Fluid handling – Line condition change responsive valves – Direct response valves
Reexamination Certificate
2000-02-04
2002-01-15
Buiz, Michael Powell (Department: 3753)
Fluid handling
Line condition change responsive valves
Direct response valves
C137S533110, C137S614200
Reexamination Certificate
active
06338361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for controlling a flow resistance of a photoresist solution, and more particularly, to an apparatus with a check function for controlling a flow resistance of a photoresist solution.
2. Description of the Prior Art
In a lithographic process, electrical patterns are formed by performing exposure and development processes to a photoresist that has been coated onto the surface of a semiconductor wafer. The photoresist solution is drawn from a storage tank, transported via pipes to a nozzle and then sprayed onto the surface of the semiconductor wafer during the coating process. The viscosity of the photoresist solution varies from one storage tank to another as photoresist solutions of different viscosities are required for different manufacturing conditions. The change of viscosity affects the flow rate of the photoresist solution. These changing flow rates of the photoresist solution cause disproportionate coatings of photoresist onto the surface of the semiconductor wafer and adversely affect the yield of the subsequent fabrication process. Hence, it is important to control the flow resistance of the photoresist solution so as to transport the photoresist solution with a substantially constant pressure.
Please refer to FIG.
1
.
FIG. 1
is a schematic diagram of a photoresist solution supply device
10
according to the prior art. The photoresist solution supply device
10
comprises a tank
12
for storing the photoresist solution, a pipe
14
partially submerged in the photoresist solution in the tank
12
to transport the photoresist solution, a buffer tank
16
connected to the pipe
14
to remove bubbles from the photoresist solution, a pump
24
connected to the buffer tank
16
to draw the photoresist solution from the buffer tank
16
, a nozzle
34
, a bellow
26
connected to the pump
24
, and an air cylinder
28
connected with the bellow
26
. The pump
24
has compression and extension cycles, and pumps photoresist to the nozzle
34
on the compression cycle. The bellow
26
is air-powered and delivers the mechanical motion required to drive the pump
24
. The air cylinder
28
comprises two valves
30
,
32
and the to-and-fro movement of the bellow
26
is generated by compressed air flowing into the air cylinder
28
from the different valves
30
,
32
.
The buffer tank
16
comprises an inlet
18
on its top that is connected to the pipe
14
, an outlet
22
on its bottom, and a vent
20
set at the top of the buffer tank
16
to vent bubbles from the photoresist solution. When the photoresist solution is introduced into the buffer tank
16
, the bubbles in the photoresist solution accumulate in the top of the buffer tank and are vented through the vent
20
to prevent bubbles from interfering with the photoresist coating on the surface of the semiconductor.
To move the photoresist solution from the tank
12
to the nozzle
34
, compressed air flows into the air cylinder
28
from the valve
32
. This causes the bellow
26
to pull on the pump
24
, which extends the pump
24
and causes it to draw photoresist from the tank
12
. Then, compressed air flows into the air cylinder
28
from the valve
30
. This causes the bellow
26
to push on the pump
24
, compressing it and forcing the photoresist solution from the pump
26
to the nozzle
34
. The buffer tank
16
draws photoresist solution from the tank
12
through the pipe
14
to replace the photoresist solution drawn by the pump
24
. When the tank
12
runs out of photoresist solution, the pipe
14
is extracted from the tank
12
and inserted into a new tank. During this change, the photoresist solution in the pipe
14
drains out and air flows in. When the pipe
14
is inserted into the new tank, bubbles form in the photoresist solution. These bubbles are coated onto the surface of the semiconductor wafer together with the photoresist solution, degrading the quality of the photoresist coating process.
The viscosity of the photoresist solution can vary from one tank to another as photoresist solutions with differing viscosities are required by various manufacturing conditions. The change of viscosity affects the volume of photoresist solution transported into the pump
24
, and may also cause bubbles to form in the photoresist solution. If the viscosity of the photoresist solution in the new tank is less than that of the previous tank, and the pump
24
draws the photoresist solution at the same speed, the volume of the photoresist solution drawn into the pump
24
will increase, leading to waste of the photoresist solution. If the flow speed of the photoresist solution drawn into the pump
24
is too great, bubbles will form in the photoresist solution. Therefore, the driving pressure of air forced into the air cylinder
28
must be changed to prevent the formation of bubbles in the photoresist solution. The optimum driving pressure, however, is arrived at through trial and error. The transport of photoresist solution to the nozzle
34
may not go smoothly during the trial and error process. This leads to uneven coatings of photoresist and decreases the quality of the coating process.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a flow-control apparatus with a check function for controlling the flow resistance of a photoresist solution.
In a preferred embodiment, the present invention provides a flow-control apparatus with a check function for controlling the flow resistance of a photoresist solution. The apparatus is connected to a photoresist supply device, the photoresist supply device comprises a tank for storing the photoresist solution, a pipe partially submerged in the photoresist solution in the tank to transport the photoresist solution, and a pump for drawing the photoresist solution out of the tank, the apparatus comprising:
a housing comprising a chamber, a top opening positioned at the top of the chamber, and a bottom opening positioned at the bottom of the chamber; wherein the top opening can be mated to an end of the pipe or to a bottom opening of another housing;
a sphere moveably set inside the chamber of the housing, the sphere being used to increase the flow resistance of the photoresist solution;
wherein the number of the apparatuses mounted in series with the end of the pipe can be changed to control the flow resistance of the photoresist solution through the pipe when drawing the photoresist solution from the tank.
It is an advantage of the present invention that the present invention can prevent back-flow of the photoresist solution into the tank so that air cannot flow into the pipe during the changing of one tank for another. The present invention controls the flow resistance of the photoresist solution by changing the number of apparatuses connected to the pipe, the density of the sphere, the number of spheres in the housing and the size of the sphere. A checklist can be made that relates the viscosity of the photoresist solution with the number of apparatuses, the density of the sphere, the number of spheres and the size of the sphere so that the flow resistance of the photoresist solution through the pipe can be easily controlled, thereby increasing the quality of the coating process.
REFERENCES:
patent: 1510609 (1924-10-01), Rush
patent: 3787149 (1974-01-01), Dane et al.
patent: 4187874 (1980-02-01), Essebaggers
patent: 4282897 (1981-08-01), de Mey, II
patent: 4601409 (1986-07-01), DiRegolo
patent: 4846218 (1989-07-01), Upchurch
patent: 5368556 (1994-11-01), Lecuyer
patent: 6071094 (2000-06-01), Yu et al.
Cheng Chia-Wen
Cheng Ying-Ming
Kao Chung-Hsien
Lee Li-Chung
Buiz Michael Powell
Krishnamurthy Ramesh
United Microelectronics Corp.
Winston Hsu
LandOfFree
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