Charged Particle Beam Surface Potential Measurement
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Solution Overview
Problem
Charged particle beam systems face challenges in focusing and measuring sample surfaces with intense charge, leading to prolonged auto-focusing times and magnification errors due to surface electrification, as existing methods are inefficient and can damage samples.
Innovation Solution
The system measures and offsets surface potentials by controlling the retarding voltage to minimize secondary electron output, allowing precise energy adjustment of the charged particle beam and reducing the need for extensive magnetic lens adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the variable range of the exciting current for the magnetic objective lens or the retarding voltage is expanded to adjust for focal point shifts caused by intense sample charge, then the auto-focusing function can be maintained, but the time required to complete the auto-focusing operation is lengthened
Solution Approach 1:
The invention measures the electric potential distribution on the sample surface before performing auto-focusing. By obtaining the potential distribution map in advance, the system can pre-determine the appropriate lens excitation current or retarding voltage adjustments needed, eliminating the need for time-consuming trial-and-error searching during the actual auto-focusing operation.
Solution Approach 2:
The invention uses a feedback mechanism where the measured electric potential distribution on the sample surface is used to adjust the lens excitation current or retarding voltage. The secondary electron detector provides feedback signals that are processed to determine the optimal focusing conditions, enabling rapid and accurate auto-focusing without extensive parameter scanning.
2Manufacturing precision
If the exciting current for the magnetic objective lens is adjusted to compensate for focal point shift due to sample surface charge, then the beam can be focused on the charged sample surface, but the calculated magnification does not coincide with the true magnification
Solution Approach 1:
The invention changes the approach from adjusting lens parameters to adjusting the retarding voltage based on measured surface potential. By using the formula V_retarding = V_accelerating - V_surface_potential, the system maintains accurate magnification calculation while compensating for focal shifts, as the retarding voltage adjustment does not affect the magnetic lens magnification relationship.
3Reliability
If the accelerating voltage for the primary electrons is increased to reach the highly charged sample surface, then the electron beam can overcome the repulsive potential, but the method does not meet the need for low accelerating voltage measurement
Solution Approach 1:
The invention measures the surface potential distribution before beam irradiation and uses this information to pre-set the appropriate retarding voltage. This preliminary measurement allows the system to use minimal accelerating voltage while still enabling the beam to reach the sample surface, as the retarding voltage compensation accounts for the surface charge effects.
4Illumination intensity
If the secondary electron detector output is maximized by controlling electric potentials while secondary electrons are emitted, then the image quality can be optimized, but considerable damage occurs to the sample surface due to electron hitting
Solution Approach 1:
The invention extracts and measures the surface potential information separately from the imaging process. By measuring the potential distribution first and using this information to control the retarding voltage during imaging, the system optimizes secondary electron signal without requiring intense electron bombardment, thereby reducing sample damage while maintaining image quality.
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 rapid, precise measurement of surface potentials, shortens auto-focus operation time, and ensures accurate magnification, improving throughput and reducing sample damage.
Implementation Method 1
the retarding voltage is so controlled as to cancel those electric potentials over the sample surface
Implementation Method 2
the secondary electrons emitted from the sample are detected
Implementation Method 3
the beam of accelerated charged particles is focused on the sample by controlling the retarding (decelerating) voltage applied to the objective lens or the sample
Data Source
AI summary
A charged particle beam system wherein the output of the secondary electron detector is detected while the retarding voltage is varied between the values for which the secondary electrons do not reach the sample and the values for which the secondary electrons reach the sample, and the surface potential of the sample is determined on the basis of the relationship between the retarding voltage and the detected output of the secondary electron detector.