CIP: A new technique for measuring doping profiles

A new technique for plotting doping profiles, CIP, involves driving a Schotky diode deposited on the surface of a semiconductor wafer with a small constant RF current (a few hundred microamps at 5 MHz). The depth of depletion layer is varied by changing the dc bias, but this is the only role of the dc voltage. The inverse doping profile n^-1(x) is obtained by monitoring the voltage across the dbde at the fundamental frequency, which is proportional to the depth x, and the second harmonic voltage, which is proportional to n^-1. An X-Y recorder is used directly to plot n^-1as a function of x as the dc voltage is varied. If desired, an analog divider circuit could be added to invert the n^-1signal so that n would be plotted. This type of plotter has the advantages of simplicity, high resolution (limited only by the Debye length in most cases), immediate results and a large reduction in cost. It can also be used to evaluate junction devices.