Plasma Processing Electrode Phase Offset for Density Control
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Solution Overview
Problem
In capacitively-coupled plasma processing systems, increasing plasma density to enhance etch rate often leads to plasma density saturation and adverse photo resist mask damage, as electrons are lost to grounded electrodes, limiting the etch rate and selectivity.
Innovation Solution
The method involves providing a first RF signal to the lower electrode and a second RF signal with a phase offset less than 10% to the upper electrode, negatively biasing the upper electrode to trap electrons and increase plasma density without increasing RF power, and using a mirroring circuit to maintain in-phase RF signals between electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma density is increased to enhance etch rate, then etch rate is improved, but photo resist selectivity deteriorates due to electron loss to grounded electrodes
Solution Approach 1:
The patent changes the electrical parameter of the upper electrode from grounded to negatively biased. This parameter change creates a potential well that traps electrons, preventing their loss to the electrode surface. The trapped electrons maintain high plasma density for high etch rates while protecting the photo resist mask from damage, thus resolving the contradiction between etch rate and photo resist selectivity
2Quantity of substance
If RF power is increased to increase plasma density, then plasma density is improved, but electron loss to electrodes increases limiting further density increase
Solution Approach 1:
The patent converts the harmful effect of the upper electrode (which normally absorbs electrons and limits plasma density) into a beneficial element. By applying a negative bias, the electrode becomes a electron-trapping mechanism that creates a potential well. This transforms the electrode from a loss pathway into a confinement structure that maintains high plasma density without requiring increased RF power
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 approach increases plasma density for higher etch rates without degrading photo resist selectivity, as electrons are repelled from the upper electrode, maintaining high etch rates and selectivity.
Implementation Method 1
providing a first RF signal to a lower electrode. The first RF signal couples with a plasma in a plasma processing chamber, thereby inducing an RF signal on an upper electrode
Implementation Method 2
negatively biasing the upper electrode to trap electrons and increase plasma density. electrons are repelled from the upper electrode
Data Source
AI summary
A method for processing a substrate in a capacitively-coupled plasma processing system having a plasma processing chamber and at least an upper electrode and a lower electrode. The substrate is disposed on the lower electrode during plasma processing. The method includes providing at least a first RF signal, which has a first RF frequency, to the lower electrode. The first RF signal couples with a plasma in the plasma processing chamber, thereby inducing an induced RF signal on the upper electrode. The method also includes providing a second RF signal to the upper electrode. The second RF signal also has the first RF frequency. A phase of the second RF signal is offset from a phase of the first RF signal by a value that is less than 10%. The method further includes processing the substrate while the second RF signal is provided to the upper electrode.