Coherent Diffraction Imaging Mask Inspection System
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Solution Overview
Problem
Current methods for detecting defects in semiconductor masks used in the EUV range are expensive and have low throughput.
Innovation Solution
A scanning coherent diffraction imaging system in reflection mode, utilizing a radiation source, focusing elements, a pinhole aperture plate, and a pixel detector to analyze the aerial image of the mask, allowing for continuous or step-wise sample displacement to detect pattern deviations and defects by analyzing differential images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If current methods are used to detect defects in semiconductor masks, then measurement precision is maintained, but productivity is low and cost is high
Solution Approach 1:
The patent replaces complex mechanical defect detection methods with a light-based coherent diffraction imaging system. The system uses coherent light sources and diffraction patterns to detect mask defects, eliminating the need for expensive and slow mechanical inspection methods while maintaining high detection accuracy and enabling parallel processing for improved throughput.
Solution Approach 2:
The patent uses partial coherence in the light source rather than requiring full coherence, which simplifies the system and reduces costs. By using partially coherent light with controlled coherence properties, the system achieves sufficient defect detection capability without the complexity and expense of fully coherent sources, thereby improving productivity while maintaining adequate reliability.
2Measurement precision
If a pinhole aperture plate is used to improve light coherence, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent extracts only the essential coherence-controlling elements (pinhole aperture plate and selective aperture) from a fully coherent optical system. By taking out only the necessary components to achieve partial coherence, the system maintains measurement precision while avoiding the complexity of complete coherence control mechanisms.
Solution Approach 2:
The patent changes the coherence parameter from full coherence to partial coherence by using aperture plates with specific dimensions and positions. This parameter change simplifies the optical system while maintaining sufficient measurement precision for aerial image reconstruction and defect detection.
3Measurement precision
If the beam diameter is reduced to improve coherence, then measurement precision improves, but loss of energy increases
Solution Approach 1:
The patent optimizes the aperture diameter parameter to achieve the right balance between coherence quality and energy transmission. By carefully selecting the aperture size and position, the system maintains sufficient coherence for accurate aerial image measurement while minimizing energy loss through the aperture plate.
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
The system provides a cost-effective and high-throughput method for detecting defects in semiconductor masks, improving light coherence with components like transparent zone plates and multilayer mirrors, enabling accurate pattern analysis and three-dimensional tomographic imaging.
Implementation Method 1
a first focusing element, such as a Fresnel plate or a toroidal mirror, in order to focus the emitted beam to the required extend
Implementation Method 2
scanning coherent diffraction imaging methods
Implementation Method 3
a mirror that reflects the focused beam towards the sample to be analyzed; the beam being directed at an angle of 2 to 25°
Implementation Method 4
a pinhole aperture plate which allows with its first aperture to focus and cut-off the beam diameter to the desired extent thereby forming also the beam to become more monochromatic
Implementation Method 5
a mechanism to displace the sample continuously or step-wise in a direction perpendicular to the normal vector of the sample surface to allow to analyze the sample which reflects the light beam
Implementation Method 6
a pixel detector to analyze the reflected beam that has passed the second aperture
Implementation Method 7
a computing unit adapted to reconstruct an aerial image of the sample, preferably including three-dimensional tomographic image
Data Source
AI summary
A reflective sample, such as a mask, is imaged in an optics system. A radiation source emits a light beam with relatively low coherence. A first focusing element focuses the beam before a mirror reflects the focused beam towards the sample at an incidence angle of between 2 and 25° A pinhole aperture plate upstream of the sample has a first aperture to focus and cut-off the beam diameter to form a more monochromatic beam. The sample is displaced by a mechanism in a direction perpendicular to the normal vector of the sample surface while it reflects the light beam. The reflected beam passes a second aperture in the pinhole aperture plate next to the first aperture on its way to a pixel detector. The second aperture limits the diameter of the reflected beam, thereby adjusting the diameter of the light beam before it reaches the pixel detector.