A lower electrode assembly configured to support a semiconductor substrate in a plasma processing chamber includes a base plate, an upper plate above the base plate, and a mounting groove surrounding a bond layer located between the base plate and the upper plate. An edge seal including a compressible ring is mounted in the mounting groove such that the compressible ring is axially compressed between the upper plate and the base plate. At least one gas passage is in fluid communication with an annular space between the compressible ring and an inner wall of the mounting groove. The at least gas one passage extends through the base plate and includes a plurality of outlets in fluid communication with the annular space. In some examples, a backing seal may be located between the edge seal and an inner wall of the mounting groove.