Patent Application
20250025986
The present invention relates to a grinding method of a wafer having a circular disc shape by grinding a region on an inside relative to an outer circumferential end part of the wafer in a radial direction of the wafer to form a thin plate part and a ring-shaped reinforcing part that surrounds an outer circumferential part of the thin plate part in the wafer.
Along with popularization of System in Package (SiP), in which a plurality of device chips each thinned are stacked to be made into one package, and so forth, a grinding technique that can thin a wafer before dividing into the plurality of device chips with a high yield is demanded. As one of grinding techniques for thinning a wafer, a grinding technique referred to as TAIKO (registered trademark) (hereinafter, abbreviated as TAIKO process for convenience) is known.
In the TAIKO process, an outer circumferential part of a wafer having a device region in which a plurality of devices are formed on the front surface side is left as a ring-shaped reinforcing part by grinding a circular region on a back surface side corresponding to the device region in the wafer. This forms a recess part with a circular disc shape on the back surface side of the wafer (for example, refer to Japanese Patent Laid-open No. 2007-19461).
By employing the TAIKO process, a strength of the wafer can be made higher compared with a case in which the whole of the back surface side is evenly thinned. Therefore, the TAIKO process has an advantage that it is possible to suppress the warpage of the wafer after thinning, the breakage of the wafer at the time of conveyance, and the like.
However, when the TAIKO process is employed, at the inner circumferential edge of a top surface of the ring-shaped reinforcing part (that is, at the inner circumferential edge of an annular surface corresponding to the back surface of the wafer), chippings are formed in such a manner as to extend from the inner circumferential edge toward the outside of the wafer in the radial direction. The chippings are likely to be generated when bottom surfaces of a plurality of grinding abrasive stones forming a grinding wheel bite into the back surface of a wafer, for example.
Furthermore, after the plurality of grinding abrasive stones bite into the wafer, the grinding wheel is vertically lowered to advance the grinding. Therefore, due to contact between the outer circumferential side surface of each grinding abrasive stone and the inner circumferential side surface of the ring-shaped reinforcing part, the number of chippings further increases at the inner circumferential edge of the top surface of the ring-shaped reinforcing part. In addition, the size of existing chippings becomes larger.
The chipping at the inner circumferential edge of the top surface of the ring-shaped reinforcing part leads to the breakage of the wafer, for example. In addition, wet etching is executed for the back surface side of the wafer after the TAIKO process in some cases. When the chippings have been formed at the inner circumferential edge of the top surface of the ring-shaped reinforcing part, etching at the inner circumferential edge progresses in such a manner that the chippings extend.
This causes the inner circumferential edge to become a wave line-shaped circle having irregular recesses and projections. When the inner circumferential edge has become such a wave line-shaped circle, there are problems such as failure in formation when a metal film is formed on the back surface side of the wafer and failure in sticking of a dicing tape due to entry of an air bubble into between the back surface of the wafer and the dicing tape in the sticking of the dicing tape to the back surface side of the wafer.
The present invention is what has been made in view of such problems and intends to reduce the number and size of chippings generated at the inner circumferential edge of the top surface of a ring-shaped reinforcing part in the TAIKO process.
In accordance with an aspect of the present invention, there is provided a grinding method of a wafer having a circular disc shape by grinding a region on the inside relative to an outer circumferential edge of the wafer in the radial direction of the wafer to form a thin plate part and a ring-shaped reinforcing part that surrounds an outer circumferential part of the thin plate part in the wafer. The grinding method of a wafer includes a holding step of holding the wafer by a chuck table rotatable around a rotating shaft disposed to pass through the center of the chuck table in the radial direction and a first grinding step of forming the ring-shaped reinforcing part by lowering a grinding wheel relative to the chuck table to bring the grinding wheel close to the wafer and grinding the wafer by bottom surfaces of a plurality of grinding abrasive stones after the holding step. The grinding wheel includes a circular annular base and the plurality of grinding abrasive stones disposed along the circumferential direction of the base on one surface side of the base. An outer diameter defined by the plurality of grinding abrasive stones in a case in which the grinding wheel is rotated around a spindle disposed at a central part of the base in the radial direction is smaller than the outer diameter of the wafer. The grinding method of a wafer includes also a second grinding step of grinding an inner circumferential side surface of the ring-shaped reinforcing part by outer circumferential side surfaces of the plurality of grinding abrasive stones by moving the grinding wheel relative to the wafer toward an outside of the wafer in the radial direction after the holding step, a first separation step of separating the outer circumferential side surfaces of the plurality of grinding abrasive stones from the inner circumferential side surface of the ring-shaped reinforcing part by moving the grinding wheel relative to the wafer toward the inside of the wafer in the radial direction after the first grinding step and the second grinding step, and a second separation step of separating the bottom surfaces of the plurality of grinding abrasive stones from a top surface of the thin plate part by raising the grinding wheel relative to the chuck table after the first grinding step and the second grinding step.
