Optical Delay System for Lithography Speckle Reduction
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Solution Overview
Problem
Lithography illumination systems using coherent sources suffer from speckle noise due to interference between different portions of the illumination pattern, which degrades the quality of the lithographic process and introduces errors.
Innovation Solution
An optical delay system comprising a beam divider, intermediate optical parts with refractive and reflective surfaces, and a beam combiner is used to split and recombine beams, reducing temporal coherence and spatial coherence by distributing beams to separate locations in the illumination pupil, thereby minimizing speckle noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a coherent source is used to generate the illumination pattern, then the illumination intensity and uniformity are improved, but speckle noise is generated due to interference between different portions of the illumination pattern
Solution Approach 1:
The illumination system divides the coherent illumination beam into multiple spatial segments using beam dividers and directional control elements. Each segment is directed at a different angle or position, reducing the interference effects that cause speckle noise while maintaining overall illumination intensity and uniformity across the target surface.
Solution Approach 2:
The system employs multiple levels of beam manipulation where beam dividers, directional controllers, and combiners are nested within each other. The beam divider segments the illumination, directional controllers adjust each segment's path, and combiners recombine them at the target, creating a nested structure that systematically reduces speckle while preserving coherent illumination benefits.
2Adaptability or versatility
If non-complex or complex illumination patterns are used, then the illumination coverage and pattern flexibility are improved, but speckle noise deteriorates the quality of the lithographic process
Solution Approach 1:
The system dynamically controls the direction and distribution of illuminated segments using adjustable directional controllers. This allows the illumination pattern to be flexibly modified for different lithographic requirements while maintaining reduced speckle noise through continuous adjustment of beam paths and distribution characteristics.
Solution Approach 2:
Different portions of the illumination pattern are given different local properties through selective directional control. Each beam segment can be independently directed and adjusted, allowing local optimization of illumination characteristics while maintaining overall pattern flexibility and reducing speckle noise through spatial distribution variations.
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 reduces speckle noise and improves the quality of the lithographic process by achieving low spatial and temporal coherence, resulting in improved image clarity and reduced errors.
Implementation Method 1
an intermediate optical part including a refractive surface that refracts the first beam
Implementation Method 2
a concave mirror that reflects the first beam from the refractive surface
Implementation Method 3
speckle noise that arises from interference between different portions of the illumination pattern
Data Source
AI summary
An optical system includes a first optical system, a second optical system, and a third optical system. The first optical system divides an input beam into a first light and a second light. The second optical system includes a concave reflective surface which reflects the first light. The third optical system directs at least one of the first light reflected from the second optical system and the second light from the first optical system to an output optical path of the third optical system.