PECVD a-Sic:H Young’s modulus obtained by MEMS resonant frequency

Abstract

In this paper we study the Young’s modulus of PECVD obtained silicon rich (x>0.5) a-SixC1−x:H thin films through the study of the resonance frequency of free standing cantilevers. These structures are fabricated based on front side bulk micromachining of Si substrate and actuated thermally. In this approach, an alternating electric current passes through a photolithography patterned metallic film deposited on the cantilever, heating the structure by Joule effect and inducing vibrations on the cantilever. This method of actuation is independent of the separation between the structure and substrate, which is its main advantage, because it allows the actuation of cantilevers that are bent upwards or downwards, which is an aspect of particular importance in the characterization of PECVD materials for MEMS applications. The work is focused on low stress silicon rich amorphous hydrogenated silicon carbide films obtained by PECVD at low temperatures (320°C). The measurements were carried out in groups of cantilevers with different length (between 550 and 200μm) and utilizing a-SiC:H films obtained with three different compositions. The results show that the films exhibit modulus of elasticity in the range of 20–35GPa, low residual stress (∼90GPa) and maintain excellent chemical inertness in KOH and HF solutions.