Mechanical properties of thin silicon films deposited at low temperatures by PECVD

This paper presents elastic and fracture properties of hydrogenated amorphous and nanocrystalline silicon thin films and correlates them with optoelectronic and structural properties of the films. Properties are extracted from the load–deflection response of membranes and include the plane-strain modulus, residual stress and failure stress. Bilayer diaphragms made of hydrogenated amorphous and nanocrystalline silicon films obtained by plasma-enhanced chemical vapor deposition onto a reference silicon nitride layer are fabricated and characterized. A comprehensive study of the mechanical properties of these silicon thin films is presented as a function of the substrate temperature and hydrogen dilution used during deposition. The extracted plane-strain modulus, 118.5 ± 3.0 GPa, is insensitive to deposition conditions, in strong contrast to the residual stress, with values between −738 and 188 MPa. The tensile and compressive stress components in the silicon films, evaluated at membrane failure, increase from 0.11 to 0.96 GPa and from −3.40 to −2.25 GPa, respectively, with increasing residual stress.