Substrate Bias Waveform Feedback for Single-Peak Plasma Etching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing plasma processing systems face challenges in achieving a well-controlled, single-peak Ion Energy Distribution Function (IEDF) due to the unpredictable nature of sheath capacitance, which complicates the use of shaped-pulse bias schemes, requiring complex and time-consuming calibration processes that are not reproducible.
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 compared to the chuck capacitance, allowing for a constant ion energy without precise estimation of sheath capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a shaped-pulse bias scheme is used to maintain constant substrate voltage, then ion energy control is improved, but the complexity of the system increases due to unpredictable sheath capacitance requiring complex calibration
Solution Approach 1:
The patent implements a feedback mechanism that monitors the actual substrate voltage waveform and dynamically adjusts the bias pulse parameters. A sensor captures the substrate voltage, and a controller modifies the shaped-pulse bias waveform in real-time to maintain the desired voltage profile, eliminating the need for complex pre-calibration of sheath capacitance values.
Solution Approach 2:
The system uses the substrate itself as the sensing element to monitor its own voltage waveform. The substrate voltage is directly measured and fed back to the control system, allowing the process to self-regulate without requiring external measurement devices or complex calibration procedures.
2Measurement precision
If sheath capacitance is precisely determined to control substrate voltage, then voltage waveform accuracy is improved, but the measurement and calibration process becomes more difficult and time-consuming
Solution Approach 1:
Instead of measuring sheath capacitance directly, the system measures the actual substrate voltage waveform and uses this feedback to adjust the bias parameters. This indirect approach avoids the difficulty of directly measuring unpredictable capacitance values while achieving the same goal of voltage waveform control.
Solution Approach 2:
The system changes the control parameter from sheath capacitance (which is difficult to measure) to substrate voltage (which is easily measurable). By controlling the bias pulse parameters based on measured substrate voltage rather than calculated capacitance values, the system achieves accurate voltage control without complex measurements.
3Manufacturing precision
If RF bias frequency is reduced to achieve higher self-bias voltages, then etch anisotropy is improved, but the ion energy distribution becomes two-peaked causing feature wall bowing
Solution Approach 1:
The patent uses periodic pulsed biasing instead of continuous RF bias. The shaped-pulse waveform applies voltage in controlled pulses with specific timing and duration, creating a single-peak ion energy distribution that maintains etch anisotropy while preventing feature wall bowing by eliminating the low-energy ion population that causes isotropic etching.
Solution Approach 2:
The system changes the bias waveform parameters (pulse width, amplitude, duty cycle) to control the ion energy distribution. By adjusting these parameters, the system achieves high self-bias voltages for anisotropic etching while maintaining a single-peak IEDF that preserves feature profile integrity.
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 IEDF, maintaining consistent ion energy during plasma processing, simplifying the process and reducing the need for complex modeling or precise capacitance determination.
Implementation Method 1
a substrate support including an electrostatic chuck
Implementation Method 2
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 3
This scheme provides compensation for the ion current, allowing for the sheath voltage and the substrate voltage to remain constant for up to 90% of each bias voltage cycle
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.