Silicon grain crystallographic orientation measurement from NIR transmission and reflection

Measurement of in-plane residual stresses in photovoltaic Si wafers with NIR polariscopy requires the knowledge of the stress-optic coefficient of the silicon, which varies with local crystallographic orientation. We have found that, all other variables being equal, the transmission of light through crystals will vary with crystallographic orientation. After measuring transmitted light intensities through monocrystalline CZ wafers of known thickness and orientation, we have created a calibration scale by which the orientation of grains in a random multicrystalline wafer may be obtained. A stereoscopic light setup was also used to compare the same grains in reflection.