Resistless, area‐selective ultrashallow P⁺/N junction fabrication using projection gas immersion laser doping

The selective fabrication of ultrashallow p⁺/n junctions in silicon using projection gas immersion laser doping is reported. The method offers substantial improvement and simplification in junction formation to integrated circuit manufacturers, since several processing steps required for conventional doping techniques like ion implantation are eliminated. Spatially selective incorporation of boron into silicon without the use of any masking layer on the wafer surface is achieved. A pulsed excimer laser beam is patterned using a chromeless reticle and the pattern is transferred through a projection system onto a wafer that is kept in a BF₃ dopant gas ambient. The depth of the fabricated junctions is 60 nm with a surface concentration of 5×10¹⁹ cm⁻³. The vertical and lateral distribution of boron in silicon after patterned laser processing is investigated using secondary ion mass spectroscopy (SIMS) and time‐of‐flight SIMS (ToF‐SIMS). Vertical and lateral dopant profiles are steep and clearly resolved.