An in situ rapid thermal hydrogenation (RTH) pretreatment of titanium prior to rapid thermal annealing (RTA), or RTH/RTA, is proposed as a silicide formation annealing in a CMOS self-aligned silicide (salicide) process. The in situ RTH is found to enhance silicidation, to reduce nitridation, and even to lower the resultant sheet resistance of titanium silicide.
During in situ RTH (e.g., at 550°C), amorphous Ti silicide (e.g., 15-nm thick) grows selectively on Si. Furthermore, Ti nitridation during subsequent RTA (690°C, N2, 10 Torr, 30 s) is reduced depending on RTH (H2, 10 Torr, 30 s) temperature. Accordingly, for 550°C RTH and an initial Ti thickness of 15 nm, the sheet resistance obtained at the 0.27-μm-wide n+ poly-Si gate after a phase transition annealing (800°C, Ar, 10 s) was lower (11.7 Ω /□, st. dev. = 6%) than that of conventional Ti silicide (15.8 Ω/□, st. dev. = 10%). The silicidation enhancement and nitridation reduction are related to crystal structure metamorphosis or to hydrogen interstitial incorporation in the Ti layer during RTH as observed by x-ray diffraction analysis. It is concluded that in situ RTH pretreatment before RTA is very promising as a sub-quarter-micron CMOS salicide process.