Title: Porosity of Nb magnetron sputtered thin films and dependence on sputtering parameters
Author: Hanna Skliarova
Institution: INFN-LNL
Abstract: Pinholes (or through film porosity) in Nb thin film deposited on the inner walls of SRF cavities are harmful for cavity performance because they may expose inferior copper that has much higher resistance than niobium at 4.2 K. Aluminated quartz substrates allowed us to make visible the pore sites for inspection and counting by production visible corrosion products. We showed the correlation between the amount of pinholes in niobium thin film prepared by magnetron sputtering and the deposition parameters, such as sputtering gas pressure, substrate temperature, applied bias, placing of the sample in UBM sputtering mode. Thus low temperature of the substrate and high sputtering gas pressure promoted growth of a voided film (that corresponds to SZM approach) with high amount of pinholes. Heating of the substrate during deposition has resulted in moderate decrease of the pinhole amount, while negative bias applied to the substrate showed stronger decrease of the pinhole amount thanks to additional bombardment of the substrate by Ar+ serving to remove weakly bounded particles during deposition.
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