Scattering Contrast Inspection for High-Throughput Defect Detection
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Solution Overview
Problem
Current optical inspection methods for photomasks, particularly in EUV lithography, face challenges in achieving high resolution, sensitivity, and throughput simultaneously, making it difficult to detect phase and amplitude defects on multilayer masks effectively.
Innovation Solution
The method employs scanning coherent scattering inspection (SCI) using a light source to diffract light beams at varying angles, detecting diffracted light with a position-sensitive detector, and analyzing diffraction images to identify defects by comparing them to a trustworthy diffraction image or pre-calculated diffraction images for defect-free patterns, focusing on regions of interest to enhance throughput and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional optical inspection methods are used to achieve high resolution for defect detection, then measurement precision is improved, but throughput decreases due to the large detector area required
Solution Approach 1:
The patent transforms the inspection problem from real space to reciprocal space (spatial frequency domain) by capturing diffraction patterns instead of direct images. This dimensionality change allows defect detection through Fourier transform relationships, where periodic defects produce characteristic diffraction signatures, enabling high-resolution defect detection with a compact detector that does not require proportionally large area for high resolution
Solution Approach 2:
The patent changes the detection parameter from direct spatial imaging to diffraction pattern analysis in reciprocal space. By measuring the diffraction pattern and its variations, the system can detect periodic defects with high sensitivity while using a detector size that is practical for high-throughput applications, thus resolving the contradiction between resolution and throughput
2Productivity
If the detector area is reduced to improve throughput, then productivity is improved, but measurement precision deteriorates due to lower resolution
Solution Approach 1:
The patent uses diffraction pattern capture in reciprocal space, where the diffraction pattern size is determined by the numerical aperture and wavelength rather than directly by the sample size. This allows a compact detector to capture information equivalent to a much larger real-space image, achieving high throughput while maintaining the precision needed for defect detection through Fourier analysis
Solution Approach 2:
The patent creates a diffraction pattern copy of the sample's periodic structure, which contains encoded information about the sample's features. By analyzing this diffraction pattern copy rather than directly imaging the sample, the system can detect defects with high precision using a smaller detector, thus improving throughput without sacrificing measurement precision
3Measurement precision
If high sensitivity is achieved by capturing all diffraction information, then measurement precision is improved, but device complexity increases due to the need for complex optics
Solution Approach 1:
The patent extracts only the diffraction pattern information that is relevant for defect detection, rather than attempting to capture and process all possible optical information. By focusing on the diffraction pattern in reciprocal space and using Fourier transform relationships, the system achieves high sensitivity for detecting periodic defects with a simplified optical setup that does not require complex imaging optics
Solution Approach 2:
The patent replaces complex mechanical imaging optics with a simpler diffraction-based measurement system. Instead of using complex lens systems to directly image the sample with high resolution, the system uses diffraction pattern capture and Fourier analysis to achieve equivalent or superior defect detection sensitivity with a simpler optical configuration
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 allows for rapid identification of defects with high sensitivity and throughput, capturing only the contrast signal between defected and defect-free structures, and can detect both amplitude and phase defects simultaneously with a 2D scan, improving inspection efficiency and reducing the need for complex optics.
Implementation Method 1
illuminating the sample with the light beam, preferably under an angle of 0 to 80°, thereby diffracting the light beam according to the actual pattern present on the sample; detecting the diffracted light beam in terms of its position related intensities with a position sensitive detector
Data Source
AI summary
Methods and a system for scanning scattering contrast inspection for the identification of defects in an actual pattern block on a sample as compared to a desired pattern block. Most of the information in the reciprocal space (spatial frequency domain) is omitted in order to increase the throughput. That information in the reciprocal space is captured which gives the highest defect information, namely contrast signal between the defective and defect-free structure. Deviations from the expected diffraction pattern allow rapid identification of defects on the actual pattern. The first method learns the correct reconstructed diffraction image by comparing the repetitive pattern blocks. The second method focuses on the appearance of predictable defects in the spatial frequency domain of the reconstructed diffraction image thereby defining regions of interest where the defects materialize. Only the regions of interest are considered and compared to the reconstruction diffraction image of a defect-free pattern block.