Chemistry of inorganic compounds – Boron or compound thereof
Reexamination Certificate
1999-07-12
2002-06-18
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Boron or compound thereof
C423S290000, C423S299000, C423S300000, C423S301000, C423S351000, C423S409000, C423S412000, C423S463000, C423S464000, C423S465000
Reexamination Certificate
active
06406677
ABSTRACT:
BACKGROUND OF THE INVENTION
Aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN) are advanced materials of emerging importance for a number of applications in the microelectronics, optoelectronics, aerospace and other industries (L. M. Sheppard,
Ceramic Bull.,
69:1801-1812 (1990), “Aluminum Nitride: A Versatile but Challenging Material”). AlN is an ideal heat transfer medium for high power electronic devices and multichip modules because of its favorable thermal and electronic conductivity. It is also highly refractory and mechanically strong, making it useful for high temperature processes and abrasion and corrosion protection of surfaces. Depending on the specific application, bulk powder or a thin film may be required.
Bulk powders are used to press shapes, such as crucibles or rods and other structures. Popular methods of preparing bulk powder AlN comprise carbothermal reduction of Al
2
O
3
in the presence of nitrogen and direct nitridation of metallic aluminum and reaction of AlCl
3
with NH
3
. (L. M. Sheppard, 1990, supra). Each method has certain advantages and drawbacks. Carbothermal reduction proceeds at 1100° C., with removal of unreacted carbon at 600-700° C. in dry air and further heating at 1400° C. in vacuum. Residual carbon and oxide impurity in the final material can be a problem for batch quality.
Direct nitridation (1200° C.) suffers from incomplete conversion of starting materials and coalescence of metallic aluminum. Gas phase approaches, such as reaction of AlCl
3
with NH
3
, are inherently low yield. Bulk polymeric aminoalane AlCl
3
precursors have been prepared electrochemically by anodization of an Al electrode in liquid NH
3
at −70° C. (C. B. Ross et al.,
Chem. Mater.,
3:768-771 (1991), “Electrochemical Synthesis of Metal Nitride Ceramic Precursors in Liquid Ammonia Electrolyte Solutions”). Thermal decomposition of polyaminoalanes prepared by direct reaction of neat N
2
H
4
with AlCl
3
has been reported (W. G. Paterson and M. Onyszchuk,
Can. J Chem.,
41:1872-1876 (1963), “The Interaction of Hydrazine with Boron and Aluminum Halides”).
Thin films commonly needed in microelectronic or surface protection applications are usually prepared by thermal decomposition of a gas phase precursor at high temperature by chemical vapor deposition (CVD). A number of these precursors have been reported including [(CH
3
)
2
AlNH
2
]
3
(L. V. Interrante et al.,
J Electrochem. Soc.,
136:472-478 (1989), “Preparation and Properties of Aluminum Nitride Films Using an Organometallic Precursor”), Al(C
2
H
5
)
3
+NH
3
(A. A. Adjaottor and G. L. Griffin,
J. Am. Ceram. Soc.,
75:3209-3214 (1992), “Aerosol Synthesis of Aluminum Nitride Powder Using Metalorganic Reactants”) and basic aluminum chloride/glucose (N. Hashiomoto et al.,
J Am. Ceram. Soc.,
75:2098-2106 (1992), “Sintering Behavior of Fine Aluminum Nitride Powder Synthesized from Aluminum Polynuclear Complexes”). The common problem of CVD with these materials is that they contain carbon and/or oxygen in their structures, which then contaminates the final product as oxide or carbide. This has implications for thermal conductivity of the material, which depends on impurity levels. CVD methods can be quite complex as well, requiring optimization of formation of the precursor in the gas phase in addition to optimization of the CVD reaction itself.
Processes using molten salts to produce metal nitrides have been reported; however, these reactions are run at temperatures higher than 200° C. See, e.g., U.S. Pat. No. 4,029,740 to Ervin, Jr. for “Method of Producing Metal Nitrides.”
Chloroaluminate molten salts combined with alkali metal chlorides to provide Lewis acid-base neutrality are described in U.S. Pat. No. 5,096,789 . This patent does not teach the desirability of acidic melts nor the preparation of nitrides.
