workpiece grinding process

Abstract

Workpiece grinding method for grinding a back side (Wb) of a workpiece (W) with a grinding stone (42b), wherein the workpiece has on a front side (Wa) thereof a fixture area (Wa1) in which a plurality of fixtures are formed and a peripheral excess area (Wa2) around the fixture area, wherein the workpiece grinding method comprises: a front protection step to cover the front of the workpiece with a protective element (T1); a holding step for holding a protective element side of the workpiece by a holding surface of a clamping table (3) which is rotated about an axis of rotation inclined at an angle of 45 to 180 degrees relative to a vertical direction after the front protective step has been performed; and a grinding step for grinding the back of the workpiece, corresponding to the fixture area, by the grinding wheel, which is rotated about an axis of rotation orthogonal to the holding surface, while grinding water (M) is supplied to form a circular recess (Wb1) and an annular reinforcement section (Wb2), corresponding to the peripheral excess area and surrounding the circular recess, wherein in the grinding step the discharge of the grinding water, which contains abrasive grains that fall from the grinding stone, is promoted by the inclination of the workpiece, wherein in the grinding step the grinding stone is positioned such that a rotational path of the grinding stone and a discharge position of the grinding water, which contains the abrasive grains falling from the grinding stone, do not overlap, since the discharge position is located at a lowest point of the clamping table, the axis of rotation of which is inclined, wherein the rotational path of the grinding stone passes through the center of rotation of the workpiece.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a method for grinding a plate-shaped workpiece, for example a semiconductor wafer, by a grindstone. Description of the state of the art

[0002] A workpiece in which a plurality of devices such as integrated circuits (ICs) and large-area integrations (LSIs) are formed on a front surface thereof and the back surface of which is ground to reduce its thickness to a predetermined thickness is divided by a dicing apparatus such as a dicing apparatus into individual device chips used for various electronic devices.

[0003] A grinding apparatus for grinding the back of a workpiece includes a chuck table configured to hold the workpiece, to which a front-side protective member made of a resin or the like is adhered, a grinding unit in which a grindstone for grinding the workpiece held by the chuck table is rotatably supported, and a grinding water supply device that supplies grinding water to the grindstone through a flow channel formed along an axis of a spindle constituting the grinding unit. The grinding apparatus configured in this manner can efficiently grind the workpiece.

[0004] In recent years, to reduce the weight and size of device chips, there has been a push to reduce the thickness of the workpiece during wafer grinding. However, these thinner wafers have lower rigidity, making them difficult to handle and potentially prone to damage or breakage during transportation or other similar situations.In view of this problem, there is a grinding method in which the workpiece is ground and its thickness is reduced, for example, to 100 µm or less, and only the area of ​​the back surface of the workpiece corresponding to the fixture area on the front surface is further ground and its thickness is reduced to leave an annular reinforcement portion on the back surface corresponding to the peripheral excess area surrounding the fixture area on the front surface, thereby ensuring easy handling of the workpiece with its thickness reduced (see, for example, JP 2007 - 19 461 A).Other related techniques can be found in JP 2015-100865 A, which is directed to a grinding apparatus for grinding a central part of a plate-shaped workpiece and for forming an annular projection on an outer peripheral region, in JP 2008-60470 A, which describes a wafer processing method in which thin-shaped wafers can be easily handled, in JP 2011-121122 A, which describes a grinding apparatus for grinding a plate-shaped workpiece such as a semiconductor wafer, and in JP 2013-154443 A, which is also directed to a grinding apparatus and a grinding method for grinding a plate-shaped member such as a wafer. SUMMARY OF THE INVENTION

[0005] However, in the above grinding method, since the annular reinforcement portion is formed on the back of the workpiece, the annular reinforcement portion would serve as a bench during grinding, so that grinding water containing abrasive grains falling off the grindstone would stagnate in the circular recess of the workpiece. Then, the fallen abrasive grains stagnating in the circular recess of the workpiece would be attracted by the grindstone during grinding and would adhere to the grinding surface at the tip of the grindstone. If grinding by the grindstone continues with the fallen abrasive grains adhering to the grinding surface at the tip of the grindstone, scratches may form on the ground surface of the workpiece, or cracking of the workpiece may occur.

