Excimer Laser Crystallization of Nanocrystalline Silicon Thin Films

Nanocrystalline silicon (nc-Si) thin film on glass substrate is subjected to excimer laser crystallized by varying the laser energy density in the range of 50~600 mJ/cm2. The effect of excimer laser crystallization on the structure of silicon film is investigated using Raman spectroscopy, X-ray diffraction, atomic force microscopy and scanning electron microscopy. The results show that polycrystalline silicon thin films can be obtained by excimer laser crystallization of nc-Si films. A laser threshold energy density of 200 mJ/cm2 is estimated from the change of crystalline fraction and surface roughness of the treated films. The growth of grain is observed and the crystallization mechanism is discussed based on the super lateral growth model. The nanocrystalline silicon grains in the films act as seeds for lateral growth to large grains.

Bottom-Gate Thin-Film Transistors Fabricated by Excimer Laser Annealing

High performance and device uniformity n-channel low-temperature poly-silicon (LTPS) bottom-gate (BG) thin film transistors (TFTs) with artificially-controlled lateral grain growth have been performed by excimer laser crystallization (ELC). The BG TFTs (W/L = 1.5 μm/1.5 μm) demonstrate field-effect-mobility of 323 cm2/Vs and high Ion/Ioff of 9.5 × 108. The proposed BG TFTs reveal the superior electrical characteristics, device uniformity, and reliability than conventional top-gate ones.