Method for grinding a workpiece

Abstract

The present application provides a grinding method of a workpiece, which can form a recess in a manner that the center of a ground surface of the workpiece coincides with the center of the bottom surface of the recess even when the workpiece is carried to a position deviated from a desired position of a chuck table. After a preliminary recess is formed on the workpiece, a displacement vector from the center of the ground surface of the workpiece to the center of the bottom surface of the preliminary recess is measured. Here, a straight line that becomes the rotational axis of the chuck table passes through the center of the bottom surface of the preliminary recess. Therefore, the displacement vector corresponds to a displacement vector from the center of the ground surface of the workpiece to the straight line that becomes the rotational axis of the chuck table. Furthermore, after the chuck table and the workpiece are relatively moved in a manner that the position of the workpiece is moved by the displacement vector, the workpiece is held again by the chuck table, and then a recess is formed on the workpiece.

Description

Technical Field

[0001] The present invention relates to a grinding method for forming a concave portion with a circular bottom surface by grinding one side of the workpiece. Background Technology

[0002] Integrated circuit (IC) chips are indispensable components in various electronic devices such as mobile phones and personal computers. Such chips are manufactured, for example, by dividing a wafer-shaped workpiece, on the front side of which multiple devices are formed, into regions containing each device.

[0003] To miniaturize the manufactured chips, the workpiece is sometimes thinned before dicing. One method for thinning the workpiece is, for example, grinding in a grinding apparatus having: a chuck table for holding the workpiece; and grinding wheels having a plurality of grinding tools discretely arranged in a ring. This grinding is typically performed in the following sequence.

[0004] First, the front side of the workpiece is held in place by a chuck table, with the back side of the workpiece exposed. Next, while rotating both the grinding wheel (which has an outer diameter longer than the workpiece's radius) and the chuck table, one of several grinding wheels is brought into contact with the center of the back side of the workpiece. Then, while the grinding wheel and chuck table are still rotating, the multiple grinding wheels are brought close to the front side of the workpiece.

[0005] As a result, the back side of the workpiece is ground to thin it. However, when the workpiece is thinned, its rigidity decreases, which may make subsequent processing difficult. Therefore, a method for grinding the workpiece by thinning only the portion that overlaps with multiple devices has been proposed (for example, see Patent Document 1).

[0006] 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, thereby leaving the outer periphery of the workpiece intact and forming a recess with a rounded bottom surface on the back side of the workpiece. This suppresses the reduction in the rigidity of the workpiece, making subsequent processing of the workpiece easier.

[0007] Patent Document 1: Japanese Patent Application Publication No. 2007-19461

[0008] In the above method, it is preferable to form the recess so that the center of the back side of the workpiece coincides with the center of the bottom surface of the recess. Moreover, in order to form the recess in this way, the front side of the workpiece needs to be held by the chuck table in such a way that the straight line that serves as the rotation axis of the chuck table passes through the center of the back side of the workpiece.

[0009] Therefore, in grinding equipment, it is common to move the workpiece into the chuck table after adjusting its position. However, even with such position adjustment, when moving the workpiece into the chuck table, it is possible that the center of the back side of the workpiece is positioned off-center from the axis of rotation of the chuck table. Summary of the Invention

[0010] In view of this, the object of the present invention is to provide a grinding method for a workpiece that can form a recess in such a way that the center of the back side (one side) of the workpiece is aligned with the center of the bottom surface of the recess, even when the workpiece is moved to a position deviating from the desired position on the chuck table.

