Abrading – Abrading process – Abradant supplying
Reexamination Certificate
2000-08-31
2003-04-08
Rachuba, M. (Department: 3724)
Abrading
Abrading process
Abradant supplying
C451S099000, C451S041000, C451S285000, C451S287000
Reexamination Certificate
active
06544109
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to chemical mechanical planarization systems and more particularly to methods and systems for supplying slurry to a single planarization machine or to a plurality of chemical mechanical planarization machines.
In an exemplary, known chemical mechanical planarization (CMP) process, with reference to
FIG. 1
, surface of a semiconductor wafer
2
is positioned over a planarization pad
5
and moved relative thereto while slurry is supplied to the planarization pad. The wafer is held against the planarization pad by wafer carrier
4
. Motor
6
provides rotational movement of wafer carrier
4
. Planarization pad
5
is attached to platen
7
, which is rotated by a second motor
9
. Dispense line
8
is configured for delivering slurry to planarization pad
5
. An acoustic transducer
3
is disposed near the output of dispense line
8
for breaking up particles of the slurry just prior its delivery to the planarization process.
Known, exemplary slurries typically include both chemical and mechanical components that facilitate planarization, etching or passivation of a wafer's surface. An exemplary slurry comprises an aqueous basic or acidic solution, such as aqueous potassium hydroxide (KOH), containing dispersed particles, such as silica or alumina. It is believed that if a slurry is delivered to the polishing pad during its optimal lifespan—i.e., its time window of optimal planarization effectiveness—particles of the slurry remain suspended. Accordingly, there is an aim to provide a consistent and controlled flow of slurry to the polishing pad within its optimal delivery time window.
Exemplary, prior art, slurry distribution systems are shown in
FIGS. 2-4
. These systems circulate slurry around a fluid loop that supplies slurry to a plurality of polishing machines. In a full-series configuration
210
, with reference to
FIG. 2
, pump
222
pumps slurry
212
from reservoir
211
, into forward line
221
. A plurality of polishing machines,
250
A
-
250
X
, are connected in series with forward line
221
. Ideally, pump
222
provides enough slurry to the distribution loop so as to maintain a return flow
225
in return line
223
, despite slurry demands of the plurality of polishing machines. A known disadvantage of the full series configuration is that servicing of a single polishing machine often requires that the whole distribution loop be shut-down, thereby impacting all polishing machines along the distribution loop.
In another known configuration, with reference to
FIG. 3
, polishing machines
350
a
-
350
x
are connected in parallel between the forward
321
and return
323
lines of the slurry distribution loop. Again, the forward
321
and return
323
lines of the distribution loop circulate slurry as provided by pump
222
. Each polishing machine receives slurry from a first line
313
which is tapped into forward line
321
. A second line
315
returns unused slurry, i.e., that is not taken in by a polishing machine, back to return line
323
of the distribution loop. This parallel-tap configuration
310
of
FIG. 3
offers an advantage over the full-series configuration of FIG.
2
. In particular, the parallel-tap configuration allows servicing of a single polishing machine, for example,
350
x
, without having to terminate operation of the other machines associated with the distribution loop.
Although, not specifically shown in the illustrated drawings of the exemplary distribution loops, known fluid flow mechanisms (such as line diameters and ratio'd tap diameters and tees) can be adjusted to establish desired velocities and pressures along different regions of the distribution loop. For example, for a given line fluid flow, a decrease in line diameter can effect a greater velocity therein. Alternatively, by increasing the diameter of the line, the drop in pressure along its length can be reduced (but at the expense of fluid velocity therein). Typically, the diameter of the parallel tapped lines that couple the polishing machines to the distribution loop are kept smaller than that of the forward and return lines of the distribution loop. By keeping the diameters of the distribution loop's forward and return lines greater than the diameter of the parallel tapped lines, slurry flow favors the distribution loop. Otherwise, slurry could by-pass outer regions of the distribution loop—i.e., by flowing through a parallel tap associated with a given polishing machine—thereby depriving the more distant polishing machines of slurry solution.
Another known distribution loop comprises a simple series-tap configuration
410
, as shown in
FIG. 4. A
plurality of polishing machines
450
A
-
450
X
receive slurry from the distribution loop by way of respective drop lines
414
. These drop lines
414
tap into the distribution loop at different locations
452
along its length. Pump
222
circulates slurry through the distribution loop.
Ideally, pump
222
provides a flow within the distribution loop for establishing a velocity that both replenishes slurry of the distribution line within a given time interval and assures suspension of the particles of the slurry. In the design of slurry distribution systems, a conflicting aim seeks to provide similar pressures at each drop line tap, e.g.,
452
A
through
452
X
. However, it is known that the greater a velocity of fluid flow within a given line, the greater the drop in pressure across its length. Accordingly, the desire to provide a rapid velocity of slurry flow within the distribution loop—i.e., so as to frequently replenish slurry and preserve suspension of particles of the slurry within the distribution line—this desire for rapid slurry velocity is set against the opposing goal of minimizing pressure drops along the length of the distribution loop.
Further referencing
FIGS. 2-4
, it is recognized, pursuant the present disclosure, that each drop line
214
,
314
,
414
may comprise a dead-zone region that may experience stagnant, or low velocity, conditions in accordance with the slurry demands of their respective polishing machines. For example, upon completing a planarization step, a polishing machine may terminate slurry demand. If the reduced demand ensues, agglomeration and/or precipitation of particles can result within the dead-zone regions of the drop lines.
Further illustrated in
FIG. 4
, relative to the planarization machine
450
A
, is another, exemplary prior art re-circulation loop comprising multiple position valve
420
and re-circulation line
422
. Valve
420
is disposed near the output of the dispense line. When slurry flow is discontinued to the planarization process, valve
420
is configured to route slurry into re-circulation line
422
for flowing slurry back to drop line
415
. In this configuration, slurry continues circulating through the drop line and re-circulation line when slurry is not being delivered to the planarization process. It is noted, however, that when the multiple position valve
420
is configured to deliver slurry to the planarization process, slurry within the re-circulation line
422
may be stagnant.
Accordingly, there exists a need to preserve suspension of particles for slurry within slurry distribution systems, such as drop-lines, or low-flow delivery lines, as are used for delivery of slurry to chemical-mechanical planarization machines. The present invention recognizes these needs and proposes solutions thereto.
SUMMARY OF THE INVENTION
In accordance with an embodiment of the present invention, a fluid delivery line is configured to provide slurry to a polishing machine. Slurry is agitated therein by way of plus-minus slurry displacements. Preferably, the plus-minus displacements are performed on a supply side of a metering pump that is used for dispensing slurry of the delivery line to the polishing machine. More preferably, the agitating is performed when a flow of slurry to the polishing machine has been terminated. In accordance with one aspect of this embodiment, an in-line displacement
Howrey Simon Arnold & White , LLP
Rachuba M.
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