Experimental Investigation of Remote Coulomb Scattering on Mobility Degradation of Ge pMOSFET by Various PDA Ambiences

Abstract

The impact of various postdeposition annealing (PDA) ambiences (N2, O2, and NH3) on the hole mobility of germanium (Ge) pMOSFET with GeO2/Al2O3 gate-stack is investigated. It is found that the mobility is about 10% higher after N2 PDA, while it is about 10% smaller after O2 and NH3 PDA than that without PDA. The physical origin is attributed to the remote Coulomb scattering. The Ge/GeO2 interface charge Q1 decreases, but the GeO2/Al2O3 interface dipole Qdipole increases after PDA in N2, O2, and NH3. The higher mobility after N2 PDA is due to a smaller Q1 and Qdipole, while the lower mobility after O2 and NH3 PDA is due to a larger Qdipole. All these three PDA ambiences are beneficial to reduce the gate leakage current. Therefore, PDA in N2 is a balance approach for both the hole mobility improvement and gate leakage current reduction.