Ion Beam Polishing Glancing Angle Sample Edge
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Solution Overview
Problem
Existing methods for preparing samples with polished surfaces for high-resolution microscopy, such as ion beam milling, often result in damaged leading edges and beveled profiles, which hinder effective scanning probe microscopy due to ion scattering and implantation, and require extensive sample preparation and frequent replacement of holders and masks.
Innovation Solution
A method involving a collimated ion beam directed at a glancing angle to the sample edge, with a shield to prevent ion beam scattering, and controlled ion beam parameters to minimize damage and achieve a sharp, flat polished facet, allowing for high-resolution analysis without excessive sample removal or holder replacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion beam milling is used to polish the sample edge, then a smooth cross-sectional profile is achieved, but the leading part of the facet becomes damaged due to ion scattering and implantation
Solution Approach 1:
The patent inverts the conventional ion beam milling approach by directing the ion beam at a glancing angle (5-30 degrees) relative to the sample surface instead of perpendicular to it. This inversion of the beam angle prevents ions from directly implanting into the leading facet region, thereby reducing ion beam damage while still achieving smooth surface polishing through controlled sputtering of the bulk material.
Solution Approach 2:
The patent introduces a mask positioned between the ion beam source and the sample, which acts as an intermediary to control ion beam distribution. The mask geometry is designed to block scattered ions from reaching the leading facet while allowing the primary ion beam to polish the bulk material, thus mediating between the polishing function and the damage prevention requirement.
2Productivity
If the ion beam is directed perpendicular to the sample surface, then efficient material removal is achieved, but a beveled or round-nosed profile is created at the leading edge
Solution Approach 1:
The patent inverts the conventional perpendicular ion beam direction to a glancing angle incidence (5-30 degrees). This inversion changes the material removal mechanism from direct sputtering to a combination of sputtering and lateral erosion, which maintains efficient material removal while producing a flat, sharp facet profile instead of a beveled or round-nosed edge.
Solution Approach 2:
The patent changes the critical parameter of ion beam incidence angle from 90 degrees (perpendicular) to a glancing angle range of 5-30 degrees. This parameter change fundamentally alters the interaction between the ion beam and sample surface, enabling simultaneous achievement of high material removal rate and desirable flat facet geometry without the harmful beveling effect.
3Object-affected harmful factors
If the sample is turned over to polish the back surface, then the leading edge damage is reduced, but considerably more sample material must be removed
Solution Approach 1:
Rather than turning the sample over to polish the back surface, the patent inverts the ion beam angle while polishing the original front surface. This inversion allows the ion beam to glide along the surface at a glancing angle, removing material efficiently from the bulk while preventing damage to the leading facet, thus avoiding both the damage problem and the excessive material removal problem.
Solution Approach 2:
The patent changes the ion beam incidence angle parameter to enable selective material removal. By setting the angle to 5-30 degrees, the ion beam preferentially removes bulk material through sputtering while the shallow trajectory prevents ions from reaching and damaging the leading facet region, thereby achieving damage-free polishing without excessive material loss.
4Manufacturing precision
If a mask is positioned close to the sample surface to define the polished region, then the polished area is precisely controlled, but ion scattering around the mask edge damages the leading facet
Solution Approach 1:
The patent inverts the conventional approach by positioning the mask far from the sample surface and using a glancing angle ion beam. This inversion causes the ion beam to skim along the sample surface, naturally limiting the polished region to areas where the beam can physically reach, thereby defining the polished area without creating scattered ions that would damage the leading facet.
Solution Approach 2:
The patent moves the mask positioning problem from the vertical dimension (close to surface) to the angular dimension (glancing incidence). By changing the beam angle rather than the mask-sample distance, the system achieves precise polished region definition through geometric constraints of oblique incidence, eliminating the ion scattering issue associated with close mask positioning.
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 method produces polished facets with low surface roughness and minimal structural damage, enabling high-resolution scanning probe microscopy with improved feature resolution and reduced scanning issues, while minimizing the need for frequent sample holder and mask replacements.
Implementation Method 1
removing a first portion of the sample by directing an ion beam onto the edge adjacent the first portion along an ion beam axis in order to leave the polished facet
Implementation Method 2
This arises from scattering of ions around the mask edge and possibly their partial implantation into the sample
Data Source
Figure 1~2
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Figure 7~8
AI summary
A method for forming a polished facet between an edge and a face of a sample, involves removing a first portion of the sample by directing an ion beam onto the edge adjacent the first portion along an ion beam axis to leave the polished facet. The ion beam axis lies on an ion beam plane oriented at a glancing incident angle, preferably from 1° to 30°, to a sample plane defined by and parallel to the first face. The ion beam is directed to flow from the edge towards the first face. Also disclosed is a sample preparation apparatus comprising a chamber adapted for evacuation with a sample holder adapted to hold a sample comprising a first face bounded by an edge, and an ion gun arranged to direct an ion beam along an ion beam axis towards the sample.