Oxygen Related Lattice Defects in Silicon: Present Status
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OXYGEN RELATED LATTICE DEFECTS IN SILICON: PRESENT STATUS HUGO BENDER AND JAN VANHELLEMONT IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium ABSTRACT The structural characterization of the oxygen related lattice defects formed under different thermal cycling conditions is discussed. The present understanding on the nature of rod-like defects and oxide precipitates is reviewed. Attention is given to the whole lattice defect spectrum which is induced by the oxygen precipitation. The influence of carbon and dopants on the defects is discussed. INTRODUCTION The impact of oxygen on the electrical properties and mechanical strength of silicon has been recognized already in the earliest days of microelectronics. Although a huge amount of publications on different aspects of oxygen in silicon is available nowadays (see e.g. [1-6]), several fundamental items are still under debate, e.g. the structure of oxygen related donors, the anomalous oxygen diffusion at low temperatures, the nature of rod-like defects, the precipitate nucleation mechanism, and the influence of carbon and dopants on the oxygen precipitation. The present paper focuses on the structural characterization of the oxygen related lattice defects formed under different thermal cycling conditions. DEFECTS IN CZ SILICON WITH HIGH INTERSTITIAL OXYGEN CONTENT In Czochralski silicon with a high oxygen and a low carbon content a large variety of lattice defects can be introduced by thermal annealing. An overview of the different kinds of defects is shown in table 1 [7] for single and two-step treatments. Single step annealing After single step low temperature (450-1000*C) annealing, essentially four types of defects are observed : plate-like precipitates, rod-like defects, dislocation dipoles (600 or 900 type) and prismatic dislocation loops. Furthermore some less defined defect structures are reported : 'loopites' and 'blobs' [8]. * Plate-like SiO, precipitates The density and size distribution of the plate-like precipitates has been studied by means of transmission electron microscopy (TEM) [7,9], small angle neutron scattering (SANS) [10, 11] and chemical etching [10]. In the temperature range 800-1050°C the precipitate density as determined by Wright etching and optical microscopy is given by 0.15exp(2.65eV/kT)/cm3 for the experimental conditions discussed by Livingston et al. [101. In general, the density strongly depends on the oxygen content and the thermal history. SANS studies have revealed at 750 and 800'C a decrease of the precipitate density and an increase of the precipitate size with anneal time [10]. A comparison of the reported densities as compiled by Bourret [2] shows very good agreement between different reports for treatments above 9000C, but a higher density at lower temperatures for anneal times of 100 h than of 750 h. These observations can be related to Ostwald ripening, i.e., the growth of larger precipitates at the expense of smaller ones, due to the increase of the critical radius as the oxygen supersaturation diminishes [12]. The nucleation
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