Pulsed DC Bias Waveforms for Uniform High-Aspect-Ratio Etching
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Solution Overview
Problem
Conventional methods for applying bias power during high aspect ratio etching processes struggle to achieve uniformity in mask patterns, especially at high aspect ratios and low critical dimensions, leading to issues such as distortion, necking, and low local critical dimension uniformity.
Innovation Solution
The method involves generating a plasma in a plasma etching chamber and applying a periodic sequence of direct current (DC) bias waveforms to the substrate, with each waveform having a non-vertical voltage transition and a voltage ranging from a reference voltage to a negative peak voltage. The periodic sequence has a duty cycle greater than 20%, allowing for improved control over the etch process and enhanced mask uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional bias power methods are used during high aspect ratio etching, then the etching process can proceed, but mask uniformity deteriorates leading to feature distortion and poor local critical dimension uniformity
Solution Approach 1:
The patent applies periodic pulsed DC bias waveforms instead of continuous bias power. The duty cycle is controlled between 1% and 50%, creating periodic on-off cycles that allow the plasma chemistry to reset between pulses. This periodic action prevents continuous ion bombardment that causes mask erosion and non-uniform etching, thereby improving mask uniformity and local critical dimension uniformity while maintaining etching capability for high aspect ratio features
Solution Approach 2:
The patent changes the bias power delivery parameters by using pulsed DC waveforms with specific duty cycles, frequencies, and voltage amplitudes. This parameter change transforms the continuous ion bombardment regime into a controlled pulsed regime, allowing precise control over ion flux to the mask surface. The parameter optimization enables simultaneous achievement of high aspect ratio etching and improved mask uniformity
2Length of moving object
If high aspect ratio etching is performed with conventional methods, then etching depth can be achieved, but local critical dimension uniformity deteriorates
Solution Approach 1:
The periodic pulsed DC bias enables deep etching while maintaining uniform critical dimensions by controlling the timing and duration of ion bombardment. The pulsed nature allows reactive species to replenish mask material between pulses, preventing mask thinning and maintaining uniform opening dimensions even at high aspect ratios of 10:1 and above
Solution Approach 2:
The patent implements process control that monitors etching progress and adjusts the pulsed DC bias parameters in real-time. This feedback mechanism ensures that as etching depth increases, the bias waveforms are optimized to maintain uniform ion flux distribution, preventing divergence in critical dimensions across different depths of high aspect ratio features
3Productivity
If continuous DC bias is applied to improve etch rate, then productivity increases, but mask uniformity deteriorates due to continuous ion bombardment
Solution Approach 1:
The pulsed DC bias delivers ion bombardment in controlled pulses rather than continuously. The duty cycle optimization (1%-50%) balances etching efficiency with mask protection: during the on-phase, etching proceeds at high rate; during the off-phase, mask material is replenished by reactive species diffusion. This periodic action maintains high productivity while preventing mask erosion and maintaining uniformity
Solution Approach 2:
The pulsed off-period serves as a preliminary protective action before the next etching pulse. During the off-phase, reactive species diffuse to the mask surface and replenish mask material that will be consumed in the upcoming on-phase. This preliminary replenishment action prevents mask thinning and maintains uniformity throughout the etching process, enabling sustained high productivity
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 effectively improves feature uniformity, particularly local critical dimension uniformity, and allows for the achievement of high aspect ratios (100:1 or higher) with critical dimensions less than 100 nm, while maintaining excellent mask uniformity and pattern transfer fidelity.
Implementation Method 1
generating a plasma in a plasma etching chamber containing a substrate
Implementation Method 2
Ions may be accelerated through the resulting plasma sheath towards the substrate surface
Implementation Method 3
coupling a periodic sequence including direct current (DC) bias waveforms to the substrate... voltage ranging from a reference voltage to a negative peak voltage
Implementation Method 4
Bias power may be applied during HAR etch processes to create a potential difference between the plasma and the substrate surface. Ions may be accelerated through the resulting plasma sheath towards the substrate surface
Data Source
AI summary
A high aspect ratio etching method includes generating plasma in a chamber containing a substrate including a patterned surface such as a hardmask, and etching one or more underlying layers through openings in the patterned surface by coupling a periodic sequence including direct current bias waveforms to the substrate. Each bias waveform has voltage ranging from a reference voltage to a peak voltage. The periodic sequence has a duty cycle greater than 20%. The bias waveforms may include a non-vertical voltage transition. The one or more underlying layers may be a dielectric and the method may be a high aspect ratio contact etch. The etching may form features having an aspect ratio of at least about 100:1 and a critical dimension less than about 100 nm. The periodic sequence may have a frequency between about 100 kHz and about 3 MHz.