7.2 Development

The final step of the lithography simulation flow depicted in Figure 3.1 is the calculation of the developed resist profile. The resist development process can be considered a surface-rate limited isotropic etching reaction [135], whereby the resist and developer chemistry as well as the PAC concentration at the surface exposed to the developer controls the rate. Since the chemistry is held constant during the simulation the PAC concentration solely determines the rate. The input for the development module is thus the latent bulk image that is either directly obtained from the exposure/bleaching module or after an intermediate post-exposure bake simulation. Generally, the development simulation consists of two distinct tasks, namely the calculation of the development rate providing inherently the linking of exposure and development modules and the advancement of the surface according to this rate. Thereby two totally different simulation challenges are faced: On the one hand, a physically meaningful model for the reaction mechanisms is required, on the other hand, the movement of the very complex surface is especially in three spatial dimensions, an extremely demanding problem. We start with the description of the most common rate models, and then proceed with a description of the used surface advancement algorithm.