Effects of laser-induced heating on Raman stress measurements of silicon and silicon-germanium structures

The authors investigate the effect of laser-induced heating on Raman measurements for different unpatterned and patterned substrates, including pure silicon, strained-silicon-on-insulator, and silicon-germanium layers on silicon. The relationship between heating and incident power of the laser used for Raman measurements is derived for unpatterned substrates, and the much stronger heating effects for line and island structures are shown. Additionally, the enormous heating of isolated silicon particles within the laser beam was investigated. The measured shifts clearly show that heating has to be considered even for moderate laser intensity when accurate stress measurements on such substrates are performed by Raman spectroscopy.