A PHYSICAL MODEL FOR BORON PENETRATION THROUGH THIN GATE OXIDES FROM P+ POLYSILICON GATES

A physical model for boron penetration through thin gate oxides from p+ polysilicon gates is presented. Based on numerical device and process simulation, it is shown that enhancement of the boron diffusivity by as much as 300 x in the thin gate oxide results in a very shallow exponential p-type profile in the underlying silicon substrate. The effect of fluorine and phosphorus co-implantation into the p-type polysilicon gate is modeled by changes in the boron diffusivity in the gate oxide and segregation at the polysilicon/oxide interface, respectively. An inverse PMOS short-channel behavior in which the threshold voltage becomes more negative with decreasing channel length is modeled by two-dimensional boron segregation effects caused by the poly gate oxidation. © 1990 IEEE