Grinding method for workpieces

Abstract

To suppress grinding defect from occurring, in grinding for forming a ring-shape reinforcement part on a rear surface side of a work-piece.SOLUTION: A work-piece grinding method, which forms a circular recessed part and a ring-shape reinforcement part in a work-piece, performs steps of: grinding the work-piece with a bottom surface of a griding stone by relatively positioning a grinding wheel with respect to a chuck table so that an advancing trajectory of the grinding stone does not overlap on / with a table rotating shaft of the chuck table and making the grinding wheel relatively approach the chuck table; grinding the work-piece with a side surface of the griding stone by relatively moving the grinding wheel and the chuck table to make the advancing trajectory of the grinding stone overlap with the table rotating shaft of the chuck table; and grinding the work-piece with the bottom surface of the grinding stone by making the grinding wheel relatively approach the chuck table to form the circular recessed part and the ring-shape reinforcement part surrounding the circular recessed part, in the work-piece.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for grinding a workpiece having a device region and an outer peripheral surplus region surrounding the device region on the front surface side, and grinding a predetermined region corresponding to the device region on the back surface side of the workpiece to form a circular recess and a ring-shaped reinforcing portion surrounding the recess.

Background Art

[0002] In order to reduce the weight and thickness of device chips mounted on electronic devices, a workpiece (wafer) having a plurality of devices formed on the front surface side is ground with a grinding device to thin the workpiece, for example, to 100 μm or less. Thereafter, when the workpiece is divided for each device, thin and lightweight device chips can be obtained.

[0003] However, if the workpiece is thinned too much, it becomes difficult to transport the thinned workpiece. Therefore, there is known a grinding method of grinding a predetermined region on the back surface side of the workpiece corresponding to the device region on the front surface side where a plurality of devices are formed to form a circular recess and a ring-shaped reinforcing portion surrounding the circular recess (see, for example, Patent Document 1).

[0004] This grinding method is called TAIKO (registered trademark). By forming a ring-shaped reinforcing portion on the outer peripheral portion of the workpiece, the warpage of the workpiece can be reduced compared to a workpiece having the entire back surface side uniformly thinned, and furthermore, the strength of the workpiece is improved. In addition, cracking of the workpiece starting from the outer peripheral portion of the workpiece can be suppressed.

[0005] For grinding to form the ring-shaped reinforcing portion, a grinding wheel having an outer diameter smaller than the outer diameter of the workpiece is used. The grinding wheel has an annular wheel base, and on one surface side of the wheel base, a plurality of segment-shaped grinding wheels are fixed along the circumferential direction of the wheel base.

[0006] A rotation axis is set perpendicular to the wheel base, passing through its center, and the grinding wheel is rotated around this axis. As a result, the grinding wheel moves along a circular orbit. In this state, when the workpiece's work surface (back side), facing upwards, is brought into contact with the bottom surface of the grinding wheel, the workpiece is ground from the work surface. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-19461 [Overview of the project] [Problems that the invention aims to solve]

[0008] The grinding wheels used to form circular recesses in a workpiece are smaller in diameter and use fewer grinding wheels compared to conventional grinding wheels used to uniformly grind the entire back surface. Furthermore, when the rotational speed of the grinding wheels is the same, the smaller the diameter of the grinding wheel, the slower the grinding wheel moves. Therefore, the amount of work done per grinding wheel is greater than the amount of work done per grinding wheel in a conventional grinding wheel with a relatively large diameter.

[0009] Therefore, compared to grinding wheels used in conventional grinding wheels, the grinding capacity of the grinding wheel used to form circular recesses in a workpiece tends to decrease, making it more prone to defects in the grinding wheel such as dulling, chipping, and clogging. In particular, when grinding a workpiece on which a relatively hard film such as an oxide film has formed on the surface, the grinding of the hard film particularly accelerates the decrease in the grinding capacity of the grinding wheel, making grinding defects due to the decrease in grinding capacity even more likely to occur.

[0010] The present invention has been made in view of the above problems, and aims to provide a grinding method that can suppress the occurrence of grinding defects in grinding in which a ring-shaped reinforcing portion is formed on the back side of a workpiece. [Means for solving the problem]

[0011] According to one aspect of the present invention, a grinding device is used to grind a workpiece, thereby forming a circular recess and a ring-shaped reinforcing portion surrounding the circular recess on the workpiece, the workpiece being ground using a grinding device having a chuck table that rotates around a table rotation axis intersecting the upper surface while holding a disc-shaped workpiece placed on the upper surface, and a grinding unit that includes a spindle and has a plurality of grinding wheels arranged in an annular shape, the grinding wheel having a diameter smaller than the radius of the workpiece mounted on the spindle, and grinding the workpiece held by the rotating chuck table while the grinding wheel is rotated around the spindle, the method comprising: a preparation step of positioning the grinding wheel relative to the chuck table such that the trajectory of the grinding wheel when the grinding wheel is rotated around the spindle does not overlap with the table rotation axis of the chuck table that holds the workpiece; and after the preparation step, rotating the grinding wheel and the chuck table respectively while the grinding wheel and the chuck A first grinding step involves bringing the chuck table relatively closer to the spindle to grind the workpiece on the bottom surface of the grinding wheel, and simultaneously with or after the first grinding step, the grinding wheel and the chuck table are rotated respectively, and the relative positions of the grinding wheel and the chuck table are moved so that the relative positions of the grinding wheel and the chuck table change in the direction along the grinding surface of the workpiece, thereby aligning the trajectory of the grinding wheel with the rotation axis of the chuck table. A method for grinding a workpiece is provided, comprising: a second grinding step of grinding the workpiece on its side; and a third grinding step, simultaneously with or after the second grinding step, of grinding the workpiece on the bottom surface of the grinding wheel by rotating the grinding wheel and the chuck table respectively while bringing the grinding wheel and the chuck table relatively closer together along the spindle, thereby forming a circular recess and a ring-shaped reinforcing portion surrounding the circular recess in the workpiece.

