Elimination of fixed pattern noise in super-8 format CCD image sensor by the use of epitaxial wafers

A new fabrication process is proposed for eliminating the fixed pattern noise in a CCD image sensor with a vertical overflow drain structure, which is sensitive to the non-uniformity of the crystal. In this method, the internally gettered epitaxial wafer is used as the starting material for fabrication of the CCD image sensor. Use of the epitaxial layer, which is free from the resistivity striation as in the CZ bulk crystals, is found to eliminate the concentric circle image pattern. It is also shown that internal gettering for epitaxial wafers remarkably suppresses the generation of thermally induced white blemishes, as a result of fixing oxygen atoms as precipitates inside the substrate. Based on this technique we have fabricated "Super-8" format CCD image sensors. By comparing the reproduced images with those of the conventional CZ-wafer CCD, the present method is shown to be extremely powerful for obtaining the noiseless CCD image sensors.