Elliptical Contact Layout for Bent 3D NAND Pillar Alignment
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Solution Overview
Problem
Conventional methods for forming microelectronic devices, such as 3D NAND memory devices, result in undesirable stresses, defects, and current leaks due to increased feature packing densities and decreased margins for formation errors, while also facing challenges in reducing electrical resistance and capacitance of word lines without causing pillar bending.
Innovation Solution
The use of tailored reticles to form openings and elliptical openings in microelectronic device structures, accommodating observed pillar bending and misalignment, improves the overlap between pillars and upper pillar structures, and between conductive contacts and access lines, thereby enhancing electrical connections and reducing dummy pillar areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If feature packing density is increased to enhance memory density, then memory capacity increases, but formation errors and manufacturing defects increase
Solution Approach 1:
The patent applies preliminary action by forming pillars with intentional offset positions before forming the upper deck. The offset amount is predetermined based on expected bending characteristics, allowing the structure to be pre-compensated for anticipated deformation. This proactive approach prevents alignment issues from arising during subsequent fabrication steps.
Solution Approach 2:
The patent changes the positional parameter of pillars by introducing intentional offsets from their ideal aligned positions. By modifying the pillar position parameter in the lower deck relative to the upper deck, the design accommodates expected bending and misalignment, thereby maintaining manufacturing feasibility at high density.
2Reliability
If word line electrical resistance is decreased to improve performance, then electrical performance improves, but pillar bending increases
Solution Approach 1:
The patent segments the word line structure into multiple conductive layers (first conductive structure, second conductive structure, third conductive structure) stacked vertically. This segmentation allows each layer to carry a portion of the electrical load, reducing the current density and associated magnetic field effects that cause pillar bending, while maintaining low overall resistance.
Solution Approach 2:
The patent transitions from a single-plane word line to a three-dimensional stacked configuration. By distributing conductive structures across multiple vertical levels (z-dimension), the design reduces the electromagnetic impact on pillars while achieving the desired electrical performance through parallel conduction paths.
3Ease of manufacture
If conventional staircase structures are used for electrical connections, then fabrication is simplified, but access line contact stresses and current leaks increase
Solution Approach 1:
The patent employs asymmetric elliptical contact structures instead of conventional symmetric staircase configurations. The elliptical shape with specific orientation and the asymmetric positioning of conductive contacts relative to pillars creates optimized stress distribution and reduced contact points that minimize both mechanical stress and current leakage pathways.
Solution Approach 2:
The patent converts the potential harm of pillar bending into a benefit by intentionally designing offset positions that anticipate and accommodate the bending. What would normally be a defect (bending) becomes a predictable parameter that is built into the design, transforming a harmful effect into a manageable design constraint.
Data Source
AI summary
A method of forming a microelectronic device including a first stack structure comprising alternating levels of insulative structures and other insulative structures, forming strings of memory cells through the first stack structure, forming a second stack structure over the first stack structure, based at least partially on observed amount of pillar bending within the first stack structure, forming a first tailored reticle specific to the observed amount of pillar bending, utilizing the first tailored reticle to form openings extending through the second stack structure and over some of the strings of memory cells, wherein centers of the openings over the strings of memory cells are at least substantially aligned with the centers of uppermost surfaces of the strings of memory cells in a direction of the observed pillar bending, and forming upper pillars extending through the second stack structure and over some of the strings of memory cells.