Self-Supporting 2D Diffraction Grating for EUV Aberration Mapping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining aberrations in projection systems, especially those using extreme ultraviolet (EUV) radiation, face challenges due to the need for transmissive supporting layers that attenuate EUV radiation and generate unwanted interference beams contributing to phase stepping signals.
Innovation Solution
A self-supporting two-dimensional diffraction grating with a square array of through-apertures, designed to reduce contributions to the first harmonic of the phase stepping signal, eliminating the need for transmissive supporting layers and minimizing unwanted interference beams by optimizing grating efficiencies and geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a transmissive supporting layer is used to support the two-dimensional diffraction grating, then the structural integrity and stability are improved, but the EUV radiation transmission is significantly reduced due to attenuation
Solution Approach 1:
The invention extracts and removes the transmissive supporting layer from the system entirely. Instead of using a supporting layer that transmits EUV radiation, the patent employs a self-supporting diffraction grating structure where the grating pattern is directly formed on a substrate that provides mechanical support without requiring additional transmissive layers. This eliminates the attenuation problem while maintaining structural integrity.
Solution Approach 2:
The invention introduces a reflective supporting structure as an intermediary between the diffraction grating pattern and the substrate. This reflective support layer provides mechanical stability while being transparent to EUV radiation transmission, unlike traditional transmissive supporting layers that attenuate the radiation. The intermediary structure allows the grating to be self-supporting without compromising radiation transmission.
2Stability of the object's composition
If a transmissive supporting layer is used to support the diffraction grating, then the structural stability is improved, but unwanted interference beams are generated that contribute to phase stepping signals
Solution Approach 1:
The invention extracts and eliminates the transmissive supporting layer that causes interference beam generation. By using a self-supporting grating structure with reflective support, the source of unwanted interference is removed entirely, preventing the generation of harmful interference beams while maintaining structural stability.
Solution Approach 2:
The invention converts the potential harm of requiring structural support into a benefit by using a reflective support structure instead of a transmissive one. This alternative support method provides the necessary structural stability while avoiding the generation of unwanted interference beams, effectively turning the support requirement into an opportunity to eliminate interference.
3Loss of energy
If the diffraction grating is made self-supporting by removing transmissive supporting layers, then EUV radiation transmission is improved, but the structural complexity increases
Solution Approach 1:
The invention merges the mechanical support function and the diffraction grating function into a single integrated structure. The self-supporting grating combines the substrate, support structure, and diffraction pattern into one unified component, eliminating the need for separate transmissive supporting layers and reducing overall structural complexity despite the advanced design.
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 enables accurate aberration mapping in EUV projection systems without significant radiation attenuation and reduces errors in aberration determination, improving imaging and overlay performance.
Implementation Method 1
A two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system, the diffraction grating comprising a substrate provided with a square array of through-apertures
Implementation Method 2
The substrate may comprise: a support layer; and a radiation absorbing layer, and the through-apertures may extend through both the support layer and the radiation absorbing layer
Data Source
AI summary
A two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system comprises a substrate provided with a square array of through-apertures, wherein the diffraction grating is self-supporting. It will be appreciated that for a substrate provided with a square array of through-apertures to be self-supporting at least some substrate material is provided between each through-aperture and the adjacent through apertures. A method of designing a two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system comprises: selecting a general geometry for the two-dimensional diffraction grating, the general geometry having at least one parameter; and selecting values for the least one parameter that result in a grating efficiency map for the two-dimensional diffraction grating so as to control the contributions to a first harmonic of a phase stepping signal.