Use of deposition pressure to control residual stress in polycrystalline SiC films

Abstract

Polycrystalline silicon carbide (poly-SiC) thin films were grown in a large-volume, low pressure chemical vapor deposition furnace using dichlorosilane and acetylene precursors. The deposition temperature was fixed at 900 °C and the pressure was varied between 0.46 and 5 Torr. The residual stress of as-deposited SiC films ranged from highly tensile to moderately compressive as the deposition pressure was increased from 0.46 to 5 Torr, with tensile stress below 50 MPa in films deposited at around 2.5 Torr. Cantilever beams with no vertical deformation were fabricated from the low tensile stress films, and they indicated that the stress gradient was also very low in these films. X-ray diffraction analysis indicated that all the films were highly textured polycrystalline (111) 3C-SiC regardless of the residual stress. Transmission electron microscopy indicated that both the tensile and compressive films were columnar in microstructure, with slight differences in the axial alignment of the grains with respect to the film/substrate interface as well as in the density of features in the grain boundaries. An explanation for the observed differences in residual stress based on differences in film microstructure is proposed.