Development of Thin-Junction Detector

Two methods to produce a thin-junction sensor covered by a layer of aluminum to substantially attenuate incident visible light are reported here. The first method is a regular boron implant (10´s of keV) through a thin oxide layer to form a junction. The aluminum layer was coated in the same vacuum system after back-sputtering to remove oxide on top of the implanted silicon substrate. The second method is a low energy boron implant into the bare silicon followed by laser annealing to activate low energy (2 keV) boron implantation with minimal diffusion to retain the ultra thin-junction. The aluminum layer was again coated in the same vacuum system after back-sputtering to remove native oxide on top of the implanted silicon. This method may have the following advantages: 1) it may improve soft X-ray radiation hardness of the device due to lack of oxide layer on the junction; 2) it satisfies the requirement to absorb the visible light; and 3) it allows detection of low energy X-ray down to 300 eV. Investigation of laser annealing method was done in comparison with control wafers which were either implanted by boron with the same energy as that of laser annealed wafers but annealed using high temperature thermal annealing, or implanted by boron with higher energy (45 keV, our standard boron implantation energy) and annealed using regular thermal annealing.