Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Molecular oxygen or ozone component
Reexamination Certificate
2001-10-31
2004-05-11
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Molecular oxygen or ozone component
C423S210000, C423S347000, C423S352000, C502S304000, C502S326000, C502S345000, C502S349000, C502S353000, C502S406000, C095S117000, C095S138000, C096S154000
Reexamination Certificate
active
06733734
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of gas purification, and to the purification of hydride gases that are useful in the microelectronics manufacturing industry. More specifically, the invention relates to methods and materials for selectively removing trace amounts of oxygen impurities and moisture from hydride 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.
Ammonia is a process gas that is very important in the semiconductor industry for the formation of nitride layers in electronic transistors through chemical vapor deposition and epitaxy processes. More specifically, ammonia is commonly used for the formation of silicon nitride and silicon oxynitride films by direct nitridation of silicon oxide. Growing films of silicon nitride and silicon oxynitride requires ammonia of very high purity. Ammonia is also used in the production of compound semiconductors such as GaN, GaAlN, etc. Oxygen is a particularly harmful contaminant because its high chemical reactivity leads to its incorporation as an impurity into films during thermal nitridation of silicon oxide or during the production of GaN and GaAlN semiconductors. The manufacturing of GaN films requires very large amounts of ammonia during the processing steps. New methods of ammonia purification are thus required to reduce the cost of manufacturing wafers in the GaN process. Regenerable purifiers are also becoming more important as the cost of ownership becomes a more critical parameter.
Water vapor and carbon dioxide gas are two other detrimental contaminants in hydride gases, and which can lead to the degradation of products formed by deposition of active layers of metals or metal compounds from a hydride gas environment. Water is one of the most common and yet most difficult impurities to remove from process gases. Most drying processes can reduce the moisture content of a gas to only a “minimum” which is still in the parts per million (ppm) range. However, in the manufacture of components such as high performance light emitting diodes (LEDs), the water content of the depositing gases must be reduced to the parts-per-billion (ppb) range.
Many of the purifier materials such as reduced nickel or copper catalysts that are effective in removing contaminants in more inert gases, such as nitrogen and the noble gases, are not effective in purifying hydride gases. The reactivity of the hydride gases such as ammonia quickly causes degradation of the purifier materials and contaminates the gas stream.
Prior art processes have been described in which oxygen has been removed from ammonia streams by various purifiers. U.S. Pat. No. 5,716,588 to Vergani, et al., describes removing oxygen from ammonia and other hydride gases at room temperature using purifier comprising elemental iron and manganese deposited on an inert material.
U.S. Pat. No. 6,241,955 to Alvarez, Jr. et al, describes high surface metal oxides (greater than 100 m
2
/g) for removing contaminants such as oxygen, carbon dioxide, and water vapor from hydride gases. The metal oxides are not deposited on a substrate, but rather are used as bulk material within a gas-purifier canister. Since only the active sites on or near the outer surface of the bulk material are accessible to and capable of removing impurities from the gas stream, the Alvarez, Jr., et al., purifier needs to have a larger surface area to be effective.
There remains a need in the art for a reagent that removes contaminants such as oxygen and water from hydride 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 oxygen from hydride gases without concurrently emitting contaminants such as moisture into the purified gas stream and without causing substantial decomposition of the hydride gas.
SUMMARY OF THE INVENTION
Accordingly, this invention provides a purifier material capable of reducing the level of contaminants such as oxygen and moisture in a hydride 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). In one embodiment, the total surface area of the thin layer coating is less than 100 m
2
/g.
This invention further provides methods of producing a purifier material of this invention, comprising:
(a) providing a precursor comprising a nonreactive substrate having deposited thereon a thin layer of a metal of a first oxidation state;
(b) heating the precursor under a flow of nitrogen at a temperature between about 100° C. and 600° C. for a period of time; and
(c) treating the precursor from step (b) under reductive conditions capable of reducing the oxidation state of the metal, thereby producing a purifier material comprising the substrate having deposited thereon a thin layer of one or more reduced forms of an oxide of the metal having a second oxidation state, wherein the second oxidation state is lower than the first oxidation state.
This invention further provides methods of purifying hydride gases comprising contacting the contaminated hydride gas with a purifier material of this invention.
Additional novel features and advantages 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. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
This invention provides methods of producing purifier materials for removing contaminants such as oxygen and moisture from hydride gases. The purifier materials produced by the methods of this invention are capable of reducing the level of contaminants such as oxygen and mo
Fraenkel Dan
Watanabe Tadaharu
Hendrickson Stuart L.
Hogan & Hartson
Matheson Tri-Gas
Medina Maribel
O'Rourke Sarah
LandOfFree
Materials and methods for the purification of hydride gases does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Materials and methods for the purification of hydride gases, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Materials and methods for the purification of hydride gases will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3220663