Edgeless silicon sensors fabricated without support wafer

Abstract

Silicon radiation detectors with minimum dead area in the sensor periphery are desirable and sometimes necessary for many applications in nuclear medicine, high energy physics, and X-ray​ science. The dead area typically includes a guard ring structure that is required for facilitating a uniform electric field distribution around the active area of the sensor, and consequently assuring high breakdown voltages, as well as for limiting the active area leakage current. The dead sensor periphery can be drastically reduced or even completely eliminated by replacing the conventional guard ring structure with the so-called ”active-edge”. The active edge is fabricated by etching through-substrate trenches surrounding the active area of the sensor using a micromachining technique known as deep reactive ion etching, followed by passivation of trench walls with doping. The active edge thus provides an excellent isolation of the active area from defects resulting from sensor separation while occupying only negligible physical space. Several laboratories worldwide have investigated the fabrication of active-edge sensors using a support wafer, which is required to provide mechanical integrity once the trenches are etched. However, the post-processing removal of the support wafer is a cumbersome and unreliable step, making this fabrication approach unsuitable for high yield manufacturing. We have recently developed a new fabrication method that eliminates the challenges associated with processing on a support wafer and thus facilitates mass-manufacturing. We have successfully demonstrated the fabrication of edgeless sensors with edge insensitivity of < 10 micrometer at SINTEF without the need for a support wafer. The design, fabrication, simulation and characterization results of these sensors are reported in this paper.