EUV Reticle Calibration Targets for In-Situ Image Quality Diagnostics
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Solution Overview
Problem
Existing actinic patterned mask inspection (APMI) tools face challenges in maintaining consistent image quality over time due to drifts in critical parameters such as EUV illumination pupil, EUV focus, and EUV wavefront error, requiring effective run time diagnostics (RTD) that are EUV specific, periodic, and minimally disruptive to the inspection process.
Innovation Solution
The implementation of EUV reticle-based diagnostic targets, such as miniaturized calibration chips and bars, within the inspection system, allowing for swift movement between APMI and RTD, with predefined EUV performance, to measure EUV-specific metrics like EUV-P, EUV-F, and EUV-WFE, and perform system health checks during inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If run time diagnostics are implemented to monitor EUV image quality metrics, then system performance consistency is improved, but inspection overhead time increases
Solution Approach 1:
The diagnostic targets are pre-positioned on the stage alongside the substrate, and the system is pre-configured with diagnostic patterns. During inspection, the system can quickly switch to these pre-prepared targets without requiring target change or system reconfiguration, thus minimizing inspection overhead while enabling continuous monitoring of EUV image quality metrics
Solution Approach 2:
Miniaturized diagnostic targets serve as intermediaries between the inspection system and the substrate. These compact targets can be rapidly imaged to diagnose system health parameters (EUV-P, EUV-F, EUV-WFE) without directly interfering with substrate inspection, enabling indirect but efficient system monitoring with minimal disruption to the primary inspection function
2Measurement precision
If EUV-specific diagnostic measurements are performed, then measurement precision for system health parameters is improved, but device complexity increases
Solution Approach 1:
The same imaging system used for substrate inspection is made multi-functional by adding diagnostic capabilities. The inspection optics can image both substrates and diagnostic targets, and the detector can capture both inspection images and diagnostic patterns, eliminating the need for separate diagnostic equipment and reducing overall system complexity while maintaining EUV-specific measurement precision
Solution Approach 2:
The diagnostic targets contain simplified copies of the substrate patterns (gratings, lines, spaces) that are specifically designed to be imaged by the EUV inspection system. These copied patterns serve as proxies for measuring EUV image quality parameters without requiring complex diagnostic setups, achieving precise measurements through pattern replication rather than system complexity
3Ease of operation
If diagnostic targets are integrated on the same stage, then ease of operation is improved, but area requirements increase
Solution Approach 1:
The stage is segmented to accommodate both substrate and miniaturized diagnostic targets simultaneously. The diagnostic targets are divided into compact, discrete elements that can be positioned in unused stage areas, allowing the stage to handle both inspection and diagnostic functions without requiring a complete redesign of the stage architecture
Solution Approach 2:
The diagnostic targets are miniaturized and positioned in the lateral dimensions of the stage rather than requiring additional vertical space or complex mechanical arrangements. By reducing the diagnostic targets to microscopic scales and placing them alongside the substrate on the same plane, the system enables easy switching between modes while minimizing the additional area required
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
Enables accurate, efficient, and non-disruptive RTD for EUV inspection systems, ensuring consistent image quality by periodically monitoring and recalibrating critical metrics, thus maintaining system performance.
Implementation Method 1
an EUV illumination source configured to generate a beam of EUV illumination
Implementation Method 2
a first set of optical elements configured to direct the beam of EUV illumination from the EUV illumination source to the stage
Implementation Method 3
a second set of optical elements configured to magnify and image the substrate or the one or more diagnostic targets
Data Source
AI summary
An inspection system includes a stage for positioning a substrate to be inspected, one or more reticle-based diagnostic targets positioned on the stage, and a reticle inspection sub-system having a field of view encompassing the stage. The system includes a controller configured to move the field of view between portions of the stage to selectively perform substrate and run time diagnostics (RTD) of predefined image quality metrics. In embodiments, the system may be an APMI system for EUV mask inspection and the diagnostic targets may be EUV reticle-based diagnostic targets having predefined EUV performance patterning. In embodiments, the diagnostic targets may be positioned adjacent to the mask to be inspected to permit contiguous scanning to perform inspection and RTD.