Bend the curve – Shape optimization in laser grayscale direct write lithography using a single figure of merit

Abstract

Laser-based pattern generators are versatile tools for transferring design layouts into resist structures. The non-linear response and the proximity effects caused by the interaction of the laser beam with the low-contrast photoresist are particularly critical for the creation of shapes with sloped, stepped and continuous topographies. Cross-sections were taken to compare topological differences of the measurement results with the graytone design. For simple shapes, an iterative adjustment of the global dose distribution is sufficient, while for more complex shapes the local correction of dose values using mathematical models is preferred. For the one-step exposure of the corrected map, it requires the careful assessment of a contrast curve and knowledge of various parameters. The coefficient of determination R2 as a unitless single figure of merit proved useful in the quantitative comparison of the two methods, and demonstrated the capability of current model-based approaches for shape optimization towards the target design within one cycle.

Keywords

• Direct write lithography
• Grayscale
• Contrast curve
• Positive resist
• Proximity exposure correction
• Figure of merit