Grinding method for workpieces

Abstract

To provide a workpiece grinding method which can accelerate the spontaneous blade generation of each of a plurality of grinding whetstones without weakening the holding power of an abrasive-holding binder.SOLUTION: A workpiece grinding method of this invention, which enables a recess having a circular bottom to be formed by grinding one face side of the central region of a workpiece, includes: a groove-forming step for forming a groove with a depth which does not reach a recess depth by using a cutting blade to cut one face side of the central region; and a grinding step for removing a part which demarcates the groove and forming a recess by using, after the groove-forming step, a grinding wheel having a plurality of grinding whetstones to grind one face side of the central region.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece, which grinds one surface side of a central region of the workpiece to form a concave portion having a circular bottom surface.

Background Art

[0002] Chips of devices 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 workpiece such as a wafer having a plurality of devices formed on the surface side into regions each including an individual device.

[0003] This workpiece may be thinned prior to its division for the purpose of miniaturizing the chips to be manufactured. The thinning of the workpiece is performed, for example, in a grinding apparatus including a holding table and a spindle provided above the holding table and having a grinding wheel attached to the lower end thereof.

[0004] In general, the grinding wheel has a plurality of grinding grains arranged in an annular shape. Each of the plurality of grinding grains includes a binder and abrasive grains dispersed inside the binder and held by the binder.

[0005] And in this grinding apparatus, for example, the workpiece is thinned in the following order. First, the surface side (lower surface side) of the workpiece is held by the holding table. Next, the positions of the holding table and the spindle are adjusted so that the center of the workpiece is positioned directly below the trajectories of the plurality of grinding grains when the spindle is rotated.

[0006] Next, while rotating both the spindle and the holding table, the grinding surfaces (lower surfaces) of the plurality of grinding grains are brought into contact with the back surface (upper surface) of the workpiece. Note that, as this grinding wheel, a grinding wheel having an outer diameter of the trajectories of the plurality of grinding grains larger than the radius of the workpiece when the spindle is rotated is used.

[0007] Furthermore, the spindle and the holding table are moved closer together while both are rotating until the workpiece reaches the desired thickness. This grinds and thins the entire back surface of the workpiece.

[0008] Here, thinning the workpiece reduces its rigidity, which may make handling the workpiece difficult in subsequent processes. Therefore, a method has been proposed to grind the back side of the workpiece using a method also known as TAIKO grinding (see, for example, Patent Document 1).

[0009] Specifically, in this method, a grinding wheel is used in which the outer diameter of the trajectories of the multiple grinding wheels when the spindle is rotated is smaller than the radius of the workpiece, and the back side of the workpiece is ground as described above.

[0010] In this case, the back side (top side) of the central region of the workpiece is ground, while the region surrounding this central region (outer peripheral excess region) remains. As a result, a recess with a circular bottom surface is formed on the back side of the workpiece. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2007-19461 [Overview of the project] [Problems that the invention aims to solve]

[0012] When a hard structure such as a wafer made of silicon carbide (SiC) or sapphire (Al2O3) is exposed on the back side of the workpiece, grinding of this workpiece causes severe wear (dulling) of the abrasive grains exposed on the grinding surfaces of multiple grinding wheels.

[0013] In this case, there is a risk of malfunctions such as an increase in the drive current of the motor that rotates the spindle to which the grinding wheel is attached at the tip. Therefore, in such cases, it is necessary to promote the self-sharpening of each of the multiple grinding wheels that occur during grinding of the workpiece (the bonding material on the grinding surface is worn away, exposing new abrasive grains on the grinding surface).

[0014] To promote self-sharpening of the abrasive grains, for example, a brittle material can be used as a binder in each of the multiple grinding wheels. However, in this case, the holding power of the binder that holds the abrasive grains will weaken, which may make grinding the workpiece difficult.

[0015] In view of this, the object of the present invention is to provide a method for grinding a workpiece that can promote the self-sharpening of each of multiple grinding wheels without weakening the holding force of the binder that holds the abrasive grains. [Means for solving the problem]

[0016] According to the present invention, a method for grinding a workpiece is provided for forming a recess having a circular bottom surface by grinding one side of the central region of the workpiece, comprising: a groove forming step of forming a groove to a depth not reaching the depth of the recess by cutting the one side of the central region using a cutting blade; and a grinding step after the groove forming step of removing the portion defining the groove and forming the recess by grinding the one side of the central region using a grinding wheel having a plurality of grinding wheels arranged in an annular shape. [Effects of the Invention]

[0017] In this invention, a groove is formed to a depth not reaching the depth of the recess by cutting one side of the central region of the workpiece using a cutting blade, and then the upper side of the central region is ground using a grinding wheel having a plurality of grinding wheels arranged in an annular shape to remove the portion defining the groove and form a recess.

