Method of making high-performance and reliable thin film transistor (TFT) using plasma hydrogenation with a metal shield on the TFT channel

摘要

A method for fabricating thin film transistors (TFTs) for SRAM devices is described having metal shields over the channel regions for improved electrical characteristics. The method involves forming N+ doped polysilicon TFT gate electrodes having a gate oxide thereon. An N- doped amorphous silicon is deposited and recrystallized. The recrystallized silicon is P+ doped to form the TFT source/drain areas and patterned to form the N- doped channel regions with P+ source/drain areas. After depositing an insulating layer, a metal layer is deposited and patterned to completely cover and shield the TFT channel regions from ion damage during the plasma hydrogenation which is subsequently performed. The patterned metal layer also serves as the bit lines for the SRAM device. The plasma hydrogenation reduces the surface states at the gate oxide channel interface, while the shielding effect of the metal layer from ion damaging radiation reduces the off current (Ioff), increases the Ion/Ioff ratio of the TFTs, and improves the long-term reliability of the threshold voltage (Vt) and swing (S) of the TFT over the unshielded TFT.