Curvature of free-standing polycrystalline SiC thick films grown by CVD: On the origin of the residual stress gradient

Abstract

Polycrystalline SiC can serve as a receiver substrate for the fabrication of engineered SiC wafers for power-electronics devices. These substrates must be as flat as possible for further processing. They can be fabricated by chemical vapor deposition (CVD) on a sacrificial substrate, which is then removed leaving a thick free-standing SiC film. When deposited by CVD, a residual intrinsic stress gradient develops through thickness of the film and results in the curvature of the free-standing film. In this study, we show that two mechanisms are responsible for the occurrence of such an intrinsic stress gradient. The first is due to a change of grain size through the film's thickness that in turn leads to a change of intrinsic stress during growth. The second mechanism is attributed to the continuous relaxation of the film during growth. Although a constant grain size through thickness can be achieved with appropriate process conditions to minimize the intrinsic stress gradient, the second mechanism occurs for any microstructure. Therefore, the intrinsic stress gradient and the resulting curvature of the free-standing films is difficult to avoid though it can be minimized through pertinent choices of growth conditions.