Illuminating a transparent mold under total internal reflection condition generates evanescent light. Near-field photolithography uses such light, and we simulated this exposure in two dimensions using the finite-difference time-domain (FDTD) method. Our simulation suggests the feasibility of resolving a 130 nm pitch grating pattern, which is finer than the diffraction limit of light. The simulation results showed fair agreement with our experimental results, confirming the strong influence of exposure light polarization to the distribution of optical near fields in photoresist films. This indicates that the FDTD simulation is promising to predict exposure results for designing molds. We further extended the simulation varying the thickness and refractive index of a photoresist film. Based on the simulation results, showing the good exposure contrast in the thin surface layer of the photoresist film, we suggested two methods to resolve a thick resist film: the multilayer resist method which allows us to use a sufficiently thin photoresist film, and the surface imaging technology which can completely dry develop a thick photoresist film even if its exposure area is confined in the surface layer.
ASJC Scopus subject areas
- Physics and Astronomy(all)