Grinding method of workpiece

Abstract

To provide a grinding method of a workpiece capable of suppressing reduction in processing efficiency by replacement of a grinding wheel.SOLUTION: Provided is a grinding method of a workpiece of grinding a circular region to be ground set in the workpiece by a grinding wheel including a grindstone to form a circular recess in the workpiece. The grinding method includes: a holding step of holding the workpiece in a holding surface of a chuck table; a first grinding step of grinding an outer peripheral part of the region to be ground by the grindstone; a separation step of separating the workpiece and the grindstone; and a second grinding step of grinding a center part of the region to be ground by the grindstone.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for grinding a workpiece, in which a recess is formed in the workpiece by grinding the workpiece with a grinding wheel. [Background technology]

[0002] In the device chip manufacturing process, a wafer is used that has a surface side with device regions, each of which has a device formed in a plurality of regions partitioned by a plurality of streets (planned dividing lines) arranged in a grid pattern. By dividing this wafer along the streets, a plurality of device chips, each of which has a device, are obtained. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, there is a demand for thinner device chips. Therefore, before dividing a wafer, a grinding device is sometimes used to grind and thin the wafer. The grinding device includes a chuck table for holding the workpiece and a grinding unit for grinding the workpiece, and an annular grinding wheel including a grinding stone is attached to the grinding unit. The wafer is held by the chuck table, and the grinding stone is brought into contact with the back side of the wafer while rotating the chuck table and the grinding wheel, thereby grinding and thinning the wafer.

[0004] When a wafer is thinned, its rigidity decreases, making it more susceptible to deformation and breakage during subsequent handling (transportation, holding, etc.). To address this issue, a method called TAIKO grinding has been proposed, in which only the area of ​​the back side of the wafer that overlaps with the device area is ground to thin it (see Patent Document 1). When TAIKO grinding is used, the center of the wafer is thinned to form a circular recess in the center of the wafer, while the outer periphery of the wafer is not thinned and remains thick, remaining as an annular reinforcing part. This prevents the rigidity of the wafer from decreasing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-19461 A Summary of the Invention [Problem to be solved by the invention]

[0006] When forming a circular recess in a workpiece such as a wafer as described above, a grinding wheel is selected according to the size of the recess. Specifically, the diameter of the recess to be formed in the workpiece is set in advance, and the grinding wheel is designed so that the rotation path of the grinding wheel is approximately equal to the radius of the recess. Then, the grinding wheel is positioned so that the rotation path of the grinding wheel passes through the center of the workpiece, and the workpiece is ground to form a recess having a desired diameter in the workpiece.

[0007] The dimensions of the recesses formed in the workpiece vary depending on the type (size, material, use, etc.) of the workpiece. Therefore, when multiple types of workpieces are ground using a grinding device, the grinding wheel needs to be replaced every time the type of workpiece is changed. However, replacing the grinding wheel is time-consuming and laborious. Therefore, if the grinding wheel is replaced frequently, the grinding of the workpiece is interrupted for a long time due to the grinding wheel replacement work, and the processing efficiency decreases.

[0008] The present invention has been made in consideration of such problems, and has an object to provide a method for grinding a workpiece that can suppress a decrease in processing efficiency due to replacement of a grinding wheel. [Means for solving the problem]

[0009] According to one aspect of the present invention, there is provided a method for grinding a workpiece, which uses a grinding wheel having a grinding stone to grind a circular area to be ground set on the workpiece to form a circular recess in the workpiece, the method comprising: a holding step of holding the workpiece on a holding surface of a chuck table; and after the holding step, rotating the chuck table and the grinding wheel while moving the grinding stone to the workpiece while the chuck table and the grinding wheel are rotated in a state where the rotational orbit of the grinding stone, the diameter of which is less than the radius of the area to be ground, is positioned so as not to overlap with the rotational axis of the chuck table. The present invention provides a method for grinding a workpiece, the method including: a first grinding step of bringing the grinding wheel into contact with a workpiece to grind an outer periphery of the area to be ground; a separating step of separating the workpiece and the grinding wheel after the first grinding step; and a second grinding step of grinding a center portion of the area to be ground by bringing the grinding wheel into contact with the workpiece while rotating the chuck table and the grinding wheel with the rotational orbit positioned so as to overlap with the rotational axis of the chuck table after the separating step.

[0010] According to another aspect of the present invention, there is provided a method for grinding a workpiece, which uses a grinding wheel having a grinding stone to grind a circular area to be ground set on the workpiece to form a circular recess in the workpiece, the method comprising: a holding step of holding the workpiece on a holding surface of a chuck table; and after the holding step, rotating the chuck table and the grinding wheel while positioning the grinding stone such that a rotational orbit of the grinding stone, the diameter of which is less than the radius of the area to be ground, overlaps with a rotational axis of the chuck table. The present invention provides a method for grinding a workpiece, the method including: a first grinding step of bringing the grinding wheel into contact with the workpiece to grind a center portion of the area to be ground; a separating step of separating the workpiece and the grinding wheel after the first grinding step; and a second grinding step of grinding an outer periphery of the area to be ground by bringing the grinding wheel into contact with the workpiece while rotating the chuck table and the grinding wheel, with the rotational orbit positioned so as not to overlap with the rotational axis of the chuck table, after the separating step.

