Photomask Blank Defect Evaluation Using Extreme Ultraviolet Light
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Solution Overview
Problem
Existing optical defect detection methods struggle to accurately evaluate the size of defects smaller than the nominal resolution of the inspection optical system, particularly in photomask blanks used for semiconductor manufacturing, due to subtle influences on reflected light.
Innovation Solution
An optical evaluation method that collects and analyzes the reflected light of inspection light on a photomask blank, using a conversion expression to estimate the actual width of defects from intensity changes, allowing for precise defect size evaluation even below the nominal resolution limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical defect detection methods are used, then defects can be detected, but the size of defects smaller than the nominal resolution cannot be accurately evaluated
Solution Approach 1:
The patent changes the parameter of light wavelength to achieve higher measurement precision. By using extreme ultraviolet light with a wavelength of 13.5 nm, the inspection optical system can accurately evaluate defects with a width of 100 nm or less, which are critical for maintaining pattern fidelity in next-generation semiconductor manufacturing processes
Solution Approach 2:
The patent introduces a new dimension of measurement by utilizing the intensity distribution profile of reflected light. Instead of relying solely on conventional optical resolution limits, the system analyzes the intensity distribution characteristics to extract defect size information, enabling accurate measurement in a previously inaccessible size range
2Manufacturing precision
If multi-patterning process is used to form smaller patterns, then resolution is improved, but the number of exposure and processing steps increases
Solution Approach 1:
The patent applies preliminary action by performing defect inspection on the photomask blank before the multi-patterning process. By detecting and evaluating defects at the blank stage using 13.5 nm extreme ultraviolet light, the system ensures that only defect-free blanks proceed to subsequent complex processing steps, preventing rework and maintaining productivity
Solution Approach 2:
The patent replaces conventional optical inspection mechanisms with an extreme ultraviolet-based inspection system. This substitution enables direct measurement of sub-100 nm defects without requiring mechanical contact or complex multi-step measurement procedures, streamlining the inspection process
3Reliability
If conventional inspection light is used, then general defects are detected, but micro defects of 100 nm or less are not sufficiently detected
Solution Approach 1:
The patent changes the fundamental parameter of inspection light wavelength from conventional ranges to extreme ultraviolet (13.5 nm). This parameter change enables the detection and accurate size evaluation of micro defects with a width of 100 nm or less, significantly improving defect detection completeness for next-generation semiconductor devices
Solution Approach 2:
The patent creates a universal inspection solution that can detect various types of defects (projected defects, recessed defects, pinholes) across different size ranges using a single extreme ultraviolet light source. The system analyzes intensity distribution profiles to universally identify and characterize all defect types without requiring multiple specialized inspection systems
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 high-accuracy defect size evaluation of photomask blanks, effectively detecting and sizing defects as small as 100 nm, improving the fidelity and accuracy of pattern transfer in semiconductor manufacturing.
Implementation Method 1
collects reflected light of a region of the inspection-target photomask blank irradiated with the inspection light
Implementation Method 2
collects reflected light of a region of the inspection-target photomask blank irradiated with the inspection light through an objective lens of the inspection optical system as a magnified image of the region
Data Source
AI summary
The defect size of a photomask blank is evaluated. An inspection-target photomask blank is irradiated with inspection light and reflected light of the region of the inspection-target photomask blank irradiated with the inspection light is collected through an objective lens of an inspection optical system as a magnified image of the region. Then, an intensity change part in the light intensity distribution profile of the magnified image is identified. Next, a difference in the light intensity of the intensity change part is obtained and the width of the intensity change part is obtained as the apparent width of the defect. Then, the width of the defect is calculated on the basis of a predetermined conversion expression showing the relationship among the difference in the light intensity, the apparent width of the defect, and the actual width of the defect, and the width of the defect is estimated.