Preferably, the first grinding step and the second grinding step are simultaneously ended.
Furthermore, preferably, the first separation step and the second separation step are simultaneously started.
Moreover, preferably, each of the plurality of grinding abrasive stones is a rough grinding abrasive stone.
The grinding method of a wafer according to the one aspect of the present invention includes the second grinding step of grinding the inner circumferential side surface of the ring-shaped reinforcing part by the outer circumferential side surfaces of the plurality of grinding abrasive stones by moving the grinding wheel relative to the wafer toward the outside of the wafer in the radial direction. The second grinding step can remove, to a certain extent, chippings formed in the inner circumferential side surface of the ring-shaped reinforcing part when the bottom surfaces of the plurality of grinding abrasive stones bite into the back surface of the wafer and when grinding feed to vertically lower the grinding wheel is executed.
Moreover, the grinding method of a wafer includes the first separation step of separating the outer circumferential side surfaces of the plurality of grinding abrasive stones from the inner circumferential side surface of the ring-shaped reinforcing part by moving the grinding wheel relative to the wafer toward the inside of the wafer in the radial direction. The first separation step can shorten the time of the contact between the outer circumferential side surfaces of the plurality of grinding abrasive stones and the inner circumferential side surface of the ring-shaped reinforcing part compared with the case in which the grinding wheel is vertically raised to be moved to the upper side relative to the top surface of the ring-shaped reinforcing part in the state in which the outer circumferential side surfaces of the plurality of grinding abrasive stones are in contact with the inner circumferential side surface of the ring-shaped reinforcing part. Therefore, the number and length of chippings generated at the inner circumferential edge of the top surface of the ring-shaped reinforcing part can be reduced.
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 some preferred embodiments of the invention.
An embodiment according to one aspect of the present invention will be described with reference to the accompanying drawings.
First, the wafer 11 will be described with reference to
In grinding of the wafer 11, part of the wafer 11 is thinned by grinding a circular region in a back surface 11b corresponding to a circular region containing the plurality of devices 15 (that is, device region 15a) in the front surface 11a. A protective component 17 that has substantially the same diameter as the wafer 11 and is made of a resin is stuck to the front surface 11a before the wafer 11 is ground.
For example, the protective component 17 is a tape having a base layer and an adhesive layer and the adhesive layer of the tape is stuck to the front surface 11a of the wafer 11. However, the protective component 17 may have only the base layer without having the adhesive layer. In this case, the protective component 17 is stuck to the front surface 11a by thermocompression bonding. Sticking the protective component 17 to the front surface 11a can alleviate shock to the devices 15 at the time of grinding.
The wafer 11 is ground in a form of a layer-stacking body 19 in which the wafer 11 and the protective component 17 are stuck to each other. Next, a grinding apparatus 2 will be described with reference to
As illustrated in
The upper surface of the porous plate 8 has a circular cone shape in sectional view. A central part of the porous plate 8 protrudes by, for example, 20 μm compared with an outer circumferential part. Note that the amount of protrusion of the central part of the porous plate 8 is exaggerated in the drawing for convenience of explanation. The upper surface of the porous plate 8 and the upper surface of the frame body 6 are substantially flush with each other and function as a holding surface 4a for sucking and holding the wafer 11 with the interposition of the protective component 17. The porous plate 8 is connected to a suction source (not illustrated) such as a vacuum pump through a predetermined flow path.
