This invention relates to a polishing tool, especially a polishing tool suitable for polishing a back side of a semiconductor wafer having processing distortion, and a polishing method and apparatus using such a polishing tool.
In a process for manufacturing semiconductor chips, many rectangular areas are demarcated by streets arranged in a lattice pattern on a face side of a semiconductor wafer, and semiconductor circuits are disposed in the respective rectangular areas. The semiconductor wafer is divided along the streets to convert the rectangular areas into semiconductor chips. To make the semiconductor chips compact and lightweight, it is often desired to grind a back side of the semiconductor wafer before separation of the rectangular areas into individual chips, thereby decreasing the thickness of the semiconductor wafer. Grinding of the back side of the semiconductor wafer is usually performed by pressing grinding means against the back side of the semiconductor wafer while rotating the grinding means at a high speed, the grinding means being formed by bonding diamond abrasive grains with a suitable bonding agent such as a resin bonding agent. When the back side of the semiconductor wafer is ground by such a grinding method, so-called processing distortion is generated in the back side of the semiconductor wafer, thereby decreasing transverse rupture strength considerably. To eliminate processing distortion generated in the back side of the semiconductor wafer and thus avoid a decrease in transverse rupture strength, it has been proposed to polish the ground back side of the semiconductor wafer with the use of free abrasive grains, or to chemically etch the ground back side of the semiconductor wafer with the use of an etching solution containing nitric acid and hydrofluoric acid. Further, Japanese Unexamined Patent Publication No. 2000-343440 discloses the polishing of a back side of a semiconductor wafer with the use of polishing means constituted by dispersing abrasive grains in a suitable cloth.
Polishing using free abrasive grains, however, involves the problems that the supply, recovery, etc. of the free abrasive grains require tiresome procedure, leading to a low efficiency, and that the free abrasive grains used in large amounts have to be disposed of as industrial wastes. Chemical etching using an etching solution also poses the problem that the etching solution used in a large amount has to be disposed of as industrial waste. Polishing by polishing means constituted by dispersing abrasive grains in cloth, by contrast, does not form a large amount of a substance to be disposed of as industrial waste. However, this type of polishing has not been successful in achieving a polishing efficiency and a polishing quality which are sufficiently satisfactory.
An object of the present invention is to provide a new and improved polishing tool which polishes a back side of a semiconductor wafer with a high polishing efficiency and a high polishing quality, without forming a large amount of a substance to be disposed of as industrial waste, thereby being capable of eliminating processing distortion existent in the back side of the semiconductor wafer.
A further object of the present invention is to provide a novel and improved polishing method and apparatus which use the above-mentioned polishing tool.
An additional object of the present invention is to provide a new and improved grinding/polishing method and a new and improved grinding/polishing machine which grind a back side of a semiconductor wafer and then polish the back side of the semiconductor wafer with a high polishing efficiency and a high polishing quality, thereby being capable of eliminating processing distortion generated owing to the grinding.
The inventors of the present invention conducted in-depth studies, and have found that the above objects can be attained by a polishing tool equipped with polishing means formed by dispersing abrasive grains in felt having a density of 0.20 g/cm3 or more and a hardness of 30 or more.
According to an aspect of the present invention, there is provided, as the polishing tool attaining the above object, a polishing tool comprising a support member and polishing means fixed to the support member, the polishing means being composed of felt having a density of 0.20 g/cm3 or more and a hardness of 30 or more, and abrasive grains dispersed in the felt.
Preferably, the density of the felt is 0.40 g/cm3 or more, and the hardness of the felt is 50 or more. The polishing means preferably contains 0.05 to 1.00 g/cm3, especially 0.20 to 0.70 g/cm3, of the abrasive grains. The polishing surface of the polishing means can include both of a course surface and a wale surface of the felt. The abrasive grains preferably have particle diameters of 0.01 to 100 μm. The abrasive grains may be those including one or more of silica, alumina, forsterite, steatite, mullite, cubic boron nitride, diamond, silicon nitride, silicon carbide, boron carbide, barium carbonate, calcium carbonate, iron oxide, magnesium oxide, zirconium oxide, cerium oxide, chromium oxide, tin oxide, and titanium oxide. The support member preferably has a circular support surface, and the polishing means preferably is in the form of a disc bonded to the circular support surface.
According to another aspect of the present invention, there is provided, as the polishing method which attains the further object, a polishing method comprising rotating a workpiece and also rotating polishing means, and pressing the polishing means against a surface of the workpiece to be polished, and wherein the polishing means is constructed by dispersing abrasive grains in felt having a density of 0.20 g/cm3 or more and a hardness of 30 or more.