[0011] According to the present invention, a grinding method for a workpiece is provided, wherein a recess having a circular bottom surface is formed by grinding one side of the workpiece, wherein the grinding method for the workpiece includes the following steps: a pre-holding step, wherein the workpiece is held on the other side using a chuck table; a pre-grinding step, wherein a pre-recess is formed by grinding the one side of the workpiece, the pre-recess having a circular bottom surface with a diameter shorter than the diameter of the bottom surface of the recess, and the pre-recess being shallower than the recess; and a measuring step, wherein in the pre-grinding step... After the step, the displacement vector from the center of one side of the workpiece to the center of the bottom surface of the pre-recessed portion is measured; in the holding step, after the measurement step, the chuck table and the workpiece are moved relative to each other in such a way that the displacement vector is moved from the position of the workpiece held by the chuck table during the pre-holding step, and then the other side of the workpiece is held by the chuck table; and in the grinding step, after the holding step, the recess is formed by grinding the one side of the workpiece.

[0012] Preferably, in the pre-grinding step, the workpiece is ground using a first grinding wheel containing a first grinding tool, and in the grinding step, the workpiece is ground using a second grinding wheel containing a second grinding tool, wherein the average particle size of the abrasive grains contained in the second grinding tool is smaller than the average particle size of the abrasive grains contained in the first grinding tool.

[0013] In this invention, after a pre-recessed portion is formed on one side of the workpiece, a displacement vector is measured from the center of one side of the workpiece to the center of the bottom surface of the pre-recessed portion. Here, the straight line that becomes the rotation axis of the chuck table passes through the center of the bottom surface of the pre-recessed portion. Therefore, this displacement vector corresponds to the displacement vector from the center of one side of the workpiece to the straight line that becomes the rotation axis of the chuck table.

[0014] Furthermore, in this invention, after the chuck table and the workpiece are moved relative to each other in a manner that moves the displacement vector of the workpiece's position, the other side of the workpiece is held in place by the chuck table, and then a recess is formed on one side of the workpiece. In this case, grinding is performed on the workpiece with the straight line that becomes the rotation axis of the chuck table passing through the center of one side of the workpiece. As a result, the recess can be formed such that the center of one side of the workpiece coincides with the center of the bottom surface of the recess. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view schematically showing an example of a grinding apparatus.

[0016] Figure 2 This is a flowchart schematically illustrating an example of a grinding method for a workpiece.

[0017] Figure 3 (A) is a schematic cross-sectional view showing the preparation of the holding step. Figure 3 (B) is a schematic top view of the workpiece after the preparatory holding step.

[0018] Figure 4 (A) is a schematic cross-sectional view showing the preparation of the grinding step. Figure 4 (B) is a schematic top view of the workpiece after the pre-grinding step.

[0019] Figure 5 (A) is a cross-sectional view schematically illustrating the measurement procedure. Figure 5 (B) is a schematic top view of the workpiece after the measurement step.

[0020] Figure 6 (A) is a cross-sectional view schematically illustrating the holding step. Figure 6 (B) is a schematic top view of the workpiece after the holding step.

[0021] Figure 7 (A) is a cross-sectional view schematically showing the grinding process. Figure 7 (B) is a schematic top view of the workpiece after the grinding step.

[0022] Label Explanation

[0023] 2: Grinding device; 4: Chuck table (4a: frame; 4b: perforated plate; 4c: flow path); 6: Grinding wheel (6a: grinding wheel base; 6b: grinding tool); 8: Camera; 11: Workpiece (11a: front; 11b: back; 11c: pre-recessed part; 11d: recessed part). Detailed Implementation

[0024] Embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a cross-sectional view schematically showing an example of a grinding apparatus. Figure 1 The grinding apparatus 2 shown has a chuck table 4. This chuck table 4 has, for example, a circular plate-shaped frame 4a made of ceramic or the like.

[0025] Furthermore, a recess with a circular bottom surface is formed in the upper part of the frame 4a, and a circular porous plate 4b made of porous ceramic or the like is fixed in the recess. Moreover, the upper surface of the porous plate 4b and the upper surface of the frame 4a surrounding the porous plate 4b are configured to be in the shape of the lateral side of a cone, which functions as a holding surface for holding the workpiece.

