Defect Inspection Apparatus Using Controlled Electron Beam Scanning Speed
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Solution Overview
Problem
Current defect inspection methods using atomic force microscopes are inefficient due to the long time required for scanning the surface of samples, making it difficult to detect minute irregularities on EUV masks.
Innovation Solution
A defect inspection apparatus and method utilizing an electron scanning unit with controlled scanning speed, detectors to capture image data, and signal processing to generate subtracted images, which helps in detecting surface irregularities by reducing noise through slower scanning speeds for conductive materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If atomic force microscope is used to scan the surface of the sample, then minute irregularities can be detected, but the observation time becomes excessively long
Solution Approach 1:
The patent replaces the mechanical scanning probe system with an electron beam-based detection system. Instead of using a physical probe that mechanically scans the surface, the invention uses an electron beam to irradiate the sample and detectors to capture emitted electrons, thereby eliminating the time-consuming mechanical scanning process while maintaining detection capability for minute irregularities.
Solution Approach 2:
The patent implements periodic scanning of the electron beam across the sample surface at controlled speeds. By using multiple detectors arranged around the optical axis to simultaneously capture data from different positions, the system achieves efficient periodic data collection that reduces total observation time compared to sequential mechanical probing.
2Productivity
If electron beam scanning is performed at high speed, then productivity is improved, but noise increases making it difficult to detect minute irregularities
Solution Approach 1:
The patent dynamically adjusts the scanning speed parameter based on the type of sample being inspected. For conductive samples like reflective masks where charge-up is less problematic, higher scanning speeds can be used. For insulating samples, lower scanning speeds are employed to minimize charge-up effects and noise. This adaptive parameter adjustment optimizes both productivity and measurement precision.
Solution Approach 2:
The system incorporates feedback mechanisms that monitor detection signals during scanning and adjust scanning parameters accordingly. By analyzing the quality of detected signals and the type of sample being scanned, the control system can dynamically optimize scanning speed to maintain low noise levels while maximizing productivity.
3Measurement precision
If electron beam scanning is performed on insulating samples, then surface irregularities can be detected, but charge-up phenomenon increases noise
Solution Approach 1:
The patent adjusts scanning parameters specifically for insulating samples by reducing scanning speed and modifying beam current. This reduces the accumulation of charge on the insulating surface, thereby minimizing the charge-up phenomenon and associated noise while maintaining the ability to detect surface irregularities.
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 effectively suppresses noise and enables the detection of minute irregularities on reflective masks, improving the accuracy of defect inspection by controlling the electron beam's scanning speed based on the sample type.
Implementation Method 1
a plurality of detectors arranged around an optical axis of the electron beam and configured to detect electrons emitted from the surface of the sample by the scanning of the electron beam
Data Source
AI summary
There is provided a defect inspection apparatus including: an electron scanning unit configured to scan a surface of a sample with an electron beam; a plurality of detectors arranged around an optical axis of the electron beam and configured to detect electrons emitted from the surface of the sample by scanning the electron beam; a signal processing unit configured to generate image data of the surface of the sample based on detection signals from the detectors; an analysis unit configured to detect a defect due to irregularities of the surface of the sample based on the image data; and a control unit configured to control a scanning speed of the electron beam depending on the type of the sample.