In a preferred embodiment, the workpiece is a semiconductor wafer, and the surface to be polished is a ground back side. The workpiece and the polishing means are preferably rotated in opposite directions. The rotational speed of the workpiece is preferably 5 to 200 rpm, especially 10 to 30 rpm, while the rotational speed of the polishing means is preferably 2,000 to 20,000 rpm, especially 5,000 to 8,000 rpm. The polishing means is preferably pressed against the workpiece at a pressing force of 100 to 300 g/cm2, especially 180 to 220 g/cm2. In a preferred embodiment, the workpiece is a nearly disc-shaped semiconductor wafer, the polishing means is disc-shaped, the outer diameter of the semiconductor wafer and the outer diameter of the polishing means are nearly the same, and the central axis of the semiconductor wafer and the central axis of the polishing means are positioned so as to be displaced from each other by a third to a half of the radius of the semiconductor wafer. The polishing means preferably is moved back and forth relative to the workpiece in a direction perpendicular to the rotation axis of the polishing means and perpendicular to a direction of displacement of the central axis of the semiconductor wafer and the central axis of the polishing means. The polishing means is preferably moved back and forth at such a speed as to be reciprocated once in 30 to 60 seconds at an amplitude equal to or somewhat larger than the diameter of the semiconductor wafer.
According to still another aspect of the present invention, there is provided, as the grinding/polishing method which attains the additional object, a grinding/polishing method comprising a grinding step of grinding a back side of a semiconductor wafer with a grinding member; and a polishing step, after the grinding step, of rotating the semiconductor wafer and also rotating polishing means, and pressing the polishing means against the back side of the semiconductor wafer, the polishing means being constructed by dispersing abrasive grains in felt.
Preferably, a cleaning step of jetting a cleaning liquid at the back side of the semiconductor wafer is included after the grinding step and before the polishing step, and a drying step of jetting air at the back side of the semiconductor wafer is included after the cleaning step and before the polishing step.
According to a further aspect of the present invention, there is provided, as the polishing apparatus which attains the further object, a polishing apparatus comprising chuck means rotatably mounted for holding a workpiece, and a polishing tool mounted rotatably, and wherein the polishing tool includes polishing means constructed by dispersing abrasive grains in felt having a density of 0.20 g/cm3 or more and a hardness of 30 or more, and the chuck means is rotated and the polishing tool is also rotated, and the polishing means of the polishing tool is pressed against the workpiece held by the chuck means, whereby the workpiece is polished.
In a preferred embodiment, a semiconductor wafer, as the workpiece, is held on the chuck means, and the polishing means polishes a ground back side of the semiconductor wafer. The chuck means and the polishing means are preferably rotated in opposite directions. The rotational speed of the chuck means is preferably 5 to 200 rpm, especially 10 to 30 rpm, while the rotational speed of the polishing tool is preferably 2,000 to 20,000 rpm, especially 5,000 to 8,000 rpm. The polishing means is preferably pressed against the workpiece at a pressing force of 100 to 300 g/cm2, especially 180 to 220 g/cm2. In a preferred embodiment, the workpiece is a nearly disc-shaped semiconductor wafer, the polishing means is disc-shaped, the outer diameter of the semiconductor wafer and the outer diameter of the polishing means are nearly the same, and the central axis of the semiconductor wafer and the central axis of the polishing means are positioned so as to be displaced from each other by a third to a half of the radius of the semiconductor wafer. The polishing tool preferably is moved back and forth relative to the chuck means in a direction perpendicular to the rotation axis of the polishing tool and perpendicular to a direction of displacement of the central axis of the semiconductor wafer and the central axis of the polishing means. The polishing means is preferably moved back and forth at such a speed as to be reciprocated once in 30 to 60 seconds at an amplitude equal to or somewhat larger than the diameter of the semiconductor wafer.
