertical direction and a horizontal movement mechanism that moves the grinding wheel 6 in the horizontal direction.

In addition, the structure, method, etc. according to the embodiments described above can be modified and implemented as appropriate without departing from the scope of the objective of the present invention.

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

Claims (2)

A method for grinding a workpiece, the method comprising: forming a recess having a circular bottom surface by grinding one side of the workpiece;
a preliminary holding step of holding the other side of the workpiece with a chuck table;
a preliminary grinding step of forming a preliminary recess having a circular bottom surface having a diameter shorter than the bottom surface of the recess and being shallower than the recess by grinding the one surface side of the workpiece; ,
After the preliminary grinding step, a measuring step of measuring a displacement vector from the center of the one surface of the workpiece to the center of the bottom surface of the preliminary recess;
After the measuring step, the chuck table and the workpiece are moved relative to each other so that the position of the workpiece held by the chuck table during the preliminary holding step is moved by the displacement vector. a holding step of holding the other side of the workpiece by the chuck table after moving;
After the holding step, a grinding step of forming the recessed portion by grinding the one surface side of the workpiece;
A method of grinding a workpiece, including: In the preliminary grinding step, the one surface side of the workpiece is ground using a first grinding wheel including a first grinding wheel,
In the grinding step, the one surface side of the workpiece is ground using a second grinding wheel including a second grinding wheel,
2. The method for grinding a workpiece according to claim 1, wherein the abrasive grains included in the second grinding wheel have a smaller average grain size than the abrasive grains contained in the first grinding wheel.

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