Atsuhiro Sono

Development of line-shaped optical system for YAG2omega laser annealing used in the manufacture of low-temperature poly-Si TFT

We have developed a new optical system that transforms the circle profile beam generated with near Gaussian intensity distribution by the YAG2ω laser (second harmonics of a Q-switched Nd:YAG laser) into a line-profile beam. This transformed bean has uniform distribution to within 5% in the longitudinal direction, and is about 100 mm long and 40 micron wide. For homogenization in the longitudinal direction, we employ a waveguide plate homogenizer. The laser beam is divided by waveguide plates, and the divided beams are overlapped on the surface of the works. We successfully reduced interference fringes by increasing the fixed optical pass difference beyond the inherent time and coherent length for every divided pair of adjacent beams under a controlled space coherent length. In the width direction, the laser beam is focused up to the limited M2 value.

Crystallization of amorphous‐Si films by pulsed YAG2ω green laser for polycrystalline Si TFT fabrication

— A pulsed YAG2ω green laser with a line-shaped beam was applied in the crystallization process to fabricate polycrystalline-Si TFTs, and this procedure was compared with excimer-laser annealing (ELA). YAG2ω lasers are superior to excimer lasers in that they have fewer items to maintain and a longer working time ratio. The crystallization mechanism for YAG2ω laser annealing (YLA) based on the lateral growth of grain is different from that of ELA. Its fluence margin was obtained from the n-channel mobility measured from fabricated TFTs and was found to be twice as large as that for ELA. We also found that overlapping irradiation does not change the mobility of TFTs. This is because the distribution of grain size is almost the same as in non-overlapping regions. This suggests the possibility of overlapping irradiation in YLA.