Conformal Silicon Nitride Etching Selective to Silicon
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Solution Overview
Problem
Current plasma etching systems fail to provide conformal etching of silicon nitride while maintaining selectivity to other materials like silicon and silicon oxide layers, as most chemistries etch these layers anisotropically and non-selectively.
Innovation Solution
A plasma etching process using a gas mixture of SF6, N2, and O2 at high pressure with no bias power, which accelerates silicon nitride etching through chemical reactions with [NO]x molecules and [N] atoms, providing a conformal (isotropic) etch that is selective to silicon and silicon oxide layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional plasma chemistries are used to etch silicon nitride, then anisotropic etching is achieved, but conformal (isotropic) etching characteristics are not obtained
Solution Approach 1:
The patent changes the chemical composition parameters by introducing a nitrogen-containing gas (N2O or NO) into the plasma chemistry mixture. This parameter change transforms the etching mechanism from anisotropic to conformal (isotropic), achieving uniform etching across horizontal and vertical surfaces while maintaining the desired etch profile shape.
2Productivity
If plasma chemistries capable of etching silicon nitride are used, then silicon nitride etching is achieved, but selectivity to silicon or silicon oxide layers is lost
Solution Approach 1:
The patent applies local quality by making the etching process selective to specific materials through controlled chemical reactions. The nitrogen-containing gas creates reactive species that preferentially react with silicon nitride through nitrogen exchange reactions, while silicon and silicon oxide layers remain protected due to their different chemical reactivity, thus achieving local selectivity.
Solution Approach 2:
The nitrogen-containing gas (N2O or NO) acts as an intermediary that facilitates selective etching of silicon nitride. It introduces nitrogen radicals that participate in nitrogen exchange reactions with silicon nitride, enabling selective removal of silicon nitride while leaving other materials intact, thereby maintaining etch selectivity.
3Reliability
If high selectivity to silicon nitride is achieved, then other materials are protected, but conformal etching characteristics are compromised
Solution Approach 1:
The patent uses a composite plasma chemistry system combining fluorine-containing gas (for etching capability), nitrogen-containing gas (for selectivity and conformal etching), and oxygen-containing gas (for surface passivation). This composite approach enables simultaneous achievement of high selectivity to silicon nitride and conformal etching profile through synergistic chemical reactions.
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 process achieves conformal etching of silicon nitride with selective etching to other materials, ensuring uniform etching across layers and maintaining desired selectivity, as demonstrated by etch rate and selectivity data across various microwave power settings.
Implementation Method 1
performing a conformal selective etching process with a non-polymerizing microwave plasma generated using a gas mixture of fluorine-containing gas, nitrogen-containing gas, and oxygen-containing gas
Implementation Method 2
non-polymerizing microwave plasma generated using a gas mixture
Implementation Method 3
The process accelerates silicon nitride etching by chemical reactions of [NO]x molecules from the plasma and [N] atoms from silicon nitride film
Implementation Method 4
The process accelerates silicon nitride etching by chemical reactions of [NO]x molecules from the plasma and [N] atoms from silicon nitride film
Data Source
AI summary
Plasma processing methods that provide for conformal etching of silicon nitride while also providing selectivity to another layer are described. In one embodiment, an etch is provided that utilizes gases which include fluorine, nitrogen, and oxygen, for example a gas mixture of SF6, N2 and O2 gases. Specifically, a plasma etch utilizing SF6, N2 and O2 gases at high pressure with no bias is provided. The process accelerates silicon nitride etching by chemical reactions of [NO]x molecules from the plasma and [N] atoms from silicon nitride film. The etch provides a conformal (isotropic) etch that is selective to other materials such as silicon and silicon oxides (for example, but not limited to, silicon dioxide).