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Effect of Ramp Annealing to Ni Induced Lateral Crystallization of Amorphous Silicon S. Shivani, M.C. Poon*, M. Chan , P.K.Ko Dept. of Electrical and Electronic Engineering, Hong Kong University of Science & Technology, Sai Kung, Hong Kong

Corresponding author: Tel: (852)2358-7047, Fax:(852)2358-1485, e-mail:[email protected] ABSTRACT Nickel Metal-Induced-Lateral-Crystallization (MILC) has been used to enlarge the grain size and improve the quality of (poly-Si) Thin-Film-Transistors (TFTs). However, the MILC temperature is still low and the grain size is still small. The feasibility of forming very large grains (single crystal like) from amorphous silicon (a-Si) by combining MILC with ramp annealing has been studied. It has been found that the grain size after ramp annealing is remarkably enhanced and can reach of the order of several ten’s of microns. The velocity of MILC with ramp annealing is faster than that of MILC with isothermal annealing. The grain size becomes maximal at around 625°C/2hrs, and saturates at higher temperatures of 6251000°C. The effect of temperature, time and other parameters has also been studied in order to maximize the grain size and quality. MILC with ramp annealing at 625°C can greatly lower the process time and reduce the need of subsequent annealing to enhance the grain size. The new technology can have numerous novel applications such as providing a low cost alternative to form silicon-on-insulator (SOI) substrates and a breakthrough for high performance TFTs and novel multi-layers SOI like devices and circuits. INTRODUCTION Nickel metal induced lateral crystalllization (NMILC) has been studied as a lower temperature alternative to solid phase crystallization(SPC) of amorphous silicon thin films. This phenomenon of lateral crystallization (NMILC) has been found to produce polycrystalline silicon thin films largely free of metal contamination, with better crystallinity than those produced by SPC and resulting in better perfomance of thin film transistors. Much research effort has been put on the metal induced lateral crystallization (MILC) of amorphous silicon (a-Si) recently. This issue has been studied intensively, using metals such as Pd 1 and Ni 2-4, and even Ge 5 to dramatically decrease the crystallization temperature of a-Si and to enhance the grain size. The potential for the use in the SOITFT application is high as this method provides a low cost alternative to form silicon-on-insulator (SOI) substrates and a key technology for ultra-dense circuit integration including SRAM and future 3-dimensional multi-layer SOI like devices. However, the mechanism behind MILC is still not well known. In this paper, effects of different conditions such as annealing temperature, time and distribution of nickel on the MILC growth are presented and the criteria to optimize the polycrystalline silicon film are described. EXPERIMENTAL DETAILS Figure 1 shows the process sequence of crystallization by MILC. A thick oxide (7000Å) was thermally grown on p-type 4 inch wafers with orientation. Amorphous