[0012] Preferably, in the first grinding step, the workpiece is ground with the grinding wheel in a state in which the region inside the trajectory of the grinding wheel and the rotation axis of the chuck table overlap, thereby forming an annular groove in the workpiece.

[0013] More preferably, in the first grinding step, the distance between the center of the trajectory of the grinding wheel and the rotation axis of the table is 5 mm or more.

[0014] Preferably, in the first grinding step, the workpiece is ground with the grinding wheel while the trajectory of the grinding wheel overlaps with the outer edge of the workpiece, thereby grinding the outer edge of the workpiece.

[0015] Preferably, the first grinding step and the second grinding step are performed simultaneously. Alternatively, preferably, the second grinding step and the third grinding step are performed simultaneously. [Effects of the Invention]

[0016] Generally, when performing grinding on a workpiece to form a circular recess and a ring-shaped reinforcing portion surrounding the circular recess, the position of the grinding wheel and other components is adjusted in advance so that the trajectory of the grinding wheel when it is rotated coincides with the rotation axis of the chuck table. In this case, when the grinding wheel and chuck table are brought close together and the workpiece is ground with the grinding wheel, the grinding wheel will contact the workpiece from the bottom surface over the entire area where the circular recess is to be formed.

[0017] In contrast, in a workpiece grinding method according to one aspect of the present invention, the position of the grinding wheel and the like is adjusted so that the trajectory of the grinding wheel when the grinding wheel is rotated does not overlap with the rotation axis of the chuck table (preparation step). In this case, when the grinding wheel and the chuck table are brought close together, the grinding wheel contacts the workpiece to be ground from its bottom surface, and the workpiece is ground in an annular shape (first grinding step). At this time, an ungrinded area remains in the workpiece inside the formed annular recess.

[0018] Subsequently, the grinding wheel and chuck table are moved relative to each other so that their relative positions change in the direction along the grinding surface of the workpiece. As a result, the side surface of the grinding wheel comes into contact with the ungrinded area of ​​the workpiece, and the ungrinded area is ground (second grinding step). In this way, in the workpiece grinding method according to one aspect of the present invention, not only the bottom surface but also the side surface of the grinding wheel is used to grind the workpiece, thus reducing the amount of material used on the bottom surface of the grinding wheel. Therefore, the decrease in the grinding capacity of the bottom surface of the grinding wheel is reduced, and the occurrence of deterioration of the grinding wheel is less likely to occur.

[0019] In particular, when a hard film such as an oxide film is formed on the back side of the workpiece, a portion of the hard film to be removed is ground on the bottom surface of the grinding wheel (first grinding step), and the remaining portion of the hard film to be removed is ground on the side surface of the grinding wheel (second grinding step). Therefore, compared to the case where all of the hard film to be removed is ground on the bottom surface of the grinding wheel, the decrease in the grinding capacity of the grinding wheel is slower, and the occurrence of deterioration of the grinding wheel is less likely to occur.

[0020] Subsequently, as the final stage of the grinding process, when the grinding wheel grinds the workpiece with the trajectory of the grinding wheel and the rotation axis of the chuck table overlapping, a circular recess can be formed in the workpiece, as in the conventional method (third grinding step). The area around the circular recess then becomes a ring-shaped reinforcement.

[0021] During this series of grinding processes, there is no need to stop the rotation of the grinding wheel or the chuck table, nor is there any need to perform actions such as raising the grinding wheel relative to the chuck table. In other words, since each step of the series of grinding processes can be performed continuously without any waiting time, the time required for grinding a workpiece according to one aspect of the present invention is short.

[0022] Therefore, according to one aspect of the present invention, a grinding method is provided that can suppress the occurrence of grinding defects in grinding in which a ring-shaped reinforcing portion is formed on the back side of a workpiece. [Brief explanation of the drawing]

[0023] [Figure 1] It is a perspective view schematically showing a grinding apparatus for grinding a workpiece. [Figure 2] It is a cross-sectional view schematically showing the grinding apparatus and the workpiece in the first grinding step. [Figure 3] FIG. 3(A) is a plan view schematically showing the positional relationship among the grinding wheel, the workpiece, and the chuck table in the first grinding step, and FIG. 3(B) is a plan view schematically showing the surface to be ground of the workpiece after the first grinding step. [Figure 4] It is a cross-sectional view schematically showing the grinding apparatus and the workpiece in the second grinding step. [Figure 5] It is a cross-sectional view schematically showing the grinding apparatus and the workpiece in the third grinding step. [Figure 6] FIG. 6(A) is a plan view schematically showing the positional relationship among the grinding wheel, the workpiece, and the chuck table in the third grinding step, and FIG. 6(B) is a plan view schematically showing the surface to be ground of the workpiece after the third grinding step. [Figure 7] It is a cross-sectional view schematically showing the grinding apparatus and the workpiece in the first grinding step according to a modified example. [Figure 8] FIG. 8(A) is a plan view schematically showing the positional relationship among the grinding wheel, the workpiece, and the chuck table in the first grinding step according to a modified example, and FIG. 8(B) is a plan view schematically showing the surface to be ground of the workpiece after the first grinding step. [Figure 9] It is a cross-sectional view schematically showing the grinding apparatus and the workpiece in the second grinding step according to a modified example. [Figure 10] It is a flowchart showing the flow of each step of a method for grinding a workpiece.

Embodiments for Carrying Out the Invention

[0024] An embodiment of one aspect of the present invention will be described with reference to the attached drawings. First, a workpiece to be ground by the grinding method of the workpiece according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 includes a schematic perspective view showing a workpiece 11 in which a circular recess 15 is formed on the back surface 11b and a ring-shaped reinforcing portion 17 is formed around the circular recess 15. Figure 2 includes a schematic cross-sectional view showing the workpiece 11 before grinding.

