EUV Illumination Optics Faceted Mirror Path Length Control
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Solution Overview
Problem
Current EUV projection lithography illumination optics face challenges in achieving uniform illumination due to interference issues between sub-beams, which affect the quality of the illumination field and lead to variations in the illumination dose across the field.
Innovation Solution
The proposed solution involves an illumination optics design with a faceted mirror system that ensures each illumination channel has a unique optical path length, using a combination of field and pupil facet mirrors to create distinct illumination channels with sufficient transit time differences, preventing interference by ensuring that the optical path length differences between sub-beams are greater than the coherence length of the illumination light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple illumination channels are used to illuminate different regions of the illumination field, then the illumination coverage is improved, but interference problems occur when sub-beams from different channels superimpose with optical path length differences less than the coherence length
Solution Approach 1:
The illumination field is divided into multiple regions, each illuminated by a dedicated illumination channel with a specific facet mirror. Each facet mirror segment is responsible for illuminating a specific region, creating spatial separation of illumination functions while maintaining comprehensive coverage through the segmented approach
Solution Approach 2:
Different regions of the illumination field are illuminated with locally optimized parameters. Each facet mirror is positioned and oriented to provide the optimal illumination angle and path length for its specific region, allowing non-uniform optical path lengths that prevent interference while maintaining local illumination quality
2Device complexity
If the optical path lengths of different illumination channels are made equal to simplify the system, then the device complexity is reduced, but interference problems arise due to insufficient transit time differences between sub-beams
Solution Approach 1:
The optical path lengths of different illumination channels are deliberately made asymmetric and non-uniform. Each illumination channel has a unique optical path length that is specifically designed to ensure transit time differences exceed the coherence length, preventing interference while maintaining illumination uniformity through the asymmetric design
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 design enhances the uniformity of the illumination field, preventing undesired interference and improving the overall quality of the illumination, thereby supporting more precise microstructured or nanostructured component production, such as semiconductor chips.
Implementation Method 1
The partial beams of the illumination light are created by reflections on faceted optical elements in the beam path
Implementation Method 2
interference problems between sub-beams of the illumination light, which are superimposed in the illumination field, arise precisely when at any point in time at any point of the illumination field at least two sub-beams of illumination light impinge, and the optical path lengths measured from the light source between at least two of these Sub-beams differ by less than the coherence length of the illuminating light
Data Source
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AI summary
An illumination optics (26) for EUV projection lithography is used to guide illumination light (16) to an illumination field (5), in which a lithography mask (7) can be arranged. A faceted mirror (19) having a plurality of facets (25) is used to guide the illumination light (16) to the illumination field (5). Each of the facets (25) specifies a respective illumination channel (27), which guides an illumination light sub-bundle. Exactly one illumination channel (27) is guided by means of each of the facets (25). The illumination optics (26) is designed in such a way that, during operation of the illumination optics (26), at every point in time at every point of the illumination field (5), any pairs of illumination light sub-bundles, which are guided by means of different illumination channels (27), hit the illumination field point at incidence times the time difference (∆t) of which is greater than a coherence duration tauk of the illumination light (16). The result is an illumination optics of which the quality of illumination of the illumination field is improved.