Gas immersion laser doping (GILD) for ultra-shallow junction formation

Abstract

Gas immersion laser doping (GILD) is a very attractive technique to realize the ultra-shallow and highly doped junctions required by the International Technology Roadmap for Semiconductors (ITRS) for future CMOS technologies. In the present work, gaseous dopant precursors (BCl3) are chemisorbed on the Si surface, and partially incorporated during the melting/recrystallisation of the Si top layer induced by an UV laser pulse (λ=308 nm, pulse duration ≈25 ns). The resulting thickness and dopant concentration of the doped layer depend on the laser energy density and the number of chemisorption/laser-induced incorporation cycles (up to 200). GILD processed junctions are box-like and exhibit depths ranging from 14 nm to 65 nm, with sheet resistances ranging from ≈110 to 20 Ω/□ (respectively), dopant concentrations well above the B solubility limit in Si (up to 3×1021 at/cm3) at local thermodynamic equilibrium (LTE) and abruptness of 5–2 nm/decade. Moreover, in situ optical characterization shows the GILD technique capabilities to realize the sub-10 nm thick shallow junctions needed for the sub-40 nm node ITRS predictions.