Effect of low RF bias potential on AlN films obtained by Microwave Plasma Enhanced Chemical Vapor Deposition

AlN films were prepared with a Microwave Plasma Enhanced Chemical Vapor Deposition reactor at 1 Pa and 700 °C using different radiofrequency bias in order to obtain polycrystalline <0001> oriented films with minimal residual stresses for piezoelectric applications. The films developed were characterized in term of microstructure, composition and mechanical properties. Crystalline development, exclusive orientation and high tensile residual stresses were observed when the substrate-holder was at the floating potential. A progressive degradation of the crystalline structure was observed with the increase in the negative bias potential, together with the evolution to compressive residual stresses. Simultaneously, significant changes in the microstructure of the surface were observed by atomic force microscopy, as well as in the preferential orientation from <0001> to <1010>. Film properties for piezoelectric applications were optimized with the adequate selection of bias potential.