Trench isolation step-induced (TRISI) narrow width effect on MOSFET

We report a new narrow-width effect that manifests as an increase in threshold voltage V/sub th/ and in its standard deviation /spl sigma//sub Vth/ as the width W of a MOSFET is reduced to be comparable to the trench isolation step height and the gate polysilicon thickness. At such small W the conformal deposition of polysilicon across the step between the active and isolation regions induces the polysilicon gate to be thicker over the active region. This increased thickness is shown to increase the poly depletion effect causing V/sub th/ shift, a higher /spl sigma//sub Vth/, and higher Vth mismatch. Thus, attention to this detrimental trench isolation step-induced (TRISI) narrow width effect is essential for scaled isolation design.