Sulfur Fluorine Etch Chemistry for High Aspect Ratio Bow Control
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Solution Overview
Problem
Current etching technologies face challenges in maintaining a straight profile for high aspect ratio features in semiconductor devices, particularly in 3D structures like ONON stacks, leading to unwanted bowing and irregular shapes due to difficulties in controlling the critical dimension and shape retention during the etching process.
Innovation Solution
The use of an etching gas comprising sulfur and fluorine, such as SF6, formed into a plasma, which is applied to etch through alternating layers in a stack, minimizing feature bowing and maintaining a more consistent shape by controlling the etching process in a plasma chamber with specific RF power and pressure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional etching technologies are used, then the etching process can be completed, but the features exhibit unwanted bowing and irregular shapes with poor shape retention
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas by introducing sulfur-containing compounds (SF6, S2F10) in combination with fluorocarbons. This chemical parameter change modifies the etching chemistry to achieve better shape retention and reduced bowing in high aspect ratio features while maintaining manufacturing precision
Solution Approach 2:
The patent uses a composite etching gas mixture combining sulfur fluorides (SF6, S2F10) with fluorocarbon compounds (C4F8, C4F6). This composite chemistry synergistically provides both the etching capability and the shape control needed to prevent feature bowing and maintain critical dimensions throughout the etch depth
2Productivity
If high aspect ratio features are etched through multiple alternating layers, then the packing density increases, but the features develop mid-bow distortion and ellipticity
Solution Approach 1:
The patent modifies the etching gas composition by adding sulfur fluorides to the fluorocarbon-based chemistry. This parameter change enables successful etching of high aspect ratio features through multiple alternating layers while maintaining feature straightness and reducing mid-bow distortion, thus allowing higher packing density without shape degradation
3Manufacturing precision
If the etching gas comprises sulfur and fluorine compounds, then the mid-bow critical dimension is reduced and ellipticity is improved, but the process complexity increases
Solution Approach 1:
The patent achieves improved manufacturing precision through parameter changes in gas composition (adding 1-20% SF6 or S2F10 to fluorocarbon mixtures). While this increases chemical process complexity, it significantly reduces mid-bow critical dimension and eliminates the need for additional process steps to correct shape distortion, potentially simplifying the overall manufacturing flow
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 results in a significant reduction of mid-bow critical dimension and improved ellipticity at the bottom of features, achieving a more uniform and desired shape, with approximately 7% improvement at 75% etch depth and ellipticity enhancement from 0.6-0.9 to greater than 0.9, addressing the issues of shape distortion and irregular profiles.
Implementation Method 1
forming the etching gas into a plasma
Data Source
AI summary
In accordance with this disclosure, there is provided several inventions, including a method for etching a plurality of features in a stack comprising alternating layers above a substrate, comprising: providing a steady state flow of an etching gas, wherein the etching gas comprises: a molecule A comprising sulfur and fluorine; a molecule B comprising carbon, fluorine, and hydrogen; and a molecule C comprising carbon and fluorine and not hydrogen; forming the etching gas into a plasma; and etching the features into the stack through the plurality of alternating layers.