Cold Trap for Charged Particle Beam Contamination Control
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Solution Overview
Problem
High-pressure scanning electron microscopes (HPSEMs) face contamination issues due to impurities like H2O and O2, which interfere with beam chemistry processes, causing unintended etching of materials like graphene and diamond, even when no etch precursor gas is supplied, leading to inconsistent processing results and material degradation.
Innovation Solution
Implementing a cold trap system that condenses contaminants without condensing the process gas, reducing the partial pressure of contaminant gases in the sample chamber and minimizing undesired beam chemistry reactions by physically immobilizing contaminant molecules on cooled surfaces within the charged particle beam system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a process gas is supplied to enable beam chemistry processes, then chemical reactions can be initiated at the work piece surface, but contaminant gases like H2O and O2 also present cause unintended etching and interfere with processing
Solution Approach 1:
The patent segments the gas environment by introducing a process gas mixture where the process gas concentration is maintained between 0.1-10% of total gas pressure. This segmentation allows the process gas to enable beam chemistry reactions while the majority composition (80-99.9% other gases) provides a cleaner environment that minimizes contaminant-induced etching.
Solution Approach 2:
The patent applies local quality by creating a non-uniform gas distribution where the process gas is concentrated at the work piece surface (0.1-10% concentration) while the bulk chamber maintains a different composition. This localized approach enables beam chemistry at the surface while keeping the overall environment cleaner to prevent unintended etching.
2Reliability
If the sample chamber is maintained in high vacuum to prevent beam scattering, then beam quality is maintained, but beam chemistry processes requiring process gas cannot be performed
Solution Approach 1:
The patent segments the chamber into two distinct pressure zones: the sample chamber maintained at high vacuum (10^-6 to 10^-3 Torr) for beam quality, and a process region near the work piece surface where process gas is introduced (0.1-10% concentration) to enable beam chemistry. This spatial segmentation allows both requirements to coexist.
Solution Approach 2:
The patent uses a process gas mixture as an intermediary, where the process gas enables beam chemistry reactions at the work piece surface while the majority composition (80-99.9% other gases) acts as a buffer that maintains overall vacuum conditions, preventing significant beam scattering while still allowing chemical processes.
3Productivity
If process gas pressure is increased to support beam-induced reactions, then reaction efficiency improves, but contaminant effects and unintended etching increase
Solution Approach 1:
The patent applies local quality by concentrating the process gas (0.1-10% concentration) specifically at the work piece surface where beam-induced reactions occur, while the bulk chamber pressure remains low (10^-6 to 10^-3 Torr). This localized high pressure enables efficient reactions without increasing overall contaminant exposure throughout the chamber.
Solution Approach 2:
The patent changes the parameter of process gas concentration to be very low (0.1-10% of total gas pressure) while maintaining the work piece surface in a region of enhanced process gas presence. This parameter optimization allows sufficient reaction efficiency while minimizing the absolute amount of contaminants present that could cause unintended etching.
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 significantly reduces inadvertent etching and contamination, allowing for consistent and high-resolution imaging and processing of materials like graphene, diamond, and carbon nanotubes by maintaining a cleaner environment within the charged particle beam system.
Implementation Method 1
providing a cooled surface within the processing chamber, the temperature of the cooled surface being sufficiently cold to remove contaminants from the processing chamber
Implementation Method 2
An electron beam is directed at the work piece, and the electrons in the beam and the emitted secondary electrons dissociate the adsorbates, generating reaction products
Data Source
AI summary
A cold trap is provided to reduce contamination gases that react with the beam during operations that use a process gas. The cold trap is set to a temperature that condenses the contamination gas but does not condense the process gas. Cold traps may be used in the sample chamber and in the gas line.