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Abstract

In this paper we report the investigation of the implantation and radiation damage during sputter profiles of 30 nm TiO2 layers on Ti with 3 keV N2+. The profiles are analysed by normal and angle-resolved XPS measurements. Supplementary electrochemical reoxidants are performed, handling the sample without any contact to air during the whole process. Additional information is obtained by comparison with 4 keV Ar+ and 3 keV air sputter profiles.

At the beginning of a 3 keV N2+ sputter profile some TiO2 at the surface is converted to TiNxOy, which is only partially oxidizable by repassivation. A portion of the implanted nitrogen exists as molecular N2. After higher sputter dosed the composition changes drastically. Preferential sputtering reduces the oxygen concentration to an extent to allow TiNxO1−x and TiN formation. The TiNxOy changes its composition since it is now fully reoxidizable, as are all compounds with a Ti oxidation state of less than 4 +. N2 reacts with TiNxO1−x by recoil excitation and no longer exists. The occurrence of TiO, Ti2O3 and Ti3N4 is unlikely, but possible in small concentrations. The products of all electrochemical repassivations are TiO2 and N2.

Angle-resolved XPS measurements show Ar- and N2-attenuated surface layers. During Ar and air implantation these layers remain constant owing to an equilibrium between outgassing and implantation of new sputter gas. After nitrogen implantation the N2-attenuated layers are constant in the beginning and increase when the N2 begins to react with TiNxO1−x until the N2 totally disappears.

An addition of oxygen to the sputter gas can decrease the surface roughening effect, which is often found after prolonged sputtering, XPS binding energies show that Ar and N2 gas do not occur in gas bubbbbles.