Fast large area reflectivity scans of wafers and solar cells with high spatial resolution

A solar cell local characterization (CELLO) set-up is modified to measure reflectivity maps of any objects in a non-destructive way. Four different laser wavelengths (BLUE 403 nm, RED 630 nm, IR 830 nm and SIR 934 nm) are applicable. This paper will present the measurement principle, the reflectivity calibration to samples previously analyzed with an integrating sphere, and demonstrate the reflectivity analysis of wafers and solar cells. Compared to other measurement techniques like integrating spheres, this approach has two advantages: First, being fast on large areas (15.6 cm x 15.6 cm sample size; 1 million pixels, measurement time 10 min to 1 hour depending on the accepted noise-level) and second, resolving details in zoom scans with high local resolution (10 µm-spot size). This may allow optimizing processes, where reflectivity is a key parameter like texturization, SiN-PECVD-Antireflective coating or wafer cutting and cleaning processes. Furthermore, independently measured reflectivity maps may be helpful for CELLO photo-impedance analysis in the future.