Substrate Bias Waveform Feedback for Stable Ion Energy in Plasma Etching
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Solution Overview
Problem
Existing plasma processing systems face challenges in maintaining a well-controlled ion energy distribution function due to unpredictable sheath capacitance, requiring complex and inaccurate calibration, which complicates the use of shaped-pulse bias schemes in commercial etch chambers.
Innovation Solution
A feedback mechanism is employed to maintain a predetermined voltage waveform at the substrate by capturing a signal representative of the substrate voltage and iteratively adjusting the shaped pulse bias waveform, rendering the sheath and stray capacitances negligible relative to the chuck capacitance, allowing for a constant ion energy without precise estimation of these capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If shaped-pulse bias scheme is used to control ion energy distribution, then manufacturing precision is improved, but device complexity increases due to requirement of precise sheath capacitance determination
Solution Approach 1:
The patent implements a feedback mechanism where the actual substrate voltage is measured and used to iteratively adjust the shaped pulse bias waveform. The controller compares the measured substrate voltage with the desired voltage waveform and modifies the bias waveform parameters (amplitude, pulse width, frequency) to minimize the difference, achieving precise ion energy distribution control without requiring prior knowledge of sheath capacitance.
Solution Approach 2:
The system uses the substrate itself as the sensing element by measuring the voltage directly at the substrate during plasma processing. The substrate voltage measurement automatically provides the necessary feedback information about the sheath conditions, eliminating the need for separate capacitance measurement devices and calibration procedures.
2Manufacturing precision
If sheath capacitance is precisely determined through calibration, then manufacturing precision is improved, but loss of time increases due to complex calibration procedures
Solution Approach 1:
The substrate serves dual purposes: as the processing target and as the voltage sensing element. By measuring the voltage directly at the substrate during normal operation, the system automatically obtains real-time information about sheath conditions without requiring separate calibration measurements or procedures.
Solution Approach 2:
The real-time substrate voltage measurement provides continuous feedback that enables dynamic adjustment of the bias waveform. This eliminates the need for preliminary calibration steps, as the system adapts to changing plasma conditions automatically during processing.
3Manufacturing precision
If sheath capacitance is accurately known, then manufacturing precision is improved, but device complexity increases due to requirement of complex modeling
Solution Approach 1:
Instead of relying on complex theoretical models to calculate sheath capacitance, the patent directly measures the substrate voltage during plasma processing. This empirical approach bypasses the need for complex modeling while providing more accurate real-time information about actual plasma conditions.
Solution Approach 2:
The patent replaces the complex theoretical calculation system (capacitance modeling) with a direct electrical measurement system. By measuring voltage directly at the substrate, the system substitutes complex computational methods with simple electrical sensing.
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 a well-controlled, single-peak ion energy distribution function, simplifying the process and improving precision in plasma etching without the need for complex modeling or precise capacitance determination.
Implementation Method 1
Non-linear, diode-like nature of the plasma sheath results in rectification of the applied RF field, such that a direct-current (DC) voltage drop, or 'self-bias,' appears between the cathode and the plasma
Implementation Method 2
a metal baseplate embedded into the 'electrostatic chuck' (ESC)
Data Source
AI summary
Systems and methods for controlling a voltage waveform at a substrate during plasma processing include applying a shaped pulse bias waveform to a substrate support, the substrate support including an electrostatic chuck, a chucking pole, a substrate support surface and an electrode separated from the substrate support surface by a layer of dielectric material. The systems and methods further include capturing a voltage representative of a voltage at a substrate positioned on the substrate support surface and iteratively adjusting the shaped pulse bias waveform based on the captured signal. In a plasma processing system a thickness and a composition of a layer of dielectric material separating the electrode and the substrate support surface can be selected such that a capacitance between the electrode and the substrate support surface is at least an order of magnitude greater than a capacitance between the substrate support surface and a plasma surface.