Measuring stress birefringence in industrial-sized photovoltaic Si ingots

Abstract

During the production of photovoltaic (PV) Si solar panels, a high level of residual stress in Si crystals often remains undetected far into the fabrication process. Available metrology is primarily limited to testing wafers, cells and panels, which is late in the manufacturing process. We describe in this poster an instrument, known as the Exicor® PV-Si birefringence measurement system, which can measure stress birefringence in Si ingots before they are sawed into wafers. This instrument measures stress-induced retardation in Si ingots at either 1550 nm or 1310 nm using photoelastic modulator (PEM) technology. It maps residual stress birefringence in squared Si ingots of typical industrial dimensions (for example, 156mm × 156mm × 500mm). It can also provide a line of stress birefringence data along the length of an as-grown Si ingot that has a circular cross-section.