Combination of Metal Nano-Imprint and Excimer Laser Annealing for Location Control of Si Thin-Film Grain
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0910-A20-05
Combination of Metal Nano-Imprint and Excimer Laser Annealing for Location Control of Si Thin-Film Grain Gou Nakagawa, and Tanemasa Asano Center for Microelectronic Systems, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka, Fukuoka, 820-8502, Japan
ABSTRACT A novel method of locating Si thin-film grains by combining metal nano-imprint and excimer laser annealing (ELA) is demonstrated. Metal nano-imprint at the a-Si film surface is used for the purpose of creating Si crystal nuclei which act as the seed for the subsequent crystallization by using ELA. The annealing to form nuclei at imprinted sites was carried out at temperatures below 450oC. ELA using XeCl laser of the sample with capping SiOx film resulted in the formation of over 2.0 ยต m-sized Si crystal grains at controlled position. Electron back-scattering pattern (EBSP) analysis showed that about 75% of the boundaries inside the location-controlled grains were the coincidence site lattice boundaries. INTRODUCTION Polycrystalline-Si (poly-Si) thin-film transistors (TFTs) are being extensively studied as a keydevice to realize not only active-matrix displays with signal processing circuits (so-called, system on panel) but also thin-film complementary metal oxide semiconductor (CMOS) integrated circuits. Grain boundaries in poly-Si films significantly degrade the performance of TFT. For example, grain boundaries in the channel region of TFT generate potential barriers that hinder the carrier transport and also generate junction leakage at the source and drain. One promising approach for fabricating high performance poly-Si TFTs is to eliminate grain boundaries from the channel region of TFT. To realize these devices, it is necessary to control the location of crystal grains whose size are large enough to cover the whole of TFT channel region. There have been proposed several methods for location control. Using excimer laser annealing (ELA), use of phase-shift mask to control the spatial distribution of laser power[1], micro-Czochralski method[2] to control the heat flow using a trench-structured heat sink, and initiating nucleation at desired location by controlling the quality of amorphous-Si (a-Si)[3,4] have been proposed. On the other hand, we have proposed metal nano-imprint technology to grow large grains at controlled sites using solid phase crystallization (SPC)[5]. In this method, a small amount of metal (Ni, Sn) transferred to location-controlled nanometer-size sites at the a-Si film surface induces only the nucleation followed by SPC. In our previous work, we reported that single-grain TFTs fabricated by aligning the position of the TFT channel and the location-controlled grain have high threshold controllability and high carrier mobility and, therefore, CMOS ring oscillator --------------------------------------------------------------------------------------------------------------------The authors are presently with Dept. of Electronics, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
with single-grain TFT
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