Facet Mirror Spatial Frequency Damping
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Solution Overview
Problem
Projection exposure apparatuses face challenges in achieving uniform mask illumination and stabilizing optical systems due to microstructures and source variations, which affect the quality of microstructured or nanostructured components.
Innovation Solution
A facet mirror with multiple facets, each equipped with mechanisms for damping spatial frequencies above a specific limit frequency, such as toroidal pupil facets with targeted defocusing and scattering functions, and diffraction structures like binary phase gratings, is used to stabilize the optical system and ensure uniform illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If microstructures are introduced into the facet mirror to damp spatial frequencies, then illumination uniformity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by carefully controlling the spatial frequency range of microstructures on the facet mirror surface. By limiting microstructures to specific frequency ranges (damping frequencies above a cutoff while preserving lower frequencies), the patent achieves illumination uniformity without requiring ultra-precise manufacturing. The scattering function parameters (amplitude, spatial frequency spectrum) are optimized to provide sufficient scattering for uniformity while remaining manufacturable.
2Reliability
If scattering structures are added to facets, then spatial frequency damping is improved, but device complexity increases
Solution Approach 1:
The patent merges the scattering function directly into the facet mirror surface microstructures, combining the illumination uniformity function and spatial frequency damping function into a single integrated component. This eliminates the need for separate scattering elements or additional optical components, reducing overall device complexity while achieving the desired optical performance and system stability.
3Reliability
If targeted defocusing is applied to pupil facets, then spatial frequency damping is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by optimizing the radius of curvature of toroidal pupil facets to achieve targeted defocusing. By carefully selecting the curvature radius parameter, the patent introduces sufficient defocus to damp spatial frequencies and stabilize the optical system against source variations, while maintaining manufacturability through reasonable curvature values that do not require ultra-precise fabrication.
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
The solution effectively dampens spatial frequencies, stabilizes the optical system, and ensures high uniformity of illumination, improving the quality of microstructured or nanostructured components produced by the projection exposure apparatus.
Implementation Method 1
The facets are respectively provided with a scattering function for scattering radiation. The scattering function is preferably a one-dimensional scattering function.
Implementation Method 2
the facets are respectively provided with at least one diffraction structure for diffracting radiation with a wavelength in the infrared region
Implementation Method 3
Targeted defocusing of the pupil facets can serve as a mechanism for damping spatial frequencies. This can be achieved by a suitable selection of the radii of curvature of the pupil facets.
Data Source
AI summary
Illumination optical unit for illuminating an object field in a projection exposure apparatus, comprising a first facet mirror with a structure, which has a spatial frequency of at least 0.2 mm−1 in at least one direction, and a second facet mirror, comprising a multiplicity of facets, wherein the facets are respectively provided with a mechanism for damping spatial frequencies of the structure of the first facet mirror.