WORKPIECE GRINDING METHOD

Abstract

A method of grinding a back side of a workpiece having a device region and a peripheral surplus region on a front side thereof includes covering the front side of the workpiece with a protective member, holding a protective member side of the workpiece by a holding surface of a chuck table that is rotated around a rotational axis inclined at an angle of 45 to 180 degrees relative to a vertical direction, and grinding the back side of the workpiece corresponding to the device region by a grindstone rotated around a rotational axis orthogonal to the holding surface while supplying grinding water, to form a circular recess and an annular reinforcement section surrounding the circular recess. When grinding, discharge of the grinding water containing abrasive grains dropped from the grindstone is promoted by the inclination of the workpiece.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of grinding a plate-shaped workpiece such as a semiconductor wafer by a grindstone.

Description of the Related Art

A workpiece in which a plurality of devices such as integrated circuits (ICs) and large scale integrations (LSIs) formed on a front side thereof has its back side ground to be thinned to a predetermined thickness, and is further divided by a dividing apparatus such as a dicing apparatus into individual device chips, which are used for various electronic apparatuses.

A grinding apparatus for grinding the back side of the workpiece includes a chuck table adapted to hold the workpiece to which a front side protective member formed 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 grinding water supplying means supplying grinding water to the grindstone through a flow passage formed along an axis of a spindle constituting the grinding unit. By the grinding apparatus configured in this way, the workpiece can be ground efficiently.

In recent years, for achieving reductions in the weight and size of device chips, it has been demanded in the wafer grinding method to make the workpiece smaller in thickness. The wafers thus made thinner, however, are lowered in rigidity, to become difficult to handle, and may be damaged or broken during when being carried or in other similar situations. In view of this problem, there is a grinding method wherein the workpiece is ground and thinned to, for example, 100 μm or below, then, only that region of the back side of the workpiece which corresponds to the device region on the front side is further ground and thinned, to leave on the back side an annular reinforcement section corresponding to the peripheral surplus region surrounding the device region on the front side, thereby ensuring easy handling of the thinned workpiece (see, for example, Japanese Patent Laid-Open No. 2007-19461).

SUMMARY OF THE INVENTION

In the grinding method as above, however, since the annular reinforcement section is formed on the back side of the workpiece, the annular reinforcement section would serve as a bank during grinding, so that grinding water containing abrasive grains dropped from the grindstone would stagnate in the circular recess of the workpiece. Then, the dropped abrasive grains stagnating in the circular recess of the workpiece are dragged in by the grindstone during grinding, and adhere to the grinding surface at the tip of the grindstone. When grinding by the grindstone with the dropped abrasive grains adhering to the grinding surface at the tip of the grindstone is continued, scratches may be formed on the ground surface of the workpiece or cracking of the workpiece may be generated.

It is therefore an object of the present invention to provide a workpiece grinding method which is of the type of grinding a region of the back side of the workpiece corresponding to a device region on the front side, to form a circular recess, and to form an annular reinforcement section in a region of the back side of the wafer corresponding to a peripheral surplus region surrounding the device region, and by which formation of scratches on the back side of the workpiece, generation of cracks in the workpiece, and the like troubles can be prevented.

In accordance with an aspect of the present invention, there is provided a workpiece grinding method of grinding by a grindstone a back side of a workpiece having on a front side thereof a device region in which a plurality of devices are formed and a peripheral surplus region surrounding the device region. 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 that is rotated around a rotational 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 device region by the grindstone rotated around a rotational axis orthogonal to the holding surface while supplying grinding water, to form a circular recess and an annular reinforcement section that corresponds to the peripheral surplus region and that surrounds the circular recess. In the grinding step, discharge of the grinding water containing abrasive grains dropped from the grindstone is promoted by the inclination of the workpiece.

Preferably, the protective member is an adhesive tape.

Preferably, in the grinding step, the grindstone is positioned in such a manner that a rotational trajectory of the grindstone and a discharge position of the grinding water containing the abrasive grains dropped from the grindstone do not overlap each other since the discharge position is located at a lowermost point of the chuck table whose rotational axis is inclined.

According to the present invention, in the grinding step, the discharge of the grinding water containing the abrasive grains dropped from the grindstone is promoted by the inclination of the workpiece. Therefore, the grindstone is restrained from dragging in the dropped abrasive grains during grinding, so that formation of scratches on the back side of the workpiece, generation of cracks in the workpiece, and the like troubles can be prevented from occurring.

