Overlay Measurement Using SEM Image Segmentation
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Solution Overview
Problem
Current methods for accurately determining overlay between layers of modern multilayer semiconductor structures, such as 3D ICs, face challenges in achieving precise alignment and registration due to the miniaturization scale, which optical microscopes cannot resolve effectively, necessitating higher resolution tools like SEMs for inspection and defect detection.
Innovation Solution
A method involving image processing techniques using SEM images, where a given image of a multilayer structure is segmented to identify layer-specific features, and combined expected images are used for registration and overlay measurement, allowing for iterative enhancement of segmentation and correction based on measured overlay values, utilizing safe areas to improve accuracy and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical microscopes are used for inspection, then the inspection process is simple and fast, but the resolution and accuracy are insufficient for modern miniaturized structures
Solution Approach 1:
The patent replaces optical microscopy with scanning electron microscopy (SEM) to achieve the required resolution for modern miniaturized structures. SEM provides sub-nanometer resolution capability through electron beam interaction with the sample, enabling accurate measurement of overlay and dimensions at 7-10 nm node scales that optical microscopes cannot resolve.
Solution Approach 2:
The patent changes the fundamental inspection parameter from optical wavelength to electron beam energy and interaction. By using electron beams with specific energies and detecting secondary electrons, backscattered electrons, or other electron signals, the system achieves the necessary spatial resolution for advanced semiconductor nodes while maintaining measurement capability through sophisticated signal processing.
2Measurement precision
If SEM is used for high resolution inspection, then measurement precision improves, but inspection time increases and throughput decreases
Solution Approach 1:
The patent applies partial action by focusing SEM inspection on specific critical regions and features rather than performing exhaustive full-wafer scanning. The method identifies and measures only the necessary overlay markers and critical dimensions, obtaining sufficient data for overlay control without requiring complete inspection of all wafer areas, thus reducing inspection time while maintaining measurement accuracy.
Solution Approach 2:
The patent employs preliminary action through automated marker design and placement strategies. Overlay markers are pre-designed into the fabrication process at locations optimized for measurement, and SEM inspection parameters are pre-configured for rapid acquisition. This preliminary preparation enables faster inspection execution without compromising measurement precision.
3Measurement precision
If complex model-based analysis methods are applied, then measurement capability improves, but processing complexity and computational requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the complex image processing task into distinct stages: image acquisition, marker identification, feature extraction, coordinate transformation, and overlay calculation. Each stage processes specific aspects of the data independently, reducing computational complexity at each step while maintaining overall measurement accuracy through systematic progression through the analysis pipeline.
Solution Approach 2:
The patent introduces intermediary processing steps including image preprocessing to enhance contrast and reduce noise, intermediate coordinate systems for transformation, and intermediate feature representations. These intermediaries simplify the relationship between raw SEM images and final overlay measurements, making the overall process more manageable and computationally efficient while preserving measurement precision.
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 enables accurate and reliable overlay measurement with sub-nm precision, minimizing throughput impact on the fabrication process and enabling on-line adjustments, while being robust to noise and suitable for complex semiconductor structures.
Implementation Method 1
exposing a 3D IC to a primary electron beam, collecting data on responsive electron beams or scattering electrons from multiple layers of the 3D IC
Implementation Method 2
collecting data on responsive electron beams or scattering electrons from multiple layers of the 3D IC
Data Source
AI summary
A method for determining overlay between layers of a multilayer structure may include obtaining a given image representing the multilayer structure, obtaining expected images for layers of the multilayer structure, providing a combined expected image of the multilayer structure as a combination of the expected images of said layers, performing registration of the given image against the combined expected image, and providing segmentation of the given image, thereby producing a segmented image, and maps of the layers of said multilayered structure. The method may further include determining overlay between any two selected layers of the multilayer structure by processing the maps of the two selected layers together with the expected images of said two selected layers.