New Precursors for the Organometallic Chemical Vapor Deposition of Aluminum Nitride
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NEW PRECURSORS FOR THE ORGANOMEfALLIC CHEMICAL VAPOR DEPOSITION OF ALUMINUM NITRIDE WAYNE L. GLADFELTER*, DAVID C. BOYD*, JEN-WEI HWANG*, RICHARD T. HAASCH*, JOHN F. EVANS*, KWOK-LUN HO#, AND KLAVS F. JENSEN# Departments of #Chemical Engineering and Materials Science, and *Chemistry, University of Minnesota, Minneapolis, Minnesota
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ABSTRACT Organometallic aluminum azides have been found to be effective precursors for the low temperature chemical vapor deposition of thin films of aluminum nitride. Quantitative analysis of the gas phase products of the reaction are used to develop an understanding of the reaction. Rate studies of the deposition were performed in the temperature range from 400 to 800°C. Below 525°C, an activation barrier of 26.4 kcal/mol was found, while above 525°C, a value of 5.23 kcal/mol was obtained. The effects of the presence of N-C bonds and the type of Al-N interaction within the precursor are evaluated. INTRODUCTION Aluminum nitride has the wurtzite crystal structure and several physical properties that make it especially interesting, both as a bulk material and as a thin film. As a large band gap (6.2 eV) III-V compound[l], which is very hard, resistant to chemical attack and high melting (2400 0 C)[2], it has useful properties for coatings. Its piezoelectric nature makes it potentially important for surface acoustic wave devices, and its high thermal conductivity may be exploited in applications for packaging electronic microcircuits[3]. The nitrogen sources in these previous studies have included ammonia[4,5] (the most common source), hydrazine[6] and alkylaluminum amido compounds[7,8].
We
describe here studies on the use of azide[9,10] group as the reactive nitrogen source and compare these results to precursors which contain direct N-C bonds. THIN ALUMINUM NITRIDE FILMS FROM [Et 2 AIN 3] 3 Two reactors were used to study the CVD of AIN.
The "survey" reactor had a hot-
wall quartz tube which was usually operated without carrier gas and had a base pressure of 5 x 10-5 torr. A removable liquid N2 trap placed between the quartz tube and the pump allowed the trapping and quantitation of all volatile products except
Mat. Res. Soc. Symp. Proc. Vol. 131. 11989 Materials Research Society
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N2, H2, and CH 4 .
A schematic of the second reactor in which all rate measurements
were performed is shown in Figure 1. Figure
1 Detector
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I
S
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Exhaust
Azide Bubbler
Heating Unit
Pure hydrogen, produced by a Matheson Pd-alloy purifier, was used as the carrier gas for the [Et 2 AIN 3 ] 3 , and was also used to purge the viewport on the reactor chamber.
The reactor chamber was a six-way stainless steel cross.
The susceptor
was a Mo plate heated radiatively by a Mo wire carrying a current of a few amperes. The growth rates were measured in situ with a 6328 A He-Ne laser interferometry assembly[ 1l].
Exhaust gases and unreacted precursor were cracked by passing them
through a high-temperature furnace and filtering before venting to a hood. Si(100) substrates were prepared b
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