Growth and structural properties of SiGe virtual substrates on Si(1 0 0), (1 1 0) and (1 1 1)

Abstract

The growth kinetics and structural properties of nominally 15–45% SiGe virtual substrates (VS) on Si(1 0 0), Si(1 1 0) or Si(1 1 1) substrates have been investigated. Our “best” (1 0 0) growth procedure has been used, which leads to the formation of high-quality SiGe(1 0 0) VS with threading dislocation densities around 10 5 cm −2. The mean SiGe growth rate (GR) on (1 0 0) is higher than the one on (1 1 1), which is itself higher than the one on (1 1 0) (more precisely: GR(1 1 0) ∼0.6×GR(1 0 0) and GR(1 1 1) ∼0.85×GR(1 0 0)). The trend is the opposite one for the mean Ge content, with %Ge×1.5 and ×1.2 higher on (1 1 0) and (1 1 1) than on (1 0 0), respectively. The Ge concentration dependence on mass-flow ratio has been quantified using a x Ge/(1− x Ge)= p(F(GeH 4)/F(SiH 2Cl 2)) relationship for all surface orientations. We have obtained (1 1 0) and (1 1 1) p values 1.8–2.0 and 1.3–1.5 times higher than on (1 0 0). We have otherwise studied the structural properties of SiGe(1 0 0), (1 1 0) and (1 1 1) VS. Original surface morphologies have been evidenced for each surface orientation. Cross-hatch, “half cross-hatch” and triangular arrays have been observed on (1 0 0), (1 1 0) and (1 1 1), with respectively slight and strong surface roughening for the latter two orientations. Higher defect densities have been evidenced by TEM on SiGe(1 1 0) and (1 1 1) VS than on (1 0 0). Whereas stacking faults have propagated from the Si(1 1 1) substrate all the way up to the surface, these defects are mostly confined in the SiGe ramp when growing on (1 1 0), with a 0.5 μm defect-free area on top. Threading dislocation densities (from Schimmel defect etching) are roughly equal to 10 8 cm −2 on both Si 0.72Ge 0.28 (1 1 0) and Si 0.80Ge 0.20 (1 1 1) VS. Finally, SiGe VS are crystalline whatever the Si surface orientation as shown by the coherent X-ray diffraction profiles or reciprocal space maps obtained. SiGe(1 0 0) and (1 1 0) VS are both fully relaxed, whereas the (1 1 1) ones may be in a tensily strained configuration.