EUV Mirror Heating Condition Determination
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Solution Overview
Problem
EUV mirrors in microlithographic projection exposure apparatuses experience temperature-related thermal expansion and deformation due to radiation absorption and hydrogen atmosphere exposure, affecting imaging quality, necessitating accurate determination of heating conditions to compensate for these effects.
Innovation Solution
A method involving deflecting an input measuring beam onto the EUV mirror, analyzing optical parameters of the output beam, and determining the heating condition without introducing additional electronics or stray light into the optical system, using techniques such as refractive index measurement, optical path length change, and beam deflection, which can be done contactlessly and during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact-less measurement method is used to determine mirror heating condition, then measurement precision is improved and the optical system operation is not worsened, but additional electronics and stray light introduction are avoided
Solution Approach 1:
The patent replaces contact-based electronic temperature sensors with a contact-less optical measurement system. A measuring beam is directed through the mirror substrate to detect temperature-induced changes in optical properties (refractive index, absorption coefficient) without requiring physical sensors inside the evacuated housing, thereby eliminating the need for additional electronics while maintaining measurement precision.
Solution Approach 2:
The patent uses the mirror substrate itself as an intermediary medium for temperature measurement. By measuring the optical properties of the substrate material (which changes with temperature), the system indirectly determines the mirror's heating condition without introducing foreign sensing devices into the optical path or evacuated environment.
2Measurement precision
If traditional temperature sensors are installed in the optical system, then heating condition can be measured, but stray light is introduced and optical system performance deteriorates
Solution Approach 1:
Traditional contact-based temperature sensors are replaced with an optical measurement method that uses the existing optical infrastructure. The measuring beam interacts with the mirror substrate's optical properties to infer temperature, eliminating the need for physical sensors that would introduce stray light and potentially contaminate the evacuated optical environment.
3Productivity
If EUV mirror operates under radiation and hydrogen atmosphere, then microlithography function is achieved, but thermal expansion and deformation occur affecting imaging quality
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the mirror's heating condition through optical measurements. The measured temperature data can be used to adjust cooling systems or compensate for thermal effects in real-time, maintaining imaging quality despite the necessary EUV radiation exposure and hydrogen atmosphere cleaning operations.
Solution Approach 2:
The system performs preliminary temperature monitoring and analysis to predict and prevent thermal deformation before it significantly degrades imaging quality. By detecting early signs of heating through optical property changes, corrective actions can be taken proactively to maintain manufacturing precision.
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
Enables reliable characterization of the heating condition with high accuracy, allowing for effective compensation of thermal effects and maintenance of optical system performance, without additional electronics or stray light introduction.
Implementation Method 1
the low coefficients of expansion which typically exist in the mirror material of EUV mirrors involve a comparatively pronounced temperature dependency in respect of the refractive index, which in turn makes it possible to infer a change in temperature of the mirror from measurement of the change in refractive index
Implementation Method 2
the EUV mirrors experience a rise in temperature and linked thereto thermal expansion or deformation, as a consequence of absorption of the radiation emitted by the EUV light source
Implementation Method 3
deflecting at least one input measuring beam on to the mirror; ascertaining at least one optical parameter of at least one output measuring beam produced from the input measuring beam after interaction with the mirror
Data Source
AI summary
The invention concerns a method of and an arrangement for determining the heating condition of a mirror in an optical system, in particular in a microlithographic projection exposure apparatus. In an embodiment the mirror is an EUV mirror and a method according to the invention comprises the following steps: deflecting at least one input measuring beam on to the mirror; ascertaining at least one optical parameter of at least one output measuring beam produced from the input measuring beam after interaction with the mirror; and determining the heating condition of the mirror on the basis of the parameter.