Patent Application
20220324082
The present invention relates to a processing method of a workpiece, which is useful in grinding workpieces, for example, wafers.
In a manufacturing process of device chips, a wafer with devices formed in respective regions defined by a plurality of intersecting streets (scheduled division lines) is used. By dividing this wafer along the streets, the device chips are obtained with the devices included therein respectively. Such device chips are incorporated in various kinds of electronic equipment such as mobile phones and personal computers.
In recent years, along with the downsizing of electronic equipment, there is an increasing need for thinner device chips. Before dividing a wafer, a thinning step may therefore be performed by grinding the wafer with a grinding apparatus. The grinding apparatus includes a chuck table that holds a workpiece thereon, and a grinding unit that applies grinding processing to the workpiece. A spindle is incorporated in the grinding unit, and a grinding wheel with grinding stones included thereon is mounted on a distal end portion of the spindle. The grinding apparatus grinds and thins the workpiece by rotating the grinding wheel and bringing the rotating grinding stones into contact with the workpiece (see JP 2014-124690A).
When a workpiece is ground by a grinding apparatus, coarse grinding and finish grinding are performed sequentially. Described specifically, the workpiece is first ground with grinding stones containing abrasive grains of large grain size until the workpiece is thinned to a predetermined thickness (coarse grinding step). The workpiece is then ground with grinding stones containing abrasive grains of small grain size until the workpiece is thinned to a finish thickness (finish grinding step). The combined use of coarse grinding and finish grinding allows fewer processing marks to remain on the workpiece after the grinding while making the grinding time shorter.
In a final stage of the coarse grinding, however, the grinding stones with the abrasive grains of the large grain size contained therein hit an outer peripheral portion of the workpiece which has been thinned and reduced in rigidity. As a result, processing failures such as chipping and/or cracking may occur at the outer peripheral portion of the workpiece. In particular, processing (chamfering) may be applied to remove corner portions formed on outer peripheral edges of the workpiece. In this case, the workpiece is formed at a side surface thereof into a curve shape from a front surface toward a back surface thereof. When the chamfered workpiece is thinned, an outer peripheral portion of the workpiece is formed into a sharp thin shape (sharp edge shape), so that, in the final stage of the coarse grinding step, processing failures are prone to occur at the outer peripheral portion of the workpiece.
Accordingly, the grinding of the workpiece is switched from coarse grinding to finish grinding before the workpiece is thinned to such an extent that processing failures would become prone to occur at the outer peripheral portion of the workpiece. Owing to this switch, after the workpiece has been thinned to some extent, the workpiece is ground with the grinding stones with the abrasive grains of the small grain size contained therein, and therefore the occurrence of processing failures at the outer peripheral portion of the workpiece is suppressed. Nonetheless, the progress of grinding of the workpiece is slow in the finish grinding compared with the coarse grinding, so that time takes to thin the workpiece. The grinding time required until the thickness of the workpiece reaches a target value (finish thickness) therefore increases if the removal amount of the workpiece by coarse grinding is reduced to suppress the occurrence of processing failures and the removal amount of the workpiece by finish grinding is increased.
With the foregoing problem in view, the present invention has, as an object thereof, the provision of a processing method of a workpiece, which can shorten the grinding time while the occurrence of processing failures is suppressed.
