Abrading – Machine – Sandblast
Reexamination Certificate
2000-05-03
2002-06-11
Hail, III, Joesph J. (Department: 3723)
Abrading
Machine
Sandblast
C451S088000, C451S060000, C451S446000
Reexamination Certificate
active
06402599
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to a polishing system and, more specifically, to a slurry conduit that is couplable to a slurry day tank that reduces the amount of slurry that dries on the storage tank wall.
BACKGROUND OF THE INVENTION
In the manufacture of integrated circuits (ICs), chemical/mechanical polishing (CMP) is used to provide smooth topographies of semiconductor wafer substrates, on which the ICs are formed, for subsequent lithography and material deposition. These CMP processes are well known within the IC fabrication industry.
One problem area associated with chemical/mechanical polishing is in the area of slurry consistency. Because the polishing slurry is a suspension of a mechanical abrasive in a liquid chemical agent, e.g., an acid or base, the slurry has two undesirable tendencies that are common to suspensions: that is, settling/agglomeration, and evaporation of the chemical agent leaving a dried abrasive residue. To minimize the settling/agglomeration problem, the slurry is kept in constant circulation through a closed loop from a slurry supply tank (day tank) through a slurry pump and back into the slurry supply tank. The slurry loop is tapped with a tee and a valve so that a relatively small amount of slurry may be diverted to the polishing platen for CMP. The second problem, evaporation of the chemical agent, is aggravated by those conditions that allow the formation of a thin slurry layer, thereby increasing the slurry surface area per unit volume and increasing the rate of evaporation. This condition occurs commonly in the day tank above the current slurry level.
Referring initially to
FIGS. 1A and 1B
, illustrated are partial sectional views of one embodiment of a conventional CMP apparatus at the start of a planarizing process and after depletion of some slurry, respectively. A CMP apparatus, generally designated
100
, comprises a polishing platen
110
; first and second rotatable shafts
121
,
122
, respectively; a carrier head
130
; a polishing pad
140
having a polishing surface
142
; first and second drive motors
151
,
152
, respectively; and a slurry delivery system
160
containing slurry
161
. The slurry delivery system
160
comprises a slurry tank
162
, a slurry supply line
163
, a slurry pump
164
, and a slurry return line
165
. Under pressure from the slurry pump
164
, the slurry
161
circulates continuously in the slurry delivery system
160
from the slurry tank
162
, through the slurry supply line
163
, the slurry pump
164
, the slurry return line
165
and back into the slurry tank
162
along a route designated by arrow
166
. A portion
161
a of the slurry
161
is diverted to the polishing surface
142
through a valve
167
while the remainder of the slurry
161
circulates to maintain the abrasive material in suspension.
A semiconductor wafer
170
is mounted in the carrier head
130
and is pressed against the polishing surface
142
that is wetted with slurry
161
. The first and second rotatable shafts
121
,
122
rotate the carrier head
130
/semiconductor wafer
170
and platen
110
, respectively, as shown, during CMP. One who is skilled in the art is familiar with the details of CMP as applied to semiconductor wafers.
As can be seen by comparing
FIGS. 1A and 1B
, a level
168
a
,
168
b
of the slurry
161
in the slurry tank
162
will vary during CMP processing. As the slurry level, collectively
168
, varies, area
169
is subjected to alternating conditions of coverage with slurry
161
and exposure to ambient conditions. Therefore, the slurry
161
clings to the inner tank area
169
when the slurry level
168
falls to level
168
b
and the slurry
161
dries in that area
169
. Exposed to the atmosphere, the chemical agent can readily evaporate, leaving behind a dried layer of abrasive. When dry, the slurry
161
may flake off of the vertical tank area
169
and fall back into the slurry
161
where the flakes remain until they are pumped to the polishing pad
140
and may come in contact with the semiconductor wafer
170
, thereby causing damage. Because the dried slurry
161
retains its abrasive qualities and the dried slurry pieces are much larger than a design particle size for the slurry
161
, these abrasive pieces must be substantially removed before the slurry
161
is deposited on the polishing pad
140
to avoid damaging features on the semiconductor wafer
170
being polished. It is impractical to control the slurry level
168
precisely in the day tank
162
because of the volume of the tank, e.g., 250 gallons or more total with fluctuations from a minimum of about 75 gallons to about 150 gallons, in order to avoid this problem.
To help alleviate this drying problem, one conventional approach has been to seal the day tank and to pump wet nitrogen, i.e., nitrogen bubbled through water, into the ullage. This approach was not particularly successful. Of course, frequent cleaning of the day tank has also be employed at considerable cost in time and manpower for fabrication system shutdown. Additionally, frequent handling of some slurries should be avoided because of safety concerns.
Accordingly, what is needed in the art is an improved slurry delivery system that minimizes the formation of dried slurry particles in the day tank and conserves time and manpower.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides a slurry delivery system comprising a slurry conduit couplable to a wall of the slurry tank and configured to receive a slurry therein and configured to deliver a stream of the slurry against an inner wall of the slurry tank.
Thus, in a broad scope, the present invention provides a system that inhibits drying of a slurry within the slurry tank that minimizes agglomeration on the sides of the slurry tank that results from slurry drying on the sides of the slurry tank's wall when the slurry level within the tank rises and falls. This minimization of agglomeration reduces the agglomerates within the slurry supply, which in turn, reduces the number of contaminants and scratches affecting the overall quality of the semiconductor wafer substrate.
In another embodiment, the slurry delivery system further comprises perforations in the slurry conduit configured to deliver the stream. In an additional aspect of this embodiment, the slurry delivery system further comprises nozzles coupled to the conduit at the perforations and configured to deliver the stream.
The slurry delivery system, in yet another embodiment, comprises a channel having outer and inner flanges. The outer flange has a height that is greater than the height of the inner flange whereby the inner flange forms a weir against the slurry. In a further aspect of this embodiment, a surface of the inner flange is contoured to transition smoothly to the inner wall.
The slurry conduit and the slurry tank, in another embodiment of the slurry delivery system, may be integrally formed. In yet another embodiment, the slurry conduit may comprise a plastic, such as polyvinyl alcohol. In a particularly advantageous embodiment, the slurry is a semiconductor wafer polishing slurry.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 2774679 (1956-12-01), Remer
patent: 3500591 (1970-03-01), Gawronski et al.
patent: 4250024 (1981-02-01), So
Crevasse Annette M.
Easter William G.
Maze John A.
Miceli Frank
Zavilla Craig R.
Agere Systems Guardian Corp.
Hail, III Joesph J.
Shakeri Hadi
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