It is the cleaning and conditioning of the surface prior to passivation gains increasing importance. It has to the applicability of three methods to clean and condition the surface of silicon wafers by an ultra-thin oxide layer. Simple cleaning has been demonstrated that organic residues resulting from wafering. It has been masking the surface during alkine texturing can be removed by UV/O_3 exposure. It used of UV/O_3 (excimer) and HNO_3 oxides result in an improvement of passivation quality and emitter saturation current in combination with Al_2 O_3/SiN_x or AIN/SiN_x passivation stacks. This important application of ultra-thin SiO_x layers is as tunnel oxides for the rear side of the Tunnel Oxide Passivated Contact (TOPCon) cell concept. The structural properties of theSiO_X layers that were analyzed by X-ray photoelectron spectroscopy (XPS) and compared to the iV_OC data. It indicate that a minimum oxide layer thickness of approx. 1.4 nm and a high amount of oxygen rich sub oxides species are required to obtain a good interface passivation stable up to annealing temperatures of 900℃