Deactivation kinetics of supersaturated boron:silicon alloys

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 degreesC to 1050 degreesC). 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 Omega/square were achieved in 200 nm layers. Following laser anneals, boron atoms remained active at concentrations of 7.5x10(20)/cm(3) up to 800 degreesC 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. (C) 2001 American Institute of Physics.