Experimental Analyses on Multiscale Structural and Mechanical Properties of ε-Si/GeSi/C-Si Materials

Strained silicon (ε-Si) is a promising material that could extend Moore’s law by enhancing electron mobility. A ε-Si material is usually composed of multiscale, multilayer heterostructures, where the strained-silicon film or strap is tens-of-nanometers thick, and its buffer layers are of the micrometer scale. The structural properties determine the electrical performance and reliability of ε-Si-based devices. Inhomogeneous residual stress is induced during the preparation, which induces ε-Si structure failure. In this work, biaxial strained-silicon films that contain graded and relaxed germanium-silicon buffer layers were prepared on monocrystalline silicon wafers through reduced-pressure chemical-vapor epitaxy. The layer components and thicknesses were measured using energy-dispersive spectroscopy and scanning-electron microscopy. Crystal and lattice characters were observed by using high-resolution transmission-electron microscopy and micro-Raman spectroscopy. The residual stress distribution along cross-sections of the ε-Si multilayer structures was examined by using micro-Raman mapping. The experimental results showed that, with a gradual increase in germanium concentration, the increasing residual stress was suppressed owing to dislocation networks and dislocation loops inside the buffer layers, which favored the practical application.