Crystallization of Amorphous Si In Al/Si Multilayers
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CRYSTALLIZATION OF AMORPHOUS Si IN Al/Si MULTILAYERS Toyohiko J. Konno and Robert Sinclair Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305 ABSTRACT The crystallization of amorphous Si in a Al/Si multilayer (with a modulation length of about 120A) was investigated using transmission electron microscopy, differential scanning calorimetry and X-ray diffraction. Amorphous Si was found to crystallize at about 175 0C with the heat of reaction of 1 1±2(kJ/mol). Al grains grow prior to the nucleation of crystalline Si. The crystalline Si was found to nucleate within the grown Al layers. The incipient crystalline Si initially grows within the Al layer and then spreads through the amorphous Si and other Al layers. Because of extensive intermixing, the original layered structure is destroyed. The Al(1 11) texture is also enhanced. INTRODUCTION The stability of amorphous Si (a-Si) in contact with Al is an important issue in view of recent developments in semiconductor electronics and electrophotography.[ 1,2] For example, the temperature rise in a-Si photoreceptor drum can crystallize the photoreceptor layer and destroy the drum. Apart from its technological significance, the crystallization kinetics of a-Si and/or amorphous Ge (a-Ge) have also attracted a number of researchers from the scientific point of view. The nucleation of crystalline Si (c-Si) in a-Si is one of the issues still under investigation.[31 Although the crystallization temperature is known to be about 600700'C,[4,5] this temperature is strongly structure dependent. For instance, an a-Si whisker is reported to crystallize at about 900°C.[6] On the other hand, a-Si and a-Ge crystallize at surprisingly low temperatures when they are in contact with metals with which they form eutectic systems.[7-12] This phenomenon is sometimes called Metal Contact Induced Crystallization (MCIC). The mechanism of MCIC is still not well known. Early RBS studies on an a-Si/metal/cSi structure indicated that the a-Si phase dissolves into the metal phase prior to the nucleation of c-Si on the substrate c-Si.[10,11] This technique can be used to induce solid phase epitaxy. Hung et al., in their study on an a-Si/Al system, observed that small crystalline phases appeared in the amorphous region at 200'C.[13] Homma et al. suggested that Pb grains might act as templates for crystalline Ge from their X-ray study on crystallization in a Pb/Ge multilayer system.[14] In the present study, crystallization of a-Si in an Al/Si multilayer system was investigated using transmission electron microscopy(TEM), calorimetry, and X-ray diffraction. The kinetics of nucleation of c-Si was examined by in-situ as well as ex-situ experiments. EXPERIMENTAL Al/Si multilayers were deposited by RF/DC magnetron sputtering on the following substrates: (100) Si wafer, slide glasses, and slide glasses coated with photo-resist. These substrates were placed on a rotating table in the chamber. The power of the guns and the speed of the rotation of the table were adjusted to ob
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