Improvement of surface carrier mobility of HfO/sub 2/ MOSFETs by high-temperature forming gas annealing

Abstract

The surface electron mobility of HfO/sub 2/ NMOSFETs with a polysilicon gate electrode was studied in terms of the effects of high-temperature forming gas (FG) annealing. The high-temperature FG annealing significantly improved the drive current or the surface electron mobility of the NMOSFETs. Improvements were also observed in the subthreshold swings and the C-V characteristics, indicating a reduction in interfacial state density (D/sub it/). The D/sub it/ reduction was quantitatively confirmed by charge pumping current measurements. The mobility enhancement was achieved without degrading the equivalent oxide thickness (EOT) or gate leakage current. Different surface preparations, such as NH/sub 3/ or NO annealing, were explored to examine their effects on the NMOSFET performance. Mobility enhancement due to high-temperature FG annealing was also observed on these samples. Whereas NH/sub 3/ surface nitridation was effective in scaling EOT, the NO-annealed sample exhibited the highest mobility. Similar improvements were also observed on HfO/sub 2/ PMOSFETs, in terms of subthreshold swings, drive current, and surface hole mobility.