Determination of the electrical properties of 2.5 nm thick silicon-based dielectric films: thermally grown SiOx

Ultra-thin (<5 nm thick) thermal oxide and oxynitride films with different compositions are candidates for complementary metal/oxide/semiconductor tec hnology in ultra-large-scale integration (ULSI) applications. The latter ar e expected to offer the best compromise between nitrides and oxides. The ai m of this work is to measure the electrical properties of a leaky 2.5 nm th ick thermally grown oxide film using the high frequency capacitance-voltage (HF C(V)) measurements. The cleanliness and the surface roughness of the S i(1 0 0) surface were measured prior to in situ oxidation by means of, resp ectively, Auger electron spectroscopy (AES) and atomic force microscopy (AF M). The physical-chemical properties of the thermal oxide film were measure d by AES (film thickness, composition), Fourier transform infrared spectros copy (FTIR) (composition, vibration modes), cross-sectional transmission el ectron microscopy (TEM) (film thickness, homogeneity) and electron energy l oss spectroscopy (EELS) (gap width determination). The results are compared to those obtained for the native oxide film and a chemical oxide film. The latter was first grown on the silicon substrate to prevent contamination a nd surface disorder after flash heating in vacuum prior to oxide growth. Th e substrate Si(1 0 0) surface cleaned in ultra-high vacuum (UHV) was then o xidized in a 10(-3) mbar oxygen (O-2) gas pressure at 900<degrees>C to get the 2.5 nm thick oxide him. The grafting of a self-assembled insulating mon olayer (SAM) of organic molecules on the grown oxide film permits us to obt ain analysable capacitance as a function of voltage data. Indeed, this mono layer made up of octadecyltrichlorosilane molecules leads to a reduction of the leakage current through the aluminium/self-assembled monolayer/oxide/s ilicon hetero structure. The resulting current as a function of voltage dat a were compared to those of a standard 2.5 am thick oxide him. The method p roposed here to extract the electrical parameters of the thermal oxide film is demonstrated to be valid. We show mainly that the reduction of the leak age current through the aluminium/self-assembled monolayer/thermal oxide/si licon heterostructure is seven orders of magnitude bigger than in the case of the native oxide film. (C) 2001 Elsevier Science B.V. All rights reserve d.