Plasma-Less SiN Etching With HF-Carboxylic Acid Selectivity
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Solution Overview
Problem
Existing dry etching methods for silicon nitride (SiN) face challenges in achieving high selectivity ratios with silicon oxide (SiO2) and polycrystalline silicon (p-Si) while preventing damage to SiO2, particularly due to by-products like NH3 generation and reduced etching rates with inert gas dilution.
Innovation Solution
A dry etching method using a mixed gas of hydrogen fluoride and a fluorine-containing carboxylic acid at low temperatures (below 100°C) in a plasma-less process, which traps NH3 by-products and prevents etching of SiO2 and p-Si, maintaining high etching rates and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HF gas is used to etch SiN film, then etching of SiN is achieved, but SiO2 film is also etched by HF and NH3 by-products resulting in low selectivity ratio
Solution Approach 1:
The patent introduces a carboxylic acid component as an intermediary substance that selectively binds with NH3 by-products generated during SiN etching. This prevents NH3 from reacting with SiO2, thereby protecting the SiO2 film while maintaining SiN etching efficiency. The carboxylic acid acts as a mediator that intercepts harmful by-products before they can damage the SiO2 layer.
Solution Approach 2:
The patent changes the chemical composition parameters of the etching gas by adding carboxylic acid components (such as formic acid, acetic acid, or their derivatives) to the HF-based etching gas. This parameter modification alters the reaction pathways, enabling selective SiN etching while preventing SiO2 damage through by-product neutralization.
2Productivity
If F2 gas is added to HF gas to increase SiN etching rate, then etching rate improves, but p-Si is etched by F2 resulting in low selectivity ratio
Solution Approach 1:
The carboxylic acid component serves as an intermediary that selectively captures NH3 by-products without interfering with the F2-SiN etching reaction. This allows F2 to maintain its high etching capability on SiN while the carboxylic acid prevents NH3 from causing unwanted etching on p-Si, thus preserving selectivity.
Solution Approach 2:
The patent extracts or removes the harmful NH3 by-product from the reaction environment by having it bind with carboxylic acid components. This extraction prevents NH3 from participating in unwanted side reactions with p-Si, thereby maintaining high selectivity between SiN and p-Si etching.
3Manufacturing precision
If inert gas is added to dilute the etching gas to prevent SiO2 damage, then SiO2 protection improves, but etching rate of SiN significantly decreases
Solution Approach 1:
Instead of using inert gas dilution, the patent employs carboxylic acid as an active intermediary that chemically neutralizes NH3 by-products. This chemical approach provides SiO2 protection without the side effect of reducing etching rate, as the carboxylic acid does not dilute the reactive components needed for SiN etching.
Solution Approach 2:
The patent converts the harmful NH3 by-product into a beneficial bound complex with carboxylic acid. This transformation eliminates the harmful effect (SiO2 etching) while maintaining the useful effect (SiN etching), achieving protection without sacrificing 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
The method achieves high etching rates of SiN with selectivity ratios of 100 or higher for SiN to SiO2 and p-Si, while ensuring minimal damage to SiO2, suitable for semiconductor device manufacturing.
Implementation Method 1
When the SiN film is etched with the HF gas, the SiO2 film is also etched with HF and NH3 generated as a reaction product
Implementation Method 2
a fluorine-containing carboxylic acid has the capabilities of trapping NH3 generated as a by-product during etching of SiN with HF
Implementation Method 3
a method of etching a SiN film formed on a SiO2 film by feeding a HF gas in a plasma-less heating environment
Data Source
AI summary
A dry etching method according to the present invention includes etching silicon nitride by bringing a mixed gas containing hydrogen fluoride and a fluorine-containing carboxylic acid into contact with the silicon nitride in a plasma-less process at a temperature lower than 100° C. Preferably, the amount of the fluorine-containing carboxylic acid contained is 0.01 vol % or more based on the total amount of the hydrogen fluoride and the fluorine-containing carboxylic acid. Examples of the fluorine-containing carboxylic acid are monofluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, difluoropropionic acid, pentafluoropropionic acid, pentafluorobutyric acid and the like. This dry etching method enables etching of the silicon nitride at a high etching rate and shows a high selectivity ratio of the silicon nitride to silicon oxide and polycrystalline silicon while preventing damage to the silicon oxide.