According to a still further aspect of the present invention, there is provided, as the grinding/polishing machine which attains the additional object, a grinding/polishing machine for grinding a back side of a semiconductor wafer and then polishing the back side of the semiconductor wafer, comprising:
a turntable rotated intermittently;
at least one chuck means rotatably mounted on the turntable;
at least one grinding device; and
a polishing apparatus, and wherein:
the semiconductor wafer to be ground and polished is held on the chuck means, with the back side of the semiconductor wafer being exposed;
the turntable is intermittently rotated, whereby the chuck means is located sequentially in at least one grinding zone and at least one polishing zone;
the grinding device includes a grinding tool, and the grinding tool is caused to act on the back side of the semiconductor wafer held by the chuck means located in the grinding zone to grind the back side of the semiconductor wafer; and
the polishing apparatus includes a polishing tool mounted rotatably, the polishing tool has polishing means constructed by dispersing abrasive grains in felt, the chuck means located in the polishing zone is rotated and the polishing tool is also rotated, and the polishing means is pressed against the back side of the semiconductor wafer held by the chuck means, whereby the back side of the semiconductor wafer is polished.
Preferably, the grinding/polishing machine is further equipped with cleaning means for jetting a cleaning liquid at the back side of the semiconductor wafer held by the chuck means located in the polishing zone, and drying means for jetting air at the back side of the semiconductor wafer held by the chuck means located in the polishing zone.
Upon further in-depth studies, the present inventors constructed polishing means in a polishing tool from a massive body formed from at least two types of fibers selected from natural fibers, including various animal hairs, and synthetic fibers, and abrasive grains dispersed in such a massive body. The inventors have found that compared with a polishing tool having polishing means constructed from a massive body, like felt, composed of fibers of a single type, and abrasive grains dispersed in such a massive body, the above polishing tool achieves heat release from the polishing means and/or workpiece even more effectively, and improves the quality and efficiency of polishing, although the reasons for these advantages are not entirely clear.
According to an additional aspect of the present invention, there is provided, as the polishing tool which attains the aforementioned object, a polishing tool comprising a support member and polishing means fixed to the support member, and wherein the polishing means is composed of a massive body formed from at least two types of fibers selected from natural fibers, including various animal hairs, and synthetic fibers, and abrasive grains dispersed in the massive body.
The term “natural fibers” used herein refers to animal-based natural fibers including not only wool and goat hair, but also pig hair, horse hair, cattle hair, dog hair, cat hair, raccoon dog hair, and fox hair, vegetable fibers such as cotton and hemp, and mineral fibers such as asbestos. The term “massive body” used herein refers to an object, such as felt or a fiber bundle, which is formed by compressing fibers into a mass form.
In a preferred embodiment, the massive body is composed of a first felt formed from first fibers, and a second felt formed from second fibers. The first fibers may be wool or goat hair, while the second fibers may be goat hair or wool. Preferably, the massive body is constructed by forming a plurality of voids in the first felt, and fitting the second felt into each of the plurality of voids. In a polishing surface of the polishing means, it is preferred that the second felts are arranged dispersedly in the first felt. In another preferred embodiment, the massive body is composed of felt formed from first fibers, and a fiber bundle formed from second fibers. The first fibers may be wool or goat hair, while the second fibers may be animal hair other than wool and goat hair. Preferably, the massive body is constructed by forming a plurality of voids in the felt, and fitting the fiber bundle into each of the plurality of voids. In a polishing surface of the polishing means, it is preferred that the fiber bundles are arranged dispersedly in the felt. In still another preferred embodiment, the massive body is composed of the felt formed by mixing at least two types of fibers. The massive body can be constructed from felt formed by mixing wool and goat hair. In any of the embodiments, the massive body preferably has a density of 0.20 g/cm3 or more, especially 0.40 g/cm3 or more, and a hardness of 30 or more, especially 50 or more.
Embodiments of the present invention will be described in further detail by reference to the accompanying drawings.
It is important for the polishing means 6 to be composed of felt and many abrasive grains dispersed in the felt. Importantly, the felt has a density of 0.20 g/cm3 or more, especially 0.40 g/cm3 or more, and a hardness of 30 or more, especially 50 or more. The term “hardness”, as used herein, refers to hardness measured according to the standards JIS K6253-5 (durometer hardness test). If the density and hardness are excessively low, the desired polishing efficiency and polishing quality cannot be achieved. The felt is not limited to one composed of wool, but may be felt composed of suitable synthetic fibers such as polyester, polypropylene, heat resistant nylon, polyester, acrylic, rayon, and Kevlar, flame resistant fibers such as silica and glass, and natural fibers such as cotton and hemp. In terms of polishing efficiency and polishing quality, felt containing 90% or more of wool, especially felt formed of 100% wool, is preferred. The amount of the abrasive grains dispersed in the felt is preferably 0.05 to 1.00 g/cm3, particularly 0.20 to 0.70 g/cm3.
