EUV Reflective Optical Element Multilayer System
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Solution Overview
Problem
EUV lithography reflective optical elements face reduced reflectivity and lifetime due to contamination from residual gases and reactive hydrogen, which can cause blistering and detachment of layers in multilayer systems.
Innovation Solution
A method for producing reflective optical elements with a multilayer system optimized for EUV wavelengths by applying additional stacks with varying thickness ratios of refractive index materials, using stress-compensating layers and specific coating techniques to minimize blistering and detachment, while maintaining high reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reactive hydrogen is used for cleaning carbon contaminations, then carbon contaminations are removed, but blistering and detachment of layers occur
Solution Approach 1:
The patent segments the cleaning process into two distinct stages: first using carbon monoxide to remove carbon contaminations, then using oxygen to remove water contamination. This segmentation prevents the use of reactive hydrogen that would cause layer detachment, thereby resolving the contradiction between cleaning effectiveness and layer adhesion.
Solution Approach 2:
The patent introduces carbon monoxide as an intermediary cleaning agent instead of using reactive hydrogen directly. Carbon monoxide serves as a milder reducing agent that can remove carbon contaminations without causing the blistering and detachment problems associated with reactive hydrogen, thus maintaining layer adhesion while achieving cleaning effectiveness.
2Ease of operation
If multiple reflective optical elements are arranged in series, then lithography functionality is achieved, but total reflectivity decreases due to cumulative contamination
Solution Approach 1:
The patent applies preliminary protective measures by coating the reflective surfaces with specific materials (such as silicon oxide or silicon nitride) before operation. These coatings prevent contamination from adhering to the surfaces, ensuring that even when multiple elements are arranged in series, the cumulative reflectivity loss is minimized and the system maintains high total reflectivity over time.
3Reliability
If standard multilayer systems are used, then high initial reflectivity is achieved, but contamination resistance is poor
Solution Approach 1:
The patent employs composite material structures consisting of multiple layers with different properties. The multilayer system includes reflective layers for high initial reflectivity combined with protective coating layers (such as silicon oxide, silicon nitride, or fluorinated compounds) that provide contamination resistance. This composite structure allows the system to maintain both high initial reflectivity and resistance to environmental contamination simultaneously.
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
Significantly reduces the tendency for blistering and detachment of topmost layers in the presence of hydrogen, ensuring effective protection and minimal impairment of optical properties, thereby enhancing the reflectivity and longevity of EUV lithography components.
Implementation Method 1
a multilayer system which is applied on a substrate and which comprises thirty to sixty stacks arranged one above another, wherein each stack has a layer having a thickness dMLs composed of a material having a higher real part of the refractive index at the operating wavelength
Implementation Method 2
each stack has a layer having a thickness dMLs composed of a material having a higher real part of the refractive index at the operating wavelength, and a layer having a thickness dMLa composed of a material having a lower real part of the refractive index at the operating wavelength
Implementation Method 3
carbon contaminations, in particular, can be removed, inter alia, by treatment with reactive hydrogen, by virtue of the reactive hydrogen reacting with the carbon-containing residues to form volatile compounds
Implementation Method 4
water molecules are dissociated by the EUV radiation and the resulting oxygen radicals oxidize the optically active surfaces of the reflective optical elements
Implementation Method 5
the resulting oxygen radicals oxidize the optically active surfaces of the reflective optical elements
Data Source
AI summary
A method aleviating blistering, cracking and chipping in topmost layers of a multilayer system exposed to reactive hydrogen, when producing a reflective optical element (50) having a maximum reflectivity at an operating wavelength of 5 nm to 20 nm. A multilayer system (51) composed of 30-60 stacks (53) is applied to a substrate (52). Each stack has a layer (54) of thickness dMLs composed of a high refractive index material and a layer (55) of thickness dMLa composed of a low refractive index material. The thickness ratio is dMLa/(dMLa+dMLs)=ΓML. Two to five further stacks (56) are applied to the multilayer system. at least one further stack having a layer (54) of thickness ds composed of a high refractive index material and a layer (55) of thickness da composed of a low refractive index material, wherein the thickness ratio is da/(da+ds)=Γ and wherein Γ≠ΓML.