3D Memory Drain Select Isolation with Segmented Sidewalls
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in effectively isolating drain select level structures, which affects the selection of memory stack structures and the replacement of sacrificial material layers, leading to inefficiencies in memory array fabrication.
Innovation Solution
The implementation of drain select level isolation structures using dielectric material with lengthwise sidewalls featuring alternating sequences of planar and convex-concave portions, allowing for precise isolation and enabling the replacement of sacrificial material layers between drain select level isolation strips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional isolation structures are used, then manufacturing process is simpler, but selection of memory stack structures and replacement of sacrificial material layers is ineffective
Solution Approach 1:
The isolation structure is segmented into alternating planar sidewall portions and convex-concave sidewall portions along the lengthwise direction. This segmentation allows different portions to serve different functions: planar portions provide structural stability while convex-concave portions enable effective isolation and sacrificial material layer replacement, thereby improving selection effectiveness without requiring complete structural redesign.
Solution Approach 2:
Different portions of the sidewalls are given different geometrical qualities - planar sections for structural integrity and convex-concave sections for isolation functionality. This local differentiation allows the isolation structure to simultaneously maintain stability and achieve effective sacrificial material layer replacement, resolving the contradiction between reliability and complexity.
2Productivity
If conventional isolation structures are used, then device structure is simpler, but fabrication efficiency is reduced
Solution Approach 1:
The sidewalls are divided into functional segments where convex portions facilitate sacrificial material layer removal and concave portions provide isolation. This segmentation enables more efficient fabrication by allowing targeted access to sacrificial layers without compromising overall structural integrity, thus improving productivity despite increased complexity.
Solution Approach 2:
The convex-concave sidewall structure is formed in advance during the isolation structure fabrication process. This preliminary action creates built-in access pathways that facilitate subsequent sacrificial material layer replacement, improving overall fabrication efficiency by preparing the structure for future operations.
3Reliability
If isolation structures with convex-concave sidewalls are implemented, then sacrificial material layer replacement is enabled, but manufacturing precision requirements increase
Solution Approach 1:
The sidewall is segmented into planar and convex-concave portions, where each segment has specific geometrical requirements. This segmentation allows manufacturing processes to focus precision on critical convex-concave transition zones while maintaining tolerance on planar sections, thereby achieving effective isolation without requiring uniform high precision across the entire sidewall.
Solution Approach 2:
Different precision requirements are applied locally - high precision is needed for convex-concave transition zones to ensure proper isolation functionality, while planar portions can tolerate broader tolerances. This localized precision approach enables effective isolation while reducing overall manufacturing complexity.
Data Source
AI summary
A three-dimensional memory structure includes an alternating stack of insulating layers and electrically conductive layers located over a substrate, an array of memory stack structures extending through the alternating stack, an array of drain select level assemblies overlying the alternating stack and having a same periodicity as the array of memory stack structures, drain select gate electrodes laterally surrounding respective rows of the drain select level assemblies, and a drain select level isolation strip located between a neighboring pair of drain select gate electrodes and including a pair of lengthwise sidewalls. Each of the pair of lengthwise sidewalls includes a laterally alternating sequence of planar sidewall portions and convexconcave sidewall portions.