The effect of oxygen on segregation-induced redistribution of rare-earth elements in silicon layers amorphized by ion im
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IC STRUCTURE AND NONELECTRONIC PROPERTIES OF SEMICONDUCTORS
The Effect of Oxygen on Segregation-induced Redistribution of Rare-Earth Elements in Silicon Layers Amorphized by Ion Implantation O. V. Aleksandrov^ St. Petersburg State Electrotechnical University (LÉTI), St. Petersburg, 197376 Russia ^e-mail: [email protected] Submitted November 16, 2005; accepted for publication January 14, 2006
Abstract—A model of segregation-induced redistribution of impurities of rare-earth elements during solidphase epitaxial crystallization of silicon layers amorphized by ion implantation is developed. This model is based on the assumption that a transition layer with a high mobility of atoms is formed at the interphase boundary on the side of a-Si; the thickness of this layer is governed by the diffusion length of vacancies in a-Si. The Er concentration profiles in Si implanted with both erbium and oxygen ions are analyzed in the context of the model. It shown that, in the case of high doses of implantation of rare-earth ions, it is necessary to take into account the formation of Rm clusters (m = 4), where R denotes the atom of a rare-earth element, whereas, if oxygen ions are also implanted, formation of the complexes ROn (n = 3–6) should be taken into account; these complexes affect the transition-layer thickness and segregation coefficient. PACS numbers: 61.72.Cc, 61.72.Ji, 61.72.Tt, 66.30.Jt, 64.75.+g DOI: 10.1134/S1063782606080021
1. INTRODUCTION Solid-phase epitaxial crystallization (so that crystalline Si, c-Si, is formed) occurs as a result of annealing of silicon layers amorphized by ion implantation (a-Si); this crystallization is accompanied by segregationinduced redistribution of impurities of rare-earth elements (REEs): Er, Ho, Yb, and Pr [1–5]. The type of redistribution is affected by the implantation conditions: the substrate temperature, the energy and dose of REE ions [6], and also additional implantation of oxygen ions [2, 4–6]. In the context of the quantitative model suggested by Aleksandrov et al. [7] previously, this phenomenon is accounted for by the formation of a transition layer in amorphous silicon adjacent to the interphase boundary; presumably, there is a high mobility of impurity atoms in this layer. With respect to segregation, this transition layer is similar to the liquid (molten) zone in the case of the zone-melting crystallization; therefore, the relevant equations for the impurity balance were found to be applicable to the layer under consideration [7]. The implantation conditions affect the thickness of the transition layer (zone), which was related to variations in the content of defects in the amorphized layer [6]. In the course of the solid-phase epitaxial crystallization, the segregation coefficient of the REE impurity (ms) increases from msmin ≈ 0.005– 0.02 to msmax ≈ 0.2–1.8 [2, 4–7]. A variation in the REE segregation coefficient was attributed in the qualitative model [2] to a change in the state of impurity that is located in the transition layer
and presumably diffuses [2] via in
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