An X-ray photoelectron spectroscopy study of the target surface composition after reactive magnetron sputtering

The target surface stoichiometry after reactive DC magnetron sputtering has been studied by X-ray Photoelectron Spectroscopy (XPS). The target was transferred in-vacuo from the deposition chamber to the XPS analysis chamber to avoid any influence by ambient exposure. The study was performed on an aluminum and a tantalum target, both reactively sputtered in different mixtures of oxygen and argon. XPS analysis showed that for the aluminum target only stoichiometric aluminum oxide (Al2O3) is formed but for the tantalum target different suboxides (Ta2O, TaO, Ta2O3, TaO2 and Ta2O5) are present. The formation of a stoichiometric or substoichiometric oxide on the target surface is related to the observed respectively decreasing or increasing discharge voltage behavior upon oxygen addition. This change in discharge voltage behavior is generally linked to a change in electron emission from the target. The material dependency of both the potential and kinetic electron emission mechanisms results in disparate electron yield values between oxides and suboxides residing on the target surface.