EUV Reticle Backside Inspection via Multi-Height 3D Profiling
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Solution Overview
Problem
In extreme ultraviolet lithography (EUVL), maintaining the cleanliness and flatness of the backside of reflective reticles is crucial to prevent distortions in the pattern, as minute contaminants can significantly impact the reflective face and lead to pattern distortions in the photoresist layer, necessitating effective in-line inspection methods that avoid offline processing and potential re-contamination.
Innovation Solution
A method and apparatus for in-line inspection of the backside of EUV reticles using 3D imaging techniques, allowing for continuous monitoring without removing the reticle from the vacuum chamber, employing a vacuum housing with illuminators and an imaging device to detect light scattered or reflected from the backside, and generating a 3D surface profile map to assess contamination and topography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offline inspection methods are used to detect contaminants on the backside of EUV reticles, then measurement precision can be improved, but productivity decreases due to removal from the vacuum chamber and potential re-contamination risks
Solution Approach 1:
The inspection system performs contaminant detection on the reticle backside before the reticle is used in lithography operations. By conducting the inspection in advance while the reticle is still in the vacuum chamber, the system prevents contaminated reticles from entering the lithography process, thereby maintaining both measurement precision and production continuity without requiring offline inspection
Solution Approach 2:
The inspection system enables continuous monitoring of reticle backside cleanliness during the normal operation cycle. The reticle remains in the vacuum chamber throughout the inspection process, allowing uninterrupted inspection without removal, thus maintaining production continuity while achieving precise contaminant detection through the integrated imaging system
2Ease of operation
If the reticle is removed from the vacuum chamber for inspection, then ease of operation is improved, but reliability decreases due to potential re-contamination
Solution Approach 1:
The system introduces an intermediary inspection mechanism that can access the reticle backside through the vacuum chamber environment without requiring removal. The imaging device and illuminators act as intermediaries that penetrate or access the chamber to perform inspection, thereby maintaining both ease of operation and reliability by avoiding exposure to external contamination
Solution Approach 2:
The inspection is performed within the vacuum chamber's inert vacuum environment, which protects the reticle from re-contamination during the inspection process. This maintains the contaminant-free status while allowing inspection operations to proceed, thus preserving both reliability and ease of operation
3Ease of manufacture
If traditional UV lithography masks are used, then ease of manufacture is improved, but manufacturing precision decreases at nanometer technology process nodes
Solution Approach 1:
The system addresses the transition from UV to EUV lithography by changing the wavelength parameter from ultraviolet to extreme ultraviolet range. This parameter change enables nanometer-scale pattern resolution while the inspection system adapts to detect contaminants on the reflective reticle structure, thereby achieving both manufacturing precision and ease of manufacture for advanced nodes
Solution Approach 2:
The inspection system is designed to work with the composite structure of EUV reflective reticles, which include multiple layers (substrate, reflective coating, absorber layer, capping layer). The system detects contaminants on the backside that could affect the reflective face, enabling precise inspection of this complex multi-layer structure while maintaining ease of manufacture for EUV lithography
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 enables rigorous and precise inspection of reticles, preventing pattern distortions and maintaining production continuity by identifying and addressing contaminants on the backside of EUV reticles, ensuring pattern fidelity and uniformity without exposing them to additional contamination risks.
Implementation Method 1
detecting light reflected and/or scattered by the reticle surface
Implementation Method 2
detecting light reflected and/or scattered by the reticle surface
Data Source
AI summary
A method of inspecting a reticle includes obtaining a first image of a surface of the reticle at a first height by scanning the reticle surface with a light source at the first height of the reticle surface relative to a reference surface height of the reticle surface and obtaining a second image of the reticle surface at a second height by scanning the reticle surface with the light source at the second height of the reticle surface relative to the reference surface height of the reticle surface. The second height is different from the first height. The first and the second images are then combined to obtain a surface profile image of the reticle.