Evaporation of Adherent Al-Films on Single Crystalline LiNbO₃ Substrates

Abstract

LiNbO₃ is used as a single crystalline substrate material for the manufacturing of surface acoustic wave devices as frequency selective components. On the polished substrate wafer, Al with a film thickness of about 400 nm is evaporated in a high vacuum.The difficulties of the inadequate adhesion of the structured Al-film were eliminated by systematical investigations. Films that were adherent to the total surface could be prepared by evaporating an intermediate film of Cr or SiO_x or, otherwise, a mixed film of Al with Si.An ultrasonic test for adhesion strength was developed that results in an assessment of local and also large-area film adhesion.