Evacuation system

Details Evacuation system Evacuation system

1997-05-21

2001-12-25

Bueker, Richard (Department: 1763)

Coating apparatus

Gas or vapor deposition

C156S345420, C055S315200, C055S342200, C062S055500

Reexamination Certificate

active

06332925

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an evacuation system used in, for example, evacuating a processing chamber of a semiconductor fabrication apparatus.
2. Description of the Related Art
A conventional evacuation system will be explained with reference to
FIG. 23. A
vacuum chamber
410
is, for example, a processing chamber in a semiconductor fabrication apparatus for performing tasks such as dry etching process or chemical vapor deposition (CVD) process, and is connected to a vacuum pump
412
through an evacuation and exhaust conduit
414
. The vacuum pump
412
is used to elevate the pressure of the process gas to an atmospheric pressure so as to evacuate the vacuum chamber
410
, and in the past, this role has been served by an oil pump, but lately it has been mainly served by a dry pump. If the degree of vacuum required by the vacuum chamber
410
is higher than that achievable by the dry pump alone, a higher performance vacuum device such as a turbomolecular pump is sometimes used in the upstream side of the dry pump.
The process gas can be toxic or explosive, depending on the nature of the process, and cannot be allowed to escape into the environment without being treated. For this reason, an exhaust gas treatment device
426
is placed downstream of the vacuum pump
412
in which those gaseous components which cannot be released to the environment are treated by being adsorbed, decomposed or absorbed, and only the detoxified gases are released. The evacuation conduit
414
is provided with valves to isolate sections, as necessary.
The conventional arrangement of evacuation systems described above share the following common faults.
1. If the reaction byproducts contain corrosive gases, the vacuum pump may be attacked, thus shortening its service life. For example, when etching silicon-based devices with a typical process gas containing CF
4
and O
2
, its exhaust gas contains SiF
4
, F
2
, CO, CO
2
in addition to the residual CF
4
and O
2
. Of these gases, F
2
is particularly strongly corrosive (because fluoride radicals are produced in the process) to the vacuum pump.
2. If the process byproduct contains a gas having a high sublimation temperature, which is exhausted by the vacuum pump, the result is the formation of deposit particles within the vacuum pump to ultimately become a reason for its failure to perform. For example, when etching aluminum-based devices by using a typical process gas containing BCl
3
, Cl
2
, the vacuum pump must exhaust a reaction byproduct gas AlCl
3
, in addition to residual BCl
3
and Cl
2
. This gas, AlCl
3
, does not decompose in the intake side of the pump because of its low partial pressure, but the partial pressure increases in the pressurized exhaust gas to produce precipitation within the vacuum pump to cause performance problems. Similar problems occur when operating a CVD apparatus, for producing SiN films, that produces byproduct gases (NH
4
)
2
SiF
6
and NH
4
Cl and the like.
3. Solid particles may be discharged from the processing chamber, which may enter the vacuum pump directly to cause operational problems. For example, in the case of a reduced pressure CVD apparatus based on tetraethyloxysilane (TEOS) process for producing Si films, the process gas containing TEOS and O
2
is used, and various types of alcohols and solid SiO
2
particles are produced. The silicon oxide particles are produced as solids in the reaction, and they impart mechanical damage to the vacuum pump.
4. When the byproduct contains a gas which is reactive at high temperatures, it may react within the vacuum pump to cause operational problems. For example, in a CVD apparatus for producing tungsten films using a typical process gas containing WF
6
and SiH
4
, the gaseous byproducts HF and H
2
along with residual WF
6
and SiH
4
gases are exhausted from the processing chamber. As the pressure and temperature within the vacuum pump increase, WF
6
and SiH
4
react with each other to precipitate W particles that cause operational problems for the vacuum pump.
5. The conventional facilities are expensive to operate because the process gases are discarded without being reused. Especially some gases such as SiH
4
are expensive, and it is desirable that they be recycled, however, recycling has not been practiced in the past. Also, in the conventional approach, there are trapped several kinds of gases in one trapping device, and it has been laborious to process the byproducts for separation into various components.
6. The entire voluminous exhaust gas must be processed in the exhaust gas treatment apparatus, which leads to a large-scale operation and a huge capital expenditure, in the first place, and the processing steps become complex and the running cost can be expensive.
Of the various problems listed above, corrosion resistant pumps have been developed to deal with the problems presented in items 1, and the problems outlined in item 2 have been dealt with by raising the operating temperature of the vacuum pump; however, such remedies relate only to the vacuum pump operations, and because the overall system problems have not been addressed, progress has been minimal. There have been no considerations given to the problems outlined in items 5 and 6.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an evacuation system having a long service life and high reliability, which can also make the exhaust gas treatment device smaller, and the process gases reusable, so that the overall costs of capital investment and operation are reduced.
The object has been achieved in an evacuation system comprising a processing chamber, and a vacuum pump communicating with the processing chamber by way of an evacuation conduit for evacuating the processing chamber, wherein the evacuation conduit are provided with not less than two trapping devices arranged in series and operating at different temperatures for capturing different components contained in an exhaust gas discharged from the processing chamber. Corrosive gases and abrasive components in the exhaust gas are thus removed before they can enter into the vacuum pump to cause damage to the pump. The adoption of at least two different temperatures for the traps enables to separate the exhaust gas having a mixture of component gases into separate components, thus facilitating the ensuing process of gas treatment and conserving expensive process gases for reuse.
The cascading arrangement of thermal traps in a descending temperature gradient, from upstream to downstream traps in the evacuation system, enables solid particles and those gases having high sublimation temperatures to be trapped in the first trap while the other components and reaction byproducts can be trapped in the second and ensuing traps downstream, according to their thermodynamic properties.
The trap temperature varies depending on the type of target gas, and should be set lower than the solidifying temperature of the target components. If the temperature is in a typical range, i.e., not lower than −60° C., the cooling medium can be chosen from such materials as-air, water, brine and organic coolants.
Especially, for those thermal traps following the second trap, the operating temperatures are often not higher than −60° C. In these cases, cooling methods include helium refrigeration device (based on the heat of expansion of helium gas) used in cryogenic pumps typically represented by GM refrigeration device. More preferably, a pulse tube refrigeration device is used to minimize vibration.
When the trap temperature is close to or higher than the vaporization temperature of the liquefied gas, it is convenient to utilize the latent heat of vaporization. Especially, liquid nitrogen is attractive because of its availability and low cost. If not less than two low-temperature traps are needed, helium refrigeration unit can be used in conjunction with a liquid nitrogen unit.
Trapping performance changes depending on the operating temperature of the low-temperature trap

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