[0006] It is therefore an object of the present invention to provide a workpiece grinding method which is of the type of grinding a portion of the back surface of the workpiece corresponding to a device portion on the front surface to form a circular recess and to form an annular reinforcing portion in a portion of the back surface of the wafer corresponding to a peripheral excess portion surrounding the device portion, and by which the formation of scratches on the back surface of the workpiece, the generation of cracks in the workpiece, and the like problems can be prevented.

[0007] The above object is achieved by a workpiece grinding method as defined by the appended independent claim 1. The dependent claim describes optional features and preferred embodiments.

[0008] According to one aspect of the present invention, there is provided a workpiece grinding method for grinding a back surface of a workpiece with a grindstone, the workpiece having, on a front surface thereof, a jig portion in which a plurality of jigs are formed, and a peripheral excess portion around the jig portion.The workpiece grinding method includes: a front-side protecting step of covering the front side of the workpiece with a protective member, a holding step of holding a protective member side of the workpiece by a holding surface of a chuck table rotated about a rotation axis inclined at an angle of 45 to 180 degrees relative to a vertical direction after the front-side protecting step is performed, and a grinding step of grinding the back side of the workpiece corresponding to the fixture area by the grindstone rotated about a rotation axis orthogonal to the holding surface while supplying grinding water to form a circular recess and an annular reinforcing portion corresponding to the peripheral excess area and surrounding the circular recess.In the grinding step, the discharge of the grinding water containing abrasive grains falling off the grindstone is promoted by the inclination of the workpiece, and in the grinding step, the grindstone is positioned such that a rotational trajectory of the grindstone and a discharge position of the grinding water containing the abrasive grains falling off the grindstone do not overlap each other because the discharge position is located at a lowest point of the chuck table whose rotational axis is inclined, the rotational trajectory of the grindstone passing through the rotational center of the workpiece.

[0009] Preferably, the protective element is an adhesive tape.

[0010] According to the present invention, in the grinding step, the discharge of grinding water containing the abrasive grains falling from the grindstone is promoted by the inclination of the workpiece. Therefore, the grindstone is prevented from attracting the falling abrasive grains during grinding, thus preventing the formation of scratches on the back of the workpiece, the generation of cracks in the workpiece, and similar problems.

[0011] During the grinding step, the discharge position of the grinding water containing the abrasive grains dropped from the grindstone is located at the lowest point of the chuck table, whose rotation axis is tilted. If the grindstone is positioned so that the rotation trajectory of the grindstone and the discharge position of the grinding water do not overlap, the discharge of the grinding water containing the abrasive grains dropped from the grindstone is carried out more efficiently.

[0012] The above and other objects, features and advantages of the present invention and the modes for carrying them out will become more apparent, and the invention itself will be best understood, from a study of the following description and the appended claims with reference to the accompanying drawings which show preferred embodiments of the invention. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 is a perspective view showing an example of a workpiece and a protective member for protecting a front side of the workpiece; Fig. 2 is a sectional view showing a state in which the workpiece held by a chuck table is ground by a grindstone; Fig. 3 is a schematic perspective view for explaining a state in which a rotational path of the grindstone and a discharge position of grinding water do not overlap; and Fig. 4 is a sectional view showing a state in which the grinding water is discharged from a position on the back side of the ground workpiece. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] One in Fig. The workpiece W shown in Figure 1 is, for example, a semiconductor wafer having a circular plate shape in its outer shape and a base material of silicon, and provided on a front side Wa thereof with a device region Wa1 and a peripheral excess region Wa2 surrounding the device region Wa1. The peripheral excess region Wa2 is the region of the front side Wa of the workpiece W that is located outside an imaginary line L1 drawn in Fig. 1 is represented by a dashed line with alternating long and two short lines. The device area Wa1 is divided into a lattice pattern by a plurality of orthogonally intersecting dividing lines (streets) S, and a device D, such as an IC, is individually formed in each of the areas divided in the lattice pattern. A back surface Wb of the workpiece W is a surface to be ground. Note that the workpiece W may be made of gallium arsenide, sapphire, gallium nitride, silicon carbide, or the like other than silicon.

