Mechanical properties of a 3C-SiC film between room temperature and 600 °C

Abstract

Silicon carbide (SiC) is widely recognized as the leading candidate to replace silicon in micro-electro-mechanical systems devices operating in harsh environments. In this work, cantilevers and bridges in SiC are designed, fabricated and evaluated between room temperature (RT) and 600 °C. The active material is a cubic poly-SiC film deposited on a poly-Si layer which is separated from the Si substrate by a thermal oxide. From surface profiling and optical observations, it is deduced that an average residual strain of +5 × 10−4 is present in the 2.7 µm thick film, with a gradient of 2.5 × 10−4 µm−1. The structures are excited either mechanically or electrostatically. Their resonance frequency is measured by laser Doppler velocimetry and used to derive the Young's modulus and residual stress in the heteroepitaxial layer (330± 45 GPa and 200± 20 MPa, respectively). The temperature coefficient of Young's modulus is found to be −53± 2 ppm K−1 in the range RT to ∼ 300 °C, while an analytical expression is given for the temperature dependence of the Young's modulus between RT and 500 °C. The residual tensile stress is found to depend on temperature in a complex manner.