3D Photomask Layout Generation for Optical Aberration Control

The patent transitions from traditional 2-D photomask patterns to 3-D patterns by adding vertical dimension through multiple layers at different z-axis positions. This dimensional change allows light to be modulated from multiple depths, effectively reducing optical aberrations like flares and distortions while maintaining exposure resolution. The 3-D patterns create more complex optical paths that interfere destructively with unwanted diffraction orders.

The patent employs composite photomask structures combining multiple pattern layers with different optical properties (phase shifters, absorbers, and pattern layers) arranged in specific configurations. These composite structures work together to simultaneously achieve high contrast, phase modulation, and suppression of optical defects, resolving the contradiction between resolution and optical quality.

The patent divides the photomask pattern into multiple segmented layers at different z-axis positions, where each layer contributes specific functions. This segmentation allows complex optical correction to be achieved through simpler individual layers that can be manufactured separately and then combined, maintaining ease of manufacture while eliminating optical defects.

By adding the z-axis dimension with multiple pattern layers, the patent creates 3-D photomask structures that can be fabricated using extended lithographic processes. The additional vertical dimension provides new degrees of freedom for optical control without fundamentally complicating the manufacturing approach, as each layer can be processed similarly to traditional 2-D patterns.