The abrasive grains dispersed in the felt preferably have a particle size of 0.01 to 100 μm. The abrasive grains may be formed from any of silica, alumina, forsterite, steatite, mullite, cubic boron nitride, diamond, silicon nitride, silicon carbide, boron carbide, barium carbonate, calcium carbonate, iron oxide, magnesium oxide, zirconium oxide, cerium oxide, chromium oxide, tin oxide, and titanium oxide. If desired, two or more types of abrasive grains may be dispersed in the felt. To disperse the abrasive grains appropriately in the felt, it is permissible to incorporate the abrasive grains into a suitable liquid, and then impregnate the felt with the liquid, or to incorporate the abrasive grains, as desired, into the fibers as a material for the felt during the manufacturing process of the felt. After the abrasive grains are appropriately dispersed in the felt, the felt is impregnated with a suitable liquid adhesive, for example, a phenolic resin adhesive or an epoxy resin adhesive, so that the abrasive grains can be bound to the interior of the felt by such an adhesive.
As schematically shown in
With reference to
A cassette carry-in zone 52, a cassette carry-out zone 54, a transport mechanism 56, semiconductor wafer accepting means 58, and cleaning means 60 are disposed in a first-half upper surface of the main portion 14 of the housing 12. Transport mechanisms 62 and 64 are disposed on an intermediate upper surface of the main portion 14 of the housing 12. A cassette C accommodating a plurality of semiconductor wafers w having a back side to be ground and polished is placed in the cassette carry-in zone 52. A cassette C for accommodating a semiconductor wafer W whose back side has been ground and polished is placed in the cassette carry-out zone 54. The transport mechanism 56 carries one semiconductor wafer W, at a time, out of the cassette C placed in the cassette carry-in zone 52, turns the semiconductor wafer W upside down, and places it on the semiconductor wafer accepting means 58. The transport mechanism 62 carries the semiconductor wafer W, which has been placed on the semiconductor wafer accepting means 58 with its back side facing upward, onto the chuck means 44 located in the carry-in/carry-out zone 46.
The semiconductor wafer W, which has been carried onto the chuck means 44 with its back side facing upward and exposed, is located in the rough grinding zone 48, together with the chuck means 44, by the intermittent rotation of the turntable 42. In the rough grinding zone 48, the chuck means 44 holding the semiconductor wafer w is rotated, and the grinding tool 38a is also rotated at a high speed. The grinding tool 38a is pressed against the back side of the semiconductor wafer W and gradually lowered, whereby the back side of the semiconductor wafer W is ground. The central axis of the grinding tool 38a and the central axis of the chuck means 44 are displaced from each other by a predetermined distance, so that the grinding tool 38a is caused to act on the entire back side of the semiconductor wafer W sufficiently uniformly. The semiconductor wafer W, which has been roughly ground in the rough grinding zone 48, is brought to the precision grinding zone 50, together with the chuck means 44, by the intermittent rotation of the turntable 42. Then, the back side of the semiconductor wafer W is precision-ground by the grinding tool 38b. The manner of the precision grinding by the grinding tool 38b is the same as the manner of the rough grinding by the grinding tool 38a. The semiconductor wafer W, which has been precision-ground in the precision grinding zone 50, is brought to the carry-in/carry-out zone 46, together with the chuck means 44, by the intermittent rotation of the turntable 42. In the carry-in/carry-out zone 46, the back side of the semiconductor wafer W is polished in a manner to be described later in further detail.
Then, the transport mechanism 64 transports the semiconductor wafer W on the chuck means 44, located in the carry-in/carry-out zone 46, to the cleaning means 60. The cleaning means 60 jets a cleaning liquid, which may be pure water, while rotating the semiconductor wafer W at a high speed, to clean the semiconductor wafer W, and dries it. The transport mechanism 56 turns the cleaned, dried semiconductor wafer W upside down again to direct it faceup, and carries it into the cassette C placed on the cassette carry-out zone 54. After all of the semiconductor wafers w in the cassette C placed in the cassette carry-in zone 52 are carried outward, this cassette C is replaced by a next cassette C accommodating semiconductor wafers W having back sides to be ground and polished. When a predetermined number of semiconductor wafers W are accommodated into the cassette C placed in the cassette carry-out zone 54, this cassette C is carried outward, and an empty cassette C is placed there.
Constitutions and actions other than the above-described constitutions and actions of the illustrated grinding/polishing machine, i.e., the constitutions and actions concerned with polishing of the back side of the semiconductor wafer W in the carry-in/carry-out zone 46, are substantially the same as the constitutions and actions in the grinding machine sold, for example, by DISCO under the trade name “DFG841”, and are already well known among people skilled in the art. Therefore, detailed descriptions of these constitutions and actions are omitted herein.
