Excimer laser recrystallization of nanocrystalline-Si films deposited by inductively coupled plasma chemical vapour deposition at 150°C

Abstract

Polycrystalline silicon thin film transistors (poly-Si TFTs) fabricated at low temperature (under 200°C) have been widely investigated for flexible substrate applications such as a transparent plastic substrate. Unlike the conventional TFT process using glass substrate, the maximum process temperature should be kept less than 200°C in order to avoid thermal damage on flexible substrates. We report the characteristics of nanocrystalline silicon (nc-Si) irradiated by an excimer laser. Nc-Si precursors were deposited on various buffer layers by inductively coupled plasma chemical vapour deposition (ICP-CVD) at 150°C. We employed various buffer layers, such as silicon nitride (SiNX) and silicon dioxide (SiO2), in order to report recrystallization characteristics in connection with a buffer layer of a different thermal conductivity. The dehydrogenation and recrystallization was performed by step-by-step excimer laser annealing (ELA) (XeCl,λ=308 nm) in order to prevent the explosive release of hydrogen atoms. The grain size of the poly-Si film, which was recrystallized on the various buffer layers, was measured by scanning electron microscopy (SEM) at each laser energy density. The process margin of step-by-step ELA employing the SiNX buffer layer is wider than SiO2 and the maximum grain size slightly increased.