Harmonic RF Control for Ion Energy Distribution in Plasma Etching
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Solution Overview
Problem
Current plasma processing technologies face challenges in controlling ion energy distribution in plasma systems, particularly for substrates with shrinking geometries, due to limitations in directly measuring and manually adjusting plasma properties, which affects process performance and controllability.
Innovation Solution
The method involves using multiple harmonic frequency components for plasma excitation, controlling relative amplitude and phase shifts between frequency components to achieve desired ion energy distributions, monitored through electrical characteristics like impedance and RF signals within the plasma processing apparatus, allowing for dynamic control of ion energy without direct measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple harmonic frequency components are used for plasma excitation, then ion energy distribution control is improved, but device complexity increases
Solution Approach 1:
The plasma excitation is segmented into multiple harmonic frequency components (fundamental frequency and harmonic frequencies). Each frequency component is independently controlled through separate RF sources or frequency multiplication circuits, allowing precise control over ion energy distribution by adjusting the relative amplitudes and phases of each component.
Solution Approach 2:
The system changes the frequency parameters of plasma excitation by introducing harmonic frequencies (2f, 3f, etc.) in addition to the fundamental frequency. By varying the amplitude ratios and phase differences between these frequency components, the ion energy distribution can be dynamically adjusted to achieve desired process outcomes.
2Measurement precision
If direct ion energy measurement is implemented, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
Instead of directly measuring ion energy, the system uses electrical characteristics (impedance, voltage, current) as intermediary parameters that correlate with ion energy distribution. These electrical measurements are easier to obtain and do not require complex ion energy sensors, while still providing sufficient control feedback.
Solution Approach 2:
The patent replaces direct physical measurement of ion energy with electrical measurement methods. By monitoring electrical characteristics of the plasma load, the system infers ion energy distribution without requiring mechanical or complex sensing equipment that would directly interact with the plasma.
3Ease of operation
If manual adjustment of plasma variables is used, then ease of operation is maintained, but productivity and dynamic control capability deteriorate
Solution Approach 1:
The system implements feedback control by continuously monitoring electrical characteristics of the plasma and automatically adjusting the amplitude and phase of harmonic frequency components. This closed-loop control enables dynamic adaptation to process conditions, improving productivity while maintaining ease of operation through automated control.
Solution Approach 2:
The system transitions from static manual adjustment to dynamic automated control. The control circuitry continuously adjusts plasma parameters in real-time based on process requirements and feedback signals, enabling rapid response to changing conditions and improving overall process efficiency and productivity.
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 enables in-situ ion energy optimization and maintains optimal operating conditions during plasma processing, enhancing control over ion energy distribution and process characteristics, such as selective etching and layer modification, without the need for an ion energy sensor.
Implementation Method 1
one or more RF sources coupled to the process chamber and configured to provide RF power to the process chamber through at least a base frequency voltage at a base frequency and a second frequency voltage at a second frequency
Implementation Method 2
monitoring one or more electrical characteristics within the plasma apparatus, such as for example, impedance levels, electrical signals in the radio frequency (RF) generator
Data Source
AI summary
Plasma ion energy distribution for ions having different masses is controlled by controlling the relationship between a base RF frequency and a harmonic RF frequency. By the controlling the RF power frequencies, characteristics of the plasma process may be changed based on ion mass. The ions that dominate etching may be selectively based upon whether an ion is lighter or heavier than other ions. Similarly, atomic layer etch processes may be controlled such that the process may be switched between a layer modification step and a layer etch step though adjustment of the RF frequencies. Such switching is capable of being performed within the same gas phase of the plasma process. The control of the RF power includes controlling the phase difference and/or amplitude ratios between a base RF frequency and a harmonic frequency based upon the detection of one or more electrical characteristics within the plasma apparatus.