Materials characterization of ZrO2–SiO2 and HfO2–SiO2 binary oxides deposited by chemical solution deposition

Abstract

The thermal stability, microstructure, and electrical properties of x ZrO 2 ⋅(100−x) SiO 2 (ZSO) and x HfO 2 ⋅(100−x) SiO 2 (HSO) (x=15%, 25%, 50%, and 75%) binary oxides were evaluated to help assess their suitability as a replacement for silicon dioxide gate dielectrics in complementary metal–oxide–semiconductor transistors. The films were prepared by chemical solutiondeposition using a solution prepared from a mixture of zirconium, hafnium, and silicon butoxyethoxides dissolved in butoxyethanol. The films were spun onto SiO x N y coated Si wafers and furnace annealed at temperatures from 500 to 1200 °C in oxygen for 30–60 min. The microstructure and electrical properties of ZSO and HSO films were examined as a function of the Zr/Si and Hf/Si ratio and annealing temperature. The films were characterized by x-ray diffraction, mid- and far-Fourier transform infrared (FTIR), Rutherford backscattering spectroscopy, and Auger electron spectroscopy. At ZrO 2 or HfO 2 concentrations ⩾50%, phase separation and crystallization of tetragonal ZrO 2 or HfO 2 were observed at 800 °C. At ZrO 2 or HfO 2 concentrations ⩽ 25%, phase separation and crystallization of tetragonal ZrO 2 or HfO 2 were observed at 1000 °C. As the annealing temperature increased, a progressive change in microstructure was observed in the FTIR spectra. Additionally, the FTIR spectra suggest that HfO 2 is far more disruptive of the silica network than ZrO 2 even at HfO 2 concentrations ⩽25%. The dielectric constants of the 25%, 50%, and 75% ZSO films were measured and were observed to be less than the linear combination of ZrO 2 and SiO 2 dielectric constants. The dielectric constant was also observed to increase with increasing ZrO 2 content. The dielectric constant was also observed to be annealing temperature dependent with larger dielectric constants observed in nonphase separated films. The Clausius–Mossoti equation and a simple capacitor model for a phase separated system were observed to fit the data with the prediction that to achieve a dielectric constant larger than 10 doping concentrations of ZrO 2 would have to be greater than 70%.