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A. Muhammad, C. Eisenmenger-Sittner:
"In Situ Assessment Of Target Poisoning Evolution In Magnetron Sputtering";
Poster: 15th International Conference on Reactive Sputter Deposition 2016 (RSD-2016), Belgium, Gent; 01.12.2016 - 02.12.2016.

We present an experimental approach for in situ monitoring of poisoning evolution of a cylindrical target during reactive magnetron sputtering by laser reflectometry. Aluminum (Al) and Titanium (Ti) targets were reactively sputtered in the presence of Nitrogen (N2) and Oxygen (O2), separately. Argon was used as working gas, and from hysteresis loops of reactive gas flow and discharge voltage, threshold flow rates of N2 and O2 were determined for complete poisoning of the Al and Ti targets, respectively. These targets were then sputtered in complete poisoning mode for different times. For each time interval, the eroded regions of the cylindrical sputtering targets were hit by a laser beam with 532 nm wavelength and reflected images were captured on a screen.
The surface of the poisoned region of the target was considered as a random arrangement of tilted plane facets whose linear extension is larger than the wavelength of the laser beam. Based on ray tracing optics, the reflected intensity distribution of the laser from the target surface was utilized for assessment of the poisoned surface. The mean tilt angle of the surface roughness for both nitride and oxide layer formation on the Al and Ti targets was measured from the reflected intensity profiles. A decrease in surface roughness of poisoned targets was observed after sputtering in the poisoning mode up to one hour. This change in surface roughness was in good agreement with the same measurements taken from a profilometer. Although, the discharge voltage instantly changes in poisoning mode, the prolonged sputtering in the poisoning mode leads to a change in the surface morphology of the sputtering target. A gradual decrease in surface roughness was observed for the Al and Ti targets with oxide poisoning up to 60 minutes of reactive sputtering at 16 sccm (standard cm3/min) of O2 flow. However, a saturation in the decreasing trend of surface roughness for both targets was observed for nitride poisoning after 30 minutes of reactive sputtering at 9 sccm of N2 flow.
This in situ method can also be applied for the estimation of the thickness of the poisoned layer on the target surface which could lead to a different composition of the sputtered material.