Characterisation of the mechanical properties of thin film cantilevers with the atomic force microscope

Abstract

The Atomic force microscope functions by monitoring the deflections of thin film cantilevers that possess relatively weak spring constants. Cantilevers that are composed of low pressure chemically vapor deposited (LPCVD) silicon nitride are frequently used. In this investigation, finite-element analysis of V-shaped cantilever structures and experimentally determined spring constants are combined in order to determine the Young's moduli for some LPCVD silicon nitride thin film cantilevers. Three different wafer batches of cantilevers provide Young's moduli of 150 ± 25, 195 ± 30 and 260 ± 50 GPa. The Young's modulus of a cantilever is related to the density of the thin film silicon nitride. By analogy with ceramic silicon nitride, the Young's modulus of a cantilever is linked to the bulk modulus, shear modulus, density and porosity of the LPCVD silicon nitride. The reported values are based on the assumption that the mechanical properties of the LPCVD silicon nitride films are isotropic and comparable to those of silicon nitride ceramics. Show more