Ultra Thin Cu film Fabrication by Supercritical Fluid Deposition for ULSI Metallization
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Ultra Thin Cu film Fabrication by Supercritical Fluid Deposition for ULSI Metallization Takeshi Momose1, Masakazu Sugiyama2, and Yukihiro Shimogaki1 1 Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan 2 Institute of Engineering Innovation, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
ABSTRACT Initial nucleation and succeeding coalescence in supercritical fluid deposition (SCFD) of Cu was studied in situ by using our devised monitoring technique, i.e. surface reflectivity measurement of visible white light. Fabrication of 10nm-thick smooth and continuous Cu film required by ULSI metallization, was succeeded. Complete filling without any seems and voids into various via patterns of 50 - 200 nm in diameter and 1 µm in depth was also achieved, which was revealed through angled polishing of patterned substrate. INTRODUCTION Cu is employed for a current ULSI interconnects material largely due to its low electrical resistivity and higher electromigration resistance than Al lines. Interconnects are assembled through damascene process, which involves Cu seed-layer formation by sputtering followed by gap-filling by electro plating into high aspect ratio features [1]. The poor step coverage by sputtering is unacceptable for features with high aspect ratio of over 5. Cu thin film depositions which enable conformal deposition onto highly complex features are getting significant attention. Supercritical fluid deposition (SCFD), which is a reduction of metal organics with H2 in supercritical CO2 (scCO2), may be a promising technology in ULSI Cu metallization because of its conformal deposition and superior gap filling [2-3]. The characteristics of SCFD come from the superior properties of supercritical fluid. For example, gas-like diffusivity of scCO2 enables excellent step coverage. Liquid-like solubility of scCO2 enables high precursor concentration, which may induce high number density of initial nuclei advantageous for making ultra thin film. Liquid-like solubility of scCO2 also enables wide range of applicable precursor [4]. Hence, SCFD is expected as a novel one-step Cu interconnects fabrication process, i.e., an alternative technology of seed layer formation by sputtering and gap-filling by electro plating due to its potentials of conformal deposition and superior gap-filling. Because Cu via size will shrink less than 50 nm [5], ultra thin, smoth, and continuous Cu film should be formed at initial growth stage in gap-filling to prevent pinch-off voids. And thus, controlling the initial nucleation and succeeding coalescence in Cu-SCFD is a key factor. To date, however, investigation of this matter has not been reported yet due to large difficulty by ex situ analysis. We developed in situ monitoring method by detecting reflected visible light spectroscopy during deposition, and found reflectivity at wavelength of 770 nm can clearly monitor the initial nucleation and succeeding coalescence in Cu-SCFD [6]. In this study, we appli
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