Nanoporous Thin Films with Hydrophilicity-Contrasted Patterns Ho-Cheol Kim,* Cortney R. Kreller, Kiet A. Tran, Vikram Sisodiya, Sarah Angelos, Gregory Wallraff, Sally Swanson, and Robert D. Miller IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 Received January 23, 2004. Revised Manuscript Received July 15, 2004 We report a simple and effective method to generate hydrophilicity-contrasted patterns on porous thin films containing nanometer sized pores. The porous thin films were prepared by removal of the organic polymer phase, denoted as porogen, from the nanohybrid of poly (methylsilsesquioxane) (PMSSQ) and the porogen where nanoscopic porogen domains are phase separated and entrapped in cross-linked PMSSQ matrix. Selective masking the UV radiation during UV/ozone treatment produces patterns of contrasted hydrophilicity. Hydrophilic patterns with resolution of ∼4 μm surrounded by hydrophobic regions were obtained by this patterning process. The nanoporous structure of patterns provides higher number density of reaction site, which was proved by the enhanced intensity of a fluorescent dye attached on patterns. Introduction Arrays of patterns containing different bioactivities enable rapid evaluation of complex bioevents and have quickly developed into an important tool in life science research. 1-3 Because of the aqueous environment, pat- terned media having hydrophilicity contrast (i.e., hy- drophilic regions surrounded by hydrophobic areas and vice versa) are ideal for confining bioactivity to within discrete regions. A few methods including traditional lithographic methods, imprinting, and contact printing have been previously used to generate hydrophilicity- contrasted patterns on substrates. 4-6 The common feature of these methods is to deliver and tether hydrophilic (or hydrophobic) molecules to the predefined regions (by mask, template, or positioned pipet) that is surrounded by hydrophobic (or hydrophilic) regions. These methods generally involve, however, a series of materials (such as photoresists, elastomers, etc.) and process steps. A simple and more effective route to generating arrays of patterns with hydrophilicity con- trast is highly desirable. Further, to reduce the overall size of an array while maximizing the number of reaction sites within the pattern and minimizing the required reagent and sample volume, substrates con- taining high surface area are also desirable. Porous materials containing nanometer sized pores are very attractive due to their potential for numerous applications including optical components, low-dielectric- constant (low-k) interlayer materials for interconnects in semiconductors, nanoscopic chemical reactors for catalysis, biotechnology, and so on. In the microelec- tronics area, effort has been devoted for developing nanoporous dielectrics to achieve better insulation between the Cu wires in back-end-of-line (BEOL) struc- tures for next generation semiconductors. A simple and effective route to thin films containing nanometer-sized pores has been developed at IBM, which utilizes phase separation of a two-component system where one com- ponent (e.g., an organosilicate matrix) cross-links into a network effectively limiting domain growth and coarsening of the porogen phase (an organic, polymeric component) that is ultimately removed from the film by thermolysis. 7-9 For this approach, the morphology of the nanohybrid, where the phase-separated porogen do- mains are entrapped within matrix materials, and hence the final morphology of pores, is strongly depend- ent on the interaction between porogen and matrix and the molecular weight, molecular architecture, and load- ing level of porogens. Poly (methylsilsesquioxane) (PMSSQ) has been rec- ognized as a promising matrix material for low-k dielectrics and studied extensively. Thermally cross- * To whom correspondence should be addressed. E-mail: hckim@ us.ibm.com. Phone: (408) 927-3725. 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Mater. 2004, 16, 4267-4272 10.1021/cm049866k CCC: $27.50 © 2004 American Chemical Society Published on Web 10/01/2004