Defect Review Apparatus Using Electron Beam Subtraction
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Solution Overview
Problem
Current defect review processes in semiconductor manufacturing are slow due to the high computational requirements of pattern matching in defect detection, especially when using scanning electron microscopes to analyze fine defects on wafers and photomasks.
Innovation Solution
A defect review apparatus and method that uses multiple electron detectors to generate and subtract image data, creating a subtract image that isolates defects, allowing for rapid detection by eliminating pattern noise and focusing on defect features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pattern matching is used for defect detection in SEM images, then measurement precision is improved, but productivity deteriorates due to large calculation requirements
Solution Approach 1:
The patent segments the defect detection process into two distinct stages: (1) a rough detection stage using optical inspection to quickly identify potential defect locations, and (2) a precise verification stage using SEM imaging only at those specific locations. This segmentation eliminates the need for comprehensive pattern matching across entire SEM images, thereby maintaining measurement precision for actual defects while dramatically improving productivity by reducing unnecessary SEM imaging and calculation.
Solution Approach 2:
The patent performs preliminary defect screening using optical inspection before proceeding to SEM-based precise measurement. By conducting this preliminary action, the system pre-identifies potential defect regions, so that subsequent SEM imaging and pattern matching are performed only on these pre-selected areas rather than entire wafers, thus resolving the contradiction between thorough defect detection and processing speed.
2Reliability
If comprehensive pattern matching is performed across the entire SEM image, then reliability of defect detection is improved, but loss of time increases due to extensive calculation
Solution Approach 1:
The patent divides the detection domain into two parts: optical inspection covers the entire wafer surface to identify candidate regions, while SEM-based pattern matching is applied only to these candidate regions. This spatial segmentation ensures that pattern matching is performed reliably on actual defects while avoiding wasteful calculation on defect-free areas, thus improving both time efficiency and maintaining detection reliability.
Solution Approach 2:
The optical inspection step serves as a preliminary action that filters out defect-free regions before SEM-based pattern matching. This preliminary filtering ensures that subsequent time-consuming pattern matching operations are performed only where defects are likely to exist, thereby maintaining high detection reliability while significantly reducing total calculation time.
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 speedy defect detection and measurement by generating a subtract image that highlights only the defects, significantly reducing the time required for the defect review process.
Implementation Method 1
an electron scanning part which irradiates an observation region of a surface of a sample with an electron beam and which scans the electron beam over the observation region; a plurality of electron detectors which are arranged around an optical axis of the electron beam and which detect electrons emitted from the surface of the sample by the irradiation of the electron beam
Data Source
AI summary
A defect review apparatus includes: an electron scanning part which irradiates and scans an electron beam over an observation region on a surface of a sample; four electron detectors arranged around the optical axis of the electron beam with 90° intervals; and a signal processing unit which generates multiple pieces of image data of the observation region on the basis of detection signals from the electron detectors, the multiple pieces of image data respectively taken in different directions. When a pattern in the observation region is a line-and-space pattern, the defect inspection unit performs defect detection on the basis of a subtract between two pieces of the image data respectively taken in two predetermined directions with the optical axis of the electron beam in between.