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Different magnetron sputtering‐based deposition methods of nickel oxide SiO₂‐passivated Si surfaces are compared. Results highlight that the presence of oxygen in the deposition chamber during reactive sputtering drastically affects the Si/SiO₂ interface. An alternative method for the preparation of NiO is the sputtering of metallic nickel in oxygen‐free atmosphere followed by a post oxidation of the deposited layer in an oxygen atmosphere without plasma exposition is proposed. This method is introduced as metal layer oxidation (MLO). Using this technique, the barrier height on n‐type silicon increases from ≈0.4 eV for reactively sputtered NiO to more than 0.6 eV for the MLO method. In situ photoelectron spectroscopy evidences the formation of an extra electronic state when NiO is reactively sputtered, which is assigned to the intense oxygen ion bombardment of the Si/SiO₂ surface during the process. This extra‐electronic state pins the silicon energy bands in an undesirable position. The extra‐electronic state is associated with oxygen interstitial in the SiO₂ implanted during reactive sputtering.