3D NAND Wordline Sidewall Contacts for Vertical Isolation
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Solution Overview
Problem
The challenge in fabricating 3D NAND structures lies in the precise etching of vertical wordlines, which requires high selectivity to avoid unintentional connections between metal layers, limiting the types of etches that can be used and risking unintended through-etching.
Innovation Solution
A method involving the formation of a horizontal contact layer and vertical isolation of wordlines, where holes are etched through contact pads and underlying oxide/metal layer pairs, filled with silicon, and subjected to oxidation to form silicon oxide layers that isolate horizontal metal wordlines from vertical holes, followed by filling with metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high selectivity etching is used to prevent unintended connections between metal layers, then manufacturing precision is improved, but device complexity increases and limits the types of etches that can be used
Solution Approach 1:
A liner layer is introduced as an intermediary between the metal layers and the etching process. This liner acts as a protective mediator that prevents direct contact between the etchant and the metal layers, thereby avoiding unintended connections while allowing the use of less selective etching processes.
Solution Approach 2:
The liner is formed in advance before the etching of vertical wordlines. This preliminary action prepares the structure to withstand the etching process without requiring high selectivity, as the liner is already in place to protect the metal layers from unintended etching.
2Device complexity
If conventional etching methods are used without high selectivity, then device complexity is reduced, but manufacturing precision deteriorates due to risking unintended through-etching
Solution Approach 1:
The liner serves as a cushioning layer that absorbs the risk of unintended through-etching. By placing this protective layer beforehand, the process can tolerate less precise etching conditions without compromising the integrity of the metal layers, thus cushioning against potential manufacturing defects.
3Reliability
If vertical wordlines are isolated from underlying metal layers, then reliability is improved by preventing unintended connections, but device complexity increases due to additional isolation layers
Solution Approach 1:
The liner serves multiple functions: it provides electrical isolation between vertical wordlines and underlying metal layers, serves as a protective barrier during etching, and can be integrated with existing fabrication processes. This multi-functionality improves reliability without proportionally increasing device 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 precision and reduces the risk of unintended connections, allowing for more effective fabrication of 3D NAND structures by isolating vertical wordlines from underlying metal layers.
Implementation Method 1
filled with silicon, and subjected to oxidation to form silicon oxide layers that isolate horizontal metal wordlines from vertical holes
Data Source
AI summary
A three-dimensional (3D) NAND memory structure may include material layers arranged in a vertical stack including alternating horizontal insulating layers and wordline layers. The material layers may be etched to form a landing pad. A vertical wordline may extend through one or more of the horizontal wordline layers beneath the landing pad. The vertical wordline may be conductively connected to a top horizontal wordline, and the vertical wordline may be insulated from any of the horizontal wordlines that the vertical wordline extends through beneath the top horizontal wordline. A liner may also be formed over a top horizontal wordline at the landing pad.