3D NAND Staircase Landing Structure for Precise Word Line Contacts
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Solution Overview
Problem
The challenge in forming 3D NAND memory devices is the difficulty in creating word line contacts due to the staircase structure of conductive and dielectric layers, which can lead to over-etching, short circuits, and leakage issues.
Innovation Solution
The solution involves forming a 3D memory device with interleaved conductive and dielectric layers that create a staircase structure, where landing structures with multiple layers (a conductive first layer, a different material second layer, and optionally a conductive third layer) are used to facilitate the formation of word line contacts without causing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a staircase structure is formed by interleaved conductive and dielectric layers, then the 3D memory device achieves higher integration density, but the word line contact formation becomes difficult and prone to over-etching
Solution Approach 1:
The word line contact structure is segmented into multiple distinct layers: a first conductive layer for electrical connection, a second dielectric layer as an etch stop, and a third conductive layer for additional connectivity. This segmentation allows each layer to be optimized independently, preventing over-etching through the etch stop layer while maintaining high integration density through the stacked configuration.
Solution Approach 2:
The second dielectric layer serves as an intermediary etch stop layer between the conductive layers. This intermediate layer prevents direct through-etching to underlying structures, thereby solving the over-etching problem while allowing the staircase structure to maintain its high density configuration.
2Volume of moving object
If the staircase structure is used to increase storage capacity, then the memory device volume is reduced, but short circuits and leakage issues occur due to improper contact formation
Solution Approach 1:
The word line contact is constructed as a composite structure with multiple materials: conductive materials for electrical connectivity and a dielectric material as an etch stop. This composite structure prevents short circuits by using the dielectric layer to block unwanted electrical paths while maintaining reliable connections through the conductive layers, all within the compact staircase geometry.
Solution Approach 2:
Different regions of the contact structure have different material properties optimized for their specific functions: the conductive layers provide electrical connectivity where needed, while the dielectric layer provides insulation and etch stopping. This local differentiation of material quality prevents short circuits while maintaining the space-efficient staircase structure.
3Ease of manufacture
If conventional single-layer contact structures are used, then the manufacturing process is simple, but the contacts cannot be properly connected to conductive layers without over-etching
Solution Approach 1:
The contact structure is divided into multiple depositable layers with distinct functions. The etch stop layer is deposited between conductive layers, creating a segmented structure that can be formed using standard sequential deposition and etching processes. This segmentation maintains manufacturing simplicity while achieving precise contact connection through the controlled etching that stops at the dielectric layer.
Data Source
AI summary
A three-dimensional (3D) memory device includes interleaved conductive layers and dielectric layers. Edges of the conductive layers and dielectric layers define a plurality of stairs. The 3D memory device may also include a plurality of landing structures each disposed on a respective conductive layer at a respective stair. Each of the landing structures comprises a first layer of a first material and a second layer of a second material. The first layer is over the second layer. The second material is different from the first material.