Deactivation kinetics of supersaturated boron:silicon alloys

Abstract

The effect of laser annealing on the electrical activity of boron-doped silicon wafers has been investigated as a function of boron concentration, annealing time, and annealing temperature (from 600 °C to 1050 °C). Metastable supersaturated alloys were produced by the laser annealing of ion-implanted Si 〈100〉 wafers using an excimer laser with a pulse duration of 30 ns. The extent of dopant activation, deactivation, and tendency towards precipitation were subsequently studied following rapid thermal annealing in an argon ambient using a four-point probe of the sample resistance. Sheet resistances as low as 15 Ω/□ were achieved in 200 nm layers. Following laser anneals, boron atoms remained active at concentrations of 7.5×1020/cm3 up to 800 °C for 210 s. A two-mode relaxation model including defect association and precipitation was proposed to describe the annealing behavior. These results show that laser processing can produce metastable B-doping levels, stable to moderate thermal processing, at concentrations adequate for all anticipated device structures.