Infrared birefringence imaging of residual stress and bulk defects in multicrystalline silicon
We explore the potential of infrared birefringence imaging (IBI) to reveal a complete picture of macro- and microscopic internal stresses and their origins in multicrystalline silicon (mc-Si). We present a method to decouple macroscopic thermally induced residual stresses and microscopic bulk defect-related stresses, and validate this method in mc-Si wafers via microstructural analysis. We then describe the unique IR birefringence signatures, including stress magnitudes and directions, of common microdefects in mc-Si solar cell materials: -SiC and -Si3N4 microdefects, twin bands, non-twin grain boundaries, and dislocation bands. We relate observed stresses to other topics of interest in solar cell manufacturing, including wafer mechanical strength and minority carrier lifetime.