Ray-Splitting Optical Element for Polarization Control in Microlithography
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Solution Overview
Problem
Microlithographic projection exposure apparatuses face challenges in generating desired polarized illumination settings from unpolarized light, particularly in EUV systems where conventional depolarizing concepts are not available, leading to issues with polarization state management and imaging contrast optimization.
Innovation Solution
The system employs a ray-splitting optical element to split input light into mutually orthogonal partial rays, which are then processed to achieve a desired polarized illumination setting with minimal light loss, and includes switchable facets to dynamically adjust polarization states, enabling flexible polarization distribution in the pupil plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional depolarizing concepts (such as Hanle-depolarizer) are used, then polarization state can be controlled, but these concepts are not available in EUV range due to non-availability of optically transmissive components
Solution Approach 1:
The patent replaces conventional transmissive optical components (mirrors, lenses) with a reflective polarization control system. A polarization-dependent reflective element (PDRE) is used to separate polarized light into different spatial paths, enabling polarization state management in EUV range where transmissive components are unavailable. This substitution of mechanical/optical transmission with reflective mechanisms solves the component availability problem while maintaining polarization control capability.
2Ease of operation
If unpolarized light is used as light source, then light source simplicity is maintained, but generation of desired polarized illumination settings becomes difficult
Solution Approach 1:
The patent segments the unpolarized light into different polarization states using a polarization-dependent reflective element. The PDRE separates the incident unpolarized light into orthogonal polarized components (e.g., s-polarized and p-polarized) that follow different spatial paths. This segmentation enables independent control of polarization states while starting from simple unpolarized light, effectively reducing the overall system complexity compared to using already polarized light sources.
Solution Approach 2:
The polarization-dependent reflective element acts as an intermediary component that converts unpolarized light into controlled polarized illumination. This intermediate element (the PDRE) mediates between the simple unpolarized light source and the desired polarized illumination settings, enabling polarization control without requiring complex polarized light sources or multiple optical components.
3Device complexity
If polarized light source is used, then polarized illumination setting can be achieved, but light loss occurs during depolarization processes
Solution Approach 1:
The patent implements a dynamic polarization control system where the polarization-dependent reflective element can be switched between different states. By dynamically adjusting the orientation or state of the PDRE, the system can switch between polarized and depolarized illumination modes without permanent light loss. This dynamic capability allows optimization of light utilization based on specific illumination requirements, reducing energy loss compared to static polarized light sources that cannot be adapted.
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 increases the degree of polarization from unpolarized to nearly fully polarized light with reduced light loss and allows for flexible polarization adjustments during operation, enhancing imaging contrast and overcoming limitations in EUV systems.
Implementation Method 1
a ray-splitting optical element, which splits a light ray incident on this element when the projection exposure apparatus is in operation into a first partial ray and a second partial ray, with the first and the second partial ray having mutually orthogonal polarization directions
Data Source
AI summary
The disclosure relates to optical systems of a microlithographic projection exposure apparatus, and to a microlithographic exposure method. According to an aspect of the disclosure, an optical system has a light source, a ray-splitting optical element, which splits a light ray incident on this element when the projection exposure apparatus is in operation into a first partial ray and a second partial ray, with the first and the second partial ray having mutually orthogonal polarization directions, and at least one ray-deflecting optical element for generating a desired polarized illumination setting from the first partial ray and the second partial ray, wherein the ray-splitting optical element is arranged such that light incident on this ray-splitting optical element when the projection exposure apparatus is in operation has a degree of polarization of less than one.