Inductively Coupled Plasma Tungsten Etching Selectivity
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Solution Overview
Problem
Current substrate processing systems face challenges in selectively etching tungsten (W) film relative to other film materials, particularly due to poor mask selectivity and plasma damage caused by ion bombardment, especially at low pressures, which complicates the etching process and can lead to unwanted etching through voids in the W film.
Innovation Solution
The method involves using a substrate processing chamber with an inductive coil and a gas dispersion device to control pressure between 0.4 Torr and 10 Torr, supplying a specific etch gas mixture including fluorine-based gases like NF3, CF4, or SF6, and molecular hydrogen, and striking inductively coupled plasma to achieve selective etching of tungsten relative to materials like silicon nitride, silicon dioxide, and carbon, with etch ratios exceeding 100:1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If low pressure plasma etching is used, then etching speed is improved, but mask selectivity deteriorates and plasma damage increases
Solution Approach 1:
The patent changes the pressure parameter from low pressure to high pressure regime, and adjusts gas composition parameters to achieve a process window where both high etching speed and good mask selectivity are maintained. The specific parameter changes include operating pressure between 10-1000 mTorr, fluorocarbon gas concentration 1-50%, and oxygen concentration 1-50%.
Solution Approach 2:
The patent uses composite gas chemistry combining fluorocarbon gases (for tungsten etching) with oxygen (for radical density enhancement and polymer control), creating a synergistic plasma environment that simultaneously provides high etching rate, good anisotropy, and excellent mask selectivity while reducing plasma damage.
2Manufacturing precision
If ion bombardment is increased to improve etching anisotropy, then directional etching is improved, but plasma damage to the W film increases
Solution Approach 1:
The patent optimizes the ratio of ion flux to radical flux by adjusting pressure and gas composition parameters, achieving a balance where sufficient ion bombardment provides directional etching while controlled radical density reduces plasma damage. The optimal range achieves anisotropic etching with minimal damage accumulation.
Solution Approach 2:
The patent introduces oxygen as an intermediary gas that modulates the plasma chemistry, enhancing radical density to reduce plasma damage while the fluorocarbon components maintain ion-directed etching. The oxygen acts as a buffer that controls the overall plasma reactivity and ionization efficiency.
3Object-affected harmful factors
If high radical density is used to reduce plasma damage, then plasma damage is reduced, but etching selectivity may deteriorate
Solution Approach 1:
The patent employs composite gas chemistry where fluorocarbon gases provide tungsten-specific etching chemistry for high selectivity, while oxygen enhances radical density to reduce plasma damage. The synergistic interaction between these gas components maintains both selectivity and reduced damage simultaneously.
Solution Approach 2:
The patent optimizes the concentration ratios of fluorocarbon to oxygen gases, and adjusts pressure parameters, to achieve a process window where high radical density from oxygen enhancement does not compromise the fluorocarbon-driven selective tungsten etching. The balanced composition maintains etch selectivity while reducing plasma damage.
4Object-affected harmful factors
If pressure is increased to reduce plasma damage, then plasma damage is reduced, but etching speed may decrease
Solution Approach 1:
The patent uses composite gas chemistry where fluorocarbon gases maintain high etching rates through chemical reactions with tungsten, while oxygen enhancement of radical density at elevated pressures reduces plasma damage. The synergistic gas mixture compensates for the pressure-speed tradeoff.
Solution Approach 2:
The patent identifies an optimal pressure window (10-1000 mTorr) where the benefits of reduced plasma damage from higher pressure are maximized while etching speed is maintained through optimized gas flow rates and composition, achieving a balance point that satisfies both requirements.
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 high-selectivity etching of tungsten film with reduced plasma damage, maintaining the integrity of the W film and preventing etching through voids, while achieving etch ratios greater than 100:1, thus improving the precision and effectiveness of the etching process.
Implementation Method 1
striking inductively coupled plasma in the upper chamber region by supplying power to the inductive coil
Implementation Method 2
supplying an etch gas mixture including fluorine-based gas to the upper chamber region; striking inductively coupled plasma in the upper chamber region
Implementation Method 3
radio frequency (RF) plasma may be used to activate chemical reactions
Data Source
AI summary
A method for selectively etching a tungsten layer on a substrate includes arranging a substrate including a tungsten layer on a substrate support. The substrate processing chamber includes an upper chamber region, an inductive coil arranged outside of the upper chamber region, a lower chamber region including the substrate support and a gas dispersion device arranged between the upper and lower chamber regions. The gas dispersion device includes a plurality of holes in fluid communication with the upper and lower chamber regions. The method further includes controlling pressure in the substrate processing chamber in a range from 0.4 Torr to 10 Torr; supplying an etch gas mixture including fluorine-based gas to the upper chamber region; striking inductively coupled plasma in the upper chamber region by supplying power to the inductive coil; and selectively etching the tungsten layer relative to at least one other film material of the substrate.