Offset Backside Contact Via Structures for 3D Memory
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Solution Overview
Problem
Current three-dimensional memory devices face challenges in efficiently forming backside contact via structures that provide adequate lateral separation and structural stability, leading to issues such as die cracking and stress distribution during manufacturing and operation.
Innovation Solution
The implementation of wiggled backside contact via structures, which laterally extend and offset along a second horizontal direction perpendicular to the first horizontal direction, are formed through an alternating stack of insulating and sacrificial layers, allowing for vertical extension and separation of memory stack structures, and include specific geometries to enhance mechanical stability and reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional backside contact via structures are used, then manufacturing process is simpler, but die cracking and stress concentration occur
Solution Approach 1:
The backside contact via structures are formed with curved or rounded corners instead of sharp 90-degree angles. This curvature distributes stress more uniformly across the via structure and surrounding substrate, preventing stress concentration at corners that would lead to die cracking. The rounded geometry maintains structural integrity while improving reliability.
Solution Approach 2:
The via structures extend not only vertically through the substrate but also laterally with offset portions in multiple directions. This three-dimensional configuration distributes the contact area and stress load across multiple dimensions, reducing stress concentration at any single point and preventing die cracking.
2Stability of the object's composition
If backside contact via structures provide adequate lateral separation, then structural stability improves, but manufacturing complexity increases
Solution Approach 1:
The backside contact via structures are segmented into multiple discrete portions rather than forming continuous patterns. Each via structure consists of separate offset portions that can be independently formed and controlled, simplifying the manufacturing process while maintaining adequate lateral separation for structural stability.
Solution Approach 2:
The via structures feature asymmetric offset portions that extend different distances in different lateral directions. This asymmetric design provides the necessary lateral separation for structural stability while being formed using standard photolithography and etching processes, avoiding excessive manufacturing complexity.
3Reliability
If uniform stress distribution is achieved, then die cracking is reduced, but via structure geometry becomes more complex
Solution Approach 1:
Curved corners and rounded transitions in the via structure geometry create smooth stress flow paths, distributing stress uniformly across the structure. This curvature eliminates sharp angles that would concentrate stress, achieving reliable stress distribution with a relatively simple modified via geometry.
Data Source
AI summary
Die cracking of a three dimensional memory device may be reduced by adding offsets to backside contact via structures. Each backside contact via structure can include laterally extending portions that extend along a first horizontal direction adjoined by adjoining portions that extend along a horizontal direction other than the first horizontal direction. In order to preserve periodicity of memory stack structures extending through an alternating stack of insulating layers and electrically conductive layers, the distance between an outermost row of a string of memory stack structures between a pair of backside contact via structures and a most proximal backside contact via structure can vary from a laterally extending portion to another laterally extending portion within the most proximal backside contact via structure. Source shunt lines that are parallel to bit lines can be formed over a selected subset of offset portions of the backside contact via structures.