[0011] Preferably, the grinding method for the workpiece further includes, after the second grinding step, a bottom grinding step in which the bottom surface of the recess is ground by moving the workpiece and the rotational orbit relatively along a direction intersecting the rotational axis of the chuck table while maintaining the grinding wheel in contact with the bottom surface of the recess. Effect of the Invention

[0012] In a method for grinding a workpiece according to one aspect of the present invention, the grinding area is ground in multiple steps using a grinding wheel whose rotation orbit diameter is set to be less than the radius of the grinding area. This makes it possible to form a recess of a desired size in the workpiece without replacing the grinding wheel even if the dimensions of the rotation orbit of the grinding wheel and the grinding area are different. As a result, the frequency of replacing the grinding wheel is reduced, and a decrease in processing efficiency is suppressed. [Brief description of the drawings]

[0013] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] 4 is a flowchart showing a method for grinding a workpiece. [Figure 4] FIG. 4(A) is a perspective view showing the grinding device in the holding step, and FIG. 4(B) is a partially sectional side view showing the grinding device in the holding step. [Diagram 5] FIG. 5(A) is a perspective view showing the grinding device in the first grinding step, and FIG. 5(B) is a partially sectional side view showing the grinding device in the first grinding step. [Figure 6] FIG. 6(A) is a perspective view showing the grinding device in the separating step, and FIG. 6(B) is a partially sectional side view showing the grinding device in the separating step. [Figure 7] FIG. 7(A) is a perspective view showing the grinding device in the second grinding step, and FIG. 7(B) is a partially sectional side view showing the grinding device in the second grinding step. [Figure 8]FIG. 8(A) is a perspective view showing the grinding device in the bottom grinding step, and FIG. 8(B) is a partially sectional side view showing the grinding device in the bottom grinding step. [Figure 9] FIG. 9(A) is a perspective view showing a grinding device in a first grinding step according to a modified example, and FIG. 9(B) is a partially sectional side view showing the grinding device in the first grinding step according to the modified example. [Figure 10] FIG. 10(A) is a perspective view showing the grinding device in the separating step according to the modified example, and FIG. 10(B) is a partial cross-sectional side view showing the grinding device in the separating step according to the modified example. [Figure 11] FIG. 11(A) is a perspective view showing a grinding device in a second grinding step according to a modified example, and FIG. 11(B) is a partially sectional side view showing the grinding device in the second grinding step according to the modified example. [Figure 12] FIG. 12(A) is a perspective view showing a grinding device in a bottom grinding step according to a modified example, and FIG. 12(B) is a partially sectional side view showing the grinding device in a bottom grinding step according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] (Embodiment 1) Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of a workpiece that can be ground by the method for grinding a workpiece according to this embodiment will be described. Fig. 1 is a perspective view showing a workpiece 11.

[0015] For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor material such as single crystal silicon, and has a front surface (first surface) 11a and a back surface (second surface) 11b that are generally parallel to each other. The workpiece 11 is divided into a plurality of rectangular regions by a plurality of streets (planned division lines) 13 arranged in a lattice shape so as to intersect with each other. Furthermore, devices 15 such as ICs (Integrated Circuits), LSIs (Large Scale Integration), LEDs (Light Emitting Diodes), and MEMS (Micro Electro Mechanical Systems) devices are formed on the front surface 11a side of the regions divided by the streets 13.

[0016] The workpiece 11 has, on the surface 11a side, a substantially circular device region 17 in which a plurality of devices 15 are formed, and an annular peripheral surplus region 19 surrounding the device region 17. The peripheral surplus region 19 corresponds to a strip-shaped region of a predetermined width (e.g., about 2 mm) including the outer periphery of the surface 11a. In the peripheral surplus region 19, no devices 15 are formed, or only devices 15 (dummy devices) that are not used in the product are formed. In FIG. 1, the imaginary boundary between the device region 17 and the peripheral surplus region 19 is indicated by a dashed line.

[0017] There are no limitations on the material, shape, structure, size, etc. of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass (quartz glass, borosilicate glass, etc.), ceramics, resin, metal, etc. There are also no limitations on the type, number, shape, structure, size, arrangement, etc. of the device 15.

[0018] A plurality of device chips each including a device 15 are manufactured by dividing the workpiece 11 along the streets 13. Furthermore, if the back surface 11b side of the workpiece 11 is ground to thin the workpiece 11 before dividing it, a thinned device chip can be obtained.

[0019] When grinding the back surface 11b side of the workpiece 11, it is preferable to provide a protective member 21 on the front surface 11a side of the workpiece 11. This protects the workpiece 11 and the device 15 during grinding of the workpiece 11.

[0020] A protective sheet can be used as the protective member 21. For example, the protective sheet includes a film-like substrate formed into a circle having approximately the same diameter as the workpiece 11, and an adhesive layer (glue layer) provided on the substrate. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy-based, acrylic-based, or rubber-based adhesive. The adhesive layer may be an ultraviolet-curable resin. The protective sheet may also be a thermocompression sheet that does not include an adhesive layer and can be thermocompression bonded to the workpiece 11.

[0021] A grinding device is used to grind the workpiece 11. Fig. 2 is a perspective view showing the grinding device 2. In Fig. 2, the X-axis direction (first horizontal direction, front-back direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. The Z-axis direction (up-down direction, height direction, vertical direction, grinding feed direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0022] The grinding device 2 includes a chuck table (holding table) 4 that holds a workpiece 11, and a grinding unit 10 that performs grinding on the workpiece 11. The upper surface of the chuck table 4 forms a holding surface 4a that holds the workpiece 11. The workpiece 11 is ground by the grinding unit 10 while being held by the holding surface 4a of the chuck table 4.

[0023] The chuck table 4 includes a cylindrical frame (main body) 6 made of metal such as SUS (stainless steel), glass, ceramics, resin, or the like. A cylindrical recess 6b is formed concentrically with the upper surface 6a in the center of the upper surface 6a of the frame 6. A disk-shaped holding member 8 made of a porous material such as porous ceramics is fitted into the recess 6b of the frame 6. The holding member 8 includes a large number of pores that communicate from the upper surface to the lower surface of the holding member 8. The upper surface of the holding member 8 forms a circular suction surface 8a that sucks the workpiece 11 when the workpiece 11 is held by the chuck table 4.

