Characterization of High-k Dielectric Films with Tunneling AFM
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Characterization of High-k Dielectric Films with Tunneling AFM Xiang-Dong Wang, Joe Kulik, N. V. Edwards, S. B. Samavedam, and Shifeng Lu Advanced Products Research and Development Labs (APRDL), Motorola Inc, 2100 E. Elliot Rd. Maildrop EL622, Tempe, AZ 85284
ABSTRACT In this paper, we report the leakage current characterization of HfO2 high-k dielectric thin films by using tunneling AFM, which utilizes a conducting AFM probe to detect current passing through the sample and the probe while simultaneously acquiring a topographic image. We have studied tunneling current behavior of HfO2 films by characterizing the hot spots, which are characterized by excessive local leakage current, as well as the overall current distribution. Tunneling AFM results show sensitive dependence of tunneling current with variation of film thickness. The current distribution can be described approximately by a log-normal distribution, which is consistent with the characteristics of the thickness variation. Furthermore, the film structure and thickness were also characterized with TEM and spectroscopic ellipsometry.
INTRODUCTION As the Si CMOS technology scales down to sub-90 nm regime, it is inevitable that the SiO2 gate dielectric will be replaced with other high-k dielectric materials to counter excessive leakage current through tunneling. However, many challenges remain in the search, processing and integration of such a material into the chip manufacturing process [1]. To achieve these goals, it is essential that the material is properly characterized structurally and electrically. Since the purpose to introduce high-k dielectric is to reduce the leakage current in such small devices, it is crucial to characterize defects and tunneling behavior on a sub-micron scale. Isolated defects or local thinning of the dielectric can result in regions with a high local gate leakage, referred to as hot spots. The current leakage from such hot spots can typically be significantly higher than the average leakage current density measured over large areas. It is important to develop techniques to characterize these defects since they might critically impact dielectric reliability. Tunneling atomic force microscope (AFM) has been successfully used to study leakage mechanism of thin dielectric films including SiO2 and high-k dielectric films [2-5], dielectric breakdown processes and mechanisms [6-8]. In this paper, we report the tunneling current characterization of HfO2 films, one of the more promising high-k dielectric candidates, using this technique. By using tunneling AFM, we have studied tunneling current behavior of HfO2 films of varying thickness. Hot spots, which are characterized by excessive local leakage current, were also characterized and are correlated with the surface topography. Furthermore, the film thickness and structure were also characterized with TEM and spectroscopic ellipsometry (SE). Tunneling AFM results show sensitive dependence of tunneling current with variation of film thickness. The current distribution can be d
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