Characterization and Evolution of Microstructures Formed by High Dose Oxygen Implantation of silicont
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CHARACTERIZATION AND EVOLUTION OF MICROSTRUCTURES FORMED BY HIGH DOSE OXYGEN IMPLANTATION OF SILICONt M. K. EL-GHOR,* S. J. PENNYCOOK, * T. P. SJOREEN,* AND J. NARAYAN** *Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 ** North Carolina State University, Raleigh, NC 27650 ABSTRACT High doses of oxygen were implanted in silicon to produce stoichiometric buried oxide structures. Microstructural analysis was performed using transmission electron microscopy, electron energy loss spectroscopy, Cavities were observed and Rutherford backscattering/channeling techniques. in the top silicon layers of the as-implanted samples in two forms: spherical cavities (30-300 A in diameter) in the first 1000 A below the surface, followed by a 500 A wide lamellar array of elongated cavities. A post implantation annealing was carried out at temperatures between 1150°C and 1250'C for 3 h during which the cavities became faceted and a denuded zone of 400 A was formed. However, with a 1300%C anneal the cavities disappeared and the density of the two prominent types of defects, namely precipitates (mostly amorphous, but occasionally crystalline) and dislocations, decreased significantly. The silicon-oxide interface became increasingly planar. Possible mechanisms of annealing of the cavities, the precipitates, and the associated planarization of the interface are proposed. INTRODUCTION There is a growing interest in forming buried oxide structures (SOI) by high dose oxygen implantation into silicon (SIMOX), due to their potential for high performance in VLSI applications. The first attempt by Watanabe and Tooi [1] initiated a series of studies that concentrated on producing a continuous stoichiometric oxide with abrupt interfaces [2-4]. Recently, attempts have been made to characterize defects in the top silicon layer as well as the highly damaged silicon oxide interfaces through different annealing studies [5-71. Nevertheless, basic questions regarding the behavior of these defects during implantation and during the annealing processes still prevail. In our experiments, detailed analysis of the silicon overlayer as well as the upper interface was carried out in the asimplanted and annealed samples. Cavities were observed for the first time in both the as-implanted material and after certain annealing conditions. Oxide precipitates were the only three-dimensional defects reported to date in the top Si layer [5-9]. Jaussaud et al. [8] reported strain free amorphous precipitates which they describe as voids filled with amorphous Si0 2 . The cavities we report are not filled with Si0 2 but are true cavities, probably stabilized by oxygen gas pressure in the as-implanted state. EXPERIMENTAL PROCEDURE N-type samples of (100) Si having resistivity of 0.2-0.3 a-cm were implanted with 180 2keV 160+ at doses of 1.6 to 2.1 x 1018 cm- 2 and a current density of 34 uA/cm . The sample was mounted on a heated copper block that was kept at a constant temperature between 450 and 5000C ± 5°C before and during implantation. The sample
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