Optical test structure for measuring charge-transfer efficiency

Abstract

An optically operated test structure for testing the charge transfer efficiency (CTE) of a charge coupled device (CCD) solid-state image sensor. A solid-state image sensor includes a substrate of a semiconductor material of one conductivity type having a surface. A plurality of spaced, parallel CCDs are in the substrate at the surface. Each CCD includes a channel region and a plurality of conductive gates extending across and insulated from the channel region. The conductive gates extend laterally across the channel regions of all of the CCDs and divide the channel regions into a plurality of phases and pixels. A drain region of the opposite conductivity type is in the substrate at the surface and extends along the channel region of at least one of the CCDs. A simply connected (rectangular) region of the plurality of spaced, parallel CCDs is photoactive. The CCDs outside this photoactive region are typically covered with metal or some other optically opaque material. One or more of the parallel CCD columns comprise optical test structures at the start and end of the CCD array and are photoactive. One or more parallel regions are adjacent and abutting on either side of the test structures; these may or may not be photoactive. These surrounding, adjacent regions are connected to a drain on the imager; the drain collects any charge captured in these adjacent regions. Each of the plurality of spaced, parallel, vertical CCDs is connected to one or more horizontal CCDs oriented in a direction perpendicular to the vertical CCDs.