[0024] The holding surface 4a of the chuck table 4 is configured by the upper surface 6a of the frame 6 and the suction surface 8a of the holding member 8. The holding surface 4a is connected to a suction source (not shown) such as an ejector via pores contained in the holding member 8, flow paths (not shown) provided inside the frame 6, valves (not shown), and the like.

[0025] A rotation drive source (not shown) such as a motor that rotates the chuck table 4 is connected to the chuck table 4. The rotation drive source rotates the chuck table 4 around a rotation axis 4b. The rotation axis 4b of the chuck table 4 is set along a direction perpendicular to the radial direction of the holding surface 4a, and passes through the center of the holding surface 4a while intersecting with the holding surface 4a.

[0026] A moving unit (not shown) that moves the chuck table 4 in the horizontal direction (XY plane) is connected to the chuck table 4. For example, the moving unit is configured with a ball screw type X-axis moving mechanism that moves the chuck table 4 along the X-axis direction. The X-axis moving mechanism includes an X-axis ball screw (not shown) arranged along the X-axis direction, an X-axis pulse motor (not shown) that rotates the X-axis ball screw, and a nut portion (not shown) that is connected to the chuck table 4 and into which the ball screw is screwed.

[0027] A grinding unit 10 is provided above the chuck table 4. The grinding unit 10 includes a cylindrical spindle 12 arranged along the Z-axis direction. A rotation drive source (not shown), such as a motor, that rotates the spindle 12 is connected to the base end (upper end) of the spindle 12. When the rotation drive source is driven, the spindle 12 rotates around a rotation axis 12a set along the Z-axis direction.

[0028] A disk-shaped wheel mount 14 made of metal or the like is fixed to the tip (lower end) of the spindle 12. An annular grinding wheel 16 for grinding the workpiece 11 is removably attached to the lower surface side of the wheel mount 14. For example, the grinding wheel 16 is fixed to the wheel mount 14 by a fastener such as a bolt.

[0029] The grinding wheel 16 includes an annular wheel base 18. The wheel base 18 is made of a metal such as aluminum or stainless steel, and is formed to have approximately the same diameter as the wheel mount 14. The upper surface side of the wheel base 18 is fixed to the lower surface side of the wheel mount 14.

[0030] A plurality of grinding wheels 20 are fixed to the underside of the wheel base 18. For example, the grinding wheels 20 are formed in a rectangular parallelepiped shape and are arranged in a ring shape at approximately equal intervals along the circumferential direction of the wheel base 18. The underside of the grinding wheels 20 constitutes a grinding surface that grinds the workpiece 11.

[0031] The grinding wheel 20 is formed by fixing abrasive grains made of diamond, cBN (cubic boron nitride), etc., with a bonding material (bond material) such as metal bond, resin bond, vitrified bond, etc. However, there are no limitations on the material, shape, structure, size, etc. of the grinding wheel 20. In addition, the number of grinding wheels 20 can be set arbitrarily.

[0032] The grinding wheel 16 rotates around the rotation axis 12a by power transmitted from a rotation drive source (not shown) via the spindle 12 and the wheel mount 14. In other words, the rotation axis 12a of the spindle 12 also corresponds to the rotation axis of the wheel mount 14 and the grinding wheel 16. When the grinding wheel 16 is rotated, each of the multiple grinding stones 20 rotates (revolves) around the rotation axis 12a along a circular rotational orbit (rotational path) that is approximately parallel to the horizontal plane (XY plane).

[0033] A moving unit (not shown) that moves the grinding unit 10 along the Z-axis direction is connected to the grinding unit 10. For example, the moving unit is configured with a ball screw type Z-axis moving mechanism that moves the grinding unit 10 along the Z-axis direction. The Z-axis moving mechanism includes a Z-axis ball screw (not shown) arranged along the Z-axis direction, a Z-axis pulse motor (not shown) that rotates the Z-axis ball screw, and a nut portion (not shown) that is connected to the grinding unit 10 and into which the ball screw is screwed.

[0034] A grinding fluid supply passage (not shown) for supplying liquid (grinding fluid) such as pure water is provided inside or near the grinding unit 10. When the workpiece 11 is ground with the grinding wheel 16, the grinding fluid is supplied to the workpiece 11 and the grinding wheel 20. This cools the workpiece 11 and the grinding wheel 20, and washes away debris (grinding debris) generated by the grinding process.

[0035] The grinding device 2 also includes a controller (not shown) that controls the grinding device 2. The controller is connected to the components of the grinding device 2, and generates control signals that control the operation of each component. For example, the controller is configured by a computer, and includes a processing unit that performs processing such as calculations necessary for the operation of the grinding device 2, and a storage unit that stores various information (data, programs, etc.) used for the operation of the grinding device 2. The processing unit is configured to include a processor such as a CPU (Central Processing Unit). The storage unit is configured to include memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0036] Next, a specific example of the grinding method of the workpiece according to the present embodiment will be described. Fig. 3 is a flowchart showing the grinding method of the workpiece. In this embodiment, the back surface 11b side of the workpiece 11 is ground using the grinding device 2 to form a circular recess in the back surface 11b of the workpiece 11, thereby partially thinning the workpiece 11.

[0037] First, the workpiece 11 is held by the holding surface 4a of the chuck table 4 (holding step S1). Fig. 4(A) is a perspective view showing the grinding device 2 in the holding step S1, and Fig. 4(B) is a partially sectional side view showing the grinding device 2 in the holding step S1.

[0038] In the holding step S1, the workpiece 11 is placed on the chuck table 4 so that the front surface 11a side (protective member 21 side) faces the holding surface 4a and the back surface 11b side is exposed upward. At this time, the workpiece 11 is positioned concentrically with the holding surface 4a so that the rotation axis 4b of the chuck table 4 passes through the center of the workpiece 11. In addition, the suction surface 8a (see FIG. 2) of the chuck table 4 is entirely covered by the workpiece 11. In this state, when the suction force (negative pressure) of the suction source is applied to the holding surface 4a, the workpiece 11 is suction-held by the chuck table 4 via the protective member 21.

