Photovoltaic Technique for Measuring Resistivity Variations of High Resistivity Silicon Slices

A description of an automated, photovoltaic system for measuring the resistivity variation of high resistivity, large diameter silicon wafers is given. The photovoltaic technique utilizes a scanning light spot to induce a bulk photovoltage and a change in resistance from which is calculated the local variation in resistivity. This nondestructive technique requires no contacts to the useful fabrication area of the wafer, and measured results have good correlation with the results of the four-probe technique. Specific examples of measured resistivity gradients are presented along with a discussion of the theory, measurement conditions and limitations, and description of a calculator-based automated system to perform the measurements.