EUV Beam Stabilization and Reference Correction for Defect Imaging
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Solution Overview
Problem
Existing inspection systems for EUV lithography struggle to accurately detect defects in photomasks and semiconductor wafers due to the challenges posed by the EUV spectral range, including short wavelengths, energetic photons, low radiance, and the absence of refractive optics, which make it difficult to measure and stabilize illumination distribution and correct distorted pixels.
Innovation Solution
The system employs a side monitor sub-system and inline detector sub-system to measure illumination intensity distribution and provide real-time feedback for beam stabilization and reference correction, using multi-cell detectors to adjust pixel intensity and stabilize the beam, ensuring accurate defect detection without increasing complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If EUV illumination is used for high-resolution inspection, then imaging resolution is improved, but illumination stability deteriorates due to low radiance and temporal fluctuations
Solution Approach 1:
The patent implements preliminary beam stabilization by measuring illumination intensity distribution before inspection and using this measurement to pre-correct for expected temporal fluctuations. The system characterizes the illumination profile in advance and applies compensation algorithms before actual defect detection, preventing stability issues from degrading measurement precision.
Solution Approach 2:
The system continuously monitors illumination intensity distribution using a reference detector and feeds this information back to adjust the inspection process in real-time. When temporal fluctuations or drift are detected, the system dynamically compensates by adjusting exposure parameters or applying correction factors, maintaining both high resolution and illumination stability.
2Measurement precision
If illumination intensity distribution measurement is implemented for reference correction, then image fidelity is improved, but system complexity increases
Solution Approach 1:
The patent designs the illumination measurement system to serve multiple functions: it characterizes the illumination profile for reference correction, monitors temporal stability for feedback control, and provides diagnostic information about source performance. This multi-functionality justifies the added complexity by delivering multiple benefits from a single measurement capability.
Solution Approach 2:
The system introduces a reference detector as an intermediary component that measures illumination intensity distribution without interfering with the primary inspection beam path. This intermediary device enables precise reference correction while maintaining a relatively simple overall system architecture, as the reference measurement is obtained separately rather than requiring complex modifications to the main imaging system.
3Stability of the object's composition
If real-time beam stabilization is implemented, then illumination homogeneity is improved, but processing time increases
Solution Approach 1:
The system performs preliminary characterization of the illumination profile and establishes correction algorithms in advance. By pre-computing reference data and stabilization parameters, the system minimizes real-time processing requirements while maintaining high illumination homogeneity during actual inspection operations.
Solution Approach 2:
The patent implements stabilization at key critical points rather than continuous full-field correction. By focusing computational resources on stabilizing the most critical regions of the illumination profile or using simplified correction models, the system achieves sufficient homogeneity without the full processing overhead of complete real-time stabilization.
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 improves image fidelity and homogeneity by stabilizing the beam and correcting distortions in real-time, enhancing defect detection accuracy and reducing noise in EUV lithography processes.
Implementation Method 1
collecting illumination reflected and/or scattered from the sample at one or more detectors to generate image data
Implementation Method 2
measuring the brightness distribution of the source and/or an image of the source
Implementation Method 3
providing feedback for stabilization of the beam
Implementation Method 4
correcting distorted pixels in the images based on a measured illumination intensity distribution at a plane of the sample
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An inspection system and a method of using the same are disclosed. The inspection system comprises an illumination source configured to emit an extreme ultraviolet (EUV) illumination beam for illuminating a sample, one or more first multi-cell detectors configured to generate a first illumination intensity distribution signal based on a first photocurrent, one or more second multi-cell detectors configured to generate a second illumination intensity distribution signal based on a second photocurrent, a detector assembly configured to receive the illumination beam and generate images, and a controller configured to: receive the images from the detector assembly, calibrate the second illumination intensity distribution signal to the images by mapping distortions in the second illumination intensity distribution signal to distorted pixels in the images, increase or decrease intensities of the distorted pixels in the images to generate corrected images, and detect defects on the samples.