Experiments on the Elastic Size Dependence of LPCVD Silicon Nitride

Abstract

AbstractRecent experimental observations showed significant elastic size effects in small scales. While surface stress theories are used to describe nanometer scale size effects, strain gradient theories describe size effect observed in micron sized epoxy. Size effects in single crystalline silicon and epoxy make it unclear whether there is size dependence of the elastic behaviors of widely used LPCVD silicon nitride thin films in submicron scale. In this paper, submicron thick LPCVD silicon nitride beams were fabricated and bending tests were conducted on the beams. Results showed fluctuating normalized bending rigidities in the beams with different thickness. XPS and XRD analyses were used to analyze the material consistency of the beams. The fluctuations maybe related to varying crystalline phase fractions in the thin films. The beams were annealed and bending tests were conducted to investigate possible correlation between the fluctuations and crystalline phase fractions. Results showed similar level of fluctuations in normalized bending rigidities before and after annealing while XRD results of the annealed films showed increase in crystalline phase fractions for all thicknesses. While LPCVD silicon nitride may have size dependence in the nanometer scale, size dependence of normalized bending rigidity of LPCVD silicon nitride appears to be insignificant in submicron scale.