Pulsed Voltage Waveform for Plasma Etch Selectivity
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Solution Overview
Problem
Conventional plasma processing methods struggle to maintain a consistent sheath voltage and control the ion energy distribution function (IEDF) in semiconductor manufacturing, leading to issues with etch profile control and selectivity, especially in high aspect ratio feature formation for 3D NAND devices.
Innovation Solution
A method involving a pulsed-voltage waveform generator that delivers a series of pulsed waveform cycles with a longer second time interval and a peak-to-peak voltage between 5 kV and 20 kV, using a fluorocarbon-containing gas and other process gases, to establish a nearly constant sheath voltage and control IEDF during plasma etching in a semiconductor processing chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional sinusoidal RF waveforms are used to control plasma properties, then plasma density and ion energy can be adjusted, but sheath voltage control becomes inconsistent and arcing problems occur
Solution Approach 1:
The patent applies periodic pulsed voltage waveforms with specific duty cycles (e.g., 10-90% duty cycle where plasma is present for longer duration than absent) to the substrate holder. This periodic action allows precise control of sheath voltage formation and collapse cycles, enabling consistent IEDF control and eliminating arcing issues that plague continuous sinusoidal RF methods. The pulsed nature creates controlled intervals for sheath formation and relaxation.
Solution Approach 2:
The invention changes the voltage waveform parameter from conventional sinusoidal RF to pulsed DC-like waveforms with adjustable pulse width, frequency, and amplitude. This parameter change enables independent control of sheath voltage magnitude and duration, providing precise control over ion energy distribution while maintaining process stability through adjustable duty cycles that prevent arcing conditions.
2Force
If lower frequency RF bias is used to achieve higher self-bias voltages, then ion energy increases, but ion energy distribution broadens causing bowing of etched feature walls
Solution Approach 1:
The pulsed voltage waveform creates distinct phases within each pulse cycle: a rising edge that accelerates ions to high energy, a plateau that maintains consistent energy, and a falling edge that allows sheath collapse. This temporal structure within each pulse delivers mono-energetic ion bursts rather than continuous broad-spectrum ion bombardment, preventing wall bowing while achieving high aspect ratio etching.
Solution Approach 2:
The system dynamically adjusts the pulsed voltage waveform parameters (pulse width, frequency, amplitude) in real-time to optimize ion energy delivery. The dynamic pulsed nature allows the sheath to form and collapse repeatedly, creating controlled ion acceleration events that deliver precise energy levels without the broad energy distribution caused by low-frequency RF bias.
3Adaptability or versatility
If multiple RF sources are used to control plasma properties, then plasma density and ion energy can be independently adjusted, but cross-talk between sources causes power diversion and potential damage
Solution Approach 1:
The invention extracts the substrate biasing function from the RF sources and implements it through separate pulsed voltage waveform generators connected to the substrate holder. This separation removes the substrate bias control from the plasma generation RF sources, eliminating cross-talk and power diversion issues while maintaining independent control capability for plasma density and ion energy through the pulsed waveform parameters.
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 the etch profile and selectivity, reducing over-etching and improving the formation of high aspect ratio features by maintaining a consistent sheath voltage and optimizing ion energy distribution, enhancing the reliability of the etching process for 3D NAND technology.
Implementation Method 1
delivering, by use of a radio frequency generator, a radio frequency signal to a first electrode disposed within the plasma processing chamber to form a plasma in the processing region
Implementation Method 2
establishing, by use of a first pulsed-voltage waveform generator, a first pulsed voltage waveform at a biasing electrode disposed within the substrate support assembly... ions from the plasma are accelerated towards a surface of a substrate
Implementation Method 3
The application of RF voltage to the power electrode causes an electron-repelling plasma sheath (also referred to as the 'cathode sheath') to form over a processing surface of a substrate... a direct-current (DC) voltage drop, or 'self-bias', appears between the substrate and the plasma
Implementation Method 4
The process gas comprises a first fluorocarbon containing gas and a first process gas... etching a first dielectric material formed on a substrate
Data Source
AI summary
Embodiments of this disclosure include a method of processing a substrate that includes etching a first dielectric material formed on a substrate that is disposed on a substrate supporting surface of a substrate support assembly disposed within a processing region of a plasma processing chamber. The etching process may include delivering a process gas to the processing region, wherein the process gas comprises a first fluorocarbon containing gas and a first process gas, delivering, by use of a radio frequency generator, a radio frequency signal to a first electrode to form a plasma in the processing region, and establishing, by use of a first pulsed-voltage waveform generator, a first pulsed voltage waveform at a biasing electrode disposed within the substrate support assembly. The first pulsed voltage waveform comprises a series of repeating pulsed waveform cycles that each include a first portion that occurs during a first time interval, a second portion that occurs during a second time interval, and a peak-to-peak voltage. The pulsed voltage waveform is substantially constant during at least a portion of the second time interval.