In accordance with an aspect of the present invention, there is provided a processing method of grinding a workpiece. The processing method includes a holding step of holding the workpiece on a side of a front surface thereof on a holding surface of a chuck table having an axis of rotation set along a direction perpendicular to the holding surface, a coarse grinding step of, after performing the holding step, adjusting a positional relationship between the chuck table and a first grinding wheel such that a moving path of first grinding stones, which are included on the first grinding wheel and contain first abrasive grains, overlaps the axis of rotation of the chuck table, and grinding the workpiece on a side of a back surface thereof with the first grinding stones until the workpiece has a predetermined thickness, an auxiliary grinding step of, after performing the coarse grinding step, adjusting the positional relationship between the chuck table and the first grinding wheel such that the first grinding stones overlap an inner side of an outer peripheral edge of the workpiece, and grinding the workpiece on the side of the back surface thereof with the first grinding stones such that an unground region remains at an outer peripheral portion of the workpiece, an unground region grinding step of, after performing the auxiliary grinding step, adjusting a positional relationship between the chuck table and a second grinding wheel such that a moving path of second grinding stones, which are included on the second grinding wheel and contain second abrasive grains having a smaller average grain size than that of the first abrasive grains, overlaps the axis of rotation of the chuck table, and grinding the unground region with the second grinding stones, and a finish grinding step of, after performing the unground region grinding step, grinding the workpiece on the side of the back surface thereof with the second grinding stones until the workpiece has a predetermined finish thickness.
Preferably, the processing method may further include a separation step of, after performing the coarse grinding step and before performing the auxiliary grinding step, separating the workpiece and the first grinding stones from each other.
In the processing method according to the aspect of the present invention, the first grinding stones with the abrasive grains of the large grain size contained therein and the second grinding stones with the abrasive grains of the small grain size contained therein are used. Following the coarse grinding of the workpiece with the first grinding stones, the workpiece is ground with the first grinding stones such that the unground region remains at the outer peripheral portion of the workpiece. Subsequently, with the second grinding stones, the unground region is ground and removed, and the finish grinding of the workpiece is performed.
If the above-described processing method is used, the outer peripheral portion of the workpiece is ground with the second grinding stones with the abrasive grains of the small grain size contained therein, so that the occurrence of processing failures at the outer peripheral portion of the workpiece is suppressed. Further, the workpiece is beforehand removed at a central portion thereof with the first grinding stones with the abrasive grains of the large grain size contained therein before the outer peripheral portion of the workpiece is ground with the second grinding stones. The processing feed rate can thus be increased when the outer peripheral portion of the workpiece is ground with the second grinding stones. It is accordingly possible to shorten the time to grind the workpiece while the occurrence of processing failures at the outer peripheral portion of the workpiece is suppressed.
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 depicting or showing a preferred embodiment of the invention.
With reference to the attached drawings, an embodiment of the aspect of the present invention will be described. First, a description will be made about a configuration example of a grinding apparatus usable in a processing method of a workpiece according to the present embodiment.
The grinding apparatus 2 includes a bed 4, which supports or accommodates individual constituent elements that make up the grinding apparatus 2. On a side of an upper surface of the base 4, a regular parallelepipedal recessed portion 4a is disposed. Inside the recessed portion 4a, a chuck table (holding table) 6 is disposed to hold a workpiece 11 as a target of processing by the grinding apparatus 2. The chuck table 6 has an upper surface, which is a flat surface substantially parallel to the X-axis direction and Y-axis direction, and a holding surface 6a that holds the workpiece 11 thereon.
Inside the recessed portion 4a, a moving mechanism (moving unit) 8 is also disposed. The moving mechanism 8 is connected to the chuck table 6 and moves the chuck table 6 along the X-axis direction. Described specifically, the moving mechanism 8 includes a ball screw 10 arranged along the X-axis direction. The ball screw 10 is in threaded engagement with a nut portion (not depicted) connected to the chuck table 6. To an end portion of the ball screw 10, a pulse motor 12 is connected to rotate the ball screw 10. When the ball screw 10 is rotated by the pulse motor 12, the chuck table 6 moves along the X-axis direction.
To the chuck table 6, a rotary drive source (not depicted) such as a motor is connected. The rotary drive source rotates the chuck table 6 about an axis of rotation that is substantially perpendicular to the holding surface 6a (substantially parallel to the Z-axis direction). In other words, the axis of rotation of the chuck table 6 is set along a direction perpendicular to the holding surface 6a.
