Effects of fluorine incorporation and forming gas annealing on high-k gated germanium metal-oxide-semiconductor with GeO₂ surface passivation

Effective pregate surface passivation and postgate treatments are very important to optimize the germanium metal-oxide-semiconductor (MOS) interface quality. In this work, pregate GeO₂ surface passivation and postgate treatments including CF₄-plasma treatment and forming gas annealing are employed to make high quality HfO₂ gated germanium MOS capacitors. Excellent electrical characteristics with negligible capacitance-voltage stretch-out and frequency dispersion are achieved. The interface trap density of TaN/HfO₂/GeO_x/Ge MOS structure is as low as 2.02×10¹¹ cm^-2 eV^-1 at the minimum. Comparing to the forming gas annealing, it is found that CF₄-plasma treatment is more effective to passivate interface states located in the upper half of Ge bandgap.