Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
2002-10-29
2004-11-30
Lawrence, Frank M. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C095S137000, C095S138000, C095S139000, C095S140000
Reexamination Certificate
active
06824589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of gas purification, and to the purification of inert, nonreactive and reactive gases. More specifically, the invention relates to methods and materials for selectively removing trace amounts of impurities such as oxygen, water, CO, CO
2
, NO, NO
2
N
2
O
4
, SO
2
, SO
3
, SO, S
2
O
2
, and SO
4
from inert, nonreactive, and reactive gases.
2. Description of the Prior Art
The provision of high purity gas streams is critically important in a wide variety of industrial and research applications. The rapid expansion of vapor-phase processing techniques, e.g. chemical vapor deposition, in the semiconductor industry has been associated with the deployment and use of manufacturing equipment that is totally reliant on the delivery of ultra-high purity process gases at the point of use in the semiconductor manufacturing facility.
Considering the impurities which are present in gas streams involved in semiconductor manufacturing, it is to be noted that the growth of high quality thin film electronic and optoelectronic cells by chemical vapor deposition or other vapor-based techniques is inhibited by a variety of low-level process impurities. These impurities can cause defects that reduce yields by increasing the number of rejects, which can be very expensive. These impurities may be particulate or chemical contaminants.
Chemical impurities may originate in the production of the source gas itself, as well as in its subsequent packaging, shipment, storage, and handling. Although source gas manufacturers typically provide analyses of source gas materials delivered to the semiconductor manufacturing facility, the purity of the gases may change because of leakage into or outgassing of the containers, e.g. gas cylinders, in which the gases are packaged. Impurity contamination may also result from improper gas cylinder changes, leaks into downstream processing equipment, or outgassing of such downstream equipment.
Inert and non-reactive gases such as nitrogen, helium, and argon are widely used in the semiconductor industry for the manufacture of microcircuitry devices. In such applications, it is critical that the gases be essentially completely free of impurities such as water and oxygen. For example, in semiconductor fabrication processes, gases such as nitrogen, helium and argon are often required to not have more than low ppb or sub-ppb impurity levels to ensure that the impurities do not degrade the quality, and hence the performance of the semiconductor chips. Such impurities, when introduced onto the semiconductor chip during its manufacture, tend to render the chip deficient or even useless for its intended purpose. Thus, a growing number of industries are now requiring gases having impurity concentrations that do not exceed about 10 parts-per-billion (ppb) levels.
One known method of gas purification involves the adsorption of process gas impurities on a bed or column of solid scavenger material. In these solid adsorption methods, impurities are caught by the surface of the scavenger material while the process gas preferably passes unaltered through the bed or column. Commonly used solid scavenger adsorption materials include alumina, silica, silica-alumina, other metal oxides such as titania and zirconia, mixed oxides, clays, molecular sieves (e.g., zeolites), and activated carbon.
There remains a need in the art for a reagent that removes contaminants such as oxygen, water, CO, CO
2
, NO, NO
2
, N
2
O
4
, SO
2
, SO
3
, SO, S
2
O
2
, and SO
4
from inert nonreactive and reactive gases. Further, there remains a need for a reagent that is more efficient (removes more contaminants per square meter of surface area) than the prior art. Moreover, there is a need for a purifier material that can be regenerated. Further, a need exists for purifier materials that remove impurities from inert, nonreactive, and reactive gases without concurrently emitting contaminants such as water into the purified gas stream.
SUMMARY OF THE INVENTION
Accordingly, this invention provides a purifier material capable of reducing the level of contaminants such as oxygen, water, CO, CO
2
, NO, NO
2
, N
2
O
4
, SO
2
, SO
3
, SO, S
2
O
2
, and SO
4
in an inert, nonreactive, or reactive gas stream to parts-per-billion levels or sub-parts-per-billion levels. The purifier materials of this invention comprise a thin layer of reduced forms of an oxide of a metal deposited or coated onto the surface of a nonreactive substrate. The reduced forms of the metal oxide thin layer coating include one or more reduced oxides of the metal in which the oxidation state of the metal is lower than the maximum oxidation state of the metal. In addition to the reduced oxides of the metal, the thin layer may further include the completely reduced form of the metal (i.e., the metal in a zero oxidation state).
This invention further provides methods of removing one or more contaminants from inert, nonreactive, or reactive gas streams using purifier materials of this invention. In one embodiment, the method of this invention for removing contaminants from an inert, nonreactive, or reactive gas stream comprises contacting said contaminated gas stream with a purifier material for a period of time sufficient to reduce the level of said contaminants to parts-per-billion levels, said purifier material of this invention, said purifier material comprising a nonreactive substrate having deposited thereon a thin layer of one or more reduced forms of a metal oxide, wherein said metal oxide is selected from the group consisting of oxides of molybdenum, antimony, bismuth, tin, chromium, cobalt, copper, tungsten, manganese, iron, and mixtures thereof.
Another embodiment of this invention for removing contaminants from an inert, nonreactive, or reactive gas stream comprises contacting said contaminated gas stream with a purifier material of this invention for a period of time sufficient to reduce the level of said contaminants to parts-per-billion levels, said purifier material comprising a nonreactive substrate having deposited thereon a thin layer of one or more reduced forms of an oxide of a metal, said thin layer having a total surface area less than 100 m
2
/g.
Yet another embodiment of this invention for removing contaminants from an inert, nonreactive, or reactive gas stream comprises contacting said contaminated gas stream with a purifier material of this invention for a period of time sufficient to reduce the level of said contaminants to parts-per-billion levels, said purifier material comprising a nonreactive, substrate having deposited thereon a thin layer of one or more reduced forms of an oxide of a metal, wherein the oxidation state of said metal in said purifier thin layer is lower than the maximum oxidation state of said metal, wherein said metal is other than nickel.
Additional features of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention
DETAILED DESCRIPTION OF THE INVENTION
This invention provides methods of producing purifier materials for removing impurities including, but not limited to, oxygen, water, CO, CO
2
, NO, NO
2
, N
2
O
4
, SO
2
, SO
3
, SO, S
2
O
2
, and SO
4
from inert, nonreactive, and reactive gases. The purifier materials of this invention are capable of reducing the level of contaminants from inert or nonreactive gases including, but not limited to, nitrogen (N
2
), hydrogen (H
2
), helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), saturated and unsaturated hydrocarbons including, but not limited to methane and butene, saturated and unsaturated halocarbons including, but not limited to tetrafluoromethane and octafluorocyclopentene (C
5
F
8
), NF3, SF
6
and mixtures thereof. The purifier materials of this invention are also capable of reducing the level of contaminants from reactive gases including, but not limited to, S
Fraenkel Dan
Torres, Jr. Robert
Watanabe Tadaharu
Hogan & Hartson L.L.P.
Lawrence Frank M.
Matheson Tri-Gas
Petersen Steven C.
Smith Sarah J.
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