KrF excimer laser annealed TFT with very high field-effect mobility of 329 cm/sup 2//V-s

Abstract

A thin-film transistor (TFT) with a maximum field-effect mobility of 320 cm/sup 2//V-s, an on/off current ratio of 7.6*10/sup 7/, a threshold voltage of 6.7 V and a subthreshold slope of 0.37 V/decade was fabricated by using pulse laser annealing processes. Amorphous silicon films (a-Si:H) with a very low impurity concentration of 4*10/sup 18/ cm/sup -3/ for oxygen, 1.5*10/sup 18/ cm/sup -3/ for carbon, and 2*10/sup 17/ cm/sup -3/ for nitrogen were deposited by a plasma chemical vapor deposition (CVD) method and annealed by KrF excimer laser (wavelength of 248 nm). The Raman spectroscopy technique was a useful tool for optimizing laser annealing conditions. Experimental results show that two factors are very important for fabricating very-high mobility TFTs: (1) utilizing high-purity as-deposited a-Si:H film; and (2) performing whole laser annealing processes sequentially in a vacuum container and optimizing illumination conditions.