Variable-frequency automatic capacitance/conductance system for impurity profile and deep level determination

Development of new semiconductor technologies frequently requires impurity density analysis on material with high leakage currents or deep level contamination. Previously described impurity profilers provide no diagnostics for such cases. We have constructed a new variable-frequency capacitance/conductance analysis system applicable to impurity profile. Schottky barrier height, MOS interface state and deep level analysis. The system, which consists almost entirely of commercial "building blocks", uses phase-sensitive detection to provide better than 40dB isolation between capacitance and conductance signals. For impurity profile measurements a two-frequency intermodulation technique avoids the stringent filtering requirements inherent in the Copeland plotter. In this mode the system can measure either capacitance, C and dC/dV or conductance, G and dG/dV over two decades in frequency. A small-scale analog computer integral with the unit allows presentation of the data as impurity profiles. A simple change of circuit parameters permits measurement of C or G with amplitude response flat within 1% over four decades of frequency. The computer may then be used to present the results in formats appropriate to Schottky barrier height or deep level determinations.