EUV Filter with Absorbing Member for Heat Load Reduction
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Solution Overview
Problem
Conventional filters used in EUV light sources reflect Out of Band (OoB) light, such as infrared radiation, towards upstream mirrors, causing heating issues and reducing the contrast of the light on the wafer, while also allowing stray infrared light to reach optical elements and the wafer surface.
Innovation Solution
A filter comprising parallel plate members with gaps, where the enveloping surface formed by the end surfaces is nonparallel to the incident light direction, reflects infrared light and transmits EUV light, with an absorbing member positioned outside the optical path to absorb the reflected infrared light, minimizing heat transfer to apparatus components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional filter reflects OoB light (infrared light) to eliminate it from the optical path, then the transmission of desired EUV light is improved, but the reflected infrared light heats mirrors and chamber components on the upstream side
Solution Approach 1:
The patent extracts the harmful reflected infrared light from the optical path by introducing an absorbing member positioned to intercept the reflected OoB light before it can reach mirrors and chamber components. This separates the function of filtering (achieved by the existing filter) from the function of absorbing reflected light (achieved by the new absorbing member), thereby eliminating the heating problem while preserving EUV light transmission.
Solution Approach 2:
The absorbing member acts as an intermediary element that intercepts the reflected infrared light between the filter and the mirrors/chamber components. This intermediary absorbs the harmful radiation, preventing it from reaching and heating the upstream optical components, while not interfering with the transmission of desired EUV light through the filter.
2Reliability
If a conventional filter with opening smaller than OoB wavelength is used to transmit only EUV light, then spectral purity is improved, but reflected infrared light becomes stray light that reaches optical elements and wafer surface through non-design optical path
Solution Approach 1:
The patent removes the stray light problem by extracting the reflected infrared light from the system using an absorbing member. This member is strategically positioned to capture reflected OoB light that would otherwise become stray light and reach optical elements and the wafer surface through non-design paths, thereby eliminating the harmful effects without compromising the filter's spectral purity function.
Solution Approach 2:
The absorbing member serves as an intermediary that intercepts reflected infrared light before it can scatter and reach sensitive components. By placing this absorbing element in the path of reflected light, the system prevents stray light from reaching optical elements and the wafer surface, thus protecting these components from thermal damage while maintaining the filter's spectral separation function.
3Productivity
If pulsed laser operates at high repetition frequency to increase average EUV intensity, then productivity is improved, but heat generation and thermal load on system components increase
Solution Approach 1:
The patent converts the harmful thermal effect of high-repetition-rate laser operation into a manageable issue by introducing an absorbing member that specifically targets and absorbs the harmful infrared radiation. This allows the system to maintain high laser repetition frequencies for high productivity while the absorbing member handles the thermal management of reflected OoB light, preventing excessive heat accumulation in critical optical components.
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 solution effectively reduces heat load on mirrors and optical elements by redirecting infrared light away from sensitive areas, maintaining high EUV light transmission efficiency and preventing stray light from reaching the wafer, thus enhancing the performance and reliability of the exposure apparatus.
Implementation Method 1
a filter which reflects first light having a first wavelength, and transmits second light having a second wavelength shorter than the first wavelength
Implementation Method 2
selectively transmit only desired EUV light so as to eliminate OoB light
Implementation Method 3
an absorbing member positioned outside the optical path to absorb the reflected infrared light
Data Source
AI summary
A filter reflects first light having a first wavelength, and transmits second light having a second wavelength shorter than the first wavelength. The filter includes a plurality of plate members positioned parallel to each other with gaps therebetween in a first direction. An enveloping surface formed by end surfaces of the plurality of plate members forms a flat surface, which is nonparallel to the first direction. The filter transmits the second light to the second direction.