Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-07-25
2004-11-23
Lieu, Julie (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S603000, C137S002000
Reexamination Certificate
active
06822575
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mass flow controllers which control the flow of process gases into a process chamber in the fabrication of integrated circuits on semiconductor wafers in the chamber. More particularly, the present invention relates to a backfill prevention system which may be operated in conjunction with a mass flow controller to measure flow of gas through a gas flow conduit and close a valve or valves in the conduit as needed to prevent gas backfilling of the conduit.
BACKGROUND OF THE INVENTION
The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.
Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic or photolithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate. Many of the various processing steps, including but not limited to etching and chemical vapor deposition (CVD), used in the semiconductor fabrication process require process fluids or chemicals for the formation of integrated circuits on the wafer substrate.
About 50 different types of gases are used in as many as 450 process steps in semiconductor manufacturing. Gases used in semiconductor fabrication are generally categorized as one of two types: bulk gases, which include oxygen, nitrogen, helium and argon; and specialty gases, which include chlorine and hydrogen chloride and are the process gases used to effect the circuit-fabricating chemical reactions on the semiconductor wafer substrate. Bulk gases, which include purge gases used to flush undesirable residual gases, atmospheric gases or water vapor from a process chamber, are stored in large storage tanks outside the wafer fab manufacturing area and are distributed into the proper workstation through a bulk gas distribution (BGD) system. Specialty gases are dispensed from cylinders in a gas cylinder cabinet containing a control panel. A local gas distribution system in the process area is used to deliver the gas from the cylinder to the chamber of the process tool.
The molecular quantities of the reactant gases utilized in semiconductor fabrication processes are important for proper control of the reactions. According to the ideal gas law, the number of gas molecules contained in a given volume changes in proportion to to the absolute pressure and temperature. Therefore, a given volume of gas flowing into a process chamber yields various quantities of gas molecules depending on the temperature and pressure of the gas. Accordingly, mass flow controllers (MFCs), which utilize a thermal sensor that senses the heat-transfer property of a gas to detect changes in the mass flow of the gas, are used to control the flow of gases into process chambers.
A typical conventional gas delivery system in a semiconductor fab facility is generally indicated by reference numeral
10
in FIG.
1
and includes a gas manifold
12
connected to a process chamber
40
of a process tool (not shown) in the facility. The gas manifold
12
may be contained in a valve manifold box (VMB, not shown) and includes a BCl
3
gas delivery conduit
14
for conducting BCl
3
to the process chamber
40
, a Cl
2
gas delivery conduit
15
for conducting Cl
2
to the process chamber
40
, an N
2
S gas delivery conduit
16
for conducting N
2
S to the process chamber
40
, a CH
3
F gas delivery conduit
17
for conducting CH
3
F to the process chamber
40
, and a CF
4
gas delivery conduit
18
for conducting CF
4
to the process chamber
40
. The BCl
3
and the Cl
2
are each delivered to the process chamber
40
typically at a pressure of about 15 psi, whereas the N
2
S, the CH
3
F and the CF
4
are delivered to the process chamber
40
typically at a pressure of about 35 psi. Each of the gas flow lines
14
-
18
is typically fitted with a manual valve
20
for manually opening and closing the corresponding gas flow line; a regulator
24
for controlling the gas pressure in the gas flow line; a filter
26
for filtering particles from the flowing gas; a mass flow controller (MFC)
30
for controlling the flow rate of each gas in the corresponding gas delivery conduit; and an upstream valve
28
and a downstream valve
32
on respective sides of the mass flow controller
30
. The gas delivery conduits are connected to a common manifold conduit
34
, from which an outlet conduit
36
conducts the gases into the process chamber
40
. A final valve
38
is provided in the outlet conduit
36
. The lower-pressure gas delivery conduits
14
and
15
may each be fitted with a V-block valve
22
which prevents backflow of gas through the respective gas delivery conduits.
One of the problems associated with the conventional gas delivery system
10
is that the final valve
38
frequently becomes blocked or clogged during use and is therefore incapable of opening to establish fluid communication between the manifold conduit
34
and the process chamber
40
. Consequently, residual gas from the higher-pressure gas delivery conduits
16
-
18
, such as the N
2
S, the CH
3
F or the CF
4
, respectively, remains in the manifold conduit
34
after flow of these gases to the process chamber
40
. Accordingly, upon subsequent flow of the lower-pressure BCl
3
to the process chamber
40
through the gas delivery conduit
14
, the upstream valve
28
and downstream valve
32
are each opened and the higher-pressure CH
3
F or CF
4
backflows from the manifold conduit
34
and through the downstream valve
32
, the mass flow controller
30
and the upstream valve
28
, respectively, of the BCl
3
gas delivery conduit
14
. This gas backfill causes contamination of the BCl
3
gas delivery conduit
14
with the CH
3
F or the CF
4
gas, thereby potentially adversely affecting processes carried out in process tools connected to the valve manifold box in which the gas manifold
12
is contained. Additionally, clearing of the CH
3
F or CF
4
gas from the BCl
3
gas delivery conduit
14
results in unnecessary downtime in the semiconductor processing sequence.
Accordingly, an object of the present invention is to provide a system which prevents undesired backfilling of a gas flow conduit with a gas.
Another object of the present invention is to provide a backfill prevention system which prevents gas contamination of a gas flow conduit.
Still another object of the present invention is to provide a backfill prevention system which is capable of closing a valve or valves in a gas flow conduit to prevent backfilling of the conduit with an undesired gas.
Yet another object of the present invention is to provide a backfill prevention system which prevents undesired gas contamination of a process tool for semiconductors.
A still fu
Chen Jing-Hou
Chen Wen-Ming
Fu Ming-Shong
Wang Wen-Chi
Lieu Julie
Taiwan SEmiconductor Manufacturing Co., Ltd
Tung & Associates
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