1. A grinding method of a workpiece, wherein the back side of a disc-shaped workpiece is ground by a grinding wheel part of a grinding wheel, the grinding wheel comprises an annular grinding wheel base and the grinding wheel part annularly arranged on one surface side of the grinding wheel base, the workpiece comprises a device area formed with a plurality of devices on the front side and an outer peripheral residual area surrounding the periphery of the device area,

it is characterized in that the preparation method is characterized in that,

the grinding method comprises the following steps:

a front surface protecting step of covering the front surface side of the workpiece with a protective member;

a holding step of performing suction holding of the front side of the object by a disc-shaped chuck table rotatable about a 1 st rotation axis;

an inclined grinding step of rotating the grinding wheel, which is attached to a lower end portion of a 2 nd rotation shaft, has a diameter smaller than that of the chuck table, and is disposed above the chuck table, around the 2 nd rotation shaft after the holding step, and relatively moving the grinding wheel and the chuck table so as to approach each other in a direction parallel to the 1 st rotation shaft in a state in which the 2 nd rotation shaft is inclined with respect to the 1 st rotation shaft such that a bottom portion of a 1 st portion of the grinding wheel, which is located above an outer peripheral portion of the chuck table, is higher than a bottom portion of a 2 nd portion, which is located above a central portion of the chuck table, to grind a central portion of the back surface side of the workpiece, which corresponds to the device region in a thickness direction of the workpiece, thereby forming a circular ground portion ground by grinding and a round ground portion surrounding the ground portion and not solid on the back surface side A disc-shaped concave part formed by the grinding annular reinforcing part; and

and an inclination changing and grinding step of grinding the back surface side while gradually changing the inclination of the 2 nd rotation axis so that the 2 nd rotation axis becomes parallel to the 1 st rotation axis after the inclination grinding step.

2. The grinding method according to claim 1,

the grinding method also has the following general grinding steps: after the inclination changing and grinding step, in a state where the 2 nd rotation axis of the grinding wheel is parallel to the 1 st rotation axis of the chuck table, the grinding wheel and the chuck table are moved relatively so as to approach each other in a direction parallel to the 1 st rotation axis, thereby grinding the part to be ground.

Background

A plurality of regions defined by a plurality of intersecting planned dividing lines are set on the front surface side of the workpiece, devices such as an IC (Integrated Circuit) and an LSI (Large Scale Integration) are formed in each region, and the workpiece is divided into a plurality of device chips by grinding, cutting, and the like. As a method of grinding a workpiece, for example, the following methods are used: only a circular central portion of the back surface side corresponding to a circular device region in which a plurality of devices are arranged in the thickness direction of the workpiece is ground (see, for example, patent document 1).

A circular concave portion is formed on the back side of the workpiece by grinding only the circular central portion on the back side, and the circular concave portion is composed of a circular grinding target portion subjected to grinding and an annular reinforcing portion surrounding the periphery of the grinding target portion and not subjected to grinding. Thus, the remaining annular reinforcing portion has an advantage that handling such as conveyance of the workpiece becomes easy even if the back surface side becomes thin.

Patent document 1: japanese laid-open patent publication No. 2007-19461

However, in the grinding step, due to the impact when the grinding wheel contacts the back surface side or the contact between the outer side surface of the grinding wheel and the inner peripheral side surface of the annular reinforcing portion, a plurality of broken edges (chipping) may be formed on the back surface side of the annular reinforcing portion, which may reduce the strength of the annular reinforcing portion.

In addition, when wet etching is performed after the grinding step, the defective portion formed in the annular reinforcing portion is etched, and unevenness is formed on the back surface side of the annular reinforcing portion. If the unevenness is formed, another problem occurs in the subsequent process. For example, the metal film deposited on the back surface side is easily peeled off from the uneven portion as a starting point. In addition, for example, when the dicing tape is attached to the back surface side, poor attachment occurs due to the uneven portion.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to reduce the amount of a defect occurring on the back surface side of the annular reinforcing portion.