[0025] The workpiece 11 in this embodiment is a disc-shaped silicon wafer having a predetermined diameter (for example, a diameter of approximately 200 mm). The workpiece 11 has a surface 11a and a back surface 11b, and the length from the surface 11a to the back surface 11b (i.e., the thickness of the workpiece 11) is a predetermined value of 200 μm to 800 μm (for example, 725 μm). A thermal oxide film (not shown) with a thickness of approximately 2000 Å to 3000 Å may be formed on the entire back surface 11b. The thermal oxide film is a hard film that is harder than other areas of the workpiece 11.

[0026] On the surface 11a, multiple intersecting division lines are arranged in a grid pattern. On the surface 11a of the workpiece 11, devices such as ICs (Integrated Circuits) (not shown) are formed in each rectangular region demarcated by the multiple division lines. The region on the surface 11a of the workpiece 11 where multiple devices are formed is called the device formation region. Surrounding this device formation region in a plan view, there is a roughly flat, annular outer peripheral surplus region where no devices are formed.

[0027] There are no restrictions on the type, material, size, shape, structure, etc., of the workpiece 11. The workpiece 11 may be a wafer or substrate made of a compound semiconductor other than silicon (GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Furthermore, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc., of the devices formed on the workpiece 11. The grinding method for the workpiece according to this embodiment will be described below, using the case where the workpiece 11 is a silicon wafer as an example.

[0028] The workpiece 11 is ground from the back surface 11b to a predetermined thickness, and then the workpiece 11 is divided along the planned division line to obtain individual device chips. In other words, the back surface 11b of the workpiece 11 becomes the grinding surface. Before grinding the workpiece 11, a circular protective tape 13 made of resin is attached to the front surface 11a to reduce damage to the device during grinding. This forms a workpiece unit in which the workpiece 11 and the protective tape 13 are laminated.

[0029] During grinding of the workpiece 11, a predetermined area on the back surface 11b that corresponds to the device formation area is ground to a predetermined depth. As a result, a circular recess 15 and a ring-shaped reinforcing portion 17 surrounding the circular recess 15 can be formed on the workpiece 11, as shown in Figure 1.

[0030] Next, with reference to Figures 1 and 2, the grinding apparatus 2 used for grinding the workpiece 11 will be described. As shown in Figures 1 and 2, the grinding apparatus 2 is equipped with a disc-shaped chuck table 4 that holds the surface 11a side of the workpiece 11 by suction. The chuck table 4 has a disc-shaped frame 4b made of ceramics.

[0031] A disc-shaped recess is formed in the center of the frame 4b. A predetermined flow path (not shown) is formed inside the frame 4b. One end of the predetermined flow path is exposed to the recess, and a suction source (not shown), such as an ejector, is connected to the other end of the predetermined flow path.

[0032] A porous plate made of porous ceramics is fixed in the recess of the frame 4b. The negative pressure from the suction source is transmitted to the upper surface of the porous plate. The upper surface of the porous plate and the upper surface of the frame are flush and function as a holding surface 4a that suctions and holds the workpiece 11.

[0033] The chuck table 4 is rotatable around a predetermined table rotation axis 4c by a rotational drive source (not shown), such as a motor, located at its lower part. The holding surface 4a is a very gently curved cone with its apex at the center, and the highest generatrix connecting the center of the holding surface 4a to its outer circumference is tilted to lie along the horizontal plane. The table rotation axis 4c penetrates the holding surface 4a at its center and is tilted to intersect perpendicularly with a plane that encompasses the entire circular outer edge of the holding surface 4a.

[0034] A grinding unit 6 is positioned above the chuck table 4. The grinding unit 6 has a cylindrical spindle housing 8. A ball screw type grinding feed mechanism (not shown) is connected to the spindle housing 8, which raises and lowers the grinding unit 6 along a direction substantially perpendicular to the holding surface 4a (for example, the vertical direction). The direction in which the grinding unit 6 moves with the grinding feed mechanism is also called the grinding feed direction.

[0035] In addition, in the grinding device 2, the chuck table 4 may be raised and lowered instead of the grinding unit 6. Alternatively, both the grinding unit 6 and the chuck table 4 may be raised and lowered. That is, the grinding feed mechanism of the grinding device 2 moves the grinding unit 6 and the chuck table 4 so that they are relatively closer to or further apart from each other.

[0036] Furthermore, the grinding device 2 is equipped with a ball screw type moving mechanism (not shown) that moves the chuck table 4 and the grinding unit 6 relative to each other in a direction perpendicular to the grinding feed direction. Activating this moving mechanism allows the horizontal positional relationship between the grinding wheel 20 (grinding wheel 18) of the grinding unit 6 (described later) and the workpiece 11 held by suction on the chuck table 4 to be changed.

[0037] A portion of a cylindrical spindle 10 is rotatably held within the spindle housing 8. The spindle 10 is positioned approximately parallel to the direction in which the grinding unit 6 moves up and down. A rotational drive source (not shown), such as a motor housed in the spindle housing 8, is connected to the upper end of the spindle 10. A disc-shaped mount 12 is fixed to the lower end of the spindle 10.

[0038] An annular grinding wheel 20 is mounted on the lower side of the mount 12. The grinding wheel 20 has an annular wheel base 16 made of a metal such as an aluminum alloy. The upper side of the wheel base 16 is fixed to the lower side of the mount 12 by fasteners 14 such as bolts. Multiple segmented grinding wheels 18 are arranged in an annular pattern along the circumferential direction of the wheel base 16 on the lower side of the wheel base 16.

[0039] When the rotational drive source housed in the spindle housing 8 is activated to rotate the spindle 10, the grinding wheel 20 rotates around the spindle 10 (wheel rotation axis 10a). At this time, the grinding wheel 18 moves along an annular trajectory centered on the wheel rotation axis 10a. The diameter of the region formed by the trajectories of the multiple grinding wheels 18 is set to be less than or equal to the radius of the back surface 11b of the workpiece 11.

[0040] Next, the grinding operation of the grinding device 2 will be described. Here, we will explain using as an example a conventional grinding method in which a predetermined area on the back surface 11b side of the workpiece 11 corresponding to the device area is ground to form a circular recess 15 and a ring-shaped reinforcing portion 17 surrounding the circular recess 15.

