A high performance HfSiON/TaN NMOSFET fabricated using a gate-last process

A gate-last process for fabricating HfSiON/TaN n-channel metal-oxide-semiconductor-field-effect transistors (NMOSFETs) is presented. In the process, a HfSiON gate dielectric with an equivalent oxide thickness of 10 angstrom was prepared by a simple physical vapor deposition method. Poly-Si was deposited on the HfSiON gate dielectric as a dummy gate. After the source/drain formation, the poly-Si dummy gate was removed by tetramethylammonium hydroxide (TMAH) wet-etching and replaced by a TaN metal gate. Because the metal gate was formed after the ion-implant doping activation process, the effects of the high temperature process on the metal gate were avoided. The fabricated device exhibits good electrical characteristics, including good driving ability and excellent sub-threshold characteristics. The device's gate length is 73 nm, the driving current is 117 mu A/mu m under power supply voltages of V-GS = V-DS = 1.5 V and the off-state current is only 4.4 nA/mu m. The lower effective work function of TaN on HfSiON gives the device a suitable threshold voltage (similar to 0.24 V) for high performance NMOSFETs. The device's excellent performance indicates that this novel gate-last process is practical for fabricating high performance MOSFETs.