[0018] In this case, from the start of grinding one side of the central region of the workpiece until the portion defining the groove is removed, the portions near the grinding surfaces of each of the plurality of grinding wheels continue to collide with the side surface of the groove.

[0019] When such a collision occurs, the binder contained in each of the plurality of grinding wheels is easily scraped off. As a result, in the present invention, the self-generated cutting edges of each of the plurality of grinding wheels can be promoted without weakening the holding force of the binder that holds the abrasive grains.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a workpiece. <०००००८१> [Figure 2] FIG. 2 is a flowchart schematically showing an example of a method for grinding a workpiece to form a recess having a circular bottom surface by grinding one side of the central region of the workpiece. [Figure 3] FIG. 3(A) is a partial cross-sectional side view schematically showing an example of the groove forming step, and FIG. 3(B) is a perspective view schematically showing the workpiece after the groove forming step shown in FIG. 3(A). [Figure 4] FIG. 4(A) is a partial cross-sectional side view schematically showing an example of the grinding step, and FIG. 4(B) is a perspective view schematically showing the workpiece after the grinding step shown in FIG. 4(A). [Figure 5] FIG. 5(A) is a partial cross-sectional side view schematically showing another example of the groove forming step, and FIG. 5(B) is a perspective view schematically showing the workpiece after the groove forming step shown in FIG. 5(A).

Embodiments for Carrying Out the Invention

[0021] Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view schematically showing an example of a workpiece to be subjected to grinding. The workpiece 11 shown in FIG. 1 is made of, for example, a single crystal semiconductor material such as silicon (Si), silicon carbide (SiC), or gallium nitride (GaN).

[0022] The workpiece 11 has a central region in which a plurality of devices 13 are formed and an outer peripheral surplus region surrounding this central region. The plurality of devices 13 are arranged in a matrix. That is, the boundaries of the plurality of devices 13 extend in a lattice pattern.

[0023] Also, the surface 11a of the workpiece 11 has an uneven shape due to the presence of the plurality of devices 13. On the other hand, the back surface 11b of the workpiece 11 is generally flat. Further, a notch 11c for indicating a specific crystal orientation of the material constituting the workpiece 11 is formed on the side surface of the workpiece 11.

[0024] FIG. 2 is a flowchart schematically showing an example of a grinding method for a workpiece in which one surface side of the central region of the workpiece 11 is ground to form a recess having a circular bottom surface. The one surface side of the central region of the workpiece 11 is the side where the plurality of devices 13 are not provided and corresponds to a part of the back surface 11b side of the workpiece 11.

[0025] In the grinding method for the workpiece shown in FIG. 2, first, a groove having a depth that does not reach the depth of the recess is formed by cutting one surface side of the central region of the workpiece using a cutting blade (groove forming step S1).

[0026] FIG. 3(A) is a partial cross-sectional side view schematically showing an example of the groove forming step S1, and FIG. 3(B) is a perspective view schematically showing the workpiece 11 after the groove forming step S1 shown in FIG. 3(A). This groove forming step S1 is carried out in the cutting device 2 shown in FIG. 3(A).

[0027] The X-axis direction and the Y-axis direction shown in FIG. 3(A) are directions orthogonal to each other on a horizontal plane, and the Z-axis direction is a direction (vertical direction) orthogonal to each of the X-axis direction and the Y-axis direction.

[0028] The cutting apparatus 2 includes a holding table 4. This holding table 4 has a disc-shaped frame with a diameter larger than the workpiece 11. This frame is made of, for example, a metal material such as stainless steel or a ceramic.

[0029] Furthermore, the frame has a disc-shaped bottom wall and cylindrical side walls that rise from the outer periphery of the bottom wall. That is, a disc-shaped recess is formed on the upper surface of the frame, defined by the bottom wall and the side walls.

