ACCURATE POSITIONING OF A WAFER

摘要

A load station is used in a planarizing machine to perform several useful functions related to handling of a wafer. By centering the wafer with respect to a spindle carrier the load station interrupts the accumulation of positional errors. The load station never makes solid contact with the wafer, but instead the wafer is continually levitated on three cushions of water that are directed upwardly against the lower face of the wafer. The presence of the wafer partially impedes the flow of water from the nozzles used for levitation causing an increase in the water pressure immediately upstream of the nozzles. This increased pressure is sensed and used as an indicator of the presence of a wafer at the load station. The load station further includes a nozzle that directs a stream against the lower side of the wafer so as to elevate the wafer from the load station into the carrier.