Recombination lifetime characterization and mapping of silicon wafers and detectors using the microwave photoconductivity decay (μPCD) technique

Recombination lifetime in oxidized high-resistivity silicon has been characterized by the microwave photoconductivity decay (mu PCD) technique. In this technique, a silicon wafer is illuminated by a laser pulse that generates electron hole pairs. The transient of the decaying carrier concentration is monitored by using a microwave signal. The recombination lifetime is a measure of the material quality, i.e., defect/impurity concentration which affects the quality of the resulting detectors and their electrical properties. The mu PCD technique is a non-contact and non-invasive technique that can map recombination lifetime of the entire wafer before it is selected for device/detector processing. The recombination lifetime mapping on a wafer is realized by a 2D color imaging code representing the range of the lifetime in mu s. In general, the recombination lifetime is the smallest around the wafer edges (about 1000-2000 mu s), and highest in the center of the wafer (5000-10,000 mu s). The recombination lifetime has been measured under different injection levels and surface charge conditions. The results show that the lifetime in investigated n-type materials is almost independent of the injection level if the passivating SiO2 film is corona charged. (c) 2006 Elsevier Ltd. All rights reserved.