Simulation of near-field photolithography using the finite-difference time-domain method

Abstract

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.

Electromagnetic modeling of near-field phase-shifting contact lithography with broadband ultraviolet illumination

“…for a quasimonochromatic field, with the assumption of no dispersion. In fact, when the field is monochromatic, i.e., E (r, t) = Re Ẽ(r)exp(−iωt) , (10) yields the identity…”

A Neural Network: Family Competition Genetic Algorithm and Its Applications in Electromagnetic Optimization

“…Nowadays, with the improving performance of high-speed computing systems and progress in computational electromagnetics, the computationally intensive full-wave EM analysis (i.e. method of moments (MoM) [1], finitedifference time-domain (FDTD) method [2,3], and finiteelement method (FEM) [4][5][6]) has become practical and thus has been performed widely in microwave circuits and electromagnetic-based designs. To obtain the optimal design variables for microwave (i.e., antennas [1,[7][8][9] and filters [10,11]) and optoelectronic (i.e., optical waveguides [12] and optical fibers [13]) devices and components, the use of numerical simulation and full-wave analysis to obtain the optimal design variables has become indispensable.…”

Large-area patterning of ∼50 nm structures on flexible substrates using near-field 193 nm radiation

“…Previous FDTD simulations of near-field photolithography using transparent-mold masks also showed a strong dependence on polarization, but the contrast obtained with such masks was much lower than that obtained with the phase-shifting masks. 16 Scaling this process to even shorter wavelengths ͑e.g., 157 nm͒ should provide resolution for isolated features on the order of 35-45 nm, with dense features approaching 25 nm and likely limited by mask fabrication and resist performance constraints. The scaling of this approach to large field sizes is limited only by the size of the mask, which currently stands at printable areas of roughly 125ϫ125 mm.…”