Pulsed Dual-Frequency RF Bias for High-Energy Narrow-Angle Ions
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Solution Overview
Problem
Current plasma processing systems face challenges in achieving peak ion energy enhancement with a low angular spread without increasing radio frequency (RF) bias voltage or power, which is essential for high aspect ratio etching and reducing substrate damage.
Innovation Solution
The implementation of a pulsing technique using high and low frequency RF signals, where a high frequency RF generator and a low frequency RF generator are synchronized to provide a voltage boost to plasma ions, resulting in a narrower ion angle and increased peak ion energy, without increasing the RF bias voltage or power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If RF bias voltage or power is increased to enhance peak ion energy, then ion energy is improved, but angular spread increases and substrate damage occurs
Solution Approach 1:
The patent applies periodic pulsing of the RF signal with duty cycles between 1% and 99%, creating alternating high and low frequency phases. This periodic action allows ions to be accelerated during the high frequency phase while the plasma sheath recovers during the low frequency phase, achieving high peak ion energy with narrow angular spread without continuous high power exposure that would increase substrate damage.
Solution Approach 2:
The system dynamically switches between high frequency (e.g., 60 MHz) and low frequency (e.g., 13.56 MHz) RF signals during the pulsing cycle. This dynamic frequency modulation allows the plasma sheath to charge during the low frequency phase and discharge during the high frequency phase, creating controlled ion acceleration that enhances peak energy while maintaining directional control and reducing angular spread.
2Duration of action of moving object
If continuous wave RF signal is used, then plasma generation is maintained, but peak ion energy is limited
Solution Approach 1:
Instead of continuous wave RF signaling, the patent implements periodic pulsing with configurable duty cycles. The RF signal is pulsed between high and low frequency states, creating discrete acceleration events that significantly boost peak ion energy compared to continuous signaling, while maintaining plasma generation through the repetitive cycling.
Solution Approach 2:
The system changes key parameters of the RF signal including frequency (switching between high and low frequencies), amplitude (through duty cycle modulation), and temporal structure (pulsing pattern). These parameter changes enable the plasma sheath to accumulate charge during low frequency phases and release it during high frequency phases, achieving peak ion energies exceeding 35% enhancement over continuous wave operation.
3Use of energy by moving object
If high frequency RF signal is applied continuously, then ion acceleration is enhanced, but angular spread increases
Solution Approach 1:
The patent alternates high frequency RF signal application with low frequency phases in a pulsed manner. During high frequency phases, ions are accelerated with enhanced energy, while during low frequency phases, the plasma sheath recovers and recharges. This periodic alternation prevents continuous high frequency exposure that would broaden angular spread, maintaining narrow ion angles while achieving high peak acceleration.
Solution Approach 2:
The low frequency phase serves as a preliminary action that charges the plasma sheath before the high frequency acceleration phase. This pre-charging ensures that when high frequency signaling begins, the electric field is already optimized for directional ion acceleration, maintaining narrow angular spread while enabling enhanced peak energy during the subsequent high frequency phase.
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 enhances peak ion energy by over 35% and reduces angular spread, leading to improved etch rates and critical dimension precision in plasma processing, while minimizing substrate damage.
Implementation Method 1
A sheath voltage of a plasma sheath charges and discharges based an equation (1)... C is a capacitance of the capacitor
Implementation Method 2
R is a resistance at an output of the plasma sheath that acts as a capacitor, RC is the time constant of the capacitor
Implementation Method 3
a radio frequency (RF) signal is provided to an electrode within a plasma chamber. The RF signal is used to generate plasma within the plasma chamber
Data Source
AI summary
Systems and methods for increasing peak ion energy with a low angular spread of ions are described. In one of the systems, multiple radio frequency (RF) generators that are coupled to an upper electrode associated with a plasma chamber are operated in two different states, such as two different frequency levels, for pulsing of the RF generators. The pulsing of the RF generators facilitates a transfer of ion energy during one of the states to another one of the states for increasing ion energy during the other state to further increase a rate of processing a substrate.