Waveguide Iris Tuning for Rotating Modes in Cylindrical Microwave Cavities
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Solution Overview
Problem
Existing methods for generating rotating microwaves in plasma reactor chambers are limited to specific modes, primarily the TE111 mode, and do not efficiently rotate other modes or maximize energy transfer efficiency for all modes.
Innovation Solution
A method is introduced to generate rotating microwaves of mode TEmnl or TMmnl in a cylindrical microwave cavity by adjusting the offset angle and temporal phase difference between microwave input ports, allowing for user-selected mode indices, and utilizing specific microwave signal forms and phase relationships to achieve clockwise or anticlockwise rotation with optimized energy transfer.
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 other modes (TEmnl or TMmnl) cannot be rotated efficiently
Solution Approach 1:
The patent applies parameter changes by making the offset angle Δθ and temporal phase difference ΔØ adjustable parameters that are optimized as functions of the mode indices (m, n, l). This allows the same dual-port configuration to rotate different TEmnl and TMmnl modes by changing these parameters, providing versatility without increasing device complexity
Solution Approach 2:
The dual-port configuration is designed to be universal by enabling it to rotate any TEmnl or TMmnl mode through optimized parameter selection. The same physical structure serves multiple mode rotation functions, achieving multi-functionality without requiring separate port configurations for each mode
2Reliability
If amplitude modulation is used for slow rotation to spread plasma, then plasma uniformity increases at high pressures, but energy transfer efficiency is reduced compared to fast rotation
Solution Approach 1:
The patent applies dynamics by enabling the system to switch between fast rotation mode (for high energy transfer efficiency) and slow rotation mode (for high plasma uniformity). The rotation characteristics become dynamic and adaptable, allowing optimization of the trade-off between energy efficiency and plasma uniformity based on operating conditions such as pressure levels
3Adaptability or versatility
If fixed port spacing is used for TE111 mode, then simple configuration is maintained, but rotation cannot be achieved for user-selected mode indices
Solution Approach 1:
The patent makes the offset angle Δθ and temporal phase difference ΔØ adjustable parameters that can be optimized for different mode indices (m, n, l). This allows users to select different modes and have the parameters adjusted accordingly, providing flexibility while maintaining ease of operation through systematic parameter optimization
Solution Approach 2:
The patent applies preliminary action by pre-optimizing the relationships between the parameters (Δθ, ΔØ) and the mode indices (m, n, l). This preliminary optimization allows users to simply select their desired mode indices, and the pre-established functional relationships automatically provide the correct parameter settings, reducing operational complexity
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.