EUV Optical Grating Coating Suppresses Higher Order Diffraction
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Solution Overview
Problem
Optical gratings used for extreme ultraviolet (EUV) radiation struggle to suppress diffraction into higher orders of diffraction, leading to unwanted radiation components and polarization effects during reflection or diffraction.
Innovation Solution
A coating with a total reflection layer and an absorber layer is applied to the periodic structure of the optical grating, where the total reflection layer has a critical angle that suppresses higher orders of diffraction by ensuring total internal reflection only for the predetermined wavelength, while the absorber layer minimizes absorption for the predetermined order and maximizes it for higher orders, using materials like Zr, Pd, and Si for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a blaze structure is used to concentrate intensity into a predetermined order of diffraction, then the intensity in the predetermined order is improved, but the suppression of higher orders of diffraction deteriorates
Solution Approach 1:
The coating is divided into multiple functional layers: a total reflection layer for suppressing higher orders through critical angle effects, and an absorber layer for selective absorption of unwanted wavelengths. This segmentation allows each layer to address specific aspects of the diffraction suppression problem independently.
Solution Approach 2:
Different regions of the optical grating receive different coating treatments. The blaze structure regions are coated with the multi-layer coating system designed for suppression, while maintaining the underlying blaze geometry that concentrates intensity. This allows local optimization of both intensity concentration and higher order suppression.
2Object-generated harmful factors
If a coating is applied to suppress higher orders of diffraction, then the suppression of unwanted radiation is improved, but the reflectivity for the predetermined wavelength may deteriorate
Solution Approach 1:
The coating parameters (layer thicknesses, materials, angles) are precisely optimized to create a critical angle that coincides with the diffraction angle of higher orders. This parameter tuning allows the total reflection layer to suppress higher orders while maintaining high reflectivity for the predetermined wavelength that falls outside the critical angle range.
Solution Approach 2:
The coating combines materials with different optical properties: the total reflection layer uses materials with high refractive index for critical angle suppression, while the absorber layer uses materials with selective absorption characteristics. This composite structure achieves both suppression and reflectivity maintenance through complementary material properties.
3Object-generated harmful factors
If the critical angle of the total reflection layer is set to suppress higher orders, then the suppression effect is improved, but the angle range for total internal reflection becomes more restrictive
Solution Approach 1:
The optical grating system is designed with adjustable incident angles that can be dynamically optimized for different operating conditions. This allows the system to adapt to the restrictive critical angle requirements while maintaining effective suppression of higher orders across varying operational parameters.
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 suppresses higher orders of diffraction, maintaining high reflectivity for the predetermined wavelength and reducing contamination from other wavelengths, with the absorber layer enhancing the suppression of unwanted radiation components and improving polarization control.
Implementation Method 1
the total reflection layer has a critical angle that suppresses higher orders of diffraction by ensuring total internal reflection only for the predetermined wavelength
Implementation Method 2
the absorber layer minimizes absorption for the predetermined order and maximizes it for higher orders
Implementation Method 3
a periodic structure is formed, said structure being embodied to diffract incident radiation, in particular incident extreme ultraviolet (EUV) radiation, with a predetermined wavelength into a predetermined order of diffraction
Data Source
AI summary
An optical grating (8) includes a substrate (9), on the surface (9a) of which a periodic structure (10) is formed that is embodied to diffract incident radiation (11), in particular incident EUV radiation, with a specified wavelength (λτ) into a predetermined order of diffraction, in particular into the first order of diffraction (m=+1). The optical grating also has a coating (12) applied onto the periodic structure with at least one layer (13, 14) that is embodied to suppress the diffraction of the incident radiation into at least one higher order of diffraction (m=+2, . . . ) than the predetermined order of diffraction.