Nitride Sidewall Layers in Memory Gate Structures
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Solution Overview
Problem
The existing memory cell design faces issues with high memory gate voltage breakdown and reduced memory current due to charge storage in regions other than the charge storage layer, leading to operation failures and poor reading performance.
Innovation Solution
The memory cell incorporates nitride sidewall layers in the sidewall spacers, which are made of an insulating material different from the insulating layer, positioned at a distance greater than the thickness of the lower gate insulating film, to separate the memory gate structure from the select gate structures, thereby improving breakdown voltage and preventing charge injection into the sidewall layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high memory gate voltage is applied to inject charge into the charge storage layer, then charge injection efficiency is improved, but breakdown voltage around the memory gate electrode deteriorates
Solution Approach 1:
A nitride layer is introduced as an intermediary between the charge storage layer and the select gate structures. This nitride layer acts as a mediator that prevents charge from migrating into the sidewall spacers while allowing the charge injection process to proceed efficiently into the charge storage layer, thus resolving the contradiction between injection efficiency and breakdown voltage
Solution Approach 2:
The insulating layer is segmented into multiple functional layers: a lower gate insulating film, a charge storage layer, an upper gate insulating film, and sidewall spacers containing nitride layers. This segmentation allows each layer to perform its specific function - the charge storage layer accepts charge during injection, while the nitride-containing sidewall spacers prevent charge migration and provide electrical isolation, thereby maintaining both high injection efficiency and adequate breakdown voltage
2Quantity of substance
If charge is stored in regions other than the charge storage layer directly below the memory gate electrode, then charge storage capacity increases, but memory current decreases due to increased resistance
Solution Approach 1:
The harmful function of charge storage in unintended regions is extracted and eliminated by introducing nitride layers in the sidewall spacers. These nitride layers act as barriers that prevent charge from being stored in the sidewall regions, ensuring that charge is stored only in the charge storage layer directly below the memory gate electrode, thus maintaining low resistance and high memory current
Solution Approach 2:
The potential harmful effect of charge migration into sidewall spacers is converted into a beneficial structure by deliberately placing nitride layers in those regions. These nitride layers, which would otherwise be simple insulating material, become active barriers that guide charge storage to the correct location, transforming a potential failure mode into a reliable charge confinement mechanism
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 the breakdown voltage around the memory gate electrode and prevents charge storage in unintended regions, improving reading performance and achieving high-speed operation by reducing resistance and preventing short-circuit defects.
Implementation Method 1
This configuration enhances the breakdown voltage around the memory gate electrode
Implementation Method 2
prevents charge storage in unintended regions
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A memory cell and a non-volatile semiconductor memory device are disclosed. Nitride sidewall layers (32a and 32b) are respectively disposed in a first sidewall spacer (28a) and a second sidewall spacer (28b), to separate a memory gate electrode (MG) and a first select gate electrode (DG) from each other and the memory gate electrode (MG) and a second select gate electrode (SG) from each other. Hence, a breakdown voltage is improved around the memory gate electrode (MG) as compared with a conventional case in which the first sidewall spacer (28a) and the second sidewall spacer (28b) are simply made of insulating oxide films. The nitride sidewall layers (32a and 32b) are disposed farther from a memory well (MW) than a charge storage layer (EC). Hence, charge is unlikely to be injected into the nitride sidewall layers (32a and 32b) at charge injection from the memory well (MW) into the charge storage layer (EC), thereby preventing an operation failure due to charge storage in a region other than the charge storage layer (EC).