Gas separation: apparatus – Degasifying means for liquid – With control means responsive to sensed condition
Reexamination Certificate
2001-01-04
2002-12-31
Smith, Duane S. (Department: 1724)
Gas separation: apparatus
Degasifying means for liquid
With control means responsive to sensed condition
C096S194000, C096S206000
Reexamination Certificate
active
06500242
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for degassing and preventing gelation in a viscous liquid used in semiconductor processing and more particularly, relates to an apparatus and a method for eliminating air and gelation in a viscous liquid of polyimide used in semiconductor fabrication processes.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, a semi-conducting wafer must be processed in a multiplicity of fabrication steps, i.e. as many as several hundred in order to produce the final finished product. These processing steps may include etching, cleaning, deposition and various other processing procedures. A variety of chemicals, including liquids and gases may be used in the processing steps wither to etch a specific feature on the IC chip, to clean after certain processing steps, to deposit layers from reactant chemicals, or to carry out other necessary processing steps.
For instance, in photomasking and metal cleaning processes, a variety of speciality chemicals are used. An important consideration in the usage of such speciality chemicals, i.e. photoresists, developers, spin-on-glass and polyimide is the transporting and storage of the materials. In the case of a photoresist material, the photosensitivity and the shelf life of the material depends on its storage temperature. It is important to maintain such material within a range of 5° C. to 20° C. for a photoresist/developer and −20° C. to 10° C. for spin-on-glass/polyimide materials.
The transporting of these speciality chemicals, especially liquids, or the delivery from a storage reservoir, i.e. a holding tank or a buffer tank, to a processing chamber where the liquid is used is another important aspect of the fabrication process. A process liquid, such as a photoresist or a developer, can be transported in a fluid passageway of a stainless steel tubing assisted by an electrical pumping means. One of such conventional liquid delivery system for a polyimide passivation material is shown in FIG.
1
.
FIG. 1
illustrates a conventional polyimide dispensing system
10
which utilizes compressed air in conduit
12
and valve
14
to exert a positive pressure in the source tank
16
such that a sufficient amount of a polyimide liquid
18
is applied to the reservoir tank
20
through conduit
22
and valve
24
. The valve
14
is an open/closed valve for controlling the air pressure in conduit
12
. Valve
14
is open when polyimide solution is requested from the reservoir tank
20
via master controller
30
. Valve
14
is closed when no request is sent from reservoir tank
20
. A sensor
26
is further provided for sensing the presence of a polyimide liquid in conduit
22
. When the source tank
16
becomes empty, compressed air is drawn into the conduit
22
and activates the sensor
26
which then sends an alarm signal to the operator for refilling the source tank
16
with new polyimide solution. The sensor
26
can be an optical type which senses an intensity change of a refracted light as air enters the conduit
22
. The function of valve
24
is the same as valve
14
which is open or closed at the same time to supply polyimide into the reservoir tank
20
.
The reservoir tank
20
is a buffer tank for the polyimide solution
18
. The major function for the reservoir tank
20
is to degas and to remove gel that flows in from the conduit
22
or the source tank
16
. The sources of bubbles or gel may be of many different kinds, i.e. from the polyimide material itself during the fabrication of the material; from the conduit
22
during the replenishment of the source tank
16
; or from the open/closed action of valve
24
during the operation of the polyimide dispensing system
10
.
The reservoir tank
20
is equipped with four different sensors
28
,
32
,
34
and
36
for maintaining a suitable solution level in the tank. The level of the solution should be kept between the high sensor
32
and the low sensor
34
. When the solution level is sufficiently low as to activate the low sensor
34
, the low sensor
34
sends a signal to the master controller
30
. The master controller
30
then controls valves
14
and
24
to refill the reservoir tank
20
, and stop the refill action as the high sensor
32
is activated by the level of the solution. A second high sensor
28
is an overflow sensor which functions when the first high sensor
32
malfunctions to drain the excess solution from drain pipe
38
. The low sensor
36
provides an interlock function when the solution level is sufficiently low to activate the low sensor
36
in order to prevent air from entering the outlet conduit
40
and the dispensing pump
42
.
The dispensing pump
42
is normally provided in a dual- stage pump, i.e. such as a MILLIPORE® Photo-250 Pump, equipped with an internal filter (not shown). The dispensing pump
42
extracts the polyimide solution along conduit
40
from the reservoir tank
20
while filtering out contaminants such as bubbles and gel by the internal filter. The dispensing pump
42
then delivers the polyimide solution along conduit
44
for dispensing to wafer
46
through a dispensing nozzle
48
. The wafer
46
is positioned on a wafer platform
50
by a vacuum means and spins by platform
50
during the polyimide spin coating process.
Under normal processing conditions, some bubbles will be found in the reservoir tank
20
and in the conduits
22
and
44
. A complete polyimide flow takes place from the reservoir tank
20
, through the conduit
40
, the dispensing pump
42
, the conduits
44
and
52
and the liquid feed conduit
60
by trapping a limited number of air bubbles by the internal filter provided in the dispensing pump
42
. At the same time, a three-way valve
54
is utilized to divert a polyimide solution from conduit
44
to the conduit
52
, while cutting out the solution flow in conduit
56
. The recycled flow is used to save the usage of the polyimide material. The operation of the sensor
26
, the valves
14
,
24
and
48
, the dispensing pump
42
and the wafer platform
50
is controlled by the master controller
30
, which is normally a micro-processor.
The conventional viscous liquid dispensing system
10
, shown in
FIG. 1
, while capable of stopping, by filtering out, some of the air bubbles trapped in the liquid, is not efficient in filtering out, or removing all the air bubbles. Furthermore, during the dispensing of a material such as polyimide for passivation of an IC device, a premature reaction or sometimes known as “a dark reaction” occurs in the polyimide liquid between the monomer and the initiator such that undesirable gel is formed. When the gel is dispensed onto the wafer surface, serious quality problems in the passivation layer occurs. An improved viscous liquid dispensing system is therefore desirable for dispensing a highly viscous liquid such as polyimide to not only degas the liquid by eliminating air bubbles, but also to prevent the formation of gel in the liquid.
While it has been found that oxygen, when contained in a polyimide solution prevents or retards the gelation process, there is little possibility that oxygen can be added to a polyimide solution in the conventional dispensing system. For example, the liquid feed conduit
60
, shown in an enlarged, cross-sectional view in
FIG. 1A
, does not allow an extended, prolonged exposure of polyimide with air, which contains approximately 20% oxygen. As shown in
FIG. 1A
, the liquid feed conduit
60
is normally provided with a sharpened tip portion
62
to facilitate a polyimide flow
64
into the solution
18
. While attempts have been made to increase the distance between the tip portion
62
and the liquid level
66
, other undesirable processing difficulties are caused by an impact between the liquid flow
64
and the liquid level
66
, resulting in a more severe air bubble problem. It should be noted that, for simplicity reason, the liquid output conduit
40
and the drain pipe
38
are not shown in FIG.
1
A.
It is therefore an objec
Fu Tzung-Chi
Yin Albert An-Ho
Smith Duane S.
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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