Detection of Microcracks in Cz-Si Wafer Manufacturing by Photoluminescence Imaging

Abstract

Photoluminescence imaging (PLI) is a widely accepted, fast, and contactless method for detecting crystal defects in crystalline silicon solar cells and solar-grade silicon wafers. However, it is less known by semiconductor wafer manufacturers despite the similarities between photovoltaic (PV) and semiconductor wafers. This study focuses on the detection of microcracks by PLI during high-quality Czochralski silicon (Cz-Si) wafer manufacturing. The results show that in case of low resistivity (<25 mΩ cm) wafers, microcracks can be detected at any stage of the processing—even after diamond-wire slicing. When resistivity increases, visibility of microcracks reduces in process steps that produce uneven surfaces. Nevertheless, they can still be detected after slurry-wire slicing, lapping, alkaline etching, and polishing. According to the results, unlike resistivity, other material parameters such as dopant species, crystal orientation, and wafer thickness have no similar impact on visibility of microcracks in PLI. Furthermore, all wafers produce a decent photoluminescence (PL) signal without a need for separate sample preparation. Based on these results, general recommendations for the in-line detection of microcracks for Cz-Si wafer manufactures are provided. While this study focuses on microcracks, the results and discussion include broader perspectives on the defect characterization in Cz-Si wafer manufacturing via PLI.