EUV Photomask Defect Analysis Using Multi-Modal Microscopy
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Solution Overview
Problem
Current methods for removing buried defects in EUV photomasks are limited by the complexity of multi-layer structures and the difficulty in precisely compensating for defects due to the small wavelength and high demands on planarity, leading to imaging errors in semiconductor manufacturing.
Innovation Solution
A method combining ultra-violet radiation exposure, scanning force microscopy, and scanning particle microscopy to analyze defects, using marks for alignment, and integrating defect analysis and repair tools to ensure precise compensation of buried defects in EUV photomasks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the multi-layer structure above the defect is removed to eliminate the buried defect, then the defect is removed, but the process becomes extremely complex and time-consuming due to the multitude of layers and their low thickness
Solution Approach 1:
The patent extracts only the essential information needed for defect characterization by using multiple measurement techniques (optical microscopy, scanning force microscopy, scanning electron microscopy) to obtain defect data without physically removing the multi-layer structure. This allows defect identification and compensation while preserving the intact mask structure.
Solution Approach 2:
The patent changes the measurement parameters and techniques used to analyze the defect, employing different wavelengths and measurement methods to characterize the defect's optical impact without physical intervention. This enables non-destructive defect analysis and compensation strategy development.
2Reliability
If the multi-layer structure is removed and redeposited to fix the defect, then the defect is corrected, but the planarity requirements and time consumption become prohibitive
Solution Approach 1:
The patent performs preliminary defect characterization and compensation design before any physical modification of the mask. By pre-calculating the compensation pattern based on measured defect parameters, the actual repair process is simplified and accelerated, avoiding iterative removal and redeposition cycles.
Solution Approach 2:
The patent creates a digital model or representation of the defect based on measurement data, then uses this model to design and simulate compensation patterns. This virtual copying and testing approach eliminates the need for repeated physical trial-and-error modifications of the multi-layer structure.
3Measurement precision
If multiple measurement techniques are used to analyze the defect, then comprehensive defect data is obtained, but the alignment and data integration become more difficult
Solution Approach 1:
The patent introduces marks on the mask as intermediary reference features that facilitate alignment between different measurement systems. These marks serve as common reference points that enable precise registration and integration of data from optical microscopy, scanning force microscopy, and scanning electron microscopy.
Solution Approach 2:
The patent develops a universal data integration framework that processes and combines measurements from multiple different measurement techniques. This unified approach allows comprehensive defect characterization while managing the complexity of coordinating multiple measurement systems through standardized data processing procedures.
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 provides comprehensive defect analysis and effective compensation by combining data from different measurement principles, ensuring accurate repair of buried defects and improving imaging quality in EUV lithography.
Implementation Method 1
EUV mirrors comprise a substrate with a low thermal expansion as for example silica. A multi-layer structure comprising 40 to 60 double layers of silicon (Si) and molybdenum (Mo) is deposited on the substrate which acts as a dielectric mirror.
Implementation Method 2
EUV and photolithographic masks or simply EUV masks have additionally an absorber structure which is arranged on the multi-layer structure and which absorbs impinging EUV photons.
Implementation Method 3
determining second data by scanning the defect with a scanning force microscope
Implementation Method 4
determining third data by scanning the defect with a scanning particle microscope
Data Source
AI summary
The invention refers to a method for analyzing a defect of an optical element for the extreme ultra-violet wavelength range comprising at least one substrate and at least one multi-layer structure, the method comprising the steps: (a) determining first data by exposing the defect to ultra-violet radiation, (b) determining second data by scanning the defect with a scanning probe microscope, (c) determining third data by scanning the defect with a scanning particle microscope, and (d) com-bining the first, the second and the third data.