[0039] In addition, a circular grinding area (recess formation area) 23 is set concentrically with the workpiece 11 in the workpiece 11. The grinding area 23 corresponds to an area to be ground by the grinding wheel 16, and is set with a predetermined diameter and depth on the back surface 11b side of the workpiece 11. For example, the grinding area 23 is set so as to overlap with the device area 17 (see FIG. 1) of the workpiece 11, and the diameter of the grinding area 23 is approximately equal to the diameter of the device area 17.

[0040] As described below, by grinding the grinding area 23 with the grinding wheel 16, the central part of the workpiece 11 is partially thinned and a circular recess is formed in the workpiece 11. In other words, the grinding area 23 corresponds to the area where the circular recess will ultimately be formed.

[0041] FIG. 4(B) shows the radius r of the area 23 to be ground and the diameter (outer diameter) φ of the rotation orbit of the grinding wheel 20. The radius r of the area 23 to be ground corresponds to the radius of the circular recess finally formed in the workpiece 11. Also, the diameter φ of the rotation orbit of the grinding wheel 20 corresponds to the diameter of the circle drawn by the outer end of the grinding wheel 20 when the grinding wheel 16 rotates (swings) about the rotation axis 12a.

[0042] In the present embodiment, a grinding wheel 16 is used in which the diameter φ of the rotation orbit of the grinding wheel 20 is set to be less than the radius r of the area 23 to be ground (φ < r). Specifically, the diameter φ of the rotation orbit of the grinding wheel 20 can be 4 / 5 or less, 3 / 4 or less, or 2 / 3 or less of the radius r of the recess. That is, the grinding wheel 16 designed to grind an area to be ground having a diameter smaller than that of the area 23 to be ground can be used for grinding the area 23 to be ground. For example, a grinding wheel 16 designed to form a recess in a 6-inch diameter wafer is used for grinding the workpiece 11 which is an 8-inch diameter wafer.

[0043] Next, by grinding the area 23 to be ground of the workpiece 11 with the grinding wheel 20, a recess is formed in the workpiece 11. In the present embodiment, a first grinding step S2 of grinding the outer peripheral portion of the area 23 to be ground, a separation step S3 of separating the workpiece 11 and the grinding wheel 20, and a second grinding step S4 of grinding the central portion of the area 23 to be ground are sequentially performed, thereby forming a recess on the back surface 11b side of the workpiece 11.

[0044] Specifically, first, the outer peripheral portion of the area 23 to be ground is ground (first grinding step S2). FIG. 5(A) is a perspective view showing the grinding apparatus 2 in the first grinding step S2, and FIG. 5(B) is a partial cross-sectional side view showing the grinding apparatus 2 in the first grinding step S2.

[0045] In the first grinding step S2, first, the positional relationship between the chuck table 4 and the grinding wheel 16 is adjusted. At this time, the grinding wheel 20 is positioned so that the rotational orbit of the grinding wheel 20 does not overlap with the rotation axis 4b of the chuck table 4 (the center of the workpiece 11).

[0046] Specifically, the position of the chuck table 4 in the X-axis direction is adjusted so that the outer periphery of the rotational orbit of the grinding wheel 20 and the outer periphery of the grinding area 23 overlap in the Z-axis direction. As a result, the multiple grinding wheels 20 are each disposed directly above an area other than the center of the workpiece 11, and are positioned so that the rotational orbit of the grinding wheel 20 does not overlap with the rotation axis 4b of the chuck table 4 and the center of the workpiece 11 in the Z-axis direction.

[0047] Next, while rotating the chuck table 4 and the grinding wheel 16, the grinding stones 20 are brought into contact with the back surface 11b of the workpiece 11. As a result, the outer periphery of the grinding area 23 set on the back surface 11b of the workpiece 11 is ground.

[0048] Specifically, first, the chuck table 4 is rotated around the rotation axis 4b, and the grinding wheel 16 is rotated around the rotation axis 12a. For example, the rotation speed of the chuck table 4 is set to 100 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 16 (the rotation speed of the spindle 12) is set to 2000 rpm or more and 6000 rpm or less.

[0049] Next, the grinding unit 10 is lowered along the Z-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along the Z-axis direction (a direction parallel to the rotation axis 12a), and the workpiece 11 and the grinding wheel 20 approach each other. The relative movement speed of the chuck table 4 and the grinding wheel 16 in the Z-axis direction at this time corresponds to the grinding feed speed in the first grinding step S2. The grinding feed speed is set, for example, to 0.1 μm / s or more and 5 μm / s or less.

[0050] When the grinding wheel 20 comes into contact with the workpiece 11, the grinding wheel 20 turns to avoid the rotation axis 4b (center of the workpiece 11) of the chuck table 4, and grinds an annular region (outer periphery) of a predetermined width including the outer periphery of the grinding area 23. As a result, only the outer periphery of the grinding area 23 is thinned, and an annular recess (groove) 25 is formed on the back surface 11b side of the workpiece 11. The width of the recess 25 is approximately equal to the diameter of the rotation orbit of the grinding wheel 20. Meanwhile, a circular unground area (protrusion) 27 that has not been subjected to grinding remains in the center of the grinding area 23.

[0051] As described above, in this embodiment, the grinding wheel 16 is used in which the diameter φ of the rotational orbit of the grinding stone 20 is set to be less than the radius r of the grinding area 23 (see FIG. 4(B)), so in the first grinding step S2, only a portion (the outer periphery) of the grinding area 23 set on the workpiece 11 is ground. Then, when the grinding amount (the difference in thickness before and after grinding) of the outer periphery of the grinding area 23 reaches a predetermined value, the descent of the grinding unit 10 is stopped, and a recess 25 of a predetermined depth is formed on the outer periphery of the grinding area 23.