[0026] Furthermore, the lower surface of the perforated plate 4b is connected to a suction source (not shown) such as an injector via a flow path 4c formed inside the frame 4a. Therefore, when the suction source is activated while the workpiece is placed on the holding surface of the chuck table 4, the workpiece is attracted and held on the side of the chuck table 4.

[0027] Furthermore, the chuck table 4 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, pulleys and a motor. Moreover, when this rotating mechanism is activated, the chuck table 4 rotates about 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 aforementioned cone as its axis of rotation.

[0028] Furthermore, the chuck table 4 is connected to a horizontal movement mechanism (not shown). This horizontal movement mechanism may include, for example, a ball screw and a motor. Alternatively, the horizontal movement mechanism may include a rotary table and a motor. Moreover, when this horizontal movement mechanism is activated, the chuck table 4 moves horizontally.

[0029] Furthermore, the chuck table 4 is connected to a tilt adjustment mechanism (not shown). This tilt adjustment mechanism, for example, includes one fixed axis and two movable axes arranged at approximately equal angular intervals along the circumference of the chuck table 4 in a manner that supports the chuck table 4. Moreover, when the tilt adjustment mechanism is activated, at least one of the two movable axes causes the chuck table 4 to rise or fall. As a result, the tilt of the rotation axis of the chuck table 4 is adjusted.

[0030] In the grinding apparatus 2, a grinding wheel 6 is positioned higher than the chuck table 4. This grinding wheel 6 includes an annular grinding wheel base 6a made of a metal such as stainless steel or aluminum. Furthermore, an annular recess is formed on the lower surface of the grinding wheel base 6a, and multiple grinding tools 6b are fixed within this recess at approximately equal angular intervals along the circumference of the grinding wheel base 6a.

[0031] Each of the multiple grinding tools 6b contains a binder such as a ceramic binder or a resin binder and abrasive grains such as diamond dispersed in the binder. Furthermore, the lower surfaces of the multiple grinding tools 6b are substantially positioned on the same plane, serving as grinding surfaces for grinding the workpiece.

[0032] Furthermore, the grinding wheel 6 is connected to a rotating mechanism (not shown). This rotating mechanism includes, for example, a spindle and a motor. When this rotating mechanism operates, the grinding wheel 6 rotates about a straight line along the vertical direction as its axis of rotation. Additionally, as the grinding wheel 6 rotates, multiple grinding tools 6b trace a circular trajectory. Furthermore, the outer diameter of this trajectory is designed to be shorter than the radius of the holding surface of the chuck table 4.

[0033] Furthermore, 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. Moreover, when this vertical movement mechanism is activated, the grinding wheel 6 moves in the vertical direction.

[0034] Additionally, a nozzle (not shown) is provided near the grinding wheel 6. This nozzle is connected to a pump (not shown) that supplies grinding fluid such as water, and supplies grinding fluid to the contact interface (machining point) between the workpiece and the multiple grinding wheels 6b when grinding the workpiece using multiple grinding wheels 6b.

[0035] In the grinding apparatus 2, a camera 8 is installed at a position higher than the chuck table 4 and separate from the grinding wheel 6. The camera 8 includes, for example, imaging elements such as a light source, an objective lens, a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, to photograph the structure located below it.

[0036] Figure 2 This is a flowchart schematically illustrating an example of a grinding method for forming a recessed portion with a circular bottom surface by grinding one side of a workpiece in a grinding apparatus 2. In this method, firstly, the other side of the workpiece is held using a chuck table 4 (preparatory holding step: S1).

[0037] Figure 3 (A) is a cross-sectional view schematically showing the preparation and holding step (S1). Figure 3 (B) is a schematic top view of the workpiece after the pre-holding step (S1). Furthermore, the workpiece 11 with the recess formed by this method is, for example, a wafer made of a semiconductor material such as silicon, and whose radius is longer than the outer diameter of the path of the plurality of grinding tools 6b when the grinding wheel 6 rotates.

