Processing of back illuminated 4096×4096 Fairchild CCDs at the University of Arizona

The University of Arizona Imaging Technology Laboratory has processed 4096×4096 15-micron Charge Coupled Devices (CCDs) fabricated at Lockheed Martin Fairchild Systems for back illuminated scientific applications. The devices have been optimized for astronomical observations in a direct imaging mode. Three types of back illuminated devices have been developed. The oldest devices are CCD4096JJ detectors which were custom fabricated for astronomical applications. The CCD485 devices are commercial sensors, originally fabricated for digital photography and medical applications. Because no frontside ground contact was included on either device, a backside contact was developed and applied as part of the backside processing. With this addition, very high quality back illuminated sensors have been developed. The CCD486 is a newer version of the 4k×4k CCD with low noise amplifiers and a backside contact. These sensors have now been produced back illuminated with >90% QE and read noise under 4 elec trons. The devices show CTE of >0.999998. Back illuminated versions CCDs have been fabricated with peak-valley flatness non-uniformity of less than 10 microns. A new epoxy underfill technique was developed to achieve this flatness and to avoid underfill voiding during epoxy application and curing. The new method applies a contact force on the CCD during the entire 48 hour cure cycle.