Abstract: A method and apparatus for planarizing semiconductor wafers utilized a sacrificial substrate. The sacrificial substrate, in the form of a sacrificial ring or a sacrificial disc, allows the wafer to sit flush inside the sacrificial substrate. The sacrificial substrate acts as a sacrificial extension of the wafer to be polished and experiences the edge roll-off effect during the polishing process instead of the wafer to be polished. As a result, the wafer to be polished has improved flatness and film thickness uniformity due to shifting the edge roll-off effects beyond the edge of the wafer to be polished outwards to the sacrificial substrate.