Deposition and Characterization of Metalorganic Chemical Vapor Deposition ZrO 2 Thin Films Using Zr(thd) 4
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DEPOSITION AND CHARACTERIZATION OF METALORGANIC CHEMICAL VAPOR DEPOSITION ZrO2 THIN FILMS USING Zr(thd) 4
Jie Si, Chien H. Peng, and Seshu B. Desu Department of Materials Engineering, Virginia Polytechnic University, Blacksburg, VA 24061.
Institute and State
ABSTRACT Excellent quality ZrO 2 thin films were successfully deposited on single crystal silicon wafers by metalorganic chemical vapor deposition (MOCVD) at reduced zirconium, tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato) pressures using 0 [Zr(thd)4]. For substrate temperatures below 530 C, the film deposition rates were
very small (_ 1 nm/min). The film deposition rates were significantly affected by: (1) source temperature, (2) substrate temperature, and (3) total pressure. As-deposited films are stoichiometric (Zr/O = 1/2) and 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 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, are reported. The measured value of the dielectric constant of the as-deposited ZrO 2 films is around 19 in the frequency range of 5 kHz to 1000 kHz. 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, buffer layers for the growth of high Tc superconducting thin films, and in high-temperature optical filters.
Many different methods, such as reactive electron beam eva poration [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. ZrC14 , which was first used as a precursor for CVD ZrO 2, requires very high deposition temperatures (> 800 0C) and could result in the formation of fine powders [4]. The organometallic alkoxides such as zirconium i-propoxide, Zr(OPri) 4, and zirconium t-butoxide, Zr(OBut) 4 , are also not suitable as precursors due to their instabilities [4]. However, zirconium acetylacetonates appear to be most suitable Use of zirconium trifluroacetylacetonate, precursors for ZrO 2 deposition. Zr(CsH 4F 302) 4 , for MOCVD of ZrO 2 films was reported earlier by our research group Although good quality ZrO 2 films were obtained using zirconium [4]. trifluroacetylacetonate, the process parameter space is limited due to the possible fluorine contamination. Here we report on the use of an acetylacetonate without fluorine, namely, [Zr(thd) 4] for the deposition of excellent quality ZrO 2 films. EXPERIMENTAL PROCEDURE ZrO 2 thin films were deposited in a reactor which was described in a previous paper [4]. Depositions were carried out at reduced pressures (4 to 10 to
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