Coaxial Cable Termination Circuit for Plasma Reactor Etch Uniformity
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Solution Overview
Problem
Plasma pre-clean reactors for silicon wafers often exhibit non-uniform etch rate distribution due to interference from HF bias frequency and its sidebands with the source power frequency, leading to variations in reactor performance and loss of control over RF power levels.
Innovation Solution
A plasma reactor design that includes a coaxial cable termination circuit reflecting the bias frequency and its sidebands back into the inductive source power applicator, while suppressing their transmission to the power generator, and selectively enhancing the presence of the bias frequency's second harmonic and its intermodulation products in the plasma, using resonant tank circuits to achieve uniform etch rate distribution across the wafer surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HF bias frequency and its sidebands are present in the plasma, then plasma mixing occurs producing intermodulation products, but etch rate uniformity deteriorates and RF power control is lost
Solution Approach 1:
The patent extracts and removes the harmful HF bias frequency and intermodulation products from the plasma environment by providing a dedicated return path through the coaxial cable to ground, separating these unwanted frequencies from the source power frequency and preventing them from affecting etch uniformity and power control
Solution Approach 2:
The patent introduces an intermediary grounding path through the coaxial cable shield and termination circuitry that mediates between the plasma and the RF generator, allowing harmful frequencies to be safely discharged to ground without interfering with the primary source power frequency or the SWR bridge measurement circuitry
2Measurement precision
If bias frequency components are coupled back to the RF generator, then SWR bridge sensing becomes erroneous, but this requires costly generator modifications
Solution Approach 1:
The patent introduces an intermediary grounding path through the coaxial cable shield that intercepts HF bias frequency components before they can reach the SWR bridge sensing circuitry, protecting the measurement accuracy without requiring any modifications to the RF generator itself
Solution Approach 2:
The patent extracts harmful HF frequency components from the signal path by providing a dedicated ground return path through the coaxial cable shield, removing these interfering frequencies before they can corrupt the SWR bridge measurements while avoiding costly generator modifications
3Manufacturing precision
If different cable lengths are used to improve etch uniformity, then reactor performance varies, but this increases reactor-to-reactor variations
Solution Approach 1:
The patent changes the electrical parameters of the coaxial cable system by providing a controlled ground return path that is independent of cable length, transforming the system from one where performance depends on cable length variations to one where performance is stabilized by the dedicated grounding arrangement
Solution Approach 2:
The patent extracts the harmful frequency components that cause reactor-to-reactor variations by providing a dedicated ground return path, removing the source of performance inconsistencies and enabling all reactors to achieve consistent etch uniformity regardless of cable length variations
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 solution ensures high etch rate distribution uniformity across the wafer surface, reduces reactor-to-reactor variations, and stabilizes RF power control, enhancing overall reactor performance and reducing standard deviation in etch rates from the wafer center to edge.
Implementation Method 1
The filter includes a set of reflection circuits coupled between the source power applicator and a ground potential and being tuned to, respectively, the bias frequency and intermodmodulation products of the bias frequency and the source frequency
Implementation Method 2
the plasma inside the reactor chamber acts as a mixer of the source and bias frequencies to produce intermodulation products including the fundamental and harmonics of the bias frequency and their sum and difference frequencies
Implementation Method 3
a coaxial cable coupled between the RF source power generator and the source power applicator
Data Source
AI summary
A plasma reactor for processing a workpiece in a reactor chamber having a wafer support pedestal within the chamber and process gas injection apparatus, an RF bias power generator coupled to the wafer support pedestal and having a bias frequency, a source power applicator, an RF source power generator having a source frequency and a coaxial cable coupled between the RF source power generator and the source power applicator includes a filter connected between the coaxial cable and the source power applicator that enhances uniformity of etch rate across the wafer and from reactor to reactor. The filter includes a set of reflection circuits coupled between the source power applicator and a ground potential and being tuned to, respectively, the bias frequency and intermodulation products of the bias frequency and the source frequency. The filter may further include a set of filter circuits coupled to the source power applicator and being tuned to, respectively, a second harmonic of the bias frequency and intermodulation products of the second harmonic of the bias frequency and the source frequency.