Mask Edge Notch for Optical Lithography Depth of Focus
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Solution Overview
Problem
Current methods for improving depth of focus during optical lithography, such as using assist features, are limited by restrictions on pitch and placement, particularly in situations like dipole illumination and fully nested line and space patterns, where assist features cannot be used.
Innovation Solution
The method involves adding notches to the edges of a mask layout to enhance depth of focus by introducing a high spatial-frequency component that degrades as the lithography process drifts out of focus, allowing more light into the pattern and maintaining critical dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If assist features are used to improve depth of focus, then depth of focus is improved, but placement is restricted due to pitch limitations and illumination technique constraints
Solution Approach 1:
The invention segments the edge modification into discrete notches that can be independently controlled. By dividing the edge into segments and applying different bias amounts to each segment, the method creates localized modifications that improve depth of focus without requiring full assist feature structures, thereby enabling use in restricted placement scenarios
Solution Approach 2:
The invention applies local quality by modifying only specific portions of the mask layout where notches are added to edges. These localized notches introduce high spatial-frequency components precisely where needed to improve depth of focus, rather than requiring global assist feature placement that is constrained by pitch and illumination restrictions
2Length of moving object
If feature size is decreased to advance circuit technology, then circuit density is improved, but depth of focus becomes more difficult to maintain
Solution Approach 1:
The invention applies preliminary anti-action by pre-compensating for the depth of focus degradation that occurs with smaller features. By adding notches to edges before lithography, the method introduces high spatial-frequency components that counteract the focusing difficulties inherent in printing smaller features, thereby maintaining manufacturing precision despite reduced feature sizes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively improves depth of focus without the limitations of assist features, maintaining critical dimensions and reducing line end shrinkage during defocusing, as demonstrated by the comparison between serifs and hammerheads.
Implementation Method 1
adding a notch to the edge adds a high spatial-frequency component to the mask layout. This high spatial-frequency component degrades as the optical lithography process drifts out of focus.
Implementation Method 2
optical lithography process drifts out of focus
Data Source
AI summary
One embodiment of the present invention provides a system that improves the depth of focus during an optical lithography process. During operation, the system receives a mask layout. The system then selects an edge in the mask layout. Next, the system adds a notch to the edge to improve the depth of focus by helping to maintain a critical dimension associated with the edge as the optical lithography process drifts out of focus. Note that adding a notch to the edge adds a high spatial-frequency component to the mask layout. This high spatial-frequency component degrades as the optical lithography process drifts out of focus. This degradation causes the mask layout to allow more light into the pattern, which helps maintain the critical dimension, thereby improving depth of focus.