Cryo-FIB SEM Navigation for Stable Photoresist TEM Lamella Prep
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Solution Overview
Problem
Conventional TEM sample preparation methods using SEM and FIB cause deformation and shrinkage of photoresist (PR) profiles due to temperature changes, which affects the accuracy of TEM-based metrology.
Innovation Solution
The method involves cooling the material sample to a cryogenic temperature, depositing a layer over the region of interest using a focused beam of charged particles, and removing a portion of the sample at cryogenic temperatures using a cryo-FIB system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional TEM sample preparation method using SEM and FIB is used, then sample preparation can be completed, but photoresist profiles undergo deformation and shrinkage due to temperature increase
Solution Approach 1:
The patent applies parameter changes by transitioning from room temperature to cryogenic temperature (e.g., liquid nitrogen temperature of -196°C or liquid helium temperature of -269°C) during FIB sample preparation. This temperature parameter change prevents photoresist deformation and shrinkage while maintaining the ability to complete TEM sample preparation, directly resolving the technical contradiction between manufacturing precision and temperature control.
Solution Approach 2:
The patent employs preliminary action by pre-cooling the sample to cryogenic temperature before initiating FIB milling and deposition processes. This preliminary cooling action ensures that the photoresist profiles remain stable throughout subsequent preparation steps, preventing thermal deformation before it can occur during the preparation process.
2Manufacturing precision
If cryogenic temperature is used during sample preparation, then photoresist deformation is reduced, but additional cooling equipment and process complexity are required
Solution Approach 1:
The patent implements universality by integrating cryogenic cooling capability into the existing FIB-SEM system, allowing the same equipment to perform both conventional room temperature preparation and cryogenic preparation. The cooling system serves multiple functions: maintaining low temperature during preparation, condensing volatile materials, and preventing ice crystal formation, thereby reducing overall system complexity despite adding cryogenic functionality.
Solution Approach 2:
The patent uses an intermediary approach by introducing a cryogenic fluid (liquid nitrogen or liquid helium) as a mediator between the sample and the thermal environment. This intermediary fluid absorbs excess heat, maintains stable cryogenic temperatures, and facilitates heat transfer without requiring direct thermal contact, thereby simplifying the thermal management system while achieving precise temperature control.
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 reduces deformation and shrinkage of PR profiles, preserving the as-fabricated geometries of thermally sensitive materials and improving the fidelity of TEM measurements.
Implementation Method 1
cooling the material sample to a cryogenic temperature
Implementation Method 2
depositing a layer over at least a portion of the ROI at the cryogenic temperature
Implementation Method 3
Depositing the layer can include introducing a precursor into an environment of the material sample. The precursor can include a metal substituent. Decomposing the precursor can use a focused beam of charged particles.
Implementation Method 4
Removing a portion of the material sample can include milling the material sample to form a lamella
Implementation Method 5
The method can include maintaining a temperature differential between the material sample and a cold reservoir, such that the material sample is relatively warmer than the cold reservoir by about 20° C.
Data Source
AI summary
Embodiments of an analytical instrument system, components, and methods for preparing dose-sensitive samples for microanalysis are described. A method includes receiving location data for a material sample, locating a region of interest (ROI) of the material sample in reference to the location data, cooling the material sample to a cryogenic temperature, depositing a layer over at least a portion of the ROI at the cryogenic temperature, and removing a portion of the material sample at the cryogenic temperature.