Low-Temperature Deposition of ZrC thin films from a Single-Source Precursor
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LOW-TEMPERATURE DEPOSITION OF ZrC THIN FILMS FROM A SINGLESOURCE PRECURSOR David C. Smith,*,t Rodrigo R. Rubiano,# Matthew D. Healy,t Robert W. Springert tLos Alamos National Laboratory, Los Alamos, NM 87545 #Department of Nuclear Engineering, MIT, Cambridge, MA 02139
ABSTRACT Stable zirconium carbide thin films have been deposited from a single source organometallic precursor, tetraneopentyl zirconium, at substrate temperatures above 500 'C. Materials deposited above this temperature are crystalline by X-ray diffraction. A metal to carbon ratio of 1:2 is observed by Auger electron spectroscopy depth profiling. X-ray photoelectron spectroscopy indicates the zirconium is single phase. The observed spectra correspond well to spectra for zirconium carbide standards. Carbon XPS reveals carbidic and graphitic or hydrocarbon species with a third unknown carbon species. Elastic recoil detection finds a large, up to 16%, hydrogen content in the thin film. INTRODUCTION Group IVB and VB carbides are of interest for a number of applications that take advantage of their refractory properties; extremely high melting points, hardness, and chemically stability.-4 Established chemical vapor deposition (CVD) routes to these materials rely on the reaction of metal halides with methane and hydrogen mixtures at temperatures in excess of 1000 'C. Many of the applications for these carbide materials focus on their use in elevated temperature environments; therefore, limitations due to the elevated deposition temperatures do not exist in most instances. The major limitations to the present technology are halide incorporation in the deposited materials and the subsequent problems this presents, the variability of the coating processes, and the extremely low volatility of the metal halide 5 precursors. An exception to the volatility limitation is TiCI4, a liquid at room temperature. An alternate approach to the deposition of metal carbides has focused on the use of 6 10 organometallic complexes (MRn) as CVD precursors. - These complexes are "tailored" for the production of metal carbides containing only the metal, carbon, and hydrogen, thus the halide does not appear in the deposition process. The organometallic complexes have greater volatility than the binary metal halides, subliming at temperatures of 75 to 100 'C at pressures of 10-3 Torr. In addition, most organometallic complexes decompose at temperatures below 400 'C. The reduced deposition temperatures opens up the possibility of coating thermally sensitive substrate materials. While the potential for lower process temperatures is not a requirement for the immediate applications of metal carbides, it provides for the possibility of a number of new applications of these materials. Lowering the deposition temperature increases the energy efficiency of the process and enables the use of the material in applications where high temperatures would lead to undesirable consequences such as interlayer atomic diffusion, delamination of overlayers due to mismatches in thermal expansion coeff
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