A lower electrode assembly useful for supporting a semiconductor substrate in a plasma processing chamber includes a temperature controlled base plate, an upper plate above the base plate, and an annular mounting groove surrounding a bond layer located between the base plate and the upper plate. The mounting groove includes an inner wall, an opening of the mounting groove faces radially outward relative to the inner wall, and the mounting groove includes a step extending downward from the upper plate on an upper wall of the groove or extending upward from the base plate on a lower wall of the groove. An edge seal including a compressible ring is mounted in the groove such that the compressible ring is compressed between the upper plate and the base plate to cause an outer surface of the compressible ring to be biased radially outward relative to the inner wall toward the step.