Specialized metallurgical processes – compositions for use therei – Processes – Producing or purifying free metal powder or producing or...
Reexamination Certificate
2002-01-28
2004-01-20
Wyszomierski, George (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or purifying free metal powder or producing or...
C075S369000
Reexamination Certificate
active
06679938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention is drawn to a spray pyrolysis method for producing particles and an apparatus for performing the method. Specifically, the present invention is drawn to a spray pyrolysis method for producing pure metal particles and/or metal oxide particles without using a reducing gas such as hydrogen or carbon monoxide. More specifically, the present invention is drawn to a spray pyrolysis method for producing uniform sized monodispersed particles, particularly microparticles or nanoparticles of a pure metal and/or a metal oxide, from a mixture of a carrier gas and a solution of a metal salt precursor, water and a co-solvent.
2. Description Of Related Art
Metal nanoparticles are of interest for a variety of applications because of their unique chemical, electrical, and optical properties. These applications include catalysis, conducting pastes, templates, and size standards for calibration of optical scattering instruments used by various industries to inspect materials for surface quality. Surface defects such as particulate contaminants and surface roughness, as well as substrate defects, are of great concern for quality control of products such as semiconductor devices, magnetic storage media and flat panel displays. As device dimensions shrink, detection of these defects plays an increasingly important role in increasing product yield. Most studies of defect detection have used optical scattering of dielectric materials such as polystyrene latex (PSL) spheres. Solutions consisting of suspensions of size-monodispersed PSL particles are commercially available, and the PSL particles can easily be deposited onto wafers.
However, it is unlikely that PSL particles are representative of actual industrial process contaminants. Furthermore, the interaction of light between particles and a silicon substrate is much simpler for dielectric materials than for other materials such as metals. A need exists for methods of producing uniform size-monodisperse (“monodispersed”) particles of other materials, particularly metals, which may be deposited onto wafer surfaces for use as optical scattering standards and for evaluating light scattering theories.
Presently in the electronics industry, metal particles have been used in the formation of conductive pastes. These particles, however, have mainly been obtained through chemical precipitation from a solution of metal salt precursor. In order to improve production yield, use of a continuous process such as spray pyrolysis is desirable. However, the reduction of metal oxide, produced from metal precursors, to form pure metal particles is a challenging problem.
The spray process method, which is composed of a carrier gas, an aerosol generator, and a high temperature reactor, has been studied by several research groups. For example, Nagashima et al.,
Chemical Society of Japan
, 1990, 1, 17 and Majumdar et al.,
Journal of Material Research
, 1996, 11, 2861, the entire disclosures of which are incorporated herein by reference, disclose using hydrogen gas as a reducing agent to obtain pure metal particles from various aqueous metal salt systems. However, these methods may be very dangerous in high temperature conditions (above 500° C.) because of the explosive property of hydrogen that creates a significant fire hazard. The ignition energy for a hydrogen-air mixture is much lower than for hydrocarbon-air mixtures. Therefore, very low energy sparks such as from a static electric discharge can lead to ignition; furthermore, if the burning gas is even slightly confined, the resulting pressure rise can lead to a detonation.
Several research groups have used hydrogen gas in spray pyrolysis as a reducing gas. Further Xia et al.,
J. Mater. Res
., 2000, 15, 2157, discloses using a co-solvent, ammonium bicarbonate to produce pure Ni particles from an aqueous Ni chloride solution, whereas Nagashima et al., J. Mater. Res., 1990, 12, 2828, discloses using Ni(NO
3
)
2
and NiCl
2
aqueous solutions in an H
2
—N
2
atmosphere to produce fine Ni particles. The entire disclosures of these references are incorporated herein by reference.
Copper metal particles have been produced using hydrogen to reduce metal oxide particles formed by spray pyrolysis of copper salt precursors. In these prior art processes, because the concentration of hydrogen required to reduce the metal oxide particles is greater than the flammability limit of hydrogen in the air, a potential safety hazard results.
U.S. Pat. No. 6,316,100 to Kodas et al. (the '100 patent), discloses a method for producing nickel metal powders. The entire disclosure of the '100 patent is incorporated herein by reference. The teachings and specific embodiments discloses therein may be used with the present invention.
The '100 patent is drawn to a method of producing nickel particles that are substantially spherical, have a weight average particle size of not greater than about five gm, a narrow particle size distribution and high crystallinity. The reference is directed to generating an aerosol of droplets including a nickel metal precursor and moving the droplets through a heating zone of 700° C.-1400° C. to form nickel particles. Embodiments of the reference use a hydrogen, nitrogen and a hydrogen-nitrogen mixture carrier gas. As such, the methods disclosed in the reference may be very dangerous in high temperature conditions for the reasons as stated above with respect to hydrogen. What is needed is a more efficient, less hazardous, method of forming pure nickel particles.
U.S. Pat. No. 5,421,854, also to Kodas et al. (the '854 patent), discloses a method for manufacturing finely divided particles of palladium, palladium oxide or mixtures thereof The entire disclosure of the '854 patent is incorporated herein by reference. The disclosed teachings and specific embodiments therein may be used with the present invention.
The '854 patent discloses a first step of forming an unsaturated solution of a thermally decomposable palladium-containing compound in a thermally volatizable solvent. The reference teaches a following step of forming an aerosol consisting essentially of finely divided droplets of the solution in an air carrier gas. The reference then teaches a third step of heating the aerosol between 300° C. and 950° C., wherein palladium oxide is formed at temperatures between 300° C. and 800° C., and pure palladium is formed only at temperatures between 800° C. and 950° C. What is needed is a more efficient method of forming pure palladium particles.
U.S. Pat. No. 5,861,136 to Glicksman et al. (the '136 patent), discloses a method for manufacturing fully dense, finely divided, spherical particles of copper I oxide (Cu
2
0) and copper II oxide (CuO) powders. The entire disclosure of the '136 reference is incorporated herein by reference. The specific teachings and exemplary embodiments therein may be used with the present invention.
The '136 patent discloses a first step of forming an unsaturated solution of a thermally decomposable copper containing compound in a thermally volatilizable solvent wherein the copper containing compound is used in concentrations not below 0.002 mole/liter or not higher than 90% of saturation, and wherein the particle size of copper I oxide is an approximate function of the cube root of the concentration of the unsaturated solution. The reference teaches a second step of forming an aerosol consisting essentially of finely divided for droplets of the solution in an inert carrier gas. The reference teaches a third step of heating the aerosol, to an operating temperature of at least 1,000° C., wherein the copper containing compound is decomposed to form the copper II oxide (CuO), and the copper II oxide is decomposed to formed pure phase copper I oxide (Cu
2
O) particles. This reference does not disclose a method for producing pure copper particles.
U.S. Pat. No. 6,277,169 to Hampton-Smith et al. (the '169 patent), discloses a method of providing high quality, micro-size
Ehrman Sheryl H.
Germer Thomas A.
Kim Jung Hyeun
Mulholland George W.
Steel Eric B.
University of Maryland
Wenderoth , Lind & Ponack, L.L.P.
Wyszomierski George
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