Enlargement of Grain Size and Location Control of Grain in Excimer-laser Crystallization of Si Film
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0910-A14-01
Enlargement of Grain Size and Location Control of Grain in Excimer-laser Crystallization of Si Film Wenchang Yeh, Dunyuan Ke, and Chunjun Zhuang Electronics, National Taiwan University of Science and Technology, No.43, Sec.4, Keelung Rd., Taipei, 106, Taiwan
ABSTRACT A technique for enlargement of grain size were shown and a technique for location controlled super lateral growth (SLG) grain in excimer laser annealing (ELA) were proposed and realized. In the technique for grain size enlargement, the grain size was enlarged to 10µm that is more than 10 times larger than that in conventional method(~0.8µm). The proposed sample structure was Si film/light absorptive film/Glass structure with applying the laser light from the back side of glass substrate. Time resolved(~1ns) optical measurement (TROM) revealed that the melt duration of Si film was increased to 800ns that is also 10 times longer than that in conventional method. As for the grain location control technique, a new method contains pre seeding process and post growth process were proposed and realized. In the pre seeding process, micro light beam(µ-light beam) was exposed to Si film to form a grain within the crystallized spot. µ-light beam was formed by micro-lens-array(MLA). After post growth process, single grain array with the diameters of 6µm was formed in a period of 10µm. INTRODUCTION In order to realize system on panel, thin-film transistors (TFTs) with high mobility and uniformity are demanded. These demands can only be satisfied by the single grain TFTs where the channel of a TFT was formed within a single grain. In order to realize single grain TFTs, technologies for both grain size enlargement and grain location control was demanded. As for the technologies on grain size enlargement, elongating the melt duration of Si during ELC was thought to be effective in enlargement of the grain size. There are many methods for elongating the melt duration. The most well known method is increasing the substrate temperature1,2 in order to decreasing the temperature gradient between the Si film and substrate. As for the 100nm-thick Si film, diameter of SLG grains was 1µm with room temperature ELA and was increased to 1.5µm with 500oC2 substrate heating. The effect was only by 1.5. The second method is to thickning the Si film to increase the thermal capacity of Si film3. Diameter of SLG grains was 2.5µm with 90nm-thick Si film and was increased to 3.8µm with 181nm. The effect is by 1.5. The third method is to elongating the pulse duration3. Diameter of SLG grains was 2.5µm with 56ns pulse duration and was enlarged to 3.5µm with 200ns. The effect is by 1.4. However, these effects are all not enough. Based on this background, we have proposed light absorptive underlayer enhanced crystallization where the SLG grain size was increased dramatically to 10µm even at room temperature4,5,6. In this method the light absorptive film7,8 with the absorption coefficient α around 0~12000cm-1 was used as the under layer of Si film, and the laser was applied from
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