Double Stigmator Layout for Beam Astigmatism and Aperture Control
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Solution Overview
Problem
Existing charged particle beam devices face challenges in correcting astigmatism and adjusting the numerical aperture, which affect precision and resolution, particularly in applications like scanning electron microscopy and focused ion beam systems, as single quadrupole stigmators are insufficient for optimal resolution.
Innovation Solution
A double stigmator system is employed, comprising a first and second stigmator spaced apart along the optical axis, allowing independent control of astigmatism and numerical aperture, with each stigmator correcting specific aberrations to improve alignment and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single quadrupole stigmator is used to correct astigmatism, then the device complexity is reduced, but the manufacturing precision and resolution are insufficient
Solution Approach 1:
The patent divides the single stigmator function into two separate quadrupole stigmators positioned at different locations in the beam path. The first stigmator corrects astigmatism while the second stigmator provides additional correction and enables numerical aperture adjustment, achieving superior precision without requiring a single complex device
Solution Approach 2:
The second quadrupole stigmator is designed to serve dual purposes: it provides additional astigmatism correction and simultaneously enables numerical aperture adjustment. This multi-functionality allows the system to achieve high precision beam control without proportionally increasing device complexity
2Manufacturing precision
If correction of astigmatism is performed, then the beam quality is improved, but other characteristics of the charged particle beam are influenced
Solution Approach 1:
By separating the correction functions into two distinct stigmators, the patent allows independent control of astigmatism correction parameters. This segmentation enables correction of beam spot quality issues without inadvertently altering other beam characteristics such as numerical aperture, as each stigmator can be optimized for its specific function
3Quantity of substance
If the beam bundle diameter is increased to reduce electron-electron interaction, then the beam current is improved, but the resolution is reduced due to higher order aberrations
Solution Approach 1:
The patent applies astigmatism correction using the double stigmator system before the beam reaches regions where higher order aberrations would significantly degrade resolution. By preliminarily correcting the beam quality and optimizing the beam parameters, the system can utilize higher beam currents without suffering from excessive aberration effects during the inspection process
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 double stigmator system effectively corrects astigmatism and adjusts the numerical aperture independently, enhancing precision and reducing cycle time in inspection and defect detection operations, while minimizing external input.
Implementation Method 1
imperfections of the electric and magnetic fields used for focusing, aligning and adjusting
Implementation Method 2
Transform Electrical Energy to Magnetic Energy
Implementation Method 3
an objective lens configured to focus the charged particle beam on a specimen
Data Source
AI summary
According to an embodiment, a method of correcting an astigmatism and adjusting a numerical aperture of a charged particle beam is described. The astigmatism is corrected and the numerical aperture is adjusted with a double stigmator. The double stigmator has a first stigmator and a second stigmator. The method comprises correcting the astigmatism of the charged particle beam with the second stigmator of a double stigmator; and adjusting the numerical aperture of the charged particle beam with the first stigmator of the double stigmator. The first stigmator and the second stigmator are spaced apart along an optical axis.