Abstract: Selective high-energy impurity implantation enables optimization of both core and peripheral field isolation without substantially degrading functionality, self-boosting efficiency or otherwise increasing program disturb, thereby improving device performance and reliability. Embodiments include high-energy impurity implantation, after forming core and peripheral field oxide regions in a semiconductor substrate, into the peripheral field oxide region and selected portions of the core field oxide regions corresponding to select transistor areas, while blocking the implant from the core memory cell channel regions. A channel stop implant is performed through the core field oxide regions after etching a first polysilicon layer. The high-energy impurity implant optimizes peripheral field isolation, without degrading self-boosting efficiency, because it is blocked from entering the memory cell channel region.