Phase Mask Inspection for 3D Structure Depth Encoding
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Solution Overview
Problem
High-end inspection systems face inefficiencies when inspecting three-dimensional structures with complex radiation patterns, requiring time-consuming z-axis scans and struggling to provide accurate and explainable results, especially for structures like 3D NAND memory.
Innovation Solution
A method utilizing a phase mask to generate difference images between a sample image and a reference image, eliminating the need for z-axis scanning by virtually expanding the depth of field and encoding depth information, allowing for fast and accurate defect detection in three-dimensional structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional inspection system is used to inspect three-dimensional structures, then the inspection can be performed, but the process is time-consuming due to z-axis scanning requirements
Solution Approach 1:
The patent replaces the mechanical z-axis scanning system with an optical field-based inspection method using a phase mask. Instead of physically moving the sample or objective lens along the z-axis to capture multiple focal planes, the phase mask encodes depth information directly into the optical field, allowing all depth information to be captured in a single exposure. This substitution of mechanical scanning with optical field encoding dramatically reduces inspection time while maintaining the ability to inspect three-dimensional structures.
Solution Approach 2:
The patent transforms the inspection approach by adding a phase dimension to the optical field. The phase mask introduces phase shifts that encode z-axis depth information into the phase component of the light wave. This allows depth information (normally requiring z-axis scanning) to be captured simultaneously in the phase domain, converting a time-consuming sequential process into a simultaneous measurement.
2Reliability
If the inspection system examines complex three-dimensional structures, then comprehensive defect detection is achieved, but the radiation patterns become highly complex and hard to analyze
Solution Approach 1:
The patent extracts and separates different types of information into different image components. By using the phase mask, the complex radiation patterns are decomposed into distinct phase and amplitude components. The phase component contains depth information while the amplitude component contains intensity information. This separation allows each component to be analyzed independently, simplifying the interpretation of complex three-dimensional structures and their radiation patterns.
Solution Approach 2:
The phase mask acts as an intermediary that transforms complex radiation patterns into more analyzable forms. It modulates the optical field to encode depth information in a way that creates distinguishable phase differences in the captured images. This intermediary transformation makes the complex interactions of light with three-dimensional structures more interpretable by converting them into phase contrast that can be directly visualized and analyzed.
3Loss of information
If conventional inspection methods are used, then inspection can be performed, but explainable inspection results are difficult to provide
Solution Approach 1:
The phase mask performs preliminary encoding of depth information before the actual defect detection process. By pre-encoding the z-axis position information into the phase of the optical field, the system prepares the data in a form that is inherently more explainable. When defects are detected, their depth positions are already encoded in the phase information, allowing for immediate and explainable defect characterization without requiring additional processing or assumptions.
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 fast and accurate inspection of three-dimensional structures without z-axis scanning, providing explainable results by concentrating on difference images and identifying defects with precise depth information, enhancing inspection efficiency for complex structures like 3D NAND memory.
Implementation Method 1
utilizing a phase mask to generate difference images between a sample image and a reference image, eliminating the need for z-axis scanning by virtually expanding the depth of field and encoding depth information
Data Source
AI summary
A method for inspecting a three dimensional structure of a microscopic scale of a sample, the method may include obtaining an image of the three dimensional structure; obtaining a reference image of a reference three dimensional structure, the reference three dimensional structure and the three dimensional structure are ideally identical to each other; wherein each one of the image and the reference image was generated using optics that includes a phase mask, wherein the phase mask virtually expands a depth of field of the optics by encoding depth information over a depth range that exceeds the depth of field; generating a difference image that represents a difference between the image and the reference image; determining, based on the difference image, whether there is at least one defect in the three dimensional structure; wherein when determining that there is the at least one defect then providing a depth of the at least one defect.