Impact of a p-type Solar Cell Process on the Electrical Quality of Czochralski Silicon

The impact of the three main process steps during p-type solar cell processing, namely phosphorus diffusion, anti- reflection coating and contact formation, on the electrical quality of Cz silicon is investigated. Adjacent wafers from the middle and tail part of three Czochralski grown silicon ingots of varying quality were treated by the process steps as well as process step combinations. The impact of the thermal budget during the process steps without the application of phosphorus dopant, ammonia and silan gases and metal contact pastes on the Cz silicon was examined. The excess charge carrier lifetime and the interstitial iron content were measured separately for each step. Besides other effects, phosphorus diffusion gettering was found to be very efficient in removing interstitial iron from the Cz silicon. The antireflection coating step as well as the contact formation step were found to be most detrimental to the Cz silicon quality. Changes observed in the Cz silicon quality were discussed within the frame of recent models.