Improvement of Poly-Silicon Thin Films and Thin Film Transistors Using Ultrasound Treatment

Abstract

AbstractUltrasound treatment (UST) was applied to improve electronic properties of polycrystalline silicon films on silica-based substrates. A strong decrease of sheet resistance by a factor of two orders of magnitude was observed in hydrogenated films at UST temperatures lower than 100°C. This is accompanied by improvement of a film homogeneity as confirmed by spatially resolved photoluminescence study. The UST effect on sheet resistance demonstrates both stable and metastable behavior. A stable UST effect can be accomplished using consecutive cycles of UST and relaxation. An enhanced passivation of grain boundary defects after UST was directly measured by nano-scale contact potential difference with atomic force microscope. Two specific UST processes based on interaction between ultrasound and atomic hydrogen are suggested: enhanced passivation of grain boundary states and UST induced metastability of hydrogen related defects. We also demonstrate a utility of UST for improvement of leakage current and threshold voltage in hydrogenated poly-Si thin film transistors.