Compositional and structural analysis of aluminum oxide films prepared by plasma-enhanced chemical vapor deposition

Aluminum oxide films were deposited on silicon wafers by plasma-enhanced chemical vapor deposition, using trimethylaluminum, N₂O and He gases. The chemical composition, states of functional groups and microstructure of the aluminum oxide films were investigated using FTIR, XPS, AES and TEM. Etch rates were measured and related to the microstructure of the films. It was found that carbon and hydrogen atoms are incorporated less at higher deposition temperatures and are almost completely removed as gas phases, such as CO₂ and H₂O, by post-deposition heat treatment at 800 °C in an oxygen environment. Carbon atoms incorporated into the films are in the chemical form of AlCH₃ or AlCOOH, and the atomic concentration varies from 2% at 300 °C to 5% at 120 °C. Hydrogen atoms are in the chemical form of AlOH, and the atomic concentration estimated from the absorbance FTIR band of the OH stretching mode varies from about 7% at 300 °C to about 28% at 120 °C. The aluminum oxide films deposited at 300 °C have a microcrystalline structure of hydrogen-stabilized γ-Al₂O₃ with an O/Al ratio of 1.6, whereas those deposited at 120 °C have an amorphous structure. Etching properties of the films were related to the change in the microstructure.