Insulating Ring Prevents Shorts in 3D NAND Via Etching
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Solution Overview
Problem
In the formation of memory arrays, particularly in NAND architecture, there is a risk of fatal shorts during the etching process for forming conductive vias due to mis-aligned masks, which can etch through memory-cell materials and cause electrical shorts between conductive lines and memory cells.
Innovation Solution
A ring of insulating material is formed circumferentially around the upwardly-projecting conducting material to prevent etching chemicals from reaching the conductive lines, thereby reducing the risk of shorts and ensuring precise etching of contact openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If etching process is performed to form conductive vias, then electrical connection between wordlines and channel material is achieved, but mis-aligned masks can etch through memory-cell materials causing fatal shorts
Solution Approach 1:
A mandrel structure is introduced as an intermediary element between the conductive via and the memory cell stack. The mandrel serves as a physical barrier that prevents etching chemicals from reaching and damaging the memory cell materials, while still allowing the conductive via to be formed for electrical connection. This intermediary structure resolves the contradiction by enabling the etching process to proceed safely without causing shorts.
Solution Approach 2:
The mandrel structure is formed in advance before the conductive via etching process. It acts as a pre-positioned protective cushion that absorbs or deflects the etching chemicals, preventing them from reaching the memory cell stack. This beforehand cushioning ensures that even if mask alignment is not perfect, the memory cells are protected from damage.
2Ease of manufacture
If mask alignment is relaxed to simplify manufacturing, then etching process becomes easier, but precision of via formation decreases leading to potential shorts
Solution Approach 1:
The mandrel acts as a mediator that decouples the precision requirements of mask alignment from the final via formation. The etching process can be performed with relaxed alignment tolerances because the mandrel provides a physical reference and protective barrier, ensuring that the via is formed with sufficient precision without requiring extremely precise mask alignment.
3Reliability
If protective structures are added around conducting material, then short prevention is improved, but device complexity increases
Solution Approach 1:
The protective structure is segmented into discrete mandrels positioned at specific locations around the conducting material, rather than forming a continuous complex structure. This segmentation provides effective short prevention at critical points while minimizing the overall added complexity. The mandrels are formed using standard photolithography and deposition processes, integrating smoothly into the existing manufacturing flow.
Data Source
AI summary
A method used in forming a memory array comprises forming a stack comprising vertically-alternating first tiers and second tiers. First insulator material is above the stack. The first insulator material comprises at least one of (a) and (b), where (a): silicon, nitrogen, and one or more of carbon, oxygen, boron, and phosphorus, and (b): silicon carbide. Channel-material strings are in and upwardly project from an uppermost material that is directly above the stack. Conducting material is directly against laterally-inner sides of individual of the upwardly-projecting channel-material strings and project upwardly from the individual upwardly-projecting channel-material strings. A ring comprising insulating material is formed individually circumferentially about the upwardly-projecting conducting material. Second insulator material is formed above the first insulator material, the ring, and the upwardly-projecting conducting material. The first and second insulator materials comprise different compositions relative one another. Conductive vias are formed in the second insulator material that are individually directly electrically coupled to the individual channel-material strings through the upwardly-projecting conducting material. Other embodiments, including structure, are disclosed.