Metal-organic chemical vapor deposition of ZrO 2 films using Zr(thd) 4 as precursors
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Ching-Yi Tsai Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received 22 September 1993; accepted 2 March 1994)
Synthesis of zirconium tetramethylheptanedione [Zr(thd)4] was optimized. Purity of Zr(thd) 4 was confirmed by melting point determination, carbon, and hydrogen elemental analysis and proton nuclear magnetic resonance spectrometer (NMR). By using Zr(thd) 4 , excellent quality ZrO 2 thin films were successfully deposited on single-crystal silicon wafers by metal-organic chemical vapor deposition (MOCVD) at reduced pressures. For substrate temperatures below 530 °C, the film deposition rates were very small (=£1 nm/min). The film deposition rates were significantly affected by (i) source temperature, (ii) substrate temperature, and (iii) total pressure. As-deposited films are carbon free. Furthermore, only the tetragonal ZrO 2 phase was identified in as-deposited films. The tetragonal phase transformed progressively into the monoclinic phase as the films were subjected to a high-temperature post-deposition annealing. The optical properties of the ZrO 2 thin films as a function of wavelength, in the range of 200 nm to 2000 nm, were also reported. In addition, a simplified theoretical model which considers only a surface reaction was used to analyze the deposition of ZrO 2 films. The model predicated the deposition rates well for various conditions in the hot wall reactor.
I. INTRODUCTION ZrO 2 thin films, due to their variety of applications, are of considerable interest. For example, ZrO 2 films were utilized as thermal barrier coatings, as buffer layers for the growth of high Tc superconducting thin films, and as active layers in high-temperature optical filters. Many different methods, such as reactive electron beam evaporation,1 dc and rf magnetron sputtering,2 and chemical vapor deposition (CVD),3 have been employed for the fabrication of ZrO 2 thin films. Among these techniques, CVD seems to be a very promising and compatible method for electronic and optical device applications. The primary issue of CVD ZrO 2 thin films is the identification of a good precursor. ZrCl4, which was first used as a precursor for CVD ZrO 2 , requires very high deposition temperatures (>800 °C) and could result in the formation of fine powders.4 The organometallic alkoxides such as zirconium i-propoxide, Zr(OPr') 4 , and zirconium f-butoxide, Zr(OBu') 4 , are also not suitable as precursors due to their instabilities.4 However, zirconium acetylacetonates appear to be the most suitable precursors for ZrO 2 deposition. Use of zirconium tri-
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to whom all the correspondence should be addressed. J. Mater. Res., Vol. 9, No. 7, Jul 1994
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fluoroacetylacetonate, Zr(C 5 H 4 F 3 O 2 ) 4 , for MOCVD of ZrO 2 films was reported earlier by our research group.4 Although good quality ZrO 2 films were obtained using zirconium trifluoroacetylacetonate, the process parameter space is limited due
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