Development of Thin-Junction Detector

Two methods to produce a thin-junction sensor are reported here. The first method consists of a regular boron implantation with energies of 2 keV (dose of 1 times 10
¹⁵
/cm
²
) and 5 keV (dose of 1 times 10
¹⁴
/cm
²
) into silicon directly, and 10 keV (1 X 10
¹⁴
/cm
²
), 45 keV (1 times 10
¹⁵
/cm
²
) into Si through a thin oxide layer (500 A and 1000 A respectively) to form a junction. An aluminum layer was coated in the same vacuum system after back-sputtering to remove oxide on top of the implanted silicon substrate. This method may have the following advantages: 1) it may improve the soft X-ray radiation hardness of the device because there is no oxide layer on the junction; 2) it substantially attenuates the incident visible light; and 3) it allows detection of low energy X-ray down to 300 eV. The second method consists of a low energy of 2 keV and dose of 1 times 10
¹⁵
/cm
²
boron implantation into the bare silicon followed by laser annealing that activates boron with minimal diffusion, to retain the ultra thin-junction. The laser annealing method was compared with control wafers. Two of the control wafers were implanted by boron with the same energy and dose as that of the laser annealed wafer. One of them was annealed using high temperature of 1000degC and time of 30 minutes thermal annealing. The other was annealed using our regular annealing temperature of 700degC and with longer annealing time of 17 hours. The remaining control wafer was implanted by boron with higher energy of 45 keV and dose of 1 times 10
¹⁵
/cm
²
(our standard boron implantation energy and dose) and annealed using regular (700degC, 30 min) thermal annealing.