Growth of GexSi1−x/Si heteroepitaxial films by remote plasma chemical vapor deposition

Abstract

GexSi1−x/Si heteroepitaxial thin films have been grown using the low-temperature remote plasma-enhanced chemical vapor deposition (RPCVD) approach, in which the substrate is kept remote from the glow discharge, and an Ar plasma is employed to indirectly activate the reactant gases (SiH4 and GeH4) and drive the chemical deposition reactions. Secondary ion mass spectroscopy (SIMS), plan-view and cross-sectional transmission electron microscopy (TEM), and in situ reflection high-energy electron diffraction (RHEED) have been employed to analyze the films with different Ge mole fractions and thicknesses. Abrupt Si/GexSi1−x heterointerfaces with the Ge concentration changing by 10× in about 30 Å (SIMS resolution limit) have been achieved. Commensurate growth has been observed for layers whose thicknesses are below the critical layer thicknesses (CLTs). Crystalline GexSi1−x/Si films with high mole fractions of Ge (up to 60%), which are thicker than the CLTs, show relaxation of misfit strain. This results in more islandlike growth, accompanied by interfacial corrugation and inhomogeneous strain in the thin films, as observed by cross-sectional TEM analysis. Plan-view TEM also shows Moiré fringes formed by the overlap between the relaxed GexSi1−x films and the Si substrate. The spacing between the fringes has been used to estimate the relaxed lattice constant, which agrees very well with the value predicted by Vegard’s law. A detailed study of the GexSi1−x growth parameter space has also been conducted. Effects of various growth variables have been investigated. Stable control over growth rate and germanium incorporation rate in RPCVD has been demonstrated.