GATE OXIDE THINNING AT THE ACTIVE DEVICE FOX BOUNDARY IN SUBMICROMETER PBL ISOLATION/

The impact of several poly buffer LOGOS processing parameters on the i ntegrity and defect density (yield) of the gate oxide has been investi gated by correlating the electrical and structural studies, We found t hat a thin PBL pad-oxide, in general, gives rise to higher defect dens ity, In addition, it results in a sharp active device/field oxide (FOX ) boundary which, by the process of screen oxide growth and etch-back and FOX pull-back, creates a step in the Si in the bird's beak region, TEM studies revealed gate oxide thinning by as much as 30% over this step, explaining the early gate oxide breakdown at the active device/F OX region.