Electrical characterization and simulation of substrate current in n-MOSFETs with nitrided/reoxidized-nitrided oxides as gate dielectrics

Abstract

Three kinds of n-MOSFETs were fabricated with different gate dielectrics: (a) OX: as-grown control oxide, (b) RTN: OX oxide with rapid thermal nitridation, and (c) RONO: OX oxide with nitridation and reoxidation by furnace annealing. Both the RTN and RONO devices show a lower substrate current ISUB as compared to the OX devices. Their ISUB can be characterized and simulated reasonably well, by using the ISUB characterization method and the basic ISUB model which are used for the OX devices. The results of characterization and simulation indicate that the nitridation or reoxidation step has little effect on the ionization rate of channel electrons. It is also confirmed that the lower ISUB of the RTN devices mainly resulted from the degradation in inversion-layer effective mobility •EFF due to nitridation, while that for RONO devices is caused by, not only the degraded •EFF, but also an increased gate-oxide thickness due to reoxidation. Therefore, the decrease in ISUB for RTN and RONO devices arises from the nitridation/reoxidation steps. In a word, even if the devices undergo a nitridation step with or without reoxidation, the basic ISUB model has been proved to be still applicable in regardless of the nitridation method.