Plagemann, A. ; Ellmer, K. ; Wiesemann, K.: Laterally resolved ion-distribution functions at the substrate position during magnetron sputtering of indium-tin oxide films. Journal of Vacuum Science and Technology A 25 (2007), p. 1341-1350
10.1116/1.2753843
Abstract:
During magnetron sputtering from an indium-tin oxide (ITO) target (76 mm 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 analyser. We obtained the IDFs for argon sputtering pressures in the range from 0.08 to 2 Pa and for DC as well as RF (13.56 MHz) plasma excitation with powers from 10 to 100 W. The IDF measurements were performed both over the target centre at a target-to-substrate distance of 65 mm 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 30 to 15 eV, when the argon pressure increased from 0.08 to 2 Pa, which is caused by a decrease of the electron temperature also by a factor of two. Indium atoms exhibit higher mean energies due to their additional energy from the sputtering process. The total metal ion flux turns out to be proportional to the discharge power and the pressure, the latter dependence being due to Penning ionisation of the metal atoms (In, Sn). From the scans across the target surface the lateral distributions of metal, oxygen and argon ions were derived. In the DC discharge the position of the erosion track is repoduced by increased ion intensities, while it is not the case for the RF excited plasma. The lateral variations of the observed species do not influence the lateral resistivity distributions of the deposited ITO films.