S-passivation of the Ge gate stack: Tuning the gate stack properties by changing the atomic layer deposition oxidant precursor

Abstract

The passivation of the interface between Ge and the gate dielectric is a critical issue for the integration of Ge into next generation CMOS devices. GeO2 has recently garnered a lot of interest, but there is always a trade-off between low interface state densities and a low equivalent oxide thickness. In this paper we investigate the S-passivation of the Ge gate stack in which only 1 monolayer of S is needed in order to improve the interface properties of the gate stack. S-passivation is achieved via exposure of the clean Ge(100) surface to H2S. The high-k dielectric is deposited via atomic layer deposition. We show that the oxidant precursor type (H2O versus O-3) will result not only in different growth behavior but also in different interface properties. The H2O based process results in low defect densities at the valence bandedge, whereas the O-3 based process results in low defect densities at the conduction bandedge. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622514]