Behind the chuck table 6 and the moving mechanism 8 (on the right side of
Described specifically, the moving mechanism 16 includes a pair of guide rails 18 fixed on the side of the front surface of the support structure 14. The paired guide rails 18 are arranged along the Z-axis direction in a state that they are apart from each other in the Y-axis direction. On the paired guide rails 18, a planar moving plate 20 is mounted on and slidably along the guide rails 18. On a side of a back surface (on a rearward side) of the moving plate 20, a nut portion 22 is disposed. Between the paired guide rails 18, a ball screw 24 is disposed along the Z-axis direction, and the ball screw 24 is in threaded engagement with the nut portion 22. To an end portion of the ball screw 24, a pulse motor 26 is connected to rotate the ball screw 24. When the ball screw 24 is rotated by the pulse motor 26, the moving plate 20 is moved (lifted or lowered) in the Z-axis direction along the guide rails 18.
On a side of a front surface (on a forward side) of the moving plate 20, the grinding unit 28 is mounted to grind the workpiece 11. The grinding unit 28 includes a hollow cylindrical support member 30 fixed on the side of the front surface of the moving plate 20. In the support member 30, a cylindrical housing 32 is accommodated. The housing 32 is supported on a side of a lower surface thereof on a bottom surface of the support member 30 via a cushion member 34 made of rubber or the like. In the housing 32, a cylindrical spindle 36 that is arranged along the Z-axis direction is accommodated. A distal end portion (lower end portion) of the spindle 36 is exposed from the housing 32, and projects downward from a lower surface of the support member 30 through an opening disposed in a bottom portion of the support member 30. To a proximal end portion (upper end portion) of the spindle 36, a rotary drive source (not depicted) such as a motor is connected to rotate the spindle 36. On the distal end portion of the spindle 36, a disc-shaped mount 38 made of metal or the like is fixed. On a side of a lower surface of the mount 38, an annular grinding wheel 40 is mounted to grind the workpiece 11. The grinding wheel 40 is fixed to the mount 38, for example, by fixing means such as bolts.
The grinding wheel 40 includes an annular base 42, which is made of metal such as aluminum or stainless steel and is formed with substantially the same diameter as the mount 38. The base 42 is fixed on a side of an upper surface thereof on the side of the lower surface of the mount 38. On a side of a lower surface of the base 42, a plurality of grinding stones 44 is fixed. The grinding stones 44 are each formed, for example, in a regular parallelepipedal shape, and are arrayed in an annular configuration at substantially equal intervals along the peripheral direction of the base 42. The grinding stones 44 have been formed by fixing abrasive grains of diamond, cubic boron nitride (cBN), or the like with a binder (bonding material) such as a metal bond, resin bond, or vitrified bond. However, no limitations are imposed on the material, shape, structure, size, and the like of the grinding stones 44. Further, the number of the grinding stones 44 can be set as desired.
By power transmitted from the rotary drive source, which is connected to the proximal end portion of the spindle 36, via the spindle 36 and the mount 38, the grinding wheel 40 is rotated about an axis of rotation that is substantially perpendicular to the holding surface 6a of the chuck table 6 (substantially parallel to the Z-axis direction). In other words, the axis of rotation of the grinding wheel 40 is set along a direction perpendicular to the holding surface 6a.
The individual constituent elements (the chuck table 6, the moving mechanism 8, the moving mechanism 16, the grinding unit 28, and so on) of the grinding apparatus 2 are connected to a control unit (control part, control device) 46 that controls the grinding apparatus 2. By generating control signals for controlling operations of the constituent elements of the grinding apparatus 2, the control unit 46 controls the operation of the grinding apparatus 2. The control unit 46 is configured, for example, by a computer. Described specifically, the control unit 46 includes a computing section that performs computing needed for the operation of the grinding apparatus 2, and a storage section that stores a variety of information (data, a program, and so on) to be used for the operation of the grinding apparatus 2. The computing section is configured including a processor such as a central processing unit (CPU). On the other hand, the storage section is configured including memories, such as a read only memory (ROM) and a random access memory (RAM), which function as a main storage device and an auxiliary storage device.