[0052] Next, the workpiece 11 and the grinding wheel 20 are separated (separating step S3). Fig. 6(A) is a perspective view showing the grinding device 2 in the separating step S3, and Fig. 6(B) is a partially sectional side view showing the grinding device 2 in the separating step S3.

[0053] In the separating step S3, the grinding unit 10 is raised along the Z-axis direction to move the grinding wheels 20 away from the workpiece 11. This brings the workpiece 11 and the grinding wheels 20 out of contact with each other, and grinding of the workpiece 11 is interrupted.

[0054] In addition, in the separating step S3, it is preferable to maintain the rotation of the chuck table 4 and the grinding wheel 16 even while the workpiece 11 and the grinding wheel 20 are not in contact with each other. This makes it possible to reduce the time (rotation acceleration time) required to rotate the chuck table 4 and the grinding wheel 16 again at a desired rotation speed in the next second grinding step S4.

[0055] Next, the center of the region to be ground 23 is ground (second grinding step S4). Fig. 7(A) is a perspective view showing the grinding device 2 in the second grinding step S4, and Fig. 7(B) is a partially sectional side view showing the grinding device 2 in the second grinding step S4.

[0056] In the second grinding step S4, first, the positional relationship between the chuck table 4 and the grinding wheel 16 is adjusted. At this time, the grinding wheel 20 is positioned so that the rotational orbit of the grinding wheel 20 overlaps with the rotation axis 4b (the center of the workpiece 11) of the chuck table 4. As a result, the rotational orbit of the grinding wheel 20 is positioned directly above the unground region 27 (see FIGS. 5(A) to 6(B)).

[0057] Next, while rotating the chuck table 4 and the grinding wheel 16, the grinding stones 20 are brought into contact with the back surface 11b of the workpiece 11. As a result, the central portion (unground area 27) of the ground area 23 set on the back surface 11b of the workpiece 11 is ground.

[0058] Specifically, first, the chuck table 4 is rotated around the rotation axis 4b, and the grinding wheel 16 is rotated around the rotation axis 12a. Next, the grinding unit 10 is lowered along the Z-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along the Z-axis direction (a direction parallel to the rotation axis 12a), and the workpiece 11 and the grinding wheel 20 approach each other.

[0059] The grinding conditions (rotation speed of the chuck table 4, rotation speed of the grinding wheel 16, grinding feed speed, etc.) in the second grinding step S4 can be set to be the same as those in the first grinding step S2. For example, the rotation speed of the chuck table 4 is set to 100 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 16 (rotation speed of the spindle 12) is set to 2000 rpm or more and 6000 rpm or less. Moreover, the grinding feed speed in the second grinding step S4 is set to, for example, 0.1 μm / s or more and 5 μm / s or less.

[0060] When the grinding wheel 20 comes into contact with the workpiece 11, the grinding wheel 20 rotates so as to pass through the rotation axis 4b (the center of the workpiece 11) of the chuck table 4, and grinds a circular area (center portion) including the center of the grinding area 23. As a result, the center portion of the grinding area 23 is thinned.

[0061] If the workpiece 11 and the grinding wheel 20 are separated in the above-mentioned separating step S3 (see Figs. 6(A) and 6(B)), a period of time during which no friction occurs between the workpiece 11 and the grinding wheel 20 is ensured before the second grinding step S4 is performed, and the workpiece 11 and the grinding wheel 20 are cooled. This makes it less likely that processing defects such as surface burning will occur in the workpiece 11 in the second grinding step S4.

[0062] In the second grinding step S4, the grinding wheel 20 comes into contact with the workpiece 11 again after being separated from the workpiece 11. At this time, the grinding wheel 20 collides with the corners on the upper surface of the unground region 27 (see Figs. 5(A) to 6(B)), accelerating wear on the lower surface of the grinding wheel 20. This improves the condition of the grinding wheel 20.

[0063] The amount of grinding of the center of the grinding region 23 in the second grinding step S4 is set to the same value as the amount of grinding of the outer periphery of the grinding region 23 in the first grinding step S2. Then, when the center of the grinding region 23 is ground to the same thickness as the outer periphery, the unground region 27 (see Figs. 5(A) to 6(B)) is removed. As a result, a circular recess (groove) 29 is formed on the back surface 11b side of the workpiece 11. The recess 29 includes a circular bottom surface 29a.

[0064] The diameter of the recess 29 is approximately the same as the diameter of the device region 17 (see FIG. 1), and the recess 29 is formed so as to overlap with a plurality of devices 15 (see FIG. 1). Meanwhile, the outer periphery of the workpiece 11 is not ground or thinned in the first grinding step S2 and the second grinding step S4, but is maintained in a thick state, and remains as an annular reinforcing portion surrounding the recess 29. By leaving the annular reinforcing portion, a decrease in the rigidity of the workpiece 11 is suppressed.

[0065] As described above, the first grinding step S2 (see FIGS. 5(A) and 5(B)) and the second grinding step S4 (see FIGS. 7(A) and 7(B)) form recesses 29 in the workpiece 11, and the workpiece 11 is partially thinned. Note that, although the grinding amount of the workpiece 11 is set to be the same in the first grinding step S2 and the second grinding step S4, in reality, a slight difference in the grinding amount may occur due to variations in the amount of wear of the grinding wheel 20, etc. In this case, a minute step due to the difference in the grinding amount remains on the bottom surface 29a of the recesses 29.

[0066] Therefore, after the second grinding step S4, the bottom surface 29a of the recess 29 may be ground with the grinding wheel 20 (bottom surface grinding step S5). Fig. 8(A) is a perspective view showing the grinding device 2 in the bottom surface grinding step S5, and Fig. 8(B) is a partially sectional side view showing the grinding device 2 in the bottom surface grinding step S5.