Ambient temperature molten salts of chloroaluminates and 1-butylpyridinium chloride and 1-ethyl-3-methylimidazolium chloride are described in Osteryoung, R. A., (1987) “Organic Chloroaluminate Ambient Temperature Molten Salts,” in
Molten Salt Chemistry
, G. Mamantov and R. Marassi (eds): 329-364 . Electrochemical and spectroscopic behavior of certain hydrocarbons in AlCl
3
-1-butylpyridinium chloride or 1-ethyl-3-methylimidazolium chloride molten salt systems have been studied as reported in Robinson, J. and Osteryoung, R. A. (1979), “An Electrochemical and Spectroscopic Study of Some Aromatic Hydrocarbons in the Room Temperature Molten Salt System Aluminum Chloride-n-Butylpyridinium Chloride,”
J. Amer. Chem. Soc.
101(2):323-327; and Uribe, F. and Osteryoung, R. A. (1988), “Electrochemical and Spectroscopic Studies of 1,4-Benzoquinone in Ambient Temperature Chloroaluminate Ionic Liquids,”
J. Electrochem. Soc.
135(2):378-381.
Plating baths for electrodeposition of aluminum using molten salt baths comprising aluminum halide and a quaternary ammonium salt comprising an alkylimidazolium halide are disclosed in U.S. Pat. No. 4,904,355 to Takahashi for “Plating Bath for Electrodeposition of Aluminum and Plating Process of Making Use of the Bath.” U.S. Pat. No. 5,135,825 to Mori et al. for “Method for Producing Ambient Temperature Molten Salt Consisting of Certain Pyridinium and Imidazolium Halides and an Aluminum Trihalide” discloses the use of an inert solvent having a low boiling point for making a molten salt. U.S. Pat. 5,543,522 to Kawahara et al. for “Process for Preparing an Ambient Temperature Molten Salt Using Thionyl Chloride” discloses ambient temperature molten salts for electroplating comprising aluminum halide and onium halide together with thionyl chloride. U.S. Pat. No. 5,552,241 to Mamantov et al. for “Low Temperature Molten Salt Compositions Containing Fluoropyrazolium Salts” discloses mixtures of metal halides and fluoropyrazolium salts for use in electrochemical cells. The use of such salts in processes for forming metal nitrides, however, is not suggested in these patents.
Molten salts of aluminum, gallium or indium with hydrocarbyl-saturated onium ions are disclosed in U.S. Pat. No. 4,764,440 to Jones and Blomgren for “Low Temperature Molten Compositions.” These salts are molten below about 100° C. U.S. Pat. No. 4,883,567 to Verbrugge et al. for “Method of Plating Metallo-gallium Films” discloses the use of a room-temperature melt consisting of GaCl
3
-dialkylimidazolium chloride and a salt of a metal to be codeposited for electrodeposition of gallium-arsenic gallium-antimony or gallium-aluminum. U.S. Pat. No. 5,463,158 to Goledzinowski et al. for “Oligomerization of Low Molecular Weight Olefins in Ambient Temperature Melts” also discloses aluminum and gallium halide and certain organic halides (containing N-heterocyclic rings and substituted onium ions) used to form molten salts in catalytic systems. Molten salts of gallium with certain organic halides have also been reported in S. P. Wicelinski et al.,
J. Electrochem. Soc.,
134:262-263 (1987), “Low Temperature Chlorogallate Molten Salt Systems.” These salts apparently display chlorogallate equilibria analogous to that of the chloroaluminates. The GaCl
3
-MEIC (MEIC, 1-ethyl-3-methylimidazolium chloride, also known as EMIC) and GaCl
3
-BPC systems (BPC, N-butylpyridinium chloride) are liquid at ambient temperature over a wide range of compositions (S. P. Wicelinski et al., supra) but require the synthesis of the organic chloride salt (J. S. Wilkes et al.,
Inorg. Chem.,
21:1263-1264 (1982), “Dialkylimidazolium Chloroaluminate Melts: A New Class of Room-Temperature Ionic Liquids for Electrochemistry, Spectroscopy and Synthesis”; S. D. Jones and G. E. Blomgren,
J. Electrochem. Soc.,
136:424-427 (1989), “Low-Temperature Molten Salt Electrolytes Based on Aralkyl Quaternary or Ternary Onium Salts”).
A dialkylimidazolium chloride:InCl
3
molten salt that melts below 45° C. for a particular basic composition, 45:55 mole % InCl
3
:RCl, used to electrodeposit mixed InSb films has been reported (M. K. Carpenter and M. W. Verbrugge, U.S. Pat. No. 5,264,111, “Methods of Making Thin InSb Films”);
Carter Michael T.
Donahue William J.
Bos Steven
Eltron Research, Inc.
Greenlee Winner and Sullivan P.C.
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