Explanation of reverse short channel effect by defect gradients

Reverse short channel effect (RSCE), the paradoxical increase in threshold voltage (V/sub t/) of short channel MOSFETs, has previously been explained by diffusion broadening of a buried channel profile. We report here on RSCE in transistors which have very shallow or flat channel profiles, where such broadening cannot be the mechanism. It is shown that for several different dopings and process sequences, both RSCE and anomalous body effects can be traced back to transient enhanced diffusion (TED) of the channel profile induced by source/drain implantation. A new mechanism for RSCE is proposed, in which the surface recombination of interstitials under the gate gives rise to an impurity flux to the surface, which raises the threshold. A coupled defect/impurity diffusion model allows all short channel effects on threshold to be accurately predicted.<
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