[0041] First, the workpiece 11 is positioned so that its surface 11a faces the holding surface 4a, and the workpiece 11 is held in place by the chuck table 4 via the protective tape 13. At this time, the position of the workpiece 11 is adjusted so that its center aligns with the center of the holding surface 4a of the chuck table 4. When the workpiece 11 is held in place by the chuck table 4, the workpiece 11 deforms to conform to the shape of the holding surface 4a.

[0042] Then, the positions of the chuck table 4 and the grinding unit 6 are adjusted so that the trajectory of the grinding wheel 18 coincides with the table rotation axis 4c of the chuck table 4. After that, the chuck table 4 is rotated around the table rotation axis 4c, and the grinding wheel 20 is rotated around the wheel rotation axis 10a.

[0043] Subsequently, the grinding feed mechanism is activated to lower the grinding unit 6 and begin grinding. As a result, the bottom surface of the grinding wheel 18, which is moving along an annular trajectory, comes into contact with the back surface 11b of the workpiece 11, and grinding of the workpiece 11 by the grinding wheel 18 begins. In this case, the area including the center of the back surface 11b of the workpiece 11 is ground.

[0044] Then, when the grinding wheel 20 descends to a predetermined height, the descent of the grinding unit 6 is stopped, and the grinding of the workpiece 11 is stopped. As a result, a circular recess 15 is formed on the back surface 11b side of the workpiece 11, which corresponds to the device formation area. On the other hand, the area around the circular recess 15 is not ground. As a result, a ring-shaped reinforcing portion 17 remains around the circular recess 15.

[0045] The grinding wheel 20 used to form the circular recess 15 in the workpiece has a smaller diameter and fewer grinding wheels compared to a normal grinding wheel. Furthermore, at the same rotational speed, the smaller the diameter of the grinding wheel, the slower the grinding wheel moves. Therefore, the amount of work done per grinding wheel 18 is greater than the amount of work done per grinding wheel in a normal grinding wheel with a relatively large diameter.

[0046] Therefore, compared to the grinding wheel in a normal grinding wheel, the grinding capacity of the grinding wheel 18 of the grinding wheel 20 used to form a circular recess 15 in the workpiece 11 tends to decrease, making it easier for poor condition of the grinding wheel, such as dulling, chipping, and clogging, to occur.

[0047] In particular, a thermal oxide film with a thickness of 0.2 μm to 0.3 μm may be formed on the back surface 11b of the workpiece 11. When grinding a workpiece 11 on which a relatively hard film such as an oxide film has been formed on the surface to be ground, the grinding of the hard film particularly accelerates the decrease in the grinding capacity of the grinding wheel 18, making grinding defects due to the decrease in grinding capacity even more likely to occur.

[0048] Therefore, in the workpiece grinding method according to this embodiment, when grinding to form a circular recess 15 and a ring-shaped reinforcing portion 17 on the back surface 11b side of the workpiece 11, the occurrence of grinding defects is suppressed by suppressing a decrease in the grinding capacity of the grinding wheel 18. The workpiece grinding method according to this embodiment can be carried out using the grinding apparatus 2 shown in Figure 1, etc. Figure 10 is a flowchart showing the flow of each step of the workpiece grinding method according to this embodiment. The workpiece grinding method according to this embodiment will be described in detail below.

[0049] In the workpiece grinding method according to this embodiment, first, preparation step S10 is performed. In preparation step S10, the relative positions of the grinding wheel 20 and the chuck table 4 are adjusted. In particular, the grinding wheel 20 is positioned relative to the chuck table 4 so that the trajectory of the grinding wheel 18 when the grinding wheel 20 is rotated around the spindle 10 does not overlap with the table rotation axis 4c of the chuck table 4 that holds the workpiece 11.

[0050] Figure 2 includes a schematic cross-sectional view showing the workpiece 11, grinding wheel 20, and chuck table 4 at the time preparation step S10 is completed. In Figure 2, suction channels and other features formed in the chuck table 4 are omitted. In Figures 2 and below, the cross-sectional views of the chuck table 4 and grinding wheel 20 are shown, cut by a plane including the table rotation axis 4c and the wheel rotation axis 10a. Figure 3(A) also includes a schematic plan view showing the workpiece 11, grinding wheel 18, and chuck table 4 at the time preparation step S10 is completed.

[0051] When preparation step S10 is completed, as shown in Figures 2 and 3(A), the trajectory of the grinding wheel 18 when the grinding wheel 20 is rotated around the spindle 10 (wheel rotation axis 10a) does not overlap with the table rotation axis 4c. In the workpiece grinding method according to this embodiment, the first grinding step S20, which will be described next, is performed in this state.

[0052] In the workpiece grinding method according to this embodiment, the first grinding step S20 is performed after the preparation step S10. In the first grinding step S20, the workpiece 11 is ground on the bottom surface of the grinding wheel 18 by rotating the grinding wheel 20 and the chuck table 4 respectively and bringing them relatively closer together along the spindle 10.

[0053] Figure 2 is a schematic cross-sectional view showing the workpiece 11, chuck table 4, and grinding unit 6 at the start of the first grinding step S20. Figure 3(A) is a schematic plan view showing the workpiece 11, chuck table 4, and grinding unit 6 at the start of the first grinding step S20. Furthermore, Figure 3(B) is a schematic plan view showing the back surface 11b (grinding surface) of the workpiece 11 at the completion of the first grinding step S20.

[0054] In the first grinding step S20, for example, the workpiece 11 is ground with the grinding wheel 18 in a state where the area inside the trajectory of the grinding wheel 18 and the table rotation axis 4c of the chuck table 4 overlap. However, the first grinding step S20 is not limited to this.

