Abrading – Machine – Rotary tool
Reexamination Certificate
1999-07-01
2001-08-14
Eley, Timothy V. (Department: 3723)
Abrading
Machine
Rotary tool
C451S398000
Reexamination Certificate
active
06273803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air pressure type carrier and polishing apparatus provided with a soft retainer ring.
2. Description of the Related Art
In general, polishing a wafer by front side reference gives a higher polishing accuracy than polishing by back side reference, so most carriers adopt an air pressure type structure.
FIG. 13
is a sectional view of an example of an air pressure type carrier of the related art.
A carrier
100
is formed with a depression
101
at its bottom surface. This depression
101
is covered with a sheet
102
to define a pressure chamber R. An air feed path
103
communicating with the pressure chamber R is provided at the center of the carrier
100
. A retainer ring
104
for holding the wafer W is attached at the outer periphery of the bottom surface of the carrier
100
by an adhesive (not shown).
Due to this configuration, the carrier
100
can be made to rotate in a state with a wafer W brought into contact with the top of a polishing pad
201
of the rotating lower platen
200
. At this time, air is fed from the air feed path
103
to the inside of the pressure chamber R to apply a uniform pressure to the back surface of the wafer W and polish the front surface of the wafer W flat by the polishing pad
201
of the lower platen
200
.
In the carrier of the above related art, however, there were the following problems.
Since the retainer ring
104
was in contact with the rotating polishing pad
201
during the polishing of the wafer W, it became worn. In particular, the retainer ring
104
of the related art was set to a thickness of a value in the range from 0.5 mm to 0.7 mm in accordance with the thickness of 6-inch diameter wafers W and 8-inch diameter wafers W. Further, the retainer ring
104
was formed by epoxy glass (EG) or another similarly soft material, so it became worn in a short time, immediately became thinner, and easily peeled off from the carrier
100
. Further, when the retainer ring
104
became worn, the wafer W moved upward by the amount of wear of the retainer ring
104
due to the force pressing the wafer against the carrier
100
. As a result, the tension caused at the outer periphery of the sheet
102
caused the polishing rate of the outer periphery of the wafer W to become higher than the polishing rate of the center portion, i.e., “face drooping”. The degree of face drooping became higher in relation to the amount of wear of the retainer ring
104
. From the viewpoint of the allowable degree of face drooping and prevention of peeling, the amount of wear allowed for a retainer ring
104
with a thickness set to a value in the range from 0.5 mm to 0.7 mm is up to about 0.1 mm. Therefore, in a carrier
100
of the related art having a retainer ring
104
set to such a thickness and formed by a soft material such as EG, the number of polishable wafers W produced within the desired range was about 200 sheets, which was extremely poor in terms of mass production.
As opposed to this, it may be considered to form the retainer ring
104
by a ceramic, titanium, or other hard material. While a retainer ring
104
made of a hard material, however, is superior in wear resistance, it is liable to be damaged during polishing work by the outer edge of the wafer W striking the inner peripheral surface of the retainer ring
104
.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a carrier and a polishing apparatus designed to improve mass production of wafers while using a retainer ring formed of a soft material.
To achieve the above object, according to a first aspect of the invention, there is provided a carrier comprising: a carrier body having a pressure chamber formed by a depression opening downward covered from below by a pliable sheet; a retainer ring for holding a wafer attached to the outer periphery of the bottom surface of the pliable sheet and formed by a soft material; and a pliable margin block provided projecting out at equal thickness at the bottom surface of the pliable sheet positioned at the inside of the retainer ring, wherein the thickness of the retainer ring set to be substantially equal to the sum of the thickness of the margin block and the thickness of the wafer being polished.
Due to this configuration, when the pressure chamber of the carrier body is filled with a fluid and the wafer is pressed against the rotating lower platen by the carrier body in the state with the wafer placed on the lower platen being held by the retainer ring, the entire surface of the wafer is uniformly pressed by the fluid pressure of the pressure chamber applied to the pliable margin block. Due to this, the wafer is polished to a high accuracy by the rotating lower platen. If the retainer ring contacts the lower platen during the polishing work, the retainer ring formed by the soft material is worn by the rotating lower platen. The thickness of the retainer ring is however set to be substantially equal to the sum of the thickness of the margin block and the thickness of the wafer is set to be much thicker than the retainer ring of the related art, so the retainer ring may be used for a long period of time.
Further, the margin block is provided at an equal thickness on the bottom surface of the pliable sheet. As an example of this, according to an embodiment of the invention, the margin block is formed by a solid rubber member. Further, the thickness of the margin block is set to a value in the range from 2 mm to 4 mm.
As another example of the margin block, according to an embodiment of the invention, the margin block is formed of a hollow rubber member and a plurality of holes communicating the pressure chamber and the hollow part of the margin block are formed in the pliable sheet. Further, according to an embodiment of the invention, the thickness of the margin block is set to a value in the range from 4 mm to 10 mm.
The retainer ring is formed of a soft material. As examples, according to an embodiment of the invention, the retainer ring is formed of a material selected from the group consisting of epoxy glass, polyvinyl chloride, polyacetal, polyimide, polyphenylene sulfide, polyether ether ketone, polyethylene terephthalate, polyether sulfone, polysulfone, polyphenylene oxide, polyarylate, and high density polyethylene.
As an example of the structure for attaching the carrier body, pliable sheet, and retainer ring, according to an embodiment of the invention, the outer periphery of the top surface of the pliable sheet is bonded to the outer periphery of the bottom surface of the carrier body by an adhesive, the top surface of the retainer ring is bonded to the outer periphery of the bottom surface of the pliable sheet by an adhesive, and a plurality of female threaded holes are provided opening to the top surface of the carrier body and passing through the pliable sheet to reach the retainer ring, and male screws are screwed into the female threaded holes to affix the retainer ring. As another example, according to an embodiment of the invention, a ring member is interposed between the outer periphery of the bottom surface of the carrier body and the outer periphery of the top surface of the pliable sheet, the bottom surface of the ring member and the outer periphery of the top surface of the pliable sheet are bonded by an adhesive, the outer periphery of the bottom surface of the pliable sheet and the top surface of the retainer ring are bonded by an adhesive, and a plurality of female threaded holes are provided opening to the top surface of the carrier body and reaching the ring member, and male screws are screwed into the female threaded holes to affix the ring member.
A polishing apparatus using the above carrier also is an invention.
Therefore, according to a second aspect of the present invention, there is provided a polishing apparatus comprising: a rotatable lower platen; a carrier provided with a carrier body having a pressure chamber formed by a depression opening downward covered from below by a pliable sheet, a retain
Izumi Shigeto
Sugiyama Misuo
Tanaka Hideo
Wang Xu-Jin
Burr & Brown
Eley Timothy V.
Nguyen Dung Van
Speedfam Co., Ltd.
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