According to one aspect of the present invention, there is provided a method of grinding a back surface side of a disk-shaped workpiece by a grindstone portion of a grinding wheel having an annular grinding wheel base and the grindstone portion annularly arranged on one surface side of the grinding wheel base, the workpiece having a device region in which a plurality of devices are formed on a front surface side and a peripheral surplus region surrounding a periphery of the device region, the method comprising: a front surface protecting step of covering the front surface side of the workpiece with a protective member; a holding step of performing suction holding of the front side of the object by a disc-shaped chuck table rotatable about a 1 st rotation axis; an inclined grinding step of rotating the grinding wheel, which is attached to a lower end portion of a 2 nd rotation shaft, has a diameter smaller than that of the chuck table, and is disposed above the chuck table, around the 2 nd rotation shaft after the holding step, and relatively moving the grinding wheel and the chuck table so as to approach each other in a direction parallel to the 1 st rotation shaft in a state in which the 2 nd rotation shaft is inclined with respect to the 1 st rotation shaft such that a bottom portion of a 1 st portion of the grinding wheel, which is located above an outer peripheral portion of the chuck table, is higher than a bottom portion of a 2 nd portion, which is located above a central portion of the chuck table, to grind a central portion of the back surface side of the workpiece, which corresponds to the device region in a thickness direction of the workpiece, thereby forming a circular ground portion ground by grinding and a round ground portion surrounding the ground portion and not solid on the back surface side A disc-shaped concave part formed by the grinding annular reinforcing part; and an inclination changing and grinding step of grinding the back surface side while gradually changing the inclination of the 2 nd rotation axis so that the 2 nd rotation axis becomes parallel to the 1 st rotation axis after the inclination grinding step.

The grinding method also has the following usual grinding steps: after the inclination changing and grinding step, in a state where the 2 nd rotation axis of the grinding wheel is parallel to the 1 st rotation axis of the chuck table, the grinding wheel and the chuck table are moved relatively so as to approach each other in a direction parallel to the 1 st rotation axis, thereby grinding the part to be ground.

In the inclined grinding step of the grinding method according to one aspect of the present invention, the grinding wheel is rotated about the 2 nd rotation axis, and the central portion on the back side of the workpiece is ground to form the disc-shaped concave portion on the back side in a state where the 2 nd rotation axis is inclined with respect to the 1 st rotation axis so that the bottom portion of the 1 st portion of the grinding wheel located above the outer peripheral portion side of the chuck table is higher than the bottom portion of the 2 nd portion located above the central portion side of the chuck table.

This eliminates the defect on the back side of the annular reinforcing portion caused by the contact of the outer peripheral side surface of the grinding wheel with the inner peripheral edge of the upper surface of the annular reinforcing portion. Therefore, the amount of the defect generated on the back surface side of the annular reinforcing portion can be reduced.

Drawings

Fig. 1 is a side view, partly in section, of a grinding device.

Fig. 2 is a perspective view of a workpiece or the like.

Fig. 3 (a) is a partial cross-sectional side view of the workpiece unit and the like, and fig. 3 (B) is a partial cross-sectional side view of the grinding wheel and the like in the inclined grinding step.

Fig. 4 (a) is a partial cross-sectional side view of a grinding wheel and the like during grinding, and fig. 4 (B) is a partial enlarged view of fig. 4 (a).

Fig. 5 is a diagram showing a change in inclination and a grinding step.

Fig. 6 is a diagram showing a general grinding step.

Fig. 7 is a flow chart of a grinding method.

Fig. 8 is a diagram showing a grinding step of a comparative example.

Description of the reference symbols

2: a grinding device; 4: a base station; 6: a chuck table; 6 a: a frame body; 6 b: a perforated plate; 6 c: a holding surface; 6c₁: a peripheral portion; 6c₂: a central portion; 8: an output shaft; 10: a column; 11: a workpiece; 11 a: a front side; 11 b: a back side; 11b₁: a peripheral portion; 11b₂: a central portion; 11 c: a recess; 11c₁: an annular reinforcing portion; 11c₂: a ground portion;11 d: a curved surface; 12: a grinding feed unit; 12 a: a guide rail; 12 b: moving the plate; 12 c: a nut portion; 12 d: a ball screw; 12 e: a pulse motor; 13: dividing the predetermined line; 14: a grinding unit; 14 a: a holding member; 14 b: a spindle housing; 14c, 14c₁、14c₂: a gasket; 14 d: a male screw; 14 e: a main shaft; 15: a device; 16: a grinding wheel mounting seat; 17 a: a device region; 17 b: a peripheral residual region; 18: grinding the grinding wheel; 18 a: a grinding wheel base station; 18 b: a lower surface; 18 c: grinding the grinding tool; 18c₁: part 1; 18c₂: part 2; 19: a protective member; 21: a workpiece unit; 23: a gap; 25: and (4) a region.

