TEM Sample Thickness Endpointing via S/TEM Signal Feedback
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Solution Overview
Problem
The challenge in semiconductor manufacturing lies in accurately determining the endpoint for sample thinning in transmission electron microscopy (TEM) sample preparation, which is crucial for achieving precise and reproducible results, especially as feature sizes shrink, leading to difficulties in achieving sufficient transparency without damaging the samples.
Innovation Solution
A method utilizing a SEM-S/TEM detector in a dual-beam FIB/SEM system, where the sample is thinned using a focused ion beam while monitoring thickness with S/TEM signals, allowing for precise endpoint detection and automation, enabling direct feedback and reproducible sample preparation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sample thinning is performed using FIB to achieve sufficient transparency for TEM imaging, then electron transmission is improved, but sample damage and loss of structural integrity occur
Solution Approach 1:
The patent implements real-time feedback by monitoring the FIB milling process using secondary electron imaging and backscattered electron imaging. The system continuously adjusts milling parameters based on observed sample thickness and structural integrity, preventing over-milling and sample damage while achieving the required transparency for TEM imaging.
Solution Approach 2:
The patent employs dynamic control of the FIB milling process by varying ion beam current, milling depth per pass, and imaging intervals based on real-time sample condition assessment. This dynamic adjustment optimizes the balance between achieving sufficient thinness for electron transmission and preventing sample damage.
2Device complexity
If manual monitoring of sample thickness is used during FIB thinning, then equipment complexity is reduced, but measurement precision and endpoint detection accuracy deteriorate
Solution Approach 1:
The patent integrates multiple functions into the FIB-SEM system, combining ion beam milling, secondary electron imaging, backscattered electron imaging, and thickness measurement capabilities in a single instrument. This multi-functionality enables precise thickness monitoring without requiring additional external equipment, resolving the contradiction between device complexity and measurement precision.
3Productivity
If automated endpoint detection is implemented using S/TEM signals during FIB thinning, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent merges the detection system with the existing FIB-SEM instrumentation by utilizing the same electron detectors and imaging systems already present in the instrument. The automated endpoint detection leverages existing S/TEM signals and detectors, combining multiple functions without requiring separate dedicated detection equipment, thus improving productivity while minimizing the increase in device complexity.
4Manufacturing precision
If repeated imaging and thinning cycles are performed to achieve precise thickness control, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The patent performs preliminary rough milling to quickly remove excess material and bring the sample close to the target thickness, followed by finer incremental milling with frequent imaging checks only when needed. This preliminary action reduces the number of repeated imaging-thinning cycles required, improving manufacturing precision while minimizing time loss.
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 precise and reproducible thinning of TEM samples, enhancing throughput and enabling the integration of TEM-based metrology for in-line process control in semiconductor manufacturing by providing accurate and reliable thickness measurements during the thinning process.
Implementation Method 1
The sample can be thinned using a focused ion beam (FIB)
Implementation Method 2
In a TEM, a broad beam impacts the sample and electrons that are transmitted through the sample are focused to form an image of the sample
Data Source
AI summary
A method for Transmission Electron Microscopy (TEM) sample creation. The use of a Scanning Electron Microscope (SEM)—Scanning Transmission Electron Microscope (STEM) detector in the dual-beam focused ion beam (FIB)/SEM allows a sample to be thinned using the FIB, while the STEM signal is used to monitor sample thickness. A preferred embodiment of the present invention can measure the thickness of or create TEM and STEM samples by using a precise endpoint detection method. Preferred embodiments also enable automatic endpointing during TEM lamella creation and provide users with direct feedback on sample thickness during manual thinning. Preferred embodiments of the present invention thus provide methods for endpointing sample thinning and methods to partially or fully automate endpointing.