EUV Reflective Optical Element Outer Layer Deposition
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Solution Overview
Problem
Reflective optical elements in EUV lithography systems face challenges with reflectivity loss and contamination due to reactive hydrogen, leading to etching attacks and reduced performance, which existing solutions fail to address effectively without causing additional damage or high costs.
Innovation Solution
A method involving atomic layer deposition (ALD) with macro cycles that include partial deposition and back-etching to create a thin, continuous outer layer on reflective optical elements, reducing reflectivity loss and preventing damage from hydrogen-induced etching, using thermal or plasma-assisted processes and inert gas separation for precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an outer layer is deposited on the reflective optical element to protect against contamination, then protection against carbon contaminations and oxidation is improved, but reflectivity loss increases due to the additional layer
Solution Approach 1:
The patent applies atomic layer deposition (ALD) to deposit ultra-thin outer layers with precisely controlled thickness parameters. By changing the deposition parameters to achieve thicknesses in the range of 0.5-5 nm, the protective function is maintained while minimizing the optical impact on EUV reflectivity
Solution Approach 2:
The patent uses composite material structures combining multiple thin layers with different materials (e.g., Ru, Rh, Ir, Mo, Si) deposited by ALD. This composite approach allows optimization of both protective properties and optical properties, where each layer contributes specific functionality while maintaining high reflectivity
2Ease of manufacture
If reactive hydrogen is used to clean contaminations from optical surfaces, then cleaning effectiveness is improved, but etching attack on optical surfaces increases
Solution Approach 1:
The patent deposits protective outer layers using ALD before the optical element is exposed to reactive hydrogen cleaning processes. These pre-deposited layers act as barriers that prevent the etching attack from reaching the underlying reflective coating, while still allowing the hydrogen to remove carbon contaminations from the surface
Solution Approach 2:
The ALD-deposited outer layer serves as an intermediary between the reactive hydrogen cleaning agent and the reflective optical element. This intermediary layer enables the cleaning process to occur without directly exposing the sensitive optical surfaces to harmful etching conditions
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 method achieves a thin, continuous outer layer that minimizes reflectivity loss and prevents damage to reflective coatings, reducing the need for premature cleaning or replacement of optical elements while maintaining high reflectivity and throughput.
Implementation Method 1
The depositing is effected in at least one macro cycle comprising: at least partly depositing the outer layer through an atomic layer deposition (ALD) process in at least one ALD cycle
Implementation Method 2
partly back-etching the outer layer
Implementation Method 3
The EUV radiation then results in dissociation of the hydrocarbons, which leads to growth of carbon contaminations on the optical surfaces of the reflective optical elements
Implementation Method 4
Optical elements that reflect EUV radiation can also be used in other optical arrangements (EUV lithography systems)
Data Source
AI summary
A method of depositing an outer layer (35) on a surface (36) of a reflective optical element (30) for the EUV wavelength range, wherein the depositing is effected in at least one macro cycle (37). The macro cycle (37) includes: at least partly depositing the outer layer (35) with an atomic layer deposition (ALD) process in at least one ALD cycle and partly back-etching the outer layer (35). Also disclosed is a reflective optical element (30) for the extreme ultraviolet (EUV) wavelength range which includes a surface (36) having an outer layer (35), wherein the outer layer (35) is deposited by the above-described method, and to an EUV lithography system having at least one such reflective optical element (30).