Design of phase-shifting masks for enhancing resolution of images in optical lithography

摘要

The problem of optimal design of phase-shifting masks for enhancing resolution of images in optical lithography is examined based on the general theory of amplitude-phase retrieval in coherent optical system. We propose a practical algorithm used for the design of phase-shifting masks. To illustrate the new approach the numerical simulation designs of the phase-shifting mask are carried out for several mode images, for instance, one-dimensional (1-D) equal-spacing lines and two-dimensional (2-D) model patterns. We find that for 1-D model images, the optimal phase distributions are automatically taken binary values, 0 and pi, between the consecutive lines. For the 2-D model images, the complicated contructions contained in the object patterns can be resolved very well by using the designed phase-shifting mask. In the new approach the phase modulation in the masks is required to encode only the clear regions of object patterns. Therefore, the new approach may provide an effective scheme for implementing systematic optimal design of phase-shifting masks used for real integrated circuit lithography. [References: 14]