3D NAND Memory Array Bridges for Electrical Isolation and Access
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Solution Overview
Problem
Current memory array technologies face challenges in efficiently forming vertically-stacked memory cells with reliable electrical access and isolation, particularly in the formation of NAND architecture, where the stair-step structure and contact regions require precise electrical connections and insulation to maintain data retention and access.
Innovation Solution
The method involves forming a memory array with a 'gate-last' or 'replacement-gate' processing approach, where vertically-alternating conductive and insulative tiers are created with sacrificial and bridging materials, and channel openings and trenches are etched to form channel-material strings, which are then electrically coupled with conductive material, ensuring reliable access and isolation between memory blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertically-stacked memory cells are formed with stair-step structure, then electrical access to wordlines is achieved, but manufacturing complexity and precision requirements increase
Solution Approach 1:
Sacrificial material is deposited and patterned in advance to define the precise locations where etching will occur. This preliminary structuring of sacrificial material creates a template that guides subsequent isotropic etching, ensuring that contact holes are formed at the correct positions with appropriate dimensions before the actual electrical connections are established
Solution Approach 2:
Sacrificial material serves as an intermediary element that temporarily occupies the space where future electrical contacts will be formed. This intermediary structure enables precise positioning of contact holes through isotropic etching, and after the contacts are established, the sacrificial material is removed, having fulfilled its mediating role in achieving precise electrical access
2Reliability
If bridges are formed between memory blocks using sacrificial material, then lateral electrical isolation is achieved, but device complexity increases
Solution Approach 1:
The sacrificial material is selectively removed through isotropic etching to create bridges between memory blocks. By extracting the sacrificial material from specific regions while leaving it in other regions, the method creates the desired bridge structures that provide lateral electrical isolation where needed, simplifying the overall device structure by using a single material system for multiple functions
Solution Approach 2:
The sacrificial material serves multiple functions: it defines contact hole positions, creates lateral bridges for electrical isolation, and can be selectively removed or retained depending on the desired structure. This multi-functional use of a single material system reduces device complexity by eliminating the need for multiple specialized materials and processing steps
3Manufacturing precision
If isotropic etching is used to remove sacrificial material, then precise contact hole formation is achieved, but etching selectivity requirements increase
Solution Approach 1:
The sacrificial material is designed with specific local properties that enable selective isotropic etching. By controlling the composition, thickness, and structure of the sacrificial material in different regions, the method achieves precise contact hole formation while maintaining adequate etching selectivity, as the local quality of the sacrificial material is optimized for the specific etching conditions
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 formation of efficient memory arrays with reliable electrical access and isolation, enhancing data retention and access capabilities, particularly in NAND architecture, by using sacrificial and bridging materials to create longitudinally-spaced bridges and intervening material for lateral electrical isolation.
Implementation Method 1
The sacrificial material is isotropically etched from the lowest first tier through the trenches selectively relative to the bridging material
Data Source
AI summary
A memory array comprises laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers. Channel-material strings of memory cells extend through the insulative tiers and the conductive tiers. Intervening material is laterally-between and longitudinally-along immediately-laterally-adjacent of the memory blocks. The intervening material in a lowest of the conductive tiers comprises intervenor material. Bridges extend laterally-between the immediately-laterally-adjacent memory blocks. The bridges comprise bridging material that is of different composition from that of the intervenor material. The bridges are longitudinally-spaced-along the immediately-laterally-adjacent memory blocks by the intervenor material and extend laterally into the immediately-laterally-adjacent memory blocks. Other embodiments, including method, are disclosed.