EUV Projection Exposure Apparatus Facet Mirror Illumination Control
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Solution Overview
Problem
Microlithographic projection exposure apparatuses in the extreme ultraviolet spectral range face challenges with low mirror reflectivity and the need for minimal mirrors, leading to issues with adjustable field stops causing light losses, edge sharpness problems, and particle abrasion defects due to rapid reticle masking blade movements.
Innovation Solution
A method utilizing a facet mirror with adjustable mirror facets that vary the size of the illumination field by adjusting individual mirror facets, eliminating the need for an adjustable field stop near the mask, and reducing the risk of particle-related defects by controlling the mirror facets' position and reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an adjustable field stop is used to control the illumination field size, then the illumination field can be adjusted, but light losses increase and edge sharpness deteriorates
Solution Approach 1:
The patent replaces the mechanical adjustable field stop system with an optical control system using mirror facets. Instead of physically moving stop elements to adjust the illumination field, the system tilts individual mirror facets to redirect or block light paths, achieving field adjustment without mechanical obstruction and minimizing light losses.
Solution Approach 2:
The mirror surface is divided into multiple independent mirror facets that can be individually tilted. This segmentation allows precise control of the illumination field by activating only the necessary facets, reducing light losses compared to a complete field stop mechanism while maintaining adjustment capability.
2Adaptability or versatility
If an adjustable field stop is used, then the illumination field size can be controlled, but the edges of the illumination field become not sharp
Solution Approach 1:
The patent replaces the mechanical field stop with an optical tilt-control mechanism. By tilting mirror facets, the system defines illumination field boundaries through optical redirection rather than physical masking, producing sharp edges without the blurring effects caused by finite distances between field stops and masks.
3Adaptability or versatility
If reticle masking blades are moved at high speed for field adjustment, then the illumination field dimensions can be continuously adjusted, but abraded particles are produced that cause defects
Solution Approach 1:
The patent replaces the mechanical reticle masking blades with a stationary mirror facet system controlled by tilting mechanisms. The mirror facets remain fixed in position while their orientation changes, eliminating the high-speed sliding contact that generates abraded particles, thus preventing defect formation on the light-sensitive layer.
Solution Approach 2:
The mirror facets act as an intermediary between the light source and the mask, providing field adjustment functionality without direct mechanical interaction near the mask. This intermediate optical control mechanism eliminates particle generation while maintaining continuous adjustment capability.
4Adaptability or versatility
If mirrors are used in EUV projection exposure apparatus, then refractive optical elements can be replaced, but the reflectivity is low causing light losses
Solution Approach 1:
The mirror surface is segmented into multiple facets that can be independently controlled. This allows the system to optimize the use of each mirror facet, tilting them to maximize light reflection toward the illumination field while minimizing stray light and losses. The segmented design enables more efficient light utilization compared to a single large mirror.
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 enhances the throughput and reduces defects by maintaining sharp illumination field edges and minimizing particle abrasion, allowing for efficient scanning without the need for adjustable field stops, thus improving the overall performance of EUV projection exposure apparatuses.
Implementation Method 1
groups of adjacent mirror facets form regions which are imaged by an optical unit onto an object plane
Data Source
Figure 1
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AI summary
In a method for operating a microlithographic projection exposure apparatus, a facet mirror (72) is illuminated with projection light (PL) having a center wavelength of between 5 nm and 30 nm. The facet mirror (72) has a plurality of adjustable mirror facets (86), wherein groups of adjacent mirror facets (86) form regions (88) which are imaged by an optical unit (83, 76, 78, 80) onto an object plane (30) of a projection objective (20) of the projection exposure apparatus (10). There the images of the regions (88) are superimposed in an object field (88'). An illumination field (24), which is identical to the object field (88') or to a part thereof, is illuminated with the projection light (PL). A mask (16) containing structures (12) to be imaged is moved in the object plane (30) of the projection objective (26) in such a way that the illumination field (24) scans over the mask (16). According to the invention, during step c) the size of the illumination field (24) is varied by adjusting at least one mirror facet (86).