Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2000-04-10
2002-04-23
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C205S358000, C205S362000, C422S198000
Reexamination Certificate
active
06375913
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an integrated system comprising an oxygen selective ion transport membrane cooperating with a silicon oxidation furnace to provide ultra-high purity oxygen to the furnace as a reactant for producing a highly pure silicon dioxide coating. This integrated system affords a particular advantage inasmuch as the heat source employed for efficient operation of the silicon oxidation furnace is also suitably employed to provide a desired elevated temperature for efficient operation of the membrane, thereby insuring production of the desired high-purity oxygen permeate.
BACKGROUND OF THE INVENTION
Silicon dioxide is a key component for the manufacturing of semiconductors. Conventional processes for oxidizing silicon to form silicon dioxide typically employ oxygen-containing reactants, such as oxygen, air, steam, or a combination thereof, in furnaces that operate at high temperatures, such as from about 900° C. to about 1,000° C. The quality of the silicon dioxide coatings produced by the oxidation process is adversely affected by the presence of impurities in the gas phase of the reactor, and the semiconductor industry demands highly pure coatings. Accordingly, oxygen itself, in very pure form, is the preferred reactant for providing thin-layer films of silicon dioxide, typically having a film thickness of from 5 to 10 nanometers (nm). More particularly, ultra-high purity (so-called “UHP”) oxygen containing contaminants in a total amount not exceeding 100 parts per billion is desirably employed to oxidize the silicon to form silicon dioxide having the desired coating purity.
In order to achieve the required high level of silicon dioxide purity, contaminants such as argon (Ar) and krypton (Kr), as well as hydrocarbons, nitrogen, and other contaminants that tend to adversely affect the quality and/or growth of the coating, are removed from the oxygen reactant before effecting silicon oxidation. Several methods are known for “off-site” production of the desired UHP oxygen. After off-site production, the UHP oxygen is then suitably shipped to the site of the semiconductor plant for use in the oxidation furnace. Heretofore, off-site UHP oxygen production was typically done by cryogenic distillation of air to form so-called “high purity” (also referred to as “HP”) oxygen, containing no more than 0.5% by weight of impurities, followed by further refinement of the HP oxygen to produce the desired UHP oxygen. This process is expensive, and the resulting UHP oxygen must then be shipped to the site of the silicon dioxide plant for use as desired. Further, if this expensive methodology is used “on-site” to purify the bulk oxygen supply to a microelectronics plant, the cost becomes prohibitively expensive. Moreover, such “bulk” purification methodology typically results in wasted oxygen purification efforts when used to produce oxygen reactant for portions of the plant that do not require such high purity, UHP oxygen, since the requirements for UHP material are typically localized within the plant.
Another method that is useful for producing contaminant free oxygen for use in industrial application involves the utilization of an oxygen selective ion transport (ceramic) membrane. These ceramic membranes are capable of selectively transporting oxygen ions across the membrane, and are used to separate pure oxygen from gas mixtures in a variety of industrial applications, although not heretofore in combination with a silicon oxidation furnace.
Ceramic membranes formed from solid electrolytes and mixed conducting oxides typically exhibit the property of oxygen selectivity. “Oxygen selectivity” means that only oxygen ions are transported across the membrane, while other elements and ions are excluded. These mixed conductor ceramic membranes (also referred to as “ionic/mixed conductor membranes”) are known to be generally useful for purifying oxygen, although not heretofore in combination with a silicon oxidation furnace.
By way of illustration, U.S. Pat. No. 5,306,411 (to Mazanec et al) discloses that ceramic membranes are suitably employed to produce oxygen for oxidation reactors. Additionally, U.S. Pat. No. 5,580,497 (to Balachandan et al) teaches the use of dense ceramic ion conductors that are suitably used to produce high purity oxygen. Further, U.S. Pat. No. 5,380,467 (to Ching-Yu Lin) teaches that ionic conductors are suitably used to produce high purity oxygen in an pressure-driven mode, whereas International Patent Application WO 95/27810 (to Renlund et al) describes such production utilizing the ionic conductor in an electrically-driven mode. None of these patents disclose the use o f a ceramic membrane for oxygen purification in connection with a silicon oxidation plant.
In view of the inconvenience and expense associated with known methods for supplying UHP oxygen to silicon oxidation furnaces, the microelectronic components manufacturing community has a need for a system for cost effectively producing on-site UHP oxygen within, or in close proximity to, the silicon oxidation furnace itself. The present invention provides an answer to that need.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide a process for integrating a mixed conductor ceramic membrane into the operation of a silicon oxidation furnace for oxidizing silicon to form silicon dioxide, and to take advantage of the energy efficiencies associated therewith.
It is a further object of this invention to provide a process that will provide UHP oxygen to specific site(s) within a silicon oxidation furnace requiring such UHP oxygen, while avoiding the requirement to ship UHP oxygen from outside the plant or use it throughout the factory environment.
Yet another object of this invention is to integrate the operation of a silicon oxidation furnace, used to form silicon dioxide and typically operating at temperatures in excess of 900° C., to provide heat for an integrated selective oxygen transport membrane cell. This facilitates using the same heat source that is required for the operation of the oxidation furnace to provide the high temperatures required for the proper functioning of the membrane.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to an integrated system for producing high purity silicon dioxide comprising:
a) a source of an oxygen-containing feed gas containing at least one impurity,
b) an oxygen transport membrane cell containing an oxygen-selective transport membrane that has a cathode side and an opposing anode side, said membrane being at an elevated temperature effective for separation of oxygen in said feed gas from said impurity by transporting oxygen ions from said oxygen-containing feed gas through said membrane to said anode to form a purified oxygen permeate on said anode side, while retaining an oxygen-depleted, impurity-containing retentate on said cathode side,
c) a passageway from said source (a) to the cathode side of said membrane cell,
d) a silicon source, (commonly a silicon wafer), and
e) a silicon oxidation furnace, in communication with said anode side of said membrane cell, for reaction of said purified oxygen permeate with silicon from said silicon source, at an elevated reaction temperature effective for said reaction, in order to produce said high purity silicon dioxide.
In another aspect, the present invention relates to a process for producing a high purity silicon dioxide coating on a substrate comprising contacting a surface of the substrate with silicon dioxide produced using the above-described integrated system.
In yet another aspect, the present invention relates to a method for preparing pure silicon dioxide comprising the steps of:
A) feeding an oxygen-containing feed gas into a cathode side of an oxygen transport membrane cell containing said cathode side and an anode side, with an oxygen transport membrane therebetween,
B) selectively transporting oxygen ions from said oxygen-containing feed gas from said cathode side through said membrane to said anode side to provide a purified oxygen
Albaugh Kevin Bruce
Keskar Nitin Ramesh
Johnson Edward M.
Pranair Technology
Rosenblum David M.
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