Focused Ion Beam Aperture and Octupole Aberration Compensation
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Solution Overview
Problem
Existing focused ion beam systems face limitations in increasing beam current due to spherical aberration, which restricts milling performance and throughput.
Innovation Solution
The use of a non-circular beam limiting aperture combined with a multipole aberration compensator, specifically an octupole element, applies four-fold astigmatism to compensate for spherical aberration, allowing increased beam current without compromising precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If beam current is increased to improve milling throughput, then productivity increases, but spherical aberration worsens and degrades manufacturing precision
Solution Approach 1:
The patent segments the beam current into two independent components: a high-current elongate beam for efficient material removal and a low-current focused beam for precision work. This is achieved through a dual-beam system where a first ion beam with high current density performs rapid milling, while a second ion beam with lower current density provides sharp positioning and outlining. The segmentation allows each beam to operate in its optimal current range without suffering from spherical aberration limitations.
Solution Approach 2:
The patent transitions from a single circular beam to an elongate beam geometry, adding dimensional asymmetry to the beam profile. The elongate beam has a long dimension parallel to the scan direction and a short dimension perpendicular to it, allowing increased current along the length while maintaining precision through the multipole compensator that controls aberrations in the perpendicular dimension. This dimensional change enables higher throughput without sacrificing edge sharpness.
2Productivity
If beam current density is increased for faster material removal, then milling rate improves, but beam focus precision deteriorates
Solution Approach 1:
The patent applies different current density characteristics to different regions of the beam path and function. The elongate beam portion parallel to the scan direction carries high current for rapid material removal, while the multipole aberration compensator maintains low current density in the perpendicular direction to preserve focus precision. This local differentiation of current density allows the system to achieve both high productivity and high precision simultaneously in different spatial dimensions.
3Productivity
If aperture size is increased to allow higher beam current, then productivity increases, but spherical aberration increases and reduces manufacturing precision
Solution Approach 1:
The patent introduces a multipole aberration compensator as an intermediary element between the aperture and the sample. This compensator actively corrects the spherical aberration that would otherwise be caused by the larger aperture, allowing the system to admit higher beam current while maintaining precise spot size control. The compensator acts as a mediator that decouples the relationship between aperture size and aberration, enabling both high current and high precision.
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 a doubling of beam current, resulting in a 2-3 times increase in milling throughput while maintaining sharp edges and precision.
Implementation Method 1
a multipole aberration compensator configured to apply a four-fold astigmatism to the ion beam to compensate for spherical aberration
Implementation Method 2
spherical aberration, which restricts milling performance and throughput
Implementation Method 3
an ion beam focusing column configured to direct ions received from the ion source to form an ion beam and focus the ion beam towards a target area
Implementation Method 4
Milling involves direct removal of material by the impact of ions. This process is known as sputtering.
Implementation Method 5
an aperture plate having a non-circular beam limiting aperture configured to limit the lateral extent of the ion beam passing therethrough
Data Source
AI summary
An ion beam system for modifying a sample or workpiece surface, comprises: an ion source for generating ions; an ion beam focusing column configured to direct ions from the ion source to form an ion beam and focus the ion beam towards a target area; and a sample stage for receiving and positioning the sample or workpiece at the target area, wherein the ion beam focusing column comprises: an aperture plate having a non-circular beam limiting aperture configured to limit the extent of a transmitted ion beam; and a multipole aberration compensator configured to apply a four-fold astigmatism to the ion beam to compensate spherical aberration produced by one or more lenses in the ion beam focusing column. The multipole aberration compensator may be a multipole element that generates an octupole field. A corresponding method is provided.