Impact of nitridation/reoxidation on performance degradation in n-MOSFETs under Fowler-Nordheim injection

Abstract

Performance degradation of n-MOSFETs with conventional oxides, thermally nitrided oxides and reoxidized nitrided oxides as gate dielectrics was studied using Fowler-Nordheim injection. Their respective performance degradation rate and interface-state generation were characterized by combining capacitor capacitance-voltage and MOSFET subthreshold methods. Shift in both threshold voltage and flatband voltage exhibited a turnaround effect for devices with a large amount of hole traps in the oxide, with their values shifted negatively at first and then positively during injection. Light nitridation could induce a large number of hole traps in the oxide which resulted in a large negative threshold voltage shift, while heavy nitridation with sufficient reoxidation could suppress this effect. Nitridation, especially one with reoxidation, could reduce the density of interface states and improve its stability against Fowler-Nordheim injection, leading to a suppression of the positive threshold voltage shift. The stability of maximum transconductance and field-effect electron mobility in the inversion channel against the Fowler-Nordheim stressing can be greatly improved by the nitridation with or without reoxidation.