Solid-State Variable Capacitors for Fast RF Impedance Matching
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Solution Overview
Problem
Existing RF matching networks using vacuum variable capacitors driven by step motors are too slow for fast impedance matching, leading to mechanical failures and process instability in semiconductor fabrication, especially with the increasing complexity and reduced processing times of semiconductor devices.
Innovation Solution
Implementing a solid state based variable capacitor using a diode array, such as Schottky or PIN diodes, to achieve ultra-fast impedance tuning by controlling capacitance values with a reverse bias circuit, eliminating the need for step motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a step motor driven vacuum variable capacitor is used for RF matching, then the mechanical adjustment is reliable, but the impedance matching speed is too slow
Solution Approach 1:
The patent replaces the mechanical step motor driven vacuum variable capacitor with a solid-state diode array based variable capacitor. The diode array uses electrical biasing instead of mechanical rotation to adjust capacitance, enabling impedance matching in the millisecond range compared to the slow mechanical adjustment of traditional systems. This substitution eliminates mechanical inertia and friction, achieving ultra-fast impedance tuning required for modern semiconductor fabrication processes.
2Reliability
If a step motor driven vacuum variable capacitor is used, then the capacitance adjustment is achievable, but mechanical failures occur frequently
Solution Approach 1:
The patent eliminates the step motor and mechanical drive train by using a solid-state diode array. The diode array adjusts capacitance through electrical biasing without any moving parts, completely removing the source of mechanical failures. This solid-state approach significantly improves reliability while reducing mechanical complexity in the RF matching network.
3Productivity
If traditional variable capacitors are used, then the impedance matching is achievable, but the processing speed is too slow for modern semiconductor fabrication
Solution Approach 1:
The patent changes the fundamental operating parameter of the variable capacitor from mechanical rotation to electrical biasing. The diode array capacitance is controlled by applying reverse bias voltage, which changes the depletion region width and thus the capacitance value. This parameter change enables ultra-fast impedance tuning in the millisecond range, matching the high-speed requirements of modern semiconductor fabrication processes with reduced processing times.
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 diode array enables impedance matching in the millisecond range, reducing mechanical failures, improving power delivery efficiency, and enhancing processing stability with faster etch rates and better on-wafer results.
Implementation Method 1
a bias circuit that applies a reverse bias to the solid state based variable capacitor to control a capacitance value of the solid state based variable capacitor
Data Source
AI summary
Embodiments of the present disclosure provide a system for fast impedance tuning. The system includes a radio frequency (RF) generator to generate power, a plasma chamber to receive the power from the RF generator and a RF matching network inserted between the RF generator and the plasma chamber configured to match a plasma load impedance to a RF generator impedance using a solid state based variable capacitor. The RF matching network includes a bias circuit that applies a reverse bias to the solid state based variable capacitor to control a capacitance value of the solid state based variable capacitor. The plasma load impedance is matched with the RF generator impedance when pulsed voltage, multi-level pulsing, or RF match ignition tuning is applied.