EUV Light Source Polarization Control for Low-Loss Lithography
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Solution Overview
Problem
Current EUV light sources for projection exposure apparatuses face challenges in generating a resolution-optimized illumination beam, particularly in achieving low transmission loss and maintaining polarization quality across varying illumination angles.
Innovation Solution
An EUV light source that generates linearly polarized EUV illumination light by converting a circularly polarized raw output beam using a polarization setting device with adjustable deflection magnets and Brewster angle incidence mirrors, allowing for tangentially polarized illumination with minimal transmission loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a circularly polarized EUV raw output beam is generated and converted to linearly polarized light using a polarization setting device, then the polarization quality is improved for resolution-optimized illumination, but transmission loss increases due to the polarization conversion process
Solution Approach 1:
The patent changes the polarization state parameter from circular to linear by adjusting the deflection magnets in the undulator and using Brewster angle incidence mirrors. This parameter change enables resolution-optimized illumination while managing transmission loss through precise control of the polarization conversion process
Solution Approach 2:
The patent generates a circularly polarized EUV raw output beam as an intermediate state before converting it to linearly polarized light. This preliminary action allows for flexible polarization orientation selection and optimizes the subsequent polarization conversion to minimize transmission loss
2Adaptability or versatility
If deflection magnets in the undulator are made displaceable to generate linearly polarized light with arbitrary polarization orientation, then the adaptability of the light source is improved, but the device complexity increases
Solution Approach 1:
The patent makes the deflection magnets displaceable rather than fixed, enabling dynamic adjustment of the polarization orientation. This dynamic capability allows the light source to adapt to different illumination requirements while maintaining a relatively simple undulator structure through controlled magnetic field adjustments
3Stability of the object's composition
If Brewster angle incidence mirrors are used to achieve tangentially polarized illumination, then the polarization consistency across the illumination field is improved, but the alignment precision requirements increase
Solution Approach 1:
The patent utilizes Brewster angle incidence as a specific parameter setting for the mirrors, which naturally produces tangentially polarized illumination with consistent polarization across the field. This parameter choice simplifies the polarization control while maintaining high polarization consistency, though it requires precise mirror alignment
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 solution enables high-resolution, low-loss illumination with consistent polarization across the illumination field, enhancing the performance of projection exposure apparatuses by maintaining polarization quality and reducing the requirements on downstream illumination optical units.
Implementation Method 1
Brewster angle incidence mirrors
Implementation Method 2
converting a circularly polarized raw output beam using a polarization setting device
Implementation Method 3
The EUV generation device of the light source can be embodied as an undulator. Deflection magnets of the undulator can be designed in a displaceable fashion
Data Source
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AI summary
An EUV light source (2) serves for generating a usable output beam (3) of EUV illumination light for a projection exposure apparatus (1) for projection lithography. The light source (2) has an EUV generation device (2c) which generates an EUV raw output beam. The latter is circularly polarized. For the purposes of setting the polarization of the usable output beam (3) and in respect of the polarization direction, a polarization setting device (32; 39) has a linearly polarizing effect on the raw output beam. This results in an EUV light source, which provides an improved output beam for a resolution-optimized illumination.