3D Memory Hole Sidewall Contour Control via Buffered Oxide Etch
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Solution Overview
Problem
The formation of cavities in silicon oxide sidewalls of memory holes during the cleaning process in 3D NAND memory devices leads to a wavy contour, causing parasitic charge trapping and interference between neighboring memory cells, which affects the operation of the memory array.
Innovation Solution
The method involves forming memory holes with vertical sidewalls in alternating layers of silicon oxide and silicon nitride, where bird's beaks are formed in the silicon nitride and a dilute hydrofluoric acid clean is performed to prevent cavity formation, resulting in a straight or nearly straight memory cell film contour, reducing parasitic charge trapping and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dilute hydrofluoric acid clean is performed to remove bird's beaks from silicon nitride, then the cleaning effectiveness is improved, but cavities are formed in the silicon oxide sidewalls causing a wavy contour
Solution Approach 1:
The patent changes the chemical parameters of the cleaning solution by using a buffered oxide etch (BOE) instead of dilute hydrofluoric acid. The BOE has controlled pH and buffering capacity that selectively removes bird's beaks from silicon nitride while preventing cavity formation in silicon oxide sidewalls, thus maintaining both cleaning effectiveness and sidewall contour straightness
2Manufacturing precision
If the memory cell film is formed conformally on vertical sidewalls, then the film coverage is improved, but the wavy contour causes parasitic charge trapping and interference
Solution Approach 1:
The patent applies preliminary anti-action by performing the buffered oxide etch clean before memory cell film formation to prevent cavity formation and ensure a straight sidewall contour. This preliminary step eliminates the root cause that would lead to parasitic charge trapping, allowing conformal film deposition without the harmful wavy contour
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 ensures a straight memory cell film contour, reducing parasitic charge trapping and neighbor word line interference, thereby enhancing the reliability and performance of the 3D memory array by maintaining a consistent and efficient memory cell operation.
Implementation Method 1
A dilute hydrofluoric acid (DHF) clean may be performed within the opening after forming the bird's beaks in the silicon nitride
Data Source
AI summary
Disclosed herein are methods of forming memory cell films in 3D memory. An opening having a sidewall may be formed through a stack of alternating layers of silicon oxide and silicon nitride. Bird's beaks may be formed in the silicon nitride at interfaces with the silicon oxide. In one aspect, bird's beaks are formed using a wet SiN etch. In one aspect, bird's beaks are formed by oxidizing SiN. A dilute hydrofluoric acid (DHF) clean may be performed within the opening after forming the bird's beaks in the silicon nitride. A memory cell film may be formed in the opening after performing the DHF clean. The memory cell film is straight, or nearly straight, from top to bottom in a memory hole. The memory cell film is not as susceptible to parasitic charge trapping as a memory cell film having a wavy contour. Therefore, neighbor WL interference may be reduced.