EUV Projection Lens Mirrors at Zero Cross Temperatures
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Solution Overview
Problem
EUV lithographic projection exposure systems face challenges in maintaining high mechanical precision and minimizing thermal deformation of reflective optical elements due to temperature variations, which affect image quality and optical aberrations.
Innovation Solution
The projection lens employs reflective optical elements made of materials with a temperature-dependent coefficient of thermal expansion that have zero cross temperatures, combined with a temperature control system to maintain the elements at specific zero cross temperatures, reducing thermal deformation and aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reflective optical elements are used in EUV projection lens, then optical resolution and wavelength reduction are achieved, but thermal deformation and optical aberrations occur due to temperature variations
Solution Approach 1:
The patent changes the physical parameter of the mirror body material by selecting materials with specific zero cross temperatures where the coefficient of thermal expansion becomes zero. This parameter change allows the mirror surface figure to remain stable despite temperature variations, resolving the contradiction between achieving optical resolution with reflective elements and maintaining manufacturing precision.
Solution Approach 2:
The patent directly addresses thermal expansion effects by using materials whose thermal expansion coefficient is zero at specific temperatures (zero cross temperatures). By operating the mirrors at these zero cross temperatures, thermal deformation is eliminated, maintaining surface figure accuracy while using reflective optical elements for EUV projection.
2Manufacturing precision
If temperature control systems are implemented to maintain zero cross temperatures, then thermal deformation is minimized, but device complexity increases
Solution Approach 1:
The patent enables the mirror bodies to self-regulate their dimensional stability by using materials that naturally have zero thermal expansion at specific temperatures. The materials themselves provide the temperature compensation function, eliminating the need for external active temperature control systems and reducing device complexity while maintaining position accuracy.
3Reliability
If multiple mirrors with different zero cross temperatures are used, then optical aberrations are reduced, but material selection and system design become more complex
Solution Approach 1:
The patent applies different material properties (different zero cross temperatures) to different mirror bodies based on their specific operational requirements and temperature environments. Each mirror is optimized with the appropriate material for its local conditions, improving overall image quality and reliability while managing material selection complexity through targeted optimization.
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 achieves surface figure accuracy and position accuracy in the nanometer range, minimizing thermal-induced optical aberrations and ensuring high-quality image formation with structures down to 10 nm or smaller lateral dimensions.
Implementation Method 1
materials with a temperature dependent coefficient of thermal expansion which is zero at at least two zero cross temperatures
Data Source
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AI summary
The invention relates to a projection lens of an EUV-lithographic projection exposure system, comprising: at least two reflective optical elements Mi, each comprising a body MBi and a reflective surface MSi for projecting an object field on a reticle onto an image field on a substrate if the projection lens is exposed with an exposure power of EUV light with a wavelength in a wavelength range of less than 50 nm, being reflected from the reticle while illuminated by an illumination system of an EUV-lithographic projection exposure system, wherein the bodies MBm, MBn of at least two reflective optical elements comprise a material with a temperature dependent coefficient of thermal expansion which is zero at least two zero cross temperatures T10mn and T20mn, and wherein the lens comprises a support structure for passively or actively supporting the reflective optical elements Mi, wherein the temperature of at least a part of the support structure is at a reference temperature TRef, at least two tempering means for independently heating and/or cooling the at least two bodies MBn, MBm, and a temperature control system for independently controlling the temperature of the at least two heated or cooled bodies MBn, MBm to respective temperatures Tkn and a Tkm, and wherein during exposure of the lens with the exposure power of the EUV light the temperatures Tkn of the temperature controlled body MBn is within an interval of ± 5K, better ± 2K centered around the first zero cross temperatures T10mn, and the temperatures Tkm of the temperature controlled body MBm is within an interval of ± 5K, better ± 2K centered around the second zero cross temperatures T20mn.