Abstract: 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.

Abstract: A method of making an imager which includes substrate of single crystalline silicon having on one surface of a plurality of spaced detectors arranged in columns and a charge-coupled device between each pair of columns of the detectors. The charge-coupled devices are formed first with the gates of the charge-coupled devices defining detector areas of the substrate surface. A guard-ring is formed in each detector area with the edges of the gates around the detector area defining one edge of the guard-ring so that the guard-rings are aligned with the edges of the surrounding gates. A layer of insulating material is formed over the detector areas with the portion of the insulating layer over the guard-ring being thicker than the remaining portion of the insulating layer. The thinner portion of the insulating layer is removed leaving the thicker portion over the guard-ring region and with an edge of the thicker portion being substantially in alignment with an edge of the guard-ring region.