Comparative study on emitter sheet resistivity measurements for inline quality control

With increasing degree of automation and throughput in latest crystalline Si solar cell manufacturing lines a quality control (QC) directly incorporated in the corresponding process equipment is of rising interest. The dominant QC parameter for the phosphorus diffusion step is the emitter sheet resistance normally measured based on manually drawn samples. In contrast, our aim was to develop and test measurement methods which can be directly incorporated in high volume diffusion equipment. Two contactless approaches have been studied, the Eddy current technique and a newly developed system based on SPV (surface-photo-voltage) probing. As reference measurement technique a four point probe FPP was used. As result it could be clearly shown that the novel SPV approach already included in a new 30 MW cell line lead to the same accuracy as an off-line FPP whereas the eddy current technique can not be applied.