Fabrication of large-area CCD detectors on high-purity, float-zone silicon

One of the problems with the fabrication of radiation detectors on high-purity, float-zone silicon is that such material is more susceptible to the formation of dislocations during high-temperature processing than Czochralski-grown material. We describe here the impact of dislocations on the electrical performance of a 1024 x 1024-pixel CCD imager that we have developed as the principal detector for the Advanced X-ray Astrophysical Facility. A technique has been developed to determine both the location (to within one gate of a pixel) and the trapping parameters of a dislocation. The processes giving rise to dislocation formation and propagation will be discussed, and techniques will be described for maintaining wafers free of dislocations even after the many high-temperature steps necessary for CCD fabrication.