Step and repeat apparatus having enhanced accuracy and increased throughput

Claim 1

A step and repeat apparatus for forming a repeated image on a wafer, the step and repeat apparatus comprising: a first wafer station comprising a first wafer chuck and a first optical apparatus, the first wafer chuck for holding a first wafer, the first wafer station for performing a first optical task on the first wafer; a second wafer station comprising a second wafer chuck and a second optical apparatus, the second wafer chuck for holding a second wafer, the second wafer station for performing a second optical task on a second wafer simultaneously while the first wafer station performs the first optical task on the first wafer, the second wafer having previously had the first optical task performed on the second wafer by the first optical station; movement means for moving the second wafer chuck to an unloading/loading position at which position the second wafer is unloaded from the second wafer chuck and a third wafer is loaded onto the second wafer chuck, for moving the first wafer chuck to the second wafer station without disturbing the first wafer and for moving the second wafer chuck from the unloading/loading position to the first wafer station; and a wafer location monitoring apparatus coupled with the movement means, the wafer location monitoring apparatus for constantly monitoring the positions of the first and second wafer chucks wherein the wafer location monitoring apparatus locates and monitors the first and second wafer chucks interferometrically, wherein each of the first wafer station and second wafer station is positioned along a first axis, the first axis defining a work path along which the first chuck is moved between the first and second stations; and wherein the wafer location monitoring apparatus comprises: a source of at least five laser beams, a first of the at least five laser beams positioned around the first station and directed along or parallel the first axis towards the first chuck, a second of the at least five laser beams positioned around the second station directed along or parallel the first axis towards the second chuck, a third of the at least five laser beams positioned around the first station and directed along or parallel a second axis towards the first chuck, the second axis being perpendicular the first axis, a fourth of the at least five laser beams positioned around the second station and directed along or parallel the second axis towards the second chuck, a fifth of the at least five laser beams positioned intermediate the first and second stations and directed along or parallel the second axis towards the work path; a first and a second plurality of at least three mirrors disposed about each of the respective first and second wafer chucks, first and second mirrors of the respective first and second pluralities positioned perpendicular the first axis for respectively reflecting the first laser beam, third and fourth mirrors of the respective first and second pluralities positioned perpendicular the first axis for respectively reflecting the second laser beam, fifth and sixth mirrors of the respective first and second pluralities positioned parallel the first axis for reflecting the third, fourth and fifth laser beams; wherein the position of each of the first and second wafers is constantly monitored by at least one of the first and second laser beams and at least one of the third, fourth and fifth laser beams.