Multi-layer Oxynitride Charge Storage for Memory Retention
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Solution Overview
Problem
Conventional SONOS structures suffer from poor data retention and non-uniform oxynitride layer stoichiometry due to leakage current and variations in nitrogen, oxygen, and silicon concentrations across the thickness of the oxynitride layer, affecting programming and erase speed and memory device lifetime.
Innovation Solution
A semiconductor memory device with a multi-layer charge storing layer comprising an oxygen-rich, silicon-rich bottom oxynitride layer and a silicon-rich, oxygen-lean top oxynitride layer, formed using different process gases and flow rates to achieve improved stoichiometry and trap density, enhancing data retention and programming speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-step deposition process is used to form the oxynitride layer, then the manufacturing process is simple and fast, but the stoichiometry of the layer is non-uniform with variations in nitrogen, oxygen and silicon concentrations
Solution Approach 1:
The single oxynitride layer is segmented into multiple sub-layers (first oxynitride layer, second oxynitride layer, and third oxynitride layer) with different stoichiometries. Each sub-layer is deposited with specific nitrogen, oxygen, and silicon concentration ratios to achieve uniform overall stoichiometry while maintaining manufacturing efficiency.
Solution Approach 2:
Different regions of the oxynitride layer are given different local compositions. The first oxynitride layer has higher nitrogen concentration, the second has balanced stoichiometry, and the third has higher oxygen concentration. This local quality variation ensures uniform charge trapping characteristics throughout the layer.
2Speed
If the oxynitride layer has high nitrogen concentration for charge storage, then programming speed is improved, but data retention deteriorates due to increased leakage current
Solution Approach 1:
The nitrogen concentration parameter is varied through the thickness of the oxynitride layer. The first oxynitride layer has higher nitrogen concentration (0.6-0.8 nitrogen atoms per formula unit) for fast programming, the second has moderate concentration (0.4-0.6) for balanced performance, and the third has lower concentration (0.2-0.4) to reduce leakage current and improve data retention.
Solution Approach 2:
The oxynitride layer is formed as a composite structure with multiple sub-layers having different chemical compositions. This composite approach combines the advantages of high nitrogen content (fast programming) with low nitrogen content (low leakage) in a single functional layer.
3Reliability
If the oxynitride layer has high oxygen concentration for reducing leakage, then data retention is improved, but programming speed deteriorates due to reduced charge trapping capability
Solution Approach 1:
The oxygen concentration parameter is varied through the thickness of the oxynitride layer. The first oxynitride layer has lower oxygen concentration (0.2-0.4 oxygen atoms per formula unit) for fast programming, the second has moderate concentration (0.3-0.5) for balanced performance, and the third has higher concentration (0.5-0.7) to reduce leakage current and improve 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
The multi-layer oxynitride structure significantly improves data retention and extends the operating life of memory devices by reducing charge loss and maintaining programming and erase voltage differences, exceeding the specified operating life of 20 years.
Implementation Method 1
an oxygen-rich, first oxynitride layer on the tunnel oxide layer in which a stoichiometric composition of the first oxynitride layer results in it being substantially trap free
Implementation Method 2
an oxygen-lean, second oxynitride layer on the first oxynitride layer in which a stoichiometric composition of the second oxynitride layer results in it being trap dense
Data Source
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AI summary
An embodiment of a semiconductor memory device including a multi-layer charge storing layer and methods of forming the same are described. Generally, the device includes a channel formed from a semiconducting material overlying a surface on a substrate connecting a source and a drain of the memory device; a tunnel oxide layer overlying the channel; and a multi-layer charge storing layer including an oxygen-rich, first oxynitride layer on the tunnel oxide layer in which a stoichiometric composition of the first oxynitride layer results in it being substantially trap free, and an oxygen-lean, second oxynitride layer on the first oxynitride layer in which a stoichiometric composition of the second oxynitride layer results in it being trap dense. In one embodiment, the device comprises a non-planar transistor including a gate having multiple surfaces abutting the channel, and the gate comprises the tunnel oxide layer and the multi-layer charge storing layer.