Offset Ground Return for Plasma Chamber Impedance Matching
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Solution Overview
Problem
Plasma fabrication processes in semiconductor and solar cell manufacturing suffer from spatial non-uniformity due to asymmetry in plasma density caused by the workpiece passageway, leading to uneven deposition or etching across the workpiece surface.
Innovation Solution
An electrical ground connection is established between the RF impedance matching network and the chamber cover, offset towards the workpiece passageway, to compensate for plasma density asymmetry, reducing load impedance and peak voltage, and enhancing the matching network's impedance matching capabilities across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the workpiece passageway is positioned on one side of the chamber wall, then the chamber structure is simplified and workpiece transfer is enabled, but plasma density asymmetry occurs causing spatial non-uniformity in plasma processes
Solution Approach 1:
The patent applies asymmetry by intentionally creating an asymmetric ground connection configuration to compensate for the asymmetric plasma density distribution caused by the workpiece passageway. Specifically, the ground connection is positioned offset from the chamber center toward the workpiece passageway side, creating an asymmetric electrical reference that counterbalances the asymmetric plasma density, thereby restoring uniformity in plasma process parameters across the workpiece surface.
2Device complexity
If the ground connection is positioned at the center of the chamber cover, then the electrical connection is symmetric and simple, but plasma density asymmetry caused by the workpiece passageway cannot be compensated
Solution Approach 1:
The patent deliberately introduces asymmetry in the ground connection configuration by positioning it offset from the chamber center toward the workpiece passageway. This asymmetric placement creates an asymmetric electrical reference potential that counteracts the asymmetric plasma density distribution, enabling compensation for the passageway-induced non-uniformity while maintaining relatively simple connection implementation.
3Manufacturing precision
If RF power is supplied with offset toward the workpiece passageway to compensate plasma density asymmetry, then spatial uniformity is improved, but the impedance matching network experiences increased inductance and higher Q factor leading to peak voltage issues
Solution Approach 1:
The patent introduces an intermediate element - the asymmetrically positioned ground connection - that serves as a mediator between the RF power supply system and the plasma chamber. This intermediate ground reference point modifies the impedance characteristics of the RF circuit, reducing the inductance seen by the matching network and lowering the Q factor, thereby reducing peak voltages and arcing risk while still enabling plasma density uniformity through the asymmetric configuration.
4Adaptability or versatility
If the Q of the resonant circuit is high, then the impedance matching network has narrow bandwidth and cannot match a wide range of load impedances, but reducing Q increases peak voltage and arcing risk
Solution Approach 1:
The asymmetric ground connection acts as an intermediary that transforms the impedance characteristics presented to the matching network. By repositioning the ground reference, the circuit inductance is reduced, which lowers the resonant circuit Q factor. This intermediate transformation enables the matching network to handle a broader range of load impedances with acceptable SWR while keeping peak voltages at safe levels, thus resolving the trade-off between matching bandwidth and arcing risk.
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 spatial uniformity of plasma processes, reduces the risk of electrical arcing, and allows for a wider range of load impedances to be matched, ensuring consistent processing across different operating conditions in the plasma chamber.
Implementation Method 1
the aforesaid offset reduces the inductance of the load impedance at the output of the impedance matching network, and thereby reduces the Q of the resonant circuit created by the impedance matching network in combination with the plasma chamber load
Implementation Method 2
Plasma chambers commonly are used to perform processes for fabricating electronic devices such as semiconductors, displays and solar cells
Data Source
AI summary
An electrical ground (36) of an RF impedance matching network (33) is connected to a connection area (50) on the grounded chamber cover (18) of a plasma chamber. The connection area is offset away from the center of the chamber cover toward a workpiece passageway (20). Alternatively, an RF power supply (30) has an electrically grounded output (32) that is connected to a connection area (52) on the chamber cover having such offset. Alternatively, an RF transmission line (37) has an electrically grounded conductor (39) that is connected between a grounded output of an RF power supply and a connection area (52) on the chamber cover having such offset.