Optical and compositional studies of buried oxide layers in silicon formed by high dose implantation

Samples of standard SIMOX material, dose 2.4×10¹⁸/cm² at 200 keV have been examined in the as-implanted and annealed condition. The samples were prepared by wet-chemical etching with the silicon overlayer being removed first. Samples were then etched to remove the buried oxide, revealing and successively exposing the interface. These samples were then examined by ellipsometry and SIMS with an emphasis on the optical properties and compositional nature of the interfaces. Ellipsometry results indicate that a final layer of the buried oxide with refractive index 2.5 to 3 and thickness 150 to 250 Å is very resistant to the oxide etch. This may be correlated with the compositional profile of the interfacial region obtained by SIMS. The interface between the buried oxide and bulk silicon includes two layers, the first of silicon with SiO₂ precipitates and the second of entirely SiO₂.