[0055] In the first grinding step S20, the grinding feed mechanism is activated to lower the grinding unit 6 toward the chuck table 4. As a result, the bottom surface of the grinding wheel 18, which is moving along an annular trajectory, comes into contact with the back surface 11b (the surface to be ground) of the workpiece 11, and grinding of the workpiece 11 begins.

[0056] When the workpiece 11 is ground on the bottom surface of the grinding wheel 18, the chuck table 4 rotates together with the grinding wheel 20. Therefore, the area of ​​the back surface 11b of the workpiece 11 that is in contact with the grinding wheel 18 is constantly changing. However, in the first grinding step S20, the trajectory of the grinding wheel 18 does not coincide with the table rotation axis 4c. Therefore, the grinding wheel 18 does not come into contact with the center 11c of the back surface 11b of the workpiece 11. Furthermore, the grinding wheel 18 does not reach the inner periphery of the ring-shaped reinforcement portion 17 (see Figure 1, etc.) that is planned to be formed.

[0057] Let me explain in more detail. In Figure 3(A), the inner and outer edges 22 and 24 of the annular region 26 in which the grinding wheel 18 contacts the back surface 11b of the workpiece 11 in the first grinding step S20 are shown by dashed lines. In the first grinding step S20, the workpiece 11 is ground by the bottom surface of the grinding wheel 18 in this region 26, and the area outside the region 26 remains unground.

[0058] The inner periphery 22 of this annular region 26 corresponds to a circle whose radius is the distance between the point on the trajectory of the grinding wheel 18 on the back surface 11b of the workpiece 11 that is closest to the table rotation axis 4c and the table rotation axis 4c. The center of this circle is the wheel rotation axis 10a. Similarly, the outer periphery 24 of the annular region 26 corresponds to a circle whose radius is the distance between the point on the trajectory of the grinding wheel 18 on the back surface 11b of the workpiece 11 that is furthest from the table rotation axis 4c and the table rotation axis 4c. The center of this circle is also the wheel rotation axis 10a.

[0059] In this case, when the first grinding step S20 is performed, the workpiece 11 is ground in an annular region 26 as shown in Figure 3(B), forming an annular groove 19. Then, an unground area 21a remains in the center 11c of the back surface 11b of the workpiece 11 surrounded by this annular groove 19. In addition, an unground area 21b remains outside the annular groove 19.

[0060] Here, the area of ​​the annular region 26, which is the region where the bottom surface of the grinding wheel 18 contacts the workpiece 11, is smaller than the area of ​​the circular recess 15 (see Figure 1, etc.) that is ultimately formed on the workpiece 11 on the back surface 11b of the workpiece 11. Therefore, compared to grinding processes that form the circular recess 15 using conventional grinding methods, the area of ​​the region in which the grinding wheel 18 grinds the workpiece 11 in the first grinding step S20 is smaller. Consequently, in the first grinding step S20, defects in the condition of the grinding wheel 18, such as crushing, chipping, and clogging, are relatively less likely to occur.

[0061] In particular, when a hard film such as an oxide film is formed on the back surface 11b of the workpiece 11, conventional grinding methods frequently resulted in deterioration of the grinding wheel 18 when forming a circular recess 15 on the workpiece 11. Therefore, by using the workpiece grinding method according to this embodiment, deterioration of the grinding wheel 18 becomes less likely, significantly increasing the processing efficiency of workpieces 11 with a hard film formed on them.

[0062] Furthermore, the depth of the annular groove 19 formed by grinding the workpiece 11 in the first grinding step S20 is set to be smaller than the depth of the circular recess 15 formed in the workpiece 11 when the grinding method for the workpiece according to this embodiment is completed. If a hard film is formed on the back surface 11b of the workpiece 11, it is preferable that the hard film is dug out in the first grinding step S20.

[0063] In order to form an annular groove 19 of a predetermined depth in the first grinding step S20, it is advisable to stop the descent of the grinding unit 6 when the bottom surface of the grinding wheel 18 reaches a predetermined height. Furthermore, if the grinding device 2 is equipped with a thickness measuring instrument for measuring the thickness of the workpiece 11, it is advisable to monitor the thickness of the workpiece 11 in the annular groove 19 being formed while the first grinding step S20 is being performed. Then, it is advisable to stop the descent of the grinding unit 6 when the thickness of the workpiece 11 reaches a predetermined thickness.

[0064] There are no particular limitations on the thickness measuring instrument provided by the grinding device 2. For example, the grinding device 2 may include a contact-type thickness measuring instrument equipped with a probe that contacts the grinding surface of the workpiece 11. The contact-type thickness measuring instrument has the function of measuring the height of the grinding surface by the probe contacting the grinding surface of the workpiece 11. Alternatively, the grinding device 2 may also include a non-contact type thickness measuring instrument. For example, the non-contact type thickness measuring instrument measures the height of the grinding surface by irradiating the grinding surface of the workpiece 11 with a laser beam or ultrasonic wave, and receiving the laser beam or ultrasonic wave reflected from the grinding surface.

[0065] The thickness measuring instrument measures the thickness of the workpiece 11 in the area exposed from the grinding wheel 20. However, at the position where the grinding wheel 18 of the grinding wheel 20 that grinds the workpiece 11 is in contact with the workpiece 11, the grinding surface (back surface 11b) of the workpiece 11 is hidden by the grinding wheel 20 and not exposed. Therefore, in order to monitor the thickness of the workpiece 11 with the thickness measuring instrument in the annular groove 19 formed in the workpiece 11, there must be a sufficiently large area of ​​the annular groove 19 exposed from the grinding wheel 20.

[0066] The area of ​​the region where the annular groove 19 is formed is determined by the distance between the table rotation axis 4c and the wheel rotation axis 10a. For example, when the distance between the table rotation axis 4c and the wheel rotation axis 10a is zero and they overlap, the trajectory of the grinding wheel 18 coincides with the region where the annular groove 19 is formed on the back surface 11b of the workpiece 11. In this case, the area of ​​the region where the annular groove 19 is formed is minimized, and the annular groove 19 is not exposed at all from the grinding wheel 20. In this case, the thickness of the workpiece 11 cannot be monitored in the annular groove 19.

