EUV Lithography Optical Element Temperature Control
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Solution Overview
Problem
EUV lithography projection lenses face significant wavefront aberrations due to inhomogeneous radiation intensity and resulting temperature distributions on optical surfaces, which cannot be fully compensated by setting the operating temperature to the zero crossing temperature, leading to deformations and aberrations.
Innovation Solution
An optical arrangement where the average temperature of optical elements is coordinated with the zero crossing temperature, with a temperature control device adjusting the temperature to minimize wavefront aberrations by setting a difference dependent on local irradiance, using a substrate material with a zero coefficient of thermal expansion at the zero crossing temperature, and employing heating or cooling mechanisms to maintain optimal temperature distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the operating temperature is set to the zero crossing temperature, then thermal expansion is minimized, but wavefront aberrations occur due to inhomogeneous temperature distribution
Solution Approach 1:
The patent applies local quality by differentiating between the average temperature requirement (zero crossing temperature for minimal thermal expansion) and local temperature variations (inhomogeneous distribution causing aberrations). The solution involves creating temperature compensation mechanisms that address local deviations from the average temperature, allowing different regions of the optical element to have tailored temperature characteristics that compensate for radiation-induced thermal gradients.
Solution Approach 2:
The patent employs parameter changes by adjusting the average temperature of the optical element away from the zero crossing temperature of the substrate material. By changing the operating temperature parameter to a value that accounts for the inhomogeneous temperature distribution, the system achieves optimal balance between minimizing overall thermal expansion and reducing wavefront aberrations caused by temperature gradients.
2Manufacturing precision
If substrate materials with low CTE are used, then geometrical tolerance is maintained, but temperature-dependent deformations occur under radiation
Solution Approach 1:
The patent applies composite materials by combining the low CTE substrate material with additional temperature compensation mechanisms or coatings. This composite approach allows the system to maintain the geometrical tolerance benefits of low CTE materials while introducing new functional properties that compensate for temperature-dependent deformations under radiation conditions.
Solution Approach 2:
The patent introduces an intermediary temperature compensation mechanism that mediates between the substrate material's low CTE property and the temperature stability requirement. This intermediary element or mechanism absorbs or compensates for the temperature-dependent deformations, allowing the substrate to maintain its geometrical precision while the compensation mechanism handles the thermal stability challenge.
3Manufacturing precision
If temperature control is implemented, then wavefront aberrations are reduced, but device complexity increases
Solution Approach 1:
The patent applies self-service by designing temperature compensation mechanisms that automatically adjust to radiation-induced temperature changes without requiring complex external control systems. The system uses the optical element's own thermal properties and built-in compensation structures to self-regulate temperature effects, reducing the need for sophisticated external temperature control apparatus.
Solution Approach 2:
The patent employs preliminary action by pre-configuring the optical element with temperature compensation features during manufacturing, such as pre-stressed structures or materials with compensating thermal properties. This preliminary preparation allows the system to automatically counteract temperature-induced aberrations during operation without requiring complex real-time control mechanisms.
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 reduces wavefront aberrations by optimizing the temperature difference between the average and zero crossing temperatures, improving the imaging quality of EUV lithography projection lenses by maintaining minimal thermal deformations and aberrations, even under varying radiation conditions.
Implementation Method 1
the coefficients of thermal expansion of the different phases almost cancel one another out
Implementation Method 2
the coefficient of thermal expansion at a zero crossing temperature related to a reference temperature is equal to zero
Implementation Method 3
a considerable proportion of radiation is absorbed by the mirrors and converted into heat
Implementation Method 4
the resulting temperature distribution at the optical surface is also inhomogeneous. Consequently, the condition that the operating temperature corresponds to the zero crossing temperature cannot be fulfilled at the entire surface
Data Source
AI summary
The invention relates to an optical arrangement comprising: at least one optical element comprising an optical surface and a substrate, wherein the substrate is formed from a material whose temperature-dependent coefficient of thermal expansion at a zero crossing temperature ΔTZC=TZC−Tref related to a reference temperature Tref is equal to zero, wherein the optical surface has, during the operation of the optical arrangement, a location-dependent temperature distribution ΔT(x, y) that is dependent on a local irradiance (5a), is related to the reference temperature Tref and has an average temperature ΔTav, a minimum temperature ΔTmin and a maximum temperature ΔTmax, wherein the average temperature ΔTav is less than the average value 1/2 (ΔTmax+ΔTmin) formed from the minimum temperature ΔTmin and the maximum temperature ΔTmax, and wherein the zero crossing temperature ΔTZC is greater than the average temperature ΔTav.