Takashi Kuwahara

Enlargement of Poly-Si Film Grain Size by Excimer Laser Annealing and Its Application to High-Performance Poly-Si Thin Film Transistor

By both numerical simulation and experimental investigation, we found it possible to enlarge the grain size (?3000 ?) of polycrystalline silicon (poly-Si) films by excimer laser annealing, using a new method to control the solidification process of molten Si - low-temperature (?400?C) substrate heating during laser annealing. Poly-Si thin-film transistors (TFTs) fabricated by this new excimer laser annealing method showed a high field-effect mobility of 230 cm2/V?s, and good uniformity of field-effect mobility (?10%) within the effective laser irradiation area.

Lateral Grain Growth of Poly-Si Films with a Specific Orientation by an Excimer Laser Annealing Method

Dramatic lateral grain growth of nondoped poly-Si films (maximum grain size: ~4.5 µm, film thickness: 500 A) with strong crystallographic (111) orientation on glass substrates has been achieved using an excimer laser annealing method, namely at low temperature below 400°C and in a processing time shorter than a second, for the first time. The surface morphology of these poly-Si films was very smooth and the crystallinity was excellent with minimal internal defects. These poly-Si films have monomodally distributed grain sizes, with an average grain size of around 1.5 µm. As a result of experimental study, we speculate that the basic driving force behind this lateral grain growth was surface free energy anisotropy, as the same mechanism was observed in high-temperature furnace annealing of doped poly-Si thin films.

Comprehensive study of lateral grain growth in poly-Si films by excimer laser annealing and its application to thin film transistors

Lateral grain growth in nondoped poly-Si films was studied by using Si thin films (500 A) with different structures as a starting material for excimer laser crystallization. It was clarified that the lateral grain growth phenomenon (micron-size grains with strong (111) orientation) upon excimer laser annealing was strongly affected by both the microstructure and the orientation of the initial Si thin films. This result supports our previous speculation that the principal driving force of the lateral grain growth phenomenon is surface energy anisotropy. Poly-Si thin-film transistors using these films show a high field effect mobility of 440 cm2/Vs, achieved through a low-temperature process below 600° C. This excellent electrical characteristic is thought to be due to the large grain size of poly-Si thin film with controlled orientation, good crystallinity, and a smooth surface.

High mobility poly-Si TFT by a new excimer laser annealing method for large area electronics

A high-mobility (280 cm/sup 2//V-s), high-throughput poly-Si TFT (thin-film transistor) formed using a low-temperature process (<or= 600 degrees C) has been achieved through a novel excimer laser annealing method. The method uses thin, active-layer poly-Si film (500 AA) and involves controlling the solidification process of molten Si by low-temperature (<or= 400 degrees C) substrate heating during laser annealing. Poly-Si film grain formed by this process is radically larger in size, and has minimal internal defects. The maximum grain size is over 5000 AA, and uniformity in field effect mobility was found to be +or-10% within the effective laser irradiation area.<<ETX>>

Improving the uniformity of poly-Si films using a new excimer laser annealing method for giant-microelectronics

Film uniformity is the main problem when applying laser-recrystallised poly-Si films to thin film transistors (TFTs) in giant micro electronics. However, this has been dramatically improved by a new excimer laser annealing method in which the solidification process of molten Si is controlled by low-temperature (400°C) substrate heating during excimer laser annealing. Poly-Si TFT fabricated around the laser irradiation overlap region exhibited a high field effect mobility uniformity of within ±8%.

Lateral Grain Growth in the Excimer Laser Crystallization of Poly-Si

We have succeeded in obtaining nondoped, thin poly-Si film (thickness ∼500A) with excellent crystallinity and large grain size (Maximum grain size ∼4.5 μ m) by an excimer laser annealing Method, which offers the features of low-temperature processing and a short processing time. The grain size distribution shrinks in the region around 1.5 μ m and this poly-Si film exhibits a strong (111) crystallographic orientation. Poly-Si thin film transistors using these films show quite a high field effect mobility of 440cm 2 /V · s below 600°C process.