Growth of strained Si on He ion implanted Si/SiGe heterostructures

Abstract

He ion implantation into Si/SiGe heterostructures and annealing are used to produce strain-relaxed SiGe layers and simultaneously thin strained Si layers. In addition we present various studies of subsequent epitaxial overgrowth by chemical vapor deposition. Up to a thickness of 8 nm strained Si on relaxed SiGe virtual substrates are made by strain transfer via dislocation propagation. An initial cubic-Si/strained-SiGe/Si(1 0 0) structure is transformed by He + ion implantation and annealing into strained-Si/partially relaxed-SiGe/Si(1 0 0). These layers show low threading dislocation densities and very smooth surfaces. Such virtual substrates were overgrown with Si to achieve 20 nm of strained Si. A tensile strain of 0.8% was measured by Raman spectroscopy for an 18.5 nm sSi layer with a surface roughness of only 0.8 nm measured by AFM. The threading dislocation density was reduced by overgrowth of an additional strain adjusted SiGe layer and sSi layer.