Non-Uniform Coaxial Waveguide for Plasma Processing
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Solution Overview
Problem
Conventional plasma processing apparatuses with uniform coaxial waveguide thickness suffer from high microwave reflection, limiting the transmission of large power due to uniform characteristic impedance along the longitudinal direction, which leads to damage and inefficiency in plasma generation.
Innovation Solution
A plasma processing apparatus with a coaxial waveguide structure where the thickness ratio of the inner and outer conductors is non-uniform along the longitudinal direction, allowing for different characteristic impedances at the input and output sides, thereby reducing microwave reflection and enabling efficient power transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a coaxial waveguide with uniform thickness is used, then the structure is simple and easy to manufacture, but the characteristic impedance is uniform along the longitudinal direction causing large microwave reflection and limiting power transmission
Solution Approach 1:
The patent applies local quality by making the thickness ratio between inner and outer conductors non-uniform along the longitudinal direction of the coaxial waveguide. Specifically, the thickness ratio at the input side (adjacent to microwave source) is made different from the thickness ratio at the output side (adjacent to plasma), creating different characteristic impedances at different locations. This resolves the contradiction by maintaining structural simplicity while achieving the desired impedance variation to reduce reflection.
2Stability of the object's composition
If large power is transmitted to generate uniform plasma, then plasma uniformity is improved, but the inner conductor is heated up causing deformation, oxidation, or damage
Solution Approach 1:
The patent applies parameter changes by varying the thickness ratio parameter of the coaxial waveguide along its length. By making the thickness ratio non-uniform, the characteristic impedance is optimized to reduce microwave reflection and improve power transmission efficiency. This reduces unnecessary heating of the inner conductor while maintaining the ability to transmit sufficient power for uniform plasma generation, thereby protecting the waveguide components from thermal damage.
3Loss of energy
If characteristic impedance is optimized to suppress microwave reflection, then power transmission efficiency is improved, but the waveguide structure becomes complex with non-uniform thickness ratio
Solution Approach 1:
The patent implements local quality by creating a coaxial waveguide where the thickness ratio between inner and outer conductors varies locally along the longitudinal direction. The input side has a different thickness ratio than the output side, allowing each section to have optimized characteristic impedance for its specific function. This achieves effective impedance matching and reduced reflection while maintaining relative structural simplicity through a systematic gradient design rather than complex multi-component assembly.
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 design effectively suppresses microwave reflection and allows for the stable transmission of large power, preventing damage to the waveguide components and ensuring uniform plasma generation.
Implementation Method 1
a plasma processing apparatus for plasma-processing an object to be processed by exciting a gas by using an electromagnetic wave
Implementation Method 2
a first coaxial waveguide, which has a structure in which a thickness ratio between an inner conductor and an outer conductor is not uniform along a longitudinal direction and transmits the electromagnetic wave output from the electromagnetic wave source
Implementation Method 3
a dielectric plate, which faces an inner side of the processing container and is adjacent to the first coaxial waveguide to emit the electromagnetic wave transmitted from the first coaxial waveguide into the processing container
Implementation Method 4
in order to generate plasma by exciting a gas, a desired microwave as energy for ionizing or dissociating the gas is transmitted to a transmission path
Data Source
AI summary
Provided is a plasma processing apparatus having a coaxial waveguide structure in which characteristic impedance of an input side and characteristic impedance of an output side are different. A microwave plasma processing apparatus, which plasma-processes a substrate by exciting a gas by using a microwave, includes: a processing container; a microwave source, which outputs a microwave, a first coaxial waveguide, which transmits the microwave output from the microwave source; and a dielectric plate, which is adjacent to the first coaxial waveguide while facing an inner side of the processing container, and emits the microwave transmitted from the first coaxial waveguide into the processing container. A thickness ratio between an inner conductor and an outer conductor of the first coaxial waveguide is not uniform along a longitudinal direction.