An instrument for the rapid determination of semiconductor impurity profiles

The instrument gives an absolute measurement of impurity concentration in a semiconductor wafer as a function of depth and surface position. A matrix of Schottky barrier diodes is deposited on the surface, contact being made with each diode in turn by a small probe. The probe is fed with a dc bias voltage and a small voltage at 100 kHz, the 100 kHz current flowing in the diode being a measure of the small-signal capacitance Cx. Another small voltage, at 1 kHz, is superimposed. and the consequent depth of modulation of the 100 kHz current is a measure of dCx/dV. The impurity concentration N and the depth are known functions of Cx and dCx/dV, and the instrument does the appropriate analogue computations to provide a direct plot of lg N against depth as the dc reverse-bias voltage is carried. This paper includes a detailed discussion of the sources of error, and also presents some typical impurity profile curves which have been obtained.