As the MOS device feature size continues to shrink, novel high-k gate dielectrics should be adopted to reduce the unacceptable high gate leakage current due to direct tunneling. HfO2 is one of the most promising high-k materials. It was reported that HfNxO(y) formed by incorporating N into HfO2 could improve the thermal stability and electrical properties of the gate dielectric films. However, N loss can occur due to subsequent high temperature processes, such as rapid thermal processing (RTP). It is necessary to understand the mechanism of N loss from the academic and application points of view. In this study, SIMS was applied to investigate the N diffusion behavior in sputter-deposited HfNxOy after RTP processing. The results showed that N loss is due to out-diffusion of N to the surface. On the other hand, segregation of N at the interface of HfNxOy/Si was observed. N acts as a good barrier to O diffusion from HfNxOy to Si. The results show that oxygen flooding is unfavorable for characterizing N in HfNxOy/Si since oxygen flooding can enhance the N background. (C) 2004 Elsevier B.V. All rights reserved.