Plasma CVD of Amorphous AlN from Metalorganic Al Source and Properties of the Deposited Films

Abstract

AlN films have been successfully deposited by plasma CVD for the first time. Al was supplied by trimethyl Al (TMA) with H₂ or N₂ carrier gas, and N was supplied as NH₃ through separate gas lines. The deposition rate depends upon the TMA supply, and is essentially independent of the NH₃ flow rate. The composition of the deposited films was almost AlN, although a small amount of oxygen was always detected. A better film was obtained for the H₂ carrier gas than for N₂ carrier gas. X-ray diffraction profiles of the deposited films exhibited no crystalline AlN diffracting peaks, suggesting that the films are not crystallized, but the infrared and ultraviolet absorption spectra exhibited the presence of the Al–N bond (650/cm) and an optical band gap of 5.55 eV. The refractive index was about 1.9. These results suggest that the plasma-deposited films possess dominant AlN properties even though they are not crystalline.