Influence of Ge implantation on the mechanical properties of polycrystalline silicon microstructures

Abstract

Polycrystalline silicon (poly-Si) based microstructures, with boron doping (B-doping), are studied, with reference to their built-in stress, for different germanium implantation (Ge-implantation) doses. The microstructures are studied free standing and under static and dynamic deformations, by a combination of macroscopic (pull-in voltage, resonance frequency) and microscopic (micro-Raman) experimental techniques, in comparison with numerical calculation methods. The counterbalancing effect of Ge-implantation versus the B-doping, with respect to the built-in stress, is examined in poly-Si. Measurements, with three different experimental methods, and calculations, on bridges designed and fabricated for micromachining applications, show, consistently, the same maximization trend for the built-in stress, with a maximum at a Ge-dose of 1015 ions/cm2, in agreement with a similar non-monotonic Ge-dependence of the growth rate and the crystalline quality of poly-Si, from the literature.