Stress and thermal expansion of β–SiC films by the vibrating-membrane method

Abstract

The internal tensile stress in heteroepitaxial films of cubic (β) SiC grown on Si substrates by chemical vapor deposition at 1520–1650 K has been determined from the resonant frequencies of membrane samples formed by removal of a central circular region of the substrate. At 293 K, the stress falls in the range 250–500 MPa, and tends to be larger for samples grown at higher temperatures. The temperature dependence of the stress has been studied over the range 90–670 K and found to exhibit a reversible, mild, but convoluted variation that includes a minimum near 160 K and a maximum near 400 K. Analysis of this behavior reveals that the thermal expansion of β–SiC is remarkably close to that of Si, with an expansion curve that intersects that of Si near 80 K and 500 K. This behavior is different from that obtained from available handbook data for α–SiC, and suggests that data for α–SiC should not be relied on to estimate the overall magnitude of the thermal stress component in β–SiC films. Annealing studies carried out in the range 673–1473 K on as-prepared membranes indicate a high degree of membrane stability, with no evidence of stress relaxation. It has also been observed that annealed membranes may exhibit very low levels of mechanical damping, corresponding to Q-values in the range 10⁶−10⁷.