(512a) Patterning of Mesoporous Silica Thing Films Using Traditional Photolithography Techniques

Authors: 
Luebbers, M., University of Illinois
Jeong, H. K., Texas A & M University
Masel, R. I., University of Illinois at Urbana-Champaign


Since the invention of mesoporous silicate materials nearly 15 years ago by Mobil Oil Corporation, there has been a surge in subsequent research trying to optimize and take advantage of the material's unique properties. It is not unusual for this family of materials to possess an extremely high specific surface area (1000 square meters per gram) and a high specific volume (1.5 cubic centimeters per gram). Most intriguing is perhaps the ability to create well-ordered materials with highly tuneable nanopores in the range of 2 to 50 nanometers and the ability for the surface to be chemically functionalized. Thin films of the material have been synthesized for around 10 years and several applications have been proposed. These applications involve optical devices which take advantage of the low-k dielectric properties, host material for nanosensor arrays, molecular sieves, and as adsorbent materials. For most applications of this material there is a demand for open accessible pores and for the ability to pattern or selectively deposit on a surface. The nanoscale self-assembly fabrication in combination with microscale patterning provides an opportunity to produce precisely patterned materials on multiple scales. Although there have been several attempts and some successes at patterning mesoporous silica, each of the previous attempts involves either severe limitations in the minimum feature size or require complex processes with extreme limitations in reproducibility.

This presentation involves a technique that combines commonly available photolithography equipment in combination with an aerosol-assisted deposition technique. Small droplets of the silica precursor sol are allowed to gravitationally settle on a developed photoresist pattern and spontaneously undergo Evaporation-Induced Self-Assembly to form the ordered mesoporous materials. The photoresist pattern and the selected areas of mesoporous silica are then selectively removed via a standard ?lift-off? procedure, leaving behind a patterned area of mesoporus silica thin film. Both water-based and ethanol-based precursor solutions are explored along with the usage of various surfactants to tune the size of the pores. Photoresist treatment before deposition is explored for some cases as well as techniques used to strip off the PR afterwards. Optical microscope images and SEM images of the patterned films are taken to record the pattern quality. High-resolution FE-SEM and TEM used in combination with X-ray techniques is used to probe the film microstructure.