Split Nitride Memory Layer for SONOS Data Retention
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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 variations in 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, separated by a thin oxide layer, to improve stoichiometry and reduce charge leakage, with tailored process parameters for CVD deposition to achieve optimal thickness and composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-step CVD process with fixed parameters is used to form the nitride layer, then the manufacturing process is simple and fast, but the stoichiometry is non-uniform and data retention is poor
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 formed with specific nitrogen and oxygen concentrations to achieve uniform overall stoichiometry while maintaining manufacturing feasibility through sequential deposition processes
Solution Approach 2:
Different regions of the nitride layer structure are assigned different local compositions: the first nitride layer has high nitrogen concentration, the second nitride layer has balanced stoichiometry, and the third nitride layer has high oxygen concentration. This local quality variation ensures uniform charge storage characteristics throughout the 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 multiple thinner sub-layers with controlled individual thicknesses. This segmentation maintains adequate charge storage capacity while ensuring each sub-layer has uniform stoichiometry, preventing leakage pathways that would occur in a single thick layer with non-uniform composition
Solution Approach 2:
The nitride layer is constructed as a composite structure with multiple materials having different stoichiometries. The combination of nitrogen-rich, stoichiometric-balance, and oxygen-rich regions creates a composite material that achieves both high charge storage capacity and low leakage current through synergistic properties of the constituent layers
3Productivity
If nitrogen concentration is increased to improve charge storage, then programming speed improves, but data retention deteriorates due to charge trapping and leakage
Solution Approach 1:
High nitrogen concentration is localized to the first nitride layer to enable fast programming, while the second and third nitride layers have balanced and oxygen-rich compositions respectively to prevent charge trapping and leakage. This spatial distribution of nitrogen concentration achieves both fast programming and reliable data retention
4Reliability
If oxygen concentration is increased to reduce leakage, then data retention improves, but programming speed decreases due to reduced charge storage capacity
Solution Approach 1:
High oxygen concentration is localized to the third nitride layer to suppress leakage and improve data retention, while the first nitride layer maintains high nitrogen concentration for fast programming. The second nitride layer provides balanced stoichiometry, creating a gradient structure that optimizes both programming speed and 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 programming and erase speed, and extends the operating life of memory devices by reducing charge leakage through the nitride boundaries, while maintaining initial voltage differences between programming and erase operations.
Implementation Method 1
The charge storing layer may include a bottom silicon-rich, oxygen-rich nitride layer and a top silicon-rich, nitrogen-rich, oxygen-lean nitride layer... Tailored process parameters for CVD deposition
Implementation Method 2
electrons are induced into a floating gate of a memory cell to be programmed by biasing a control gate and grounding a body region
Implementation Method 3
An oxide-nitride-oxide (ONO) stack may be used as either a charge storing layer, as in silicon-oxide-nitride-oxide-silicon (SONOS) transistor
Data Source
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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.