Cylindrical Microwave Cavity Iris Tuning for Rotating Plasma Modes
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Solution Overview
Problem
Existing technologies for generating rotating microwaves in plasma reactor chambers are limited to rotating the TE111 mode, and there is a need to provide rotation for any mode, not just the TE111 mode.
Innovation Solution
A method is provided for generating rotating microwaves of mode TEmnl or TMmnl in a cylindrical microwave cavity, where n, m, and l are user-selected values. This is achieved by introducing microwave signals with a temporal phase difference into the cavity through coupling apertures, and adjusting the offset angle and temporal phase difference as a function of the user-selected mode indices to produce rotating microwaves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If microwaves are radiated from two ports with fixed spatial separation for TE111 mode rotation, then the TE111 mode rotates circularly, but the solution is limited only to the TE111 mode and cannot be applied to other modes
Solution Approach 1:
The patent makes the port spatial separation angle a variable parameter that can be adjusted according to different mode requirements. By defining the angle as θ = (2p+1)π/(2m) where m is the mode index and p is an integer, the same dual-port configuration can excite rotating fields for any TE or TM mode, not just TE111, thus achieving universal applicability across multiple modes.
Solution Approach 2:
The patent changes the parameter of port spatial separation from a fixed value to a variable determined by the mode indices. The temporal phase difference is also adjusted as a function of mode parameters, allowing the system to adapt to different modes by changing these parameters rather than requiring different physical configurations.
2Adaptability or versatility
If the offset angle and temporal phase difference are adjusted as a function of mode indices, then rotating microwaves can be generated for any user-selected mode, but the configuration and control become more complex
Solution Approach 1:
The patent employs monitoring antennas and feedback control systems that automatically adjust the temporal phase difference and amplitude ratios based on the desired mode. This feedback mechanism simplifies operation by eliminating the need for manual calculation and adjustment of complex parameters, as the system self-regulates to achieve the desired rotating field configuration.
Solution Approach 2:
The system uses monitoring antennas to detect the actual field distribution and automatically adjusts the excitation parameters to maintain the desired rotating mode. This self-service approach allows the system to compensate for variations and maintain optimal performance without requiring continuous manual intervention.
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
The method allows for the generation of rotating microwaves for any user-selected mode, enhancing plasma uniformity and energy transfer efficiency by adjusting the chamber impedance using irises in the power-supplying waveguides.
Implementation Method 1
a first waveguide having a first iris for shifting a first impedance of the chamber; a second waveguide having a second iris for shifting a second impedance of the chamber
Implementation Method 2
a cylindrical cavity resonant at a microwave frequency
Data Source
AI summary
A plasma reactor has a cylindrical microwave cavity overlying a workpiece processing chamber, a microwave source having a pair of microwave source outputs, and a pair of respective waveguides. The cavity has first and second input ports in a sidewall and space apart by an azimuthal angle. Each of the waveguides has a microwave input end coupled to a microwave source output and a microwave output end coupled to a respective one of the first and second input ports, a coupling aperture plate at the output end with a rectangular coupling aperture in the coupling aperture plate, and an iris plate between the coupling aperture plate and the microwave input end with a rectangular iris opening in the iris plate.