Multilevel Memory Stack Structure with Support Pillar Integrity
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in efficiently forming monolithic vertical NAND strings with multiple levels above a single substrate, as existing methods often result in structural defects and leakage paths due to surface damage during the formation of support pillars and memory stacks.
Innovation Solution
The method involves forming a lower tier structure with alternating insulating and sacrificial layers, creating memory and support openings, and then forming upper tier structures with additional alternating layers, where dopant species are implanted to differentiate support pillar materials from memory stack materials, allowing for the simultaneous formation of memory stack structures and support pillar structures without removing the sacrificial materials from memory openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If support pillars and memory stacks are formed using conventional methods, then the memory device structure is created, but surface damage occurs during formation causing structural defects and leakage paths
Solution Approach 1:
The patent applies preliminary action by forming a protective sacrificial layer (e.g., silicon nitride) before forming the support pillars and memory stacks. This sacrificial layer is deposited conformally across the substrate before any etching or pillar formation occurs. The layer protects the underlying substrate and prevents surface damage during subsequent processing steps. After the memory structure is formed, the sacrificial layer is selectively removed to complete the structure without having caused damage to the final device.
Solution Approach 2:
The patent uses a sacrificial material layer as an intermediary element that facilitates the formation of the memory structure without causing damage. This intermediate layer is deposited between the substrate and the memory stack structures, serving as a protective mediator during the formation process. The sacrificial material allows for selective removal after serving its protective function, eliminating the need for damaging removal processes while maintaining structural integrity throughout manufacturing.
2Quantity of substance
If multiple levels of memory arrays are stacked above a single substrate, then storage density is increased, but the process complexity and difficulty of formation increase significantly
Solution Approach 1:
The patent applies segmentation by dividing the memory device into multiple discrete tiers or levels, each containing alternating insulating and sacrificial material layers. Each tier can be formed and processed independently, with the first tier formed on the substrate, then subsequent tiers stacked above it. This segmentation allows for modular manufacturing where each level is processed separately, reducing the overall complexity compared to forming all levels simultaneously, while achieving high storage density through vertical stacking.
Solution Approach 2:
The patent transitions from two-dimensional planar memory structures to three-dimensional vertical stacking by adding the vertical dimension. Multiple memory tiers are stacked vertically above a single substrate, with each tier containing alternating layers of insulating and sacrificial materials. This dimensional change from 2D to 3D architecture dramatically increases storage density without proportionally increasing process complexity, as the same fabrication techniques are applied repeatedly in the vertical direction rather than requiring entirely new processes for each additional storage level.
3Ease of manufacture
If dopant species are implanted to differentiate support pillar materials from memory stack materials, then selective etching is enabled, but additional processing steps are required
Solution Approach 1:
The patent applies parameter changes by modifying the material properties of the sacrificial layer through dopant implantation. The sacrificial material is doped with specific dopant species (e.g., phosphorus or boron) to alter its etch selectivity parameters. This parameter change enables selective removal of the sacrificial material from the memory stack regions while leaving the support pillar regions intact, or vice versa. The dopant concentration and distribution are carefully controlled to achieve the desired etch selectivity, allowing for precise differentiation between support and memory structures through chemical parameter modification rather than requiring entirely separate formation processes.
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
This approach enables the creation of monolithic three-dimensional NAND memory devices with reduced leakage current and structural defects, improving the integrity and performance of the memory stacks by maintaining the integrity of the support pillar structures and memory stacks through precise material differentiation and selective etching.
Implementation Method 1
support opening fill structures are formed by implanting a dopant species into each upper portion of the support-opening semiconductor material portions
Data Source
AI summary
Memory-opening semiconductor material portions and support opening fill structures can be simultaneously formed through a first alternating stack of first insulating layers and first sacrificial material layers. Dopant species that retard or prevent etching of the material of the support opening fill structures can be implanted into an upper portion of each support opening fill structure, while memory-opening semiconductor material portions are masked from implantation. After formation of a second alternating stack and second openings therethrough, the sacrificial material of the memory-opening semiconductor material portions is removed while the support opening fill structures is not removed. Damage to the first sacrificial material layers during formation of the staircase contact region and resulting leakage paths from word lines to the substrate through support pillar structures can be avoided or reduced by not removing the support opening fill structures.