Detection of Residual Stress in SiC MEMS Using micro-Raman Spectroscopy

摘要

Micro-Raman (mu-Raman) spectroscopy is used to measure residual stress in two silicon carbide (SiC) poly-types: single-crystal, hexagonally symmetric 6H-SiC, and polycrystalline, cubic 3C-SiC thin films deposited on Si substrates. Both are used in micro-electrical-mechanical systems (MEMS) devices. By employing an incorporated piezoelectric stage with submicron positioning capabilities along with the Raman spectral acquisition, spatial scans are performed to reveal areas in the 6H-SiC MEMS structures that contain residual stress. Shifts in the transverse optical (TO) Stokes peaks of up to 2 cm(caret)-1 are correlated to the material strain induced by the MEMS fabrication process through the development of phonon deformation potential curves for this material. The 3C-SiC films, with thicknesses ranging from 1.5-5 microns, are deposited by CVD on (100) Si substrates and are also investigated to determine their residual stress. An ultraviolet excitation source (lambda = 325 nm, hv = 3.82 eV) was determined to be more effective for the detection of Raman shifts in these thin films than the 514-nm source, since the absorption coefficient in SiC at 300 K at 325 nm is 3660 cm-1, while that at 514 nm is less than 100 cm- 1.