Bulb-Shaped Memory Stack Structures for Direct Source Contact
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Solution Overview
Problem
Current methods for forming three-dimensional memory devices, such as vertical NAND strings, face challenges in efficiently creating memory stack structures with bulging portions and source strap structures that effectively contact semiconductor channels, leading to limitations in memory density and performance.
Innovation Solution
A method involving the formation of a vertically alternating stack of electrically conductive and insulating layers over a source semiconductor layer, with memory stack structures that include a semiconductor channel surrounded by a memory film, and the use of source strap structures that contact the semiconductor channels at the bulging portion of each memory stack, enabling efficient electrical connectivity and expanded contact areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional methods are used to form memory stack structures, then manufacturing simplicity is maintained, but memory density and electrical connectivity are limited
Solution Approach 1:
The patent transitions from planar memory structures to three-dimensional vertical memory stacks, utilizing the vertical dimension to increase memory density. Multiple memory stacks are formed vertically over a substrate, with each stack containing multiple memory cells arranged in series, thereby expanding the storage capacity beyond the limitations of two-dimensional layouts.
Solution Approach 2:
The memory device is divided into multiple discrete memory stack structures, each comprising segmented components including semiconductor channels, memory films, blocking dielectric layers, and source/drain regions. This segmentation allows for independent formation and optimization of each component, enabling complex three-dimensional architectures while maintaining manufacturability through modular fabrication processes.
2Reliability
If source strap structures are formed to contact semiconductor channels, then electrical connectivity is improved, but manufacturing complexity increases
Solution Approach 1:
Source strap structures are formed prior to the formation of memory stack structures in the fabrication sequence. sacrificial semiconductor structures are initially formed, then source-level memory openings are created, followed by the formation of source strap structures that contact the semiconductor channels. This preliminary action ensures proper electrical connectivity is established before the more complex memory stack assembly is completed.
Solution Approach 2:
Source strap structures serve as intermediary conductive elements that bridge the connection between the source region and the semiconductor channels within memory stacks. These strap structures are formed as separate intermediate components that facilitate electrical contact without requiring direct integration into every memory stack, thereby simplifying the overall manufacturing process while ensuring reliable connectivity.
Data Source
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AI summary
The contact area between a source strap structure of a buried source layer and semiconductor channels within memory structures can be increased by laterally expanding a source-level volume in which the memory stack structures are formed. In one embodiment, sacrificial semiconductor pedestals can be formed in source-level memory openings prior to formation of a vertically alternating stack of insulating layers and sacrificial material layers. Memory openings can include bulging portions formed by removal of the sacrificial semiconductor pedestals. Memory stack structures can be formed with a greater sidewall surface area in the bulging portions to provide a greater contact area with the source strap structure. Alternatively, bottom portions of memory openings can be expanded selective to upper portions during, or after, formation of the memory openings to provide bulging portions and to increase the contact area with the source strap structure.