Insulated Electrode Plasma Parameter Measurement
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Solution Overview
Problem
Conventional plasma diagnostic tools are limited in measuring ion flux and other plasma parameters during processing due to deposition of weakly conducting materials, requiring complex setups and being unsuitable for continuously biased substrates like silicon wafers.
Innovation Solution
A method involving the measurement of time-varying voltage and current at an electrode insulated by an insulating layer, using mathematical transforms to isolate and calculate ion current, resistive terms, and other plasma parameters like electron temperature and density, without the need for special probes or pulsed RF signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional diagnostic tools like Langmuir probes are used to measure plasma parameters, then measurement capability is provided, but the probes become contaminated by deposited material which reduces or removes conduction current path
Solution Approach 1:
The patent introduces an insulating layer as an intermediary between the plasma and the electrode surface. This mediator allows the measurement of ion flux through capacitive coupling without direct contact, preventing material deposition on the electrode while still enabling plasma parameter measurement through the insulating layer's electrical properties
Solution Approach 2:
The patent replaces the mechanical/electrical contact-based Langmuir probe measurement system with a capacitive coupling system. Instead of relying on direct conduction current through a probe, the measurement is performed through displacement current across the insulating layer, substituting the conduction mechanism with a capacitive mechanism
2Measurement precision
If pulsed RF train is supplied to measure ion flow, then measurement capability is achieved, but plasma perturbation occurs and system complexity increases
Solution Approach 1:
The patent enables continuous RF biasing of the substrate without interruption, allowing plasma processing to proceed continuously while measurements are performed. The capacitive coupling mechanism allows ion flux measurement during the entire RF cycle rather than requiring pulsed measurement sequences, maintaining continuous plasma action without interruption
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
Enables accurate measurement of ion flux and other plasma parameters on RF-biased substrates without interrupting the process, reducing complexity and cost, and overcoming limitations of existing techniques.
Implementation Method 1
an insulating layer, by which said electrode is insulated from said plasma
Implementation Method 2
performing a mathematical transform effective to: (i) express said current and voltage values as a relationship between the real component of current through said electrode and the voltage by obtaining an average of the current values measured for each of the plurality of discrete voltage values, thereby eliminating a capacitive contribution to the current through the electrode
Data Source
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AI summary
A method of measuring ion current between a plasma and an electrode in communication with the plasma is disclosed. A time-varying voltage at the electrode and a time- varying current through the electrode are measured. The method comprise recording, for each of a plurality of voltage values, v ', a plurality, n, of current values I(v'); and obtaining from the current and voltage values a value of the ion current. The electrode is insulated from the plasma by an insulating layer, so that the current values lack a DC component. The method includes performing a mathematical transform effective to: express the current and voltage values as a relationship between the real component of current through the electrode and the voltage, thereby eliminating a capacitive contribution to the current through the electrode; isolate from the real component of current through the electrode an isolated contribution attributable to an ion current and a resistive term, the contribution being free of any electron current contribution; and determine from the isolated contribution a value of ion current.