[0030] Furthermore, a disc-shaped porous plate (not shown) having a diameter approximately equal to the diameter of the recess formed on the upper surface of the frame is fixed thereto. This porous plate is made of, for example, porous ceramics. Also, the upper surface of the holding table 4 (the upper surface of the frame and the upper surface of the porous plate) is approximately parallel to the X-axis and Y-axis directions.

[0031] Furthermore, the porous plate communicates with a suction source (not shown), such as an ejector, through a through-hole formed in the bottom wall of the frame. When this suction source is activated, a suction force acts on the space near the top surface of the porous plate.

[0032] Furthermore, the holding table 4 is connected to an X-axis movement mechanism (not shown). This X-axis movement mechanism includes, for example, a ball screw and a motor. When this X-axis movement mechanism is operated, the holding table 4 moves along the X-axis.

[0033] Furthermore, the holding table 4 is connected to a rotational drive source (not shown), such as a motor. When this rotational drive source is operated, the holding table 4 rotates with a rotation axis that passes through the center of the upper surface of the holding table 4 and is aligned with the Z-axis direction.

[0034] A cutting unit 6 is provided above the holding table 4. This cutting unit 6 includes a spindle 8 that extends along the Y-axis. An annular cutting blade 10 is mounted on the tip of the spindle 8.

[0035] Furthermore, the base end of the spindle 8 is connected to a rotational drive source (not shown), such as a motor. When this rotational drive source is operated, the cutting blade 10 rotates together with the spindle 8, with a straight line along the Y-axis as the axis of rotation.

[0036] Furthermore, the cutting unit 6 is connected to a Y-axis movement mechanism (not shown) and a Z-axis movement mechanism (not shown). Each of the Y-axis movement mechanism and the Z-axis movement mechanism includes, for example, a ball screw and a motor. When the Y-axis movement mechanism and / or the Z-axis movement mechanism are operated, the cutting unit 6 moves along the Y-axis and / or Z-axis directions.

[0037] When performing the groove forming step S1 in the cutting device 2, first, protective tape 15 is attached to the surface 11a of the workpiece 11 to protect the multiple devices 13 and to flatten their surface 11a.

[0038] Next, the workpiece 11 is placed on the holding table 4 via the protective tape 15. Then, the suction source communicating with the porous plate of the holding table 4 is activated. This causes the workpiece 11 to be held by the holding table 4.

[0039] Next, the X-axis movement mechanism adjusts the position of the holding table 4 and / or the Y-axis movement mechanism adjusts the position of the cutting unit 6 so that a point (first point) included in the boundary between the central region and the outer peripheral excess region of the workpiece 11 is positioned directly below the lower end of the cutting blade 10.

[0040] Next, a rotational drive source connected to the base end of the spindle 8 rotates the spindle 8 so as to rotate the cutting blade 10. Then, while the cutting blade 10 is still rotating, the Z-axis movement mechanism lowers the cutting unit 6 so that the lower end of the cutting blade 10 is positioned to a predetermined depth from the back surface 11b of the workpiece 11.

[0041] As a result, the lower end of the cutting blade 10 cuts into the back surface 11b side of the workpiece 11. This predetermined depth is shallower than the depth of the recess formed in the grinding step S2 described later.

[0042] Next, while keeping the cutting blade 10 rotating, the holding table 4 is moved along the X-axis until the lower end of the cutting blade 10 reaches a point (the second point) on the boundary that is different from the first point mentioned above.

[0043] As a result, a linear groove 17 is formed on the back surface 11b of the workpiece 11, more specifically, on one side of its central region. Furthermore, the above operation is repeated so that a grid-like groove 17 is formed on one side of the central region of the workpiece 11. With this, the groove formation step S1 is completed.

[0044] After the groove forming step S1, the portion defining the groove 17 is removed and a recess is formed by grinding one side of the central region of the workpiece 11 using a grinding wheel having multiple grinding wheels arranged in an annular shape (grinding step S2).

[0045] Figure 4(A) is a schematic partial cross-sectional side view showing an example of grinding step S2, and Figure 4(B) is a schematic perspective view showing the workpiece after grinding step S2 shown in Figure 4(A). This grinding step S2 is performed in the grinding apparatus 12 shown in Figure 4(A).

[0046] The grinding apparatus 12 includes a holding table 14. This holding table 14 has a disc-shaped frame with a diameter larger than the workpiece 11. This frame is made of, for example, a metal material such as stainless steel or a ceramic.

