The near-field power density distribution characteristics for different types of optical fiber probes

When the mechanism of near-field photolithography is analyzed, the most important work is the near-zone field analysis of the optical fiber probe. In this paper, the electromagnetic theory for near-field radiation using the magnetic current and electric current as sources is adopted as the model of the near-field optics. By applying this theorem, the near-field distribution characteristics of the uncoated probe and metal-coated probe are explored. Furthermore, the simulations of the near-field for different light source, such as parallel beam of light (plane wave) and Gaussian-distributed light passing through the optical fiber probe are also discussed. Based upon the model of this research, the time-average Poynting vector distribution of the radiation field, and the relationship between the power density and near-field distance for the optical fiber probe can be estimated. According to the results, when the near-field distance between the metal-coated probe and sampling is maintained at 0.3ρ₀≤Z≤0.6ρ₀, the process is proved to be more adequate for the near-field photolithography. Meanwhile, from the analysis of the near-field power density distribution, it provides an evaluation of concentration of photo active compound (PAC) in the photoresist after exposure and contour after development. The relationship between the power density and near-field distance can be used as a rule of tip-sampling distance modulation when controlling the magnitude of exposure energy. This near-field photolithography engineering perplexity encountered can therefore be solved.