Memory Array Conductor Tiers for Reliable Through-Array Vias
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Solution Overview
Problem
Existing memory array architectures face challenges in efficiently forming vertically-stacked memory cells with reliable electrical connections and minimizing undesired silicide formation during the manufacturing process.
Innovation Solution
The method involves forming a memory array with a 'gate-last' or 'replacement-gate' process, creating a through-array-via (TAV) region using metal-rich refractory metal nitrides, and conducting materials to establish reliable electrical connections between vertically-stacked memory cells while minimizing silicide formation through controlled etching and material replacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional memory array formation processes are used, then manufacturing simplicity is maintained, but undesired silicide formation occurs and electrical connection reliability deteriorates
Solution Approach 1:
A sacrificial layer (e.g., silicon nitride or silicon oxide) is introduced as an intermediary between the conductor tier and the substrate during TAV formation. This sacrificial layer prevents direct contact between metal layers that would otherwise form unwanted silicides, while still allowing electrical connections to be established through controlled etching processes. The sacrificial layer is subsequently removed to complete the TAV structure.
Solution Approach 2:
The invention changes the material composition and structural parameters of the TAV region by incorporating multiple conductor tiers with different materials (e.g., copper, cobalt, tungsten) and introducing sacrificial layers with specific dielectric properties. These parameter changes enable precise control over silicide formation while maintaining reliable electrical connections through the vertically-stacked memory cells.
2Reliability
If vertically-stacked memory cells are formed with through-array-via regions, then electrical connection reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The sacrificial layer is deposited and patterned before the conductor tiers are formed. This preliminary action establishes the TAV region boundaries and prevents silicide formation in advance, simplifying subsequent manufacturing steps. The sacrificial layer serves as a template that guides the formation of conductor tiers and ensures proper TAV alignment without requiring complex real-time adjustments.
Solution Approach 2:
The TAV structure is segmented into multiple conductor tiers (first conductor tier, second conductor tier, etc.) separated by insulative layers and sacrificial layers. This segmentation allows each tier to be formed and controlled independently, enabling precise electrical connections while managing manufacturing complexity through modular fabrication processes.
3Reliability
If metal-rich refractory metal nitrides are used in conductor tiers, then electrical conductivity is improved, but silicide formation risk increases
Solution Approach 1:
The sacrificial layer acts as a protective intermediary between metal-rich refractory metal nitride conductor tiers and the substrate. This intermediary prevents direct silicide formation reactions while allowing the high-conductivity metal nitrides to be deposited and patterned in the TAV region. The sacrificial layer is removed after conductor formation, leaving clean TAV interfaces without silicide contamination.
Data Source
AI summary
A memory array comprising strings of memory cells comprises a conductor tier. The conductor tier comprises upper conductor material directly above and directly against lower conductor material of different composition from that of the upper conductor material. The channel-material strings directly electrically couple to the upper and lower conductor materials of the conductor tier. A through-array-via (TAV) region is included and comprises TAVs. The TAVs individually comprise the upper conductor material, the lower conductor material, and a conducting material that is directly below the conductor tier. The lower conductor material is directly against the upper conductor material and directly against the conducting material. The lower conductor material comprises a metal-rich refractory metal nitride directly above and directly against a non-metal-rich refractory metal nitride that is directly against the conducting material. The lower conductor material may also comprise a first elemental-form metal directly above and directly against a second elemental-form metal that is directly against the conducting material Methods are also disclosed.