Thioether Plasma Etching for SiO2 Selectivity and Vertical Profile
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Solution Overview
Problem
In the miniaturization of semiconductor devices, high aspect ratio etching of multilayer structures such as SiO2 and SiN in 3D-NAND and Fin-FET structures poses challenges in achieving selective etching and maintaining desirable shape accuracy due to ion-assisted etching methods, which often result in swelling, thinning, or bending of patterns.
Innovation Solution
A dry etching method using a plasma of a gas compound with a specific thioether skeleton, represented by the general formula Rf1—S—Rf2, where Rf1 and Rf2 are monovalent organic groups, enhances selectivity and accuracy in etching Si-containing films by forming a polymer film with low fluorine content, allowing vertical etching while inhibiting sidewall reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion-assisted etching is used for high aspect ratio etching of SiO2 and SiN, then etching selectivity and vertical profile are improved, but mask material damage and pattern shape distortion occur
Solution Approach 1:
The patent introduces a sulfur-containing compound (COS or SO2) as an intermediary substance that mediates between the ion-assisted etching process and the mask material. The sulfur compound forms a protective layer on the mask material surface, preventing direct damage from ion bombardment while allowing the etching process to proceed vertically on the SiO2 and SiN layers. This resolves the contradiction by protecting the mask from harmful ion effects while maintaining the benefits of ion-assisted etching.
Solution Approach 2:
The patent changes the chemical composition parameters of the etching atmosphere by adding sulfur-containing compounds (COS or SO2) to the plasma environment. This parameter change modifies the surface chemistry of the mask material, creating a sulfur-passivated layer that reduces ion damage. Simultaneously, the etching selectivity and vertical profile are maintained through the ion-assisted mechanism, thus resolving the contradiction between etching quality and mask protection.
2Manufacturing precision
If fluorocarbon gas is used for SiO2 etching, then carbon atoms react with oxygen to enable selective etching, but carbon components remain on mask material reducing selectivity
Solution Approach 1:
The patent converts the harmful effect of carbon deposition on the mask into a beneficial protective layer. By introducing sulfur-containing compounds, the carbon components that would normally accumulate and reduce selectivity are transformed into a sulfur-passivated protective layer on the mask surface. This layer prevents further carbon accumulation and ion damage, while the underlying carbon layer continues to provide the necessary chemistry for selective SiO2 etching through carbon-oxygen reactions.
Solution Approach 2:
The patent creates a composite protective structure on the mask material surface consisting of multiple layers: the original carbon-containing layer from fluorocarbon gas, and an outer sulfur-passivated layer formed by the sulfur-containing compound. This composite structure combines the benefits of carbon-based selectivity enhancement with sulfur-based protection against ion damage and carbon accumulation, resolving the contradiction between achieving selective etching and preventing mask contamination.
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 method enables highly selective and accurate plasma etching of SiO2 and SiN, preventing etching of mask materials and maintaining vertical processing integrity, thus improving the shape accuracy and selectivity in high aspect ratio structures.
Implementation Method 1
a gas plasma containing a compound represented by general formula (1) below... generating a plasma of a gas compound
Implementation Method 2
carbon atoms contained in an FC or HFC react with oxygen of SiO2 to form volatile products, such as CO and CO2
Implementation Method 3
ion bombardment of the SiO2 surface, on which CFx radicals have been deposited, promotes reactions between the SiO2 surface and CFx radicals due to the kinetic energy of ions
Implementation Method 4
CFx radicals generated when forming a plasma of an FC gas or HFC gas are adsorbed onto the surface of SiO2
Implementation Method 5
forming a polymer film with low fluorine content, allowing vertical etching while inhibiting sidewall reactions
Implementation Method 6
the passivation effects of C═S since sulfur atoms were detected in the ACL mask treated with a plasma added with COS
Data Source
AI summary
Provided is a plasma etching method that enables, in a semiconductor fabrication process, selective processing of a film consisting of a single material, such as SiO2 or SiN, or a composite material of SiO2 and SiN over a mask material as well as processing into satisfactorily vertical processed shapes.It is possible, for example, to enhance selectivity over a mask material or other materials excluding an etching target, to reduce damage on sidewalls, and to suppress etching in the lateral direction by generating a plasma of a gas compound having a thioether skeleton represented by general formula (1) or a mixed gas thereof and etching a film consisting of a composite material or a single material, such as SiO2 or SiN, thereby depositing a protective film that contains sulfur atoms and has a lower content of fluorine atoms than the cases of using common hydrofluorocarbon gases:general formula (1): Rf1—S—Rf2 (1)where Rf1 is a monovalent organic group represented by CxHyFz and Rf2 is a monovalent organic group represented by CaHbFc.