Analysis of buried oxide layer formation and mechanism of threading dislocation generation in the substoichiometric oxygen dose region

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Abstract
The structure of SIMOX wafers implanted at 180 keV with doses of 0.1 × 1018-2.0 × 101816O+ cm−2 at 550 °C, followed by annealing over the temperature range of 1050–1350 °C, has been investigated using cross-sectional transmission electron microscopy and a chemical etching. With doses of 0.35 × 1018-0.4 × 1018 cm−2, a continuous buried oxide layer having no Si island inside is formed by high-temperature annealing at 1350 °C. At a dose of 0.7 × 1018 cm−2, multilayered oxide striations appear in the as-implanted wafer. These striations grow into multiple buried oxide layers after annealing at 1150 °C. The multiple layers lead to a discontinuous buried oxide layer, resulting in the formation of a number of Si micropaths between the top Si layer and the Si substrate when the wafer is annealed at 1350 °C. These Si paths cause the breakdown electric field strength of the buried oxide layer to deteriorate. With doses of 0.2 × 1018-0.3 × 1018 cm−2 and of higher than 1.3 × 1018 cm−2, an extremely high density of threading dislocations is generated in the top Si layer after annealing at 1350 °C. The dislocation density is greatly reduced to less than 103 cm−2 when the oxygen dose falls in the range of 0.35 × 1018-1.2 × 1018 cm−2. Here we propose a mechanism that accounts for the threading dislocation generation at substoichiometric oxygen doses of less than 1.2 × 1018 cm−2.