Contactless determination of base resistivity on silicon wafers with highly doped surfaces

Abstract

In this paper a contactless and non-destructive method for the determination of base resistivity of silicon wafers with highly doped surfaces is introduced. The method is based on photoconductance and photoluminescence measurements. Unlike existing methods for the determination of base resistivity, the proposed method does not require an experimental setup, which simultaneously measures photoconductance and photoluminescence signals synchronized in time. The method is applied to a set of test samples with highly doped surfaces representing a broad variety of samples present in industrial and laboratory environments. The results of the proposed method are compared to reference values which are inductively measured after the removal of highly doped surfaces. An mean absolute error with respect to the reference values below 4% is obtained for the investigated set of samples. This corresponds to a deviation of less than 0.1 Ωcm for typical solar wafers with resistivities below 5 Ωcm. Sources of uncertainties in the proposed method are discussed in detail. From that discussion rules of thumb for a reasonable choice of calibration and test samples are derived. A maximum error of less than 10% is expected if rules of thumb are followed.