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

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.