Preparation of amorphous fluoride films by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Amorphous ZnF2, ZnF2–BaF2, AlF3 and AlF3–BaF2 films were prepared on CaF2(1 1 1) substrates by an electron cyclotron resonance plasma-enhanced chemical vapor deposition (CVD) technique. Metal β-diketone chelates and NF3 gas were used as starting materials and a fluorinating gas, respectively. ZnF2 films deposited on the substrates kept at 300°C and 100°C were crystalline and amorphous, respectively. The crystalline ZnF2 thin film prepared at a deposition rate of 0.2 μm h−1 was oriented along a [1 1 0] direction. The amorphous ZnF2 film, tinted yellowish brown, had an IR spectra which were due to contaminants. Colorless and contaminant-free amorphous films were obtained for a 60ZnF2·40BaF2 composition. On the other hand, AlF3 films generated on the CaF2(1 1 1) substrate kept at 300°C were amorphous and colorless. We also found that amorphous 80AlF3·20BaF2 and 60AlF3·40BaF2 films could be synthesized at a deposition rate of 1.5 μm h−1.