Texture process monitoring in solar cell manufacturing using optical metrology

A novel optical metrology technique has been developed to study textured silicon wafers used to manufacture solar cells. This high efficiency optical design to maximize the signal from surfaces with reflectivity well below 1% was developed. Pyramid dimensions were measured on as sawed p-type Czochralski wafers having a bulk resistivity of 1-5 Ohm-cm. These wafers were subjected to a single step texturization process by using a non-alcoholic chemical etching formulation. Results were compared with SEM imaging. Reflectivity tests and pyramid height measurements were used to study the efficiency of the texturing processes. In a related study [2] it was found that 20 μm of material removal was required to attain minimum surface reflectivity. Further removal of material affected pyramid dimensions, but did not improve surface reflectivity.