Anamorphic Projection Lens Aberration Control
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Solution Overview
Problem
In EUV microlithography, anamorphic projection lenses face challenges in correcting field-dependent image aberrations, which affect the resolution and throughput of semiconductor component production, particularly due to increased object-side numerical apertures leading to shading effects and reduced reflectivity of narrowband masks.
Innovation Solution
The method involves synchronously rotating the mask and substrate about respective axes perpendicular to their planes during scanning, with coordinated rotation angles to set a desired image aberration profile while compensating for parasitic aberrations, thereby enhancing imaging quality without requiring additional manipulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the object-side numerical aperture is increased to improve resolution capability, then the resolution capability is improved, but shading effects occur due to the reticle coating and layer transmission problems
Solution Approach 1:
The patent applies asymmetry by using an anamorphic projection lens with different imaging scales in the scanning direction and cross-scan direction. This asymmetric optical design allows the system to achieve high object-side numerical aperture in the cross-scan direction for improved resolution, while maintaining more favorable illumination angles in the scanning direction to reduce shading effects from the reticle coating.
2Productivity
If a reducing imaging scale of 1:4 is used to maintain throughput, then the throughput is maintained, but the object-side numerical aperture remains high causing shading effects
Solution Approach 1:
The anamorphic projection lens creates asymmetric imaging scales where the reduction ratio differs between scanning and cross-scan directions. This allows the system to achieve effective resolution improvement without requiring a uniform reduction of throughput, as the different directional scales optimize both performance metrics simultaneously.
3Object-affected harmful factors
If an anamorphic projection lens with different imaging scales is used to reduce object-side numerical aperture, then shading effects are reduced, but field-dependent image aberrations occur
Solution Approach 1:
The patent employs dynamic manipulation of the mask and substrate during scanning, including coordinated rotations about respective axes. These dynamic adjustments compensate for the field-dependent image aberrations introduced by the anamorphic projection lens, allowing the system to maintain both reduced shading effects and high imaging precision throughout the exposure field.
4Object-affected harmful factors
If the imaging scale is reduced to 1:8 to halve the object-side numerical aperture, then shading effects are reduced, but the exposed field size is reduced and throughput decreases
Solution Approach 1:
The anamorphic projection lens uses asymmetric imaging scales to achieve the benefit of reduced object-side numerical aperture (halving it in the scanning direction to reduce shading) while compensating for the throughput loss by maintaining a more favorable reduction ratio in the cross-scan direction, thereby preserving a larger effective exposed field size.
Data Source
AI summary
A projection exposure method for exposing a radiation-sensitive substrate with at least one image of a pattern of a mask in a projection exposure apparatus includes using an anamorphic projection lens