We present a study of the stress state of polycrystalline 3C-SiC thin films grown on a-SiO2/Si(100) substrates by low-pressure chemical-vapor deposition using an organometallic precursor, tetramethylsilane (TMS), that contains both Si and C atoms. Substrate curvature and x-ray stress measurements indicate a change from compressive to tensile stress with increasing deposition temperature. Film thickness and TMS flow also influence the total stress of the films. The different microstructure of the films with growth temperature and the presence of impurities are at the origin of the observed differences in the stress. While samples grown below 1100°C have a columnar structure, are highly oriented along , and show compressive stress, those grown at 1130°C are randomly oriented, with an equiaxial grain shape, and are tensile stressed. The thermal stress is tensile and relatively constant over the temperature range investigated. We speculate the observed intrinsic stress is composed of a tensile and a compressive component. Within the grain-boundary relaxation model we calculate the intrinsic stress variations with temperature due to differences in grain size and density of grain boundaries. The compressive component originates from the presence of oxygen impurities within the film. Peak broadening analysis of the x-ray signal reveals the existence of important microstresses due to low adatom mobility during the deposition process. © 2000 American Institute of Physics.