[0067] Therefore, for example, the distance between the center of the trajectory of the grinding wheel 18 (wheel rotation axis 10a) and the table rotation axis 4c is set to 5 mm or more. In this case, during the process in which the annular groove 19 is formed by the grinding wheel 18, the annular groove 19 is exposed from the grinding wheel 20 over a sufficient area, so that the thickness of the workpiece 11 can be measured in the annular groove 19 using a thickness measuring instrument.

[0068] However, in the first grinding step S20, the distance between the center of the trajectory of the grinding wheel 18 (wheel rotation axis 10a) and the table rotation axis 4c may be set to less than 5 mm. When the distance between the two is reduced, the area of ​​the grinding surface (back surface 11b) of the workpiece 11 that is ground by the grinding wheel 18 becomes smaller, making it less likely for the bottom surface of the grinding wheel 18 to become clogged, chipped, or jammed.

[0069] In particular, when the center of the trajectory of the grinding wheel 18 (wheel rotation axis 10a) and the table rotation axis 4c coincide, the area of ​​the region on the workpiece surface (back surface 11b) that is ground by the grinding wheel 18 is minimized. This is because there is virtually no change in the positional relationship between the trajectory of the grinding wheel 18 and the workpiece 11 due to the rotation of the chuck table 4. At this time, the load on the grinding wheel 18 is minimized, and defects are least likely to occur on the bottom surface of the grinding wheel 18.

[0070] In the workpiece grinding method according to this embodiment, the second grinding step S30 is performed after the first grinding step S20. For example, the second grinding step S30 is started when the first grinding step S20 has been performed, a portion of the grinding wheel 18 has entered the annular groove 19, and the grinding wheel 20 and the chuck table 4 are continuing to rotate. Figure 4 is a schematic cross-sectional view showing the workpiece 11, the chuck table 4, and the grinding unit 6 at the start of the second grinding step S30.

[0071] In the second grinding step S30, the grinding wheel 20 and the chuck table 4 are rotated respectively and moved relative to each other in a direction along the grinding surface (back surface 11b) of the workpiece 11. Then, by moving the grinding wheel 20 and the chuck table 4 relative to each other so that their relative positions in this direction change, the trajectory of the grinding wheel 18 is aligned with the table rotation axis 4c of the chuck table 4, thereby grinding the workpiece 11 with the side surface of the grinding wheel 18.

[0072] When the grinding wheel 20 or the like begins to move relative to the planned position in a direction along the surface to be ground (back surface 11b), the side surface of the grinding wheel 18 (the side surface on the inner peripheral edge of the movement trajectory) comes into contact with the outer periphery of the unground area 21a (see Figures 3(B) and 4). As a result, the circular unground area 21a is ground from the outer periphery by the side surface of the grinding wheel 18, and the diameter of the unground area 21a gradually decreases.

[0073] Simultaneously, the side surface of the grinding wheel 18 (the side surface on the outer edge of the trajectory) comes into contact with the inner side of the annular ungrinded region 21b outside the annular groove 19. As a result, the ungrinded region 21b is ground from the inner side by the side surface of the grinding wheel 18, and the width of the ungrinded region 21b gradually decreases.

[0074] Figure 5 shows a cross-sectional view of the chuck table 4, etc., at the time the second grinding step S30 is completed. Figure 6(A) shows a schematic plan view of the workpiece 11, chuck table 4, and grinding unit 6 at the time the second grinding step S30 is completed.

[0075] As the second grinding step S30 reaches its final stage, when the trajectory of the grinding wheel 18 coincides with the table rotation axis 4c of the chuck table 4, the entire ungrinded area 21a on the back surface 11b of the workpiece 11 is ground. At the same time, all of the ungrinded area 21b on the outer peripheral edge of the back surface 11b of the workpiece 11, except for the area that will ultimately become the ring-shaped reinforcement portion 17, is ground. As a result, a relatively shallow circular recess 15a is formed in the area where the circular recess 15 will ultimately be formed.

[0076] In the second grinding step S30, the ungrinded areas 21a and 21b remaining on the back surface 11b of the workpiece 11 in the first grinding step S20 are ground with the side surface of the grinding wheel 18 instead of the bottom surface. Therefore, compared to the case where the workpiece 11 is ground only with the bottom surface of the grinding wheel 18 and the ring-shaped reinforcing portion 17 remains on the workpiece 11, the grinding method of the workpiece according to this embodiment makes it less likely for defects to occur on the bottom surface of the grinding wheel 18.

[0077] In the workpiece grinding method according to this embodiment, the third grinding step S40 is performed after the second grinding step S30. When the second grinding step S30 is performed, the trajectory of the grinding wheel 18 coincides with the table rotation axis 4c of the chuck table 4. The third grinding step S40 is performed in this state, immediately following the second grinding step S30. The third grinding step S40 is started with the grinding wheel 20 and the chuck table 4 both continuing to rotate.

[0078] Figure 5 is a schematic cross-sectional view showing the chuck table 4, grinding wheel 20, and workpiece 11 at the start of the third grinding step S40. Figure 6(A) is a schematic plan view showing the workpiece 11, chuck table 4, and grinding unit 6 in the third grinding step S40. Figure 6(B) is a schematic plan view showing the workpiece 11 at the completion of the third grinding step S40.

[0079] In the third grinding step S40, as shown in Figure 5, the grinding wheel 20 and the chuck table 4 are rotated while being brought relatively closer together along the spindle 10. This grinds the workpiece 11 with the bottom surface of the grinding wheel 18, forming a circular recess 15 and a ring-shaped reinforcing portion 17 surrounding the circular recess 15 in the workpiece 11.

[0080] The third grinding step S40 is performed as the final stage of the workpiece grinding method according to this embodiment. When the bottom surface of the grinding wheel 18 reaches the height of the bottom surface of the circular recess 15 that is to be formed, the descent of the grinding unit 6 is stopped and the grinding of the workpiece 11 is completed.

