Ccd image sensor with stacked charge transfer gate structure

Abstract

A CCD imager has an array of rows and columns of picture elements on a semiconductor substrate. A vertical charge transfer gate section extends in a first direction on the substrate to be associated with the columns. The transfer gate section includes CCD channels in the substrate, and insulated transfer gate electrodes overlying these CCD channels. A plurality of buffer electrodes are formed at a first level over the substrate surface to overlie the transfer gate electrodes. A plurality of shunt wires are formed at a second level over the substrate surface to overlie the buffer electrodes. The charge transfer gate electrodes and the buffer electrodes are connected with each other by first contact holes. The buffer electrodes and the shunt wires are coupled together by second contact holes. The second contact holes are distributed so that the repeat period thereof as defined at least in a second direction transverse to the first direction on the substrate is equal to or less than two picture elements, whereby their spatial frequency at least in the second direction is half the sampling frequency of photoconversion in the CCD imager, or more.