Analysis of stress in laser-crystallized polysilicon thin films by Raman scattering spectroscopy

We investigated the tensile stress in poly-Si thin films crystallized by excimer-laser annealing (ELA). The stress was analyzed with the frequency shift of the optical-phonon line, Deltaomega, detected by Raman scattering spectroscopy. The value of Deltaomega is affected not only by stress but also by the presence of microcrystals. In the case of the full-width at half-maximum (FWHM) of the spectrum being smaller than 8 cm(-1), the stress can be estimated from Deltaomega without the influence of microcrystals. The primary origin of the stress was attributed to the thermal stress generated by selective heating of films by ELA. The presence of thermal stress in poly-Si was confirmed by comparing the stress in solid-phase crystallized films on fused quartz and on Si substrates. The stress in ELA poly-Si varied widely with conditions, such as irradiated-shot number, substrate temperature and postannealing temperature. It was deduced that the thermal stress being the dominant stress factor is relaxed by annealing performed after laser irradiation.