Non-volatile Memory Sidewall Nitride and Air Gap Isolation
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Solution Overview
Problem
As semiconductor memory features shrink, voltage breakdown between neighboring word lines becomes a significant issue, and conventional techniques to combat this often lead to charge trapping in dielectric materials, impairing device performance.
Innovation Solution
A method involving the formation of a silicon nitride layer on the sidewalls of memory cell stacks, excluding the charge storage regions, and the use of air gaps between word lines to enhance electrical isolation and prevent charge trapping, while using a sacrificial material to control the silicon nitride layer's formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon nitride is formed on sidewalls to protect word lines during fabrication, then word line protection is improved, but charge trapping occurs that degrades memory cell performance
Solution Approach 1:
The patent applies local quality by forming silicon nitride only in specific regions where it is needed for protection, while deliberately excluding areas where charge trapping would occur. The silicon nitride is deposited on sidewalls adjacent to word lines but stops before reaching charge storage regions, creating spatially varying material properties that simultaneously achieve protection and avoid harmful charge trapping effects.
2Productivity
If feature size is reduced to increase memory density, then productivity is improved, but voltage breakdown between word lines worsens
Solution Approach 1:
The patent introduces air gaps as intermediary structures between adjacent word lines. These air gaps act as mediators that provide electrical isolation and prevent direct contact between word lines, thereby preventing voltage breakdown while allowing continued scaling of feature sizes to maintain high memory density.
3Reliability
If conventional techniques are used to combat voltage breakdown, then voltage breakdown resistance is improved, but charge trapping in dielectric materials occurs that impairs device performance
Solution Approach 1:
The patent extracts the harmful charge trapping function from the protective structure by removing silicon nitride from regions adjacent to charge storage areas. Instead of using conventional dielectric materials throughout, the invention extracts the nitride layer in specific zones where it would cause charge trapping, replacing it with air gaps that provide isolation without the harmful side effect.
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 effectively increases memory cell current and improves voltage breakdown resistance between word lines, reducing the degradation caused by trapped charges and enhancing overall device operation.
Implementation Method 1
Silicon nitride covers the silicon oxide adjacent to the word lines
Implementation Method 2
Air gaps are formed between neighboring pairs of the lines of memory cell stacks
Data Source
AI summary
Non-volatile storage devices and methods for fabricating non-volatile storage device are described. Sidewalls of the memory cells and their associated word line may be covered with silicon oxide. Silicon nitride covers the silicon oxide adjacent to the word lines, which may provide protection for the word lines during fabrication. However, silicon nitride can trap charges, which can degrade operation if the trapped charges are near a charge trapping region of a memory cell. Thus, the silicon nitride does not cover the silicon oxide adjacent to charge storage regions of the memory cells, which can improve device operation. For example, memory cell current may be increased. Techniques for forming such a device are also disclosed. One aspect includes a method that uses a sacrificial material to control formation of a silicon nitride layer when forming a memory device.