While being held on the chuck table 6, the workpiece 11 is ground with the grinding unit 28. Described specifically, the rotating grinding stones 44 are brought into contact with the side of the upper surface of the workpiece 11 held on the chuck table 6, whereby the workpiece 11 is ground off on the side of the upper surface thereof. As a consequence, the workpiece 11 is ground and thinned.
The workpiece 11 is defined into a plurality of rectangular regions by a plurality of streets (scheduled division lines) 13 arrayed in a grid pattern such that the streets 13 intersect each other. On the side of the front surface 11a of the regions defined by the streets 13, devices 15 such as integrated circuits (ICs), large scale integration (LSI) circuits, light emitting diodes (LEDs), or micro electro mechanical systems (MEMS) devices are formed, respectively. The workpiece 11 includes a substantially circular device region 17 where the devices 15 are formed, and an annular outer peripheral margin 19 which surrounds the device region 17. The outer peripheral margin 19 forms an annular region of a predetermined width (for example, approximately 2 mm) that includes the outer peripheral edge of the workpiece 11. In
However, no limitations are imposed on the material, shape, structure, size, and the like of the workpiece 11. For example, the workpiece 11 may be a wafer (substrate) made of semiconductor (GaAs, InP, GaN, SiC, or the like) other than silicon, glass, ceramics, resin, metal, or the like. Further, no limitations are imposed either on the type, number, shape, structure, size, arrangement, and the like of the devices 15, and no devices 15 may be formed on the workpiece 11. Furthermore, the workpiece 11 may also be a package substrate such as a chip size package (CSP) substrate or a quad flat non-leaded package (QFN) substrate.
A description will next be made about a specific example of the workpiece processing method by use of the grinding apparatus 2. In the present embodiment, the workpiece 11 is ground using a grinding wheel 40A (see
First, the workpiece 11 is held on the side of the front surface 11a thereof by the holding surface 6a of the chuck table 6 (holding step).
The workpiece 11 is placed on the chuck table 6 such that the workpiece 11 faces the holding surface 6a on the side of the front surface 11a and is exposed upward on the side of the back surface 11b. When a suction force (negative pressure) of the suction source is applied to the holding surface 6a in the above-described state, the workpiece 11 is held on the side of the front surface 11a under suction on the chuck table 6. On the side of the front surface 11a of the workpiece 11, a protective sheet may be bonded to protect the workpiece 11. The protective sheet may include, for example, a film-shaped base material formed in a circular shape, and an adhesive layer (glue layer) applied on the base material. The base material is made of resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy-based, acrylic, or rubber-based adhesive, or the like. By the protective sheet bonded to the side of the front surface 11a of the workpiece 11, the devices 15 (see FIG. 3) formed on the workpiece 11 are protected. The workpiece 11 is held on the holding surface 6a of the chuck table 6 via the protective sheet.
The chuck table 6 with the workpiece 11 held thereon is positioned below the grinding unit 28 by the moving mechanism 8 (see
When the spindle 36 is rotated, the grinding stones 44A each rotate about an axis of rotation that is substantially perpendicular to the holding surface 6a of the chuck table 6. In other words, the grinding stones 44A move along an annular moving path (rotation path) that is substantially parallel to a horizontal plane (X-Y plane). In
The grinding wheel 40A is designed such that the outer diameter φ of the moving path of the grinding stones 44A becomes equal to or greater than a radius Rw of the workpiece 11 and smaller than a diameter φw of the workpiece 11. It is particularly preferred to design the grinding wheel 40A such that the inner diameter of the moving path of the grinding stones 44A becomes equal to or greater than the radius Rw of the workpiece 11. If the workpiece 11 is an 8 inch silicon wafer, for example, the grinding stones 44A are arrayed such that the outer diameter φ of the moving path of the grinding stones 44A becomes equal to or greater than 100 mm and smaller than 200 mm.
