RF Generator Frequency Control for Plasma Stability
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Solution Overview
Problem
RF generators with output power less than 100 watts experience transient instability in output frequency during mode transitions, leading to ringing phenomena in the output voltage waveform, which can result in sparks on the plasma chamber and wafer defects, making precise control of output frequency and voltage challenging.
Innovation Solution
An RF generator design incorporating a rectifier, DC/DC converter, inverter with PWM control, LC filter, transformer, ignition module, operation module, and a signal controller to manage switching frequencies and eliminate ringing phenomena through a ringing removal unit, ensuring stable output current and voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the RF generator transitions from ignition mode to steady state mode, then the operation frequency changes to meet different load requirements, but the output frequency becomes transiently unstable
Solution Approach 1:
The patent applies preliminary action by setting the switching frequency in the steady state mode to be the same as the resonance frequency used in the ignition mode. This pre-planning of frequency continuity eliminates the transient instability that would normally occur during mode transition, as the oscillator already operates at the target frequency before the transition begins.
Solution Approach 2:
The patent implements dynamics by allowing the switching frequency to be dynamically adjusted based on the operating mode. The control system automatically selects between ignition mode frequency and steady state mode frequency, enabling the system to adapt its frequency characteristics to match the current operational requirements while maintaining stability during transitions.
2Adaptability or versatility
If the output power is frequently changed to match load conditions, then the RF generator can adapt to different plasma chamber requirements, but it becomes particularly difficult to control the output power precisely
Solution Approach 1:
The patent employs feedback control by continuously monitoring the load conditions and adjusting the output power accordingly. The control system uses the detected plasma chamber state to regulate the RF output, ensuring precise power control even when frequently changing output levels to match varying load requirements.
Solution Approach 2:
The patent applies parameter changes by adjusting the switching frequency and duty cycle of the RF generator to precisely control the output power. By varying these parameters based on load conditions, the system achieves accurate power regulation while maintaining adaptability to different plasma chamber requirements.
3Power
If a ringing phenomenon occurs in the output voltage waveform, then resonance is caused by transformer leakage inductance and plasma chamber capacitance, but sparks occur in the upper electrode and wafer defects result
Solution Approach 1:
The patent applies preliminary anti-action by designing the circuit to operate at the resonance frequency, which counteracts the harmful ringing phenomenon. By matching the switching frequency to the resonant frequency of the transformer and plasma chamber combination, the system prevents the buildup of dangerous voltage oscillations that would cause sparks and wafer defects.
Solution Approach 2:
The patent converts the harmful resonance effect into a beneficial one by deliberately operating at the resonant frequency. The leakage inductance and plasma chamber capacitance, which normally cause harmful ringing, are instead utilized to create efficient power transfer and stable operation when properly tuned, turning a potential problem into a performance advantage.
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 solution significantly improves yield by preventing transient and ringing phenomena, allowing precise control of output current and voltage, thereby reducing defects and enhancing stability in the plasma chamber.
Implementation Method 1
a rectifier configured to rectify an AC voltage of a commercial power supply into a DC voltage
Implementation Method 2
a DC/DC converter configured to convert the DC voltage outputted from the rectifier into a second DC voltage
Implementation Method 3
an inverter including first and second switching elements controlled by a PWM control signal and operating alternately, and configured to convert a DC voltage having a predetermined level outputted from the DC/DC converter into an AC voltage having a predetermined level
Implementation Method 4
an LC filter including an inductor and capacitors coupled in series and parallel at an output terminal of the inverter, and configured to output a sine wave resonance signal having a predetermined resonance frequency from a high frequency signal outputted from the inverter
Implementation Method 5
a transformer configured to induce a high frequency power signal of a pulse waveform outputted from the LC filter to a secondary side
Data Source
AI summary
Disclosed herein is an RF generator that includes an inverter including first and second switching elements controlled by a PWM control signal and converting a DC voltage having a predetermined level outputted from the DC/DC converter into an AC voltage having a predetermined level, an LC filter that outputs a sine wave resonance signal having a predetermined resonance frequency from a high frequency signal, a transformer that induces a high frequency power signal of a pulse waveform outputted from the LC filter to a secondary side, an ignition module that sets a switching frequency at the termination of an ignition mode as an ignition mode escape frequency, an operation module that applies the ignition mode escape frequency as an initial value of a switching frequency in an operation mode, and a signal controller that generates the PWM control signal by using the switching frequency.