EUV Mirror Multilayer Design for Stable Reflectivity
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Solution Overview
Problem
Existing EUV mirrors exhibit significant variation in reflectance over large angle of incidence ranges, making them challenging to produce reproducibly with high precision, and current broadband designs are complex to manufacture.
Innovation Solution
An EUV mirror design featuring a multilayer arrangement with a first layer group having a sufficient number of high refractive index and low refractive index layer pairs, where layer thicknesses follow simple monotonic profile functions, ensuring high reflectivity with minimal variation across the angle of incidence range, and optionally a second layer group for enhanced broadband effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer arrangement with periodic layer sequence is used to achieve high reflectivity, then reflectivity is improved, but the full width at half maximum of the reflectivity curve becomes relatively low, resulting in significant variation over angle of incidence range
Solution Approach 1:
The multilayer arrangement is divided into multiple layer groups, each with a different periodic layer sequence. The first layer group has a first periodic layer sequence optimized for high reflectivity at normal incidence, while the second layer group has a second periodic layer sequence optimized for broader angular coverage. This segmentation allows each group to specialize in different angular ranges, resolving the contradiction between peak reflectivity and angular bandwidth.
Solution Approach 2:
Different regions of the multilayer arrangement (different layer groups) are assigned different optical properties through distinct periodic layer sequences. The first layer group provides high reflectivity at normal incidence, while the second layer group provides extended reflectivity over larger angle ranges. This local differentiation of optical properties allows the overall structure to achieve both high peak reflectivity and broad angular coverage simultaneously.
2Adaptability or versatility
If broadband multilayer mirrors are designed to reduce reflectance variation over angle of incidence, then adaptability is improved, but manufacturing complexity increases
Solution Approach 1:
The complex broadband mirror is segmented into multiple layer groups, each with relatively simple periodic layer sequences. This segmentation reduces the manufacturing complexity of each individual layer group while achieving the overall broadband effect through their combination. Each layer group can be manufactured using standard deposition processes, avoiding the need for complex aperiodic structures.
Solution Approach 2:
The patent introduces depth-graded multilayer arrangements where the layer thicknesses vary continuously or in steps through the depth of the multilayer structure. This dynamic variation in layer parameters allows broadband reflectivity to be achieved with systematic layer constructions that are more manufacturable than fully aperiodic designs, balancing performance and manufacturing complexity.
3Adaptability or versatility
If complex depth-graded multilayer arrangements are used to achieve broadband effect, then adaptability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The depth-graded multilayer arrangement is segmented into discrete layer groups with well-defined periodic structures. Each layer group has controlled thickness variations that follow systematic patterns rather than fully aperiodic sequences. This segmentation reduces the precision requirements compared to fully continuous depth-graded structures, as each layer group can be manufactured with standard tolerances while the overall graded structure achieves broadband performance.
Solution Approach 2:
The patent systematically varies layer thickness parameters in discrete steps through the depth of the multilayer arrangement, creating depth-graded structures with controllable precision. Rather than requiring continuous parameter optimization, the design uses stepped variations in layer thickness that can be controlled with standard manufacturing tolerances, reducing the precision requirements while maintaining broadband effectiveness.
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 design achieves stable reflectivity over a wide angle of incidence range while allowing for precise and reproducible production, with the layer thickness profiles simplifying the interpretation of measurement results and reducing manufacturing errors.
Implementation Method 1
One class of EUV mirrors operates at relatively high angles of incidence of the incident radiation, that is to say with grazing incidence according to the principle of total internal reflection
Implementation Method 2
a multilayer arrangement having a reflective effect for radiation from the extreme ultraviolet range (EUV), said multilayer arrangement comprising many layer pairs comprising alternately low refractive index and high refractive index layer material
Data Source
AI summary
An EUV mirror has a multilayer arrangement applied on a substrate. The multilayer arrangement includes a first layer group having ten or more first layer pairs. Each first layer pair has a first layer composed of a high refractive index first layer material having a first layer thickness, has a second layer composed of a low refractive index second layer material having a second layer thickness and has a period thickness corresponding to the sum of the layer thicknesses of all the layers of a first layer pair. The layer thicknesses of one of the layer materials are defined, depending on the period number, by a simply monotonic first layer thickness profile function, e.g. by a linear, quadratic or exponential layer thickness profile function. The layer thicknesses of the other of the layer materials vary, depending on the period number, in accordance with a second layer thickness profile function.