Pulsed Multi-Frequency RF Bias for High-Energy Narrow-Angle Ions
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Solution Overview
Problem
Existing plasma processing systems face challenges in achieving peak ion energy enhancement with a low angular spread without increasing the radio frequency (RF) bias voltage or power.
Innovation Solution
The system employs a pulsing technique involving high and low frequency RF generators to synchronize RF voltage pulses, enhancing peak ion energy and narrowing the angular spread. This is achieved by applying a high frequency RF signal after a low frequency RF signal, utilizing the voltage boost from the low frequency level to increase the peak ion energy and reduce the angular spread.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If continuous wave RF signal is used, then ion energy is maintained at a steady level, but peak ion energy enhancement is limited and angular spread remains wide
Solution Approach 1:
The patent applies periodic pulsing of RF signals at different frequencies (e.g., 13.56 MHz and 27 MHz or 60 MHz) to achieve peak ion energy enhancement. The pulsed nature creates synchronized voltage peaks that boost ion energy while the periodic timing controls angular spread, resolving the contradiction between energy enhancement and angular precision.
Solution Approach 2:
The patent changes RF signal parameters by using multiple frequencies and pulsed duty cycles. By switching between different frequency levels (e.g., low frequency for sheath formation, high frequency for ion acceleration) and adjusting pulse widths, the system achieves both peak ion energy enhancement and narrow angular spread simultaneously.
2Use of energy by moving object
If RF bias voltage is increased to enhance peak ion energy, then ion energy increases, but angular spread also increases
Solution Approach 1:
The patent segments the RF signal into multiple frequency components applied in sequence or combination. Instead of using a single high voltage that increases angular spread, the system uses segmented frequency pulses (e.g., low frequency followed by high frequency) that achieve energy enhancement through synchronized voltage peaks while maintaining narrow angular spread through precise timing control.
Solution Approach 2:
The patent uses periodic pulsing at specific duty cycles to create synchronized voltage peaks from multiple frequency sources. This periodic action allows peak ion energy enhancement through constructive voltage addition while the controlled pulse timing prevents angular spread increase, overcoming the limitation of continuous wave approaches.
3Speed
If high frequency RF signal is applied continuously, then ion acceleration is maintained, but voltage peaks are insufficient for maximum ion energy enhancement
Solution Approach 1:
The patent applies preliminary low frequency RF pulsing before high frequency pulsing to prepare the plasma sheath and ion population. This preliminary action creates optimal conditions for subsequent high frequency acceleration, enabling maximum peak ion energy enhancement through synchronized voltage peaks rather than continuous high frequency alone.
Solution Approach 2:
The patent dynamically changes RF frequency parameters by switching between low and high frequency levels in a pulsed sequence. This parameter modulation allows the system to achieve both sustained ion acceleration and maximum peak ion energy by timing the high frequency pulses to coincide with optimal sheath conditions created by previous low frequency pulses.
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
The approach results in a significant increase in peak ion energy by more than 35% compared to continuous wave technology, while maintaining a narrow angular spread, thereby enhancing etch rates and critical dimension precision.
Implementation Method 1
A sheath voltage of a plasma sheath charges and discharges based an equation (1)... C is a capacitance of the capacitor... During the onset of the high frequency level, plasma ions receive a voltage boost from a previous, such as a preceding, low frequency level
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... The low frequency level increases the resistance R and the increase in the resistance R increases the time constant RC
Implementation Method 3
The increase in the plasma sheath voltage level increases a denominator in an equation (2)... where Vs is a voltage of the plasma sheath... The increase in the denominator of equation (2) provides the narrower ion angle σθ
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.