Microlithography Projection Objective Stray Light Compensation
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Solution Overview
Problem
Projection objectives for microlithography face challenges in managing stray light components, particularly in immersion lithography and EUV lithography, where new optical materials with polycrystalline structures generate more stray light due to inhomogeneities and refractive index variations, affecting image contrast and manufacturing processes.
Innovation Solution
Introducing an additional stray light component with a non-constant profile over the exposure field by adjusting the surface roughness of field-proximate optical elements, specifically increasing the RMS surface roughness at the borders relative to the center, to complement the existing stray light component and reduce its variation across the field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If new optical materials with polycrystalline structures are used in projection objectives, then the material can be used in immersion lithography and EUV lithography applications, but the stray light component increases due to inhomogeneities and refractive index variations
Solution Approach 1:
The patent applies local quality by creating a non-uniform stray light compensation profile across the exposure field. Different regions of the field receive different amounts of compensating stray light, with the compensation being strongest where needed most (typically at field edges) and tapering off toward the center. This localized approach allows the system to counteract the position-dependent stray light variations caused by polycrystalline materials without requiring uniform compensation across the entire field.
Solution Approach 2:
The patent implements preliminary anti-action by intentionally introducing a controlled stray light component before the actual imaging process. The compensation mechanism pre-establishes a stray light profile that opposes and counteracts the harmful stray light generated by the optical materials. This proactive compensation occurs as part of the imaging process itself, rather than attempting to eliminate the root cause of stray light generation in the optical materials.
2Object-generated harmful factors
If the stray light component is reduced through careful layout and anti-reflex coatings, then secondary causes of stray light are minimized, but the primary causes from inhomogeneities in optical materials remain significant
Solution Approach 1:
The patent converts the harmful effect of stray light into a beneficial compensation mechanism. By deliberately introducing a controlled stray light component with a specific spatial profile, the system transforms the problem of stray light into a solution. The intentionally generated stray light acts as a compensation signal that counterbalances the position-dependent stray light variations, thereby improving image contrast and enabling the use of polycrystalline materials that would otherwise be unsuitable for high-precision lithography.
3Measurement precision
If projection objectives are designed for high numerical aperture, then imaging resolution is improved, but stray light management becomes more challenging
Solution Approach 1:
The patent employs parameter changes by dynamically adjusting the stray light compensation profile across different regions of the exposure field. The compensation mechanism varies key parameters such as the intensity and spatial distribution of the compensating stray light component to match the local requirements of different field positions. This parameter variation allows the system to maintain effective stray light compensation across the entire field while supporting high numerical aperture designs that require precise imaging performance.
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 helps equalize the stray light profile, reducing its variation and improving image contrast, enabling more efficient manufacturing processes by compensating for the inherent stray light issues in polycrystalline materials and preparing for future high-numerical-aperture projection objectives.
Implementation Method 1
The stray light component of an objective has different reasons, which are described in: Heinz Haferkorn, 'Optik; Physikalisch-technische Grundlagen and Anwendungen' (Optics, Physical and Technical Theory and Applications), Fourth Revised and Expanded Edition; Verlag WileY-VCH, Weinheim; pages 690-694. On the one hand, there is the kind of stray light which is caused by the scattering of light at inhomogeneities within a transparent optical material, and on the other hand the kind of stray light which is caused by the scattering of light at irregularities of the surfaces of the optical elements.
Data Source
AI summary
A projection objective for applications in microlithography, a microlithography projection exposure apparatus with a projection objective, a microlithographic manufacturing method for microstructured components, and a component manufactured using such a manufacturing method are disclosed. The projection objective includes an optical component configured so that, during use of the projection objective, the optical component generates a stray light component in the exposure field of the projection objective which adapts a parameter of the projection objective to a parameter of a second projection objective. The parameter is the stray light component at the exposure field of the projection objective and/or a variation of the stray light component at the exposure field of the projection objective. The parameter of the second projection objective is a stray light component at an exposure field of the second projection objective and/or a variation of the stray light component at the exposure field of the second projection objective. The second projection objective is different from the projection objective.