[0067] In the bottom surface grinding step S5, after the grinding feed (lowering of the grinding wheel 16) is stopped or decelerated, the chuck table 4 and the grinding wheel 16 rotate, and while maintaining the state in which the grinding wheel 20 is in contact with the bottom surface 29a of the recess 29, the workpiece 11 and the rotational orbit of the grinding wheel 20 are moved relatively along a direction intersecting the rotation axis 4b of the chuck table 4. Specifically, while the grinding wheel 20 is pressed against the bottom surface 29a of the recess 29, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along a direction perpendicular to the rotation axis 4b of the chuck table 4 (X-axis direction).

[0068] The direction of movement of the chuck table 4 is set so that the rotational orbit of the grinding wheel 20 moves away from the rotation axis 4b of the chuck table 4 (the center of the workpiece 11) and approaches the outer periphery (reinforcement) of the workpiece 11. Then, when the rotational orbit of the grinding wheel 20 reaches the outer periphery (reinforcement) of the workpiece 11, the movement of the chuck table 4 is stopped. This causes the grinding wheel 20 to slide along the bottom surface 29a of the recess 29, grinding so as to even out the area from the center of the bottom surface 29a to the outer periphery. As a result, minute steps remaining on the bottom surface 29a of the recess 29 are removed.

[0069] The rotation speeds of the chuck table 4 and the grinding wheel 16 may be the same as or different from those in the second grinding step S4. For example, the rotation speed of the chuck table 4 is set to 100 rpm or more and 300 rpm or less, and the rotation speed of the grinding wheel 16 (the rotation speed of the spindle 12) is set to 2000 rpm or more and 6000 rpm or less. In addition, the relative movement speed (processing feed speed) between the chuck table 4 and the grinding wheel 16 in the direction intersecting with the rotation axis 4b of the chuck table 4 (X-axis direction) is set to, for example, 0.5 mm / s or more and 5 mm / s or less.

[0070] There is no limit to the amount of grinding of the workpiece 11 in the bottom grinding step S5 (difference in depth of the recess 29 before and after grinding) as long as it is possible to remove the step remaining on the bottom surface 29a of the recess 29. For example, the amount of grinding of the workpiece 11 in the bottom grinding step S5 is set to 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. This shortens the processing time in the bottom grinding step S5.

[0071] In the bottom grinding step S5, the workpiece 11 and the grinding wheel 20 may be moved back and forth relative to each other along a direction intersecting with the rotation axis 4b of the chuck table 4. Specifically, after the grinding wheel 20 reaches the outer periphery (reinforcement) of the workpiece 11, the chuck table 4 is moved in the opposite direction. As a result, the workpiece 11 and the grinding wheel 20 move relatively along the X-axis direction so that the rotation orbit of the grinding wheel 20 moves away from the outer periphery (reinforcement) of the workpiece 11 and approaches the rotation axis 4b of the chuck table 4 (the center of the workpiece 11). Then, when the rotation orbit of the grinding wheel 20 overlaps with the rotation axis 4b of the chuck table 4, the movement of the chuck table 4 is stopped. The number of reciprocations may be one or more than two.

[0072] In addition, in the above, the case where the chuck table 4 is moved along the X-axis direction has been described. However, if the grinding wheel 16 is configured to be movable along the horizontal direction (XY plane direction), the chuck table 4 and the grinding wheel 16 may be moved relatively along a direction intersecting with the rotation axis 4b of the chuck table 4 by moving the grinding wheel 16 instead of the chuck table 4.

[0073] After the bottom surface grinding step S5, the workpiece 11 is divided along the streets 13 (see FIG. 1), whereby the device regions 17 (see FIG. 1) of the workpiece 11 are separated into individual pieces, and thin device chips each having a device 15 (see FIG. 1) are obtained. To divide the workpiece 11, various processing devices can be used, such as a cutting device that cuts the workpiece 11 with an annular cutting blade, or a laser processing device that performs laser processing on the workpiece 11.

[0074] As described above, in the method for grinding a workpiece according to this embodiment, the grinding area 23 is ground in multiple steps using the grinding wheel 16 in which the diameter of the rotational orbit of the grinding wheel 20 is set to be less than the radius of the grinding area 23. This makes it possible to form a recess 25 of a desired size in the workpiece 11 without replacing the grinding wheel 16, even if the dimensions of the rotational orbit of the grinding wheel 20 and the grinding area 23 differ. As a result, the frequency of replacing the grinding wheel 16 is reduced, and a decrease in processing efficiency is suppressed.

[0075] In this embodiment, the grinding conditions (rotation speed of the chuck table 4, rotation speed of the grinding wheel 16, grinding feed speed, etc.) of the workpiece 11 are set to be the same in the first grinding step S2 and the second grinding step S4. However, the first grinding step S2 and the second grinding step S4 may be performed under different grinding conditions.

[0076] For example, if the area of ​​the grinding region 23 ground in the second grinding step S4 is smaller than the area of ​​the grinding region 23 ground in the first grinding step S2, the grinding feed rate in the second grinding step S4 may be set to be faster than the grinding feed rate in the first grinding step S2. On the other hand, if the area of ​​the grinding region 23 ground in the second grinding step S4 is larger than the area of ​​the grinding region 23 ground in the first grinding step S2, the grinding feed rate in the second grinding step S4 may be set to be slower than the grinding feed rate in the first grinding step S2.

[0077] In the present embodiment, the grinding area 23 of the workpiece 11 is ground in two separate steps. However, the grinding area 23 may be ground in three or more separate steps. For example, when the diameter φ (see FIG. 4B) of the rotation orbit of the grinding wheel 20 is less than 1 / 2 of the radius r (see FIG. 4B) of the grinding area 23, the grinding area 23 is divided into three or more areas in the radial direction, and each area is ground in order to form the recess 29. In this case, the first grinding step S2 and the separating step S3 are alternately performed multiple times while changing the contact area between the grinding wheel 20 and the grinding area 23, and then the second grinding step S4 is performed, thereby forming the recess 29 in the workpiece 11.

