Memory Arrays with Dummy Structures for Block-Bending Control
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Solution Overview
Problem
Memory arrays face issues with 'block-bending' during fabrication, where memory-cell pillars exhibit lateral bowing or bending due to intrinsic compressive mechanical stress, affecting the longitudinal orientation and electrical isolation between memory blocks.
Innovation Solution
Incorporating dummy structures with intrinsic tensile mechanical stress at the lateral edges and longitudinal ends of memory-cell pillars to counteract the bending force, using materials like AlOx and Si3N4, and forming these structures through specific processing techniques such as 'gate-first' processing to maintain the integrity of the memory array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory arrays are fabricated with vertically-stacked memory cells, then storage density is improved, but block-bending occurs due to intrinsic compressive mechanical stress in memory-cell pillars
Solution Approach 1:
The patent applies preliminary anti-action by forming dummy structures with tensile stress before the memory-cell pillars are fully formed. These dummy structures pre-counteract the compressive stress that will develop in the memory-cell pillars, preventing block-bending from occurring during fabrication. The dummy structures are strategically positioned at lateral edges and longitudinal ends of memory blocks to provide the necessary counterbalancing tensile force.
Solution Approach 2:
The dummy structures serve as intermediary elements that mediate between the compressive stress in memory-cell pillars and the substrate. These dummy structures transfer and balance the mechanical stresses, preventing the memory blocks from bending while maintaining the vertically-stacked architecture. The dummy structures are formed from materials with intrinsic tensile stress that compensates for the compressive stress in the operational memory structures.
2Area of stationary object
If vertically-stacked memory cells are used, then area efficiency is improved, but electrical isolation between memory blocks deteriorates due to block-bending
Solution Approach 1:
By forming dummy structures with tensile stress before completing the memory-cell pillar formation, the patent preemptively prevents block-bending that would compromise electrical isolation. This preliminary counteraction ensures that memory blocks remain properly oriented and isolated electrically throughout the fabrication process, maintaining reliability while achieving area efficiency through vertical stacking.
3Stability of the object's composition
If dummy structures are added to counteract compressive stress, then block-bending is prevented, but device complexity increases
Solution Approach 1:
The patent merges the formation of dummy structures with the existing memory fabrication process by integrating dummy structure formation into the same processing steps used for memory-cell pillars. The dummy structures are formed using the same alternating deposition of insulative and conductive tiers, and the same etching processes, thereby preventing block-bending without requiring entirely separate fabrication sequences. This merging approach minimizes the increase in device complexity.
Solution Approach 2:
The dummy structures serve multiple functions: they provide mechanical stress counterbalancing to prevent block-bending, they maintain longitudinal orientation of memory blocks, and they can be formed using the same materials and processes as the operational memory structures. This multi-functionality reduces the overall complexity by reusing existing process capabilities rather than introducing entirely new fabrication steps.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The introduction of dummy structures with tensile mechanical stress effectively offsets the compressive stress in memory-cell pillars, preventing block-bending and ensuring stable longitudinal orientation and electrical isolation between memory blocks, thereby enhancing the reliability and performance of the memory array.
Implementation Method 1
memory-cell pillars have intrinsic compressive mechanical stress... dummy structures have intrinsic tensile mechanical stress... offsets the compressive stress
Data Source
AI summary
A memory array comprising strings of memory cells comprises laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers. A horizontal pattern of operative memory-cell pillars extends through the insulative tiers and the conductive tiers in individual of the memory blocks. The operative memory-cell pillars have intrinsic compressive mechanical stress. At least one dummy structure in the individual memory blocks extends through at least upper of the insulative tiers and the conductive tiers. The at least one dummy structure is at least one of (a) and (b), where (a): at a lateral edge of the horizontal pattern, and (b): at a longitudinal end of the horizontal pattern. The at least one dummy structure has intrinsic tensile mechanical stress. Other embodiments, including methods, are disclosed.