Next, the workpiece 11 is ground on the side of the back surface 11b thereof with the grinding stones 44A (coarse grinding step).
In the coarse grinding step, a positional relationship between the chuck table 6 and the grinding wheel 40A is adjusted such that the moving path of the grinding stones 44A overlaps the axis of rotation of the chuck table 6. Described specifically, the chuck table 6 is moved by the moving mechanism 8 (see
The grinding unit 28 is then lowered by the moving mechanism 16 (see
It is to be noted that a grinding fluid supply channel (not illustrated) is disposed inside or near the grinding unit 28 to supply fluid (grinding fluid) such as pure water. When the workpiece 11 is ground by the grinding unit 28, the grinding fluid is supplied to the workpiece 11 and the grinding stones 44A. As a consequence, the workpiece 11 and the grinding stones 44A are cooled, and in addition, debris (ground debris) caused by the grinding processing is washed away.
Next, the grinding stones 44A are separated from the workpiece 11 (separation step).
In the separation step, the grinding unit 28 is slightly lifted by the moving mechanism 16 (see
Next, the workpiece 11 is ground on the side of the back surface 11b thereof with the grinding stones 44A such that an unground region remains at an outer peripheral portion of the workpiece 11 (auxiliary grinding step).
In the auxiliary grinding step, the positional relationship between the chuck table 6 and the grinding wheel 40A is adjusted such that the grinding stones 44A overlaps an inner side of the outer peripheral edge of the workpiece 11. Described specifically, the chuck table 6 is moved by the moving mechanism 8 (see
The grinding unit 28 is then lowered by the moving mechanism 16 (see
When the grinding stones 44A come, at the lower surfaces thereof, into contact with the back surface 11b of the workpiece 11, the workpiece 11 is ground off on the side of the back surface 11b of the central portion thereof with the grinding stones 44A. As a result, an annular hollow 11c is formed in the central portion of the workpiece 11. On the other hand, the grinding stones 44A do not come into contact with the outer peripheral portion of the workpiece 11, so that the annular unground region 11d remains without being ground with the grinding stones 44A. When the hollow 11c is further ground to a predetermined depth, the lowering of the grinding unit 28 is stopped, and the auxiliary grinding of the workpiece 11 is completed.
It is to be noted that the separation step (see
After the completion of the auxiliary grinding step, the grinding unit 28 is lifted by the moving mechanism 16 (see
The grinding wheel 40B includes an annular base (second base) 42B, and a plurality of grinding stones (second grinding stones) 44B. The base 42B and the grinding stones 44B are similar in material, structure, shape, and the like to the above-mentioned base 42A and grinding stones 44A, respectively. However, abrasive grains (second abrasive grains) contained in the grinding stones 44B have an average grain size smaller than that of the grits (first grits) contained in the grinding stones 44A. As the second abrasive grains, diamond having an average grain size of 0.5 μm or greater and 20 μm or smaller is used, for example. No particular limitation is imposed on the outer diameter of a moving path of the grinding stones 44B insofar as it is equal to or greater than the radius Rw (see
Next, the unground regions 11d and 11e are ground with the grinding stones 44B (unground region grinding step).
