ATOMIC-FORCE MICROSCOPY INVESTIGATION OF TENSILE-STRESSED SILICON GROWN BY RAPID THERMAL CHEMICAL-VAPOR-DEPOSITION ON SI0.68GE0.32 RELAXED PSEUDO-SUBSTRATES

Rapid thermal chemical vapour deposition (RTCVD) has been applied to the growth of silicon layers under tensile stress on relaxed Si0.68Ge0.32 buffer layers at 610 and 810 degrees C. Their surface morphology was characterised with atomic height resolution by Tapping-mode atomic force microscopy (TM-AFM). While a uniform isotropic nanoroughness is revealed on pseudo-substrates, a quite different roughness can be observed for silicon films. For high temperature grown films, high surface diffusion rates of adsorbed species enable an extended reconstruction of the Si (100) surface: large domains showing terraces as well as faceted planes appear; the resulting non-uniform silicon film exhibits early mechanical failure. In contrast, low temperature grown Si films exhibit almost the same morphology as pseudo-substrates for thicknesses up to 15 nm with no apparent mechanical failure. For thicknesses beyond 20 nm, terraces form on the steepest part of the slopes, whereas beyond 80 nm [110] slip lines indicate the plastic yield of the film.