Measurement of the Sheet Resistivity of a Square Wafer with a Square Four-Point Probe

Abstract

The sheet resistivity of a thin sample of semiconductor may be measured by the placement of four probes on the surface of the sample. When current is passed between two of the probes, the potential difference between the other two probes is proportional to the current and the sheet resistivity of the sample. Sheet resistivity is then proportional to PD÷current, the proportionality or correction factor being dependent on the geometry of the sample and the probe. Calculations have been made for the correction factors in the case of a square probe array placed symmetrically on a square wafer. The correction factors for conversion of PD÷current to sheet resistivity are given for square dimensions, in units of probe spacing, over the range one to 50. The data include the special case d/s=1 wherein the probe points are on the corners of the square.