In the grinding step, the discharge position of the grinding water containing the abrasive grains dropped from the grindstone is located at the lowermost point of the chuck table whose rotational axis is inclined. Therefore, where the grindstone is positioned in such a manner that the rotational trajectory of the grindstone and the discharge position of the grinding water do not overlap each other, the discharge of the grinding water containing the abrasive grains dropped from the grindstone is thereby performed more efficiently.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view depicting an example of a workpiece and a protective member for protecting a front side of the workpiece;

FIG. 2 is a sectional view depicting 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 trajectory of the grindstone and a discharge position of grinding water do not overlap each other; and

FIG. 4 is a sectional view depicting a state in which the grinding water is discharged from a position on the back side of the workpiece ground.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A workpiece W depicted in FIG. 1 is, for example, a semiconductor wafer which is circular plate-like in external form, the base material of which is silicon, and which is provided on a front side Wa thereof with a device region Wa1 and a peripheral surplus region Wa2 surrounding the device region Wa1. The peripheral surplus region Wa2 is that region of the front side Wa of the workpiece W which is on the outside of an imaginary line L1 represented by an alternate long and two short dashes line in FIG. 1. The device region Wa1 is partitioned in a grid pattern by a plurality of division lines (streets) S intersecting orthogonally, and a device D such as an IC is formed individually in each of regions partitioned in the grid pattern. A back side Wb of the workpiece W is a to-be-ground surface to be subjected to grinding. Note that the workpiece W may be formed from gallium arsenide, sapphire, gallium nitride, silicon carbide or the like, other than silicon.

Each of steps in the case of carrying out a grinding method according to the present invention to grind the workpiece W depicted in FIG. 1 to a predetermined thickness will be described.

(1) Front Side Protecting Step

In subjecting the workpiece W to grinding, for example, a circular protective member T1 substantially the same in diameter as the workpiece W is adhered to the front side Wa of the workpiece W, resulting in a state in which the device region Wa1 and the peripheral surplus region Wa2 are covered and protected by the protective member T1. The protective member T1 may be, for example, an adhesive tape including a base material layer and an adhesive layer, but it not limited thereto. A hard plate having rigidity such as a glass substrate may be adhered to the front side Wa with an adhesive, to serve as the protective member, or a liquid resin may be applied to the front side Wa and the resin may be cured by heating, irradiation with ultraviolet rays, or the like, to form a protective member covering the front side Wa of the workpiece W.

(2) Holding Step

The workpiece W with its front side Wa covered with the protective member T1 is carried to a grinding apparatus 2 depicted in FIG. 2. The grinding apparatus 2 includes a chuck table 3 adapted to hold the workpiece W by suction, and a grinding unit 4 adapted to grind the workpiece W by grindstones 42b. The chuck table 3 includes, for example, a holding section 30 which is circular plate-like in external form, is formed from a porous member or the like and is adapted to hold the workpiece W by suction, and a frame body 31 supporting the holding section 30. The holding section 30 is communicating with a suction source (not depicted) composed of a vacuum generating apparatus, a compressor or the like through a piping, a rotary joint or the like. A suction force generated by a suction operation of the suction source (not depicted) is transmitted to the holding surface 30a, whereby the chuck table 3 holds the workpiece W on the holding surface 30a by suction.

The chuck table 3 can be reciprocated in a Y-axis direction by Y-axis direction feeding means (not depicted). In addition, one end of a rotary shaft 33 is connected to a bottom surface side 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 at 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 around an axis of the rotary shaft 33 which is inclined at the predetermined angle.

The grinding unit 4 includes a rotary shaft 40, a motor (not depicted) for rotationally driving the rotary shaft 40, a circular mount 41 connected to a lower end of the rotary shaft 40, and a grinding wheel 42 detachably connected to a lower surface of the mount 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 at a peripheral portion of a bottom surface of the wheel base 42a. The grindstones 42b are formed, for example, by binding diamond abrasive grains or the like with a resin bond, a metal bond or the like. The grindstones 42b arranged in an annular pattern are so arranged that, for example, the diameter of an outermost circumference thereof is larger than the radius of the device region Wa1 of the workpiece W and is smaller than the diameter of the device region Wa1, and that the diameter of an innermost circumference thereof is smaller than the radius of the device region Wa1.

