Laterally resolved ion-distribution functions at the substrate position during magnetron sputtering of indium-tin oxide films

During the magnetron sputtering from an indium-tin oxide (ITO) target (76mm diameter) we measured the ion-distribution functions (IDFs) of energetic ions (argon, indium, and oxygen ions) at the substrate surface using a combination of a quadrupole mass spectrometer and an electrostatic energy analyzer. We obtained the IDFs for argon sputtering pressures in the range from 0.08to2Pa and for dc as well as rf (13.56MHz) plasma excitation with powers from 10to100W. The IDF measurements were performed both over the target center at a target-to-substrate distance of 65mm and at different positions along the target radius in order to scan the erosion track of the target. The mean kinetic energies of argon ions calculated from the IDFs in the dc plasma decreased from about 30to15eV, when the argon pressure increased from 0.08to2Pa, which is caused by a decrease of the electron temperature also by a factor of 2. Indium atoms exhibit higher mean energies due to their additional energy from the sputtering process. Th...