Fabrication of large area Si cylindrical drift detectors

The processing of an advanced silicon detector, a large area cylindrical drift detector (CDD), was carried out in the BNL Instrumentation Division Fabrication Facility. The double-sided planar process technique was developed for the fabrication of the CDD. Important improvements of the double-sided planar process in this fabrication include the introduction of an AI implantation protection mask and implantation of boron through an 1000 angstrom oxide layer in the step of opening the p-window. Another important aspect of the design of the CDD is the structure called “river,” which allows the current generated on the Si-SiO₂ interface to “flow” into the guard anode, and thus minimize the leakage current at the signal anode. The test result showed that for the best detector most of the signal anodes have leakage currents of about 0.3 nA/cm²