Focused ion beam based sputtering yield measurements on ZnO and Mo thin films

In order to facilitate the lateral structuring of solar cell multilayer structures, the ion beam sputtering behaviour of Mo and ZnO thin films deposited onto soda-lime glass and single crystalline Si substrates was studied. Prior to ion beam processing the layers were analyzed by Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Diffractometry (XRD) and Rutherford Backscattering (RBS). In order to characterize the ion beam sputtering of the investigated layers, 2×2 μm2 fractions of the thin films were removed by a scanned 30 keV focused Ga+ ion beam (FIB) in a dual beam system. SEM images taken during the milling process allowed continuous monitoring of the process without breaking the vacuum. The depth of the groove after removal of the layers was measured by Atomic Force Microscopy (AFM) and was plotted as a function of the ion dose. The sputtering depth has a dependence on the ion dose that is close to linear. The deviation from linearity is produced by heating effects at high beam currents. Sputtering yield values calculated from the experiments and simulations showed good agreement in the case of Mo but deviation was found in the case of ZnO.