[0014] Each of the steps which, in the case of carrying out a grinding method according to the present invention for grinding the Fig. 1 shown workpiece W up to a predetermined thickness is described below. (1) Front protection step

[0015] When the workpiece W is ground, a circular protective member T1 having substantially the same diameter as the workpiece W is adhered to the front surface Wa of the workpiece W, resulting in a state where the jig portion Wa1 and the peripheral excess portion Wa2 are covered and protected by the protective member T1. The protective member T1 may be, for example, an adhesive tape having a base material layer and an adhesive layer, but is not limited thereto. A hard plate having rigidity such as a glass substrate may be adhered to the front surface Wa with an adhesive to serve as a protective member, or a liquid resin may be applied to the front surface Wa, and the resin may be cured by heating, irradiation with ultraviolet rays, or the like to form a protective member covering the front surface Wa of the workpiece W. (2) Holding step

[0016] The workpiece W, whose front side Wa is covered with the protective element T1, is turned into a Fig. 2. The grinding device 2 includes a chuck table 3 capable of holding the workpiece W by suction, and a grinding unit 4 capable of grinding the workpiece W by grinding stones 42b. The chuck table 3 includes, for example, a holding portion 30 having a circular plate-like outer shape, formed of a porous member or the like, and configured to hold the workpiece W by suction, and a frame body 31 that holds the holding portion 30. The holding portion 30 is connected via a piping, a rotary joint, or the like to a suction source (not shown) consisting of a vacuum generating device, a compressor, or the like. A suction force generated by a suction action of the suction source (not shown) is transmitted to the holding surface 30a, whereby the chuck table 3 holds the workpiece W on the holding surface 30a by suction.

[0017] The chuck table 3 can be reciprocated in the Y-axis direction by a Y-axis direction feed device (not shown). Furthermore, one end of a rotary shaft 33 is connected to a bottom surface of the chuck table 3, and a motor 34 is connected to the other end of the rotary shaft 33. The rotary shaft 33 is inclined at an angle of 45 to 180 degrees relative to the vertical direction (Z-axis direction), and the chuck table 3 is also inclined relative to the vertical direction by the same angle as the inclination angle of the rotary shaft 33. With the motor 34 rotating the rotary shaft 33, the chuck table 3 is also rotated about an axis of the rotary shaft 33 inclined at the predetermined angle.

[0018] The grinding unit 4 includes a rotating shaft 40, a motor (not shown) for rotating the rotating shaft 40, a circular support 41 connected to a lower end of the rotating shaft 40, and a grinding wheel 42 detachably connected to a lower surface of the support 41. The grinding wheel 42 includes a wheel base 42a and a plurality of grindstones 42b having a substantially rectangular parallelepiped shape and arranged in an annular pattern on a peripheral portion of a bottom surface of the wheel base 42a. The grindstones 42b are formed, for example, by bonding diamond abrasive grains or the like with a resin bond, a metal bond, or the like.The grinding stones 42b arranged in an annular pattern are arranged such that, for example, the diameter of an outermost circumference thereof is larger than the radius of the jig portion Wa1 of the workpiece W and smaller than the diameter of the jig portion Wa1, and that the diameter of an innermost circumference thereof is smaller than the radius of the jig portion Wa1.

[0019] In addition, like the rotary shaft 33 of the chuck table 3, the rotary shaft 40 is inclined at an angle of 45 to 180 degrees relative to the vertical direction (Z-axis direction), and the grinding unit 4 as a whole is also inclined relative to the vertical direction by the same angle as the inclination angle of the rotary shaft 40. Specifically, in the case where the rotary shaft 33 of the chuck table 3 is inclined at 45 degrees from the vertical direction, for example, the rotary shaft 40 is also inclined at 45 degrees from the vertical direction, and the grindstones 42b grind the back surface Wb of the workpiece W while rotating around an axis of the rotary shaft 40 that is orthogonal to the support surface 30a of the chuck table 3.

[0020] The grinding unit 4, which is inclined by a predetermined angle relative to the vertical direction, can be moved by grinding feed means (not shown) in a direction (the axial direction of the rotary shaft 40) to be at a distance from or closer to the inclined support surface 30a of the chuck table 3.

[0021] The rotary shaft 40 is formed with a flow channel 43 serving as a passage for grinding water, penetrating the rotary shaft 40 in the axial direction of the rotary shaft 40. The flow channel 43 extends through the bracket 41 and has a lower end opening on a bottom surface of the wheel base 42a, allowing the grinding water to be discharged toward the grindstones 42b. Furthermore, a grinding water supply device 44, which supplies grinding water, such as pure water, into the flow channel 43, is connected to the upper end of the flow channel 43.

