TEM Sample Preparation Using Two-Step FIB Cutting and ALD Void Filling
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Solution Overview
Problem
Existing methods for preparing TEM samples using FIB often result in ion beam cutting marks, known as the 'curtain effect,' which degrade imaging quality and render samples unusable, especially when dealing with thin-film pre-samples containing voids, and attempts to address this through thicker samples or inverted cutting methods are either structurally flawed or excessively time-consuming.
Innovation Solution
A two-step FIB cutting process combined with atomic layer deposition (ALD) to fill voids in the TEM sample, where the first cutting forms a thicker surface to allow for ALD material deposition, followed by a second cutting to achieve the target thickness, eliminating ion beam cutting marks and improving sample quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If one-step FIB cutting is applied to thin-film pre-samples, then sample preparation time is reduced, but ion beam cutting marks (curtain effect) are created that degrade imaging quality
Solution Approach 1:
The patent divides the single FIB cutting operation into multiple sequential cutting steps. The first cutting step creates an initial TEM sample with controlled thickness, and subsequent cutting steps refine the sample to achieve the final target thickness. This segmentation allows each cutting step to be optimized independently, reducing ion beam damage accumulation while maintaining preparation efficiency.
Solution Approach 2:
The patent performs preliminary FIB cutting to create an intermediate sample structure before final thinning. This preliminary action removes bulk material and creates a pre-shaped sample that requires less aggressive final cutting, thereby reducing ion beam exposure time and minimizing curtain effect formation during the critical final thinning stages.
2Strength
If thicker TEM samples are prepared to increase sample strength, then sample structural integrity is improved, but structural overlap signals increase making analysis impossible
Solution Approach 1:
The patent precisely controls the thickness parameter of the TEM sample through multiple staged FIB cutting operations. By adjusting cutting depth, ion beam current, and exposure time in each step, the sample thickness is optimized to provide sufficient mechanical strength while maintaining the ultra-thin requirement for acceptable electron transmission and minimal structural overlap signals.
3Manufacturing precision
If inverted cutting method is used to eliminate ion beam cutting marks, then cutting mark defects are reduced, but preparation time increases 3-5 times
Solution Approach 1:
The patent segments the cutting process into multiple steps with varying ion beam parameters. Rather than using the time-consuming inverted cutting method throughout, the patent applies conventional cutting for bulk material removal and uses low-current polishing cuts only for the final thinning stages, achieving mark-free samples with significantly reduced total preparation time.
Solution Approach 2:
The patent dynamically changes ion beam parameters (current, voltage, gas flow) during the cutting process. High current is used for rapid bulk removal, then current is progressively reduced in subsequent steps, and ultra-low current is used for final surface polishing. This parameter optimization eliminates curtain effects without requiring the excessive preparation time of inverted cutting.
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 method effectively reduces or eliminates ion beam cutting marks, enhancing the quality and yield rate of TEM samples while maintaining operational simplicity and cost-effectiveness.
Implementation Method 1
performing a first cutting to form a first front surface and a first back surface of the TEM sample in the target region of the thin-film pre-sample by applying a first focused ion beam (FIB)
Implementation Method 2
forming a first material layer to fill the voids in the TEM sample by applying an atomic layer deposition (ALD) process
Data Source
AI summary
The present application discloses a method for preparing a TEM sample, including the following steps: step 1: providing a thin-film pre-sample with undesirable voids; step 2: performing a first cutting with a first FIB to form the TEM sample located in the target region of the thin-film pre-sample. The first thickness is reached after the first cutting. The voids are exposed from the front surface or the back surface of the TEM sample after the first cutting; step 3: depositing a first material layer by an ALD process to fill the voids in the TEM sample; step 4: performing the second cutting with a second FIB to form the target thickness of the TEM sample in the target region of the thin-film pre-sample. The present application can reduce or eliminate ion beam cutting marks related to the voids in the thin-film pre-sample.