Abrading – Abrading process – Abradant supplying
Reexamination Certificate
2001-10-05
2004-10-12
Wilson, Lee D. (Department: 3723)
Abrading
Abrading process
Abradant supplying
C451S056000, C451S028000, C451S041000
Reexamination Certificate
active
06802762
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for supplying a slurry, particularly a slurry having an agglomerating property, and a slurry feeder suitable for use with a polishing apparatus for chemical mechanical polishing an object.
The present invention also relates to a slurry feeder for feeding a slurry (polishing fluid) to a main body of a polishing apparatus for polishing a surface of an object such as a semiconductor wafer to an even surface and a mirror-finished surface, a polishing apparatus having the main body and the slurry feeder, and a method for operation of the slurry feeder.
Hitherto, circuit wiring has become finer and distance between wires has become narrower as the integration of semiconductor devices develops. In particular, in a case of photolithography having a line width of at most 5 microns, an allowable focal depth is so shallow that a high degree of evenness on an imaging plane of a stepper is required. Therefore, a surface of a semiconductor wafer has to be made even. One of method for flattening a surface of a semiconductor wafer involves polishing the surface of the wafer with a chemical mechanical polishing apparatus.
FIG. 8
illustrates an example of an essential portion of a chemical mechanical polishing apparatus. This apparatus has a turntable
142
with a polishing cloth (a polishing tool)
140
attached on top thereof, a top ring
144
for rotatably pressing and holding a semiconductor wafer W as an object to be polished, and a slurry feed nozzle
146
for feeding slurry Q to the polishing cloth
140
. The top ring
144
is connected to a top ring shaft
148
and held with an air cylinder (not shown) so as to be vertically movable. The top ring
144
has an elastic mat
150
, e.g., a polyurethane mat, attached closely to bottom surface thereof, to hold the semiconductor wafer W. The top ring
144
also has a cylinder-shaped guide ring
152
disposed at an outer edge portion thereof in order to prevent the top ring
144
from dropping during polishing operations. The guide ring
152
is fixed to the top ring
144
, and a bottom end surface of the guide ring
152
protrudes from a holding surface of the top ring
144
and is provided with a depressed portion inside a bottom end thereof for holding the semiconductor wafer W.
With this arrangement of the chemical mechanical polishing apparatus, the semiconductor wafer W is held under the elastic mat
150
below the top ring
144
. The semiconductor wafer W is pressed against the polishing cloth
140
on the turntable
142
by the top ring
144
, and is polished while rotating the turntable
142
and the top ring
144
and moving the semiconductor wafer W relatively to the polishing cloth
140
. The slurry Q is supplied to the polishing cloth
140
from the slurry feed nozzle
146
during polishing operations.
In order to allow a good polishing of the semiconductor wafer W with the chemical mechanical polishing apparatus, a slurry feeder is required which can stably provide the chemical mechanical polishing apparatus with slurry (polishing or grinding fluid) at a constant concentration and a flow rate. The slurry feeder generally includes, for example, a stock solution tank for storing a stock solution of slurry, a preparation tank for adjusting concentration of slurry by diluting the stock solution with a deionized water (pure water), a chemical liquid or the like to a given concentration, a slurry supply tank for temporarily storing slurry adjusted in the preparation tank, and a slurry feed pipe for feeding the slurry from the slurry supply tank to the slurry feed nozzle
146
of the chemical mechanical polishing apparatus.
A conventional slurry feed pipe connecting the slurry supply tank to the chemical mechanical polishing apparatus adopts a so-called general circulation and supply system for discharging slurry via a roller pump from a circulating line to a table in the chemical mechanical polishing apparatus. This slurry feed pipe is provided with a circulating pipe for returning slurry discharged from the slurry supply tank back to the slurry supply tank, and a pipe branched from the circulating pipe for feeding the slurry to the chemical mechanical polishing apparatus. The slurry feed pipe is arranged so as to carry out the circulating operations for returning the slurry discharged from the slurry supply tank back to the slurry supply tank via circulating pump disposed in the circulating pipe, even if the chemical mechanical polishing apparatus is operated for polishing or is idling.
It is to be noted that slurry having an agglomerating property becomes more likely to agglomerate into particles having larger particle sizes, when the slurry is in a fluid state. Therefore, if such slurry is used for this invention, it may present a problem in that agglomeration of the slurry may be accelerated when the slurry is always in a fluid state due to circulating operations by virtue of the circulating pump in the manner as described above. In other words, the above feeding system cannot suspend circulation operations of the circulating pump. And thus the slurry has to be constantly circulated unless all chemical mechanical polishing apparatuses are brought into an idling status. Otherwise, agglomeration of the slurry would be accelerated.
In recent years, when manufacturing semiconductor devices, there is an increasing demand that plural device layers are formed on a semiconductor wafer. In order to accurately form plural device layers, it is necessary to make a surface of a layer covering each device layer flat and mirror-finished by utilizing a polishing apparatus. The polishing apparatus includes a main body having turntables, each rotating at an independent number of rotations, and also includes a top ring and a slurry feeder. Between a corresponding one of the turntables and the top ring is disposed an object such as a semiconductor wafer, and a surface of the object is polished to an even and mirror-finished surface by rotating this turntable while feeding a slurry for use during polishing.
The slurry feeder is required to supply a slurry (polishing fluid) continually to the polishing apparatus. In order to prevent interruption of supply of slurry during a process of polishing, a buffer tank is disposed which contains a slurry of a capacity that can polish at least one surface of a semiconductor wafer. The buffer tank is provided with a stirring device so as to stir the slurry well in order to prevent the slurry from remaining in the buffer tank and polishing particles from settling to make t concentration of the slurry irregular. The stirring device can stir the slurry in the buffer tank to keep a uniform concentration of the slurry to be fed to the polishing apparatus and enable polishing of the object at a high accuracy.
SUMMARY OF THE INVENTION
The present invention has been made with the above situation taken into account and an object of the present invention is to provide a method for supply of slurry, and a slurry feeder, which can provide a chemical mechanical polishing apparatus with slurry, including slurry with an agglomerating property, in an appropriate manner without causing the acceleration of agglomeration of the slurry.
Because such a conventional slurry feeder has a the buffer tank with a stirring device, however, an apparatus is rendered complex in structure and stirring causes a temperature of the slurry to rise so as to render a cooling load of the slurry high.
The present invention has been made with the above disadvantages taken into account and it has an object to provide a slurry feeder having a simplified structure capable of feeding a slurry having a uniform concentration, a polishing apparatus installed with the slurry feeder, and a method for operation of the slurry feeder.
In order to achieve the object as described above, the present invention provides a method for supply of slurry from a slurry supply tank, that stores slurry at a given concentration, to a chemical mechanical polishing apparatus for polishing an object, wherein opera
Tanaka Takashi
Toyomasu Fujihiko
Tsuzuki Takashi
Ebara Corporation
Wilson Lee D.
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