[0022] As in Fig. 2, in the holding step, first, the workpiece W with the protective member T1 attached to its front side Wa is mounted on the holding surface 30a of the chuck table 3, with the rotary shaft 33 inclined, for example, at 45 degrees to the vertical direction such that the center of the holding surface 30a and the center of the workpiece W substantially coincide, and that the back side Wb of the workpiece W is exposed. Then, the suction force generated by the suction source (not shown) is transmitted to the holding surface 30a, resulting in the protective member T1 side of the workpiece W being sucked onto the holding surface 30a of the chuck table 3. (3) Grinding step

[0023] Next, the chuck table 3 with the workpiece W held thereby is moved in the Y-axis direction to a position below the grinding unit 4 which is inclined at an angle of 45 degrees relative to the vertical direction, and alignment between the grinding wheel 42 belonging to the grinding unit 4 and the workpiece W is performed. The alignment is performed, for example, such that an inner peripheral edge of the peripheral excess portion Wa2 of the workpiece W or an imaginary line L1 on the back surface Wb and a part of an outermost periphery of a rotational trajectory of the grindstones 42b overlap with each other, and the rotational trajectory of the grindstones 42b passes through the rotation center of the workpiece W. Further, in the grinding step, a discharge position of the grinding water containing abrasive grains dropped from the grindstones 42b, as described later, is a lowest or lowest position.lowest point of the clamping table 3, which is inclined by 45 degrees to the vertical direction, as shown in the . Fig. 2 and Fig. 3. Therefore, in order to ensure that the rotational path of the grinding stones 42b, which is shown by a dotted line in Fig. 3, and the discharge position of the grinding water do not overlap each other, the grinding stones 42b are positioned, for example, at a predetermined position on the -Y direction side, which is on the opposite side of the center of the workpiece W from the discharge position on the +Y direction side. It should be noted that the positioning of the grinding stones 42b is not limited to the example of the present embodiment. The grinding stones 42b may be positioned at a predetermined position on the back side Wb of the workpiece W to describe one of the rotational trajectories indicated by lines with alternating long and short dashes in Fig. 3, so that the discharge position of the grinding water containing the abrasive grains and the rotation path of the grinding stones 42b do not overlap.

[0024] After the alignment between the grinding stones 42b and the workpiece W has been performed as shown in Fig. 2, the grinding stones 42b are rotated when the motor (not shown) drives the rotary drive 40. In addition, grinding feed is performed in the direction of arrow E by bringing the grinding unit 4 closer to the holding surface 30a of the chuck table 3, whereby the rotating grinding stones 42b are brought into contact with the back surface Wb of the workpiece W and the back surface W is ground. In addition, during grinding, the workpiece W held on the chuck table 3 is also rotated, which is related to the rotation of the chuck table 3 about an axis of the rotary shaft 33, which is inclined at an angle of 45 degrees from the vertical direction.

[0025] During grinding, for example, the grindstones 42b are rotated so that the rotation center of the workpiece W is always located on the inner side of the outermost circumference of the rotation path of the grindstones 42b and on the outer side of the inner circumference of the rotation path. Furthermore, the grindstones 42b are rotated so that the outermost circumference of the rotation path of the grindstones 42b does not touch a peripheral portion of the back surface Wb corresponding to the peripheral excess portion Wa2 of the workpiece W or does not greatly protrude to the outside beyond the imaginary line L1. Therefore, the grindstones 42b grind a central portion of the back surface Wb corresponding to the fixture portion Wa1 of the workpiece W in a circular recess shape, thereby forming a circular recess Wb1 in the central portion of the back surface Wb corresponding to the fixture portion Wa1, as shown in Fig. 2. In addition, on the back surface Wb of the workpiece W, an annular reinforcing portion Wb2 corresponding to the peripheral excess area Wa2 and surrounding the circular recess Wb1 is formed so as to protrude in the +Z direction.