Detailed Description

An embodiment of one embodiment of the present invention will be described with reference to the drawings. First, the grinding apparatus 2 will be described with reference to fig. 1. Fig. 1 is a partially cut-away side view of a grinding apparatus 2. The grinding device 2 includes a substantially rectangular parallelepiped base 4 that supports a plurality of components.

A disk-shaped chuck table 6 is provided on the base 4. The chuck table 6 has a ceramic frame 6 a. A flow path (not shown) is provided in the housing 6a, and one end of the flow path is connected to a suction source (not shown) such as an ejector.

The frame 6a has a recess formed of a disk-shaped space on the upper surface side. A disk-shaped porous plate 6b is fixed to the concave portion. The diameter of the concave portion and the porous plate 6b is set to be substantially the same as the diameter of a workpiece 11 (see fig. 2) to be described later (for example, 200 mm).

The other end of the flow path of the frame 6a is connected to the porous plate 6 b. When the suction source is operated, a negative pressure is generated on the upper surface of the porous plate 6b, and the upper surface functions as a holding surface 6c for sucking and holding the workpiece 11.

A 1 st rotation driving source (not shown) such as a motor is disposed on the lower surface side of the chuck table 6. The output shaft (1 st rotation axis) 8 of the 1 st rotation drive source is disposed substantially parallel to the Z-axis direction (height direction, vertical direction).

The output shaft 8 is connected to the lower surface side of the chuck table 6. When the 1 st rotation driving source is operated, the chuck table 6 rotates about the output shaft 8. A rectangular parallelepiped pillar 10 is provided on the rear side of the base 4.

A grinding and feeding unit 12 is provided on the front side of the column 10. The grinding and feeding unit 12 has a pair of guide rails 12a fixed to the front side surface of the column 10 substantially in parallel with the height direction. In fig. 1, one guide rail 12a is shown on the back side of the drawing.

A moving plate 12b is slidably attached to the pair of guide rails 12 a. A nut portion 12c is provided on the back surface (rear) side of the moving plate 12 b. The ball screw 12d disposed substantially parallel to the height direction is rotatably coupled to the nut portion 12 c.

A pulse motor 12e is connected to an upper end portion of the ball screw 12 d. If the ball screw 12d is rotated by the pulse motor 12e, the moving plate 12b moves along the guide rail 12 a.

A cylindrical holding member 14a constituting the grinding unit 14 is fixed to the front (front) of the moving plate 12 b. A cylindrical spindle housing 14b is disposed in a space inside the holding member 14 a.

A plurality of block-shaped spacers 14c (14 c) are annularly arranged on the lower portion of the spindle housing 14b₁，14c₂). The upper surface of each pad 14c is in contact with the lower surface of the spindle housing 14b, and the lower surface of each pad 14c is disposed on the upper surface side of the bottom plate of the holding member 14 a.

In FIG. 1, the shim 14c is shown disposed proximate (i.e., rearward of) the post 10₁And a pad 14c disposed at a position farthest from the column 10 (i.e., in front)₂. At the spacer 14c₂Is formed with a threaded hole.

Further, a through hole is formed in the bottom plate of the holding member 14a positioned below the screw hole. The shaft portion of the male screw 14d is fastened to the screw hole through the through hole. The head of the male screw 14d is exposed downward from the bottom plate of the holding member 14a, and an output shaft of a driving mechanism (not shown) such as a motor is connected to the head of the male screw 14 d.

For example, if the driving mechanism is operated to rotate the male screw 14d in one directionTurning, then gasket 14c₂Moves upward and the pad 14c₂Slightly away from the upper surface of the base plate of the holding member 14 a. On the other hand, if the male screw 14d is rotated to the other side, the washer 14c₂Moves downward and the pad 14c₂Is in contact with the upper surface of the bottom plate of the holding member 14 a. The shim 14c is appropriately adjusted to realize a grinding method of the workpiece 11 to be described later₂Thickness, amount of movement, etc.

