BJT Switches in Plasma Impedance Matching Networks
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Solution Overview
Problem
Existing impedance-matching networks in plasma processing chambers face challenges in efficiently handling high voltage and current while minimizing losses, particularly due to the high cost and complexity of PIN diodes used as switches in variable reactance circuits.
Innovation Solution
The use of bipolar junction transistors (BJTs) as switches in impedance-matching networks, where BJT switches are operated in a novel mode with AC current flowing between the collector and base, allowing for low-loss, high-voltage handling and avoiding the need for complex isolation circuitry by using a three-terminal device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PIN diodes are used as switches in variable reactance circuits, then high voltage and current handling capability is achieved, but cost and device complexity increase significantly
Solution Approach 1:
The patent replaces expensive PIN diodes with cheaper BJT transistors that can be easily replaced. The BJT switches perform the same function of switching reactive elements in and out of the match network but at lower cost and with simpler circuitry, accepting that they may need replacement over time rather than being designed for indefinite reuse like PIN diodes
Solution Approach 2:
The patent extracts the switching function from the complex PIN diode-based variable reactance circuit and implements it separately using BJT switches that control the connection of fixed capacitors and inductors. This separation allows the use of simpler, cheaper components while maintaining the variable reactance functionality through discrete switching of fixed elements
2Power
If PIN diodes are used as switches, then high current-carrying capacity is achieved, but on-state losses increase
Solution Approach 1:
The patent changes the operating parameters of the switch from PIN diode operation to BJT operation in a specific mode where the AC current flows between collector and base with the emitter held at a fixed potential. This parameter change enables the BJT to achieve low on-state losses while maintaining high current-carrying capacity, resolving the contradiction between power handling and energy efficiency
3Adaptability or versatility
If vacuum variable capacitors are used for impedance matching, then continuous reactance adjustment is achieved, but device complexity and cost increase
Solution Approach 1:
The patent segments the continuous reactance adjustment function into discrete steps by using multiple fixed capacitors and inductors that can be switched in and out of the circuit. The BJT switches enable selective connection of these discrete reactive elements to achieve variable impedance matching without requiring complex vacuum variable capacitors, thus maintaining adaptability while reducing device complexity
Solution Approach 2:
The patent replaces expensive vacuum variable capacitors with combinations of fixed capacitors and inductors controlled by solid-state BJT switches. This substitution uses cheaper, more reliable solid-state components to achieve the same functional goal of variable reactance, reducing both cost and device complexity while maintaining continuous or near-continuous adjustment capability through digital control of the switches
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 configuration achieves low on-state losses and high current-carrying capacity similar to PIN diodes, with low leakage current and high voltage capacity in the off-state, while simplifying the circuitry by enabling DC control via a terminal other than the RF signal terminal.
Implementation Method 1
With the BJT switch configured as described above, the base-emitter junction is forward biased and AC current flows between the collector and base
Implementation Method 2
The reverse-biased base-collector junction provides low leakage current
Data Source
AI summary
This disclosure describes systems, methods, and apparatuses for impedance-matching radio frequency power transmitted from a radio frequency generator to a plasma load in a semiconductor processing chamber. Impedance-matching can be performed via a match network having a variable-reactance circuit. The variable-reactance circuit can comprise one or more reactive elements all connected to a first terminal and selectively shorted to a second terminal via a switch. The switch can comprise a bipolar junction transistor (BJT) or insulated gate bipolar transistor (IGBT) controlled via bias circuitry. In an on-state, the BJT base-emitter junction is forward biased, and AC is conducted between a collector terminal and a base terminal. Thus, AC passes through the BJT primarily from collector to base rather than from collector to emitter. Furthermore, the classic match network topology used with vacuum variable capacitors can be modified such that voltages do not overload the BJT's in the modified topology.