Time Multiplexed EUV Illumination System for Reticle Inspection
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Solution Overview
Problem
Current illumination systems for EUV reticle inspection lack sufficient brightness and uniformity, with single source systems being inadequate and multiple source systems exceeding size restrictions or failing to meet uniformity requirements, limiting defect detection capabilities.
Innovation Solution
A compact illumination system utilizing a multiplexing mirror system to combine pulses from multiple EUV illumination sources, directing them through field and pupil mirror facets to achieve sufficient brightness and uniformity, while maintaining a compact design compatible with existing optics and cost-effective manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple illumination sources are used to increase brightness, then illumination intensity is improved, but system size exceeds restrictions
Solution Approach 1:
The patent employs pulsed illumination from multiple sources where sources are activated sequentially in time rather than simultaneously in space. The first source emits a first pulse, then the second source emits a second pulse, creating periodic illumination that achieves high brightness without requiring all sources to be present at once, thus maintaining compact system size.
Solution Approach 2:
The system uses dynamic switching between multiple illumination sources through a multiplexing mirror system that redirects light paths based on temporal sequencing. This dynamic reconfiguration allows the system to achieve the brightness of multiple sources while maintaining a compact physical footprint by activating sources sequentially rather than requiring simultaneous spatial arrangement of all sources.
2Illumination intensity
If multiple illumination sources are used to increase brightness, then illumination intensity is improved, but uniformity deteriorates
Solution Approach 1:
By activating illumination sources sequentially with precisely timed pulses rather than simultaneously, the system maintains uniform irradiance patterns. The temporal separation of source activation prevents interference and uniformity degradation that would occur with simultaneous multi-source operation, while still achieving high overall brightness through cumulative pulse energy.
Solution Approach 2:
The multiplexing mirror system acts as an intermediary that sequentially directs light from different sources through the same optical path. This intermediary mechanism ensures that each source's contribution to the illumination pattern is temporally separated and spatially aligned, maintaining uniformity while achieving high brightness through the cumulative effect of multiple pulsed sources.
3Area of stationary object
If single source illumination is used to maintain compact size, then system size is improved, but illumination intensity deteriorates
Solution Approach 1:
The system uses periodic pulsed illumination from multiple sources activated in sequence. The first source emits a pulse, followed by the second source emitting another pulse, creating time-multiplexed illumination that achieves high brightness equivalent to multiple simultaneous sources while maintaining a compact physical footprint similar to a single-source system.
Solution Approach 2:
The multiplexing mirror system dynamically switches between different illumination sources on timescales much faster than the detector integration time. This dynamic switching creates the effect of high-intensity illumination without requiring physically large multi-source arrangements, achieving high brightness in a compact configuration through temporal multiplexing.
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 system provides enhanced brightness and uniformity for EUV reticle inspection, overcoming previous limitations and enabling more effective defect detection within constrained size and cost parameters.
Implementation Method 1
A multiplexing mirror system is configured to receive pulses of illumination from the plurality of illumination sources and further configured to direct the pulses of illumination along an illumination path to a plurality of field mirror facets. The field mirror facets are each configured to receive a portion of illumination from the illumination path and direct at least a portion of the illumination to a plurality of pupil mirror facets.
Data Source
AI summary
The disclosure is directed to a system and method of providing illumination for reticle inspection. According to various embodiments of the disclosure, a multiplexing mirror system receives pulses of illumination from a plurality of illumination sources and directs the pulses of illumination along an illumination path to a plurality of field mirror facets. The field mirror facets receive at least a portion of illumination from the illumination path and direct at least a portion of the illumination to a plurality of pupil mirror facets. The pupil mirror facets receive at least a portion of illumination reflected from the field mirror facets and direct the portion of illumination along a delivery path to a reticle for imaging and/or defect inspection.