Electron Beam Inspection Coordinate Error Compensation
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Solution Overview
Problem
Sample pattern inspection apparatuses face challenges in achieving accurate results due to stage guide distortions, orthogonal errors, and variable moving speeds, leading to position errors and reduced throughput in detecting defects on patterns with minimum line widths of 0.1 μm or less.
Innovation Solution
An electron beam apparatus that calculates and compensates for coordinate errors, orthogonal errors, and mirror distortion errors using recursive processing and beam deflection, allowing for precise alignment and inspection of sample patterns despite stage guide distortions and speed variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If stage guides are used to guide the stage in X- and Y-directions, then the stage can move along defined paths, but distortion and non-orthogonality of stage guides cause position errors and reduce inspection accuracy
Solution Approach 1:
The patent replaces mechanical stage guide systems with a laser interferometer-based measurement system. Instead of relying on physical guides that introduce distortion and non-orthogonality errors, the invention uses optical interference patterns to precisely determine stage position and orientation, eliminating mechanical guide errors from the measurement process
Solution Approach 2:
The patent introduces a laser interferometer as an intermediary measurement device between the stage and the inspection system. This intermediary provides accurate position and orientation data without being affected by stage guide distortions, serving as a reference that compensates for mechanical guide errors
2Ease of operation
If the stage moves at variable speeds during continuous movement, then flexibility in operation is improved, but position errors occur and reduce inspection accuracy
Solution Approach 1:
The patent implements a feedback system using a laser interferometer to continuously monitor stage position and velocity. The measured position data is fed back to the control system, which compensates for velocity-induced position errors by adjusting the relationship between stage position and image position, maintaining accuracy despite variable speeds
3Adaptability or versatility
If the XY coordinate of the sample does not coincide with the XY coordinate of the stage, then loading flexibility is improved, but rotational direction errors occur and reduce inspection accuracy
Solution Approach 1:
The patent uses a laser interferometer as an intermediary to establish an accurate reference coordinate system that is independent of the stage coordinate system. By measuring the actual position and orientation of the sample relative to this reference, the system can compensate for coordinate misalignment and rotational errors, maintaining accuracy despite flexible loading configurations
4Measurement precision
If the number of memories and comparison circuits is increased to ensure inspection accuracy, then measurement precision is improved, but defect inspection speed decreases and throughput is reduced
Solution Approach 1:
The patent replaces complex hardware-based image comparison systems with a coordinate compensation approach using laser interferometry. Instead of using multiple memories and comparison circuits to handle position errors, the invention uses precise position measurement and computational correction, reducing hardware complexity while maintaining accuracy and enabling higher throughput
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 solution enables high-accuracy and high-throughput defect inspection by correcting position errors and maintaining precise alignment, even when stage guides are distorted and moving speeds are not constant, thereby improving the reliability of defect detection.
Implementation Method 1
illuminate an electron beam(s) on a sample to be inspected such as a wafer to generate electrons having information relating to a device pattern formed on the sample surface
Implementation Method 2
a laser interferometer is adapted to measure position coordinates (x, y) of a plurality of reference points on the sample W
Implementation Method 3
beam deflection, allowing for precise alignment and inspection of sample patterns
Data Source
AI summary
An electron beam apparatus for inspecting a pattern on a sample using multiple electron beams includes a plurality of primary electro-optical systems and a plurality of secondary electro-optical systems associated with the respective primary electro-optical systems. The primary electro-optical systems are for irradiating multiple primary electron beams on a surface of the sample, and each includes an electron gun having an anode and an objective lens. The secondary electro-optical systems are for inducing secondary electrons emitted from a surface of the sample by irradiation of the primary electron beams. Detectors are each for detecting the secondary electrons and generating electric signals corresponding to the detected electrons. The anodes of the electron guns of the primary electro-optical systems comprise an anode substrate in common having multiple holes corresponding to the axes of the respective primary electro-optical systems. The anode substrate has metal coatings around the respective holes.