Memory Array Insulator Stack and Contact Isolation
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Solution Overview
Problem
Current memory array fabrication methods face challenges in efficiently forming vertically-stacked memory cells with precise electrical coupling and isolation structures, which affects the reliability and performance of memory arrays.
Innovation Solution
The method involves forming a stack of vertically-alternating insulative and conductive tiers with channel-material strings, using conductor-material contacts directly coupled to the channel material, and forming insulator materials and conductive vias to create isolation structures, enabling direct electrical access and isolation between memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional memory array fabrication methods are used, then the manufacturing process is simpler, but the electrical coupling and isolation between memory cells is less reliable
Solution Approach 1:
The fabrication process is segmented into distinct sequential steps: forming insulator material layers, patterning contact openings, forming conductor material contacts, patterning via openings, and forming conductive material fills. This segmentation allows each step to be optimized independently for both reliability and manufacturability, with clear process boundaries and control points.
Solution Approach 2:
Insulator material layers are formed and prepared in advance before conductor material contacts are deposited. Contact openings are patterned and etched through the insulator layers beforehand, creating a prepared substrate that ensures precise electrical coupling when conductors are later added. This preliminary preparation of isolation structures before interconnect formation enhances reliability by ensuring proper insulation is in place before electrical connections are made.
2Reliability
If direct electrical access to channel material is implemented, then the electrical coupling is improved, but the manufacturing precision requirements increase
Solution Approach 1:
Conductor material contacts serve as intermediary elements between the channel material and upper interconnect structures. These contacts are formed by depositing conductive material into patterned openings through the insulator layers, creating reliable electrical pathways. The intermediary contact structure provides a larger surface area and more tolerant alignment margins compared to direct through-via connections, thereby improving electrical coupling while reducing the stringency of manufacturing precision requirements.
Solution Approach 2:
The electrical connection is achieved by transitioning from a planar contact approach to a vertical stacked architecture. Conductor material contacts extend vertically through the insulator layers to reach the channel material, creating three-dimensional electrical pathways. This vertical dimensionality allows for better electrical coupling through direct contact while providing multiple degrees of freedom for alignment tolerance in the lateral dimensions, effectively reducing manufacturing precision constraints.
3Reliability
If isolation structures are formed between memory blocks, then the electrical isolation is improved, but the device complexity increases
Solution Approach 1:
The isolation structures are merged with the existing insulator material layers that are already present in the memory array fabrication process. By forming isolation regions using the same insulator materials and processing steps used for general dielectric layers, the patent achieves electrical isolation between memory blocks without adding separate complex isolation processing sequences. This merging approach provides reliable electrical isolation while minimizing the increase in device complexity.
Solution Approach 2:
The insulator material layers serve multiple functions simultaneously: they provide electrical isolation between conductor contacts, form the dielectric matrix for the stacked memory structure, and create isolation regions between adjacent memory blocks when patterned appropriately. This multi-functionality of the insulator layers achieves comprehensive electrical isolation without requiring dedicated isolation structures, thereby improving reliability while avoiding unnecessary complexity.
Data Source
AI summary
A method used in forming a memory array comprising strings of memory cells comprises forming a stack comprising vertically-alternating first tiers and second tiers comprising memory-block regions having channel-material strings therein. Conductor-material contacts are directly against the channel material of individual of the channel-material strings. First insulator material is formed directly above the conductor-material contacts. 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. Second insulator material is formed directly above the first insulator material and the conductor-material contacts. The second insulator material is devoid of each of the (a) and (b). Third insulator material is formed directly above the second insulator material, the first insulator material, and the conductor-material contacts. The third insulator material comprises at least one of the (a) and (b). At least one horizontally-elongated isolation structure is formed in the first and second insulator materials and in a top part of the stack in individual of the memory-block regions. Additional methods, including structure independent of method, are disclosed.