UV and Visible Raman Spectroscopy Applied to sSi/Si1-XGeX and sSOI Stacks

Abstract

Mechanical strain can be used to improve electronic transport properties in advanced short gate length Si-based Metal Oxide Semiconductor Field Effect Transistors. The controlled introduction of strain in the channel area of transistors (thanks to recessed SiGe sources and drains, contact etch stop layers or to previous processing at the wafer scale) can indeed increase the carrier mobility by a factor of up to two. We have used here ultra-violet and visible Raman Spectroscopy to study the processes that can influence strain during the elaboration of strained Si On Insulator (sSOI) substrates. The results obtained during analyses of tensily-strained Si layers grown on polished Si1-xGex virtual substrates (VS) show that the strain can be preserved for 20% of Ge. However, we observed a relaxation of the strain for 40% Ge, after layer transfer onto oxidized silicon. A definite strain relaxation at the edges of lines patterned in sSOI wafers was also demonstrated. A good agreement between experimental results and simulation has been achieved