Numerical optimization of illumination and mask layout for the enlargement of process windows and for the control of photoresist profiles in proximity printing

Abstract

Although proximity printing is the oldest and, in view of the basic optical setup, simplest photolithographic technique, it still remains in heavy use in the semiconductor manufacturing industry. The fact that this technique exists for a long time does not mean that there is no more room for improvements or new applications. Lending concepts developed for modern projection scanners and steppers and adapting them for our purposes, we demonstrate how numerical simulation and optimization can help to make the proximity printing process more stable against process variations and to increase the resolution for critical features. For this purpose, we numerically optimize the angular spectrum of the illumination and the mask layout. Furthermore, we couple the optimization of the optical degrees of freedom to the simulation of photoresist development to assess the effects of changes to the illumination and mask on the final photoresist profile

High-resolution proximity lithography for nano-optical components

“…These techniques work best in combination with adapted configurations of incidence angles (pupil maps) which can, for example, accentuate features with a specific critical dimension or enhance edges in matched orientations. Motzek and Erdmann have investigated in-depth the prospects of this method [170][171][172][173][174] and clear improvements with respect to aerial image quality and process latitude have been demonstrated. Since the divergence of light which propagates from the photomask to the substrate is, however, just slightly affected by OPC; no significant reduction of transferable minimum feature size compared to shadow printing can be realized.…”

Using computational methods for mask aligner lithography

“…The basic idea is to adapt OPC techniques for mask aligner lithography and to use assist structures on the mask to compensate for unwanted distortions of the design pattern during lithographic exposure. 7 Figure 3 shows a comparison between the simulated light-intensity distribution and experimental photoresist profiles demonstrating the effect of placing assist structures at different positions on the mask.…”