A four-point probe method with increased accuracy for the local determination of the thickness of thin, electrically conducting layers

The error analysis for an infinite thin conductive plate shows that a four-point probe resistivity-to-thickness ratio measurement method with circularly arranged contact tips based on two pairs of measured current and voltage values obtained by cyclical exchange of the connections yields extremely low measurement errors due to contact misalignment. These errors are by one to several orders lower than those obtained with the “classical” method which uses only one pair of measured values. The measurement may thus be carried out at any probe station; the precision probe head required so far is no longer needed. Conventional four-point probe measurement methods are unsuitable if Schottky behavior occurs between the metallic contact and the sample. For this reason, a novel four-point probe measurement method using an ohmic (alloyed) auxiliary contact at the edge of the sample for current feed-in is presented here. Both methods were tested for thickness measurement on thin epitaxial InP and GaAs layers and compared with each other. The results showed very good agreement. The accuracy was about 3 percent.