Stepping Motor Electronic Registering Focus
Original Publication Date: 1985-Aug-01
Included in the Prior Art Database: 2005-Feb-19
Increased photolithographic resolution necessary to high density integrated circuit manufacture requires that the wafer plane be located within narrow limits in non-contact focal-plane registration (NCFR [*]) wafer mask-alignment equipment. Lack of an ability to determine location of the wafer plane between the location limits in such equipment, however, reduces tool stability and leads to increased maintenance requirements. This article concerns a technique and apparatus for precisely locating the wafer plane at the bisect of the location limits, thereby maximizing tool stability and minimizing calibration requirement. The disclosed technique features steps for determining the physical distance between the wafer location limits, optimally determining the wafer plane location within the noted limits, i.e.