ULTRA-SHALLOW BOX-LIKE PROFILES FABRICATED BY PULSED ULTRAVIOLET-LASER DOPING PROCESS

Ultra-shallow, boxlike impurity profiles are produced using gas immersion laser doping (GILD) and then analyzed by spreading resistance profilometry (SRP) and secondary ion mass spectrometry (SIMS) to determine the impurity distribution. At high concentrations, the profiles obtained by SRP exhibit the expected boxlike shape over the entire range of junction depths: The measured concentration within the junction region is uniform while the dopant gradient at the junction exceeds 1 decade/5 nm. In comparison, the same profiles analyzed using high primary ion energy SIMS show a broader transition at the metallurgical junction. Caused by knock-ons and ion mixing during the sputtering process, the inaccuracy is markedly reduced by lowering the acceleration energy of the primary Cs+ ion beam. At lower concentrations (<10(19)/cm3), profiles analyzed by SRP exhibit shallower junctions than expected. Electrical measurements of diodes and Hall structures show that high-quality, ultra-shallow n+p, np, and pn junctions are fabricated with good dose control using GILD. For complete characterization of GILD, accurate measurement of both chemical and electrically active dopant profiles are required. At present, neither SIMS nor SRP provides an entirely accurate impurity profile.