[0038] Furthermore, multiple devices are arranged in a matrix on the front (other side) 11a side of the workpiece 11. That is, the boundaries of the multiple devices extend in a grid pattern. In addition, it is preferable to attach a protective member (not shown) made of resin or the like to the front 11a side of the workpiece 11. In this case, the impact applied to the front 11a side when grinding the back (one side) 11b side of the workpiece 11 can be mitigated, thus protecting the multiple devices.

[0039] In the pre-holding step (S1), the workpiece 11 is first moved into the chuck table 4 with its back side 11b facing upwards and the entire area of ​​the upper surface of the perforated plate 4b covered by the workpiece 11. Alternatively, high-precision position adjustment of the workpiece 11 before its movement can be omitted here.

[0040] Therefore, the center of the front surface 11a of the workpiece 11 is often positioned off-center from the center of the holding surface of the chuck table 4, i.e., the point through which the straight line that forms the rotation axis of the chuck table 4 passes. Next, the suction source communicating with the lower surface of the perforated plate 4b is activated. As a result, the front surface 11a of the workpiece 11 is attracted and held by the chuck table 4.

[0041] After the preparation holding step (S1), a preparation recess with a round bottom surface is formed by grinding the back (one) side of the workpiece 11 (preparation grinding step: S2). Figure 4 (A) is a cross-sectional view schematically showing the preparatory grinding step (S2). Figure 4 (B) is a schematic top view of the workpiece 11 after the pre-grinding step (S2).

[0042] In the pre-grinding step (S2), firstly, the tilt of the chuck table 4 is adjusted so that the line segment connecting the highest point on the outer periphery of the retaining surface of the chuck table 4 and the center of the retaining surface is perpendicular to the vertical direction. However, if the chuck table 4 is tilted so that this line segment is already perpendicular to the vertical direction, this adjustment is not necessary.

[0043] Next, when viewed from above, the chuck table 4 is moved horizontally such that the trajectory of the multiple grinding tools 6b that cause the grinding wheel 6 to rotate overlaps with the center of the holding surface of the chuck table 4. Specifically, the portion slightly outside the inner circumference of the aforementioned trajectory is positioned directly above the center of the holding surface of the chuck table 4 in such a way that the diameter of the preparatory recess 11c is made smaller.

[0044] Next, the chuck table 4 and the grinding wheel 6 are rotated. Then, while the chuck table 4 and the grinding wheel 6 are rotating, the grinding wheel 6 is lowered so that the grinding surfaces of the plurality of grinding tools 6b press against the back surface 11b of the workpiece 11. As a result, the back surface 11b of the workpiece 11 is ground by the plurality of grinding tools 6b, forming a pre-recessed portion 11c with a circular bottom surface.

[0045] After the pre-grinding step (S2), the displacement vector from the center of the back side (one side) 11b of the workpiece 11 to the center of the bottom surface of the pre-recess 11c is measured (measurement step: S3). Figure 5 (A) is a cross-sectional view schematically showing the measurement step (S3). Figure 5 (B) is a schematic top view of the workpiece 11 after the measurement step (S3).

[0046] In the measurement step (S3), firstly, the chuck stage 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 pre-recess 11c are included within the range that can be captured by the camera 8. Next, by alternately repeating the capturing of images by the camera 8 and the rotation of the chuck stage 4, an image containing the outer periphery of the workpiece 11 and the outer periphery of the pre-recess 11c is formed.

[0047] Next, using this image, three points (e.g., on the outer periphery of the workpiece 11 in the XY coordinate plane perpendicular to the vertical direction) are determined. Figure 5 Points P1, P2, P3 shown in (B) and three points on the outer periphery of the pre-recessed portion 11c (e.g.) Figure 5 The coordinates of points P4, P5, and P6 shown in (B) are then determined. 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 pre-recessed portion 11c are determined.

