Micro-Raman analysis and finite-element modeling of 3 C-SiC microstructures

Micro- and nano-electromechanical systems (MEMS and NEMS) fabricated in 3?C-SiC are receiving particular attention thanks to the material physical properties: its wide band gap (2.3?eV), its ability to operate at high temperatures, its mechanical strength and its inertness to the exposure in corrosive environments. However, high residual stress (which is normally generated during the hetero-epitaxial growth process) makes the use of 3?C-SiC in Si-based MEMS fabrication techniques very limited leading to a failure of micro-machined/sensor structures. In this paper, micro-Raman characterizations and finite-element modeling (FEM) of microstructures realized on poly and single-crystal (100) 3?C-SiC/Si films are performed. Transverse optical (TO) Raman mode analysis reveals the stress relaxation on the free standing structure (796.5?cm-1) respect to the stressed unreleased region (795.7?cm-1). Also, microstructures as cantilever, bridge and planar rotating probe show an intense stress field located around the undercut region. Here, the TO Raman mode undergoes an intense shift, up to 2?cm-1, ascribed to the modification of the Raman stress tensor. Indeed, the generalized axial regime, described by diagonal components of the Raman stress tensor, cannot be applied in this region. Raman maps analysis and FEM simulations show the activation of the shear stress, i.e. non-diagonal components of the stress tensor. The stress-Raman modes shift correlation, in the case of fully non-diagonal stress tensors, has been investigated. The aim of future works will be to minimize the stress field generation and the defects density within the epitaxial layer.