A pedestal for supporting a semiconductor substrate in an R.F. plasma reactor chamber includes a conductive disk platen having a diameter exceeding the diameter of the substrate so that an outer annular portion of the conductive disk platen provides a direct path of R.F. power from the plasma while a remaining inner portion of the conductive disk provides a path of R.F. power from the plasma through the substrate, an etch-resistant cover shielding the conductive platen from the plasma, a portion of the etch-resistant layer underlying the substrate, the etch-resistant cover including a raised disk overlying a central portion of the conductive disk platen and underlying the substrate and having a diameter less than the diameter of the substrate so that a peripheral portion of the substrate extends beyond the circumference of the raised disk, a recessed ring annulus overlying an outer portion of the conductive disk platen and having a top surface which is depressed below a top surface of the raised disk, an inner portion of the recessed ring annulus underlying the peripheral portion of the substrate, leaving a top portion of a side wall of the raised disk exposed to the plasma.