Use of ozone in process effluent abatement

Details Use of ozone in process effluent abatement Use of ozone in process effluent abatement

1997-02-24

2001-08-21

Dunn, Tom (Department: 1754)

Chemistry of inorganic compounds

Modifying or removing component of normally gaseous mixture

Halogenous component

C423S245300, C423S235000, C204S157150, C422S186000

Reexamination Certificate

active

06277347

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to the abatement of gaseous effluents created during semiconductor substrate processing. More specifically, the present invention relates to a method and apparatus for reducing effluent levels in the gaseous discharge of semiconductor substrate processing equipment by using ozone in the abatement process.
In recent years, the release of certain gaseous chemical compounds into the environment has become the subject of various laws and regulations administered by regulatory agencies such as the Environmental Protection Agency (EPA). Many of these compounds are monitored by agencies such as the EPA for potentially harmful effects on the environment.
The semiconductor industry is particularly affected by these concerns because of the numerous kinds of chemicals involved in the fabrication of integrated circuits. The release of chlorofluorocarbons (CFCs) and perfluorinated compounds such as CF
4
, C
2
F
6
and NF
3
(also called perfluorocarbons, or PFCs), which are used in semiconductor processing operations such as thin film etching, chemical vapor deposition (CVD) and the cleaning of processing chambers, among other operations, is regulated by the EPA. Also regulated is the release of nitrogen oxide (NO
X
) compounds, which may be emitted by certain semiconductor processing systems.
Illustrated in
FIG. 1
is a substrate processing system
100
of the prior art capable of carrying out one or more processes that may discharge such effluent gases, such as CFCs, PFCs, nitrogen oxides and ozone (e.g., a CVD system). The process gases required for the process being performed are introduced into a processing chamber
105
via process gas lines
110
(
1
)-(M). These process gases are then energized (e.g., thermally or by radio-frequency (RF) energy), to promote reactions that form the desired layer(s) on one or more substrates (not shown) disposed within processing chamber
105
. The CFCs, PFCs, nitrogen oxides and other effluent gases generated by these reactions, along with unreacted portions of the process gases, are removed from processing chamber
105
by a vacuum pump (not shown) and are exhausted through effluent line
120
into an abatement device
130
. Optionally, one or more combustion fuels may be introduced into a combustion chamber (not shown) of abatement device
130
via combustion fuel lines
140
(
1
)-(N). In the combustion chamber, chemical reactions occur between the effluent gases and optional combustion fuels.
One technique commonly used in the abatement of effluent gases is thermal abatement. Thermal abatement devices use thermal energy sources such as an open flame or electric arc to promote the chemical reactions that convert the undesirable compounds into less volatile, environmentally safer compounds. If a thermal abatement technique is employed, various combustion fuels may be introduced into the combustion chamber along with the effluent gases to further promote the decomposition of undesirable compounds. Which combustion fuels are used, if any, depends on the abatement technique employed. Combustion fuels such as oxygen-containing gases (e.g., oxygen or air) and hydrogen are often employed due to their reactivity and the high heat produced by their reactions with each other and various effluent gases.
Another common abatement technique is the use of RF energy to dissociate compounds within the effluent gas stream. An example of this is a plasma technique in which a plasma is formed from effluent gases introduced into the combustion chamber. This ionization promotes decomposition of undesirable compounds within the effluent gases, converting them into safer, more tractable compounds.
Regardless of the abatement technique employed, energy is applied to the effluent gases and optional combustion fuels to promote combustion. The by-products of the abatement reactions are then exhausted along with any unreacted gases. Depending upon the configuration, more abatement operations may be performed to further reduce levels of undesirable compounds within the exhaust gases, using methods such as water scrubbing, catalysis and filtering. For example,
FIG. 1
shows abatement device
130
connected to a water scrubber
150
. In water scrubbing, effluent gases are brought into contact with water, using methods such as bubbling the effluent gases through the water, sending the effluent gases through a water spray or the like. Certain of the effluent gases then react with the water, forming inert or, at least, less hazardous compounds. Alternatively, the exhaust gases may be discharged directly into the atmosphere. However, regardless of the abatement technique employed, several types of compounds in an effluent gas stream may not be abated sufficiently using traditional techniques. This is particularly true of PFCs. Moreover, newer methods capable of abating these compounds such as plasma abatement are often expensive and require large amounts of energy.
As illustrated in
FIG. 1
, substrate processing system
100
may also include an ozone generator
160
that generates ozone (O
3
) for use in some substrate processing operations. For example, substrate processing system
100
might be capable of depositing a silicon oxide film (SiO
X
). Such a film may be deposited at atmospheric pressure and at a temperature as low as 250° C. by reacting tetraethylorthosilicate (Si(C
2
H
5
O)
4
), also called tetraethoxysilane (TEOS), with ozone. TEOS/ozone silicon oxide films are desirable because they exhibit smooth oxide profiles over steps, good filling of high aspect-ratio gaps (i.e., gaps with a high depth-to-width ratio) and desirable electrical characteristics. A TEOS/ozone process is suitable for depositing silicon oxide films for applications such as intermetal dielectrics. The thermal reaction that takes place between TEOS and ozone is given by:
Si(C
2
H
5
O)
4
+8O
3
- - - >SiO
2
+10H
2
O+8CO
2
Ozone generator
160
may use any one of several ozone generation techniques. For example, ozone generator
160
might use an electric arc technique, generating ozone by passing an oxygen-containing gas through an electric arc. An example of an ozone generation system employing this method is AX8200A from Astex, Inc., of Woburn, Mass. Normally, in processes such as the TEOS/ozone process described above, ozone is generated continuously throughout operation of the chamber to maintain stable process parameters and flow rates, rather than simply shutting down ozone generator
160
.
Thus, ozone is directed to processing chamber
105
when the process being performed requires ozone. However, when the process being performed does not require ozone or when a substrate is not being processed (e.g., while a substrate is being transferred into or out of the chamber or during the cleaning of processing chamber
105
), a bypass valve
170
directs the unused ozone through a bypass line
180
that feeds into an ozone abatement device
190
. Ozone abatement device
190
normally renders ozone inert by converting the ozone into oxygen. Such conversion methods include thermal abatement, ultraviolet (UV) catalysis (in which the ozone is photolytically decomposed) and chemical catalysis (in which ozone is chemically decomposed by reaction with a compound such as manganese dioxide (MnO
2
)).
As is evident from the above, it is desirable, from both a regulatory and an environmental perspective, to reduce or eliminate the effluents emitted by substrate processing equipment, such as CFCs, PFCs, nitrogen oxides and ozone. It is also desirable to provide more effective abatement of these compounds using the facilities already available in certain substrate processing systems. Moreover, it is desirable to increase abatement efficiency, in terms of power and fuel consumed in the abatement process.
Aside from its use in processing substrates, ozone has also found use in the abatement of various toxic or undesirable chemicals. For example, ozone has been employed in the destruction of certain chemical weapons, combining with the letha

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