[0081] For example, if a hard film is formed on the back surface 11b of the workpiece 11 before grinding, removing this hard film in the first grinding step S20 and the second grinding step S30 will prevent the hard film from being ground in the third grinding step S40. In this case, since not only the back surface but also the sides of the grinding wheel 18 can be used to remove the hard film, the grinding capacity of the bottom surface of the grinding wheel 18 is less likely to decrease. Therefore, in the third grinding step S40, a circular recess 15 can be formed on the workpiece 11 with the bottom surface of the grinding wheel 18, which still has a sufficiently high grinding capacity.

[0082] Furthermore, even when a hard film is not formed on the back surface 11b of the workpiece 11, the grinding method for the workpiece according to this embodiment is less prone to defects in the condition of the bottom surface of the grinding wheel 18 compared to the case where the workpiece 11 is ground using only the bottom surface of the grinding wheel 18 to form a circular recess 15. Therefore, when grinding to form a ring-shaped reinforcing portion 17 on the back surface 11b side of the workpiece 11, the occurrence of grinding defects can be suppressed.

[0083] Furthermore, in the workpiece grinding method according to this embodiment, it is not necessary to raise the grinding unit 6 while the series of grinding steps, the first grinding step S20, the second grinding step S30, and the third grinding step S40, are carried out. In addition, the first grinding step S20, the second grinding step S30, and the third grinding step S40 can be performed continuously while the grinding wheel 20 and the chuck table 4 are rotating, respectively.

[0084] Therefore, there is no need to wait for the grinding unit 6 to rise, adjust its position, or lower again during the series of grinding steps. Furthermore, there is no need to stop the rotation of the grinding wheel 20 and the chuck table 4 midway, nor is there any need to restart the grinding wheel 20 and the chuck table 4 once their rotation has stopped. Accordingly, in the workpiece grinding method according to the embodiment described above, there is no need to provide waiting time between each grinding step, and the circular recess 15 and the ring-shaped reinforcing portion 17 can be formed on the workpiece 11 in a short time.

[0085] In the above embodiment, the case described was one in which the grinding wheel 20 is positioned relative to the chuck table 4 such that the table rotation axis 4c of the chuck table 4 is inside the trajectory of the grinding wheel 18 during the preparation step S10. However, the method of grinding a workpiece according to one aspect of the present invention is not limited thereto.

[0086] In other words, in preparation step S10, the table rotation axis 4c of the chuck table 4 may be positioned outside the trajectory of the grinding wheel 18, and the grinding wheel 20 may be positioned relative to the chuck table 4 to achieve this. Then, the first grinding step S20 may be performed in this state.

[0087] Figure 7 is a schematic cross-sectional view showing the workpiece 11, chuck table 4, and grinding wheel 20 when the preparation step S10 for the modified example is performed and the first grinding step S20 for the modified example is started. Figure 8(A) is a schematic plan view showing the grinding wheel 18, workpiece 11, and chuck table 4 in the first grinding step S20 for the modified example. Figure 8(B) is a schematic plan view showing the workpiece 11 at the time the first grinding step S20 for the modified example is completed.

[0088] As shown in Figures 7 and 8(A), in the modified first grinding step S20, the grinding wheel 18 grinds the workpiece 11 with the grinding wheel 18 while the trajectory of the grinding wheel 18 overlaps with the outer edge 11d of the workpiece 11, thereby grinding the outer edge 11d of the workpiece 11. As a result, an annular removal portion 19a is formed so as to overlap with the outer edge 11d of the workpiece 11. For example, if a hard film is formed on the back surface 11b of the workpiece 11, in the first grinding step S20, the grinding unit 6 should be lowered so that the bottom surface of the grinding wheel 18 reaches a position lower than the hard film.

[0089] Next, the second grinding step S30 is performed. Figure 9 is a schematic cross-sectional view showing the workpiece 11, chuck table 4, and grinding wheel 20 at the start of the second grinding step S30 according to a modified example. In the second grinding step S30, the grinding wheel 20 is moved horizontally relative to the chuck table 4 (parallel to the back surface 11b of the workpiece 11) until the trajectory of the grinding wheel 18 and the table rotation axis 4c overlap.

[0090] In the second grinding step S30, the ungrinded area inside the removal portion 19a on the back surface 11b of the workpiece 11 is ground with the side surface of the grinding wheel 18. Then, as described above, when the third grinding step S40 is performed, a workpiece 11 is obtained in which a circular recess 15 is formed on the back surface 11b and a ring-shaped reinforcing portion 17 remains on the outer circumference of the circular recess 15.

[0091] For example, if an unwanted film is formed on the back surface 11b of the workpiece 11, the first grinding step S20 and the second grinding step S30 can be performed in this manner to remove this film from the entire back surface 11b of the workpiece 11. Therefore, when the third grinding step S40 is performed to form the ring-shaped reinforcement portion 17 on the workpiece 11, no hard film remains on this ring-shaped reinforcement portion 17 either.

[0092] In the above embodiment, the case in which the second grinding step S30 is started after the first grinding step S20 is completed has been described. However, the grinding method of a workpiece according to one aspect of the present invention is not limited thereto.

[0093] For example, in a workpiece grinding method according to one aspect of the present invention, the first grinding step S20 and the second grinding step S30 may be performed simultaneously. That is, the grinding wheel 20 and the chuck table 4 may move relative to each other while moving closer together, and both may move relative to each other along the grinding surface (back surface 11b) of the workpiece 11. In this case, the workpiece 11 is dug out by the bottom surface of the grinding wheel 18, and the ungrinded areas 21a and 21b are gradually ground down by the side surface of the grinding wheel 18.

[0094] For example, if a hard film is formed on the back surface 11b of the workpiece 11, a large load is applied to the area of ​​the grinding wheel 18 that is in contact with the hard film during the second grinding step S30, and it is possible that a defect will occur in that area of ​​the grinding wheel 18. Therefore, the grinding wheel 18 is lowered while grinding the ungrinded areas 21a and 21b on the side of the grinding wheel 18. In this case, the area of ​​the grinding wheel 18 that is in contact with the hard film changes moment by moment.

