Silicon Nitride Etching Selectivity via Self-Assembled Monolayer
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Solution Overview
Problem
Hot phosphoric acid solutions used for wet etching of silicon nitride also undesirably etch silicon oxide, leading to reduced etching selectivity and potential device characteristic fluctuations.
Innovation Solution
The method involves forming a hot phosphoric acid-resistant self-assembled monolayer (SAM) more densely on the surface of a silicon oxide film than on a silicon nitride film, preventing the etchant from penetrating the silicon oxide film while allowing etching of the silicon nitride film, thereby enhancing etching selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hot phosphoric acid solution is used to etch silicon nitride film, then etching rate of silicon nitride is improved, but silicon oxide film is also undesirably etched
Solution Approach 1:
A self-assembled monolayer (SAM) is introduced as an intermediary protective layer on the silicon oxide film surface. This SAM layer acts as a mediator that prevents the hot phosphoric acid etchant from directly contacting and etching the silicon oxide film, while allowing the etchant to effectively remove the silicon nitride film. The SAM layer is formed by immersing the substrate in a solution containing SAM-forming compounds, which selectively assemble on the silicon oxide surface to create a protective barrier.
2Productivity
If hot phosphoric acid solution is used for wet etching, then etching capability is improved, but device characteristic stability deteriorates due to unwanted silicon oxide etching
Solution Approach 1:
The self-assembled monolayer serves as a protective intermediary that stabilizes the device characteristics by preventing unwanted etching of the silicon oxide film. This protective layer ensures that only the intended silicon nitride film is etched, thereby maintaining the structural integrity and electrical characteristics of the device during the etching process.
3Device complexity
If no protective layer is used on silicon oxide, then process simplicity is maintained, but etching selectivity is reduced
Solution Approach 1:
The silicon oxide film protects itself by forming a self-assembled monolayer when immersed in the SAM-forming solution. The SAM compounds selectively assemble on the silicon oxide surface through self-organization, creating a protective layer without requiring additional manual intervention or complex process steps. This self-service mechanism maintains process simplicity while achieving high etching selectivity.
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 increases the selectivity of silicon nitride etching with respect to silicon oxide, preventing unwanted etching of the silicon oxide film and maintaining device stability.
Implementation Method 1
forming a hot phosphoric acid-resistant self-assembled monolayer (SAM) more densely on the surface of a silicon oxide film
Implementation Method 2
supplying an etching-resistant material to a processing surface including a surface of a silicon nitride film and a surface of a non-etching film
Data Source
AI summary
According to one embodiment, an etching method includes: supplying an etching-resistant material; and etching the silicon nitride film. The supplying includes supplying the etching-resistant material to a processing surface including a surface of a silicon nitride film and a surface of a non-etching film, the non-etching film including a material different from the silicon nitride film. The etching includes etching the silicon nitride film using an etchant in a state of the etching-resistant material being formed relatively more densely on the surface of the non-etching film than on the surface of the silicon nitride film.