Method and apparatus for the contactless monitoring carrier lifetime in semiconductor materials

Abstract

The lifetime of minority carriers in semiconductor materials is measured by a noncontacting steady-state method adapted for monitoring of the condition of wafers during device manufacture. The method comprises coupling the sample into an LC resonant circuit which is the frequency-determining portion of a marginal-oscillator adapted to maintain either a constant amplitude RF signal, or be driven by a constant current generator, and measuring either the current required to so maintain the signal, or the difference in RF voltage, either of which is related to the sample's conductivity. Illuminating the sample with light of appropriate frequency from an intermittent source modulates the conductivity, and the difference in the steady-state values of conductivity in the illuminated and the dark condition is proportional to the minority carrier lifetime. Exemplary apparatus has a lifetime resolution of about 0.1 .mu.sec, with a measurement time of 0.4 sec, and a sampled area of about 0.3 cm.sup.2.

Dependencies are inferred from the claim text.