Thin-film transistors in polycrystalline silicon by blanket and local source/drain hydrogen plasma-seeded crystallization

Thin film n-channel transistors have been fabricated in polycrystalline sil icon films crystallized using hydrogen plasma seeding, by using several pro cessing techniques with 600 to 625 OC or 1000 degrees C as the maximum proc ess temperature, The TFT's from hydrogen plasma-treated films with a maximu m process temperature of 600 OC, have a linear field-effect mobility of sim ilar to 35 cm(2)/Vs and an ON/OFF current ratio of similar to 10(6), and TF T's with a maximum process temperature of 1000 OC, hare a linear field-effe ct mobility of similar to 100 cm(2)/Vs and an ON/OFF current ratio of simil ar to 10(7). A hydrogen plasma has also then been applied selectively in th e source and drain regions to seed large crystal grains in the channel. Tra nsistors made with this method with maximum temperature of 600 degrees C sh owed a nearly two-fold improvement in mobility (72 versus 37 cm(2)/Vs) over the unseeded devices at short channel lengths. The dominant factor in dete rmining the field-effect mobility in all cases was the grain size of the po lycrystalline silicon, and not the gate oxide growth/deposition conditions. Significant increases in mobility are observed when the grain size is in o rder of the channel length, However, the gate oxide plays an important role in determining the subthreshold slope and the leakage current.