Non-melt Laser Thermal Annealing of Shallow Boron Implantation for Back Surface Passivation of Backside-Illuminated CMOS Image Sensors

Back surface passivation is one of the major challenges in the backside illuminated sensor technology. Ion implantation followed by non-melt pulsed Laser Thermal Annealing (LTA) has been identified as a promising candidate to address this issue. In this work, a shallow B-doped layer is implanted at the backside, further activated using LTA in the non-melt regime. LTA process effectiveness in terms of crystal damage recovery as well as dopant diffusion and activation is studied through room-temperature photoluminescence, Secondary Ion Mass Spectroscopy and four-point probe sheet resistance. These studies demonstrate that non-melt LTA with multiple pulses induces high activation without visible diffusion with an effective curing of the implantation-induced crystalline defects. This is made possible thanks to a submicrosecond process timescale coupled to a reasonable number of shots as shown by thermal simulations and simple diffusion estimations.