Puzzling Energy and Angle Distributions of Atoms Ejected during Reactive Magnetron Sputtering: Effects of Target Texture?

During reactive magnetron sputtering of TiN in an Ar/N2 gas mixture, energy and angle distributions of sputtered Ti neutrals have been measured using a HIDEN EQP energy-resolving mass spectrometer. Both kind of distributions show features which are not consistent with the expectations from standard collisional sputtering theory being valid for a random structure of the target. Distributions of the energy E have been obtained from both metallic and poisoned areas of the target. As expected from the Thompson distribution, f(E) ~ E/(E+Us)^3, they peak at half of the surface binding energies Us, but are significantly narrower than predicted. The distributions of the emission angle (with respect to the surface normal) exhibit pronounced maxima tilted by ~40° from the target normal, thus strongly deviating from the expected cosine behaviour, f(alpha) ~ cos(alpha).
Any experimental artifacts can be excluded which might result in the above observations. As the only reasonable explanation we propose potential effects of texture, which might be originally present at the target surface or develop during ion bombardment. For the angular distributions, this is in qualitative accordance with sputter ejection patterns from crystals at keV incident energy as reported in literature. Corresponding collisional computer simulations for the present conditions are in preparation, as are detailed structural diagnostics of the target surface.