Lithographic Projection System Wavefront Control via Localized Pupil Weighting
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Solution Overview
Problem
Existing lithographic apparatuses face inefficiencies in compensating for aberrations caused by lens heating, particularly when using strongly localized illumination modes such as dipole and conventional illumination with small sigma values.
Innovation Solution
A method involving an illuminator and projection system with an adjustable element, where a region of interest in the pupil plane is determined, and orthogonal basis functions are used to express the wavefront, allowing for optimized control settings to minimize aberrations by weighting the region of interest higher than the rest of the pupil plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dipole or quadrupole illumination modes are used to improve imaging precision, then manufacturing precision is improved, but lens heating increases causing aberrations that worsen manufacturing precision
Solution Approach 1:
The patent applies local quality by providing different adjustable elements at different locations in the projection system. Specifically, it uses a first adjustable element in a first region and a second adjustable element in a second region, allowing localized compensation of aberrations caused by heating in different areas of the projection system, thereby maintaining imaging precision while addressing local heating issues.
2Manufacturing precision
If adjustable elements are added to compensate for aberrations, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the aberration compensation function by dividing the projection system into different regions with separate adjustable elements. This segmentation allows independent control and optimization of aberrations in different areas, achieving comprehensive compensation while keeping each individual element relatively simple and manageable.
3Reliability
If conventional aberration compensation methods are used, then general imaging quality is maintained, but imaging precision deteriorates under localized illumination modes
Solution Approach 1:
The patent addresses the limitation of conventional compensation methods by implementing location-specific adjustable elements tailored to different regions of the projection system. This local quality approach ensures that aberrations are compensated effectively for localized illumination modes by targeting specific heated regions with dedicated adjustable elements, thereby maintaining high imaging precision.
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 minimizes wavefront errors and improves imaging quality, especially under conditions of lens heating, thereby enhancing the process window and imaging precision.
Implementation Method 1
the projection system absorbs a significant amount of energy from the projection beam and heats up
Implementation Method 2
expressing the wavefront in the pupil plane in terms of the basis functions and a set of coefficients; and determining a value of the control setting to minimize the values of the coefficients
Data Source
AI summary
In a lithographic projection apparatus, adjustment of the projection system, e.g. to compensate for lens heating effects, is performed by determining a region of interest for a given pattern and illumination arrangement, the region of interest being a non-circular region of a pupil plane of the projection system through which substantially all of the radiation of the modulated beam that contributes to formation of the image passes; obtaining a set of basis functions that are orthogonal over the region of interest; expressing the wavefront in the pupil plane in terms of the basis functions that are orthogonal over the region of interest and a set of coefficients; and determining a value of a control setting to minimize the values of the coefficients.