[0095] In other words, the load is distributed over a wider area of ​​the side surface of the grinding wheel 18, so the load does not concentrate in a specific area on the side surface of the grinding wheel 18. Therefore, deterioration of the surface condition of the grinding wheel 18 can be suppressed. In addition, when the first grinding step S20 and the second grinding step S30 are performed simultaneously, the time required for the grinding method of the workpiece according to this embodiment can be shortened.

[0096] Furthermore, when the second grinding step S30 is performed simultaneously with the first grinding step S20, the start times of each step do not need to coincide, nor do the end times of each step need to coincide. For example, the second grinding step S30 may start after the first grinding step S20 has started but before the first grinding step S20 has finished. Also, the first grinding step S20 may finish after the second grinding step S30 has started but before the second grinding step S30 has finished.

[0097] Furthermore, the above embodiment described a case in which the third grinding step S40 is started after the second grinding step S30 is completed. However, the grinding method of a workpiece according to one aspect of the present invention is not limited thereto.

[0098] For example, in a workpiece grinding method according to one aspect of the present invention, the second grinding step S30 and the third grinding step S40 may be performed simultaneously. That is, the grinding wheel 20 and the chuck table 4 may move relatively closer to each other while they move relatively along the grinding surface (back surface 11b) of the workpiece 11. In this case, the workpiece 11 is dug out by the bottom surface of the grinding wheel 18, and the ungrinded areas 21a and 21b are gradually ground down by the side surface of the grinding wheel 18.

[0099] Even in this case, the area of ​​the grinding wheel 18 that contacts the hard film changes moment by moment. That is, the load is distributed over a wider area of ​​the grinding wheel 18's side surface, so the load does not concentrate on a specific area of ​​the grinding wheel 18's side surface. Furthermore, when the second grinding step S30 and the third grinding step S40 are performed simultaneously, the time required for grinding the workpiece according to this embodiment can be shortened.

[0100] Indeed, when the second grinding step S30 is performed simultaneously with the third grinding step S40, the start times of each step do not need to coincide, nor do the end times of each step need to coincide. For example, the third grinding step S40 may start after the second grinding step S30 has started but before the second grinding step S30 has finished. Also, the second grinding step S30 may finish after the third grinding step S40 has started but before the third grinding step S40 has finished.

[0101] Furthermore, the structures, methods, etc., according to the embodiments described above can be modified as appropriate without departing from the scope of the object of the present invention. [Explanation of Symbols]

[0102] 11 Workpiece 11a surface 11b Back side 11c center 11d Peripheral edge 13 Protective tape 15,15a Circular recess 17 Ring-shaped reinforcing section 19 Groove 19a Removal section 21a, 21b Unground areas 2. Grinding device 4 Chuck Table 4a Holding surface 4b Frame 4c Table rotation axis 6 Grinding Unit 8 Spindle Housing 10 spindles 10a Wheel rotation axis 12 mounts 14 Fixtures 16 Wheel base 18 grinding wheels 20 grinding wheels 22 Inner periphery 24 Outer edge 26 areas

Claims

1. A chuck table that holds a disc-shaped workpiece placed on its upper surface and rotates around a table rotation axis that intersects the upper surface, A grinding unit comprising a spindle and a plurality of grinding wheels arranged in an annular pattern, wherein a grinding wheel with a diameter smaller than the radius of the workpiece is mounted on the spindle, and the grinding wheel is rotated around the spindle to grind the workpiece held by the rotating chuck table, A method for grinding a workpiece, wherein a circular recess and a ring-shaped reinforcing portion surrounding the circular recess are formed on the workpiece by grinding the workpiece using a grinding apparatus having the following: A preparatory step of positioning the grinding wheel relative to the chuck table such that the trajectory of the grinding wheel when it is rotated around the spindle does not overlap with the rotation axis of the chuck table that holds the workpiece, After the preparation step, a first grinding step is performed in which the workpiece is ground on the bottom surface of the grinding wheel by rotating the grinding wheel and the chuck table respectively and bringing them relatively closer together along the spindle, Simultaneously with the first grinding step, or after the first grinding step, a second grinding step is performed in which the grinding wheel and the chuck table are rotated respectively, and the grinding wheel and the chuck table are moved relative to each other so as to change their relative positions in the direction along the grinding surface of the workpiece, thereby aligning the trajectory of the grinding wheel with the rotation axis of the chuck table, and grinding the workpiece with the side surface of the grinding wheel. A method for grinding a workpiece, comprising: a third grinding step, performed simultaneously with or after the second grinding step, in which the grinding wheel and the chuck table are rotated respectively while bringing the grinding wheel and the chuck table relatively closer together along the spindle, thereby grinding the workpiece on the bottom surface of the grinding wheel, and forming a circular recess and a ring-shaped reinforcing portion surrounding the circular recess in the workpiece.

2. The method for grinding a workpiece according to claim 1, characterized in that in the first grinding step, the workpiece is ground with the grinding wheel in a state in which the region inside the trajectory of the grinding wheel and the rotation axis of the chuck table overlap, thereby forming an annular groove in the workpiece.

3. The method for grinding a workpiece according to claim 2, characterized in that in the first grinding step, the distance between the center of the trajectory of the grinding wheel and the rotation axis of the table is 5 mm or more.

4. The method for grinding a workpiece according to claim 1, characterized in that in the first grinding step, the workpiece is ground with the grinding wheel while the trajectory of the grinding wheel overlaps with the outer edge of the workpiece, thereby grinding the outer edge of the workpiece.

5. A method for grinding a workpiece according to any one of claims 1 to 4, characterized in that the first grinding step and the second grinding step are performed simultaneously.

6. A method for grinding a workpiece according to any one of claims 1 to 4, characterized in that the second grinding step and the third grinding step are performed simultaneously.

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