Advanced Lateral Crystal Growth of a-Si Thin Films by Double-Pulsed Irradiation of All Solid-State Lasers
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A16.5.1
Advanced Lateral Crystal Growth of a-Si Thin Films by Double-Pulsed Irradiation of All Solid-State Lasers Toshio Kudo, Koji Seike, Kazunori Yamazaki, Hirohito Komori, Sachi Yawaka+, Shiro Hamada+, and Cheng-Guo Jin* Research & Development Center and +Laser System Division, Sumitomo Heavy Industries Ltd., 19 Natsushima-cho, Yokosuka-shi, Kanagawa-ken 237-8555, JAPAN * ACT Center, TIC Corporation, 2-20-29 Takanawa, Minato-ku, Tokyo 108-0074, JAPAN ABSTRACT A compact annealing machine with all solid-state green lasers has been developed, which has the advantage of widely adjustable solidification rate through the delay time control of two long pulses (pulse width ~100ns). Advanced lateral crystal growth (ALCG) process has been proved by the double-pulsed all solid-state laser annealing. The laser beam has a line shape 0.1mm wide and 17mm long, and the beam profile on the short axis is quasi-Gaussian (FWHM 0.1mm). Scanning the line beam along the short axis at the 86% overlapping ratio, the lateral crystal growth area of width 14µm, parallel to the long axis, is sequentially formed at the pitch of 14µm towards the scanning direction. The advanced lateral growth mechanism is easily explained as follows: (1) At the first irradiation, twin seed lines of width 4µm, parallel to the long axis, generates at a boundary between a near-complete melting region and a complete melting region. (2) At the second irradiation of scanning step 14µm, the front seed line in the scanning direction grows symmetrically toward both sides. (3) At the third irradiation of scanning step 2x14µm, the seeds laterally grow until stopped by the growing of seeds on both sides. Finally the ALCG process by the scanning line-beam technique like the current ELA enables us to produce the laterally grown Si thin-films sequentially arranging the belt-shaped texture at the pitch of 14µm. The quality of the laterally grown Si films is quite well except for the projections generated by the bump of lateral growing seeds. INTRODUCTION In the roadmap of low-temperature poly-Si (LTPS) technologies [1], the high performance of thin-film transistors (TFTs) is to be demanded with the transition of TFT generations. High-quality LTPS films naturally are required for the high performance of TFTs. The current excimer laser annealing (ELA) method for crystallization, which is one of the key technologies in the LTPS-TFT process, is not able to apply in the next generation because of small Si grains of 0.5µm at maximum. In order to obtain high-quality poly-Si films, several crystallization methods by an excimer laser [2,3] and also by a reliable solid-state laser [4-6] were proposed, and are founded on controllable grain size and grain boundary position. We propose a challenging crystallization method, appending the function of solidification rate control to the scanning line-beam technique like the current ELA. Our crystallization method, named advanced lateral crystal growth (ALCG), is based on double-pulsed laser irradiation controlling a delay time between two pu
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