Microwave Plasma Silicon Nitride Etching for 3D NAND Trenches
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Solution Overview
Problem
Wet etching processes used in 3D NAND device fabrication lead to yield losses due to silicon oxide layer collapse and difficulty in etching deep trenches, resulting in non-uniform etching across the structure.
Innovation Solution
A dry etching process using a microwave plasma source with sulfur hexafluoride (SF6) and an inert gas, such as argon, achieves a selectivity of 50:1 or greater for etching silicon nitride over silicon oxide, avoiding fluorine residue and maintaining etching uniformity across high aspect ratio structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wet etching is used to remove silicon nitride layers, then the etching process is simple, but the silicon oxide layers collapse due to surface tension during drying, causing yield losses
Solution Approach 1:
The patent transitions from wet etching to dry etching using microwave plasma, fundamentally changing the etching medium from liquid to gas phase. This parameter change eliminates surface tension effects during drying while achieving the required etching selectivity of 50:1 or greater for silicon nitride over silicon oxide
Solution Approach 2:
The patent replaces the mechanical/chemical wet etching process with a plasma-based dry etching process. The microwave plasma source generates reactive species that etch silicon nitride selectively without requiring subsequent drying steps, thereby eliminating the collapse issue entirely
2Manufacturing precision
If wet etching is used for deep trenches in scaled 3D NAND devices, then the process works for shallow structures, but the liquid etchant cannot fill deep trenches uniformly, resulting in non-uniform etching
Solution Approach 1:
The patent uses gas-phase plasma instead of liquid etchant to access deep trenches. The plasma, being in gas form, can penetrate and fill deep high-aspect-ratio trenches uniformly, enabling consistent etching throughout the entire trench depth regardless of structure scaling
Solution Approach 2:
By changing the etching medium from liquid to gas phase through microwave plasma, the process gains the ability to uniformly etch deep trenches. The gas phase allows complete penetration and uniform distribution of reactive species throughout the trench, achieving consistent etching results
3Productivity
If the number of alternating silicon oxide and silicon nitride layers increases for future scaling, then device capacity increases, but wet etching becomes ineffective due to inability to reach and etch all layers uniformly
Solution Approach 1:
The microwave plasma dry etching process uses gas-phase reactive species that can uniformly penetrate and etch through large numbers of alternating layers. This enables the process to handle increased device capacity with higher layer counts while maintaining uniform etching across all layers
Solution Approach 2:
The replacement of wet etching with microwave plasma dry etching enables the process to scale to higher layer counts. The plasma process provides uniform etching throughout the stack regardless of the number of alternating layers, supporting future device scaling
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 ensures high etch selectivity and uniformity, reducing etching time and preventing corrosion, while eliminating the need for a post-etch drying step that could damage the structure.
Implementation Method 1
etching silicon nitride selective to silicon oxide using a microwave plasma source
Implementation Method 2
microwave plasma chamber
Implementation Method 3
flowing a first gas into the microwave plasma chamber, where the first gas comprises sulfur and fluorine
Data Source
AI summary
Embodiments disclosed herein include a method of etching a 3D structure. In an embodiment, the method comprises providing the 3D structure in a microwave plasma chamber. In an embodiment, the 3D structure comprises a substrate, and alternating layers of silicon oxide and silicon nitride over the substrate. In an embodiment, the method further comprises flowing a first gas into the microwave plasma chamber, where the first gas comprises sulfur and fluorine. In an embodiment, the method comprises flowing a second gas into the microwave plasma chamber, where the second gas comprises an inert gas. In an embodiment, the method further comprises striking a plasma in the microwave plasma chamber, and etching the silicon nitride, where an etching selectivity of silicon nitride to silicon oxide is 50:1 or greater.