Mask Stitching Assistive Features for EUV Lithography
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Solution Overview
Problem
High-NA EUV lithography requires multiple mask exposures, leading to process variations and defects in the boundary region where the exposures meet, particularly for smaller or denser features.
Innovation Solution
The method involves determining locations within the mask pattern to place assistive features that reduce sensitivity to lithographic process variations and stray light at the boundary during mask exposures. These assistive features are strategically placed to mitigate the effects of double exposure in the boundary region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple mask exposures are used to achieve smaller spot sizes and pitches, then manufacturing precision is improved, but process variations and defects increase in the boundary region
Solution Approach 1:
The patent applies preliminary action by pre-placing assistive features (such as dummy features, spacer features, or reinforcement features) in the boundary region before the actual lithographic exposure process. These features are strategically positioned to compensate for expected process variations and stitching errors, thereby reducing sensitivity to lithographic process variations and preventing defects before they occur during multi-exposure stitching
Solution Approach 2:
The patent introduces intermediary elements (assistive features) in the boundary region that act as mediators between the first and second mask exposures. These features serve as reference markers or compensation structures that help align and stitch the boundary regions accurately, reducing the impact of process variations and preventing defects caused by misalignment or exposure inconsistencies
2Manufacturing precision
If numerical aperture is increased to 0.55 for smaller features, then manufacturing precision is improved, but sensitivity to lithographic process variations increases
Solution Approach 1:
The patent applies preliminary action by pre-placing assistive features (such as dummy features, spacer features, or reinforcement features) in the boundary region before the actual lithographic exposure process. These features are strategically positioned to compensate for expected process variations and stitching errors, thereby reducing sensitivity to lithographic process variations and preventing defects before they occur during multi-exposure stitching
Solution Approach 2:
The patent applies parameter changes by modifying the mask pattern parameters in the boundary region, such as adjusting feature dimensions, adding assistive features with specific geometries, or changing material properties of the mask pattern. These parameter modifications are designed to reduce sensitivity to lithographic process variations while maintaining the desired high-NA EUV lithography precision for smaller features
Data Source
AI summary
A first location within a mask pattern of a semiconductor circuit layout is determined, based on a feature of the mask pattern that is within a threshold distance of a boundary in the mask pattern. The mask pattern is based on a first mask exposure and a second mask exposure that meet at the boundary. The first location defines where to place a first assistive feature that reduces a sensitivity to lithographic process variations of the feature of the mask pattern. A second location of the mask pattern is also determined. The second location defines where to place a second assistive feature that reduces stray light at the boundary during the first mask exposure and the second mask exposure. The mask pattern is then modified to place the first assistive feature in the first location and the second assistive feature in the second location.