QUALIFICATION OF THE FABRICATION PROCESS FOR SI-DETECTORS BY NEUTRON-ACTIVATION ANALYSIS

Using neutron activation analysis (NAA) the individual process steps of the fabrication of Si radiation detectors have been investigated for trace contaminants. These steps include chemical cleaning procedures, thermal oxidation, photolithographic patterning of the oxides, ion implantation doping, annealing and metallization with aluminum. It was found, that the most critical technological processes are photolithography, ion implantation and metallization as they can lead to severe contamination of the Si wafers with Ag, Au, Co, Cr and Fe in the ppb-ppm level, while other impurities are controlled in the ppt level. However, applying proper cleaning procedures and careful wafer processing, these impurities can also be reduced to a degree not deteriorating the quality of the detectors.