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A6.6.1

TCAD Modeling of Metal Induced Lateral Crystallization of Amorphous Silicon 1

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Aleksey M.Agapov , Valeri V.Kalinin , Alexandre M.Myasnikov , Vincent M.C.Poon , Bert 3 Vermeire 1 Institute of Semiconductors Physics, 13 Lavrent'ev Avenue, Novosibirsk, Russia 630090 2 Hong Kong University of Science and Technology, Kowloon, Hong Kong 3 Ridgetopt Group, Inc., 6595 N.Oracle Road, Tucson, AZ 85704-5645, U.S.A. a On leave from Institute of Semiconductors Physics, 13 Lavrent'ev Avenue, Novosibirsk, Russia 630090 ABSTRACT In our previous publications [1, 2] nickel diffusion and spreading resistance probe (SRP) measurements for quality control of metal induced lateral crystallization (MILC) of amorphous silicon (a-Si) were studied. Now we present TCAD modeling and an explanation of experimental results. By using ISE TCAD the Ni concentration distributions were calculated and compared with results obtained by experiments using SIMS analysis. INTRODUCTION Amorphous silicon (a-Si) has attracted a great deal of interest as material for large area applications such as thin film transistors [3-9]. However, the field-effect mobility in a-Si is very low, and solid phase crystallization (SPC) is a typical method to improve its structure. The temperature of SPC is too high, though, for large-area glass substrates to be used. The SPC temperature can be lowered by different methods, such as microwave-induced [5], field-aided crystallization [3], or lateral crystallization with different metal seeds, such as Ni [3-4, 7-9], Pt [10], Au [6] or other metals having low temperature compounds with silicon. Unfortunately, the addition of a great quantity of seed metal can induce the degradation of devices formed in a-Si or reduce to zero almost all of the advantages of a-Si recrystallization. A small quantity of seed metal, in turn, could cause non-optimal conditions of recrystallization. It is known that, at metal induced crystallization of a-Si, the Ni islands should be used as seeds and for getting the maximum size of MILC regions, it needs to introduce the largest amount of Ni possible, because there is a limit concentration, below which NiSi2 silicide formation is impossible. Secondly, increasing the Ni concentration to higher levels induces the failure of any devices formed in the recrystallized layer. Therefore, it is very important to know

A6.6.2

about Ni distributions in MILC process. EXPERIMENT Structures for MILC process were prepared as follows: ● 0.7 µm thick oxide was formed by wet oxidation at 1000 °C on (100) 20 Ohm.cm p-Si wafers. ● 3000 Å of a-Si was deposited on the oxide by LPCVD at 550 °C. ● Deposition of 3000 Å of low temperature oxide (LTO) at 425 °C. ● Windows were patterned. ● 50 Å Ni film was deposited onto the a-Si using an electron beam evaporator at high vacuum. The lateral crystallization of the a-Si was performed at 640 °C for 1, 2, and 4 hours in 99% pure N2 to form the MILC regions. Figure 1 shows the schematic and TEM cross-section of structure.

Figure 1. The schematic and TEM cross-section