Phase contrast alignment system for a semiconductor manufacturing

Abstract

A masking apparatus for use in the production of semiconductor devices. In order to achieve alignment beween successive masking operations, alignment targets are formed on a semiconductor wafer adjacent circuit patterns which are exposed onto the wafer. The alignment targets are viewed during subsequent masking steps in order to align the previously exposed circuit patterns with a new pattern contained on a reticle. In many masking steps, the alignment target is covered with one or more highly reflective films, which decreases the ability to view the alignment target. A phase contrast microscope is utilized to enable the embedded alignment targets to be viewed despite the existence of the overlying reflective films. The micrscope incorporates an illumination subsystem containing an annular diaphragm and an observation subsystem containing a phase plate. The image of the alignment target which is formed by the phase contrast microscope includes a bright edge halo which may be utilized in determining the position of the target.