By Martin Zimmer, Wet Chemical and Plasma Technologies, Fraunhofer ISE; Antje Oltersdorf, Fraunhofer ISE; Jochen Rentsch, Wet Chemical and Plasma Technologies / Process Transfer Group, Fraunhofer ISE; Ralf Preu, Department for PV Production Technology and Quality Assurance, Fraunhofer ISE
Crystalline silicon solar cell fabrication involves many wet chemical process steps. Like most processes in solar cell manufacturing, many of these wet chemical processes were transferred from the semiconductor industry. In contrast to microchip fabrication with maximum throughputs of 100 wafers/hour, state-of-the-art solar cell equipment relies on several 1000 wafers/hour. Furthermore, specific processes have been developed for the texturisation of the wafer surface. Therefore, there is a need for dedicated methods of characterization of these wet chemical processes. Fraunhofer ISE has developed several analytical methods such as titration, ion chromatography and near infrared (NIR) spectroscopy for the complete analysis of the chemical composition of wet chemical processes baths. These methods were compared considering the inline/online capability, measurement cycle and running costs, with the result that NIR spectroscopy was identified as a complex but very powerful tool for process characterization, as outlined in this paper.