Fluorine passivation of metal surface for self-cleaning semiconductor equipment

Fluorine passivation of metal surfaces for ULSI process equipment is investigated and passivated film quality is evaluated. Well-polished and pretreated bare surfaces of stainless steel and nickel are passivated with oxygen-free, high-purity fluorine (O₂ and HF less than 1 p.p.m.), and a uniform and stable passivated surface is obtained by introducing two-step fluoridation, i.e. direct fluoridation and the succeeding thermal modification (heat treatment in nitrogen). The fundamental mechanism of the surface fluoridation is investigated by differential thermal analysis. The chemical structure of the passivated films is examined by X-ray diffraction and X-ray photoelectron spectroscopy. Passivated films of stainless steel exhibit a double-layer structure, such as FeF₂ covered by CrF₂, which has a lower vapor pressure than divalent metal fluorides such as FeF₂ , NiF₂, and MnF₂. It has been confirmed that the first fluoridation step produces a nonstoichiometric fluoride which is converted to the stoichiometric structure by the heat treatment in nitrogen. Good passivation performance is achieved as a result of this thermal modification