PureB low-energy electron detectors with closely-packed photodiodes integrated on locally-thinned high-resistivity silicon

A Pure Boron (PureB) photodiode technology is developed for low-energy (down to 200 eV) electron detectors, and implemented in a versatile production-ripe process for highspeed detectors for Scanning Electron Microscopy (SEM). It is here investigated with respect to transfer from the existing low-resistivity-silicon (LRS) process to a locally-thinned high-resistivity- silicon (HRS) process. In this way a lower capacitance, i.e., a wider low-doped region, can be achieved. A trade-off must be made to meet the demands of optimized SEM imaging: the larger lateral depletion of each photodiode can be in conflict with the requirement to have the detector divided into arrays of several electrically-separated closely-packed photodiodes. Here a 37% reduction in total capacitance is achieved, with junction capacitance of < 1 pF/mm ², while detection efficiency, series resistance, dark current, and packing density are kept within specifications.