Technology development for 4k × 4k, back- illuminated, fully depleted scientific CCD imagers

We have developed scientific charge-coupled devices (CCDs) that are fabricated on high-resistivity, n-type silicon substrates, and have demonstrated fully depleted operation for substrate thicknesses of 200-675 mum with formats as large as 2048 times 4096 (15 mum pixels) and 3512 times 3512 (10.5 mum pixels). The main application area for these devices is space and ground-based astronomy, and the CCDs are operated at cryogenic temperatures with slow-scan readout for good performance in terms of dark current and noise. In this work we describe the technology development efforts needed to realize a 4k times 4k (15 mum pixel) CCD with a die area of (64 mm)
²
. In particular, we describe improved gettering techniques for low dark current and high charge transfer efficiency that have been developed in order to improve fabrication yields for these very large format CCDs.