Thermal donor generation in Czochralski silicon particle detectors

Abstract

In this report, the processing of thermal donor (TD) compensated detectors is described. Heat treatment of Czochralski silicon (Cz-Si) wafers between 400 and 600 °C leads to aggregation of interstitial oxygen atoms resulting in electrically active shallow levels in the silicon band gap. This process is known as TD formation. It depends on the temperature, the oxygen concentration in the silicon material and the presence of hydrogen in device manufacturing process. The oxygen concentration in silicon wafers grown by Magnetic Czochralski (MCz) method is sufficiently high in order that the concentration of TDs is comparable with the initial phosphorous or boron doping of high-resistivity Cz-Si. The TD formation has been studied by monitoring the detector full depletion voltage with respect to the heating time at 430 °C. The TD formation has been verified by Deep Level Transient Spectroscopy (DLTS) measurements. In addition, the annealing behavior of the irradiated samples at different temperatures is discussed. The TD formation in n +/p −/p + pad detectors has been observed not to influence the leakage current of the devices. Thus, the full depletion voltage of the detectors processed on p-type MCz-Si wafers can be modified by this method.