[0026] During grinding, the grinding water M is supplied through the flow channel 43 in the rotating shaft 40 to the contact point between the grindstones 42b and the workpiece W to cool and wash the contact point between the grindstones 42b and the back surface Wb of the workpiece. The wash water arriving at the contact point is forced to flow outward through gaps between the grindstones 42b by a centrifugal force generated due to the rotation of the chuck table 3, together with grinding chips and the abrasive grains that have fallen off the grindstones 42b.Then, in the grinding method according to the present invention, the inclination of the workpiece W held on the chuck table 3 by suction, which is inclined at 45 degrees from the vertical direction, causes the grinding water M containing the abrasive grains dropped from the grindstones 42b to flow on the circular recess Wb1 toward the discharge position shown in FIG. Fig.4. In addition, the grinding water M is accelerated by the inclination of the workpiece W and flows over the annular reinforcement portion Wb2 at the discharge position to be discharged to the outside of the workpiece W. Furthermore, since the discharge position of the grinding water M and the rotational trajectory of the grindstones 42b do not overlap with each other, the discharge of the grinding water M containing the abrasive grains that have fallen off from the grindstones 42b is not hindered. After the workpiece W is ground to a desired thickness with the supply of the grinding water M, the grinding unit 4 is spaced apart from the workpiece W, thereby completing the grinding.

[0027] As described above, the grinding method according to the present invention includes the front surface protecting step of covering the front surface Wa of the workpiece W with the protecting member T1, the holding step of holding the protecting member T1 of the workpiece W by the holding surface 30a of the chuck table 3 rotated about the rotation axis 33 inclined at an angle of 45 to 180 degrees relative to the vertical direction after the front surface protecting step is performed, and the grinding step of grinding the back surface Wb of the workpiece corresponding to the jig area Wa1 by the grindstones 42b rotated about the rotation axis 40 perpendicular to the holding surface 30a while supplying the grinding water M to form the circular recess Wb1 and the annular reinforcing portion Wb2 corresponding to the peripheral excess area Wa2 and surrounding the circular recess Wb1.Therefore, in the grinding step, the discharge of the grinding water M containing the abrasive grains falling off the grinding stones 42b is promoted by the inclination of the workpiece W. Accordingly, the grinding stones 42b are prevented from dragging the falling abrasive grains during grinding, and the formation of scratches on the back surface Wb of the workpiece W, the generation of cracks in the workpiece W, and similar problems can be prevented.

[0028] Furthermore, in the grinding step, the discharge position of the grinding water M containing the abrasive grains dropped from the grinding stones 42b is located at the lowest point of the chuck table 3 whose rotation axis 33 is inclined. Therefore, if the grinding stones 42b are positioned so that the rotation trajectory of the grinding stones 42b and the discharge position of the grinding water M do not overlap, the discharge of the grinding water M containing the abrasive grains dropped from the grinding stones 42b is performed more efficiently.

[0029] It should be noted that the grinding method according to the present invention is not limited to the above embodiment. Furthermore, each configuration of the grinding device 2 shown in the accompanying figures is not limitative, and appropriate modifications can be made within a range that can achieve the effects of the invention. For example, the supply of grinding water to the contact point between the grinding stones 42b and the workpiece W may not be performed through the rotary shaft 40 of the grinding unit 4, and the grinding water may be supplied to the contact point between the grinding stones 42b and the workpiece W from the outside using a jet nozzle.

[0030] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims.

Claims

[1] A workpiece grinding method for grinding a back surface (Wb) of a workpiece (W) with a grindstone (42b), the workpiece having on a front surface (Wa) thereof a jig portion (Wa1) in which a plurality of jigs are formed, and a peripheral excess portion (Wa2) around the jig portion, the workpiece grinding method comprising: a front side protection step for covering the front side of the workpiece with a protective member (T1); a holding step for holding a protective element side of the workpiece by a holding surface of a chuck table (3) rotated about a rotation axis inclined at an angle of 45 to 180 degrees relative to a vertical direction after the front side protecting step is performed; and a grinding step for grinding the back of the workpiece corresponding to the fixture area by the grindstone rotated about a rotation axis orthogonal to the holding surface while supplying grinding water (M) to form a circular recess (Wb1) and an annular reinforcing portion (Wb2) corresponding to the peripheral excess area and surrounding the circular recess, wherein in the grinding step, the discharge of the grinding water containing abrasive grains falling off the grindstone is promoted by the inclination of the workpiece, wherein in the grinding step, the grindstone is positioned such that a rotational trajectory of the grindstone and a discharge position of the grinding water containing the abrasive grains falling off the grindstone do not overlap each other because the discharge position is located at a lowest point of the chuck table whose rotational axis is inclined, the rotational trajectory of the grindstone passing through the rotational center of the workpiece. [2] The workpiece grinding method according to claim 1, wherein the protective member is an adhesive tape.

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