Strain Tuning in Graded SiGe on Insulator: Interplay between Local Concentration and Nonmonotonic Lattice Evolution after Ge Condensation

Germanium condensation has proven to be a reliable route for obtaining smoothly graded composition SiGe layers with good reproducibility and reduced defect density. The process is known as a crucial tool to induce well-defined strain on Si or SiGe layers with potential use in semiconductor devices. In this work, we show that starting from a low concentration Si0.92Ge0.08 layer grown on top of a crystalline Si(001) on SOI substrates, we can reach desirable concentration with a nonmonotonic interplay on in-plane and out-of-plane strain. The Ge concentration is evaluated by a combination of ultralow energy secondary ion mass spectroscopy (ULE-SIMS) and synchrotron X-ray measurements (diffraction and reflectivity). After the evaluation of Ge content, the strain-sensitive process of rolling up tubes from the flat layers is used and combined with X-ray diffraction to provide a concise scenario of the strain evolution along an in-growth oxidation series, pointing out the conditions that maximize strain, as well as its fading, as the Ge content rises.