Investigation of Thermal Expansion Effects on Si-Based MEMS Structures

This paper presents a study of the effects of stress and thermal expansion of inductively coupled plasma enhanced chemical vapor deposited (ICPCVD) amorphous Si thin films on low-temperature microelectromechanical systems test structures. Experimental data were used in conjunction with finite-element modeling (FEM) to predict deformation in simple microstructures across a wide temperature range from 85 to 300 K. Temperature dependence of residual stress and the coefficient of thermal expansion (CTE) of ICPCVD Si thin films was investigated by characterizing the curvature of bilayer thin-film samples through the use of optical profilometry at low temperature. Extracted parameters were used in an FEM package to confirm the experimental results by correlating with observed deformation of fabricated test structures. It is demonstrated that the experimentally determined CTE enables accurate modeling of the mechanical behavior of thin-film microstructures across a wide range of temperatures.