Electrical activation in silicon-on-insulator after low energy boron implantation

Abstract

We have investigated the electrical activation of implanted boron in silicon-on-insulator (SOI) material using Hall effect, four-point probe, and secondary ion mass spectrometry. Boron was implanted at energies ranging from 1keVto6.5keV with a dose of 3×1014cm−2 into bonded SOI wafers with surface silicon thickness ranging from 300Åto1600Å. In one sample set, furnace anneals at 750°C were performed in a nitrogen ambient for times ranging from 5minto48h. A second sample consisted of isochronal furnace anneals performed from 450°Cto1050°C for 30min. Significantly less activation of boron is observed in SOI at temperatures below 750°C, regardless of the implant energy and surface silicon thickness. Between 750°C and 900°C, the active dose of boron in SOI is similar to that of bulk Si. As the implant energy increases, the fractional activation in thin SOI increases, due to a reduction in boron interstitial clusters (BIC) in the surface Si layer. It is concluded that an increase in the BIC population is the likely source of the low activation observed in SOI. This may be due to an increase in the interstitial supersaturation within the surface Si layer, due to the interface acting as a reflective boundary for interstitials.