Journal of the Microscopy Society of Thailand 24 (2), 108-111 (2010) 108 Laser Interference Lithography for Photonic Crystals Template B. Saekow 1,4 , S. Rahong 2,4 , A. Pankiew 1,3,4 , R. Sanboontan 3,4 , W. Bunjongpru 1,3,4 , G. Tumcharern 2 , C. Hruanan 3 , A. Poyai 3 , S. Porntheeraphat 3,4* and J. Nukeaw 1,4 1 College of Nanotechnology, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road,, Ladkrabang, Bangkok, 10520 Thailand 2 National Nanotechnology Center (NANOTEC), 111 Thailand Science Park, Pahonyothin Road, Pathumtani, 12120 Thailand 3 Thai Microelectronic Center (TMEC), National Electronics and Computer Technology Center (NECTEC), Chacheongsao, 24000 Thailand 4 ThEP Center, CHE, 328 Si Ayutthaya Road, Bangkok, 10400 Thailand 5 National Electronics and Computer Technology Center (NECTEC), 112 Thailand Science Park, Pahonyothin Road, Pathumtani, 12120 Thailand *Corresponding author, e-mail: supanit.porntheeraphat@nectec.or.th Abstract Laser interference method is successfully used as the efficient tool for photonic crystal template patterning. This technique can produce a sub-wavelength grating within a large area. The interference angles are chosen at 10 and 15 degrees in order to produce 850 and 1300 nm of grating period. The surface morphology of fabricated templates was characterized using Field-Emission Scanning Electron Microscope (FE-SEM) and Atomic Force Microscope (AFM). This template is used as a master mold for polydimethylsiloxane (PDMS) duplication. The photonic crystals device is obtained by evaporation of TiO 2 thin film on PDMS-grating which have advantages for optical biosensor applications. Background Currently, photonic crystal label-free optical biosensors have been demonstrated as a high resolution device for a diversity of cell assays and biochemical detection [1, 2]. The device comprises of a sub-wavelength grating and a waveguide which can be embedded within a same layer[3]. Due to its guided mode resonance effect, the structure behaves as a narrow-band-reflection filter. At resonance, it is able to totally reflect light with very high wavelength selectivity. That makes this device highly sensitive to the change on the device’s surface and giving a high resolution bio- sensor device. With the small feature size periodic pattern, it requires fabricating using Electron Beam Lithography (EBL), or Focused Ion Beam (FIB) lithography which takes long time to produce pattern and is a very expensive techniques. Here, laser interference lithography [4] is used as an alternative approach to produce the photonic crystals template, as it is a fast and low-cost technique that can produce a sub-wavelength grating within a large area. The grating period can be achieved down to one half of the laser wavelength that used to produce the pattern. Using a He-Cd laser with 442 nm wavelength, it is able to generate the grating with the period down to 221 nm, for example. In this work, the photonic crystal template was fabricated using a laser interference process to generate a grating pattern on a photoresist film coated on a silicon (Si) substrate. Field-Emission Scanning Electron Microscope (FE-SEM) and Atomic Force Microscope (AFM) are suitable tools to investigate the quality of fabricated template. Materials and Methods All grating templates have been prepared on Si substrates. The Si substrate was first spun with adhesive primer (HMDS) then the photoresist (PR) (AZ 6112) was applied with 3000 rpm. The coat silicon was baked at 100°C for 30. After spinning process, the deposited PR film was exposed to HeCd laser lithography. The grating pattern was optically inscribed onto the PR film using a He-Cd (λ=442 nm) laser interference lithography system as shown in Fig. 1. The period of the grating ( Λ ) is controllable through the interference angle (θ=θ 1 =θ 2 ) and the wavelength of the laser (λ) that can be written as θ λ sin 2 = Λ . (1) The interference angle (θ) of our experiment was set at 10 and 15 degree. From Eq.1, at θ=10° and θ=15°, the calculated grating periods are ~1300 and 850 nm, respectively.