Pulsed Bias Circuit for Plasma Charge Neutralization
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Solution Overview
Problem
Ion beam processing systems face challenges in charge neutralization, particularly when dealing with workpieces that are poor conductors or insulators, as the existing methods using pulsed ion implantation systems often result in insufficient electron flux during 'off' periods, leading to excessive positive charge buildup.
Innovation Solution
A plasma processing system with a pulsed bias circuit that alternates between high positive and negative voltage states to effectively neutralize the workpiece by controlling the plasma source's bias voltage, ensuring adequate electron flux during 'off' periods to counteract positive charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulsed ion implantation is used to treat workpieces, then ion beam processing can be performed, but excessive positive charge builds up on the workpiece surface during off periods
Solution Approach 1:
The system applies periodic voltage pulses to the plasma source, alternating between positive voltage during ion implantation and negative voltage during electron neutralization phases. This periodic switching enables both ion implantation and charge neutralization to occur in sequence, resolving the charge buildup problem while maintaining processing productivity
Solution Approach 2:
Electrons from the plasma serve as an intermediary to neutralize the positive charge that accumulates on the workpiece during ion implantation. By controlling the plasma source voltage to attract electrons during off periods, the system uses these electrons as a mediator to counteract the harmful positive charge buildup
2Object-generated harmful factors
If workpiece holder is grounded to dissipate charge, then charge dissipation path is provided, but non-conductive workpieces cannot dissipate charge
Solution Approach 1:
The plasma electrons act as an intermediary charge carrier that can transfer charge to the workpiece surface directly, bypassing the need for a conductive path through the workpiece holder. This allows even non-conductive workpieces to receive charge neutralization through direct electron bombardment from the plasma
Solution Approach 2:
The system replaces the mechanical/electrical conduction path (grounded workpiece holder) with a plasma-based charge transfer mechanism. Instead of relying on electrical conduction through the holder and workpiece, charge neutralization is achieved through direct electron transport from the plasma to the workpiece surface
3Object-generated harmful factors
If plasma bias is set negative during off periods to attract electrons, then electron flux increases, but positive ions are not attracted to workpiece during on periods
Solution Approach 1:
The system uses periodic voltage switching on the plasma source, applying positive voltage during ion implantation phases and negative voltage during electron neutralization phases. This time-separated approach ensures that positive ions are attracted during on periods while electrons are attracted during off periods, resolving the contradiction between ion implantation efficiency and charge neutralization effectiveness
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
The system effectively neutralizes the workpiece by alternating pulses of ions and electrons, preventing excessive positive charge buildup and ensuring efficient processing, even for non-conductive workpieces.
Implementation Method 1
A desired impurity material is ionized in an plasma source
Implementation Method 2
the ions are accelerated to form an ion beam of prescribed energy
Implementation Method 3
electrons in the plasma may be repelled from the workpiece holder due to its relatively negative potential with respect to the plasma
Implementation Method 4
During 'off' periods when the implantation system no longer sets the workpiece holder at a negative potential with respect to the plasma, electrons may drift towards the workpiece
Data Source
AI summary
A processing system may include a plasma source for providing a plasma and a workpiece holder arranged to receive ions from the plasma. The processing system may further include a pulsed bias circuit electrically coupled to the plasma source and operable to switch a bias voltage supplied to the plasma source between a high voltage state in which the plasma source is biased positively with respect to ground and a low voltage state in which the plasma source is biased negatively with respect to the ground.