Boron Diffusion Profiles in Ultrathin Silicon-on-Insulator Structures and Their Relation to Crystalline Quality

Abstract

Boron (B) diffusion is carried out for four kinds of silicon-on-insulator (SOI) structures at 860°C in N2 ambient. SOIs used are low-dose separation-by-implanted-oxygen (SIMOX) with/without internal-thermal-oxidation (ITOX) treatment, UNIBOND and ELTRAN. The B diffusion in the SOI is retarded as compared with that in bulk Si. Retardation of the B diffusion is more marked in the SIMOX with/without ITOX than in the ELTRAN or UNIBOND. Simulation is carried out to clarify the mechanism of the B diffusion retardation. The diffusion depth depends on the recombination velocity of interstitial silicon (ISi) at the BOX interface, Ksurf, and the annihilation rate of ISi at defects in the active layer, Ktrap. For ELTRAN and UNIBOND, the profiles can be fitted using only one parameter, Ksurf. For SIMOX with/without ITOX, the two parameters Ksurf and Ktrap need to be used because the SIMOX with/without ITOX has many extended defects, e.g., dislocations in the active layer.