Humidity sensitivity of optical structures prepared by r.f.-biased r.f. sputtering

In an attempt to produce optical structures with a lower humidity sensitivity than that of structures deposited by conventional evaporation, we used r.f.-biased r.f. sputtering for the preparation of coatings. The sensitivity was effectively reduced owing to the high density of bias-sputtered films which are subjected to controlled ion bombardment during their growth. Our experiments suggest that neither rate monitoring nor optical monitoring is necessary, at least not in the preparation of simple structures with few layers, if glow discharge sputtering processes comprising r.f. substrate biasing in diode, triode or magnetron set-ups are used to deposit the coatings.