Simulation Of Structure Profiles In Optical Lithography Of Thick Dnq-Novolak Based Photoresists

DNQ-Novolak based photoresists are applied in many fields of microstructure technology. A common feature of such resist structures (>10 mu m) described in the literature is a concave profile with the narrowest part at approximately 2/3 of the resist height. By newly including effects of residual solvent concentration, the simulation program accurately describes characteristic resist profiles for AZ4562 between 10 and 100 mu m resist thickness. The: program calculates the vertical distribution of the residual solvent concentration by modeling the evaporation during prebake as a three step process: diffusion of solvent within the resist film to the surface, a transfer to the ambient air described by a phase equilibrium and a transport away from the surface described by convection. Required parameters of the model have been obtained by fitting measured evaporation rates as function of time with the prebake temperature as a parameter to calculated ones. Resist exposure is simulated in vertical and one lateral dimension using the well known Dill's theory with ABC-parameters for DNQ resists. The development process is described by percolation theory where the residual solvent concentration increases the percolation parameter and therefore the local development rate. This paper describes details of the mathematical models used, demonstrates good agreement between experimentally observed profiles and simulated ones and shows that the influence of process parameters such as prebake temperature or time on resist profiles can be accurately simulated.