BACK-ILLUMINATED CCDS MADE BY GAS IMMERSION LASER DOPING

Back-illuminated CCDs with high quantum efficiency in the soft X-ray r ange have been developed by EEV in collaboration with the Space Resear ch Organisation Netherlands. By using Gas Immersion Laser Doping (GILD ) for producing the backside accumulation layer very shallow doping pr ofiles can easily be achieved. Additionally the GILD process does not affect the silicon behind the p(+) layer in contrast to the commonly u sed ion implantation process. This implies that only the electrons gen erated in, or reaching the very small accumulation layer will have a p robability to recombine at the surface or in the accumulation layer it self. Therefore only a small fraction of the electron clouds produced by the absorbed soft X-rays will suffer charge loss, resulting in a hi gh quantum efficiency. X-ray measurements of back-illuminated CCDs wit h doping profiles of 50 and 100 nm depth are presented and shown to be consistent with calculations based on minority carrier transport.