Influence of strong magnetic fields on the growth of DC magnetron sputtered ZNO:Al films from a ceramic target

When sputtering aluminum doped zinc oxide from a ceramic target, the layer is damaged perpendicular to the erosion area by high energetic oxygen ion bombardment [1]. The ions receive their energy from the potential difference between cathode and floating substrate. Their impact leads to a higher resistivity and lower mobility of the deposited layer. This counteracts the necessary properties of a TCO as front contact in a-Si/?c-Si solar cells, where good transparency and conductivity is desired. To diminish the damaging effect of the oxygen ions the use of stronger magnets for magnetron sputtering was examined. Static imprints with a standard and a strong magnetron were performed by using a new plane ZnO:Al2O3 (1 wt.%) target. Thickness, resistivity, mobility, carrier density, aluminum concentration and doping efficiency were determined. The results show a clear reduction of target voltage by 40 V at the same applied power of 6 kW and also a loss of damage opposite to the race tracks. Hereby resistivity was lowered by a factor of 1.5 and mobility was increased from 22.5 to 28.8 cm²/ Vs at the position opposite to the race track. The new approach of using stronger magnets during sputtering was shown regarding a planar target and can be applied at rotatable tube targets.