Measurement of intrinsic and laser heating-induced stress in microcrystalline silicon thin films

Abstract

In this work we employed a relatively simple experimental procedure to separate the mechanisms that contribute to the total stress of partially crystalline silicon thin films. Raman spectroscopy has been utilized to elucidate the influence of the laser irradiation (λ0=441.6nm) on the μc-Si:H thin film by analyzing the observed peak shift of the Si–Si TO phonon mode in an effort to separate the different mechanisms that impose spectral changes after the applied laser treatment. When external mechanical stress is not applied, only two distinct mechanisms contribute to the frequency shift of the Raman band, namely the heating-induced stress and the internal stress due to the deposition conditions.The use of the appropriate fitting procedure of the experimental spectrum allows the estimation of the observed frequency shift, which is attributed to both local heating due to the laser irradiation and the intrinsic tensile stress of the μc-Si:H films. In the limit where the laser is highly attenuated, the induced heating is negligible and we are able to isolate and evaluate tensile stress directly from the spectroscopic data in the context of current theoretical models. Beyond this limit, the values of internal and total stress have been used to calculate the laser-induced stress. Crystallinity seems to be the key factor to control the volume change induced by the displacement of the surrounding atoms, which is spread over medium in long-range order.