Substrate engineering for reduction of alpha-particle-induced charge collection efficiency

Measurements of alpha-particle-induced charge collection efficiency (CCE) together with simulation analysis have been carried out for several types of substrates: a double well, a p-well in a p^- epitaxial layer grown on p⁺ substrate (epi-substrate) and a p-well with a buried defect layer. As a result, the following have been clarified. CCE for the double well is low because the bottom n-layer acts as an effective electron absorber. CCE for the p-well in the epi-substrate increases with increase in the thickness of the epilayer because the potential difference between the heavily doped substrate and the lightly doped epilayer forms a barrier which prevents electrons from traveling into the substrate. Even for the p-well in a thin epilayer, CCE is comparable to that for the p-well in the conventional p^- substrate. CCE for the p-well with a buried defect layer formed by high-energy and high-dosage ion implantation is as low as CCE for the double well because the carrier lifetime is short in the buried layer due to lattice defects.