Metal-organic chemical vapor deposition of ZrO₂ films using Zr(thd)₄ as precursors

Abstract

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 ZrO₂ 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 ZrO₂ 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 ZrO₂ 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 ZrO₂ films. The model predicated the deposition rates well for various conditions in the hot wall reactor.