In the unground region grinding step, the positional relationship between the chuck table 6 and the grinding wheel such 40B is adjusted that the moving path of the grinding stones 44B overlaps the axis of rotation of the chuck table 6. Described specifically, the chuck table 6 is moved by the moving mechanism 8 (see
The grinding unit 28 is then lowered by the moving mechanism 16 (see
As described above, the unground region 11d that remains at the outer peripheral portion of the workpiece 11 is ground and removed with the grinding stones 44B, which contain the abrasive grains of the small grain size, in the unground region grinding step. Therefore, processing failures such as chipping and/or cracking hardly occur at the outer peripheral portion of the workpiece 11 even if the grinding stones 44B hit the outer peripheral portion of the workpiece 11 when the unground region 11d is removed. In the unground region grinding step, the workpiece 11 with the center portion thereof locally thinned by the formation of the hollow 11c is ground with the grinding stones 44B. The removal amount hence decreases compared with a case in which the hollow 11c is not formed and the workpiece 11 is ground on the side of the entire back surface 11b thereof. This enables to quickly remove the unground regions 11d and 11e by increasing the feed rate.
Next, the workpiece 11 is ground on the side of the back surface 11b thereof with the grinding stones 44B (finish grinding step).
With the chuck table 6 and the grinding wheel 40B kept rotating after the completion of the unground region grinding step, the finish grinding step is performed by lowering the grinding wheel 40B. When the procedure proceeds from the unground region grinding step to the finish grinding step, it is preferred to reduce the lowering speed of the grinding wheel 40B and hence to make the lowering speed of the grinding wheel 40B slower in the finish grinding step than in the unground region grinding step. In this manner, the surface roughness of the workpiece 11 can be effectively reduced through the finish grinding. For example, the rotational speed of the chuck table 6 is set at 60 rpm or higher and 300 rpm or lower, and the rotational speed of the grinding wheel 40B is set at 3,000 rpm or higher and 6,000 rpm or lower. Further, the lowering speed (processing feed rate) of the grinding wheel 40B is set, for example, at 0.1 μm/s or higher and 1 μm/s or lower.
If the grinding wheel 40B is lowered further after the unground region grinding step, the workpiece 11 is ground off on the side of the entire back surface 11b thereof with the grinding stones 44B, and is thinned to a predetermined thickness. In the finish grinding step, the workpiece 11 is ground until its thickness reaches the target value (finish thickness) of the thickness of the final workpiece 11. Subsequently, the lowering of the grinding wheel 40B is stopped, and the finish grinding of the workpiece 11 is completed.
The above-described grinding of the workpiece 11 by the grinding apparatus 2 is realized through control of operations of the individual constituent elements of the grinding apparatus 2 by the control unit 46 (see
The workpiece 11 which has been ground by the grinding apparatus 2 is cut, for example, along the streets 13 (see
As described above, the grinding stones 44A with the abrasive grains of the large grain size contained therein and the grinding stones 44B with the abrasive grains of the small grain size contained therein are used in the processing method according to the present embodiment. Following the coarse grinding of the workpiece 11 with the grinding stones 44A, the workpiece 11 is ground with the grinding stones 44A such that the unground region 11d remains at the outer peripheral portion of the workpiece 11. Subsequently, with the grinding stones 44B, the unground region 11d is ground and removed, and the finish grinding of the workpiece 11 is performed. If the above-described processing method is used, the outer peripheral portion of the workpiece 11 is ground with the grinding stones 44B with the abrasive grains of the small grain size contained therein, so that the occurrence of processing failures at the outer peripheral portion of the workpiece 11 is suppressed. Further, the workpiece 11 is beforehand removed at the central portion thereof with the grinding stones 44A with the abrasive grains of the large grain size contained therein before the outer peripheral portion of the workpiece 11 is ground with the grinding stones 44B. The processing feed rate can thus be increased when the outer peripheral portion of the workpiece 11 is ground with the grinding stones 44B. It is accordingly possible to shorten the time to grind the workpiece 11 while the occurrence of processing failures at the outer peripheral portion of the workpiece 11 is suppressed.
In the above-described embodiment, the description is made about the case in which, after the coarse grinding step and the auxiliary grinding step have been performed, the grinding wheel 40A (see
Moreover, the above-described structures, methods, and the like according to the above embodiment can be practiced with modifications as needed within the scope not departing from the objects of the present invention.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-065241 | Apr 2021 | JP | national |
