EUV Reflective Optical Element High Thermal Conductivity Substrate
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Solution Overview
Problem
Conventional reflective optical elements for EUV lithography systems face challenges with high thermal loads due to low thermal conductivity, leading to severe heating, bending, and thermal degradation, especially when exposed to high radiation powers.
Innovation Solution
A reflective optical element with a substrate material having a thermal conductivity greater than 50 W/(mK), combined with a polishing layer and large cooling channels to facilitate turbulent flow, ensuring efficient heat dissipation and maintaining high surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional substrate materials (glass, quartz, glass ceramic) are used for reflective optical elements, then the surface can be polished to high quality (microroughness < 0.2 nm rms), but the thermal conductivity is too low to handle high thermal loads from high radiation powers
Solution Approach 1:
The patent applies a polishing layer composed of amorphous material (such as amorphous silicon, amorphous silicon oxide, or amorphous silicon dioxide) onto a substrate made of material with high thermal conductivity (such as silicon, silicon carbide, or metal alloys). This composite structure combines the high thermal conductivity of the substrate with the excellent polishability and surface quality of the amorphous polishing layer, thereby resolving the contradiction between thermal load handling and surface quality.
2Temperature
If cooling channels are arranged in the base body to improve heat dissipation, then thermal load management improves, but the production complexity and cost increase
Solution Approach 1:
The patent changes the parameter of cooling channel dimensions from conventional small-diameter microchannels to large-diameter channels with cross-sectional areas of at least 0.5 mm². This parameter change enables turbulent flow of the cooling medium, significantly improving heat dissipation efficiency. The larger dimensions also simplify the manufacturing process compared to precise microchannel fabrication, thereby addressing both heat dissipation and production complexity.
3Power
If high radiation power is used in the EUV source, then the radiation output in the EUV wavelength range increases, but the thermal load on the optical elements increases due to radiation outside the EUV wavelength range
Solution Approach 1:
The composite structure of high thermal conductivity substrate combined with amorphous polishing layer enables the optical element to withstand high radiation powers. The substrate efficiently conducts away heat generated by radiation outside the EUV wavelength range, while the polishing layer maintains the required surface quality for EUV reflection, thus allowing high power operation without excessive thermal loading.
Solution Approach 2:
The patent converts the harmful thermal effect of radiation outside the EUV wavelength range into a manageable parameter by using the high thermal conductivity substrate to efficiently conduct and dissipate the heat. The cooling channels with turbulent flow further enhance this heat removal process, transforming the potential harmful thermal load into an controllable operating condition that allows high radiation power output.
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 manages high thermal loads, preventing thermal degradation and maintaining optical quality by enhancing heat dissipation and surface accuracy while being cost-effective and simple to produce.
Implementation Method 1
At least one cooling channel through which a cooling medium can flow is arranged in the base body
Implementation Method 2
a thermal conductivity of the known mirror materials is often too low to conduct away enough heat from the reflective surface
Data Source
AI summary
A reflective optical element for use in an EUV system is disclosed. The reflective optical element includes a base body, which is produced at least partly from a substrate material. At least one cooling channel through which a cooling medium can flow is arranged in the base body. A material having a thermal conductivity of greater than 50 W/mK is provided as substrate material. The reflective optical element also includes a polishing layer, which is applied on the substrate material. The polishing layer includes an amorphous material which can be processed via polishing.