Memory Array Sacrificial Rail Etching Isolation
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Solution Overview
Problem
The existing methods for forming memory arrays face challenges in reducing the risk of shorts between conductor and conductive tiers during the etching process, which can lead to undesirable etching of insulative tiers and exposure of conductive tiers, affecting the integrity of the memory cell structure.
Innovation Solution
The method involves forming a stack with alternating conductive and insulative tiers, where sacrificial rails are used to create channel openings and trenches, and specific etching chemistries are employed to selectively remove materials, ensuring that channel-material strings are directly electrically coupled to the conductor tier while maintaining lateral isolation between memory blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional etching methods are used to form channel openings and trenches, then the etching process can be completed, but shorts between conductor and conductive tiers may occur due to undesirable etching of insulative tiers
Solution Approach 1:
A sacrificial rail made of sacrificial material is introduced as an intermediary structure between the conductor tier and the insulative tier. This sacrificial rail serves as a protective barrier during the etching process, preventing the etch chemistry from contacting and eroding the insulative tier material. The sacrificial rail is selectively removed after etching completes, having fulfilled its protective function. This intermediary structure resolves the contradiction by enabling complete etching while preventing shorts through the sacrificial protection mechanism.
Solution Approach 2:
The sacrificial rail is formed in advance before the etching process begins. By preliminarily placing this protective structure in position, the patent ensures that the insulative tier is protected from unwanted etching before the harmful etching action occurs. This preliminary protective action allows the subsequent etching process to proceed fully without risk of exposing the conductive tier, thereby resolving the contradiction between completing the etching and preventing shorts.
2Manufacturing precision
If aggressive etching chemistries are used to ensure complete removal of sacrificial material, then the etching process is thorough, but there is increased risk of etching into insulative tiers and exposing conductive tiers
Solution Approach 1:
The sacrificial rail acts as a protective intermediary that enables the use of aggressive etching chemistries. Because the sacrificial rail material is selectively removable and serves as a barrier, aggressive etch chemistries can be employed to ensure complete removal of the sacrificial material without directly contacting and damaging the insulative tier. The sacrificial rail absorbs the aggressive etching action, protecting the insulative tier while allowing thorough cleaning of the sacrificial material.
Solution Approach 2:
The patent employs selective etching chemistries with specific parameters tailored to differentiate between the sacrificial rail material and the insulative tier material. By changing the chemical parameters of the etching process, the system achieves high removal efficiency for the sacrificial material while maintaining selectivity that prevents etching of the insulative tier. This parameter control resolves the contradiction between thorough removal and preventing harmful etching.
3Object-generated harmful factors
If the insulative tier is completely etched away to ensure electrical isolation, then isolation between memory blocks is achieved, but conductive tiers become exposed creating shorts
Solution Approach 1:
The sacrificial rail serves as a protective intermediary that remains in place during etching to prevent exposure of the conductive tier. This intermediary structure allows the etching process to create sufficient isolation between memory blocks while simultaneously protecting the conductive tier from being exposed. The sacrificial rail is positioned such that it maintains the necessary electrical isolation without compromising the integrity of the conductive tier, thereby resolving the contradiction between achieving isolation and preventing shorts.
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 effectively reduces the risk of shorts and ensures reliable electrical coupling of channel-material strings to the conductor tier, enhancing the structural integrity and operational efficiency of the memory array.
Implementation Method 1
The etching chemistry is introduced to selectively remove the sacrificial rail through the trench
Data Source
AI summary
A memory array comprising strings of memory cells comprises laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers above a conductor tier. Strings of memory cells comprise channel-material strings that extend through the insulative tiers and the conductive tiers. The channel-material strings directly electrically couple to conductor material of the conductor tier. The insulative tier immediately-above a lowest of the conductive tiers comprises a lower first insulating material and an upper second insulating material above the upper first insulating material. The upper second insulating material is of different composition from that of the lower first insulating material. Intervening material is laterally-between and longitudinally-along immediately-laterally-adjacent of the memory blocks. Other embodiments, including method, are disclosed.