Inverted TEM Lamella Support Structure for Sub-20 Nm Flatness
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Solution Overview
Problem
Conventional methods for preparing ultra-thin TEM lamellae face challenges in maintaining orientation stability and achieving sub-20 nm thickness without lamella bending, with existing techniques limiting the height of the thinned area and resulting in considerable thickness variations.
Innovation Solution
The method involves directing a focused ion beam at a specimen's back surface with specific angles and doses to form S-shaped cut faces, creating double-tapered lamellae with a waist, using a charged particle beam system and a substrate stage to secure and orient the specimen, and control system to define tapered cut faces extending from the front to the back surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional top-down lamella method with frames is used, then lamella bending is prevented, but sub-20 nm lamella preparation is not repeatable and thickness control is poor
Solution Approach 1:
The patent inverts the conventional top-down approach by using an inverted wedge lamella method where the support structure is positioned at the bottom rather than the top. The FIB process creates a wedge-shaped lamella with the thickest portion at the back surface, providing support from below, which enables repeatable sub-20 nm thickness preparation while maintaining thickness control through precise dose modulation.
Solution Approach 2:
The patent employs parameter changes by modulating the FIB dose during the lamella formation process. By varying the ion beam dose across different regions and stages of the process, precise control over lamella thickness is achieved, enabling repeatable sub-20 nm preparation. The dose parameters are specifically optimized to create the inverted wedge shape with controlled thickness gradient.
2Manufacturing precision
If inverted wedge lamella method is used, then sub-20 nm thick lamellae can be achieved, but the height of the thinned area is limited by the wedge angle and thickness varies considerably
Solution Approach 1:
The patent applies dynamics by making the wedge angle adjustable rather than fixed. The system allows dynamic modification of the wedge angle parameter during the FIB process, enabling optimization of both the thinned area height and thickness uniformity. This dynamic adjustment capability resolves the contradiction by allowing the operator to select appropriate wedge angles based on the specific specimen and imaging requirements.
Solution Approach 2:
The patent incorporates feedback mechanisms through real-time monitoring and adjustment of the FIB process parameters. By monitoring the lamella formation process and adjusting the ion beam dose and wedge angle accordingly, the system achieves both sub-20 nm thickness precision and adequate height of the thinned area. The feedback loop enables compensation for variations and maintains optimal process conditions throughout.
3Reliability
If 5-degree taper angle is used in inverted wedge method, then lamella bending is reduced, but thickness varies considerably in the thinned area
Solution Approach 1:
The patent applies local quality by implementing different FIB dose rates and process parameters in different regions of the specimen. The region of interest receives optimized low-dose processing to maintain uniform thickness, while surrounding areas receive higher doses for support structure formation. This spatial variation in process quality enables both bending control through adequate support and thickness uniformity in the thinned area.
Solution Approach 2:
The patent segments the FIB processing into distinct stages and regions: initial support structure formation, intermediate lamella thinning, and final precision thickness control. Each segment uses optimized parameters specific to that stage, with the 5-degree taper applied selectively in support regions while maintaining different parameters in the thinned area to ensure thickness uniformity.
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 allows for the production of lamellae with a thinnest portion at the region of interest, maintaining flatness and reducing thickness variations, enabling effective TEM imaging with tapered cut faces that extend from the back to the front surface, thereby overcoming the limitations of existing methods.
Implementation Method 1
directing an ion beam to a back surface of a specimen at a first angle and at a first dose to form a first cut face having an S-shape and directing the ion beam to the back surface of the specimen at a second angle and at a second dose to form a second cut face having a second S-shape
Data Source
AI summary
Lamellae with thin regions for TEM of regions of interest include oppositely situated S-shaped cut faces that define a waist region. In some examples, the waist has a thickness of less than 25 nm and defines a double tapered region of height of between 400 nm and 800 nm that is suitable for TEM. A portion of the lamella at the top surface can comprising a metallic or other coating than serves to support the lamella.