Analysis of the diffraction pattern for optimal assist feature placement

In this paper, a method will be detailed to optimise the placement of the AF. For the purpose of this study, the diffraction pattern induced by the insertion of one or several AF is analysed in frequency space. This analysis details the evolution of the intensity of even and odd orders during the insertion of AF. The calculation of the optimum placement is detailed, and the DOF resulting from the insertion of one or more AF is also presented.