Vertical Charge-Trap Memory Structure for VNAND Retention
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Solution Overview
Problem
The retention characteristics of VNAND flash memory devices deteriorate due to charge trapping layers extending vertically, leading to reliability issues.
Innovation Solution
A vertical memory device design featuring charge storage structures with tunnel insulation, charge trapping, and blocking patterns sequentially stacked on the sidewalls of vertical channels, along with gate electrodes, where the charge trapping patterns are spaced apart and formed using nitridation and oxidation processes to enhance retention characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If charge trapping layer extends vertically along the outer sidewall of vertical channel, then storage capacity is increased, but retention characteristic deteriorates
Solution Approach 1:
The charge trapping layer is divided into multiple discrete charge trapping patterns arranged vertically along the outer sidewall of the vertical channel. These patterns are spaced apart from each other in the vertical direction, preventing continuous vertical charge movement while maintaining storage capacity. The segmentation approach transforms a continuous problematic structure into discrete functional units.
Solution Approach 2:
The patent extracts and removes portions of the charge trapping layer to create gaps between charge trapping patterns. By taking out sections of the charge trapping material, the continuous vertical path for charge movement is interrupted, thereby improving retention characteristics while preserving the overall storage function.
2Ease of operation
If multiple gate electrodes are used at multiple levels to move charges, then charge control capability is improved, but charge movement in vertical direction increases causing retention deterioration
Solution Approach 1:
Different regions of the charge storage structure are designed with different properties: the charge trapping patterns have localized charge storage regions with varying materials or structures to control charge movement in specific areas. This allows selective charge control at different vertical levels without enabling unwanted vertical charge migration throughout the entire structure.
3Reliability
If charge trapping patterns are spaced apart vertically, then vertical charge movement is prevented improving retention, but storage capacity may be reduced
Solution Approach 1:
The charge trapping patterns are arranged not only vertically but also extend in horizontal directions (radially outward from the channel). By utilizing multiple spatial dimensions for charge storage, the patent compensates for the vertical spacing between patterns, maintaining storage capacity while preventing vertical charge movement through the spaced arrangement.
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 enhanced retention characteristics and reliability of the vertical memory device are achieved by preventing excessive vertical movement of charges, thereby improving the overall performance and durability of the device.
Implementation Method 1
performing a first nitridation process on the preliminary charge trapping pattern through the first gap to form charge trapping patterns spaced apart from each other in a vertical direction
Implementation Method 2
performing a first oxidation process on the preliminary charge trapping pattern through the first gap to form a division pattern between the charge trapping patterns
Data Source
AI summary
A vertical memory device includes a channel extending in a vertical direction on a substrate, a charge storage structure on an outer sidewall of the channel and including a tunnel insulation pattern, a charge trapping pattern, and a first blocking pattern sequentially stacked in a horizontal direction, and gate electrodes spaced apart from each other in the vertical direction, each of which surrounds the charge storage structure. The charge storage structure includes charge trapping patterns, each of which faces one of the gate electrodes in the horizontal direction. A length in the vertical direction of an inner sidewall of each of the charge trapping patterns facing the tunnel insulation pattern is less than a length in the vertical direction of an outer sidewall thereof facing the first blocking pattern.