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 (μPCD) 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 μPCD 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 μs. In general, the recombination lifetime is the smallest around the wafer edges (about 1000–2000 μs), and highest in the center of the wafer (5000–10,000 μs). 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.