Method and apparatus for chemical-mechanical polishing using pneumatic pressure applied to the backside of a substrate

A novel method and apparatus for uniformly polishing thin films formed on a semiconductor substrate. A substrate is placed face down on a moving polishing pad so that the thin film to be polished is placed in direct contact with the moving polishing pad. The substrate is forcibly pressed against the polishing pad with pneumatic or hydraulic pressure applied to the backside of the substrate during polishing. Additionally, a wear ring is placed on the polishing pad around and adjacent to the substrate and forcibly pressed onto the polishing pad with a downward pressure from a second source so that the wear ring is coplanar with the substrate in order to eliminate edge rounding effects.