Highly-Insulating Ultra-Thin SiO 2 Film Grown by VUV Photo-Oxidation
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Highly-Insulating Ultra-Thin SiO2 Film Grown by VUV Photo-Oxidation Atsuyuki Fukano and Hiroyuki Oyanagi National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan ABSTRACT Insulating performance of high-density SiO2 films on Si(100) wafer grown by VUV irradiation in oxygen atmosphere at low-temperatures (300 ~ 400 °C ) is reported. Comparing the SiO2 films grew with various wavelength irradiation, i.e., 126, 172 and 222nm, we found a strong wavelength dependence in density and insulating performance. The results suggest that electrical characteristics are highly correlated with film density. Higher density films are formed by shorter wavelength photo-oxidation whereas higher breakdown voltage and lower leakage current are achieved by the dense films. This shows that lower density of defects, dangling bonds, existing at the Si-O interface strongly affects the insulating performance. VUV photo-oxidation is a promising silicon oxide growth technique with greater insulating performance beyond the conventional limit for thermally oxidized films. INTRODUCTION In recent years, tracking Moore’s law became a subject of growing concern in silicon technology. As a result of rapid miniaturization of semiconductor devices, serious problems have emerged e.g., increasing heat power because of exponentially increasing number of transistors, leakage tunneling current from source to drain due to short channel distance, as gate dielectric film thickness and length scale are both miniaturized. The ITRS (International Technology Roadmap for Semiconductor) published their assessment of the semiconductor technology requirement. The specification of semiconductor devices required is becoming hard every year, as thickness of gate dielectric oxide layers approaches that of the sub-oxide layer (about 1 nm). For instance, the gate dielectric film of high-performance logic devices case, e.g., 1.3 nm physical oxide thickness, is required to have leakage current density of 2.2 × 102 A/cm2 at 1.2 Volt, 1.0 nm is 6.0 × 102 A/cm2 at 1.1 Volt [1]. The gate dielectric materials which are intensively studied are high-k and nitride materials. Among candidate high-k dielectric materials, HfO2 family is focused on. However, these materials have a problem to be solved e.g., mismatching of phase boundary, micro-crystalline growth, lateral oxidization for gate edge, lower mobility, fixed charge and flat-band shift, lower reliability, and so on. Meanwhile, high quality silicon dioxide film attracts attention as a material filling the gap between the conventional oxide films and high-k materials. The conventional thermally grown-oxide film accompanies a sub-oxide (SiOx) layer know as the transition layer. Defects (oxygen vacancy) leaving silicon dangling bonds degrades the insulation performance. Efforts were taken to improve the quality of thermally oxidized SiO2 films, e.g., the rapid thermal, ISSG (in-situ steam generation) [4] oxidizing method and plasma oxidization are studied. We repo
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