A rotational drive source (not illustrated) such as a motor for rotating the chuck table 4 is disposed at a lower part of the frame body 6. The chuck table 4 can rotate around a rotating shaft 4b by power of the rotational drive source. Note that the rotating shaft 4b is illustrated with simplification by a one-dot chain line in
The chuck table 4 and the rotational drive source are supported movably along the X-axis direction by an X-axis direction movement mechanism (not illustrated) including a ball screw (not illustrated). As illustrated in
Part of a spindle 12 with a circular column shape is rotatably housed in a space inside the spindle housing. In the first embodiment, the longitudinal direction of the spindle housing and the spindle 12 is disposed along the Z-axis direction. A rotational drive source (not illustrated) such as a motor is disposed at part of the upper side of the spindle 12. A lower end part of the spindle 12 protrudes to the lower side relative to a lower end part of the spindle housing.
A central part of the upper surface of a mount 14 with a circular disc shape is fixed to the lower end part of the spindle 12. A circular annular rough grinding wheel (grinding wheel) 16 is fixed to the lower surface of the mount 14 by using a fixing member (not illustrated) such as a bolt. In this manner, the rough grinding wheel 16 is mounted to the lower end part of the spindle 12 with the interposition of the mount 14.
The rough grinding wheel 16 includes a circular annular wheel base (base) 18 formed of a metal such as an aluminum alloy. The spindle 12 is disposed at a central part of the wheel base 18 in the radial direction. A center 18a of the wheel base 18 in the radial direction, a center 14a of the mount 14 in the radial direction, and a rotation center 12a of the spindle 12 substantially correspond with each other.
On the side of a bottom surface (one surface) 18b of the wheel base 18, a plurality of rough grinding abrasive stones (grinding abrasive stones) 20 are disposed at substantially equal intervals along the circumferential direction of the wheel base 18. The rough grinding abrasive stones 20 contain abrasive grains formed of cubic boron nitride (cBN), diamond, or the like and a bond material such as a vitrified bond or resin bond for fixing the abrasive grains. The average grain diameter of the abrasive grains of the rough grinding abrasive stones 20 is larger compared with the average grain diameter of generally-called finish grinding abrasive stones.
As the abrasive grains of the rough grinding abrasive stones 20, for example, abrasive grains having a grain size of #240 to #1200, preferably #240 to #1000, are used. The grain size is described in JIS R6001-2:2017 (Bonded Abrasives—Determination and Designation of Grain Size Distribution—Part 2: Microgrits) of the JIS standards established by the Japanese Industrial Standards Committee. Note that the grain size of #240 to #1200 and the grain size of #240 to #1000 may be evaluated by a sedimentation test method or may be evaluated by an electrical resistance test method.
The outer diameter of the plurality of rough grinding abrasive stones 20 defined by outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 is smaller than the outer diameter of the wafer 11 and is larger than the radius of the device region 15a in the front surface 11a. Moreover, the inner diameter of the plurality of rough grinding abrasive stones 20 defined by inner circumferential side surfaces of the plurality of rough grinding abrasive stones 20 is smaller than the radius of the device region 15a in the front surface 11a. In one example, the segment width of one rough grinding abrasive stone 20 (that is, the length of one rough grinding abrasive stone 20 in the radial direction of the wheel base 18) is 4 mm. Therefore, the difference between the outer diameter and the inner diameter of the plurality of rough grinding abrasive stones 20 is 8 mm (=4 mm×2).
As described above, the rotation center 12a of the spindle 12 substantially corresponds with the center 18a of the wheel base 18 in the radial direction. However, deviation of approximately 100 μm to 300 μm is permitted. If such deviation exists between the rotation center 12a and the center 18a, rotational runout of the plurality of rough grinding abrasive stones 20 occurs when the rough grinding wheel 16 is rotated around the spindle 12. Note that, even if the rotational runout occurs, the outer diameter defined by the plurality of rough grinding abrasive stones 20 when the rough grinding wheel 16 is rotated around the spindle 12 is smaller than the outer diameter of the wafer 11 and is larger than the radius of the device region 15a.
