Concentration dependence of boron-interstitial cluster (BIC) formation in silicon-on-insulator (SOI)

Abstract

The effect of boron concentration on boron-interstitial cluster (BIC) dissolution was studied in separation by implantation of oxygen (SIMOX) and SOITEC silicon-on-insulator (SOI) materials. SOI substrates having surface silicon thickness of 750 Å and 1450 Å were ion implanted with 11B+ at a energy of 15 keV. The dose of the implant was varied from 3×1014 cm-2 to 1×1015 cm-2 to provide different boron peak concentrations. Anneals were performed at 825°C in a nitrogen ambient using RTA for short times and furnace anneals for longer times. The retained dose of boron in the surface silicon layer was estimated using simulations from UT-Marlowe 5.0. Hall Effect was used to measure the sheet resistance, mobility, sheet number, and fraction of active boron. At lower concentrations, SOI exhibited significantly lower sheet numbers. As the boron concentration was increased SOI began to approach bulk Si. However, degraded mobility and sheet resistance was observed at all concentrations. Truncating the boron profile over the surface Si/buried oxide interface enhanced the fraction of active boron in the 750 Å SOI. This also lead to a higher fractional activation in 750 Å SOI than bulk Si as the concentration increased due to a loss of interstitials, effectively reducing the BIC population.