EUV Baseplate Low-Reflecting Edges for Reticle Inspection
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Solution Overview
Problem
Reticle backside inspection systems in EUV photolithography face challenges with false positive readings due to light being reflected off the EUV baseplate and directed towards the camera, which incorrectly identifies particle contamination.
Innovation Solution
The design of the EUV baseplate incorporates low-reflecting surfaces on its edge structures, such as beveled surfaces or surfaces with a low radius of curvature, to minimize light reflection towards the camera, and may include light screens to block inspection light from reaching the baseplate edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light is directed at the reticle backside surface at a shallow angle for particle detection, then particle contamination can be detected through light scattering, but light may be reflected off the baseplate and reach the camera causing false positive readings
Solution Approach 1:
The baseplate is designed with differentiated surface properties: the central region maintains high reflectivity for normal operation, while the edge regions are specifically modified with low-reflecting surfaces (such as black anodized aluminum or roughened textures) to prevent light scattering toward the camera. This local quality differentiation resolves the contradiction by allowing particle detection functionality while eliminating the harmful baseplate reflection effect at specific locations.
Solution Approach 2:
A light screen or mask is introduced as an intermediary component positioned between the light source and the baseplate edges. This intermediary blocks inspection light from reaching the baseplate edges, preventing the reflection path that causes false positives. The light screen acts as a mediator that eliminates the harmful interaction between light and baseplate edge structures while preserving the necessary particle detection functionality.
2Ease of operation
If the baseplate has a highly reflective surface to support the reticle, then the reticle can be properly positioned and supported, but light may be reflected towards the camera causing false particle detection
Solution Approach 1:
The baseplate implements spatially varying surface properties where the central support area maintains high reflectivity for effective reticle positioning and support, while the peripheral edge areas are treated with low-reflecting surfaces. This local differentiation allows the baseplate to simultaneously fulfill its mechanical support function and its optical non-interference function during inspection.
Solution Approach 2:
The baseplate surface is segmented into functionally distinct zones: a central reflective zone for reticle support and peripheral non-reflective zones for light management. This segmentation allows each zone to be optimized for its specific function, resolving the contradiction between support effectiveness and optical interference prevention.
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 solution effectively reduces the occurrence of false positive readings by minimizing light reflection from the baseplate edges, thereby enhancing the accuracy of particle contamination detection on the reticle surface.
Implementation Method 1
light being reflected off the EUV baseplate and directed towards the camera
Implementation Method 2
The baseplate can include features that reduce the amount of that light that is deflected or reflected from an edge structure of the baseplate toward the camera
Implementation Method 3
If particles are present at the surface, light that is directed at the surface at the shallow angle is re-directed (deflected, reflected, scattered, etc.) away from the reticle surface in various directions other than the shallow angle of reflection
Data Source
AI summary
Described are baseplate devices used to support, transport, and process a reticle, including to support a reticle during a step of detecting particle contamination at a surface of the reticle prior to using the reticle in an extreme ultraviolet (EUV) lithography process.