[0047] Furthermore, the frame has a disc-shaped bottom wall and cylindrical side walls that rise from the outer periphery of the bottom wall. That is, a disc-shaped recess is formed on the upper surface of the frame, defined by the bottom wall and the side walls.

[0048] Furthermore, a disc-shaped porous plate (not shown) having a diameter approximately equal to the diameter of the recess formed on the upper surface of the frame is fixed thereto. This porous plate is made of, for example, porous ceramics. In addition, the upper surface of the holding table 14 (the upper surface of the frame and the upper surface of the porous plate) has a shape corresponding to the side surface of a cone.

[0049] Furthermore, the porous plate communicates with a suction source (not shown), such as an ejector, through a through-hole formed in the bottom wall of the frame. When this suction source is activated, a suction force acts on the space near the top surface of the porous plate.

[0050] Furthermore, the holding table 14 is connected to a horizontal movement mechanism (not shown). This horizontal movement mechanism includes, for example, a ball screw and a motor. When this horizontal movement mechanism is operated, the holding table 14 moves along the horizontal direction.

[0051] Furthermore, the holding table 14 is connected to a rotational drive source (not shown), such as a motor. When this rotational drive source is operated, the holding table 14 rotates around a straight line passing through the center of the upper surface of the holding table 4 as the axis of rotation.

[0052] A grinding unit 16 is provided above the holding table 14. This grinding unit 16 includes a spindle 18 that extends vertically. A disc-shaped mount 20, whose diameter is approximately equal to the radius of the central region of the workpiece 11, is fixed to the lower end of the spindle 18.

[0053] An annular grinding wheel 22, having an outer diameter approximately equal to the diameter of the mount 20, is attached to the lower surface of the mount 20 using fixing members (not shown), such as bolts. This grinding wheel 22 includes an annular wheel base 24 made of a metal such as stainless steel or aluminum.

[0054] Furthermore, an annular recess is formed on the lower surface of the wheel base 24, and multiple grinding wheels 26 are fixed in this recess at approximately equal angular intervals along the circumferential direction of the wheel base 24. The lower surfaces (grinding surfaces) of the multiple grinding wheels 26 are positioned on approximately the same plane.

[0055] Furthermore, a rotational drive source for the spindle, such as a motor, is connected to the upper end of the spindle 18. When this rotational drive source for the spindle is operated, the grinding wheel 22 rotates together with the spindle 18 and mount 20, with a straight line along the vertical axis of rotation.

[0056] Furthermore, the grinding unit 16 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 is operated, the grinding unit 16 moves along the vertical direction.

[0057] When performing the grinding step S2 in the grinding device 12, first, the workpiece 11 is placed on the holding table 14 via the protective tape 15. Next, the suction source communicating with the porous plate of the holding table 14 is activated. As a result, the workpiece 11 is held by the holding table 14.

[0058] Next, the horizontal movement mechanism adjusts the position of the holding table 14 so that the center of the back surface 11b of the workpiece 11 is positioned directly beneath the trajectories of the multiple grinding wheels 26 when the grinding wheel 22 is rotated together with the spindle 18 and mount 20. The outer diameter of these trajectories is approximately equal to the diameter of the central region of the workpiece 11.

[0059] Next, the vertical movement mechanism lowers the grinding unit 16 while operating the rotational drive source for the holding table and the rotational drive source for the spindle to rotate the holding table 14 and the grinding wheel 22. When the grinding surfaces (bottom surfaces) of the multiple grinding wheels 26 come into contact with the back surface 11b of the workpiece 11, one side of the central region of the workpiece 11 is ground.

[0060] Furthermore, this grinding is continued until the portion defining the grid-like grooves 17 on the back surface 11b of the workpiece 11 is removed and a recess 19 of the desired depth is formed on the back surface 11b of the workpiece 11. With this, grinding step S2 is completed.

[0061] In the workpiece grinding method shown in Figure 2, a groove 17 is formed to a depth not reaching the depth of the recess 19 by cutting one side of the central region of the workpiece 11 using a cutting blade 10, and then the portion defining the groove 17 is removed and the recess 19 is formed by grinding one side of the central region of the workpiece 11 using a grinding wheel 22.