In the illustrated grinding/polishing machine, a polishing apparatus 66 for polishing the ground back side of the semiconductor wafer w is disposed in addition to the rough grinding device 18a and the precision grinding device 18b for grinding the back side of the semiconductor wafer W. With reference to
Referring to
The actions of the polishing apparatus 66 will be described in summary. When the turntable 42 is intermittently rotated, or when the semiconductor wafer w is carried onto the chuck means 44 located in the carry-in/carry-out zone 46, or when the semiconductor wafer W is carried outward from the chuck means 44 located in the carry-in/carry-out zone 46, the piston 102 of the pneumatic cylinder mechanism 94 is contracted to a position indicated by two-dot chain lines in
Then, the piston 102 of the pneumatic cylinder mechanism 94 is stretched to a position indicated by solid lines in
According to the inventors' experience, in polishing the back side of the semiconductor wafer w by the polishing tool 2 in the foregoing manner, it is preferred to rotate the chuck means 44 at a relatively low rotational speed of, preferably 5 to 200 rpm, particularly 10 to 30 rpm, and rotate the polishing tool 2 at a relatively high rotational speed of, preferably 2,000 to 20,000 rpm, particularly 5,000 to 8,000 rpm. The direction of rotation of the chuck means 44 and the direction of rotation of the polishing tool 2 may be the same, but advantageously are in opposition to each other. In regard to the forward and backward movements of the polishing tool 2 in the directions indicated by the arrows 82 and 84, the polishing tool 2 can be reciprocated once in 30 to 90 seconds at an amplitude equal to or somewhat larger than the diameter of the semiconductor wafer W. The pressing force of the polishing tool 2 imposed on the back side of the semiconductor wafer W is preferably 100 to 300 g/cm2, especially 180 to 220 g/cm2. As shown in
When the back side of the semiconductor wafer W is rough-ground by the rough grinding device 18a and precision-ground by the precision grinding device 18b, a so-called saw mark is generated in the back side of the semiconductor wafer W, and so-called processing distortion (such processing distortion can be clearly grasped by observation with a transmission electron microscope) is generated over a depth of about 0.2 μm from the back side. After grinding, the back side of the semiconductor wafer W is polished by the polishing tool 2 constructed according to the present invention to remove the surface layer over a depth of about 1.0 μm. By this means, the back side of the semiconductor wafer W can be mirror-finished, and the processing distortion can be substantially eliminated.
It is important for the polishing means 206 to be composed of a massive body formed from at least two types of fibers selected from natural fibers and synthetic fibers, and abrasive grains dispersed in the massive body. Examples of the natural fibers are animal fibers such as wool, goat hair, pig hair, horse hair, cattle hair, dog hair, cat hair, raccoon dog hair, and fox hair, vegetable fibers such as cotton and hemp, and mineral fibers such as asbestos. Examples of the synthetic fibers are nylon fibers, polyethylene fibers, polypropylene fibers, polyester fibers, acrylic fibers, rayon fibers, Kevlar fibers, and glass fibers. The massive body formed by compressing the fibers into a mass form may be felt or a bundle of fibers, and preferably has a density of 0.20 g/cm3 or more, especially 0.40 g/cm3 or more, and a hardness of 30 or more, especially 50 or more. Too low a density and too low a hardness tend to result in a decrease in the polishing efficiency and deterioration in the polishing quality.
The amount of the abrasive grains dispersed in the massive body is preferably 0.05 to 1.00 g/cm3, particularly 0.20 to 0.70 g/cm3. The abrasive grains dispersed in the massive body may themselves be substantially the same as the abrasive grains in the polishing means 6 shown in
As will be clearly understood by reference to
FIGS. 13 to 15 show modified modes of combination of the first felt 210 and the second felt 212 forming the massive body. In the polishing means 206 of the polishing tool 202 shown in
The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, it is to be understood that the present invention is not restricted to these embodiments, but various changes and modifications may be made without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2001-93397 | Mar 2001 | JP | national |
2001-93398 | Mar 2001 | JP | national |
2001-93399 | Mar 2001 | JP | national |
2001-311450 | Oct 2001 | JP | national |
Number | Date | Country | |
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Parent | 10100901 | Mar 2002 | US |
Child | 11987382 | Nov 2007 | US |