Spin-Coated Periodic Mesoporous Organosilica Thin Films?Towards a New Generation of Low-Dielectric-Constant Materials

Abstract

Periodic mesoporous organosilica (PMO) thin films have been produced using an evaporation‐induced self‐assembly (EISA) spin‐coating procedure and a cationic surfactant template. The precursors are silsesquioxanes of the type (C2H5O)3Si–R–Si(OC2H5)3 or R′–[Si(OC2H5)3]3 with R = methene (–CH2–), ethylene (–C2H2–), ethene (–C2H4–), 1,4‐phenylene (C6H4), and R′ = 1,3,5‐phenylene (C6H3). The surfactant is successfully removed by solvent extraction or calcination without any significant Si–C bond cleavage of the organic bridging groups R and R′ within the channel walls. The materials have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD), and 29Si and 13C magic‐angle spinning (MAS) NMR spectroscopy. The d‐spacing of the PMOs is found to be a function of R. Nanoindentation measurements reveal increased mechanical strength and stiffness for the PMOs with R = CH2 and C2H4 compared to silica. Films with different organic‐group content have been prepared using mixtures of silsesquioxane and tetramethylorthosilicate (TMOS) precursors. The dielectric constant (k) is found to decrease with organic content, and values as low as 1.8 have been measured for films thermally treated to cause a “self‐hydrophobizing” bridging‐to‐terminal transformation of the methene to methyl groups with concomitant loss of silanols. Increasing the organic content and thermal treatment also increases the resistance to moisture adsorption in 60 and 80 %‐relative‐humidity (RH) environments. Methene PMO films treated at 500 °C are found to be practically unchanged after five days exposure to 80 % RH. These low dielectric constants, plus the good thermal and mechanical stability and the hydrophobicity suggest the potential utility of these films as low‐k layers in microelectronics.

Highly Ordered Mesoporous Organosilica Hybrid Materials

“…110 Ha and Park synthesized high quality free standing and oriented ethylenebridged thin films with a uniform thickness between 180 and 800 nm. 111 In a very recent report, Ozin and co-workers 112 have demonstrated the preparation of periodic mesoporous thin films via a spin-coating method and studied their low-dielectric constant properties, including some of the mechanical and hydrophobic properties for microelectronic applications. Hamoudi et al synthesized an arene acid-functionalized ethane-bridged periodic mesoporous organosilica (surface area = 1040 m 2 g À1 and pore diameter = 4.5 nm), which showed high acidity (H þ ¼ 1:38 mmol g À1 ) and reasonable proton conductivity (1:6 Â 10 À2 S cm À1 ) suitable for fuel cell applications.…”

Aerosol-assisted synthesis of mesoporous organosilica microspheres with controlled organic contents

“…Accordingly, the presence of organic groups in the frameworks leads to the increase in wall thickness because the volume of the ethane fragment (Si-C-C-Si in Samples 2 and 3) is larger than that of the pure silica framework (Si-O-Si in Sample 1). This would be related to the increase in pore-to-pore distance, as indicated in [42,43]. The N 2 adsorption-desorption isotherms of the PMO spherical particles are shown in figure 5.…”

Self-Structuring of Lamellar Bridged Silsesquioxanes with Long Side Spacers

“…7 Typically, BSs are synthesized by means of the solÀgel process from bridged organosilanes. Although usually obtained as amorphous materials, BSs have also been produced in the form of periodic mesoporous organosilicas 8 via the addition of external template or as nanostructured materials via self-templating effects.…”