Magnetron Microwave Output Stabilization via Anode Current Feedback

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Solution Overview

Problem

Existing plasma processing apparatuses face issues with unstable microwave output due to poor response speed of detectors, leading to ripple fluctuations and potential damage from moding and parasitic oscillations, which affect processing accuracy and equipment longevity.

Innovation Solution

A plasma processing apparatus and microwave output device that feed back only the AC component of the anode current monitor signal to control the high voltage power supply, allowing for rapid adjustment and stabilization of microwave output, and detect anomalies like moding and parasitic oscillations to prevent damage and maintain equipment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a detector is used to detect microwave output and feedback control is implemented, then output stability is improved, but response speed is too slow to remove ripple fluctuations

Engineering Contradiction:

Improvemicrowave output stabilityVSAvoiddetector response speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent introduces an anode current monitor signal as an intermediary parameter that correlates with microwave output but can be detected and processed faster than direct microwave detection. This intermediary signal serves as a proxy that enables faster feedback control while maintaining output stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct microwave detection mechanism with an electrical signal-based monitoring system. By substituting electromagnetic wave detection with electrical current measurement and processing, the system achieves faster response speeds while maintaining control effectiveness.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a large coil or condenser is used in the primary rectification smoothing circuit to suppress ripple, then ripple removal is improved, but manufacturing cost and device volume increase

Engineering Contradiction:

Improveripple suppressionVSAvoiddetector volume and mounting area

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent implements feedback control using the anode current monitor signal to actively suppress ripple fluctuations. By detecting ripple through the current signal and applying corrective feedback to the high voltage power supply, the system achieves ripple suppression without requiring large passive components.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the control parameter from direct microwave power regulation to anode current regulation. This parameter change enables more responsive and efficient ripple suppression through electrical control rather than relying on the physical characteristics of large coils or condensers.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If feedback control is implemented using microwave output detection, then output precision is improved, but moding and parasitic oscillations cause damage

Engineering Contradiction:

Improvemicrowave output precisionVSAvoidmoding and parasitic oscillation damage

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent monitors the anode current signal to detect moding and parasitic oscillations before they cause damage. By taking preliminary detection action through current monitoring, the system can identify harmful conditions early and take preventive measures before physical damage occurs.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the potentially harmful anode current fluctuations caused by moding and parasitic oscillations into useful diagnostic information. By monitoring these current variations, the system transforms harmful phenomena into detectable signals that enable preventive control and protection.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution stabilizes microwave output, reduces ripple fluctuations, and prevents damage from moding and parasitic oscillations, ensuring accurate and reliable plasma processing by controlling the high voltage power supply based on real-time anode current feedback.

Implementation Method 1

A magnetron 7, a microwave output device 105 which forms plasma inside a processing chamber 122 using microwave formed by a magnetron 7

Methodology Applied

Scientific EffectElectromagnetic oscillation: Electromagnetic Induction

Implementation Method 2

a detector for detecting a microwave output from the magnetron

Methodology Applied

Scientific EffectMicrowave detection: Absorption (EM radiation)

Implementation Method 3

a high voltage power supply for supplying a high voltage power to the magnetron

Methodology Applied

Scientific EffectElectrical energy conversion: Electromagnetic Induction

Data Source

PatentUS10652991B2Plasma processing apparatus and microwave output device

Publication Date: 2020.05.12 HITACHI HIGH TECH CORP

AI summary

A plasma processing apparatus includes: a high voltage power supply for supplying a high voltage power to a magnetron; and a detector for detecting a microwave output from the magnetron, wherein based on a result of comparing a signal, which is obtained by adding an output from the detector to an AC component of a current detected from an output of the high voltage power supply, with a setting value of the output of the high voltage power supply, the output of the high voltage power supply is adjusted.