3D NAND Support Pedestals Prevent Stack Collapse
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Solution Overview
Problem
Current methods for forming three-dimensional memory devices, such as vertical NAND strings, face challenges in creating stable and efficient structures due to mechanical stress and stack collapse during manufacturing, particularly in the formation of source conductive layers and dielectric pillars.
Innovation Solution
The approach involves forming an alternating stack of electrically conductive and insulating layers over a substrate, with an array of memory stack structures that include a semiconductor channel surrounded by a memory film, and using dielectric pillars and sacrificial rail structures to create laterally extending cavities for the source conductive layer, which reduces mechanical stress and prevents stack collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to form source conductive layers and dielectric pillars in three-dimensional memory devices, then the manufacturing process is simpler, but mechanical stress increases and stack collapse occurs
Solution Approach 1:
The patent introduces support pedestal structures and sacrificial rail structures before forming the source conductive layer. These preliminary structures provide mechanical support during the formation process, preventing stack collapse. The support pedestals are formed at the bottoms of trenches, and sacrificial rail structures are formed between memory stack structures, creating a scaffold that maintains structural integrity throughout subsequent manufacturing steps.
Solution Approach 2:
The patent uses dielectric material layers as intermediary structures between the substrate and the source conductive layer. These dielectric pillars and support structures act as mediators that distribute mechanical stress and prevent direct contact between the source conductive layer and the memory stack structures during formation, thereby reducing mechanical stress and preventing collapse.
2Reliability
If support pedestal structures and sacrificial rail structures are introduced to reduce mechanical stress, then stack stability improves, but the manufacturing process becomes more complex
Solution Approach 1:
The patent combines multiple functions into the support pedestal structures and sacrificial rail structures. These structures simultaneously provide mechanical support, define the geometry of the source conductive layer, and serve as templates for subsequent material deposition. By merging these functions into single structures, the patent reduces the number of separate manufacturing steps required.
Solution Approach 2:
The patent employs sacrificial rail structures that are temporarily formed to provide structural support during manufacturing, then selectively removed after serving their purpose. These sacrificial structures are discarded after the source conductive layer is formed, having fulfilled their temporary support function. This approach allows complex structural support without permanent complexity in the final device.
3Strength
If continuous source structures are formed using the new method, then mechanical stress is reduced and stack collapse is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies different material properties and structural characteristics to different locations within the device. Support pedestals are formed at specific locations at the bottoms of trenches, while sacrificial rail structures are formed between memory stack structures. Each local region has optimized properties for its specific function, allowing the structure to achieve high overall strength without requiring uniform high precision throughout the entire device.
Solution Approach 2:
The patent divides the source conductive layer formation into segmented steps using discrete support pedestals and sacrificial rail structures rather than forming a continuous source structure in a single step. This segmentation allows each component to be formed with relaxed precision requirements, as the overall continuous source structure emerges from the assembly of multiple precisely-positioned but individually simpler components.
Data Source
AI summary
A three-dimensional memory device includes an alternating stack of electrically conductive layers and insulating layers located over a substrate, an array of memory stack structures. A source conductive line structure is provided between the substrate and the alternating stack. The source conductive line structure includes a plurality of parallel conductive rail structures extending along a same horizontal direction and adjoined to a common conductive straddling structure. Each memory stack structure straddles a vertical interface between a conductive rail structure and a support matrix. A semiconductor channel in each memory stack structure contacts a respective conductive rail structure and the support matrix.