The improvement of polypropylene surfaces by means of fluorine gas was investigated. It was found that polypropylene surfaces treated with fluorine gas diluted with nitrogen became hydrophilic. The optimum fluorination condition was a fluorine concentration of 0.5-1.0% and treatment times of 1-10 minutes. Hydrophilic properties were evaluated by contact angle. The polar-force component and dispersion-force component in surface free energy were calculated from contact angle using water and methylene diiodide. In particular, the lower polar-force component increased from 1.6mJ/m2 to 25.0mJ/m2. ESCA data showed that -CF-CF- and -C-CF- bondings formed on the upper surface. It has thus been demonstrated that these C-F bondings are given polarity by the fluorine which is the strongest electronegativity. The hydrophilic properties are thought to be due to this polarity. Adhesive strength was tested by cross-cut test with the hydrophilic surface coated with urethan paint. The painting exhibited good results. The high adhesion strength is thought to be the result of polar interaction. It is clear that good coating can be obtained by treating polypropylene surfaces with fluorine gas.
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An ultraclean dry etching system using HF gas has been developed. It has been demonstrated experimentally that there exists a critical concentration of HF in N/sub 2/ gas for etching of various Si oxide films. The critical concentration for native oxide obtained in wet processing or UV O/sub 3/ organic contamination cleaning is lower than those for thermal oxide, CVD (chemical vapor deposition) oxide, and CVD BSG. The difference becomes large with decreasing moisture level. Based on the results obtained, dry processing using HF gas is proposed as a surface cleaning technique in the ULSI process.< >
An optimal nickel difluoride film‐formation technology has been investigated for electroless Ni‐P deposited films, where highly sensitive electrochemical anodic polarization measurement and thin‐film x‐ray diffraction (XRD) studies using low incident angle have been employed to establish this technology. Electroless Ni‐P deposited films have an amorphous structure as deposited which is converted into crystalline structure such as nickel phosphides ( or ) with heating, this is undesirable for the formation of homogeneous fluorine passivation films. Low incident angle XRD allows us to determine the fluoridation conditions where the films little include these nickel phosphides crystals. Further, anodic polarization measurement curves support the film‐formation conditions (temperatures, fluorine concentration) of nickel difluoride and the effect of heat‐treatment after fluoridation. The low fluoridation temperature at ca.300°C is not sufficient and low fluorine concentration is also unfavorable for the fluoridation of the electroless Ni‐P deposited films. We conducted several evaluations such as corrosion resistance, outgassing characteristics, and plasma resistance using the nickel difluoride films formed by the most favorable condition.
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 (O/sub 2/ 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 FeF/sub 2/ covered by CrF/sub 2/, which has a lower vapor pressure than divalent metal fluorides such as FeF/sub 2/, NiF/sub 2/, and MnF/sub 2/. 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.< >
The optimum conditions for the fluorine passivation of 316L stainless steel are described. The direct fluoridation products formed at temperatures of 320 degrees C or lower are composed solely of FeF/sub 2/, while those which were formed at the temperatures of 330 degrees C or higher have a compound-phase composition of FeF/sub 2/ and FeF/sub 3/. At a critical temperature (400 degrees C for 316L stainless steel) of the thermal modification process, FeF/sub 3/ is converted to FeF/sub 2/ and disappears completely as the temperature rises. Meanwhile, CrF/sub 3/ is formed at a certain temperature (440 degrees C for 316L stainless steel). The two-phase composition gets further crystallized as the thermal modification temperature rises. As the crystal growth induces the cracks on the fluoridated film, it is very difficult to form a satisfactory passivation film from the two-phase composition by thermal modification. It is confirmed that excellent passivation film has been obtained from the single-phase composition by the optimum fluoridation following the optimum thermal modification.< >
We have studied the conductivity of extremely anhydrous hydrogen fluoride (AHF) and obtained a minimum conductivity of at 0°C. We have recognized that water in AHF at concentrations below shows an ideal dissociation and that the limiting equivalent conductance of AHF is 436 S cm2 mol−1 at 0°C. The ideal relationship between the conductivity and water concentration obtained in this work was extrapolated to the ultra‐micro water concentration region. The conductivity of corresponds to a water concentration of (0.033 ppm) in the above relationship; however, this conductivity is not due to the dissociation of water but to that of hydrogen fluoride. We recognized that the relationship between the conductivity and water concentration of AHF coincides completely with that of ultra‐pure water in the ultra‐micro conductivity region (10−8 S cm−1).
