Impact of UV annealing on the hole effective mobility in SnO pFET

Abstract

Using ultraviolet (UV) annealing through wide energy bandgap HfO 2 /SiO 2 gate dielectric, nanosheet SnO pFET achieved hole effective mobility (µ eff ) from 55 cm 2 /V-s at low hole density (Q h ) to 13.38 cm 2 /V-s at 5 × 10 12 cm -2 Q h , compared to that of 9.03 cm 2 /V-s at 5 × 10 12 cm -2 Q h for SnO device without UV annealing. This is the highest µ eff among oxide semiconductor pFETs at high Q h , which is required to realize low-power high-density monolithic 3D CMOS logic. This requires excellent surface roughness, good uniformity and free-from grain boundaries that is beyond the thermally-annealed poly-Si. Excellent on-current/off-current (I ON /I OFF ) value of 1.05 × 10 5 were measured simultaneously in the UV-annealed SnO pFET, which is due to the ultra-thin 8 nm thick SnO nanosheet channel to pinch off the channel leakage. From X-ray photoelectron spectroscopy (XPS) analysis, the 48% µ eff improvement by UV irradiation is due to increased Sn 2+ and decreased Sn 0 . Such high µ eff at high Q h , large I ON /I OFF , smooth surface, good uniformity and low thermal budget process are the enabling technologies for monolithic 3D CMOS.