The thermal stability, microstructure, and electrical properties of xZrO2.(100-x)SiO2 (ZSO) and xHfO2.(100-x)SiO2 (HSO) (x= 15, 25, 50, 75%) binary oxides were evaluated to help asses their suitability as a replacement for silicon dioxide gate dielectric in complementary metal oxide semiconductor (CMOS) transistors. The films were prepared by chemical solution deposition (CSD) using a solution prepared from a mixture of zirconium, hafnium and silicon butoxyethoxides dissolved in butoxyethanol. The films were spun onto SiOxNy coated Si wafers and furnace annealed at temperatures from 500-1200 oC in oxygen for 30 minutes. The microstructure and electrical properties of ZSO and HSO films were examined as a function of Zr/Si and Hf/Si ratio and annealing temperature. The films were characterized by X-ray diffraction, FTIR, RBS and AES. At ZrO2 or HfO2 concentrations > 50%, phase separation and crystallization of tetragonal ZrO2 and HfO2 was observed at 800 oC. At ZrO2 or HfO2 concentrations < 25%, phase separation and crystallization was observed at 1000 oC. As annealing temperature increased, a progressive change in microstructure was observed in the FTIR spectra. Additionally, the FTIR spectra suggest that HfO2 is far more disruptive of the silica network than ZrO2 even at HfO2 concentrations < 25%. The dielectric constant of the 25, 50 and 75% ZSO films were measured and were observed to be less than the linear combination of ZrO2 and SiO2 dielectric constants. The dielectric constant was observed to increase with increasing ZrO2 content. The dielectric constant was also observed to be annealing temperature dependent with larger dielectric constants observed in non-phase seperated films. The Clausius-Mossoti equation and a simple capacitor model for a phase separated system was observed to fit the data with the prediction that to achieve a dielectric constant larger than 10 doping concentrations of ZrO2 would have to be greater than 70%.
By: D. A. Neumayer, E. Cartier
Published in: RC21932 in 2001
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