Speaker
Description
We present our concept of using aluminum oxide deposited by atomic layer deposition (ALD) as field insulator and coupling dielectric in segmented n-in-p silicon detectors. As opposed to the commonly used SiO2, alumina thin films exhibit a significant negative charge, which enables us to omit the critical high-temperature p-spray/p-stop implantation steps. Furthermore, the dielectric constant of alumina is higher than that of SiO2, so that a thinner layer of alumina is sufficient for insulation.
Alumina thin films with thicknesses of 50-70 nm were deposited at 200 and 300 °C and their properties were compared. The electrical properties of unprocessed thin films were characterized by the contactless COCOS (corona oxide characterization of semiconductor) method, which provides information on the total oxide charge, interface trap density, as well as flatband voltage and dielectric constant of the films. Similar films were used in processing of diodes and MOS capacitor structures, whose properties were then characterized by capacitance-voltage and current-voltage measurements.
The electrical characterization shows that deposition temperature has a strong effect on the properties of the films. It appears that alumina films deposited at higher temperatures are not ideal for the use in segmented detectors. Negative charge formation in the film is promoted by the annealing step required for aluminum sintering in device processing, which simultaneously improves the quality of the oxide-silicon interface. The MOS capacitor C-V measurements show a dependency on frequency. The comparability of conventional C-V measurements and the COCOS method is discussed.
