Mechanisms of Transition Metal Diffusion into Semiconductor Film
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MECHANISMS OF TRANSITION METAL DIFFUSION INTO SEMICONDUCTOR FILM M. G. GOLDINER* AND A. V. VAYSLEYB** *Department of Nuclear Engineering, University of Michigan, Ann Arbor, MI 48109 "**Department of Materials Science, Henry Krumb School of Mines, Columbia University, New York, 10027
ABSTRACT Descriptions of metal (Me) diffusion into semiconductor (Se) film by diffusion-kinetic and purely kinetic methods were compared. To analyze thin film diffusion, thin film surfaces were considered as a substantial source/sink of point defects. Conditions of transition from one Me diffusion transport mechanism/regime to another, when Se sample thickness is changed, were found to be practically the same in both considerations. Critical Se film size,
dislocation density, and temperature of diffusion mechanisms and regimes coincide, providing a correct interpretation of the experimental results in terms of the corresponding diffusion mechanism.
1. INTRODUCTION Diffusion transport of transition metal into semiconductor Si and Ge crystals is the physical basis for electronic devices production technology. Unfortunately, today there is no generally accepted theory of the metal diffusion into semiconductor crystals for certain pairs which are the most important in practice, such as, e.g., Au-Si [1-4]. It was shown that impurity interstitial atoms Me1 , impurity substitutional atoms Me,, vacancies V, and intrinsic interstitial atoms I may take a part in Me-Se diffusion. The dissociative diffusion mechanism (see, e.g., [4-6]) is based on the conclusion that vacancies are the main point defects in Se (see, e.g. [3]). It was presumed that the quickly diffusing impurity interstitial atoms Me1 move via interstices and are captured by trap-vacancies V, occupying lattice sites and turning into substitutional Me, atoms Me, + V 0 Me,.
(1)
In the case of Au-Si system Au, atoms diffuse more slowly than interstitial atoms Au,. It means that the capture results in effective slowing down of the impurity diffusion. Studying the physical nature of swirls in Si crystals Seeger et al. [7,8] came to the conclusion that selfinterstitial silicon atoms I are the main type of point defects in Si crystals at high temperatures. This made it possible for Gosele et al. (2] to suggest the kickout mechanism for explanation of the diffusion anomalies of Au into Si. The kickout mechanism assumes that interstitial impurity atoms Me1 push out host Si atoms from crystal lattice positions and occupy their sites Me,
Me 1 0*me$ +I.
(2)
This model can account for some additional anomalies during Me-Se diffusion [2], not explained within the scope of the dissociative model. The different role of vacancies V and Se self-interstitial atoms I in the metal transport is explained by the fact that the former bind Me, atoms, while the latter release them. It is clear, that the kinetics of Me diffusion in Se is determined by the possibilities of point defect delivery to and from the diffusion zone. These Mat. Res. Soc. Symp. Proc. Vol. 311. ©1993 Materials Research Society
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