Characterization of thermal oxides grown on TaSi2/polysilicon films

Abstract

Oxidation of tantalum disilicide films deposited by cosputtering on highly phosphorus doped polycrystalline silicon was investigated as a function of various film preparation parameters. The thermal oxides, with a thickness of about 100 nm, were characterized by cross-sectional TEM, AES, and SIMS depth-profiling as well as breakdown strength measurements on small-area and large-area capacitors. No limitation on oxide growth for dry and steam oxidation was found in the investigated temperature range of 800 to 1000 °C. The removal of the native oxide on the poly-Si prior to TaSi2 deposition by an HF dip or by backsputtering is crucial for reproducible oxide growth. The nature of the oxide is similar to thermal SiO2 on (100) Si. The TaSi2 film integrity is maintained during oxidation. The high surface and interface roughnesses cause oxide thickness variations of about 50%. A high mass fraction of the order of 0.5 wt.% phosphorus was found in the oxides. The breakdown strength of both steam and dry oxides is about one order of magnitude lower than the values for thermal oxides on n+-poly-Si. These low breakdown strength values are attributed mainly to large pores in the oxides observed in the TEM. No restrictions on process compatibility were found.