Ion Implanter Control Module for Displacement Current Measurement
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Solution Overview
Problem
Existing ion implanters in plasma immersion mode face challenges in accurately determining the displacement current, which is essential for precise estimation of the implanted dopant dose, due to the complexity of equivalent capacitance and the influence of the plasma sheath, and also struggle to account for the contribution of secondary electrons to the implantation current.
Innovation Solution
A control module for the ion implanter that includes a current measurement circuit to accurately measure displacement current between the substrate holder plate and a neutralization terminal, and a control circuit to estimate the implantation current by differentiating supply and displacement currents, while also considering the contribution of secondary electrons through a secondary electron detector and spectrometer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the displacement current is measured using a measuring capacitor in parallel with the substrate holder, then the displacement current can be estimated, but the measurement precision is insufficient because the equivalent capacitance is practically impossible to determine accurately due to plasma sheath variations
Solution Approach 1:
The patent introduces a Rogowski coil as an intermediary device to measure the displacement current. Instead of directly measuring the current through complex capacitance calculations, the Rogowski coil indirectly measures the current by detecting the magnetic field generated by the current flow, thereby avoiding the complexity of determining equivalent capacitance while achieving accurate displacement current measurement
Solution Approach 2:
The patent replaces the electrical measurement approach (using measuring capacitors and voltage integration) with a magnetic field-based measurement approach using a Rogowski coil. This substitution eliminates the need for electrical connections to the high-voltage substrate holder and avoids the complexities of capacitance measurement, providing a more robust and accurate solution
2Measurement precision
If the supply current is used to estimate the implanted dose, then the dose estimation is simplified, but the measurement precision is insufficient because the supply current includes both implantation current and displacement current
Solution Approach 1:
The patent segments the total supply current into two distinct components: implantation current and displacement current. By using the Rogowski coil to specifically measure the displacement current component and subtracting it from the total supply current, the system accurately isolates the implantation current, thereby achieving precise implanted dose estimation
Solution Approach 2:
The patent implements a feedback mechanism where the measured displacement current is continuously subtracted from the supply current to obtain the accurate implantation current. This feedback loop ensures that the dose estimation is continuously corrected based on the actual displacement current conditions, improving measurement precision
3Measurement precision
If the implantation current is calculated by subtracting displacement current from supply current, then the implantation current is improved, but the measurement precision is still insufficient because secondary electron contribution is not accounted for
Solution Approach 1:
The patent introduces a secondary electron detector as an intermediary device to measure the secondary electron current. This detector captures the secondary electrons emitted during ion implantation and provides a separate measurement of this current component, which is then used to further refine the implantation current calculation by accounting for the secondary electron contribution
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 solution allows for a more precise estimation of the implanted dose by accurately accounting for displacement and secondary electron currents, leading to improved accuracy in determining the ion implantation depth and concentration.
Implementation Method 1
a current measurement circuit configured to measure, during use, the displacement current flowing between the second pole of the second switch and the neutralization terminal
Implementation Method 2
Ion implantation of a substrate consists of immersing it in a plasma and polarizing it with a negative voltage, from a few tens of volts to a few tens of kilovolts (generally less than 100 kV), in order to create an electric field capable of accelerating the plasma ions towards the substrate
Implementation Method 3
create an electric field capable of accelerating the plasma ions towards the substrate
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a control module for an ion implanter, comprising a power supply, said power supply including: an electrical generator (HT), the positive pole of which is connected to the ground; a first switch (SW1), the first pole of which is connected to the negative pole of the generator (HT) and the second pole of which is connected to the output terminal (S) of said power supply; and a second switch (SW2), the first pole of which is connected to the output terminal (S) and the second pole of which is connected to the neutral terminal (N). In addition, said control module includes a circuit (AMP) for measuring the current that flows between the second pole of the second switch (SW2) and the neutral terminal (N). The invention also relates to an ion implanter provided with said control module.