Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1997-06-05
2001-01-09
Popovics, Robert J. (Department: 1723)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S258000, C096S004000, C210S094000, C210S097000, C210S188000, C210S194000, C210S744000
Reexamination Certificate
active
06171367
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for delivering and recycling a liquid chemical by a recirculating system and more particularly, relates to a method and apparatus for delivery and recycling liquid chemical that is capable of delivering an air bubble-free liquid to a process machine and to reduce the liquid chemical usage by recycling unused liquid into a reservoir for the liquid chemical.
BACKGROUND OF THE INVENTION
In most manufacturing processes, a variety of chemicals are used in a multiplicity of manufacturing steps. For instance, there are frequently several hundred manufacturing steps involved in the fabrication of an integrated circuit. The manufacturing steps may include etching, cleaning, deposition and various other necessary steps. A variety of chemicals, including liquid chemicals, are used in the processing steps either to etch a specific circuit on an IC chip, to clean after certain processing steps, to deposit layers from reactant chemicals, or to carry out any other necessary fabrication steps. An important consideration in using chemical liquids is the transporting/storage of the material. For instance, when a photoresist liquid is used in IC processing, the photosensitivity and the lifetime of the material depends on its storage temperature and its exposure to light. It is therefore important to maintain a photoresist liquid within a temperature range of between 5° C. and 20° C. and in a relatively dark environment.
In the transporting of IC processing liquids, plastic piping such as Teflon pipes are frequently used due to the fact that the liquid being transported is frequently volatile and flammable. The Teflon pipes are also ideal for chemical liquids that are highly corrosive. The use of plastic piping greatly reduces the risk of explosion or fire that are sometimes caused by sparks generated between metal pipes. When Teflon pipes are used, they are frequently connected together by Teflon couplings between various sections of the pipes. The pipes and the couplings are connected by male and female threads provided on the pipes and in the couplings respectively. Based on the low rigidity of plastic materials a connection between a Teflon pipe and a Teflon coupling can only be made by hand tightening the two parts together. Any tightening force larger than that provided by hand tightening would cause the stripping of threads on the Teflon pipes. A joint formed between a Teflon pipe and a Teflon coupling therefore is not extremely tight and consequently, would allow air to enter the pipe and forms bubbles or micro-bubbles. The micro-bubbles are bubbles formed on a microscopic scale and sometimes cannot be observed by human eyes.
An illustration of a conventional liquid supply system
10
is shown in FIG.
1
. In system
10
as presently used in a semiconductor fabrication facility, a liquid reservoir or holding tank
12
is first provided for storing liquid
14
. Liquid
14
can be fed to the tank
12
from a liquid inlet
18
through a shut-off valve
20
. At the uppermost portion of the liquid reservoir
12
, a vent outlet
24
is provided for venting the tank to the atmosphere. A filter
26
is provided in conduit
28
for the vent system such that only air and not liquid can be vented out the vent outlet
24
. Conduit
32
allows the delivery of liquid
14
in tank
12
to a pump
34
that is driven by motor
36
. The pump
34
is controlled by a host computer (not shown) of the process machine such that it dispenses liquid of a predetermined volume in a predetermined interval of time as instructed by the computer. The pump
34
can be suitably provided of the bellow-type which has a preset volume of displacement during each activation of the bellow such that a predetermined amount of liquid is delivered through conduit
40
to a liquid/air separating device, or filter
42
. For instance, in a liquid supply system for a photoresist coating material, a bellow-type pump can be preset to deliver 8 cm
3
of the photoresist upon activation of the bellow to coat a wafer.
The liquid/air separating device, or filter
42
can separate trapped air from the liquid when such a mixture is delivered to filter
42
through conduit
40
. The trapped air after being separated out of the liquid cumulates at an upper portion of filter
42
. The filter
42
is designed as a one-way filter such that back flow of liquid into conduit
40
is not possible. A liquid flow that is substantially without air bubbles can be pumped by the bellow pump
34
to enter conduit
46
through shut-off valve
48
for dispensing onto a wafer (not shown). Since conduits are normally made of a plastic material, such as Teflon, and therefore are translucent or semi-transparent, any trapped air bubbles in the liquid can be visually observed by the machine operator. When air bubbles are observed, the operator opens valve
52
and discharges a significant amount of the liquid into a waste collection tank
54
through conduit
56
in order to get rid of the air bubbles.
As previously discussed, since plastic piping can not be tightly joined together, air leaks into the conduit and forms trapped air bubbles in the liquid. In the conventional liquid supply system
10
shown in
FIG. 1
, each time air bubbles are observed in the liquid conveying conduit, a large quantity of liquid must be drained through conduit
56
into the waste collection tank
54
in order to purge out all the trapped air bubbles. This presents a significant source of waste of the process liquid used in a manufacturing process and adds significantly to the cost of fabrication since most process liquids used in IC fabrication are high cost materials.
It is therefore an object of the present invention to provide a method for supplying a liquid to a process machine that does not have the drawbacks and shortcomings of the conventional methods.
It is another object of the present invention to provide a method for supplying liquid to a process machine that is capable of supplying a liquid which is substantially without trapped air.
It is a further object of the present invention to provide a method for supplying a liquid to a process machine that is capable of recirculating a liquid containing air bubbles into a liquid reservoir such that the draining of the liquid is not necessary.
It is another further object of the present invention to provide a method for recirculating a process liquid such that a substantially air bubble-free liquid can be delivered to a process machine.
It Is yet another object of the present invention to provide a method for recirculating a liquid containing air bubbles that have leaked into the plastic pipes is sent back to a liquid reservoir for venting.
It is still another object of the present invention to provide a method for recirculating a liquid that is capable of removing air bubbles in the liquid while not wasting any of the liquid to a drain tank.
It is still another further object of the present invention to provide a recirculating liquid supply and recovery system that is capable of supplying an air bubble-free liquid to a process machine while recirculating a liquid flow containing air bubbles back into a liquid reservoir.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for recirculating a liquid to deliver a substantially air bubble-free liquid to a process machine without wasting any liquid that contains air bubbles is provided.
In a preferred embodiment, a method for recirculating a liquid to deliver a substantially air bubble-free liquid to a process machine can be carried out by the operating steps of first providing a liquid reservoir for storing a liquid, then transporting the liquid through a first conduit to a pump, then pumping a predetermined amount of liquid through a second conduit to a first liquid/air separating device having a first outlet and a second outlet, then dispensing a substantially air bubble-free liquid from the first outlet through a third conduit, and then recirculating a liquid containing
Lin Y. F.
Liu T. Y.
Peng Ray
Wang R. C.
Popovics Robert J.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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