Air Gap Rails Reduce RC Delay in 3D NAND Memory
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Solution Overview
Problem
The RC (resistance-capacitance) delay of signals in word lines adversely affects the performance of three-dimensional NAND memory devices, which existing technologies have not effectively addressed.
Innovation Solution
Incorporating air gap rails between electrically conductive layers in a three-dimensional memory device to reduce RC delay, achieved through a method involving the formation of alternating stacks of insulating and conductive layers, memory stack structures, and the creation of air gap rails within the device's structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solid conductive rails are used in three-dimensional NAND memory devices, then structural simplicity is maintained, but RC delay increases adversely affecting signal transmission performance
Solution Approach 1:
The patent applies composite materials by combining solid conductive rails with air gaps to form a hybrid structure. The air gap rail structure comprises alternating layers of conductive material and air gaps, creating a composite that reduces capacitive coupling while maintaining electrical conductivity. This composite approach resolves the contradiction by improving signal transmission performance through reduced RC delay without completely abandoning traditional solid rail structures.
Solution Approach 2:
The patent employs porous material concepts by introducing air gaps within the conductive rail structure. The air gap rail structure contains void spaces (air gaps) periodically distributed along the rail, effectively creating a porous-like configuration. This reduces the effective capacitance between adjacent rails while maintaining the structural framework, thereby reducing RC delay and improving signal transmission performance.
2Productivity
If air gap rails are introduced to reduce RC delay, then signal transmission efficiency improves, but manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by forming air gaps between conductive layers during the stacking process itself, rather than attempting to create them afterward. The alternating stack of insulating layers and electrically conductive layers is constructed with air gaps already incorporated, and subsequent recessing operations simply expose these pre-formed air gaps. This approach simplifies manufacturing by integrating air gap formation into the existing stacking sequence.
Solution Approach 2:
The patent applies segmentation by dividing the continuous conductive rail into segmented sections separated by air gaps. The air gap rail structure consists of multiple conductive segments alternating with air gap regions, which reduces capacitive coupling between adjacent rails. This segmentation is achieved through selective recessing of conductive layers to expose the air gaps, creating a series of electrically conductive segments along the rail length.
3Reliability
If air gap rails are formed through lateral recessing operations, then RC delay is reduced, but manufacturing steps increase
Solution Approach 1:
The patent applies universality by designing the alternating stack structure to serve multiple functions: it provides both the conductive pathways for signal transmission and the air gaps for RC delay reduction simultaneously. The same alternating stack formation process that creates the conductive layers also creates the air gap regions, eliminating the need for separate air gap formation steps and reducing overall manufacturing complexity.
Solution Approach 2:
The patent merges the formation of conductive rails and air gaps into a single integrated structure. The air gap rail structure combines conductive material regions and air gap regions in an alternating pattern, where both elements are formed together during the stacking process. This merging approach reduces the number of separate manufacturing operations needed compared to forming solid rails and then adding air gaps as a separate step.
Data Source
AI summary
An alternating stack of insulating layers and spacer material layers located over a substrate. The spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers. Memory stack structures are formed through the alternating stack. After formation of a backside trench, electrically-conductive-layer-level recessed cavities are formed by laterally recessing the electrically conductive layers around the backside trench. Electrically conductive rails are formed on remaining portions of the electrically conductive layers by selective deposition of a conductive material. Insulating-layer-level recessed cavities are formed by laterally recessing the insulating layers around the backside trench. A continuous insulating material layer can be formed in the insulating-layer-level recessed cavities with air gap rails cavities to reduce capacitive coupling among the electrically conducive rails.