A cylindrical spindle 14e is disposed inside the spindle housing 14 b. The spindle 14e is rotatably supported by the spindle housing 14 b. A 2 nd rotation drive source (not shown) such as a servo motor is connected to an upper end of the main shaft 14 e.

The main shaft 14e is disposed to penetrate an opening formed in the center of the bottom plate of the holding member 14 a. The lower end of the main shaft 14e is located below the lower surface of the bottom plate of the holding member 14 a. A central portion of the upper surface of the disc-shaped grinding wheel mounting base 16 is connected to the lower end portion of the main shaft 14 e.

An upper surface side of an annular grinding wheel base 18a made of aluminum alloy or the like is attached to a lower surface side of the grinding wheel attachment base 16. That is, the grinding wheel base 18a is attached to the lower end portion of the main shaft 14e via the grinding wheel attachment base 16.

The grinding wheel base 18a is disposed above the chuck table 6. The diameter of the grinding wheel base 18a is smaller than that of the chuck table 6. For example, the diameter of the grinding wheel base 18a is set to a predetermined length smaller than the diameter of the holding surface 6c (about 200mm in this example).

A plurality of grinding stones 18c (grinding stone portions) in a block shape are annularly arranged on the lower surface (one surface) 18b side of the grinding wheel base 18a (arranged in stages). Instead of the plurality of grinding stones 18c (arranged in series), one annular grinding stone (stone portion) may be provided.

The grinding wheel base 18a and the plurality of grinding stones 18c constitute a grinding wheel 18. When the 2 nd rotation drive source is operated, the spindle 14e rotates, and the grinding wheel 18 rotates around the spindle (2 nd rotation axis) 14 e.

A predetermined flow path (not shown) for supplying a grinding fluid such as pure water to the grinding wheel 18c is formed inside the main shaft 14e and the grinding wheel base 18a, and the grinding fluid is supplied from a grinding fluid supply source (not shown) to the grinding wheel 18c during grinding.

Next, the workpiece 11 to be ground will be described. Fig. 2 is a perspective view of the workpiece 11 and the like. The workpiece 11 of the present embodiment is a disk-shaped wafer made of a semiconductor material such as silicon, for example. The workpiece 11 has a predetermined thickness of 100 μm to 800 μm, for example.

The front surface 11a side of the workpiece 11 is divided into a plurality of regions by a plurality of lines to divide (streets) 13 intersecting each other, and devices 15 such as ICs and LSIs are formed in each region.

The material, shape, structure, size, and the like of the workpiece 11 are not limited. For example, a substrate made of a semiconductor material other than silicon may be used as the object 11. In addition, the kind, number, shape, structure, size, arrangement, and the like of the devices 15 are also not limited.

When the front surface 11a side of the workpiece 11 is observed, the plurality of devices 15 are arranged inside the circular device region 17 a. Outside the device region 17a, an outer peripheral surplus region 17b having no device 15 is arranged so as to surround the device region 17 a.

In fig. 2, a boundary line between the circular device region 17a and the annular outer peripheral residual region 17b is indicated by a broken line. However, the boundary line is an imaginary line and is not actually marked on the workpiece 11. In addition, a chamfered portion is formed at each of the outer peripheral portions of the front surface 11a side and the rear surface 11b side (see fig. 3 (a) and the like).

Next, a method of grinding the workpiece 11 will be described with reference to fig. 2 to 7. Fig. 7 is a flowchart of the grinding method. First, as shown in fig. 2, a circular protective member 19 made of resin is stuck to the front surface 11a side. Thereby, the workpiece unit 21 having the front surface 11a covered with the protective member 19 is formed (front surface protecting step S10).

The protective member 19 is attached so as to cover the front surface 11a and the inclined surface portion on the front surface 11a side. The protective member 19 is a disk-shaped sheet made of resin, and includes a base material layer and a paste layer (adhesive layer) provided on one surface of the base material layer.

