Characteristics of sub-1/4-μm gate surface channel PMOSFET´s using a multilayer gate structure of boron-doped poly-Si on thin nitrogen-doped poly-Si

This paper reports the effects of a new p⁺ gate structure (MBN gate) on the properties of surface channel PMOSFET´s with an extremely thin gate oxide. The MBN gate is a multilayer gate structure of boron-doped poly Si on thin nitrogen-doped poly-Si. The thin nitrogen-doped Si layer effectively suppresses boron diffusion, so that the gate poly Si can be doped with boron in high concentration without the fear of boron penetration. Gate depletion effects are well suppressed. Effective hole mobility is improved due to the reduction of the initial interface state density. The hot-hole induced interface state generation is shown to be the dominant clause of degradation in the 1/4-μm level PMOSFET´s, and less Gm degradation is found in the MBN-gate PMOSFET´s than in conventional p⁺-gate PMOSFET´s. Finally, with respect to the reliability of the gate oxide, a conventional p⁺ gate with boron penetration exhibits an increase in short-time defect related breakdown during constant-current FN stressing. Short-time defect-related breakdown is not observed in the MBN gate but a slight decrease in charge to breakdown