SEM Probe Beam Position Control for Dark Ring Current Fluctuations
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Solution Overview
Problem
Existing SEM systems face challenges in maintaining consistent probe beam quality due to uneven current density and temporal variations in electron beam distributions, leading to unstable image quality and reduced inspection efficiency, particularly exacerbated by the 'dark ring phenomenon' which causes periodic current fluctuations and requires apparatus halts for correction.
Innovation Solution
A charged particle beam apparatus incorporating a distribution detecting unit, fluctuation predicting unit, position determining unit, and position control unit to measure and predict current density distributions, determine optimal beam positions, and control the beam's application to maintain consistent probe beam properties without halting the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a Schottky emitter is used to maintain continuous electron beam emission, then the apparatus can operate continuously for long-term inspection, but the current density distribution becomes uneven and varies with time, degrading image quality consistency
Solution Approach 1:
The system performs preliminary measurement of the current density distribution before the dark ring phenomenon significantly degrades the probe beam quality. Based on the measured distribution, the system predicts future fluctuations and proactively adjusts the beam position to avoid regions where dark rings are expected to form or move, thereby preventing quality degradation before it occurs.
Solution Approach 2:
The system continuously measures the actual current density distribution of the electron beam and uses this feedback information to update the fluctuation prediction model. The measured distribution data is fed back to adjust the beam position control, creating a closed-loop system that adapts to changing beam conditions and maintains consistent image quality over long operation periods.
2Reliability
If the probe beam position is adjusted to avoid dark ring regions, then image quality consistency is improved, but additional measurement and control systems increase device complexity
Solution Approach 1:
The system uses the existing final diaphragm structure for dual purposes: as a beam aperture and as a measurement target for detecting current density distribution. By measuring the beam distribution at the diaphragm position, the system avoids needing separate measurement apparatus, thereby reducing overall device complexity while still achieving reliable beam position control.
Solution Approach 2:
The system introduces a prediction model as an intermediary between the measured current density distribution and the beam position control decisions. Rather than directly controlling based on raw measurement data, the prediction model processes the distribution information to forecast future beam quality issues, enabling more intelligent and efficient control with simpler hardware.
3Productivity
If the beam position is dynamically controlled to maintain optimal probe beam properties, then inspection velocity and repeatability are improved, but the control system requires real-time measurement and prediction capabilities
Solution Approach 1:
The system performs beam distribution measurement and fluctuation prediction in advance, before the dark ring phenomenon significantly impacts the probe beam quality. This preliminary action allows the control system to prepare optimal beam positions ahead of time, enabling smooth transitions and maintaining high inspection velocity without requiring complex real-time reaction systems.
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 solution enables continuous high-quality image inspection with improved repeatability and inspection velocity, suppressing variations in inspection performance and allowing for accurate and efficient semiconductor pattern analysis without apparatus downtime.
Implementation Method 1
An electric current is carried through a filament to heat such an electron source at a high temperature of 1,500 to 1,900 K, a strong electric field of 5×108 to 1.5×109 V/m is applied, and a stable emission is implemented.
Implementation Method 2
a strong electric field of 5×108 to 1.5×109 V/m is applied, and a stable emission is implemented
Data Source
AI summary
An embodiment is to provide a technique that continuously applies a certain amount of an electron beam to a sample by selecting a beam applied to the sample from an electron beam emitted from an electron source in a scanning electron microscope. A charged particle apparatus is configured, including: a mechanism that detects the distribution of electric current strength with respect to the emitting direction of an electron beam emitted from an electron source; a functionality that predicts a fluctuation of an electric current applied to a sample by predicting the distribution of the electric current based on the detected result; a functionality that determines a position at which a beam applied to the sample is acquired based on the predicted result; and a mechanism that controls a position at which a probe beam is acquired based on the determined result.