K-M-S (keep-molecules sputtering) deposition of optical MgF{sub}2 thin films

摘要

Magnesium fluoride thin film depositions by rf magnetron sputtering are successfully carried out When magnesium fluoride targets at high temperature were sputtered in oxygen, Mg, O, and MgF emission lines were observed. This indicates thatsputtering in the form of molecules occurred. The refractive index of the obtained film was near 1.39, and the extinction coefficient k was less than 1×10{sup}-4 in the visible region, small enough for anti-reflection coatings. The film deposited without additional heat supplied to the substrate was as hard as that deposited on a heated substrate by vapor evaporation. The deposition rate was 50-350 nm/min. The ratios of F:Mg and O:Mg in the film were near 1.9, and near 0.0, respectively. Those areconcluded that high temperature of the target keeps sputtered particles in the molecular state, and that most of molecules are still preserved at substrates. This deposition technique may be applied for various optical films because of its advantages over vapor evaporation in factory automation, and applicability to substrates at room temperature.