Surface potential determination in metal-oxide-semiconductor capacitors

Abstract

Different methods using the relationship between surface potential ΨS and gate bias VG in metal-oxide-semiconductor (MOS) capacitors have been compared. These methods can be applied even if the doping profile is very abrupt and the interface state density very high. The shifts of midgap, flatband, and threshold voltages, observed after Fowler–Nordheim electron injection, and deduced from the various ΨS(VG) relationships obtained by these different methods, are in good agreement. These shifts give the number of effective oxide trapped charges (Nox) per unit area and acceptor-like and donor-like interface states (NSSA and NSSD) which are created during the electron injection. We reveal that the number of positive charges created in the gate oxide, unlike the number of generated interface states, strongly depends on the position of the post-metallization annealing step in the process. After relaxation of the stressed MOS capacitors, most of the generated positive charges can be attributed, in the MOS capacitors studied, to hydrogen-related species. It seems that the interface states are essentially created by the recombination of holes generated by electron impact.