Amorphous to Polycrystalline Transformation in High Dose Ion Implanted Silicon
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AMORPHOUS TO POLYCRYSTALLINE TRANSFORMATION IN HIGH DOSE ION IMPLANTED SILICON E. NYGREN*, J.C. MCCALLUM*, R. THORNTON*, J.S. WILLIAMS• and G.L. OLSON*** *RMIT, Microelectronics Technology Centre, Melbourne 3000, Australia **Melbourne University, School of Physics, Parkville 3052, Australia •HHughes Research Laboratories,
Malibu, CA,
90625,
U.S.A.
ABSTRACT The amorphous to polycrystalline transformation of silicon implanted with high doses of In, Bi, Ga, and Sn is investigated. Each of these elements forms a low temperature eutectic with crystalline silicon and the details of the phase transformations in these systems are found to be very similar. A general model for the transformation based on the nature of the binary solutions is presented.
INTRODUCTION Amorphous-to-polycrystalline (a-p) transformations in high dose ion implanted Si have been widely studied [for examples see 1,2,3]. In recent work we have investigated the phase transformation in In-implanted amorphous Si (a-Si) and have proposed a mechanism for the a-p transformation [4,5]. In the present paper we report on new observations in the In system and extend our earlier studies to include the Si(Bi,Ga,Sn) systems. Four main features of the (a-p) transformation in In implanted a-Si are described below. 1) The transformation is preceded by an incubation period. The length of this period varies inversely with increasing temperature and In concentration. During the incubation period the sample remains amorphous and no In diffusion within the resolution of typical RBS evaluation is observed. 2) After the incubation period the sample rapidly crystallizes. Although the crystallization rates were not precisely determined before the in situ TEM measurements presented in this paper, they were known to be much faster than normal solid phase crystallization in Si. Samples had been observed to 0 crystallize at temperatures as low as 350 C. The final microstructure is polycrystalline with grain size typically less than 10 nm. 3) A massive redistribution of In throughout the entire transformed region accompAnies crystallization. We have determined that the impurity transport can be very long range (greater than 500 nm). 4) The transformation appears to be a bulk effect most probably initiated at the peak of the implant distribution. For shallow amorphous layers (a few 2 thousand angstroms or less) containing an implanted In dose of 5x10/om the entire layer will be converted to polycrystal. The transformation in layers a micron or more thick will be incomplete leaving amorphous material between a polycrystalline layer and the single crystal substrate. Solid phase epitaxial crystal growth (SPEG) can be competitive with the a-p transformation with the extent of either transformation depending on the temperature and In concentration [E4. We have observed that the a-p crystallization rate is much faster than that for the normal solid phase process and we have proposed that crystallization is mediated by liquid phase, In rich, precipitates [4,5]. Mat. Res. Soc.Symp. Pr
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