Wavelength-Based Optical Filtering for EUV Light Sources
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Solution Overview
Problem
Extreme ultraviolet (EUV) light sources face challenges in reducing amplified spontaneous emission (ASE) noise, which interferes with the efficient production of EUV light in photolithography processes by interacting with the target material and depleting excited carriers in the amplifier, leading to reduced EUV light production and potential defects in electronic features.
Innovation Solution
A wavelength-based optical filter system is introduced between the light-generation module and the optical amplifier, utilizing dispersive and filtering elements such as gratings, prisms, and multi-layer coatings to selectively remove wavelengths within the gain band that are not intended for the target region, thereby mitigating ASE and ensuring only specific wavelengths propagate to the plasma site.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a wavelength-based optical filter system is introduced to remove unwanted wavelengths, then ASE noise is reduced and EUV light production efficiency is improved, but the device complexity increases due to the addition of dispersive and filtering elements
Solution Approach 1:
The patent extracts and removes unwanted wavelengths from the optical beam path using a wavelength-based optical filter system. The filter system selectively transmits the desired wavelength (e.g., 10.6 μm) while blocking other wavelengths that cause ASE noise, thereby improving EUV light production efficiency by eliminating harmful spectral components.
Solution Approach 2:
The patent introduces dispersive elements (prisms, gratings) and filtering elements as intermediary components between the light source and the target. These intermediaries separate the wavelengths spatially and selectively transmit only the desired wavelength, acting as mediators that resolve the conflict between maintaining beam intensity and eliminating ASE noise.
2Object-affected harmful factors
If dispersive optical elements like gratings and prisms are used to filter wavelengths, then ASE noise is mitigated, but the manufacturing precision requirements increase for the optical components
Solution Approach 1:
The patent segments the optical filtering function into multiple specialized components: dispersive elements (prisms, gratings) that separate wavelengths spatially, and filtering elements (absorbing materials, multi-layer coatings) that selectively block unwanted wavelengths. This segmentation allows each component to be optimized for its specific function, managing manufacturing precision requirements through functional decomposition.
Solution Approach 2:
The patent employs composite optical structures, including multi-layer coatings on filtering elements and combinations of different dispersive materials. These composite structures enable precise wavelength selectivity by combining the properties of multiple materials, achieving the required spectral filtering performance while managing manufacturing tolerances through material composition rather than relying solely on geometric precision.
3Measurement precision
If multiple optical filtering elements are arranged in series to define beam paths, then wavelength selectivity is improved, but the loss of energy increases due to multiple reflections and transmissions
Solution Approach 1:
The patent applies local quality optimization by designing filtering elements with spatially varying properties. Different regions of the optical path have different filtering characteristics optimized for their specific function: some elements prioritize transmission efficiency while others prioritize wavelength selectivity. This local optimization reduces overall energy loss while maintaining the required wavelength discrimination capability.
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 filter system effectively reduces ASE noise, enhancing the efficiency of EUV light production by preventing uncontrolled wavelengths from reaching the target, thus improving the consistency and quality of EUV light provided to photolithography tools.
Implementation Method 1
The dispersive optical element may include one or more of a prism and a grating
Implementation Method 2
the grating being positioned to reflect light having a wavelength in the first set of wavelengths onto the beam path, and to reflect light having a wavelength in the second set of wavelengths away from the beam path
Implementation Method 3
an optical element configured to absorb light having one or more wavelengths in the second set of wavelengths
Implementation Method 4
an optical element including a multi-layer coating
Data Source
AI summary
An optical source for an extreme ultraviolet (EUV) photolithography tool includes a light-generation system including a light-generation module; an optical amplifier including a gain medium associated with a gain band, the gain medium configured to amplify light having a wavelength in the gain band; and a wavelength-based optical filter system on a beam path between the light-generation module and the optical amplifier, the wavelength-based optical filter system including at least one optical element configured to allow light having a wavelength in a first set of wavelengths to propagate on the beam path and to remove light having a wavelength in a second set of wavelengths from the beam path, the first set of wavelengths and the second set of wavelengths including different wavelengths in the gain band of the optical amplifier.