Secondary electron emission from magnetron targets

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Ion-induced secondary electron emission of surfaces occurs in all gas discharges which have contact to surfaces such as electrodes or chamber walls. These secondary electrons (SEs) play an important role, for instance, in the performance of DC discharges, RF discharges and magnetron sputtering discharges. SE generation can be separated into potential electron emission (PEE) due to the neutralization of the incident ion upon impact and kinetic electron emission (KEE) due to the electronic stopping of the penetrating ion in the solid. SE due to neutralization is usually described by Auger processes and the density of states of the electrons in the solid, whereas KEE scales with the electronic stopping of the ion in the solid, as being calculated by ion collision simulations. The measurement of the energy distribution of the SEs of three metals (Al, Ti, Cu) and their oxides reveals the occurrence of Auger peaks, which are not reflected by standard models such as the Hagstrum model. Instead, in this paper, a model is proposed describing these Auger peaks by Auger neutralization of holes created by the collision cascade of the incident ion. This shows decent agreement. The contribution of Auger peaks in the metals Al and Ti is very significant, whereas it is negligible in the case of Cu. The implication of these energy distributions to the performance of magnetron sputtering discharges is discussed.