EUV Mask Phase Shifting and Pupil Filtering for Lithography
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Solution Overview
Problem
Existing EUV lithography techniques face challenges in improving throughput and uniformity of critical dimension, particularly due to limitations in reflective optics and light absorption at 13.5 nm wavelengths.
Innovation Solution
The implementation of a nearly on-axis illumination with partial coherence less than 0.3 and a pupil filter that removes over 70% of non-diffracted light and higher-order diffraction light, combined with an EUV mask featuring a low thermal expansion material substrate, a reflective multilayer, and a patterned phase-shifting layer providing a 180-degree phase difference between adjacent main and assist polygons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If reflective optics are used in EUV lithography, then the lithography process can be performed at 13.5 nm wavelength, but the throughput and uniformity of critical dimension are limited
Solution Approach 1:
The patent segments the illumination into different spatial coherence regions by using multiple illumination zones with different coherence values (σ1, σ2, σ3, etc.), where some zones provide high coherence for resolution and others provide low coherence for throughput, allowing simultaneous optimization of both critical dimension uniformity and lithography productivity
Solution Approach 2:
Different regions of the illumination source are assigned different local qualities in terms of spatial coherence. The illumination system provides locally optimized coherence characteristics for different parts of the mask, enabling high precision in critical areas while maintaining overall throughput through lower coherence regions
2Illumination intensity
If conventional illumination is used, then the process is simple, but aerial image contrast and throughput are insufficient
Solution Approach 1:
The illumination system dynamically adjusts spatial coherence parameters across different zones rather than using a fixed uniform illumination. This dynamic control of coherence characteristics enables optimized aerial image contrast while managing system complexity through programmable illumination patterns
Solution Approach 2:
The patent changes the parameter of spatial coherence (σ) across different illumination zones, creating a multi-parameter illumination system where coherence values are optimized for specific imaging requirements, thereby improving aerial image contrast without requiring complete system redesign
3Manufacturing precision
If non-diffracted light and higher-order diffraction light are not filtered, then the optical path is simple, but lithography performance deteriorates
Solution Approach 1:
The patent extracts and removes specific unwanted light components (non-diffracted light and higher-order diffraction light) from the optical path using filtering elements, separating the useful diffracted light from harmful components to improve lithography performance while adding only necessary filtering functionality
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 enhances aerial image contrast and throughput by effectively filtering out unwanted light components and utilizing phase-shifting layers to improve light interference, resulting in improved lithography performance.
Implementation Method 1
a patterned phase-shifting layer providing a 180-degree phase difference between adjacent main and assist polygons
Implementation Method 2
a pupil filter that removes over 70% of non-diffracted light and higher-order diffraction light
Implementation Method 3
reflective optics, rather than refractive optics, are commonly used in EUV lithography
Data Source
AI summary
A system and process of an extreme ultraviolet lithography (EUVL) is disclosed. The system and process includes receiving a mask with two states, which have 180 degree phase difference to each other. These different states are assigned to adjacent main polygons and adjacent assist polygons of the mask. A nearly on-axis illumination (ONI) with partial coherence σ less than 0.3 is utilized to expose the mask to produce diffracted lights and non-diffracted lights. A majority portion of the non-diffracted lights and diffracted light with diffraction order higher than 1 are removed. Diffracted light having +1-st and −1-st diffracted order are collected and directed by a projection optics box (POB) to expose a target.