Mesh filter design for LPCVD TEOS exhaust system

Details Mesh filter design for LPCVD TEOS exhaust system Mesh filter design for LPCVD TEOS exhaust system

2000-03-31

2002-10-01

Bueker, Richard (Department: 1763)

Coating apparatus

Gas or vapor deposition

C055S385200, C055S463000, C055S521000, C055S487000, C055S486000, C055S525000, C055SDIG003

Reexamination Certificate

active

06458212

ABSTRACT:

TECHNICAL FIELD
The present invention generally relates to improved TEOS CVD processing. In particular, the present invention relates to reducing unwanted build-up in TEOS CVD exhaust systems thereby permitting temporary process stops substantially increasing the time intervals between servicing a CVD exhaust system.
BACKGROUND ART
Chemical vapor deposition (CVD) involves the formation of a solid film on a substrate by the reaction of vapor phase chemicals that contain the required constituents. The reactant gases are introduced into a reactant chamber and are decomposed and reacted at a heated surface to form the film. CVD techniques are widely employed in the fabrication of semiconductor structures; therefore, CVD techniques are some of the fundamental building blocks in semiconductor processing. Plasma enhanced chemical vapor deposition (PECVD) techniques involves using an rf-induced glow discharge to transfer energy into the reactant gases, thereby permitting the substrate to remain at relatively low temperatures (compared to other CVD techniques). Low pressure chemical vapor deposition (LPCVD) techniques involve, as the name implies, low pressures and are advantageous in that films having high purity, excellent uniformity, and conformal step coverage are obtainable. LPCVD techniques are disadvantageous in that high temperatures are typically required.
Another disadvantage associated with LPCVD processes involves the formation of tetraethylorthosilicate (TEOS) or Si(OC
2
H
5
)
4
films (or silicon dioxide layers made from TEOS starting material). During the LPCVD TEOS film formation process, the starting gas is continuously introduced into the reactor vessel, but a vacuum is continuously drawn from the reactor vessel through a vacuum extraction system typically containing an exhaust system connected to thereto, so that a predetermined low pressure is maintained in the reactor vessel to properly control the growth of the TEOS film. In many instances, the starting gas is not completely used in the formation of the TEOS film, and a large part thereof is undesirably pulled from the reactor vessel into the vacuum extraction/exhaust systems. As a result, the vacuum/exhaust systems that contribute to the low pressures, such as a mechanical booster pump, a rotary pump, a blower, various filters, and other related system elements, are damaged by the deposition therein of the starting gas pulled from the reactor vessel. In particular, the starting gas pulled from the reactor vessel is undesirably deposited on/in the filters thereby creating an unwanted build-up on/in filters of the exhaust system. TEOS byproducts also create an unwanted build-up on/in the exhaust system. TEOS material build-up is characterized by a very sticky film. This is problematic because the build-up on/in the filters of the exhaust systems requires frequent vigorous cleanings and/or replacement of the filters. If the clogged filters are not cleaned or replaced, a back stream is created wherein materials may undesirably flow back into the reactor vessel or processing chamber.
Conventionally, exhaust filters must be cleaned every five passes. One pass is defined as performing a CVD process on one set of wafers in a processing chamber. Such repetitive cleaning/replacement increases costs and/or constitutes “down time” in which the CVD process is not practiced.
The problem of unwanted build-up on/in the exhaust system of a TEOS LPCVD apparatus is better understood referring to
FIG. 1
, wherein a schematic representation of a prior art exhaust system
11
of a TEOS LPCVD apparatus
10
is shown. Specifically, TEOS LPCVD apparatus
10
includes a prior art exhaust system connected to a CVD process chamber
12
. The exhaust system
11
includes exhaust line
14
housing a filter
18
and connected to a vacuum pump
16
.
FIG. 2
is a cross-sectional illustration of a prior art filter
18
for the exhaust system
11
of the TEOS LPCVD apparatus
10
of FIG.
1
. The prior art filter
18
includes a cylindrical mesh filter element
20
and interior space
22
. Gas flow, shown by arrows in both
FIGS. 1 and 2
, leaves the CVD process chamber
12
and travels through the cylindrical mesh filter element
20
of the prior art filter
18
and then to the vacuum pump
16
. The unwanted build-up of TEOS byproducts on/in filter
18
of the exhaust system
11
is especially problematic at the bottom of the cylindrical mesh filter element
20
where the process stream first contacts the filter element
20
.
Moreover, TEOS is particularly problematic in LPCVD processes because TEOS gas condenses in the vicinity of 35° C. Problems ensue when an LPCVD TEOS film formation process is temporarily stopped, such as during evening hours or during a power glitch. In particular, after the LPCVD apparatus is turned off, the apparatus cools down to room temperatures from its high operating temperatures. Since TEOS gas condenses around 35° C., TEOS materials build-up on various elements of the LPCVD apparatus including the exhaust system as the temperature of the LPCVD apparatus cools down. Upon turning the LPCVD apparatus back on, filter elements cannot function properly due to the solid build-up of TEOS material. In many instances, within only 30 minutes after stopping and LPCVD TEOS film formation process, TEOS material builds-up so extensively that it is impossible to return to the same LPCVD process conditions. Although it is sometimes desirable to temporarily interrupt the LPCVD TEOS film formation process in order to make minor process adjustments, such interruptions are avoided due to the possibility that the LPCVD apparatus cannot be turned back on.
Cleaning a filter in an LPCVD TEOS film formation process requires one to disconnect the filter from the LPCVD apparatus, disassemble the filter mechanism, clean the individual parts, reassemble the filter mechanism, connect the filter back to the LPCVD apparatus, and testing the cleaned system. Not only is this cleaning process cumbersome, but the LPCVD apparatus is rendered useless during the long cleaning time, thus inhibiting further semiconductor processing. It is desirable to have a properly functioning and long lasting filter element in the exhaust system of the TEOS LPCVD apparatus because the life and function of the gas lines and pump system are markedly improved.
SUMMARY OF THE INVENTION
The present invention provides an improved TEOS CVD process by providing an improved exhaust system for the TEOS CVD apparatus. The improved exhaust system contains a filter having a conical shape, thereby increasing the flow area of TEOS byproducts making filtering markedly more efficient. The improved exhaust system minimizes the need to clean and or replace the filter element and/or having to interrupt the CVD process to remove and insert a new and/or cleaned filter into the exhaust system. This is because TEOS material build-up in/on a CVD exhaust filer is minimized. Undesirable back streams of TEOS byproducts are minimized and/or eliminated by the present invention. The improved exhaust system enables operating the TEOS CVD apparatus at high pressures (such as those encountered in PECVD techniques) as well as low pressures (such as those encountered in LPCVD techniques). The present invention also provides methods for minimizing the accumulation of TEOS material in the pump/vacuum system of the CVD apparatus due to the improved exhaust system. As a result of the present invention, TEOS CVD processing capabilities are lengthened, temporary stops in TEOS CVD processing are facilitated, and cumbersome cleaning/replacement of the exhaust system filters of the CVD apparatus is minimized.
One aspect of the present invention relates to a tetraethylorthosilicate chemical vapor deposition method, involving the steps of forming a film on a substrate using tetraethylorthosilicate in a chemical vapor deposition chamber; and removing tetraethylorthosilicate byproducts from the chemical vapor deposition chamber via a pump system and an exhaust line connected to the chemical vapor deposition chamber,

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