The paste layer is made of, for example, an ultraviolet curable resin, but may be made of a thermosetting resin or a naturally curable resin. Further, the paste layer may not necessarily be provided on the base material layer. For example, the protective member 19 may be formed of only a base material layer and may be bonded to the front surface 11a by thermocompression bonding or the like.

After the front surface protecting step S10, the front surface 11a side of the workpiece 11 (i.e., the other surface of the protective member 19 on the opposite side of the one surface) is sucked and held by the holding surface 6c of the chuck table 6 (holding step S20). Fig. 3 (a) is a partially cross-sectional side view of the workpiece unit 21 and the like.

After the holding step S20, the back surface 11b side is ground by the grinding wheel 18 using the grinding device 2. In the present embodiment, first, the driving mechanism is operated to rotate the male screw 14d and adjust the spacer 14c₂The position of (a).

The lower end of the main shaft 14e is disposed so as to be positioned on the outer peripheral portion 6c of the holding surface 6c₁With the central portion 6c of the holding surface 6c₂In the meantime. By adjusting the shim 14c₂The main shaft 14e is directed toward the center 6c of the holding surface 6c₂The side is inclined by a predetermined angle theta.

The predetermined angle θ (expressed by degree (arc degree)) is, for example, greater than 0 degree and not greater than 2 degrees (0 degree)<Theta is less than or equal to 2 degrees). As shown in fig. 3B, the main shaft 14e (dashed-dotted line) is inclined at a predetermined angle θ with respect to a straight line (broken line) parallel to the output shaft 8, whereby the plurality of grinding stones 18c are positioned at the outer peripheral portion 6c₁Lateral upper 1 st part 18c₁Is located at the central portion 6c₂Lateral upper 2 nd part 18c₂Is slightly higher at the bottom.

In this state, the grinding wheel 18 is rotated around the spindle 14e, and the chuck table 6 is rotated around the output shaft 8. For example, the rotation speed of the main shaft 14e is 3000rpm, and the rotation speed of the output shaft 8 is 300 rpm.

Next, the pulse motor 12e is operated to move the grinding wheel 18 and the chuck table 6 relative to each other in a direction parallel to the output shaft 8 so that the grinding wheel 18 and the chuck table 6 approach each other.

For example, the grinding unit 14 is ground and fed downward in the Z-axis direction at 1.0 μm/sec. Thereby, the back surface 11b side is ground (inclined grinding step S30). Fig. 3 (B) is a partial cross-sectional side view of the grinding wheel 18 and the like in the inclined grinding step S30.

When the grinding stone 18c is brought into contact with the back surface 11b side, the back surface 11b side is ground and removed. In the present embodiment, the outer peripheral portion 11b on the rear surface 11b side corresponding to the outer peripheral surplus region 17b is not provided₁Grinding is performed to remove the central portion 11b of the back surface 11b side corresponding to the device region 17a in the thickness direction of the workpiece 11₂And (6) grinding.

Fig. 4 (a) is a side view, partially in section, of the grinding wheel 18 and the like during grinding. Center part 11b₂A grinding target portion 11c which is ground into a circular shape₂. The ground portion 11c₂Is formed as an annular reinforcing portion 11c without grinding₁。

Passes through the ground part 11c₂And to surround the ground portion 11c₂The annular reinforcing part 11c arranged as described above₁A disc-shaped recess 11c is formed in the center of the rear surface 11 b. FIG. 4B shows the ground portion 11c of FIG. 4A₂And a ring-shaped reinforcing portion 11c₁Is enlarged in part near the boundary.

In the inclined grinding step S30, the main shaft 14e is inclined at a predetermined angle θ with respect to the output shaft 8. Therefore, the grinding wheel 18c is guided from the annular reinforcing portion 11c to the outer peripheral side surface thereof₁Upper surface (i.e., outer peripheral portion 11b of back surface 11 b)₁) Is ground in a state where the inner peripheral edge of the grinding wheel is separated. That is, during grinding, the grinding wheel 18c is provided on the outer peripheral side surface and the annular reinforcing portion 11c₁Is formed with a gap 23 between the inner peripheral edges of the upper surface.