[0048] Specifically, given that the coordinates of points P1 to P3 are (X1, Y1), (X2, Y2), and (X3, Y3) respectively, the coordinates of the back surface 11b of the workpiece 11 in the XY coordinate plane are (X1, Y1), (X2, Y2), and (X3, Y3). C1 Y C1 The following mathematical expressions (1) and (2) are used to calculate the result.

[0049]

[0050]

[0051] Similarly, given that the coordinates of points P4 to P6 are (X4, Y4), (X5, Y5), and (X6, Y6), respectively, the coordinates of the bottom surface of the preparatory recess 11c in the XY coordinate plane are (X... C2 Y C2 The following mathematical expressions (3) and (4) are used to calculate the result.

[0052]

[0053]

[0054] 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 pre-recessed portion 11c is measured. Specifically, the displacement vector is calculated using the following mathematical formulas (5) and (6).

[0055] Δx=x c2 -X C1 …(5)

[0056] ΔY=Y C2 -Y C1 …(6)

[0057] After the measurement step (S3), the chuck table 4 and the workpiece 11 are moved relative to each other in such a way that the displacement vector (ΔX, ΔY) moves the position of the workpiece 11. Then, the chuck table 4 is used to hold the front (other side) 11a side of the workpiece 11 (holding step: S4). Figure 6 (A) is a cross-sectional view schematically showing the holding step (S4). Figure 6 (B) is a schematic top view of the workpiece 11 after the holding step (S4).

[0058] In the holding step (S4), firstly, the operation of the suction source communicating with the lower surface of the perforated plate 4b is stopped. Next, the workpiece 11 is lifted directly upward by the conveying mechanism (not shown) of the grinding device 2 and removed from the chuck table 4. Then, the conveying mechanism holding the workpiece 11 is moved by the displacement vector (ΔX, ΔY).

[0059] Alternatively, the chuck table 4 is moved by the inverse vector (-ΔX, -ΔY) of the displacement vector (ΔX, ΔY). Then, the workpiece 11 is lowered directly downwards by the conveying mechanism and re-entered onto the chuck table 4. Next, the suction source connected to the lower surface of the perforated plate 4b is activated again. As a result, the front side 11a of the workpiece 11 is attracted by the chuck table 4 and held again.

[0060] After holding step (S4), a recess with a round bottom surface is formed by grinding the back side (one side) 11b side of the workpiece 11 (grinding step: S5). Figure 7 (A) is a cross-sectional view schematically showing the grinding step (S5). Figure 7 (B) is a schematic top view of the workpiece 11 after the grinding step (S5).

[0061] In the grinding step (S5), firstly, when viewed from above, the chuck table 4 is moved horizontally such that the trajectory of the multiple grinding tools 6b that cause the grinding wheel 6 to rotate overlaps with the center of the holding surface of the chuck table 4. Specifically, the portion slightly inside the outer periphery of the aforementioned trajectory is positioned directly above the center of the holding surface of the chuck table 4 in such a way that the diameter of the recess 11d becomes relatively large.

[0062] Next, the chuck table 4 and the grinding wheel 6 are rotated. Then, while the chuck table 4 and the grinding wheel 6 are rotating, the grinding wheel 6 is lowered so that the grinding surfaces of each of the multiple grinding tools 6b press against the back surface 11b of the workpiece 11. Thus, firstly, the portion of the back surface 11b of the workpiece 11 located slightly outside the side surface of the pre-recessed recess 11c is ground using the multiple grinding tools 6b.

[0063] Then, if the grinding surfaces of the multiple grinding tools 6b contact the bottom surface of the prepared recess 11c, the back surface 11b side of the workpiece 11 is ground until the area of ​​the workpiece 11 overlapping with the multiple devices reaches the specified finished thickness. As a result, by grinding the back surface 11b side of the workpiece 11 using multiple grinding tools 6b, a recess 11d is formed with a circular bottom surface having a diameter longer than the diameter of the bottom surface of the prepared recess 11c and a depth greater than the prepared recess 11c.

