Synthetic holographic mask design for computational proximity lithography using the lithography-guided OMRAF method

Mask aligner lithography does not rely on complex projection lens systems, offering a cost-effective and high-yield approach for chip manufacturing. However, its limited resolution restricts application in advanced chip manufacturing. Holographic lithography enhances lithographic resolution by introducing phase information onto the mask. Nevertheless, conventional holographic lithography masks face challenges in adapting to increasingly complex patterns and smaller feature sizes. This paper introduces a synthetic holographic mask design method based on the OMRAF projection iterative algorithm, applying stepwise discretization of the amplitude and phase distributions of the holographic mask in compliance with mask manufacturing constraints. Simulation results demonstrate that the proposed approach achieves high-fidelity imaging with excellent uniformity and sub-micron resolution. By using the holographic mask, the aerial image with a minimum linewidth of 0.4 µm for non-periodic structures can be constructed with a proximity gap of 50 µm. Limited by mask fabrication constraints, holographic masks with a minimum feature size of 0.8 µm were fabricated using electron-beam lithography, and the experimental results confirm the validity and feasibility of the proposed method.