[0078] In addition, the structures, methods, etc. according to the present embodiment can be modified as appropriate without departing from the scope of the object of the present invention.

[0079] (Embodiment 2) In the above embodiment 1, a case was described in which the outer periphery of the grinding area 23 is ground in the first grinding step S2 (see Figures 5(A) and 5(B)), and then the center of the grinding area 23 is ground in the second grinding step S4 (see Figures 7(A) and 7(B)). However, there is no restriction on the order in which the grinding area 23 is ground. In this embodiment, a modified example is described in which the center of the grinding area 23 is ground in the first grinding step S2, and the outer periphery of the grinding area 23 is ground in the second grinding step S4. Note that matters that are not described in this embodiment are the same as in embodiment 1.

[0080] Fig. 9(A) is a perspective view showing the grinding device 2 in the first grinding step S2 according to the modified example, and Fig. 9(B) is a partially sectional side view showing the grinding device 2 in the first grinding step S2 according to the modified example. In this embodiment, the center of the region to be ground 23 is ground in the first grinding step S2.

[0081] In the first grinding step S2, first, the positional relationship between the chuck table 4 and the grinding wheel 16 is adjusted. At this time, the grinding wheel 20 is positioned so that the rotational orbit of the grinding wheel 20 overlaps with the rotation axis 4b of the chuck table 4 (the center of the workpiece 11).

[0082] Next, while rotating the chuck table 4 and the grinding wheel 16, the chuck table 4 and the grinding wheel 16 are moved relatively along the Z-axis direction (a direction parallel to the rotation axis 12a) to bring the multiple grinding wheels 20 into contact with the back surface 11b of the workpiece 11. As a result, the center of the grinding region 23 set on the back surface 11b of the workpiece 11 is ground.

[0083] Specifically, first, the chuck table 4 is rotated around the rotation axis 4b, and the grinding wheel 16 is rotated around the rotation axis 12a. Next, the grinding unit 10 is lowered along the Z-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along the Z-axis direction (a direction parallel to the rotation axis 12a), and the workpiece 11 and the grinding wheel 20 approach each other. The grinding conditions in the first grinding step S2 can be set similarly to those in the first embodiment.

[0084] When the grinding wheel 20 comes into contact with the workpiece 11, the grinding wheel 20 rotates so as to pass through the rotation axis 4b (the center of the workpiece 11) of the chuck table 4, and grinds a circular area (center) including the center of the grinding area 23. As a result, only the center of the grinding area 23 is thinned, and a circular recess (groove) 25A is formed on the back surface 11b side of the workpiece 11.

[0085] The radius of the recess 25A is approximately equal to the diameter of the rotation orbit of the grinding wheel 20. Meanwhile, an annular unground area (convex portion) 27A that has not been subjected to grinding remains on the outer periphery of the grinding area 23. Then, when the grinding amount at the center of the grinding area 23 reaches a predetermined value, the grinding unit 10 stops descending, and a recess 25A of a predetermined depth is formed at the center of the grinding area 23.

[0086] Next, the workpiece 11 and the grinding wheel 20 are separated (separating step S3). Fig. 10(A) is a perspective view showing the grinding device 2 in the separating step S3 according to a modified example, and Fig. 10(B) is a partially sectional side view showing the grinding device 2 in the separating step S3 according to a modified example.

[0087] In the separating step S3, the grinding unit 10 is raised along the Z-axis direction to move the grinding wheels 20 away from the workpiece 11. This brings the workpiece 11 and the grinding wheels 20 out of contact with each other, and grinding of the workpiece 11 is interrupted.

[0088] Fig. 11(A) is a perspective view showing the grinding device 2 in the second grinding step S4 according to the modified example, and Fig. 11(B) is a partially sectional side view showing the grinding device 2 in the second grinding step S4 according to the modified example. In this embodiment, the outer periphery of the grinding target region 23 is ground in the second grinding step S4.

[0089] In the second grinding step S4, first, the positional relationship between the chuck table 4 and the grinding wheel 16 is adjusted. At this time, the grinding wheel 20 is positioned so that the rotational orbit of the grinding wheel 20 does not overlap with the rotation axis 4b (the center of the workpiece 11) of the chuck table 4. Specifically, the position of the chuck table 4 is adjusted so that the outer periphery of the rotational orbit of the grinding wheel 20 and the outer periphery of the grinding region 23 overlap in the Z-axis direction.

[0090] Next, while rotating the chuck table 4 and the grinding wheel 16, the chuck table 4 and the grinding wheel 16 are moved relatively along the Z-axis direction (a direction parallel to the rotation axis 12a) to bring the multiple grinding wheels 20 into contact with the back surface 11b of the workpiece 11. As a result, the outer periphery of the grinding area 23 set on the back surface 11b of the workpiece 11 is ground.

[0091] Specifically, first, the chuck table 4 is rotated around the rotation axis 4b, and the grinding wheel 16 is rotated around the rotation axis 12a. Next, the grinding unit 10 is lowered along the Z-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along the Z-axis direction (a direction parallel to the rotation axis 12a), and the workpiece 11 and the grinding wheel 20 approach each other. The grinding conditions in the second grinding step S4 can be set similarly to those in the first embodiment.

[0092] When the grinding wheel 20 comes into contact with the workpiece 11, the grinding wheel 20 grinds the unground region 27A (see FIGS. 9(A) to 10(B)) while rotating so as to avoid the rotation axis 4b of the chuck table 4. As a result, only the outer periphery of the ground region 23 is thinned.

