Fast Slow Level Control for Focal Plane Registration
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-10
A control system permits wafers to be leveled in the focal plane of a projection printing apparatus within 0.5 micron. By providing a slow driver control when the wafer approaches a level condition, the response of the non-contact focal registration (NCFR) is made compatible with the response of the pressure differential switch.