Periodic 3D Structures Prepared by Photolithography
- PDF / 300,161 Bytes
- 1 Pages / 612 x 792 pts (letter) Page_size
- 21 Downloads / 209 Views
RESEARCH/RESEARCHERS Periodic 3D Structures Prepared by Photolithography Methods for large-scale production of micron-sized periodic structures are of great interest for the manufacture of photonic crystals, membranes, data-storage materials, and catalyst supports. Recently, Shu Yang and co-workers at Bell Laboratories, Lucent Technologies and Princeton University have demonstrated a photolithographic method for producing organic epoxy structures in an area larger than 1 mm in diameter. The structures have hexagonal, square, or fcc symmetries with periods of 0.9–8 µm. The symmetry and periodicity of the structures were templated by the interference pattern of continuous-wave (CW) laser radiation in the visible wavelength range. According to Yang, “the use of CW visible laser radiation results in a manufacturing speed and structure size advantages over two-photon infra red and pulsed ultraviolet interference photolithographic methods, respectively.” As described in the July issue of Chemistry of Materials, the researchers controlled the acid catalyzed polymerization of the Epon SU-8 epoxy monomer through the use of 2,4,5,7-tetraiodo-6-hydroxy-3-fluorene as the photosensitizing dye, diaryliodionium hexaflouroantimonate as the photoacid generator, and triethylamine (TEA) as the photoacid neutralizer. These reagents were mixed in tetrahydrofuran and spin-cast onto a cover glass to produce a solid 4–10-µm-thick resist film. The researchers initiated polymerization by irradiating the resist for 1 s with three or four non-coplanar beams of 514-nm Ar ion laser radiation to produce localized photoacids, and polymerization was chemically amplified when heating at 65°C. The triethylamine played a key role in the resist to neutralize the background photoacids and to increase the sharpness of the structure features. Following polymerization, the structure was washed with propylene glycol methyl ether acetate to remove the unexposed film, and dried in supercritical CO2. Scanning electron microscopy was used to confirm the formation of the highly periodic structure of the specified size and symmetry. The use of visible laser radiation in the photolithographic process resulted in higher substrate penetration efficiency and more even intensity distribution than UV radiation. This allowed for the production of larger structures and structures with fewer defects. The number of defects was further reduced by the inherent stability of CW radiation. Visible radiation also allows CW lithography to be used on a wider range of substrates than does UV radia662
tion. The researchers were able to alter lattice constants, porosities, and symmetry of the lattice by varying TEA concentrations, exposure times, laser intensities, beam orientations, and beam polarizations, and by using a laser mask. GREG KHITROV
Polymer Molds Replicate Micropatterns to Ceramic Surfaces Micropatterning of ceramic surfaces is becoming increasingly important in ceramic manufacturing. Micropatterned components make it possible to integrate more entities into a small
Data Loading...
