An edge seal for sealing an outer surface of a lower electrode assembly configured to support a semiconductor substrate in a plasma processing chamber, the lower electrode assembly including an annular groove defined between a lower member and an upper member of the lower electrode assembly. The edge seal includes an elastomeric band configured to be arranged within the groove, the elastomeric band having an annular upper surface, an annular lower surface, an inner surface, and an outer surface. When the elastomeric band is in an uncompressed state, the outer surface of the elastomeric band is concave. When the upper and lower surfaces are axially compressed at least 1% such that the elastomeric band is in a compressed state, an outward bulging of the outer surface is not greater than a predetermined distance. The predetermined distance corresponds to a maximum outer diameter of the elastomeric band in the uncompressed state.