Focused Ion Beam Aperture Shaping for Higher-Current Milling
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Solution Overview
Problem
Focused ion beam systems face limitations in increasing milling performance and throughput due to spherical aberration, which restricts the use of higher beam currents and results in reduced precision and efficiency in material removal.
Innovation Solution
The implementation of a multipole aberration compensator that applies four-fold astigmatism to the ion beam, specifically using an octupole field, to compensate for third-order spherical aberration, allowing for increased beam current while maintaining precision by aligning the non-circular beam limiting aperture and multipole element to optimize spot size and shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher beam current densities are used to increase material removal rate, then productivity is improved, but manufacturing precision deteriorates due to reduced focusing capability
Solution Approach 1:
The beam cross-section is segmented into different current density regions through the non-circular aperture shape, creating a distributed current profile that maintains precision while increasing total current capacity
Solution Approach 2:
Different regions of the beam cross-section have different current density characteristics, with the center region providing precision and the peripheral regions contributing to increased total current and material removal rate
2Productivity
If beam current is increased to improve milling throughput, then productivity is improved, but manufacturing precision deteriorates due to spherical aberration
Solution Approach 1:
The spherical aberration effect is converted from a harmful limitation into a beneficial feature by using the non-circular aperture to distribute current such that the aberration affects primarily the peripheral regions, while the central region maintains sharp focus for precision work
Solution Approach 2:
The aperture geometry parameter is changed from circular to non-circular, fundamentally altering the current distribution pattern to enable higher currents while maintaining focus 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 solution enables a significant increase in milling throughput by doubling the beam current, allowing for 2-3 times more material to be removed in a given time interval while maintaining sharp edges and precision, effectively overcoming the limitations of spherical aberration.
Implementation Method 1
a multipole aberration compensator configured to apply a four-fold astigmatism to the ion beam to compensate for spherical aberration produced by one or more lenses of the ion beam focusing column
Implementation Method 2
spherical aberration produced by one or more lenses of the ion beam focusing column
Implementation Method 3
Milling involves direct removal of material by the impact of ions. This process is known as sputtering
Implementation Method 4
In deposition of material, a gas such as an organometallic compound is directed towards the impact point of the ion beam on the sample surface. The gas decomposes in the presence of the ion beam to add material to the sample surface
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
There is provided an ion beam system for modifying a sample or workpiece surface, the system comprising: an ion source for generating ions; 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; and a sample stage for receiving the sample or workpiece to be modified and for positioning the sample or workpiece surface 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 the ion beam passing therethrough; and a multipole aberration compensator configured to apply a four-fold astigmatism to the ion beam to compensate for spherical aberration produced by one or more lenses in the ion beam focusing column. The multipole aberration compensator may be a multipole element configured to generate an octupole field. A corresponding method of modifying a sample or workpiece using an ion beam is provided.