3D Memory Array Pillar Structure for Stable Vertical Cell Strings
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Solution Overview
Problem
The challenge in memory array fabrication is the occurrence of 'block-bending' during the process, where vertically-stacked memory cell blocks tilt sideways relative to their longitudinal orientation, leading to structural instability and potential defects in the memory array.
Innovation Solution
The method involves forming a memory array using a 'gate-last' or 'replacement-gate' process, where a lower stack with alternating insulative and conductive tiers is created, followed by the formation of channel openings and sacrificial material, which is later removed to form channel material strings. This process ensures direct electrical coupling and stability of the memory cells, with additional steps involving the formation of upper and lower holes and the replacement of sacrificial material to create conductive lines and insulative pillars, resulting in a stable array of memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional fabrication processes are used to form vertically-stacked memory cell blocks, then memory array fabrication can proceed with standard processes, but block-bending occurs causing structural instability and defects
Solution Approach 1:
The method performs preliminary actions by forming sacrificial material in holes before forming the memory cell blocks, and then removing the sacrificial material to create voids that prevent block-bending during fabrication. This preliminary preparation of the structural environment ensures stable vertical orientation of memory cell blocks throughout the fabrication process.
2Quantity of substance
If memory cell blocks are formed with vertical stacking to increase density, then storage capacity improves, but block-bending occurs leading to structural instability
Solution Approach 1:
The sacrificial material acts as an intermediary substance formed in holes between memory cell blocks during fabrication. This material is temporarily present to provide structural support and prevent block-bending, then removed to create voids that maintain the vertical orientation of the high-density stacked memory cell blocks throughout operation.
3Device complexity
If standard fabrication processes are used without sacrificial material, then the manufacturing process is simpler, but channel material strings cannot be properly formed
Solution Approach 1:
The method performs preliminary action by forming sacrificial material in holes before forming channel openings and channel material. The sacrificial material defines the precise location where channel material will be deposited, ensuring accurate formation of channel material strings that connect source and drain regions vertically through the memory cell blocks.
Data Source
AI summary
In some embodiments, a memory array comprising strings of memory cells comprise laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers. Operative channel-material strings of memory cells extend through the insulative tiers and the conductive tiers. Insulative pillars are laterally-between and longitudinally-along immediately-laterally-adjacent of the memory blocks. The pillars comprise vertically-spaced and radially-projecting insulative rings in the conductive tiers as compared to the insulative tiers. Other embodiments, including methods, are disclosed.