Integration of fluorinated amorphous carbon as low-dielectric constant insulator: Effects of heating and deposition of tantalum nitride

We investigated the effects of heating and deposition of tantalum nitride on fluorinated amorphous carbon (a-C:F) thin films, deposited by a cosputtering process using polytetrafluoroethylene and graphite targets. Carbon is observed by x-ray photoelectron spectroscopy (XPS) in four distinct chemical states, C-C, C-F, C-F-2, C-F-3, and the relative intensity of C-F-x to C-C increases with increasing fluorine content and decreasing deposition temperature. Heat treatment of this material in vacuum up to 450 degrees C results in reduction of the intensities of C-F-x relative to that of C-C. The predominant desorbing masses detected by a mass spectrometer were consistent with CF3, CF, C3F5, CF2, COF, COF2, and Ar. The temperature at which desorbing CFx species are detected increases with decreasing fluorine concentration and increasing deposition temperature. This improved thermal stability is attributed to the decreasing amount of volatile, small molecular weight CFx species and more C-C crosslinking in the less fluorinated film. To integrate with copper metallization, the interface between a-C:F and tantalum nitride was studied by depositing tantalum nitride on a a-C:F films and monitoring the interfacial chemical reactions in situ using XPS. Substantial defluorination was observed upon deposition of tantalum nitride. This leads to the formation of tantalum fluoride, whose relatively high vapor pressure and susceptibility to hydrolysis could lead to delamination. (C) 1999 American Vacuum Society. [S0734-2101(99)06505-7].