Split Nitride SONOS Stack for Leakage Reduction
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Solution Overview
Problem
Conventional SONOS structures suffer from poor data retention and non-uniform stoichiometry in the nitride or oxynitride layer, leading to leakage current and limited device lifetime due to varying nitrogen, oxygen, and silicon concentrations across the layer thickness.
Innovation Solution
A multi-layer charge storing structure is introduced, comprising a silicon-rich, oxygen-rich bottom nitride layer and a silicon-rich, nitrogen-rich, oxygen-lean top nitride layer, with a thin oxide layer in between, tailored to improve stoichiometric compositions and reduce charge loss while maintaining programming and erase speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-step deposition process is used to form the nitride layer, then the manufacturing process is simple, but the stoichiometry becomes non-uniform across the layer thickness
Solution Approach 1:
The single nitride layer is segmented into multiple sub-layers (first nitride layer, second nitride layer, third nitride layer) with different stoichiometries. Each sub-layer is deposited with controlled nitrogen and oxygen concentrations to achieve uniform overall stoichiometry while maintaining manufacturing simplicity through sequential deposition.
Solution Approach 2:
Different regions of the nitride layer structure are assigned different local qualities (stoichiometries). The first nitride layer has higher nitrogen concentration, the second has balanced stoichiometry, and the third has higher oxygen concentration. This local differentiation ensures uniform charge storage characteristics throughout the entire layer thickness.
2Quantity of substance
If the nitride layer thickness is increased to improve charge storage capacity, then more charge can be stored, but leakage current increases due to non-uniform stoichiometry
Solution Approach 1:
The thick nitride layer is divided into sub-layers with optimized local stoichiometries. The first nitride layer (higher nitrogen) provides strong charge trapping capability, the second nitride layer (balanced) ensures uniform charge distribution, and the third nitride layer (higher oxygen) reduces leakage at the interface. This local optimization allows thick layer design without proportionally increasing leakage.
Solution Approach 2:
The nitride layer is constructed as a composite structure with multiple materials having different stoichiometries. This composite approach combines the advantages of high nitrogen content (for charge storage) and high oxygen content (for leakage reduction) in different sub-layers, achieving both high charge storage capacity and low leakage current simultaneously.
3Device complexity
If conventional ONO stack is used, then the device structure is simple, but data retention is poor due to leakage through the nitride layer
Solution Approach 1:
The conventional single nitride layer is segmented into three sub-layers with different stoichiometries. This segmentation maintains the overall ONO stack simplicity while significantly improving data retention by reducing leakage current through the optimized multi-layer nitride structure.
Solution Approach 2:
The nitride layer is replaced with a composite oxynitride structure having graded stoichiometry. This composite material approach maintains structural simplicity while improving reliability by creating a more effective charge storage medium that reduces leakage and enhances data retention.
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 configuration enhances data retention, increases device speed, and extends the operating life of memory devices by reducing leakage current and improving charge storage characteristics.
Implementation Method 1
a bottom nitride layer closer to the tunnel oxide and oxygen-rich relative to the other nitride layer to reduce stored charge loss
Implementation Method 2
a top nitride layer having a stoichiometric composition of oxygen, nitrogen and/or silicon different from that of the bottom nitride layer... the top nitride layer has high silicon and a high nitrogen concentration with a low oxygen concentration
Implementation Method 3
with a thin oxide layer in between
Data Source
AI summary
Embodiments of a non-planar memory device including a split charge-trapping region and methods of forming the same are described. Generally, the device comprises: a channel formed from a thin film of semiconducting material overlying a surface on a substrate connecting a source and a drain of the memory device; a tunnel oxide overlying the channel; a split charge-trapping region overlying the tunnel oxide, the split charge-trapping region including a bottom charge-trapping layer comprising a nitride closer to the tunnel oxide, and a top charge-trapping layer, wherein the bottom charge-trapping layer is separated from the top charge-trapping layer by a thin anti-tunneling layer comprising an oxide. Other embodiments are also disclosed.