Backside Contact Via Structure for 3D Memory Trench Reliability
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Solution Overview
Problem
Existing three-dimensional memory devices face challenges in efficiently forming composite backside metal fill structures that ensure reliable electrical connectivity and structural integrity, particularly in the context of vertical NAND strings with one bit per cell.
Innovation Solution
The formation of a three-dimensional memory device involves creating a backside trench fill structure with a backside trench insulating spacer and a backside contact via structure, comprising a first metal layer, a metallic nitride liner, and a core fill conductive material, which includes a tapered metallic nitride liner to enhance electrical connectivity and structural support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a simple metal fill structure is used in the backside trench, then the manufacturing process is simpler, but the electrical conductivity and structural integrity are insufficient
Solution Approach 1:
The backside contact via structure uses a composite material system consisting of a metal layer (e.g., tungsten), a metallic nitride liner (e.g., titanium nitride), and a core fill conductive material. This composite structure combines the advantages of each material: the metal provides structural strength, the nitride liner provides electrical conductivity and adhesion, and the core fill material provides additional conductivity and stress relief, thereby achieving both high reliability and controlled complexity
Solution Approach 2:
The backside contact via structure is divided into multiple functional layers: a first metal layer forming the base structure, a metallic nitride liner providing electrical contact and adhesion to the insulating spacer, and a core fill conductive material providing additional conductivity. This segmentation allows each layer to be optimized for its specific function while working together to achieve overall electrical connectivity and structural integrity
2Reliability
If a uniform metallic nitride liner is used throughout the backside trench, then the manufacturing process is simpler, but the electrical connectivity at different depths is insufficient
Solution Approach 1:
The metallic nitride liner is applied selectively at different locations within the backside trench with different thicknesses or compositions. The liner is conformally deposited on the sidewalls to ensure electrical contact at all depths, while a tapered or reduced liner thickness is used in the upper portion to reduce stress and accommodate the core fill material. This local variation in liner quality optimizes electrical connectivity throughout the trench while managing structural constraints
Solution Approach 2:
The solution transitions from a two-dimensional uniform liner to a three-dimensional tapered liner structure. The liner thickness varies vertically along the trench depth, being thicker at the bottom for optimal electrical contact and thinner at the top to reduce stress and accommodate the core fill. This dimensional variation allows the structure to satisfy electrical connectivity requirements at different depths while maintaining overall structural integrity
3Strength
If the backside trench is left empty or filled with simple insulating material, then the manufacturing process is simpler, but the structural support and stress distribution are insufficient
Solution Approach 1:
The backside trench is filled with a composite structure combining the metallic nitride liner, the first metal layer, and the core fill conductive material. This composite fill structure provides both mechanical support to maintain trench integrity and electrical conductivity for signal transmission. The combination of materials with different mechanical and electrical properties creates a structurally robust and electrically functional fill that prevents trench collapse while supporting the overall device architecture
Solution Approach 2:
The backside contact via structure serves multiple functions simultaneously: it provides structural support to maintain the integrity of the backside trench, acts as an electrical conductor for signal transmission, and distributes mechanical stress to prevent device failure. By integrating these multiple functions into a single composite structure, the design achieves high structural integrity without proportionally increasing manufacturing complexity
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 enhances the electrical conductivity and structural integrity of the memory device by providing a robust backside trench fill structure, ensuring reliable connections and improved performance of vertical NAND strings.
Implementation Method 1
nitriding the first metal layer to form a second metallic nitride liner
Data Source
AI summary
A three dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers located over a substrate; memory stack structures vertically extending through the alternating stack; and a backside trench fill structure. The backside trench fill structure includes a backside trench insulating spacer and a backside contact via structure. The backside contact via structure may include a tapered metallic nitride liner and at least one core fill conductive material portion. Alternatively, the backside contact via structure may include a tungsten nitride liner, a metallic nitride liner other than tungsten nitride, and at least one core fill conductive material portion.