For example, in the annular reinforcing part 11c₁When the depth of the inner peripheral side surface of (2) is 600 μm, if θ is 1.9 degrees, the annular reinforcing portion 11c is removed₁Is 20 μm from the inner peripheral edge of the upper surface to the outer peripheral side surface of the grinding stone 18 c. Thus, in grinding the grinding toolWhen the protrusion amount of the abrasive grains on the outer peripheral side surface of the grinding whetstone 18c is 10 μm, the abrasive grains of the grinding whetstone 18c do not contact the annular reinforcing part 11c₁Is in contact with the inner periphery of the upper surface.

In the inclined grinding step S30 of the present embodiment, since the gap 23 is formed in this way, the outer peripheral side surface of the grinding stone 18c and the annular reinforcing portion 11c can be eliminated from being abraded₁Is formed by contacting the inner peripheral edge of the upper surface of the base member with the annular reinforcing portion 11c₁The back surface 11b side. Therefore, the annular reinforcing portion 11c can be reduced₁The back surface 11b side of (3).

After the bevel grinding step S30, the drive mechanism is operated in a state where the grinding feed of the grinding unit 14 is stopped, and the male screw 14d is rotated toward the other side. Thereby, the inclination angle of the spindle 14e is gradually changed in the direction opposite to the direction inclined in the inclination grinding step S30.

In the present embodiment, the inclination of the main shaft 14e is adjusted so that the main shaft 14e is parallel to the output shaft 8, without the predetermined angle θ formed in the inclination grinding step S30. However, in this inclination change, the grinding of the back surface 11b side is continued (inclination change and grinding step S40).

FIG. 5 shows a ground portion 11c₂And a ring-shaped reinforcing portion 11c₁The enlarged partial view of the vicinity of the boundary of (a) is a view showing the inclination change and the grinding step S40. In fig. 5, the grinding wheel 18c in the inclined grinding step S30 is indicated by a two-dot chain line, and the grinding wheel 18c in a state where the inclination is changed and removed in the grinding step S40 is indicated by a solid line.

In the inclination change and grinding step S40, the main shaft 14e is made parallel to the output shaft 8, so that the portion to be ground 11c can be made to be parallel to the output shaft, as compared with the case where grinding is completed only in the inclination grinding step S30₂Becomes flat.

In the inclination change and grinding step S40, the inclination change operation of the main shaft 14e causes the annular reinforcing portion 11c to move₁The bottom portion of the inner peripheral side surface and the ground portion 11c₂The vicinity of the boundary of (2) forms an annular curved surface 11 d.

In the inclination change and grinding step S40 of the present embodiment, the grinding unit 14 is not ground and fed downward, but the main shaft 14e may be made parallel to the output shaft 8 while grinding and feeding at 1.0 μm/sec in the same manner as in the inclination grinding step S30.

After the inclination change and grinding step S40, the grinding target portion 11c is further ground in a state where the main shaft 14e is parallel to the output shaft 8₂(grinding step S50 is usual). Fig. 6 is a diagram showing a normal grinding step S50.

In the normal grinding step S50, the grinding wheel 18 and the chuck table 6 are relatively moved so that the grinding wheel 18 and the chuck table 6 approach each other in a direction parallel to the output shaft 8. For example, the grinding unit 14 is fed downward at 1.0 μm/sec for grinding.

In the grinding method according to the present embodiment, the grinding step S50 is not always necessary. That is, the grinding of the workpiece 11 may be finished from the front protection step S10 to the inclination change and grinding step S40.

Next, a comparative example will be explained. Fig. 8 is a diagram showing a grinding step of a comparative example. In the comparative example, after the front protection step S10 and the holding step S20, the main shaft 14e and the output shaft 8 are rotated in a state where the main shaft 14e is parallel to the output shaft 8, and grinding feed is performed.

In this case, the outer peripheral side surface of the grinding stone 18c and the annular reinforcing portion 11c are ground₁Is contacted (refer to the area 25 indicated by the dotted circle in fig. 8). Therefore, compared to the above embodiment, the annular reinforcing portion 11c₁The amount of the defect on the back surface 11b side becomes large.

The structure, method, and the like of the above embodiments can be modified as appropriate without departing from the object scope of the present invention. For example, the grinding method of the present embodiment can be applied to any of rough grinding and finish grinding.