Self‐calibrating Approach for Non‐Contact Electrical Doping Profiling

We present a self‐calibrating version of non‐contact electrical doping profiling that is a refinement of our method based on monitoring of the decays of two voltages during the collapse of deep depletion. Small signal ac‐photovoltage, appropriately calibrated, provides a measure of the depletion capacitance, C_D, while the corresponding depletion layer voltage, V, is obtained using a vibrating Kelvin probe. Deep depletion is created by a pulse of corona charge placed on the wafer surface. Doping depth profile is calculated from the set of C‐V data obtained from two voltage decays. The in‐situ self‐calibration is introduced in order to obtain, for each measurement, a constant that relates the ac‐photovoltage and the depletion capacitance. This constant depends on the condition of the wafer surface, and therefore, is not universal. Self‐calibration is realized by corona charging up to the avalanche breakdown limit and using the breakdown voltage relation to the dopant concentration. Application of the method is illustrated using epitaxial silicon wafers.