Enhanced Dill exposure model for thick photoresist lithography

Thick photoresist lithography is one of the most important techniques for micro-electro-mechanical-system (MEMS). In order to design and manufacture the novel and complex MEMS elements with a high aspect ratio, low cost and higher efficiency, it is necessary to develop a simulation approach for the thick photoresist in lithography process. However, the nonlinear factors presented in the thick photoresist during the exposure process affect the final resist profile severely. The conventional Dill model, which is suitable for describing the thin photoresist exposure process, will cause great deviations from its experiment results when it is used directly to thick photoresist exposure process. In this paper, an enhanced Dill model for the thick photoresist exposure process is presented. This model takes into account of the effects caused by the light diffraction or the scattering in the thick photoresist and the change of photoresist refractive index in the exposure process. The exposure parameters of thick photoresist AZ4562 have been extracted by experiment measurements with the aids of theoretical analysis. The simulation results of the latent exposure profile under the different exposure conditions for photoresist AZ4562 have been given with the enhanced exposure model. (c) 2005 Elsevier B.V. All rights reserved.