MHz RF Generator Tuning for kHz Cycle Reflection Control

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Solution Overview

Problem

In plasma tools, the reflection of power from the plasma chamber back to the RF generators reduces efficiency and causes damage, particularly when tuning a megahertz (MHz) RF generator within a cycle of operation of a kilohertz (kHz) RF generator.

Innovation Solution

A method is provided to tune the MHz RF generator by determining frequency and phase parameters of the kHz RF generator, calculating instantaneous complex voltage reflection coefficients, and optimizing frequency parameters to minimize the average power reflection coefficient, thereby reducing voltage and power reflection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a single combination of variable capacitor and higher RF frequency is used, then the voltage reflection coefficient can be tuned near zero at one specific load impedance value, but the power reflection coefficient becomes very high (up to 50%) when the load impedance varies during the kHz RF cycle

Engineering Contradiction:

Improvevoltage reflection coefficient tuning accuracyVSAvoidpower reflection coefficient

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent applies dynamics by making the higher RF frequency variable and modulating it dynamically during the kHz RF cycle. Instead of using a fixed frequency, the system adjusts the higher RF frequency in real-time to track and compensate for load impedance variations, thereby maintaining low power reflection coefficient throughout the entire cycle

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operating parameters by introducing frequency modulation of the higher RF generator. The frequency is varied within a range (e.g., 57-63 MHz) and modulated at the kHz frequency to match the load impedance variations, transforming the static tuning approach into a dynamic parameter adjustment strategy

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the higher RF frequency is held constant, then the system operation is simple, but the load impedance modulation by kHz RF causes high power reflection and reduced processing efficiency

Engineering Contradiction:

Improvesystem operation simplicityVSAvoidprocessing efficiency

Core Design Contradiction:

Ease of operationVSProductivity

Solution Approach 1:

The patent implements periodic action by modulating the higher RF frequency at the same frequency as the kHz RF generator. This periodic frequency modulation synchronizes with the load impedance variations, ensuring that the impedance matching remains effective throughout each cycle, thereby maintaining high processing efficiency

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS12322572B2Systems and methods for tuning a MHz RF generator within a cycle of operation of a kHz RF generator

Publication Date: 2025.06.03 LAM RES CORP

AI summary

Systems and methods for tuning a megahertz radio frequency (RF) generator within a cycle of operation of a kilohertz (kHz) RF generator are described. In one of the methods, a predetermined periodic waveform is provided to a processor. The processor uses a computer-based model to determine plurality of frequency parameters for the predetermined periodic waveform. The frequency parameters are applied to the megahertz RF generator to generate an RF signal having the frequency parameters during one or more cycles of operation of the kilohertz RF generator.