Boron Redistribution During SOI Wafers Thermal Oxidation

We fabricated silicon-on-insulator (SOI) pressure sensors intended for operation in a wide temperature range. After the thermal oxidation process, the measured sheet resistance of the silicon active layer was higher than expected for the case when the dopant distribution in the active layer is uniform and the layer thickness reduced. The reason was the redistribution of dopant (boron) in the active layer during the high temperature thermal oxidation processes. We developed a model to calculate the boron redistribution in an SOI wafer which was initially uniformly doped. The temperature dependence of hole mobility (and, based on it, the sheet resistance and its temperature dependence) was determined for a calculated impurity profile after oxidation in wet O ₂. The experimental temperature dependence of sheet resistance was obtained by measuring the temperature dependence of piezoresistor resistance. The best match between the theoretical and experimental TCR (temperature coefficient of resistance) was achieved by slightly modifying the Arora´s model for hole mobility