A study of the electric field intensity distribution of a modified probe for NSOM lithography

Abstract

In this work, the shape of a near-field scanning optical microscopy (NSOM) probe was modified using the results of numerical analysis based on a finite-difference time-domain (FDTD) algorithm. This probe has a narrow slit or small tip on its aperture. Especially in the near-field area, the electric field intensity distribution is heavily dependent on the polarization of the incident light. In the plane of polarization, the electric field intensity of the NSOM aperture probe is strongly enhanced at the edge of the aperture. Simulation results show that this enhancement can be totally or partially removed according to the size of the slit, if the slit carved on the probe is aligned with the polarization direction of the incident light. When a long slit is carved on the probe, the electric field intensity of the NSOM aperture probe in the plane of polarization shows a Gaussian distribution because the points of enhanced electric field intensity are totally removed. However, when a short slit is carved on the probe, the point of enhanced electric field intensity is removed at one edge of the aperture, and consequently the electric field intensity is enhanced only at the other edge. Moreover, when a tip is put on the probe, the electric field intensity is enhanced only near the tip. This means that a higher intensity electric field can be obtained on the surface to be processed in an area smaller than the aperture size. Therefore, the modified probe is expected to improve the fabrication of extremely small patterns. Furthermore, this type of probe can be easily realized compared to any other new-type probes, because it can be manufactured directly from existing probes. ？ 2007 IOP Publishing Ltd.