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The growth of heteroepitaxial yttria-stabilized zirconia (YSZ) has attracted considerable attention over the past 15 years due to its usefulness as a heteroepitaxial buffer layer. A specific example of its utility is in the growth of yttrium barium copper oxide (YBCO) on Si substrates. 1 Direct contact between the Si substrate and the YBCO film results in interdiffusion of components, which will spoil the superconducting properties of the YBCO film. The YSZ material forms an effective chemical buffer layer separating the Si substrate and the oxide superconducting film, while still permitting the transfer of the crystalline template structure to the superconducting film. The YSZ material film has also been used in superconductor material combinations that utilize substrate materials other than Si; e.g., rolling assisted biaxially textured Ni substrates. Another application for epitaxial YSZ material is in the formation of silicon-on-insulator (SOI). 3,4 The YSZ material is an effective electrical insulator with a relative dielectric constant of 27 at a frequency of 10 GHz. In theory, a top Si epitaxial layer can be regrown on the YSZ film to form the SOI structure. This could be performed on blanket wafers or accomplished later in the fabrication process to form isolated islands on the chip surface. Another application involving the dielectric properties of YSZ is in the formation of advanced dielectrics for dynamic random access memory devices. 5 The diffusivity of O 2 in YSZ is very high, and it is possible to grow a thermal oxide on the Si surface, subsequent to the growth of a YSZ film. The YSZ/SiO 2 sandwich structure combines the high electrical permittivity of the YSZ layer with the effective passivation of a thermal SiO 2 layer.To date, single-crystal YSZ films have been deposited on Si substrates by a variety of techniques including ion beam sputtering, 6 electron beam evaporation, 7-9 pulsed laser deposition, 10-12 reactive sputtering, 13 and metallorganic chemical vapor deposition. 14 An important component of these investigations has involved the development of a model which describes the growth of the YSZ material film at its initial stages on the Si substrate. Previous discussions were often concerned with the presence or absence of a silicon oxide film on the Si surface prior to film growth. In this investigation, the oxide layer has been shown to be essential for the heteroepitaxial growth process. Further, once epitaxial growth is established in a thin seed layer, subsequent epitaxial material can be deposited at temperatures as low as 200ЊC. ExperimentalThe YSZ thin-film samples were deposited by a reactive sputter process in an electron cyclotron resonance (ECR) reactor. Briefly, an Ar plasma stream generated in a broad beam ECR reactor was directed at the Si substrate located in the downstream position. The YSZ material was sputtered from a radio frequency (rf) coupled magnetron sputter gun located above the substrate. This apparatus was used previously to perform a similar investigation on the...

During technology development, the study of ultra low-k (ULK) TDDB is important for assuring robust reliability. As the technology advances, several critical ULK TDDB issues were faced for the first time and needed to be addressed. First, the increase of ULK leakage current noise level induced by soft breakdown during stress was observed. Second, it was found that ULK had lower field acceleration than dense low-k. Such process and material dependences of ULK TDDB kinetics were investigated, and an optimal process to improve ULK voltage acceleration was identified. Last, as the reliability margin for ULK TDDB of via-related structures is greatly reduced at advanced CMOS technologies, a systematic study of via TDDB regarding area scaling and test structure design was conducted. It was found that only a portion of the total vias possibly determines the low-k via TDDB. A new "fatal" via ratio concept is introduced to replace the as-designed area ratio for TDDB area scaling in structures with vias, and a methodology called shift and compare (S&C) is proposed to determine the "fatal" via ratio.Keywords -time-dependent dielectric breakdown, low-k soft breakdown, Cu interconnect, low-k hard breakdown, reliability, Schottky emission, Poole-Frenkel, low-k TDDB voltage acceleration, low-k via TDDB, I-V conduction slope

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