Matched Source Impedance RF Generator for Plasma Uniformity
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Solution Overview
Problem
Conventional plasma processing systems face challenges in maintaining uniform deposition or etch rates over substrates due to difficulties in controlling the amplitude and phase relationships between multiple antenna inputs, and in providing well-matched impedances when using a single RF generator and distribution network.
Innovation Solution
A matched source impedance driving system utilizing multiple phase-locked RF generators, each controlling a linear combination of voltage and current at a reference point to drive multiple inputs of a plasma chamber, allowing for coherent amplitude and phase relationships and well-matched impedances, with the ability to absorb and deliver power in a controlled manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single RF generator with a distribution network is used to drive multiple antenna inputs, then device complexity is reduced, but control precision of amplitude and phase relationships deteriorates
Solution Approach 1:
The system divides the plasma chamber into multiple independently controllable antenna inputs, each driven by a separate RF generator. This segmentation allows precise independent control of amplitude and phase for each antenna input, resolving the contradiction by prioritizing control precision over device simplicity.
Solution Approach 2:
The system implements feedback control by measuring the actual amplitude and phase relationships at each antenna input and adjusting the RF generator outputs accordingly. This closed-loop control ensures precise amplitude and phase relationships are maintained despite variations in plasma load or generator characteristics.
2Manufacturing precision
If multiple separate RF generators are used to drive antenna inputs, then control precision of electromagnetic field distribution is improved, but device complexity and generator interaction problems increase
Solution Approach 1:
The system introduces an impedance matching network as an intermediary between the RF generators and antenna inputs. This matching network coordinates the multiple generators by providing proper impedance transformation and isolation, reducing direct interactions between generators while maintaining precise electromagnetic field control.
Solution Approach 2:
The system dynamically adjusts operating parameters (amplitude, phase, frequency) of each RF generator based on plasma conditions and desired field distribution. By changing these parameters in real-time, the system achieves precise electromagnetic field control while managing the complexity of multiple generators through adaptive coordination.
3Device complexity
If conventional impedance matching is used with a single RF generator, then device simplicity is maintained, but uniformity of plasma excitation over the substrate deteriorates
Solution Approach 1:
The plasma excitation is segmented into multiple independent antenna inputs, each capable of independent control. This allows different regions of the substrate to receive optimized plasma excitation, improving overall uniformity while maintaining relative system simplicity through modular antenna design.
Solution Approach 2:
The system applies local quality control by allowing each antenna input to have independently optimized amplitude and phase settings tailored to specific regions of the plasma chamber. This enables non-uniform plasma excitation patterns that compensate for spatial variations in the chamber, achieving uniform overall plasma distribution across the substrate.
Data Source
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Figure 3A~3B
AI summary
A radio frequency (RF) generator having an effective source impedance Z g at a reference point (e.g. at the generator output) includes a reference input and controls the magnitude and phase with respect to a signal received at the reference input of K(v + Z g i) at the reference point where v and i are the voltage at the reference point and current out of the generator at the reference point, respectively, and K is a scalar. The generator maintains control of K(v + Z g i) when delivering and when absorbing power.