Growth of SiGe/Si superlattices on silicon-on-insulator substrates for multi-bridge channel field effect transistors

Abstract

We have studied in reduced pressure chemical vapor deposition the growth kinetics of Si and Si0.8Ge0.2 on bulk Si(001) and on silicon-on-insulator (SOI) (100nm buried oxide/20nm Si over-layer) substrates. For this, we have grown miscellaneous Si/Si0.8Ge0.2 superlattices on both types of substrates that we have studied mainly in secondary ions mass spectrometry but also in X-ray diffraction. Systematic Si and SiGe growth rate decreases (together with a Ge concentration increase) occurred on SOI substrates as the stack thickness increased from zero to more than 100nm. Such phenomena are most likely associated to a decrease of the SOI surface temperature by 12–13°C compared to bulk. For Si, the growth rate on SOI increased back again towards the bulk value as the stack thickness neared two hundred nanometers. This is linked to a SOI surface temperature that went 5°C back up. Such a knowledge will be most useful to form in the near future regular superlattices on SOI substrates that will serve as the active regions of multi-bridge channel field effect transistors. Three periods Si/SiGe superlattices with either 20% or 31% of Ge and varying SiGe layer thickness were also grown on bulk Si(001) to study the critical thickness for plastic relaxation of the compressive strain that builds up in such stacks.