Registration Enhancement Through an Opaque Underlayer for a Step and Repeat Exposure System
Original Publication Date: 1988-Sep-01
Included in the Prior Art Database: 2005-Feb-15
Disclosed is a method for aligning and registering through thick multilayer photoresist (PR) coatings on a semiconductor wafer. The method suggests registering, exposing and developing the first coating and then applying a less opaque imaging resist coating and registering through the remaining coatings. This permits the site-by-site alignment tool to register through thinner and less opaque photoresist coatings. Referring to Fig. 1, conventional processing of a wafer 1, an etched alignment mark 2 is located beneath a barrier layer 3 and a thick hard-baked PR coating 4 surmounted by an imaging photoresist top coat 5. The process sequence is to coat, align and expose a wafer with all the resist coatings in place. However, since the thick coatings tend to be rather opaque, the alignment of the reticle to the wafer is hindered.