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MODELING OF THE DIFFUSION OF HYDROGEN IN SILICON D. MATHIOT*, D. BALLUTAUD**, P. DE MIERRYC*, and M. AUCOUTURIER** * CNET-CNS, BP. 98, 38243 Meylan CUdex, France ** Laboratoire Physique des Solides, CNRS, 1, place A. Briand, 92135 Meudon Principal, France ABSTRACT A model is proposed to describe hydrogen motion in silicon near 150*C. This model leads to a consistent view of H* behaviour in low doped n and p-type Si, with a diffusivity in agreement with the high temperature data. On the other hand, a systematic variation of DH+ with the boron concentration forces us to conclude that some still unknown interactions take place and contribute to hydrogen trapping in highly doped p-Si. INTRODUCTION One of the major questions concerning the behaviour of hydrogen in Si is the determination of its microscopic mechanisms of motion. The pioneer permeation results of Van Wieringen and Warmoltz (VWW) lead to a migration enthalpy of about 0.48 eV [1]. Extrapolation of these high-temperature data in the 100-2000 C temperature range leads to values of hydrogen diffusivity of the order of 10-9-10-7 cm 2 s-1 .However, direct measurements of deuterium profiles indicate penetration depths of only a few micrometers for plasma hydrogenation at 150 0 C, corresponding to effective diffusivities several orders of magnitude lower than the values extrapolated from VWW data, and which depend on both dopant dype and concentration [2,3]. Recently, one of us proposed a diffusion model which takes into account all the interactions, reported in the litterature, between the hydrogen species (in its various charge states) and the dopant atoms [4]. It was shown that reliable fits are obtained in both n- and p-type silicon. The main result was that deuterium diffusion profiles in low doped silicon can be simulated with a diffusivity of neutral hydrogen in agreement with the extrapolated high temperature data. On the other hand the situation in highly doped p-type silicon was more confusing. Good simulations on the existing experimental data were possible only with very low H+ diffusivity. Moreover the fits were not unique, and as a consequence it was not possible to extract definitive values for the various parameters of the model. The aim of this paper is thus to present new experimental deuterium diffusion profiles and their analysis with an improved version of the model of Ref.4. THEORY In this analysis it is considered that hydrogen has both an acceptor (Ea) and a donor (Ed) level in the band gap, and thus can exist in the three charge states H+ H 0 and H-. The relative concentrations of these species depend only on the local Fermi level position and follow the usual deep impurity statistics. In the following we will focus only on the reactions in p-type Si were the relevant species are H 0 and H + (analogous reactions occur in n-type Si). Mat. Res. Soc. Symp. Proc. Vol. 163. @1990 Materials Research Society

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H+ can react with the ionized B- dopant atoms to form neutral complexes, following the reaction

kBH

H++B-

BH(1

kVBH The forward r