3D NAND Silicon Pillar Crank-Shaped Through-Hole Alignment
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Solution Overview
Problem
In three-dimensionally integrated nonvolatile semiconductor memory devices, increasing the number of stacks to enhance memory capacity is hindered by the difficulty in collectively forming through-holes, leading to small cross-sectional areas and increased resistance in silicon pillars due to shifting central axes, which complicates the manufacturing process and increases costs.
Innovation Solution
A method involving the alternately stacked insulating and electrode films with through-holes having central axes that shift in a crank-like configuration, ensuring a larger connecting portion cross-sectional area, thereby maintaining low resistance and reducing manufacturing complexity by forming sacrificial members and insulating layers within these holes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of stacks is increased to enhance memory capacity, then bit density is improved, but it becomes difficult to collectively make through-holes, requiring multiple processes and increasing manufacturing complexity
Solution Approach 1:
The through-hole formation process is divided into multiple stages corresponding to different stacked bodies. Each stacked body's through-holes are formed collectively in one lithography process, then subsequent stacked bodies are added and their through-holes are formed in subsequent lithography processes. This segmentation allows collective patterning at each stage while accommodating increased stack numbers.
Solution Approach 2:
Sacrificial members are preliminarily formed in the through-holes before the through-holes are completely formed. These sacrificial members (such as oxide films or nitride films) are deposited in advance and then removed later by etching after the through-holes are formed through all stacked bodies. This preliminary action protects the through-hole structure during manufacturing and ensures proper formation.
2Ease of manufacture
If through-holes are made by multiple processes due to difficulty in collective patterning, then through-hole formation becomes feasible, but shifting of central axes occurs between processes, reducing cross-sectional area and increasing resistance
Solution Approach 1:
Sacrificial members act as intermediaries during the through-hole formation process. They are preliminarily formed in the through-holes, then the through-holes are formed through multiple lithography processes. The sacrificial members protect the through-hole structure and ensure that even when central axes shift slightly between processes, the cross-sectional area is maintained and resistance is prevented from increasing.
Solution Approach 2:
The sacrificial members provide beforehand cushioning against the harmful effect of central axis shifting. By having these protective layers in place before the through-holes are completely formed, any misalignment between lithography processes is compensated, preventing reduction in cross-sectional area and maintaining low resistance in the silicon pillars.
3Adaptability or versatility
If central axes of through-holes shift between stacked bodies, then manufacturing flexibility is improved, but cross-sectional area of connecting portions decreases and resistance increases
Solution Approach 1:
Sacrificial members serve as intermediaries that maintain the structural integrity of through-holes even when central axes shift between stacked bodies. These preliminarily formed sacrificial members ensure that the connecting portions maintain adequate cross-sectional area, preventing resistance increase and ensuring reliable electrical connections between silicon pillars across multiple stacked bodies.
Data Source
AI summary
A nonvolatile semiconductor memory device includes a first stacked body on a silicon substrate, and a second stacked body is provided thereon. The first stacked body includes a plurality of insulating films alternately stacked with a plurality of electrode films, and a first portion of a through-hole extending in a stacking direction is formed. The second stacked body includes a plurality of insulating films alternately stacked with a plurality of electrode films, and a second portion of the through-hole is formed. A memory film is formed on an inner face of the through-hole, and a silicon pillar is buried in an interior of the through-hole. A central axis of the second portion of the through-hole is shifted from a central axis of the first portion, and a lower end of the second portion is positioned lower than an upper portion of the first portion.