Stair-Step Memory Array Fabrication via Gate-Last Process
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Solution Overview
Problem
The challenge in integrated circuitry fabrication is the occurrence of 'block-bending' during the formation of vertically-stacked memory cells, where the block stack tilts sideways relative to its longitudinal orientation, leading to structural instability and potential electrical connectivity issues.
Innovation Solution
A 'gate-last' or 'replacement-gate' process is employed, where a stair-step structure is formed with vertically-alternating insulative and conductive tiers, and sacrificial material is used to create cavities with insulative material filling, ensuring direct electrical coupling and preventing structural defects like delamination and voids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertically-stacked memory cells are formed using conventional processes, then memory array fabrication can proceed, but block-bending occurs causing structural instability and electrical connectivity issues
Solution Approach 1:
The method performs preliminary actions by forming insulative material within cavities of the stair-step structure before completing the memory cell formation. This preliminary filling action prevents block-bending by establishing structural support in advance, ensuring proper alignment and eliminating voids that would compromise structural stability and electrical connectivity.
Solution Approach 2:
The insulative material acts as an intermediary substance within the cavities of the stair-step structure. This intermediary material provides structural support and prevents direct contact between adjacent conductive tiers that would cause short circuits, while also preventing void formation that would lead to electrical connectivity issues. The intermediary insulative material resolves the contradiction by maintaining both structural stability and proper electrical isolation.
2Reliability
If sacrificial material is used to create cavities in the stair-step structure, then electrical connectivity can be enhanced, but voids and delamination may occur
Solution Approach 1:
The method extracts the sacrificial material from the cavities after it has served its purpose of defining the cavity structure and ensuring proper electrical connectivity. By removing the sacrificial material and replacing it with insulative material, the process eliminates the source of potential voids and delamination while maintaining the electrical connectivity benefits provided by the cavity structure.
Solution Approach 2:
The method changes the material parameter within the cavities from sacrificial material to insulative material. This parameter change maintains the cavity structure necessary for electrical connectivity while eliminating the weaknesses associated with sacrificial material, such as void formation and delamination. The insulative material provides both structural integrity and electrical isolation.
Data Source
AI summary
A method used in forming integrated circuitry comprises forming a stack comprising vertically-alternating first tiers and second tiers. The stack comprises a cavity therein that comprises a stair-step structure. At least a portion of sidewalls of the cavity is lined with sacrificial material. Insulative material is formed in the cavity radially inward of the sacrificial material. At least some of the sacrificial material is removed from being between the cavity sidewalls and the insulative material to form a void space there-between. Insulator material is formed in at least some of the void space. Other embodiments, including structure independent of method, are disclosed.