Mesoporous Low Dielectric Poly(silsesquioxane) Thin Films Templated by Various Surfactants
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Mesoporous low dielectric poly(silsesquioxane) thin films templated by various surfactants Jingyu Hyeon-Lee *, Jong-Baek Seon, Myungsup Jung, Jongmin Kim Materials Laboratory, Samsung Advanced Institute of Technology, Suwon, 440-600, South Korea ABSTRACT Mesoporous low dielectric poly(silsesquioxane) thin films have been fabricated by templating various surfactants such as cetyltrimethyl ammonium bromide (CTAB) or 4octylphenol polyethoxylate (OPE) in the silsesquioxane polymer matrix and their properties of the thin films characterized by electrical, mechanical and structural characterization. Depending on the types of the surfactants, mesoporous poly(silsesquioxane) thin films with different porosities have been formed. The dielectric constant (k) of the films depended on the content or porosity of the surfactants. The dielectric constants of ca. 2.2 - 2.4 were obtained for the films with relative porosities of about 15 – 30 vol. % to the polymer matrix itself. The elastic modulus of the films showed a dependency on the type, content of the surfactants and was ca. 2.9 GPa with the k value of ca. 2.38. INTRODUCTION As the minimum geometry of microelectronic devices continues to shrink, it results in problems with interconnect resistance-capacitance (RC) delays, signal crosstalk, and power consumption [1]. To reduce such problems, new materials with a low dielectric constant, 2.02.5 for feature dimensions below 0.15 micrometers, are greatly needed for future integrated circuit process technologies. Besides their ultra low dielectric constants, good mechanical strength is greatly demanded. Nanoporous low dielectric thin films can be prepared usually by molecular templating approaches, which employ removable pore generators (porogens) such as hyperbranched polycaprolactones [2], block copolymers [3] and surfactants [4] inside a curable resin. The porogen leaves pores following its thermal decomposition, ultimately forming porous solid films. Owing to the porous nature of the low-k films, their mechanical strengths are sometimes insufficient. However, a high mechanical strength is an important requirement for integrated the dielectric film into back-end processes such as chemical mechanical polishing (CMP). Such a factor as porosity is critical, affecting the dielectric constant and mechanical properties of the film. Tuning such a factor may enhance or improve mechanical properties.
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In this study, we have prepared spin-on mesoporous films by using the CTAB or OPE as a template. The templates were removed by curing the films. The resulting mesoporous films exhibit low dielectric constants, within the range of 2.2 to 2.4, with good mechanical strengths. EXPERIMENTAL DETAILS 5.2 g of methyltrimethoxysilane, 3.2 g of 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetra (trimethoxysilylethyl) cyclotetrasiloxane, 100 ml of tetrahydrofuran, and 1.1 mM of diluted HCl were mixed, and reacted at 70 oC for 16 hours [5]. White powder was obtained after purification and drying process [5]. The CTAB/OPE was used as a molecular t
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