EUV Projection Lens Film Element Wavefront Correction
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Solution Overview
Problem
EUV projection lenses face challenges in achieving precise adjustment and correction during production and operation due to the limitations of refractive optical elements in extreme ultraviolet lithography, requiring complex disassembly for wavefront aberration correction and lacking effective concepts for sustained correction of lifetime effects.
Innovation Solution
A film element with specific layer configurations, comprising a wavefront correction layer and a transmission correction layer, is introduced into the projection beam path to alter the wavefront profile and intensity distribution, allowing for targeted wavefront correction without altering the mirror positions, and enabling correction of lifetime effects through controlled layer thickness profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If complex partial disassembly of the projection lens is performed to correct wavefront aberrations, then imaging performance can be improved, but the adjustment process becomes more complex and time-consuming
Solution Approach 1:
The wavefront correction function is segmented from the main projection lens system by using a separate film element that can be independently adjusted. This allows correction of wavefront aberrations without requiring disassembly of the complex mirror system, thus improving manufacturing precision while reducing adjustment complexity.
Solution Approach 2:
A film element acts as an intermediary component between the illumination source and the projection mirrors. This thin film serves as a mediator to correct wavefront aberrations by introducing controlled phase shifts, enabling precision adjustment without complex mechanical modifications to the mirror positions.
2Manufacturing precision
If rigid-body movements of mirrors are used for correction, then wavefront aberrations can be adjusted, but lifetime effects cannot be sustainably corrected
Solution Approach 1:
The film element provides a dynamic correction mechanism that can be adjusted during operation to compensate for lifetime effects. Unlike rigid mirror positions, the film's optical properties can be modified over time through controlled thickness variations, enabling sustained correction as the system ages.
Solution Approach 2:
The invention changes the physical parameter of the film element (thickness profile) to achieve wavefront correction. By controlling the thickness distribution of the film, the optical path difference is adjusted, providing a flexible mechanism that can adapt to long-term drifts and lifetime effects without mechanical reconfiguration.
3Manufacturing precision
If thick layers are used for wavefront correction, then correction effectiveness increases, but transmission losses increase
Solution Approach 1:
The film element implements local quality by having spatially varying thickness across its surface. Thinner regions provide minimal correction with high transmission, while locally thicker regions provide stronger phase correction only where needed. This gradient structure achieves effective wavefront correction while minimizing overall transmission losses.
Solution Approach 2:
The film element can be constructed as a composite structure combining materials with different optical properties. By selecting materials with appropriate refractive indices and absorption coefficients, the film achieves high correction effectiveness per unit thickness while maintaining high EUV transmission, resolving the contradiction between correction strength and transmission.
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 film element achieves significant wavefront correction with minimal transmission losses, maintaining high EUV radiation transmission (up to 85%) and allowing for precise adjustment and maintenance without disassembling the projection lens, thereby enhancing imaging performance and operational stability.
Implementation Method 1
a first layer and a second layer which, in each case, act in a defined manner on rays of the projection beam passing through and change the profile of a wavefront in a predefinable manner
Implementation Method 2
A mirror (EUV mirror) having a reflective effect for radiation from the EUV range typically has a substrate, on which is applied a multilayer arrangement having a reflective effect for radiation from the extreme ultraviolet range and having a large number of layer pairs comprising alternately relatively low refractive index and relatively high refractive index layer material and acting in the manner of a distributed Bragg reflector
Data Source
AI summary
A film element of an EUV-transmitting wavefront correction device is arranged in a beam path and includes a first layer of first layer material having a first complex refractive index n1=(1−δ1)+iß1, with a first optical layer thickness, which varies locally over the used region in accordance with a first layer thickness profile, and a second layer of second layer material having a second complex refractive index n2=(1−δ2)+iß2, with a second optical layer thickness, which varies locally over the used region in accordance with a second layer thickness profile. The first and second layer thickness profiles differ. The deviation δ1 of the real part of the first refractive index from 1 is large relative to the absorption coefficient ß1 of the first layer material and the deviation δ2 of the real part of the second refractive index from 1 is small relative to the absorption coefficient ß2 of the second layer material.