Comparative Studies of Ultra Low- k Porous Silica Films with 2-D Hexagonal and Disordered Pore Structures
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Comparative Studies of Ultra Low-k Porous Silica Films with 2-D Hexagonal and Disordered Pore Structures Nobutoshi Fujii1, Kazuhiro Yamada1, Yoshiaki Oku1, Nobuhiro Hata2, Yutaka Seino2, Chie Negoro2 and Takamaro Kikkawa2, 3 1 MIRAI-ASET, Tsukuba, Japan 2 MIRAI-ASRC-AIST, Tsukuba, Japan 3 RCNS, Hiroshima Univ., Higashi-Hiroshima, Japan ABSTRACT Periodic 2-dimensional (2-D) hexagonal and the disordered pore structure silica films have been developed using nonionic surfactants as the templates. The pore structure was controlled by the static electrical interaction between the micelle of the surfactant and the silica oligomer. No X-ray diffraction peaks were observed for the disordered mesoporous silica films, while the pore diameters of 2.0-4.0 nm could be measured by small angle X-ray scattering spectroscopy. By comparing the properties of the 2-D hexagonal and the disordered porous silica films which have the same porosity, it is found that the disordered porous silica film has advantages in terms of the dielectric constant and Young’s modulus as well as the hardness. The disordered porous silica film is more suitable for the interlayer dielectrics for ULSI. INTRODUCTION In order to reduce interconnect delays for high-speed ULSIs, it is necessary to develop ultra-low-k materials whose dielectric constants are less than 2.5. The mesoporous silica films using a sol-gel self-assembly technique with a surfactant as the template are formed for the interlayer dielectrics (ILD). The pore structures have been controlled by the sol-gel self-assembly technique using various surfactants for forming the 2-D hexagonal, the cubic, the 3-D hexagonal and disordered phases [1-5]. A 2-D hexagonal periodic structure has been developed for ILD, however, it is difficult to control the orientation of pore channels in 2-D hexagonal porous silica films, resulting in the possibility of anisotropic dielectric constant. Therefore, a disordered mesoporous silica film, which has no periodic pore structures, was formed by controlling the static electrical interaction between the micelle and the silica oligomer. In this study, the 2-D hexagonal and disordered porous silica films were produced and compared in terms of the dielectric constant and the Young’s modulus to reveal the potential of the material as ultra-low-k dielectrics.
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EXPERIMETNTAL PROCEDURE The precursor of the 2-D hexagonal and the disordered porous silica films were synthesized based on the raw materials such as tetraethyl-orthosilicate (TEOS), ethanol, H2O, HNO3 as acid catalyst and the tri-block copolymer ((EO)x(PO)y(EO)x ; where (EO) is polyethylene oxide and (PO) is polypropylene oxide block. These surfactants, PluronicTM, such as P45 [(EO)13(PO)20(EO)13], F485 [(EO)74(PO)20(EO)74], and P103 [(EO)15(PO)55(EO)15] were employed in this study (Table 1). F485 ascertains to form the periodic pore structure by the (EO) blocks, which periodically assemble via the interaction with the silica oligomer. On the other hand, the (EO) blocks of P45 makes difficult to for
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