Plasma Processing System Synchronized Signal Modulation
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Solution Overview
Problem
Plasma processing systems face challenges in achieving uniform plasma density across substrates, particularly at VHF frequencies, leading to non-uniform etch or deposition rates, which can result in yield issues in semiconductor manufacturing.
Innovation Solution
A system and method that utilize a combination of high and low frequency RF signals, where the high frequency signal is amplitude modulated and synchronized with the phase of the low frequency signal to control the plasma density profile, optimizing the coupling duration to achieve a target spatial distribution of plasma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If VHF frequency RF power is used to generate plasma, then plasma generation efficiency and plasma density are improved, but spatial uniformity of plasma density deteriorates
Solution Approach 1:
The patent applies periodic modulation to the VHF RF power signal, switching it between ON and OFF states in synchronization with the LF RF power cycle. This periodic action allows the plasma density to be controlled in discrete phases, enabling the system to achieve both high average plasma density and improved spatial uniformity by adjusting the duty cycle and phase of the modulation.
Solution Approach 2:
The patent introduces dynamic control of the VHF RF power by modulating its amplitude and phase relative to the LF RF power. This dynamic adjustment allows the system to optimize plasma density distribution in real-time, transitioning from static continuous power delivery to adaptive time-varying power control that responds to plasma conditions.
2Force
If low frequency RF power is added to high frequency RF power, then ion energy is improved, but plasma density profile becomes unpredictable and varies by application
Solution Approach 1:
The patent employs periodic modulation where the VHF RF power is switched ON and OFF in sync with the LF RF power cycle. This creates a predictable, repeating pattern that ensures consistent plasma density profiles across different applications. The synchronized periodic action eliminates the unpredictability observed when LF and VHF powers are simply added together.
Solution Approach 2:
The patent implements a control system that monitors plasma conditions and adjusts the VHF RF power modulation parameters (duty cycle, phase) to maintain consistent plasma density profiles. This feedback mechanism ensures that the combination of LF and VHF powers produces predictable and repeatable results across different processing applications.
3Productivity
If VHF RF power is used, then etch rate is improved, but center peak plasma density causes non-uniform processing
Solution Approach 1:
By modulating the VHF RF power with a duty cycle less than 100%, the patent creates periodic bursts of high plasma density followed by periods of lower density. This periodic action allows the plasma to relax and redistribute, reducing the persistent center peak effect and improving uniformity across the substrate while maintaining high average etch rates.
Solution Approach 2:
The patent uses partial modulation where the VHF RF power is applied only during specific phases of the LF cycle rather than continuously. This partial action approach applies VHF power intensively when needed for high etch rate while allowing the plasma to equilibrate during OFF phases, achieving a balance between productivity and uniformity.
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 allows for the modification of plasma properties, enhancing spatial uniformity and reproducibility by adjusting the plasma density distribution, thereby improving etch or deposition rates and yield in semiconductor device fabrication.
Implementation Method 1
an amplitude modulation circuit for modulating the first signal between a high amplitude state and a low amplitude state in response to an amplitude modulation signal
Implementation Method 2
plasma generated at an RF (radio frequency) frequency in the VHF (very high frequency) range (30-300 MHz)
Implementation Method 3
a first signal generator for coupling a first signal at a first frequency to plasma in the plasma processing system
Data Source
AI summary
A system and method for using plasma to treat a substrate are described. The system includes a substrate holder disposed within a plasma processing system, and arranged to support a substrate, a first signal generator for coupling a first signal at a first frequency to plasma in the plasma processing system, and a second signal generator for coupling a second signal at a second frequency to plasma in the plasma processing system, wherein the second frequency being less than the first frequency. The system further includes an amplitude modulation circuit for modulating the first signal between a high amplitude state and a low amplitude state in response to an amplitude modulation signal, and a timing circuit configured to define the amplitude modulation signal that synchronizes the amplitude modulation of the first signal with a target phase for each cycle of the second signal.