Novel high-performance TFTs fabricated by selectively enlarging laser x'tallization (SELAX) technology

摘要

We have developed a new crystallization technique using the pulse-like modulated CW-laser (LD-pumped Nd:YVO{sub}4 SHG λ=532nm). During the each scanning, the irradiation is frequently suspended by pulse-like modulation so that the in-plane tensile strain in the irradiated areas is periodically relieved. By using this technique, large (4μm × 0.5μm average) columnar grains are uniformly obtained. The crystal orientation is {110} normal to the substrate and {100} normal to the growth direction, and surface at grain-boundaries is fairly flat. Surface density of trapping-state at grain-boundary in this poly-Si is larger than that in conventional excimer-laser crystallized poly-Si. However， due to large size of grains, volume density of trapping-state is rather small and, therefore, the height of potential barrier in conduction band is low. We have fabricated TFTs (typically W/L=4μm/2-4μm, t{sub}(ox)=100nm, t{sub}(Si)=50nm) on the glass-substrate and obtained the field-effect mobility of 480 cm{sup}2/Vs (n-ch.) and 130 cm{sup}2/Vs (p-ch.), respectively. The sub-threshold swing (S-value) is less than 0.2 V/dec for both types.