An Anomalous Vacancy Diffusion in Silicon during the Antimony Drive-in Diffusion

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AN ANOMALOUS VACANCY DIFFUSION IN SILICON DURING THE ANTIMONY DRIVE-IN DIFFUSION W. WIJARANAKULA AND J.H. MATLOCK Materials Characterization Laboratory, SEI America, Incorporated 4111 Northeast 112th Avenue, Vancouver, Washington 98682-6776, USA ABSTRACT In the substrate region underneath the antimony buried layer, an enhanced oxygen donor generation and a retardation of the oxygen precipitation were observed. Both phenomena can be explained by the vacancy mechanism in which the charged vacancies dominate at high temperatures. Based upon this hypothetical model, it is suggested that the intrinsic vacancy concentration could play a significant role in both oxygen thermal donor generation and oxygen precipitation in silicon.

INTRODUCTION In the junction-isolated bipolar integrated circuit device fabrication, a high temperature processing sequence consisting of an Sb buried layer diffusion followed by epitaxial deposition is commonly used. In the usage of a high temperature process, a retarded oxygen precipitation and reduction in internal gettering efficiency could be anticipated. A retardation of oxygen precipitation can occur as a result of a dissolution of "grown-in" nuclei. It can also be caused by a reduction in the vacancy concentration, e.g. via a complex formation between doping impurities and vacancies. The latter mechanism has been used to explain a retardation of oxygen precipitation in silicon heavily doped with Sb (1). Thus far, no direct evidence of the Sb V complex formation has been presented. If it is assumed that this mechanism is to prevail in the case of Sb buried layer diffusion, a localized reduction in the vacancy concentration could occur, particulary underneath the buried layer. Charged vacancies could be attracted by indiffusing Sb and form the Sb V complexes. This is a hypothetical model that requires an experimental verification. In this work, the 450*C oxygen thermal donors (TDs) were used as a point defect monitor in silicon after an Sb drive-in diffusion. Based upon the results for TD generation and oxygen precipitation, a hypothetical model for charged vacancy diffusion is developed. MICROSCOPIC MODEL FOR THE 4500 C OXYGEN DONORS The generation mechanism of TDs formed in the temperature range between 400*C and 500*C has been a subject of study for the past thirty years. The exact microscopic model of these donors is still being debated, but the most plausible one is the model in which the donor activity arises from the two broken bonds of a silicon interstitial (Si.) located at the core of the donor (2). In this model, the donor activit§ is terminated when the double-positively charged Sii is annihilated. In the bulk silicon, an annihilation of Sii occurs via a recombination process involving vacancies. Substitutional impOrities having a tetrahedral covalent radius much smaller than silicon (1.17A), e.g. carbon (0.77 A), act also as a Si. trap. Both reactions are described by (3): 1 Si. + V 111- Si [1] and Sii

+ Cs

-

00- [Ci-Sii] complex

Mat. Res. Soc. Symp. Proc. Vol. 163. c1990

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