Reflective Loop System for Incoherent Lithography Illumination
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Solution Overview
Problem
Conventional lithographic systems face challenges in eliminating speckle patterns caused by coherent illumination, which can lead to errors in pattern formation on substrates, due to the difficulty in moving optical elements quickly enough to compensate for these patterns within the limited integration time and reduced laser pulse durations.
Innovation Solution
The implementation of two or more optically coupled reflective loop systems within a lithography system to convert coherent or partially coherent beams into more incoherent beams, thereby eliminating interference and speckle patterns by extending the loop path beyond the coherence length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional coherent or partially coherent laser beams are used for illumination, then the illumination intensity and brightness are improved, but speckle patterns are generated causing errors in pattern formation on substrates
Solution Approach 1:
The patent segments the coherent illumination beam into multiple separate coherent beams using beam splitting elements. Each beam travels through a different optical path and is then recombined. This segmentation prevents the beams from interfering with each other, thereby eliminating speckle patterns while maintaining high illumination intensity and pattern formation accuracy.
2Reliability
If optical elements are moved quickly to compensate for speckle patterns, then the speckle compensation effectiveness is improved, but large oscillations and high acceleration are generated within the lithography system
Solution Approach 1:
The patent extracts the speckle compensation function from mechanical movement of optical elements. Instead of moving elements to change phase distributions, the invention uses stationary beam splitting and recombination optics that inherently prevent speckle pattern formation through optical path separation. This eliminates the need for high-speed mechanical compensation and avoids generating large oscillations and acceleration.
3Reliability
If the loop path length is extended beyond the coherence length to reduce speckle, then the speckle reduction effectiveness is improved, but the device complexity and optical path length are increased
Solution Approach 1:
The patent uses beam splitting elements to divide the coherent beam into multiple separate coherent beams that travel through different optical paths. By segmenting the beam and ensuring the optical path difference exceeds the coherence length, speckle patterns are prevented from forming. This approach achieves effective speckle reduction without requiring excessively long single-loop paths, thereby controlling device complexity.
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 effectively reduces speckle patterns by ensuring that no coherent parts of the illumination interfere, resulting in a more uniform and stable illumination for pattern formation on substrates, improving the accuracy and efficiency of the lithographic process.
Implementation Method 1
The loop path length is longer than a coherence length of the at least partially coherent beam such that the coherent beam reflected through the loop forms an incoherent beam
Implementation Method 2
a reflective loop system receives a coherent or a partially coherent beam and reflects the beam through a loop
Data Source
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AI summary
A system and method are used to form incoherent beams from a coherent beam. A system comprises a source of radiation and a reflective loop system. The source of radiation produces a coherent or partially coherent beam. The reflective loop system receives the partially coherent beam and reflects the partially coherent beam through a loop, or alternatively through non-overlapping loops, to form an incoherent beam.