[0064] exist Figure 2 In the method shown, after forming the pre-recessed recess 11c on the back side 11b of the workpiece 11, the displacement vector (ΔX, ΔY) is measured from the center of the back side 11b of the workpiece 11 to the center of the bottom surface of the pre-recessed recess 11c. Here, the straight line that becomes the rotation axis of the chuck table 4 passes through the center of the bottom surface of the pre-recessed recess 11c. Therefore, this displacement vector (ΔX, ΔY) corresponds to the displacement vector (ΔX, ΔY) of the straight line that becomes the rotation axis of the chuck table 4, as observed from the center of the back side 11b of the workpiece 11.

[0065] Furthermore, in this method, after the chuck table 4 and the workpiece 11 are moved relative to each other in a manner that moves the position of the workpiece 11 by a displacement vector (ΔX, ΔY), the chuck table 4 is used to hold the workpiece 11 on its front side 11a, and then a recess 11d is formed on the back side 11b of the workpiece 11. In this case, the workpiece 11 is ground with the straight line that becomes the rotation axis of the chuck table 4 passing through the center of the back side 11b of the workpiece 11. As a result, the recess 11d can be formed in such a way that the center of the back side 11b of the workpiece 11 coincides with the center of the bottom surface of the recess 11d.

[0066] Furthermore, the above-described method is one aspect of the present invention, and the content of the present invention is not limited to the above description. For example, in the present invention, the grinding wheel (first grinding wheel) used in the pre-grinding step (S2) and the grinding wheel (second grinding wheel) used in the grinding step (S5) may be different. Specifically, the outer diameter of the second grinding wheel may be larger than the outer diameter of the first grinding wheel.

[0067] Alternatively, the first grinding wheel can be a grinding wheel for rough grinding, and the second grinding wheel can be a grinding wheel for finish grinding. Furthermore, the grinding wheel for finish grinding (the second grinding wheel) typically contains abrasive grains with an average grit size smaller than those contained in the grinding wheel for rough grinding (the first grinding wheel).

[0068] Furthermore, in this invention, there are no limitations on the moving mechanism that causes the chuck table 4 and the grinding wheel 6 to move relative to each other. For example, this invention can also be implemented in a grinding apparatus having a vertical moving mechanism that moves the chuck table 4 in the vertical direction and a horizontal moving mechanism that moves the grinding wheel 6 in the horizontal direction.

[0069] In addition, the structure and method of the above-described embodiments can be implemented with appropriate modifications without departing from the purpose of the present invention.

Claims

1. A grinding method for a workpiece, wherein a concave portion having a circular bottom surface is formed by grinding one side of the workpiece, wherein... The grinding method for the workpiece includes the following steps: The preparatory holding step involves using the chuck table to hold the workpiece on the other side. The pre-grinding step involves grinding one side of the workpiece to form a pre-recess, the pre-recess having a circular bottom surface with a diameter shorter than the diameter of the bottom surface of the recess, and the pre-recess being shallower than the recess. The measurement step involves measuring the displacement vector from the center of one side of the workpiece to the center of the bottom surface of the pre-recess, as observed from the center of that side of the workpiece. In the holding step, after the measurement step, the chuck table and the workpiece are moved relative to each other in such a way that the displacement vector is moved from the position of the workpiece held by the chuck table during the pre-holding step, and then the other side of the workpiece is held by the chuck table; and The grinding step, after the holding step, forms the recess by grinding one side of the workpiece.

2. The grinding method for a workpiece according to claim 1, wherein, In this pre-grinding step, the workpiece is ground on one side using a first grinding wheel containing a first grinding tool. In this grinding step, a second grinding wheel containing a second grinding tool is used to grind that side of the workpiece. The average particle size of the abrasive grains contained in the second grinding wheel is smaller than that of the abrasive grains contained in the first grinding wheel.

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