Discrete Charge Trap Segments in 3D NAND Memory
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Solution Overview
Problem
Conventional three-dimensional NAND memories suffer from data retention issues due to charge migration in continuous charge trap layers, leading to degradation of stored data.
Innovation Solution
The method involves forming discrete charge trap segments instead of continuous layers, using a sacrificial blocking layer, buffer layer, and front side recesses to create separate charge storage segments, which improves data retention by isolating charge storage within each device level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous charge trap layers are used, then manufacturing process is simpler, but charge migration occurs between memory cells causing data retention issues
Solution Approach 1:
The continuous charge trap layer is divided into discrete charge trap segments, with each segment confined to a specific device level and separated by blocking dielectric material. This segmentation prevents charge migration between adjacent memory cells while maintaining manufacturing feasibility through selective etching processes.
2Reliability
If discrete charge trap segments are formed, then charge migration is prevented, but manufacturing process becomes more complex involving multiple etching steps
Solution Approach 1:
A blocking layer is formed over the charge trap layer before subsequent processing steps. This preliminary blocking layer serves as a mask during selective etching operations, enabling the formation of discrete charge trap segments without requiring complex alignment procedures. The blocking layer is later removed to complete the segmentation process.
3Reliability
If blocking layer and buffer layer are added, then discrete charge trap segments are achieved, but device structure becomes more complex
Solution Approach 1:
The blocking layer and buffer layer are introduced as temporary structural elements that enable precise formation of discrete charge trap segments. These layers are strategically positioned and subsequently removed after serving their masking and protection functions, leaving behind the desired segmented charge trap structure without permanent additional complexity.
Data Source
AI summary
A method of making a monolithic three dimensional NAND string includes forming a stack of alternating layers of a first material and a second material different from the first material over a substrate, etching the stack to form at least one opening in the stack, forming a buffer layer over a sidewall of the at least one opening, forming a charge storage material layer over the buffer layer, forming a tunnel dielectric layer over the charge storage material layer in the at least one opening, and forming a semiconductor channel material over the tunnel dielectric layer in the at least one opening. The method also includes selectively removing the second material layers without removing the first material layers and etching the buffer layer using the first material layers as a mask to form a plurality of separate discrete buffer segments and to expose portions of the charge storage material layer.