Multi-Frequency RF Phase Control for Uniform Plasma Etching
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Solution Overview
Problem
Existing plasma etching processes for semiconductor fabrication face challenges in achieving uniform ion energy distribution and directionality, leading to non-uniform etching results and bowing of high aspect ratio features.
Innovation Solution
The implementation of a method that generates a combined RF signal with a sloped square wave shape by combining RF signals at different frequencies, including a fundamental frequency and its harmonics, and adjusting their phases to optimize ion energy distribution and directionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional single-frequency RF signals are used for plasma generation, then the process is simple and easy to control, but spatial non-uniformities in ion energy distribution and directionality occur, leading to non-uniform etching results and bowing of high aspect ratio features
Solution Approach 1:
The RF signal generation system is segmented into multiple independent RF generators, each operating at a different frequency (e.g., 13.56 MHz, 27.12 MHz, 40.68 MHz). Each generator produces RF signals that are combined through a signal combiner to create a composite waveform. This segmentation allows independent optimization of each frequency component to achieve uniform ion energy distribution and directionality across the plasma processing volume, resolving the spatial non-uniformities caused by single-frequency signals while maintaining systematic control.
Solution Approach 2:
Multiple RF signals at different frequencies are merged through a signal combiner to create a composite RF signal with enhanced properties. The combined signal produces a plasma with improved ion energy distribution uniformity and directionality across the processing volume. This merging approach achieves the manufacturing precision needed for uniform etching results while distributing the complexity across multiple manageable frequency components rather than requiring a single complex signal source.
2Manufacturing precision
If multiple RF signals at different frequencies are combined to improve ion energy distribution, then manufacturing precision and uniformity improve, but device complexity and control difficulty increase
Solution Approach 1:
The system changes the frequency parameter by using multiple discrete frequency components (e.g., fundamental frequency and its harmonics) rather than a single frequency. Each frequency component is carefully selected and controlled to contribute specifically to the desired ion energy distribution profile. This parameter change approach enables precise control over plasma characteristics and ion behavior, achieving uniform manufacturing results while the modular frequency-based structure keeps the complexity manageable through systematic parameter selection.
3Manufacturing precision
If RF signals are transmitted through plasma processing volume to generate plasma, then plasma generation is achieved, but spatial non-uniformities in plasma characteristics occur, affecting etching uniformity
Solution Approach 1:
The plasma generation process is segmented into multiple frequency-driven components, where each RF generator at a different frequency contributes to specific aspects of plasma characteristics. This segmentation allows independent optimization of plasma properties (such as ion density, ion energy, and reactive constituent distribution) across different spatial regions of the plasma processing volume, thereby achieving uniform plasma characteristics and consistent etching results across the entire wafer surface.
Solution Approach 2:
The system employs parameter changes by varying the frequency composition of the RF signals transmitted through the plasma processing volume. By adjusting the relative powers and phases of multiple frequency components, the plasma characteristics can be tuned to achieve uniform ion energy distribution and directional ion flux across the wafer, directly improving etching uniformity while stabilizing plasma composition throughout the processing volume.
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 results in a narrow distribution of high energy ions with improved directionality, reducing bowing effects and enhancing the verticality of high aspect ratio features during etching.
Implementation Method 1
combining the first, second and third RF signals to generate a combined RF signal, wherein a wave shape of the combined RF signal is configured to approximate a sloped square wave shape
Implementation Method 2
The plasma can be generated using radiofrequency signals to energize the specific reactant gases
Implementation Method 3
the wave shape of the combined RF signal is configured to compensate for a capacitance of the chuck, so that the combined RF signal that reaches a wafer supported by the chuck has a wave shape that approximates a non-sloped square wave shape
Implementation Method 4
a semiconductor wafer that includes semiconductor devices under manufacture is exposed to a plasma generated within a plasma processing volume
Implementation Method 5
The plasma can be generated using radiofrequency signals to energize the specific reactant gases
Data Source
AI summary
A method for applying RF power in a plasma process chamber is provided, including: generating a first RF signal; generating a second RF signal; generating a third RF signal; wherein the first, second, and third RF signals are generated at different frequencies; combining the first, second and third RF signals to generate a combined RF signal, wherein a wave shape of the combined RF signal is configured to approximate a sloped square wave shape; applying the combined RF signal to a chuck in the plasma process chamber.