Synthesis of Mesoporous Organosilicate Films in Supercritical Carbon Dioxide

Abstract

ered with a thin fluorocarbon film. This wafer acted as a handling substrate for the resist. After spin-coating, the polymer was gently softbaked at 40°C to evaporate the solvent. The SU-8 was then structured by UV lithography (k= 365 nm) and post-exposure-baked at 40°C to polymerize the exposed material. Three-dimensional microsystems were achieved by adding further SU-8 layers and repeating the resist processing steps. The microdevices were finally developed in propylene glycol methyl ether acetate (PGMEA) to remove the unexposed SU-8. After development, the SU-8 structures were released from the fluorocarbon-coated handling wafer by tweezers. The fluorocarbon film exhibits low free surface energy, which reduced the adhesion between the resist and the wafer and eased the release [17]. Before the experiments for stress tailoring, the polymer structures were hardbaked in an oven at 120°C for 30 min to remove residual resist solvent, which could affect the processing. Moreover, the polymer surface was cleaned in oxygen plasma. [1] sensing and detection, [2] low-k dielectrics, [3] separation, [4] and numerous other areas. Their utility depends primarily on their framework chemistry and morphology, but in some cases pore-surface composition, periodicity of the pore structure, and long-range order are defining factors. Conventional methods for preparation are based on the cooperative assembly of network-forming precursors and structure-directing organic templates, such as surfactants or block copolymers. These methods include sol-gel processes via spin-coating [5] and dip-coating, [6] and hydrothermal processes at the liquid/air and the solid/liquid interfaces. [7] More recently, hybrid mesoporous materials functionalized with organic groups at the internal pore surfaces [8,9] or containing functional organic groups distributed homogeneously within the framework [10,11] have been prepared. Films of homogeneous composition can be directly obtained by direct cocondensation of the silica precursor, tetraethylorthosilicate (TEOS), and organosilicate precursors containing the desired functional group. Alternatively, post-synthesis functionalization of the internal pore surfaces of mesoporous materials can modify the performance of silicate materials with respect to adsorption, wetting, and catalytic properties. [8,12,13] One potential limitation is that the extent of grafting can be limited by the accessibility and number of surface silanol groups. To date, most reports deal with the synthesis of granular materials by either or both of these methods. Numerous applications, however, require uniform, defect-free films. Here, we focus on the rapid preparation of device-quality films using an alternative approach in supercritical carbon dioxide. This work significantly extends our recent report of a novel method of synthesis of ordered mesostructured films for use as low-k dielectrics by the selective mineralization of preorganized block-copolymer templates in supercritical carbon diox- COMMUNICATIONS

Single Step Preparation of Novel Hydrophobic Composite Films for Low‐k Applications

“…Such materials are synthesized typically by the traditional solgel process [3][4][5][6][7] or a template directed procedure. [8][9][10][11][12][13][14][15] Sol-gel derived silicas have a high porosity (60-90%) and offer a tunable k value, but their low mechanical stability, wide pore size distribution, and hydrophilicity limit their applications in microelectronic industry. Compared to sol-gel derived silica, surfactant-templated mesoporous silica has much more uniform and controllable pores.…”

Templating multiple length scales by combining phase separation, self-assembly and photopatterning in porous films

“…Acid catalyzed (generated by UV exposure of the photoacid) reactive modification of the polymer blend film converts part of the organic template to a silica network through exposure to precursor vapors [31,32]. This follows the experimental protocol from previous reports of using preformed polymeric templates for the synthesis of ordered mesoporous films [33][34][35][36][37][38]. The use of preformed templates enables processing of the film to alter its morphology prior to formation of the network that replicates the structure of the template.…”

Periodic Mesoporous Organosilicas

“…92 The two-step process offers the potential for exceptional control of the mesoporous film structure at multiple length scales through the preorganization and manipulation of the template prior to infusion. This process is rapid and yields uniform, defect-free films over 8 in.…”