Shaped-Pulse Wafer Bias for Multi-Peak Ion Energy Control
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Solution Overview
Problem
Existing plasma processing systems struggle to achieve precise control over ion energy distribution functions (IEDF) due to the non-linear nature of the plasma sheath, leading to issues with feature profile control and etch anisotropy, particularly in high aspect ratio applications.
Innovation Solution
A shaped-pulse bias scheme is employed to modulate the amplitude and frequency of voltage pulses, allowing for the creation of arbitrarily-shaped IEDF by controlling the relative number of pulses at specific amplitudes and durations, thereby maintaining a constant sheath voltage and substrate potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a lower frequency RF bias generator is used to achieve higher self-bias voltages, then the ion energy distribution can be enhanced, but the difference in energy between peaks becomes significant causing isotropic etching and feature wall bowing
Solution Approach 1:
The patent applies periodic RF bias voltage at a lower frequency (e.g., 2 MHz) to generate higher self-bias voltages, creating a periodic oscillation in the plasma sheath voltage. This periodic action results in a two-peak IEDF where ions are accelerated at different phases of the RF cycle, achieving high ion energy while maintaining controllable feature profiles through the periodic modulation.
Solution Approach 2:
The patent changes the frequency parameter of the RF bias generator to a lower value (e.g., 2 MHz) to achieve higher self-bias voltages. By adjusting this key parameter, the system transforms the ion energy distribution from a single-peak to a two-peak structure, enabling better control over etch anisotropy and feature profile while maintaining high ion energy for deep etching applications.
2Power
If DC voltage is applied to the power electrode to maintain constant substrate voltage, then the sheath voltage can be controlled, but the ion current charges the substrate surface causing voltage drop across the substrate and ceramic instead of the plasma sheath
Solution Approach 1:
The patent uses periodic RF bias voltage instead of DC voltage to control the sheath voltage. The periodic oscillation allows the system to dynamically manage the voltage distribution, where the time-averaged effect maintains the desired sheath voltage while the instantaneous variations accommodate the ion current charging effect without causing permanent voltage drops across the substrate and ceramic layers.
Solution Approach 2:
The patent transitions from static DC voltage control to dynamic RF voltage control. The dynamic nature of the RF bias allows the system to adapt to the ion current charging effect in real-time, maintaining proper voltage distribution across the plasma sheath while accommodating the time-varying ion flux to the substrate surface.
3Object-generated harmful factors
If low-energy ions are used to reduce mask material sputtering, then mask protection is improved, but ion directionality and corner reaching capability are reduced
Solution Approach 1:
The patent employs periodic RF bias to create a two-peak IEDF that includes both low-energy and high-energy ion populations. The low-energy peak reduces mask sputtering by providing gentler ion bombardment, while the high-energy peak ensures adequate ion directionality and corner reaching capability. The periodic oscillation allows both energy components to contribute to the etching process simultaneously.
Solution Approach 2:
The patent creates different ion energy populations (low-energy and high-energy peaks) that serve different local functions in the etching process. The low-energy ions provide gentle bombardment for mask protection in areas where precision is critical, while the high-energy ions provide strong directional etching for corner reaching and anisotropic profile formation, achieving local optimization of etch quality.
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 precise control over IEDF, enhancing feature profile control and etch anisotropy, particularly in high aspect ratio etch applications, by creating well-defined and customizable ion energy distributions.
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
modulating an amplitude of the wafer voltage to produce a train of groups of pulse bursts with different amplitudes
Implementation Method 3
all of the applied DC voltage would drop across the substrate and the ceramic portion of the ESC (i.e., chuck capacitance) instead of the plasma sheath (i.e., sheath capacitance)
Data Source
AI summary
Systems and methods for creating arbitrarily-shaped ion energy distribution functions using shaped-pulse-bias. In an embodiment, a method includes applying a negative jump voltage to an electrode of a process chamber to set a wafer voltage for a wafer, modulating an amplitude of the wafer voltage to produce a train of groups of pulse bursts with different amplitudes, and repeating the modulating of the amplitude of the wafer voltage to repeat the train of the groups of pulse bursts to create an ion energy distribution function having more than one energy peak. In some embodiments, the negative jump voltage can include a single-cycle voltage waveform with a voltage ramp during an ion-current phase, in which the voltage ramp can be positive or negative and a duration of the ion-current phase can comprise more or less than fifty percent of a period of the waveform.