Channel length dependence of negative bias temperature instability on pMOSFETs with either B- or BF₂ -implanted source/drain

We evaluated the channel length dependence of the negative bias temperature instability in deep-submicrometer p-type metal oxide semiconductor field effect transistors (pMOSFETs) having either a boron- or B F2 -implanted source/drain (S/D) and a poly-Si film. We found that long-channel-length (10 μm) pMOSFETs having a B F2 -implanted S/D exhibit a larger negative threshold voltage shift (Δ Vth) than do those having a B-implanted S/D. This phenomenon indicates that fluorine atoms enhance boron diffusion into the gate oxide region, resulting in the increase in fixed-positive oxide charges and the decreased density of interface states. In contrast, the shorter-channel-length device having a B F2 -implanted S/D displays a smaller value of Δ Vth than does that possessing a B-implanted S/D. These observations indicate that fluorine atoms not only induce negative interface states but also suppress the positive interface traps that occur during NBTI stressing.