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

The grinding unit 4 inclined at the predetermined angle relative to the vertical direction can be moved in a direction (the axial direction of the rotary shaft 40) for spacing away from or coming closer to the holding surface 30a of the chuck table 3 which is inclined, by grinding feeding means (not depicted).

The rotary shaft 40 is formed therein with a flow passage 43 serving as a passage for grinding water, in the manner of penetrating the rotary shaft 40 in the axial direction of the rotary shaft 40. The flow passage 43 passes through the mount 41, and has a lower end side opening at a bottom surface of the wheel base 42a such that the grinding water can be jetted toward the grindstones 42b. In addition, grinding water supplying means 44 supplying the grinding water such as pure water into the flow passage 43 communicates with the upper end side of the flow passage 43.

As illustrated in FIG. 2, in the holding step, first, the workpiece W with the protective member T1 adhered to the front side Wa thereof is mounted on the holding surface 30a of the chuck table 3 having the rotary shaft 33 inclined, for example, at 45 degrees relative to the vertical direction, in such a manner that the center of the holding surface 30a and the center of the workpiece W are substantially in register and that the back side Wb of the workpiece W is exposed. Then, the suction force generated by the suction source (not depicted) is transmitted to the holding surface 30a, resulting in that the protective member T1 side of the workpiece W is suction held by the holding surface 30a of the chuck table 3.

(3) Grinding Step

Next, the chuck table 3 with the workpiece W held thereby is moved in the Y-axis direction to a position under the grinding unit 4 inclined at an angle of 45 degrees relative to the vertical direction, and alignment between the grinding wheel 42 possessed by the grinding unit 4 and the workpiece W is conducted. The alignment is performed, for example, in such a way that an inner circumferential edge of the peripheral surplus region Wa2 of the workpiece W, or an imaginary line L1 on the back side Wb, and part of an outermost circumference of a rotational trajectory of the grindstones 42b overlap each other, and that the rotational trajectory of the grindstones 42b passes through the rotational 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 will be described later is a lowermost point, depicted in FIGS. 2 and 3, of the chuck table 3 inclined at 45 degrees relative to the vertical direction. Therefore, in order that the rotational trajectory of the grindstones 42b represented by a dotted line in FIG. 3 and the discharge position of the grinding water do not overlap each other, the grindstones 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. Note that the positioning of the grindstones 42b is not limited to the example in the present embodiment. The grindstones 42b may be positioned at a predetermined position for describing either one of the rotational trajectories represented by alternate long and short dash lines in FIG. 3, on the back side Wb of the workpiece W, such that the discharge position of the grinding water containing the abrasive grains dropped and the rotational trajectory of the grindstones 42b do not overlap each other.

After the alignment between the grindstones 42b and the workpiece W is conducted, as illustrated in FIG. 2, the grindstones 42b are rotated attendant on rotational driving of the rotary shaft 40 by the motor (not depicted). In addition, grinding feeding in a direction of arrow E, in which the grinding unit 4 is brought closer to the holding surface 30a of the chuck table 3, is performed, whereby the grindstones 42b in rotation are put into contact with the back side Wb of the workpiece W, and the back side Wb is ground. Besides, during grinding, the workpiece W held on the chuck table 3 is also rotated, attendant on the rotation of the chuck table 3 around an axis of the rotary shaft 33 inclined at an angle of 45 degrees relative to the vertical direction.

During the grinding, for example, the grindstones 42b are rotated in such a manner that the rotational center of the workpiece W is always located on the inner side of the outermost circumference of the rotational trajectory of the grindstones 42b and on the outer side of the inner circumference of the rotational trajectory. Further, the grindstones 42b are rotated in such a manner that the outermost circumference of the rotational trajectory of the grindstones 42b does not contact a peripheral region of the back side Wb corresponding to the peripheral surplus region Wa2 of the workpiece W, or does not largely protrude to the outer side beyond the imaginary line L1. Therefore, the grindstone 42b grind a central region of the back side Wb corresponding to the device region Wa1 of the workpiece W in a circular recess form, whereby a circular recess Wb1 is formed in the central region of the back side Wb corresponding to the device region Wa1, as depicted in FIG. 4. In addition, an annular reinforcement section Wb2 which corresponds to the peripheral surplus region Wa2 and surrounds the circular recess Wb1 is formed on the back side Wb of the workpiece W, in the manner of projecting in the +Z-direction.

