Ion Source Shutter Control for Stable Ion Milling Uniformity
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Solution Overview
Problem
The uniformity of the processing shape in ion milling apparatuses is compromised due to uncontrolled disturbances, particularly the influence of adsorbed atmospheric gases on discharge and ion beam currents, leading to issues like short circuits and non-uniform ion beam distribution.
Innovation Solution
An ion milling apparatus with a conductive shutter and control unit that shields the ion beam during initial operation to measure and release adsorbed gases, ensuring a stable ion beam current by retracting the shutter when the current falls below a predetermined value, thereby maintaining consistent discharge and ion beam parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the ion source is operated immediately after atmospheric exposure, then the discharge current and ion beam current are initially high, but the processing uniformity deteriorates due to adsorbed gas interference
Solution Approach 1:
The patent applies preliminary action by introducing a pre-discharge step before the actual ion beam processing. During this preliminary phase, the ion source is activated to generate ions that desorb atmospheric gases from the ionization chamber walls and electrode surfaces. Only after this gas release phase, when the discharge current stabilizes below a predetermined threshold, does the system transition to the main processing mode. This ensures that adsorbed gases do not interfere with the ion beam current stability during sample processing, thereby maintaining processing shape uniformity while enabling rapid productivity.
2Productivity
If the discharge voltage is increased to improve ion beam current, then the processing efficiency improves, but the sputtering of cathode and anode increases causing more deposits and short circuits
Solution Approach 1:
The patent uses preliminary action by performing a pre-discharge phase at elevated voltage before the main processing. During this preliminary phase, the ion source operates at higher discharge voltage to generate sufficient ion beam current for effective gas desorption from chamber walls and electrodes. This preliminary high-power operation removes deposits and prevents short circuits. After this preparatory phase, the system transitions to the stable processing mode with controlled ion beam current, ensuring both high productivity during processing and reliability by preventing deposit accumulation that would cause short circuits.
3Reliability
If the inner wall surface of the anode is roughened to prevent short circuits, then the reliability improves, but the amount of adsorbed gas increases affecting ion beam distribution
Solution Approach 1:
The patent applies the 'blessing in disguise' principle by converting the harmful effect of increased gas adsorption on roughened surfaces into a beneficial process. The intentionally roughened anode inner wall surface, which would normally trap more adsorbed gas and disrupt ion beam distribution, is instead utilized as a gas reservoir during the pre-discharge phase. The elevated discharge voltage during this preliminary phase actively desorbs the excess gas from the rough surface, converting the potential harm into a controlled gas release mechanism. This ensures that by the time main processing begins, the rough surface has already released its adsorbed gas, maintaining both the reliability benefit of the rough surface and the uniformity of ion beam distribution.
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 improves processing reproducibility by releasing adsorbed gases before sample processing, stabilizing the ion beam and enhancing the uniformity of the processing shape.
Implementation Method 1
an ion generated by an electron generated by discharge between an anode and a cathode
Implementation Method 2
accelerating the ion by an acceleration electrode
Implementation Method 3
a conductive shutter disposed between the ion source and the sample stage and configured to shield the ion beam
Implementation Method 4
flip atoms on a surface of the sample by a sputtering phenomenon, polish the surface of the sample without a stress
Implementation Method 5
an influence of an adsorption gas derived from the atmosphere on a discharge current value and an ion beam current value
Data Source
AI summary
In a state in which an ion beam from an ion source 101 is shielded by a shutter 102, an ion milling apparatus applies a discharge voltage Vd between an anode 203 and cathodes 201 and 202 and an acceleration voltage Va between the anode and an acceleration electrode 205 with respect to the ion source, and retracts the shutter by a shutter drive source 103 to a position where the ion beam is not shielded after any one of a discharge current flowing between the anode and the cathodes due to discharge and an ion beam current flowing caused by irradiation on the shutter the ion beam falls below a predetermined reference value.