Gas processing techniques

Details Gas processing techniques Gas processing techniques

1999-06-25

2001-05-01

McDermott, Corrine (Department: 3744)

Refrigeration

Low pressure cold trap process and apparatus

Reexamination Certificate

active

06223540

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to gas processing techniques employing condensation on a cold surface in vacuum.
BACKGROUND OF THE INVENTION
Vacuum processing techniques are employed in many fabrication techniques, such as for example semiconductor fabrication. Examples of vacuum fabrication techniques include thin film deposition, etching and surface preparation. These techniques employ a variety of processing gases. Additionally, gases can be formed as by-products of these techniques. Many process and by-product gases are toxic, combustible or corrosive. Consequently, vacuum fabrication techniques generally require treatment of the effluent gases to remove noxious substances.
An example of a conventional vacuum fabrication system, including treatment of effluent gases is schematically illustrated in
FIG. 1
, showing vacuum fabrication system
100
. A conventional vacuum fabrication chamber
110
is provided with a process gas inlet
112
and a vacuum outlet
114
. Vacuum fabrication chambers are typically equipped with one or more vacuum gauges (not shown) and one or more temperature gauges (not shown). Ports (not shown) can also be provided, for example, to introduce purge gas into the chamber. These chambers are typically equipped with a load-lock chamber (not shown) to introduce a substrate into the fabrication chamber while keeping the fabrication chamber under vacuum.
Vacuum fabrication systems employ one or more vacuum pumps to obtain the required vacuum level and to remove process gases and by-product gases from the system. Pump selection is generally determined by the required vacuum level and the type and throughput quantities of the various gases as well as the potential for process contamination by pump substances such as pump oils.
FIG. 1
illustrates a prior art vacuum fabrication system
100
including a conventional vacuum pump system
140
. Typical conventional vacuum pump systems include a single vacuum pump, such as a mechanical pump, or a combination of for example two vacuum pumps. Such conventional pump combinations can include a turbo molecular pump in series with a mechanical roughing/backing pump or a cryopump in parallel with a roughing/backing pump. Cryopumps (also known as cryogenic pumps) trap molecules on a cold surface in high vacuum generally ranging from about 10
−1
torr to about 10
−10
torr, while turbo molecular pumps achieve high vacuum by expelling molecules through collisions between the molecules and turbine blades spinning at high speeds. Roughing/backing pumps include displacement pumps which are initially used to rough out the fabrication chamber before vacuum fabrication is started and which can subsequently be used to remove effluent gases. Systems, such as system
100
, typically employ components (not shown) such as isolation valves, throttle valves, pressure gauges, temperature gauges and one or more forelines for process control.
Conventional cryopumps condense effluent process and by-product gas molecules on one or more cold surfaces at temperatures ranging from about 100 K to about 7 K. At about 10 K, all gases except helium and hydrogen condense on the cold pump surface resulting in high vacuum and in containment of all condensable effluent substances other than helium and hydrogen. Cryopump helium and hydrogen condensation requires the use of adsorption materials. The gas condensation process forms solid and/or liquid condensate on the cold surfaces of the cryopump. This process is continued until the pump efficiency starts to decrease. At this point, the pump is regenerated by increasing the pump temperature to evaporate the condensate. The regenerated effluent gases are then treated in treatment facility
140
(
FIG. 1
) which includes such treatment processes as reclamation, dry scrubbing, wet scrubbing, or combustion followed by dry or wet scrubbing. The remaining non-noxious gases can then be vented into the atmosphere.
The noxious gas treatment techniques of system
100
require that the gas treatment facility for removing noxious substances from regenerated gases is physically connected to the vacuum pump system and thus to the vacuum fabrication process. Consequently, each vacuum fabrication location requires its own treatment facility to which several vacuum fabrication processes may be connected. Also, vacuum fabrication processes which are at the same location may require different treatment facilities if these fabrication processes do not have similar noxious gases. The need for local treatment facilities precludes the economies of scale which can be realized if gases originating at several remote vacuum fabrication facilities can all be treated at one location for centralized gas treatment. Also, changes in gas treatment processing methods or equipment are more effectively made at a centralized treatment facility.
Accordingly, a need exists for cost effective, improved processing techniques for treating vacuum fabrication effluent gases.
SUMMARY OF THE INVENTION
The present invention provides novel processing techniques for treating vacuum fabrication effluent gases which overcome the prior art problems described above.
In one embodiment of the present invention, gases are condensed on a cold surface in a pumping chamber of a pump adapted for chamber pressures of at least about 10,343 torr (200 psi), preferably for pressures of about 103,430 torr (2,000 psi). The gases are condensed at a pressure which is below atmospheric pressure. Typically, the temperature of the cold surface ranges from about 7 K to about 20 K, while the pressure in the pumping chamber typically ranges from about 10
−1
torr to about 10
−10
torr. The pumping chamber is closed when the efficiency of the gas condensation process starts to decrease as a result of the formation of a substantial layer of liquid and/or solid condensate on the cold surface. The cold surface is then warmed, causing the evaporation of the condensate, resulting in the formation of regenerated gases. The regenerated gases cause a pressure increase inside the pumping chamber. The pumping chamber is opened to a vessel, for example a high pressure vessel, when the pressure inside the chamber reaches a predetermined level, such as atmospheric pressure. Evaporation of condensate is continued until substantially all condensate has evaporated to form regenerated gases. Condensate evaporation generally results in high pressures, typically ranging from about 10,343 torr to about 103,430 torr, inside the pumping chamber and inside the vessel. The vessel and pumping chamber are then closed, after which the vessel can be separated from the pumping chamber. Noxious substances in the regenerated gases which are isolated in the vessel can subsequently be subjected to treatment, on-site or at a remote location, in order to remove the noxious substances. Advantageously, the inventive technique thus results in a gas treatment process wherein vacuum process gases and by-product gases can be treated at a remote location, for removal of noxious substances.
In another embodiment of the present invention, an additional cold surface is employed inside the pumping chamber, preferably adapted for cooling at temperatures ranging from about 50 K to about a 100 K, for more effective gas condensation.
In still another embodiment of the present invention, the pumping chamber is provided with a housing including an inner housing adapted for chamber pressures ranging from about 10
−10
torr to atmospheric pressure and an outer housing adapted for inside pressures ranging from atmospheric pressure to at least about 10,343 torr and preferably to about 103,430 torr.
In still another embodiment of the present invention a vacuum fabrication process is provided which includes a novel effluent gas containment system wherein the novel pump is connected to a vessel, preferably a pressure vessel.
In another embodiment of the present invention, a novel gas processing system is provided for processing vacuum fabrication effluent gases. The system includes a

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