RELUCTANT ETCHABILITY OF DIELECTRIC AL2O3 FILMS SPUTTERED IN WATER-VAPOR AND AR-O2 ENVIRONMENTS

Aluminum oxide thin films were deposited by r.f. sputtering on ferrite, glass, and graphite substrates in a vacuum system deliberately contaminated with water vapor and Ar-O2 mixtures. The films were analyzed for thickness, etch rate, chemical composition and microstructure using transmission electron microscopy (TEM). The presence of water vapor or oxygen in the vacuum chamber during deposition decreased the film deposition rates, and the etch rate of the films in hot H3PO4 was also drastically reduced. TEM micrographs and selected area electron diffraction patterns of films deposited in water vapor and Ar-O2 environments showed the existence of a crystalline gamma-Al2O3 phase in the film at the substrate-film interface. The gamma-Al2O3 structure depended on the abundance of oxygen or water vapor in the vacuum. The formation of the gamma-Al2O3 phase at the interface is the cause of reluctant etchability because gamma-Al2O3 is much less soluble in phosphoric acid etchants than in amorphous Al2O3.