Optical Focusing Technique
Original Publication Date: 1979-Nov-01
Included in the Prior Art Database: 2005-Feb-20
In a projection printing lithographic system, dependence upon a mechanical reference point for accurate focussing may be avoided by optically linking the resist-coated wafer to the image of the projection mask. This is accomplished by monitoring light scattered from the edges of focussing marks on the wafer as the wafer is moved along the optical axis through the projected mask image.