Angled Word Line Contact in 3D Memory Stacks
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in efficiently manufacturing angled word lines and forming reliable contact structures within the complex stack structures of monolithic NAND strings, which affects the density and reliability of memory arrays.
Innovation Solution
The approach involves forming a mesa structure over a substrate with alternating stacks of insulating and conductive layers, where the conductive layers have horizontal and non-horizontal sub-portions, and forming memory stack structures with vertical semiconductor channels, enabling the creation of angled word lines and contact via structures directly on the top surfaces of these conductive layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional manufacturing methods are used for three-dimensional memory devices, then the structure can be formed, but the manufacturing complexity increases and yield decreases
Solution Approach 1:
The conductive layers are formed with pre-defined angled orientations during the alternating stack formation process, before the actual word line contact structures need to be created. This preliminary structuring eliminates the need for complex post-processing alignment steps, directly reducing manufacturing complexity and improving yield.
Solution Approach 2:
The conductive layers are divided into distinct horizontal sub-portions and non-horizontal sub-portions, each serving specific functions. The horizontal portions provide planar contact surfaces while the non-horizontal portions create the angled word line trajectories, simplifying the overall manufacturing process by breaking down the complex angled contact formation into manageable segments.
2Quantity of substance
If angled word lines are formed in complex stack structures, then memory density can be improved, but the difficulty of forming reliable contact structures increases
Solution Approach 1:
The conductive layers are extended into the vertical dimension with non-horizontal sub-portions that angle downward toward the substrate. This three-dimensional configuration allows word lines to traverse through the memory stack at angles, increasing the effective memory density by utilizing vertical space more efficiently while maintaining reliable contact formation through the horizontal sub-portions.
Solution Approach 2:
Different regions of the conductive layers are assigned different orientations and functions: horizontal sub-portions provide stable contact surfaces for via structures, while non-horizontal sub-portions create the angled word line paths. This local differentiation simplifies contact structure formation by providing dedicated contact regions while achieving high density through angled routing in other regions.
3Quantity of substance
If alternating stacks with multiple layers are used, then memory density increases, but the manufacturing process becomes more complex
Solution Approach 1:
The alternating stack of insulating and conductive layers serves multiple functions simultaneously: it provides the memory structure, defines the word line pathways through angled conductive layers, and creates contact regions through horizontal sub-portions. This multi-functionality reduces the need for additional specialized processing steps, simplifying manufacturing while maintaining high density.
Solution Approach 2:
The formation of the alternating stack combines the creation of memory structures, word line pathways, and contact regions into a single integrated process sequence. By merging these functions into one unified stack formation approach, the manufacturing process avoids multiple separate complex steps, thereby simplifying production while achieving high memory density.
Data Source
AI summary
A mesa structure is formed over peripheral devices on a substrate. An alternating stack of insulating layers and spacer material layers is formed over the substrate and the mesa structure. A region of the alternating stack overlying the mesa structure is removed to provide a region in which the layers in the alternating stack extend along a non-horizontal direction that is parallel to the dielectric sidewall of the mesa structure. Memory stack structures and backside contact via structures are formed through another region of the alternating stack that includes horizontally-extending portions of the layers within the alternating stack. The spacer material layers are provided as, or are replaced with, electrically conductive layers. Top surfaces of portions of the electrically conductive layers that extend parallel to the dielectric sidewall of the mesa structure can be contacted by word line contact via structures.