Simulation of near-surface proton-stimulated diffusion of boron in silicon
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IC STRUCTURE AND NONELECTRONIC PROPERTIES OF SEMICONDUCTORS
Simulation of Near-Surface Proton-Stimulated Diffusion of Boron in Silicon O. V. Aleksandrova^ and V. V. Kozlovskib^^ aSt.
Petersburg State Electrotechnical University LÉTI, St. Petersburg, 197376 Russia ^e-mail: [email protected] bSt. Petersburg State Polytechnical University, St. Petersburg, 195251 Russia ^^e-mail: [email protected] Submitted June 28, 2007; accepted for publication July 6, 2007
Abstract—A quantitative model for near-surface redistribution of doping impurity in silicon in the course of proton-stimulated diffusion is developed for the first time. According to the model, the near-surface peak of the impurity concentration is caused by migration of neutral impurity–self-interstitial pairs to the surface with subsequent decomposition of these pairs and accumulation of the impurity at the silicon surface within a thin layer (referred to as δ-doped layer). The depletion and enhancement regions that are found deeper than the near-surface concentration peak are caused by expulsion of ionized impurity by an electric field from the near-surface region of the field penetration. The field appears due to the charge formed in the natural-oxide film at the silicon surface as a result of irradiation with protons. The diffusion-kinetic equations for the impurity, self-interstitials, vacancies, and impurity–self-interstitial pairs were solved numerically simultaneously with the Poisson equation. It is shown that the results of calculations are in quantitative agreement with experimental data on the proton-stimulated diffusion of boron impurity in the near-surface region of silicon. PACS numbers: 61.72.Bb, 66.30.Jt, 61.72.Tt, 85.40.Ry DOI: 10.1134/S1063782608030020
1. INTRODUCTION Irradiation of silicon with protons (H+) or other light ions (Ne+, Ar+) brings about the formation of Frenkel pairs and excess intrinsic point defects, i.e., vacancies and self-interstitials. At elevated temperatures of irradiation (500–800°C), enhanced proton-stimulated diffusion (PSD) of doping impurities (B, P, As, and Sb) is observed [1–6]; as a result, alteration of maxima and minima in the concentration profiles of impurities [7, 8] is observed in the region of the projected ion range (Rp). It was shown previously [9] that, in the region of x = Rp, a maximum in the impurity concentration is observed at a low impurity concentration (C < 1018 cm–3) and a minimum is observed at higher impurity concentrations (C > 1019 cm–3). Formation of the maximum at low concentrations of the impurity was accounted for in the context of the vacancy mechanism by the flux of impurity toward the flux of vacancies from the region of their highest generation at x = Rp (the up-diffusion) [10, 11] and also by interaction of impurity ions with charged defects [12]. Formation of the minimum at high impurity concentrations was accounted for in the context of the two-flux mechanism (slow diffusion via the lattice sites and fast diffusion via interstices or in the form of pairs composed of
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