Plasma Excursion Detection via DC Bias Voltage Monitoring
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Solution Overview
Problem
Existing methods for detecting plasma excursions during plasma processing, such as arcs or micro-arcs, are inadequate due to slow sampling rates and susceptibility to delay and distortion, leading to reduced product yield and increased system downtime.
Innovation Solution
A system and method that directly senses the bias voltage from an RF-powered electrode within the plasma chamber, using a series of analog filters and a comparator to generate an alarm signal when the voltage exceeds a preset value, allowing for timely detection and alerting of plasma excursions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If RF waveform is measured in analog form and digitized for plasma excursion detection, then the measurement can be performed using standard equipment, but the sampling rate is too slow (millisecond range) to detect arcs occurring within microseconds
Solution Approach 1:
The patent replaces the mechanical/electronic analog measurement system with an optical detection system. A photodiode detector converts electromagnetic radiation (light) emitted during plasma excursions into electrical signals, enabling microsecond-level detection speed while maintaining arc detection accuracy. This substitution of measurement domain (from electrical analog to optical) resolves the contradiction between speed and precision.
2Reliability
If prior art plasma excursion detection methods are used, then the system can operate with existing equipment, but the detection is susceptible to delay and distortion resulting in poor recognition of plasma instabilities
Solution Approach 1:
The patent introduces an optical intermediary (photodiode detector) that converts plasma excursion events into detectable electrical signals without being subject to the delay and distortion problems of direct electrical measurement. The optical mediator transfers information from the plasma environment to the detection system, improving reliability while keeping the overall system relatively simple.
3Ease of operation
If analog RF waveform measurement is used for plasma excursion detection, then the measurement process is straightforward, but the overall sampling rate is in the millisecond range which is too slow for microsecond-scale arc detection
Solution Approach 1:
The patent replaces the analog electrical measurement approach with an optical detection approach using a photodiode. This substitution maintains operational simplicity (the detector simply measures light intensity) while achieving the required microsecond sampling rate, as optical detection is inherently faster than analog-to-digital conversion of RF waveforms.
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 approach enables more sensitive and reliable detection of plasma instabilities, reducing downtime and improving process control by providing immediate alerts and potential system shutdowns during plasma processing.
Implementation Method 1
A photodiode detector is positioned to face a substrate during plasma processing
Implementation Method 2
filtering the bias voltage using a plurality of analog filters to obtain an output voltage signal
Data Source
AI summary
The present invention provides a system and method for the detection of plasma excursions, such as arcs, micro-arcs, or other plasma instability, during plasma processing by directly monitoring direct current (DC) bias voltage on an RF power electrode of a plasma processing chamber. The monitored DC bias voltage is then passed through a succession of analog filters and amplifiers to provide a plasma excursion signal. The plasma excursion signal is compared to a preset value, and at points where the plasma excursion signal exceeds the preset value, an alarm signal is generated. The alarm signal is then fed back into a system controller so that an operator can be alerted and/or the processing system can be shut down. In certain embodiments, multiple processing regions can be monitored by a single detection control unit.