FIB Milling Charge Neutralization Using Local Negative Bias
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Solution Overview
Problem
Milling of electrically nonconductive materials using focused ion beams often results in the accumulation of a positive charge in the milled region, which can adversely impact the milling process due to the inability of electrons to freely replace escaping electrons, leading to potential deflection of the ion beam and suboptimal material removal.
Innovation Solution
Applying a negative bias voltage to an electrically conductive structure, such as a gas injection nozzle or voltage pin, positioned in close proximity to the milled region, to repel secondary electrons back to the sample surface, thereby maintaining a neutral charge and improving the milling process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional FIB milling is used on nonconductive materials, then material removal is achieved, but positive charge accumulates in the milled region adversely impacting the process
Solution Approach 1:
A conductive structure (gas injection nozzle, voltage pin, or nano-manipulator) is introduced as an intermediary element positioned close to the milled region. This intermediary applies a negative bias voltage to repel secondary electrons back to the sample surface, preventing positive charge accumulation without interfering with the ion beam milling process
Solution Approach 2:
The electrical parameter (voltage) is changed by applying a negative bias to the conductive structure near the milled region. This parameter change creates an electric field that influences secondary electron trajectories, causing them to return to the sample surface rather than escape and leave positive charge
2Stability of the object's composition
If electrons are prevented from escaping the milled region, then charge neutrality is maintained, but the milling process may be interfered with
Solution Approach 1:
The negative bias voltage is applied locally only in the immediate vicinity of the milled region through a conductive structure positioned within 5mm (preferably 50-500 microns) of the sample surface. This localized approach maintains charge neutrality at the critical milled area without creating a broad electric field that would interfere with the ion beam or require complex system-wide modifications
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 effectively reduces or prevents the formation of a positive charge in the milled region, ensuring more accurate and efficient milling of nonconductive materials by maintaining a neutral charge and minimizing interference with the ion beam.
Implementation Method 1
applying a negative bias voltage to an electrically conductive structure proximate the region to alter a trajectory of the secondary electrons and repel the secondary electrons back to the sample surface
Implementation Method 2
focusing the ion beam on the sample and scanning the focused ion beam across the region of the sample thereby generating secondary electrons that are ejected from a surface of the sample within the region
Data Source
AI summary
A method of processing a region of a sample, the method comprising: positioning a sample within a vacuum chamber; generating an ion beam with a focused ion beam (FIB) column; focusing the ion beam on the sample and scanning the focused ion beam across the region of the sample thereby generating secondary electrons that are ejected from a surface of the sample within the region; and during the scanning, applying a negative bias voltage to an electrically conductive structure proximate the region to alter a trajectory of the secondary electrons and repel the secondary electrons back to the sample surface, wherein the electrically conductive structure is one of a gas injection nozzle, a voltage pin or a nano-manipulator.