[0062] In this case, from the start of grinding on one side of the central region of the workpiece 11 until the portion defining the groove 17 is removed, portions near the grinding surfaces of each of the multiple grinding wheels 26 continue to collide with the side surface of the groove 17.

[0063] When such collisions occur, the binder contained in each of the multiple grinding wheels 26 becomes more easily worn away. As a result, this method can promote the self-sharpening of each of the multiple grinding wheels 26 without weakening the holding force of the binder that holds the abrasive grains.

[0064] It should be noted that the above description represents one aspect of the present invention, and the present invention is not limited to the above description. For example, in the groove forming step S1 of the present invention, instead of the grid-like grooves 17, one or more annular grooves may be formed on one side of the central region of the workpiece 11.

[0065] Figure 5(A) is a schematic partial cross-sectional side view showing an example of a groove forming step S1 for forming one or more annular grooves on one side of the central region of the workpiece 11, and Figure 5(B) is a schematic perspective view showing the workpiece 11 after the groove forming step S1 shown in Figure 5(A).

[0066] This groove-forming step S1 is performed, for example, in the cutting apparatus 2 described above. Specifically, first, a protective tape 15 is attached to the surface 11a of the workpiece 11 to protect the multiple devices 13 and to flatten their surface 11a.

[0067] Next, the workpiece 11 is placed on the holding table 4 via the protective tape 15. Then, the suction source communicating with the porous plate of the holding table 4 is activated. This causes the workpiece 11 to be held by the holding table 4.

[0068] Next, the X-axis movement mechanism adjusts the position of the holding table 4 and / or the Y-axis movement mechanism adjusts the position of the cutting unit 6 so that the central region of the workpiece 11 is positioned directly below the lower end of the cutting blade 10.

[0069] Next, a rotational drive source connected to the base end of the spindle 8 rotates the spindle 8 so as to rotate the cutting blade 10. Then, while the cutting blade 10 is still rotating, the Z-axis movement mechanism lowers the cutting unit 6 so that the lower end of the cutting blade 10 is positioned to a predetermined depth from the back surface 11b of the workpiece 11.

[0070] As a result, the lower end of the cutting blade 10 cuts into the back surface 11b side of the workpiece 11. This predetermined depth is shallower than the depth of the recess 19. Next, while the cutting blade 10 is still rotating, the rotational drive source connected to the holding table 4 rotates the holding table 4 at least once.

[0071] As a result, an annular groove 21 is formed on the back surface 11b of the workpiece 11, more specifically, on one side of its central region. Furthermore, when multiple grooves 21 are to be formed on one side of the central region of the workpiece 11, the distance from the center of the back surface 11b of the workpiece 11 in plan view is changed, and the above operation is repeated. With this, the groove formation step S1 is completed.

[0072] Furthermore, if one or more annular grooves 21 are formed on one side of the central region of the workpiece 11, then in the grinding step S2 described above, each of the multiple grinding wheels 26 is more likely to collide head-on with the side surface of the groove 21.

[0073] In other words, in this case, the angle between the tangent to the trajectory of the multiple grinding wheels 26 and the normal to the groove 21 at the point where the trajectories of the multiple grinding wheels 26 overlap when the spindle 18 is rotated tends to be small. Therefore, in this case, the self-sharpening of each of the multiple grinding wheels 26 can be further promoted.

[0074] Furthermore, the structures and methods of the embodiments described above can be modified as appropriate without departing from the scope of the present invention. [Explanation of Symbols]

[0075] 2:Cutting device 4: Holding Table 6: Cutting Unit 8: Spindle 10: Cutting blade 11: Workpiece (11a: front side, 11b: back side, 11c: notch) 12: Grinding equipment 13: Devices 14: Holding Table 15: Protective tape 16: Grinding Unit 17: Groove 18: Spindle 19: Recess 20: Mount 21: Groove 22: Grinding Wheel 24: Wheel base 26: Grinding Wheel

Claims

[Claim 1] A method for grinding a workpiece, wherein one side of the central region of the workpiece is ground to form a recess having a circular bottom surface, A groove forming step in which a groove is formed to a depth not reaching the depth of the recess by cutting one side of the central region using a cutting blade, A grinding step is performed after the groove forming step, by grinding the one side of the central region using a grinding wheel having a plurality of grinding wheels arranged in an annular shape to remove the portion defining the groove and form the recess, A method for grinding a workpiece, comprising the following components.

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