Substrate heating in cylindrical magnetron sputtering sources

The magnetic plasma confinement in magnetron sputtering sources makes the plasma ionization process very efficient and allows high sputtering rates to be achieved with reduced substrate heating, particularly in the cylindrical-post magnetron geometry where a virtual anode separates the substrates from the plasma. Heating flux measurements at typical substrate locations surrounding cylindrical-post magnetron sputtering sources were made for the argon sputtering of seventeen metals, representing a range of atomic masses, crystallographic structures and sputtering yields. The heating flux data are combined with deposition rate measurements and are reported as energy per coating atom deposited. They are consistently interpreted in terms of four basic heating processes: (1) heat of condensation; (2) sputtered atom kinetic energy; (3) plasma radiation; (4) ion neutralization and reflection at the cathode. Ion reflection becomes increasingly important for the high mass materials. The energy per atom deposited is independent of the deposition rate and the argon pressure and varies from 15 to 25 eV atom −1 for light metals to over 50 eV atom −1 for heavy metals with moderate sputtering yields. The sputtering efficiency is shown to be a useful concept in accounting for ion reflection. Comparative data are reported for sputtering with nitrogen and oxygen and for cylindrical-hollow magnetron sources. The energy per atom is relatively high in nitrogen and oxgyen sputtering because of a high sputtering efficiency and a reduced metal sputtering yield. The closer proximity of the plasma in hollow cathodes introduces a plasma bombardment contribution to the heating flux.