Sputtered Al-Nd alloy films were anodized in nonaqueous electrolyte solutions at various current densities, on which the amounts of incorporated carbon species into the oxide films depend. The resultant oxide films were characterized by Fourier transform infrared ͑FTIR͒, cross-sectional transmission electron microscopy ͑XTEM͒, and secondary-ion mass spectroscopy ͑SIMS͒. Electrical properties such as relative permittivity and dielectric strength were also measured for these films. The FTIR peak position associated with Al-O stretching vibration was correlated with the relative permittivity and dielectric strength of the anodic oxide film. Since the peak position is dependent on the condition of anodization, FTIR measurement will be useful in developing high insulating oxide films for microelectronic devices.Aluminum metal and its alloys have begun to be widely used for the production of high quality thin-film transistor liquid crystal displays, because high resolution and large screen size panels require a low resistivity interconnection material. However, aluminum interconnects have a serious problem of hillock formation during heating. Recently, it was suggested that hillocks are considerably suppressed by adding a small amount of neodymium. 1,2 Thereafter, Al-Nd alloy has become one of the best interconnection materials for high quality liquid crystal displays. The processes of covering aluminum interconnects with various overlayers have been developed to suppress hillocks. 3-7 Among such overlayers, Al 2 O 3 films formed by anodization suppress hillocks effectively. Moreover, anodic films have very low pinhole density. Therefore, it seems better to use an Al-Nd alloy for interconnection material and an anodic alumina for its cap overlayer. For anodizing aluminum interconnects, a mixture of tartaric acid aqueous solution and ethylene glycol neutralized with an ammonia aqueous solution have been used as an electrolyte solution, since the resultant films have good electrical properties. 5-7 However, in relation to the design of thin-film transistor devices, further improvement is still required.We have reported on the anodization of pure aluminum and aluminum alloys in nonaqueous electrolyte solutions. 8-11 When anodizing aluminum in nonaqueous electrolyte solution, carbon species originating from the electrolyte solution incorporate into the anodic oxide film. Using an aqueous electrolyte solution, which contains organic anions, carbon species also incorporate into the anodic film, but the amount is much smaller. 11 The electrical properties of the anodic oxides were highly affected by the incorporated carbon species, even when the amount of carbon incorporated was relatively low. 10,11 Therefore, it is important to control the amount of carbon incorporated by anodization condition, when an anodic oxide film is used as the overlayer of interconnects. In this study, insulating properties of anodic films formed in nonaqueous electrolyte solutions at various forming current densities were examined.
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