Coaxial Waveguide for Uniform VHF Plasma
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Plasma processing apparatuses face non-uniform plasma distribution and film quality issues due to higher order mode propagation of VHF-band electromagnetic waves, leading to non-uniform film thickness and refractive index distributions when frequencies above 100 MHz are used.
Innovation Solution
A plasma processing apparatus with a coaxial waveguide design that blocks higher order mode propagation by ensuring the cutoff frequency of the coaxial path is greater than the VHF-band frequency, using a central conductor and dielectric window configuration within a chamber, thereby generating a uniform surface wave plasma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If VHF-band electromagnetic waves with frequency greater than 100 MHz are supplied to the chamber, then plasma processing can be performed, but higher order mode propagation occurs causing non-uniform plasma distribution
Solution Approach 1:
The patent changes the physical parameters of the electromagnetic wave propagation path by defining specific dimensional relationships between the central conductor diameter (d), hole diameter (D), and wavelength (λ) to achieve cutoff frequency control. By setting d/λ ≥ 0.05 and D/λ ≤ 0.25, the cutoff frequency is adjusted to block higher order modes while allowing fundamental mode propagation, thus resolving the contradiction between plasma processing capability and plasma uniformity
Solution Approach 2:
The patent segments the electromagnetic wave propagation path into distinct regions: the central conductor region, the dielectric window region, and the chamber region. This segmentation allows independent optimization of each region's dimensions to control wave mode propagation, enabling the blocking of higher order modes while maintaining effective plasma generation
2Use of energy by moving object
If the outer diameter of the central conductor and hole size are increased, then electromagnetic wave transmission is improved, but cutoff frequency decreases allowing higher order mode propagation
Solution Approach 1:
The patent establishes optimal parameter ranges for the central conductor diameter (d) and hole diameter (D) relative to the wavelength (λ). By setting d/λ ≥ 0.05 to ensure sufficient transmission and D/λ ≤ 0.25 to maintain cutoff frequency above operating frequency, the design achieves both efficient electromagnetic wave transmission and reliable higher order mode blocking
Solution Approach 2:
The patent uses a dielectric window with permittivity greater than 1 in the propagation path, which excessively increases the cutoff frequency beyond what would be achieved with air alone. This partial excessive action ensures that even with larger conductor and hole dimensions for better transmission, the cutoff frequency remains sufficiently high to block higher order modes
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 blocks higher order mode propagation, resulting in a uniform plasma distribution and improved film quality by ensuring the cutoff frequency of the coaxial waveguide is greater than the applied VHF-band frequency, reducing plasma non-uniformity and enhancing film uniformity.
Implementation Method 1
an outer diameter of the central conductor and the size of the hole of the ceiling wall are defined such that a cutoff frequency of a coaxial path composed of the central conductor and the ceiling wall is greater than the frequency of the electromagnetic wave
Implementation Method 2
a central conductor disposed, via a dielectric window, in a hole formed in the center of the ceiling wall
Implementation Method 3
supplying an electromagnetic wave in a VHF band of 100 MHz or higher to a chamber to form a plasma
Data Source
AI summary
A plasma processing apparatus is provided, in which an electromagnetic wave in a VHF band of 100 MHz or higher is supplied to a chamber to form a plasma. The plasma processing apparatus includes a ceiling wall that defines a part of the chamber, and a central conductor for supplying the electromagnetic wave that is disposed in a hole formed in the center of the ceiling wall. A central position of the central conductor substantially coincides with a central position of a stage on which a workpiece is placed, and an outer diameter of the central conductor and a size of the hole of the ceiling wall are defined such that a cutoff frequency of a coaxial path composed of the central conductor and the ceiling wall is greater than a frequency of the electromagnetic wave.