For use with a chemical mechanical polishing apparatus for polishing a semiconductor wafer having a platen, a polishing pad and a wafer carrier, an optical closed-loop control system. The container may also include a first nesting step located below the lip and extending circumferentially around the container, the nesting step extending outwardly to a maximum circumference and including a container-stacking stop surface extending between the sidewall and the maximum circumference and a extending vertically from the maximum circumference. The first conductive polymer layer has recesses on its surface against the dielectric layer. A lateral displacement of the sheet is corrected by laterally shifting the sheet according to the third position of the sheet lateral edge.