In grinding, on the basis of the holding surface 4a with the circular cone shape and the minute tilt of the rotating shaft 4b, the wafer 11 is ground in a region corresponding to not the whole of the circumference of a circular ring formed by the plurality of rough grinding abrasive stones 20 (see
Next, the grinding method of the wafer 11 will be described according to
Moreover, the position of the rough grinding unit 10 in the X-axis direction is adjusted by the X-axis direction movement mechanism to cause the trajectory of the plurality of rough grinding abrasive stones 20 to overlap with the rotating shaft 4b of the chuck table 4 in plan view. In this state, the rough grinding wheel 16 is lowered relative to the chuck table 4 by moving the rough grinding unit 10 downward by the Z-axis direction movement mechanism. In this manner, the rough grinding wheel 16 is brought close to the wafer 11 and the circular region in the back surface 11b that is located inside relative to an outer circumferential edge 11d of the wafer 11 in a radial direction 11c of the wafer 11 and corresponds to the device region 15a is ground by bottom surfaces 20a of the plurality of rough grinding abrasive stones 20.
Thereby, as illustrated in
Incidentally, when the bottom surfaces 20a of the rough grinding abrasive stones 20 get contact with the back surface 11b (that is, at the moment when the rough grinding wheel 16 bites into the back surface lib of the wafer 11), chippings lie (see
If the chippings lie remain in the ring-shaped reinforcing part 21b, this leads to the breakage of the wafer 11, failure in formation of a metal film in the back surface lib, failure in sticking of a dicing tape to the back surface lib, and the like as described above. Thus, in the first embodiment, after the first grinding step S32, the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b is ground by the outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 to enlarge the diameter of the recess part 21c (second grinding step S34).
The inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b is ground by moving the rough grinding wheel 16 relative to the wafer 11 toward the outside of the wafer 11 in the radial direction 11c in this manner. One example of grinding conditions in the second grinding step S34 will be indicated below.
Incidentally, in the normal TAIKO process, after the first grinding step S32, the rough grinding wheel 16 is drawn out from the recess part 21c and is moved to the upper side relative to the wafer 11 by vertically raising the rough grinding unit 10 by the Z-axis direction movement mechanism. However, at this time, the rough grinding wheel 16 rises in the state in which the outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 are in contact with the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b. Therefore, at the inner circumferential edge of the top surface 21b2 of the ring-shaped reinforcing part 21b, new chippings lie are formed and the size of the existing chippings lie becomes larger.
Against this problem, a consideration is being made about devising a grinding mode to suppress the contact between the outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 and the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b when the rough grinding wheel 16 is raised. Specifically, first, the back surface lib is ground by lowering the rough grinding wheel 16 along the Z-axis direction and moving the chuck table 4 along the X-axis direction to bring the rough grinding wheel 16 closer to the center of the wafer 11 in the radial direction 11c.
This causes the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b to become not a circular cylindrical shape but an inverted truncated cone shape. Subsequently, the rough grinding wheel 16 is raised straight along the Z-axis direction. At this time, the outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 do not get contact with the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b. However, when such a grinding mode is employed, the inner circumferential side surface 21b1 becomes the inverted truncated cone shape and therefore there arises a new problem that the range that can be used as the device region 15a becomes smaller correspondingly. Moreover, the chippings lie formed in the top surface 21b2 when the bottom surfaces 20a of the plurality of rough grinding abrasive stones 20 bite into the back surface lib of the wafer 11 still remain.
In order to solve this problem, in the first embodiment, as illustrated in
By the first separation step S42, the time of the contact between the outer circumferential side surfaces 20b and the inner circumferential side surface 21b1 can be shortened compared with the case in which the rough grinding wheel 16 is vertically raised to be moved to the upper side relative to the top surface 21b2 of the ring-shaped reinforcing part 21b in the state in which the outer circumferential side surfaces 20b of the plurality of rough grinding abrasive stones 20 are in contact with the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b. Therefore, the number and length of chippings lie generated at the inner circumferential edge of the top surface 21b2 of the ring-shaped reinforcing part 21b can be reduced.
