Simulation of mask proximity printing

The paper presents a simulation approach for mask proximity printing. The simulation steps include image formation in air and in photoresist, post-exposure bake, and chemical development and analysis of resist profiles. The intensity distribution in air and in resist in proximity distance from the mask is described by a fast frequency domain method, that is based on scalar diffraction analysis. The accuracy and the performance of the method are compared with rigorous electromagnetic field computations that take mask topography effects and the finite conductivity of absorber materials into account. The computed intensity distributions inside the resist are coupled to an established standard simulation flow, which is also used in the simulation of projection printing. The resulting resist profiles can be evaluated in terms of linewidth, sidewalls, and other parameters. Finally, an application of the simulation procedure for the simulation of process windows and optimization of linewidth biasing is shown.