[0093] The amount of grinding of the outer periphery of the grinding region 23 in the second grinding step S4 is set to the same value as the amount of grinding of the center of the grinding region 23 in the first grinding step S2. Then, when the outer periphery of the grinding region 23 is ground to the same thickness as the center, the unground region 27A (see Figs. 9(A) to 10(B)) is removed. As a result, a circular recess 29 is formed on the back surface 11b side of the workpiece 11.

[0094] After the second grinding step S4, a bottom surface grinding step S5 may be performed to grind the bottom surface 29a of the recess 29. Fig. 12(A) is a perspective view showing the grinding device 2 in the bottom surface grinding step S5 according to a modified example, and Fig. 12(B) is a partially sectional side view showing the grinding device 2 in the bottom surface grinding step S5 according to a modified example.

[0095] In the bottom surface grinding step S5, after the grinding feed (lowering of the grinding wheel 16) is stopped or decelerated, the chuck table 4 and the grinding wheel 16 rotate, and while maintaining the state in which the grinding wheel 20 is in contact with the bottom surface 29a of the recess 29, the workpiece 11 and the rotational orbit of the grinding wheel 20 are moved relatively along a direction intersecting the rotation axis 4b of the chuck table 4. Specifically, while the grinding wheel 20 is pressed against the bottom surface 29a of the recess 29, the chuck table 4 is moved along the X-axis direction by a moving unit (not shown). As a result, the chuck table 4 and the grinding wheel 16 move relatively along a direction perpendicular to the rotation axis 4b of the chuck table 4 (X-axis direction).

[0096] The direction of movement of the chuck table 4 is set so that the rotational orbit of the grinding wheel 20 approaches the rotation axis 4b of the chuck table 4 (the center of the workpiece 11) and moves away from the outer periphery (reinforcement part) of the workpiece 11. Then, when the rotational orbit of the grinding wheel 20 reaches the rotation axis 4b of the chuck table 4, the movement of the chuck table 4 is stopped. This causes the grinding wheel 20 to slide along the bottom surface 29a of the recess 29, grinding the bottom surface 29a from the outer periphery to the center so as to be even. As a result, minute steps remaining on the bottom surface 29a of the recess 29 are removed.

[0097] The grinding conditions in the bottom surface grinding step S5 can be set similarly to those in the embodiment 1. In the bottom surface grinding step S5, the workpiece 11 and the grinding wheel 20 may be moved back and forth relative to each other along a direction intersecting with the rotation axis 4b of the chuck table 4. In this case, the number of reciprocations may be one or more than two.

[0098] The grinding area 23 may be ground in three or more steps. In this case, after the first grinding step S2 and the separating step S3 are performed, the second grinding step S4 and the separating step S3 are alternately performed multiple times while changing the contact area between the grinding wheel 20 and the grinding area 23, thereby forming a recess 29 in the workpiece 11.

[0099] In addition, the structure, method, and the like according to this embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention. In addition, this embodiment can be appropriately combined with the first embodiment. [Explanation of symbols]

[0100] 11 Workpiece 11a Surface (first side) 11b Back side (2nd side) 13th Street (Planned division line) 15 Devices 17 Device Area 19 Surplus outer area 21 Protective materials 23 Area to be ground (recess formation area) 25,25A Recess (groove) 27, 27A Unground area (convex part) 29 Groove 29a Bottom 2 Grinding equipment 4 Chuck table (holding table) 4a Holding surface 4b Rotation axis 6 Frame (main body) 6a Top side 6b Recess 8 Retaining member 8a Suction surface 10 Grinding unit 12 Spindle 12a Rotation axis 14 Wheel mount 16 Grinding Wheel 18 Wheel base 20 Grinding Wheel

Claims

1. A method for grinding a workpiece, comprising the steps of: grinding a circular grinding area set on the workpiece with a grinding wheel having a grinding stone to form a circular recess in the workpiece, the method comprising the steps of: a holding step of holding the workpiece on a holding surface of a chuck table; a first grinding step in which, after the holding step, the grinding wheel is brought into contact with the workpiece while rotating the chuck table and the grinding wheel in a state in which the rotational orbit of the grinding wheel, the diameter of which is less than the radius of the area to be ground, is positioned so as not to overlap with the rotational axis of the chuck table, thereby grinding the outer periphery of the area to be ground; a separation step of separating the workpiece from the grinding wheel after the first grinding step; and a second grinding step of grinding a center portion of the area to be ground by contacting the grinding wheel with the workpiece while rotating the chuck table and the grinding wheel after the separating step, while positioning the rotational orbit so as to overlap with the rotational axis of the chuck table.

2. A method for grinding a workpiece, comprising the steps of: grinding a circular grinding area set on the workpiece with a grinding wheel having a grinding stone to form a circular recess in the workpiece, the method comprising the steps of: a holding step of holding the workpiece on a holding surface of a chuck table; a first grinding step in which, after the holding step, a rotational orbit of the grinding wheel, the diameter of which is less than the radius of the region to be ground, is positioned so as to overlap with a rotational axis of the chuck table, and the grinding wheel is brought into contact with the workpiece while rotating the chuck table and the grinding wheel, thereby grinding a center portion of the region to be ground; a separation step of separating the workpiece from the grinding wheel after the first grinding step; and a second grinding step of grinding an outer periphery of the area to be ground by contacting the grinding wheel with the workpiece while rotating the chuck table and the grinding wheel after the separating step, while positioning the rotational orbit so as not to overlap with the rotational axis of the chuck table.

3. The method for grinding a workpiece as described in claim 1 or 2, further comprising a bottom grinding step of grinding the bottom surface of the recessed portion by moving the workpiece and the rotational orbit relatively along a direction intersecting the rotational axis of the chuck table while maintaining the grinding wheel in contact with the bottom surface of the recessed portion after the second grinding step.

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