Plasma nitridation of very thin gate dielectrics

Abstract

The performance of NMOSFET devices with nitrided gate oxides has been compared using two plasma-based nitridation techniques. Specifically, remote plasma nitridation (RPN) and decoupled plasma nitridation (DPN) of 1.4 nm base oxides were evaluated. It is found that both nitridation techniques give comparable leakage current performance, where 4–10× leakage current reduction can be achieved compared to un-nitrided oxides. The flatband voltages of the DPN-nitrided gate dielectric are larger (more negative) than those of RPN-nitrided gate dielectric, possibly indicating more fixed charge for the DPN process conditions used. The normalized peak transconductance of RPN and DPN-nitrided gate dielectrics depends on the detailed nitridation conditions, but can be comparable to that of un-nitrided oxides. The normalized drive currents are largest for the DPN-nitrided oxides, most likely because of the smaller threshold voltage measured after DPN nitridation. The results suggest that for NMOSFET devices, the two nitridation processes (RPN and DPN), if properly optimized, can give comparable device performance.