In the first embodiment, after the first separation step S42, as illustrated in
In the first embodiment, the chippings lie formed in the inner circumferential side surface 21b1 of the ring-shaped reinforcing part 21b can be removed to a certain extent by the second grinding step S34. Furthermore, by the first separation step S42, the number and length of chippings lie generated at the inner circumferential edge of the top surface 21b2 of the ring-shaped reinforcing part 21b can be reduced compared with the case in which the normal TAIKO process is employed.
Note that finish grinding is executed for the thin plate part 21a after the end of the flow illustrated in
As the abrasive grains of the finish grinding abrasive stones, for example, abrasive grains having a grain size of #5000 to #10000 are used. The grain size may be evaluated by a sedimentation test method or may be evaluated by an electrical resistance test method. The grain size that is not described in JIS R6001-2:2017 follows or conforms to a representation ordinarily used in the business field that manufactures and sells abrasive stones.
Note that, in the finish grinding, the thin plate part 21a located inside relative to the ring-shaped reinforcing part 21b in the radial direction 11c of the wafer 11 is ground in such a direction as to advance from the back surface 11b toward the front surface 11a. That is, the finish grinding abrasive stones do not get contact with the ring-shaped reinforcing part 21b and therefore new chippings lie are not formed in the inner circumferential side surface 21b1 (including also the inner circumferential edge of the top surface 21b2) of the ring-shaped reinforcing part 21b.
Next, a second embodiment will be described with reference to
Next, a third embodiment will be described with reference to
Next, a fourth embodiment will be described with reference to
The second grinding step S34 may be started later than the first grinding step S32 as illustrated by a solid line frame in
In the fourth embodiment, the total time required for the grinding processing can be further shortened compared with the first to third embodiments. Besides, structures, methods, and so forth according to the above-described embodiments can be carried out with appropriate changes without departing from the range of the object of the present invention. Various modification examples that can be applied to the above-described embodiments will be described below.
In the above-described embodiments, approach and separation between the rough grinding wheel 16 and the chuck table 4 in the Z-axis direction are executed by the Z-axis direction movement mechanism fixed to the rough grinding unit 10. However, instead of or in addition to this, the chuck table 4 may be moved along the Z-axis direction.
Furthermore, in the above-described embodiments, the movement of the rough grinding unit 10 toward the outside and the inside in the radial direction 11c of the wafer 11 is executed by the X-axis direction movement mechanism that supports the chuck table 4. However, instead of or in addition to this, the rough grinding unit 10 may be moved along the X-axis direction.
Moreover, in the above-described embodiments, the longitudinal direction of the spindle 12 is disposed substantially in parallel to the Z-axis direction and the rotating shaft 4b of the chuck table 4 is tilted from the Z-axis direction. However, as long as the thin plate part 21a and the ring-shaped reinforcing part 21b can be formed, the longitudinal direction of the spindle 12 may be tilted from the Z-axis direction and the rotating shaft 4b of the chuck table 4 may be disposed substantially in parallel to the Z-axis direction.
Furthermore, the holding surface 4a of the chuck table 4 has the circular cone shape in the above-described embodiments. However, the holding surface 4a may have a dual recess shape instead of this. When having the dual recess shape, the holding surface 4a has a shape in which an outer circumferential end part and a central part protrude compared with an intermediate region between the outer circumferential end part and the central part in sectional view. The intermediate region between the outer circumferential end part and the central part hollows compared with the outer circumferential end part and the central part by at most, for example, a predetermined value that is equal to or larger than 1 μm and is equal to or smaller than 20 μm, and a smooth curved surface is formed in the holding surface 4a excluding the outer circumferential end part and the central part.
Incidentally, the outer diameter defined by the plurality of rough grinding abrasive stones 20 when the rough grinding wheel 16 is rotated around the spindle 12 may be smaller than the radius of the device region 15a. In the case in which the rough grinding wheel 16 with such a small diameter is employed, when the wafer 11 is ground according to the flow illustrated in
The present invention is not limited to the details of the above described preferred embodiments. 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 |
|---|---|---|---|
| 2023-116858 | Jul 2023 | JP | national |
