Plasma Electrode Impedance Control for Uniform Field Distribution
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Solution Overview
Problem
In plasma processing apparatuses, high frequency power leads to nonuniform electric field strength distribution between parallel plate electrodes, causing uneven plasma density due to the skin effect, which is exacerbated by differences in thermal expansion and machining accuracy when using tapered dielectric materials.
Innovation Solution
Incorporating a metal resistor with a predetermined pattern between the dielectric material and the plasma, which adjusts the impedance to distribute high frequency energy more uniformly, reducing the electric field strength at the central portion and minimizing the need for tapered dielectric materials, thus avoiding stress concentration and contamination issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high frequency power is supplied to generate plasma, then plasma generation efficiency is improved, but electric field strength distribution becomes nonuniform due to skin effect
Solution Approach 1:
The patent applies local quality by embedding dielectric materials with different dielectric constants at different locations on the electrode surface. Specifically, a first dielectric material with a higher dielectric constant is placed at the central portion where electric field strength is higher, while a second dielectric material with a lower dielectric constant is placed at the peripheral portion. This spatial variation in dielectric properties compensates for the nonuniform electric field distribution caused by the skin effect, thereby improving both plasma generation efficiency and field uniformity simultaneously.
2Manufacturing precision
If tapered dielectric material is used to improve electric field uniformity, then plasma density uniformity is improved, but stress concentration and machining complexity increase
Solution Approach 1:
The patent segments the dielectric material into multiple discrete portions with different properties rather than using a single tapered structure. The electrode surface is divided into a central portion and a peripheral portion, each equipped with dielectric materials having different dielectric constants. This segmentation achieves the desired electric field uniformity while avoiding the stress concentration and machining complexity associated with tapered structures.
Solution Approach 2:
The patent employs composite materials by combining dielectric materials with different dielectric constants in specific spatial arrangements. The first dielectric material (higher dielectric constant) and second dielectric material (lower dielectric constant) are used together to create a composite structure that optimizes electric field distribution. This approach achieves plasma density uniformity without requiring complex tapered geometries.
3Manufacturing precision
If dielectric material is buried in electrode to reduce electric field strength at central portion, then electric field distribution is improved, but thermal expansion differences cause stress and contamination
Solution Approach 1:
The patent changes the dielectric constant parameter of the materials used at different electrode portions. By selecting dielectric materials with appropriate dielectric constants for the central and peripheral portions, the patent achieves improved electric field distribution while also considering thermal expansion compatibility. The parameter selection balances electric field control with structural reliability under thermal stress.
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 configuration achieves a more uniform plasma density across the electrode surface, reducing contamination risks and machining costs while maintaining effective plasma generation, even at high frequencies.
Implementation Method 1
a high frequency current flows along the plasma-side surface of the electrode from its end portion to its central portion due to the skin effect
Implementation Method 2
Incorporating a metal resistor with a predetermined pattern between the dielectric material and the plasma, which adjusts the impedance to distribute high frequency energy more uniformly
Implementation Method 3
the electric field energy consumed for the generation of plasma at the central portion of the electrode is higher than that at the end portion of the electrode, and thus ionization or dissociation of a gas is further accelerated
Implementation Method 4
applies high frequency power to at least one of an upper electrode and a lower electrode facing each other, to generate electric field energy, thereby exciting a gas to generate plasma
Data Source
AI summary
A plasma processing apparatus includes a processing chamber that plasma processes a target object therein, first and second electrodes that are provided in the processing chamber to face each other and have a processing space therebetween, and a high frequency power source that is connected to at least one of the first and second electrodes to supply high frequency power to the processing chamber. At least one of the first and second electrodes includes a base formed of a metal, a dielectric material provided at a central portion of a plasma side of the base, and a first resistor provided between the dielectric material and plasma, and formed of a metal with a predetermined pattern.