EUV Mask Sub-Resolution Polygons for Exposure Uniformity
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Solution Overview
Problem
Existing EUV lithography techniques face challenges with non-uniformity of exposure intensity, particularly affecting edge patterns, which hinders the achievement of high resolution and uniformity in semiconductor feature sizes.
Innovation Solution
The implementation of a nearly on-axis illumination with partial coherence less than 0.3 and the use of an EUV mask with sub-resolution polygons in a second region adjacent to the main polygon region, along with a spatial filter to remove most non-diffracted light, enhances the exposure intensity uniformity and spatial frequency resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional EUV lithography illumination is used, then the lithography process can be performed, but non-uniformity of exposure intensity occurs particularly at edge patterns
Solution Approach 1:
The patent introduces sub-resolution polygons in a second region adjacent to the main polygon region. These sub-resolution polygons have different properties (smaller size, lower resolution) than the main polygons, creating local quality variations that compensate for edge effects and improve exposure uniformity across the mask.
Solution Approach 2:
The patent changes the illumination parameters by using a coherence value of less than 0.3 (partially coherent illumination) and introduces sub-resolution polygons with specific area ratios. These parameter changes modify the diffraction pattern and improve exposure intensity uniformity, particularly at edge patterns.
2Length of moving object
If higher resolution is pursued for smaller feature sizes, then feature size decreases, but exposure intensity non-uniformity worsens
Solution Approach 1:
The sub-resolution polygons create local quality variations in the second region that compensate for the non-uniformity caused by high-resolution main polygons at the edges. This allows small feature sizes to be achieved while maintaining exposure uniformity through the localized correction features.
Solution Approach 2:
The sub-resolution polygons act as intermediary elements between the main polygons and the substrate. They mediate the optical field distribution by introducing controlled diffraction that compensates for the non-uniformity produced by the high-resolution main polygon patterns.
3Manufacturing precision
If sub-resolution polygons are added to the mask, then aerial image fidelity improves, but mask complexity increases
Solution Approach 1:
Instead of modifying the entire mask, sub-resolution polygons are added only in the second region adjacent to the main polygon region. This localized approach improves aerial image fidelity while minimizing the increase in overall mask complexity.
Solution Approach 2:
The sub-resolution polygons are intentionally designed to be smaller than the resolution threshold (excessive action in terms of smallness) so they don't print on the substrate. This partial action approach allows them to influence the optical field without adding complexity to the final pattern.
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 results in improved aerial image fidelity and resolution enhancement for patterns near the edge of the polygon region, addressing the non-uniformity issues and enhancing the lithography process for smaller feature sizes.
Implementation Method 1
exposing the EUV mask with a nearly on-axis illumination (ONI) with partial coherence σ less than 0.3 to produce diffracted light and non-diffracted light
Implementation Method 2
removing most of the non-diffracted light by a spatial filter
Data Source
AI summary
An extreme ultraviolet lithography (EUVL) system for patterning a semiconductor wafer includes an extreme ultraviolet (EUV) mask. The EUV mask includes first and second states, and further includes a polygon region and an open-spacing region. The polygon region includes a plurality of main polygons separated by a plurality of first fields. The open-spacing region is located outside the polygon region, and includes a plurality of sub-resolution polygon and second fields, and does not include any main polygons. The system also includes a nearly on-axis illumination (ONI) to expose the EUV mask and optics to direct diffracted lights reflected from the EUV mask towards the semiconductor wafer.