Alignment key and method of making the same

摘要

A substrate includes an alignment key for forming features in or on both surfaces of the substrate which are in alignment with each other. The alignment key includes a plurality of adjacent but spaced apart small openings formed in one surface of the substrate through a P-type region at said one surface and a large opening extending through the substrate from its other surface to the P-type region. The larger opening exposes the smaller openings so that they can be seen from both sides of the substrate. The smaller openings are arranged to form an alignment mark.