Optical measurement techniques for in-line process control in CdS/CdTe solar cell manufacturing

Optical techniques are promising as a non-destructive process monitoring and control tool in high-throughput CdTe photovoltaic manufacturing. Three such techniques - spectroscopic ellipsometry, reflectometry, and scanning white light interferometry - were evaluated using devices made under diverse process conditions in the CSU Advanced Research Deposition System (ARDS). CdS/CdTe devices made at rough and smooth film process conditions as well as mechanically polished films were examined. With a proper model for surface roughness in the CdTe layer, an accurate thickness measurement can be made both of the CdTe layer and the underlying CdS layer for a variety of CdS thicknesses. Ellipsometry data taken through the glass can be used to measure CdS thickness for rough and smooth devices alike. Reflectometry results closely match ellipsometry results for CdS films. Finally, SWLI is being examined for measurement of surface morphology and TCO scribing.