Sonos Memory Stack Split Nitride Oxynitride Layers
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Solution Overview
Problem
Conventional SONOS structures suffer from poor data retention and nonuniform stoichiometry in the nitride or oxynitride layer, leading to leakage current and adverse effects on charge storage characteristics, programming speed, and erase efficiency.
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 data retention and programming speed by optimizing the distribution of charge traps and reducing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer nitride or oxynitride layer is used in conventional SONOS structures, then the structure is simple to manufacture, but data retention is poor and leakage current is high
Solution Approach 1:
The patent divides the single-layer nitride or oxynitride charge storing layer into multiple sub-layers (first nitride layer, first oxynitride layer, second nitride layer, second oxynitride layer) with different stoichiometries and thicknesses. This segmentation allows each sub-layer to contribute differently to charge storage and leakage prevention, improving data retention while managing the complexity through systematic layering.
Solution Approach 2:
The patent employs a composite structure combining multiple nitride and oxynitride layers with varying compositions (different N:O ratios and thicknesses). This composite approach enables optimization of both data retention and leakage current by leveraging the complementary properties of each material layer, resolving the contradiction between reliability and structural simplicity.
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 nonuniform stoichiometry
Solution Approach 1:
The patent applies local quality by creating regions with different stoichiometries within the charge storing layer. The first nitride layer has higher nitrogen content for strong charge trapping, while the oxynitride layers have optimized N:O ratios to reduce leakage. This spatial variation in material composition allows the structure to simultaneously achieve high charge storage capacity and low leakage current.
Solution Approach 2:
The oxynitride layers serve as intermediary layers between the nitride layers. These intermediate layers with balanced N:O ratios act as transition zones that prevent direct charge tunneling pathways while maintaining overall charge storage capacity, thus reducing leakage current without sacrificing storage capability.
3Manufacturing precision
If a single process gas mixture is used to deposit the nitride layer, then the manufacturing process is simple, but the stoichiometry is nonuniform resulting in poor charge storage characteristics
Solution Approach 1:
The patent employs periodic action by alternating between different deposition processes (PLD and sputtering) and different gas mixtures (O2/Ar and Ar/N2) to create the multi-layer structure. This periodic switching of deposition conditions allows precise control over the stoichiometry of each layer while maintaining a systematic and repeatable manufacturing process.
Solution Approach 2:
The patent utilizes parameter changes by varying deposition parameters (power, gas flow rates, chamber pressure) and material composition (N:O ratios) for each layer. These controlled parameter changes enable precise stoichiometry uniformity within each layer while creating the desired compositional gradient across the multi-layer structure, balancing manufacturing precision with process complexity.
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 multi-layer structure enhances data retention, increases the difference between programming and erase voltages, and extends the operating life of memory devices while maintaining device speed, significantly reducing leakage current.
Implementation Method 1
electrons are induced into a floating gate of a memory cell to be programmed
Implementation Method 2
significantly reducing leakage current
Data Source
AI summary
A semiconductor device and method of manufacturing the same are provided. In one embodiment, method includes forming a first oxide layer over a substrate, forming a silicon-rich, oxygen-rich, oxynitride layer on the first oxide layer, forming a silicon-rich, nitrogen-rich, and oxygen-lean nitride layer over the oxynitride layer, and forming a second oxide layer on the nitride layer. Generally, the nitride layer includes a majority of charge traps distributed in the oxynitride layer and the nitride layer. Optionally, the method further includes forming a middle oxide layer between the oxynitride layer and the nitride layer. Other embodiments are also described.