Optical Correction Plate for Microlithography Reticle Sagging
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Solution Overview
Problem
Microlithographic projection exposure systems face challenges in accurately adjusting for reticle sagging-induced spatial displacements without introducing pupil errors, which can vary with reticle changes and illumination settings, affecting image quality and precision in semiconductor fabrication.
Innovation Solution
A projection objective for microlithography incorporating an optical correction plate with non-rotationally symmetric aspheric surfaces and a varying thickness profile, positioned along the optical path to induce dominant field aberrations while minimizing pupil aberrations, allowing for independent adjustment of spatial displacements and pupil errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional projection objectives are used, then the system can operate with standard optical elements, but reticle sagging induces spatial displacements that cannot be corrected without introducing pupil errors
Solution Approach 1:
The correction plate is designed with separate, independently adjustable optical surfaces (first and second surfaces) that can be optimized for different correction functions. This segmentation allows the plate to address spatial displacement correction while maintaining pupil error control through independent surface optimization.
Solution Approach 2:
The correction plate employs non-rotationally symmetric aspheric surfaces instead of conventional symmetric optical elements. This asymmetry enables the plate to correct for the specific distortion patterns caused by reticle sagging while maintaining control over pupil errors that would arise from symmetric correction approaches.
2Adaptability or versatility
If the projection objective is adjusted for different reticles, then adaptability to various reticle types is improved, but pupil errors vary with reticle changes and illumination settings
Solution Approach 1:
The correction plate is designed as a universal optical element that can function with multiple reticle types and illumination settings. Its non-rotationally symmetric aspheric surfaces are optimized to provide consistent correction across different operating conditions, eliminating the need for reticle-specific adjustments that would introduce varying pupil errors.
Solution Approach 2:
The correction plate's optical parameters (surface profiles, thickness distribution) are specifically designed to remain effective across varying operational parameters including different reticle configurations and illumination settings. This parameter optimization ensures consistent performance without introducing variable pupil errors.
3Ease of manufacture
If rotationally symmetric optical elements are used, then the design simplifies manufacturing and alignment, but they cannot effectively correct non-rotationally symmetric reticle sagging distortions
Solution Approach 1:
The invention deliberately employs non-rotationally symmetric aspheric surfaces in the correction plate to match the non-rotationally symmetric distortion patterns caused by reticle sagging. This asymmetric design prioritizes correction accuracy over manufacturing simplicity, as the asymmetric surfaces can be fabricated using modern precision optical manufacturing techniques.
Solution Approach 2:
The correction plate utilizes complex aspheric curvatures on both surfaces instead of simple spherical or planar surfaces. These carefully designed curvatures enable precise correction of reticle sagging distortions while the plate's overall geometry and mounting configuration maintain ease of integration into the projection objective.
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
Enables precise correction of reticle sagging-induced spatial displacements without altering pupil errors, maintaining image quality and precision across different reticles and illumination settings, thereby improving the accuracy of semiconductor device fabrication.
Implementation Method 1
an optical correction plate (450) that includes a body made from a material transparent to the operating radiation... having a first optical surface, a second optical surface... with non-rotationally symmetric aspheric surface profiles
Data Source
AI summary
A projection objective is disclosed. The projection objective can include a plurality of optical elements arranged to image a pattern from an object field in an object surface of the projection objective to an image field in an image surface of the projection objective with electromagnetic operating radiation from a wavelength band around an operating wavelength λ. The plurality of optical elements can include an optical correction plate that includes a body comprising a material transparent to the operating radiation, the body having a first optical surface, a second optical surface, a plate normal substantially perpendicular to the first and second optical surfaces, and a thickness profile defined as a distance between the first and second optical surfaces measured parallel to the plate normal. The first optical surface can have a non-rotationally symmetric aspheric first surface profile with a first peak-to-valley value PV1>λ. The second optical surface can have a non-rotationally symmetric aspheric second surface profile with a second peak-to-valley value PV2>λ. A thickness of the optical correction plate can vary by less than 0.1*(PV1+PV2)/2 across the optical correction plate.