During the grinding, the grinding water M is supplied through the flow passage 43 in the rotary shaft 40 to the site of contact between the grindstones 42b and the workpiece W, to cool and wash the site of contact between the grindstones 42b and the back side Wb of the workpiece W. The washing water reaching the site of contact is caused by a centrifugal force generated due to the rotation of the chuck table 3 to flow through gaps between the grindstones 42b to the exterior, together with grinding swarf and the abrasive grains dropped from the grindstones 42b. Then, in the grinding method according to the present invention, the inclination of the workpiece W suction held on the chuck table 3 inclined at 45 degrees relative to 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 depicted in FIG. 4. Besides, the grinding water M is accelerated by the inclination of the workpiece W, and flows over the annular reinforcement section Wb2 at the discharge position, to be discharged to the outside of the workpiece W. In addition, since the discharge position of the grinding water M and the rotational trajectory of the grindstones 42b do not overlap each other, discharge of the grinding water M containing the abrasive grains dropped from the grindstones 42b is not obstructed. After the workpiece W is ground to a desired thickness while supplying the grinding water M, the grinding unit 4 is spaced away from the workpiece W, whereby the grinding is finished.

As has been described above, the grinding method according to the present invention includes the front side protecting step of covering the front side Wa of the workpiece W with the protective member T1, the holding step of holding the protective member T1 side of the workpiece W by the holding surface 30a of the chuck table 3 that is rotated around the rotational axis 33 inclined at an angle of 45 to 180 degrees relative to the vertical direction, after the front side protecting step is performed, and the grinding step of grinding the back side Wb of the workpiece W corresponding to the device region Wa1 by the grindstones 42b rotated around the rotational axis 40 orthogonal to the holding surface 30a while supplying the grinding water M, to form the circular recess Wb1 and the annular reinforcement section Wb2 that corresponds to the peripheral surplus region Wa2 and surrounds the circular recess Wb1. Therefore, in the grinding step, the discharge of the grinding water M containing the abrasive grains dropped from the grindstones 42b is promoted by the inclination of the workpiece W. Accordingly, the grindstones 42b is restrained from dragging in the dropped abrasive grains during grinding, and formation of scratches on the back side Wb of the workpiece W, generation of cracks in the workpiece W, and the like troubles can be prevented.

In addition, in the grinding step, the discharge position of the grinding water M containing the abrasive grains dropped from the grindstones 42b is located at the lowermost point of the chuck table 3 whose rotational axis 33 is inclined. Therefore, where the grindstones 42b are positioned in such a manner that the rotational trajectory of the grindstones 42b and the discharge position of the grinding water M do not overlap each other, the discharge of the grinding water M containing the abrasive grains dropped from the grindstones 42b is thereby performed more efficiently.

Note that the grinding method according to the present invention is not limited to the above embodiment; in addition, each of the configurations of the grinding apparatus 2 illustrated in the attached drawings is not limitative, and appropriate modifications can be made within such a range that the effects of the invention can be produced. For instance, the supply of the grinding water to the site of contact between the grindstones 42b and the workpiece W may not be conducted through the rotary shaft 40 of the grinding unit 4, and the grinding water may be supplied to the site of contact between the grindstones 42b and the workpiece W from the outside by use of a jet nozzle.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.

Claims

1. A workpiece grinding method of grinding by a grindstone a back side of a workpiece having on a front side thereof a device region in which a plurality of devices are formed and a peripheral surplus region surrounding the device region, the workpiece grinding method comprising:

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 that is rotated around a rotational 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 device region by the grindstone rotated around a rotational axis orthogonal to the holding surface while supplying grinding water, to form a circular recess and an annular reinforcement section that corresponds to the peripheral surplus region and that surrounds the circular recess,

wherein in the grinding step, discharge of the grinding water containing abrasive grains dropped from the grindstone is promoted by the inclination of the workpiece.

2. The workpiece grinding method according to claim 1, wherein the protective member is an adhesive tape.

3. The workpiece grinding method according to claim 1, wherein in the grinding step, the grindstone is positioned in such a manner that a rotational trajectory of the grindstone and a discharge position of the grinding water containing the abrasive grains dropped from the grindstone do not overlap each other since the discharge position is located at a lowermost point of the chuck table whose rotational axis is inclined.