Multi-Layer ONO Charge Storage for SONOS Data Retention
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Solution Overview
Problem
Conventional SONOS structures suffer from poor data retention and non-uniform stoichiometry of the oxynitride layer, leading to leakage current and adverse effects on programming, erase speed, and device lifetime.
Innovation Solution
The formation of a multi-layer charge storing layer with multiple oxynitride layers, each with tailored compositions of oxygen, nitrogen, and silicon, using differing process gases and temperatures to optimize the stoichiometry and reduce charge loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-layer oxynitride layer is formed using conventional single-step deposition, then the manufacturing process is simple, but the stoichiometry is non-uniform and data retention is poor
Solution Approach 1:
The patent divides the single oxynitride charge storing layer into multiple sub-layers (first oxynitride layer, second oxynitride layer, and optionally third oxynitride layer), each with different nitrogen and oxygen concentrations. This segmentation allows optimization of stoichiometry throughout the layer thickness, resolving the contradiction between manufacturing precision and device complexity by achieving uniform stoichiometry through controlled stratification rather than single-step deposition.
Solution Approach 2:
The patent applies local quality by creating regions with different compositions within the charge storing layer. The first oxynitride layer has higher nitrogen concentration for charge trapping, while the second oxynitride layer has higher oxygen concentration for stability. This local differentiation of properties enables each region to perform its specific function optimally, improving overall data retention without requiring excessive structural complexity.
2Speed
If the oxynitride layer is formed with high nitrogen concentration for charge storage, then programming speed improves, but leakage current increases and data retention deteriorates
Solution Approach 1:
The patent segments the charge storing layer into multiple oxynitride layers with different nitrogen concentrations. The first oxynitride layer contains higher nitrogen for efficient charge trapping and fast programming, while the second oxynitride layer contains lower nitrogen but higher oxygen for reduced leakage and improved data retention. This segmentation allows the system to achieve both fast programming and reliable data retention simultaneously.
Solution Approach 2:
The patent implements local quality by creating spatial variation in nitrogen concentration within the charge storing layer. Regions closer to the floating gate have higher nitrogen for rapid charge injection, while regions farther away have lower nitrogen to minimize tunneling leakage. This local optimization of nitrogen distribution enables the device to achieve both high programming speed and excellent data retention.
3Reliability
If the oxynitride layer is formed with high oxygen concentration for stability, then data retention improves, but nitrogen concentration decreases and programming speed slows
Solution Approach 1:
The patent segments the charge storing layer into multiple oxynitride layers with different oxygen concentrations. The first oxynitride layer has lower oxygen concentration to facilitate rapid charge trapping and programming, while the second oxynitride layer has higher oxygen concentration to provide stability and reduce leakage for improved data retention. This segmentation resolves the contradiction by allowing each layer to optimize for its primary function.
Solution Approach 2:
The patent applies local quality by creating spatial variation in oxygen concentration within the charge storing layer. Regions closer to the floating gate have lower oxygen to enable fast charge injection, while regions farther away have higher oxygen to provide stability and minimize leakage. This local optimization of oxygen distribution enables the device to achieve both fast programming and excellent data retention.
4Quantity of substance
If a thick oxynitride layer is formed to improve charge storage capacity, then data retention improves, but stoichiometry uniformity deteriorates due to top and bottom effects
Solution Approach 1:
The patent divides the thick charge storing layer into multiple thinner oxynitride sub-layers, each deposited under controlled conditions. This segmentation reduces the impact of top and bottom effects within each individual layer, as the deposition conditions can be better controlled over shorter thicknesses. The cumulative charge storage capacity of multiple layers matches that of a single thick layer, while stoichiometry uniformity is improved within each segment.
Solution Approach 2:
The patent applies local quality by creating different composition profiles in different layers to compensate for top and bottom effects. The first oxynitride layer is formulated with higher nitrogen to compensate for nitrogen depletion at the top interface, while the second oxynitride layer has higher oxygen to compensate for oxygen depletion at the bottom interface. This local compensation strategy maintains stoichiometry uniformity throughout the entire thick charge storing layer.
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 enhances data retention, improves programming and erase speed, and extends the operating life of memory devices by optimizing the oxynitride layer's composition and structure.
Implementation Method 1
The first layer of the multi-layer charge storing layer including nitride is formed on a surface of the first oxide layer. The second layer of the multi-layer charge storing layer is then formed on a surface of the first layer
Data Source
AI summary
A semiconductor device including an oxide-nitride-oxide (ONO) structure having a multi-layer charge storing layer and methods of forming the same are provided. Generally, the method involves: (i) forming a first oxide layer of the ONO structure; (ii) forming a multi-layer charge storing layer comprising nitride on a surface of the first oxide layer; and (iii) forming a second oxide layer of the ONO structure on a surface of the multi-layer charge storing layer. Preferably, the charge storing layer comprises at least two silicon oxynitride layers having differing stoichiometric compositions of Oxygen, Nitrogen and/or Silicon. More preferably, the ONO structure is part of a silicon-oxide-nitride-oxide-silicon (SONOS) structure and the semiconductor device is a SONOS memory transistor. Other embodiments are also disclosed.