Laser processing for thin film transistor applications

Abstract

Key issues for fabricating polycrystalline silicon thin film transistors (poly-Si TFTs) at a low temperature are discussed. A method of rapid laser melting (< 100 ns) provides a formation of poly-Si films with a high carrier mobility and a low defect density at room temperature, although crystalline grains are very fine (< 100 nm). Plasma hydrogenation further reduces the defect density from initial value of 1 × 10 17 to 4 × 10 16 cm −3 eV −1. Methods of remote plasma chemical vapor deposition (CVD) and SiO evaporation with an oxygen ambient realize formation of SiO 2 with a low density of interface trapping states less than 3 × 10 10 cm −2 eV −1. Poly-Si TFTs fabricated at 270 °C using these methods of laser annealing and plasma processing had a high carrier mobility of 640 cm 2 V −1 s −1 and a low threshold voltage of 0.8 V.