Degradation of oxynitride gate dielectric reliability due to boron diffusion

Abstract

In this letter, we report on the impact of the suppression of boron diffusion via nitridation of SiO2 on gate oxide integrity and device reliability. SiO2 subjected to rapid thermal nitridation in pure nitric oxide (NO) is used to fabricate thin oxynitride gate dielectrics. Both n+ polycrystalline silicon (polysilicon) gated n-MOS (metal–oxide semiconductor) and p+-polysilicon gated p-MOS devices were subjected to anneals of different times to study the effect of dopant diffusion on gate oxide integrity. As expected, an advanced oxynitride gate dielectric will effectively alleviate the boron-penetration-induced flatband voltage instability in p+-polysilicon gated p-MOS capacitors due to the superior diffusion barrier properties. However, such improvements are observed in conjunction with some degradation of the oxide reliability due to the boron-blocking/accumulation inside the gate dielectric. Results show that even though the oxide quality is slightly degraded for NO-nitrided SiO2 with p+-polysilicon gates, p-MOSFETs (metal–oxide semiconductor field effect transistors) with these dielectrics still show improved interface stability as compared to conventional SiO2 due to the reduced boron penetration into the Si/SiO2 interface and underlying channel region.