Stress-induced formation of structural defects on the {311} planes of silicon
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P. Krulevitch") Department of Mechanical Engineering, University of California-Berkeley, Berkeley, California 94720
R. Gronsky Department of Materials Science & Mineral Engineering, University of California-Berkeley, and Lawrence Berkeley Laboratory, Materials Sciences Division, Berkeley, California 94720
G. C. Johnson Department of Mechanical Engineering, University of California-Berkeley, Berkeley, California 94720 (Received 7 January 1994; accepted 29 March 1994)
Structural defects occurring on the {311} planes of single crystal silicon have been observed near the bottom oxide corner in silicon-on-insulator structures formed by selective epitaxial growth. These {311} defects exhibit a preferential orientation and are clustered near the silicon/silicon dioxide interface. This new observation provides an opportunity to study the mechanism of {311} defect generation in a system with discernible microstructure and stress state. High resolution electron microscopy combined with analytical and numerical three-dimensional stress modeling are used to show the dependence of these {311} defects on the local stress field, and to establish their origin in terms of a homogeneous dislocation nucleation model.
I. INTRODUCTION There has been much debate in the literature concerning the local atomic structure and the formation mechanism of the so-called {311} defects. Previously, these defects had been observed in ion-implanted silicon or germanium,1'2 in separation of silicon by implanted oxygen (SIMOX) structures beneath the implanted layer after annealing,3-4 and in electron-irradiated (400 keV or above) silicon at 400 °C.5'6 Structurally similar rodlike defects, which form along the (110) direction with an overall (100) Burger's vector, were also observed in annealed Czochralski silicon7 and in electron-irradiated silicon.8 These observations have led to various proposals regarding the nature of these defects. In one, the defect is attributed to the presence of a metastable hexagonal phase of silicon,1'6'9 while in another, it is attributed to the presence of a crystalline high pressure phase of silicon dioxide, known as coesite,11 or a substoichiometric form of silicon oxide, SiO*.12 Identification of the structures, even using a combination of high resolution electron microscopy images and image simulation techniques, remains ambiguous. For example, high resolution
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address: Lawrence Livermore National Laboratory, P.O. Box 808, L-222, Livermore, California 93551.
images reveal hexagonal ABAB type stacking as would be expected for coesite imaged along a [100] direction,11 but the formation of coesite in either ion-implanted or electron-irradiated silicon is generally not favored as its presence requires enhanced oxygen diffusion.2 The presence of interstitial oxygen may also play a role in the formation of these defects. In previous observations reported in the literature, the concentration of interstitial oxygen in both silicon and germanium is not negligible, especially in Czochralski silicon.13 A small c
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