EUV Reflective Optics with Volume Noble-Metal Doping Against Hydrogen Etching
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Solution Overview
Problem
Existing methods for protecting reflective optical elements in EUV lithography systems from reactive hydrogen species, such as hydrogen radicals and ions, are inefficient and complex, particularly when dealing with structured optics like those with grating structures.
Innovation Solution
Doping the substrate and structured layers of reflective optical elements with noble metals throughout their volume, rather than just near the surface, using methods like sputter deposition, to enhance hydrogen recombination and prevent volatile hydride formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protective layers made of precious metals are applied to cover components exposed to hydrogen-containing atmosphere, then protection against hydrogen ion penetration and radical attack is improved, but device complexity and manufacturing effort increase significantly
Solution Approach 1:
The patent changes the concentration parameter of noble metals from surface-only or near-surface distribution to volume distribution throughout the substrate. This is achieved by adding noble metal dopants (Au, Pt, Pd, Rh, Ir, Ru, or Os) at concentrations of 10^19 to 10^21 atoms/cm³ during substrate manufacturing, eliminating the need for complex surface coating processes while maintaining protection against hydrogen species.
Solution Approach 2:
The noble metal doping is performed preliminarily during substrate manufacturing rather than as a subsequent surface treatment step. This preliminary action integrates the protective function into the substrate itself, avoiding the need for separate protective layer application processes and reducing overall device complexity.
2Reliability
If noble metal ions are implanted only into the near-surface volume region, then hydrogen recombination is enhanced at the surface, but protection is insufficient for structured optics with steep edges
Solution Approach 1:
The patent changes the spatial distribution parameter of noble metals from near-surface concentration (depth < 1000 nm) to volume distribution throughout the entire substrate. This volume doping approach ensures that all surfaces, including steep edges and complex structures, are protected without requiring precise control of implantation depth.
3Reliability
If complete coverage of structured surfaces with reflective coating is attempted, then protection against etching attack is improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent extracts the protective function from the reflective coating and transfers it to the substrate itself through volume doping with noble metals. This eliminates the requirement for complete and complex coating coverage of structured surfaces, as the substrate provides inherent protection throughout its volume.
Solution Approach 2:
The substrate is given multiple functions: it serves as the structural base, the reflective element, and the protective barrier against hydrogen species. The volume-doped noble metals provide universal protection throughout the substrate, eliminating the need for separate protective coatings on complex structured surfaces.
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
This approach effectively prevents etching by reactive hydrogen species with minimal effort, improving the durability and radiation resistance of reflective optical elements in EUV systems.
Implementation Method 1
The doping with the noble metal atoms dopant serves to reduce the formation of volatile hydrides
Implementation Method 2
The structurable layer and/or the reflective coating is/are applied by sputter deposition, wherein a sputter target doped with a noble metal is used in the sputter deposition
Data Source
Figure 1
Figure 2~4
AI summary
The invention relates to a reflective optical element (17), in particular for reflecting EUV radiation (16), comprising: a substrate (25) and a reflective coating (26) that is applied to the substrate (25). In one aspect of the invention, the volume (V) of the substrate (25) is doped with at least one noble metal (27). In a further aspect of the invention, the reflective coating (26) and/or a structured layer (28), which is situated between the substrate (25) and the reflective coating (26), is doped with at least one noble metal (27). The invention also relates to an optical arrangement, preferably a projection exposure system for microlithography, in particular for EUV lithography, which arrangement comprises at least one such reflective optical element (17), and to a method for manufacturing such a reflective optical element (17).