Vertical NAND Flash Pillar Orthogonality via Layer Thickness Variation

Solution Overview

Problem

In three-dimensional microelectronic devices, such as vertical NAND flash memory devices, it is challenging to maintain orthogonal pillars through a large number of stacked flash memory cells, leading to deviations in performance due to oblique walls, which cause variations in current drive characteristics among cells.

Innovation Solution

The solution involves varying the thickness of at least two of the repeating layer patterns to compensate for deviations from orthogonality, ensuring that the pillar includes at least one oblique wall, thereby reducing drive current variations among the flash memory cells to less than 20% or 5%, by making the pillar wider and thicker further from the substrate face.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If orthogonal pillars are maintained through stacked flash memory cells, then manufacturing precision is improved, but device complexity increases due to the large number of stacked cells

Engineering Contradiction:

Improvepillar orthogonalityVSAvoidnumber of stacked cells

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies local quality by varying the thickness of repeating layer patterns at different positions within the stack. Specifically, layer patterns closer to the substrate have different thicknesses compared to those farther away, creating localized structural variations that compensate for the cumulative effect of oblique walls in tall stacks, thereby maintaining pillar orthogonality without requiring uniform thickness throughout the entire device

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent implements parameter changes by deliberately modifying the thickness parameter of repeating layer patterns. By changing the thickness of specific layer patterns based on their position in the stack (closer to or farther from the substrate), the invention compensates for deviations from orthogonality that accumulate over many stacked cells, thus maintaining manufacturing precision in complex multi-cell structures

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If the pillar extends through a large number of repeating layer patterns, then integration density is improved, but manufacturing precision deteriorates due to deviations from orthogonality

Engineering Contradiction:

Improvenumber of stacked cellsVSAvoidpillar orthogonality

Core Design Contradiction:

Quantity of substanceVSManufacturing precision

Solution Approach 1:

The patent applies local quality by varying the thickness of repeating layer patterns at different positions within the stack. Specifically, layer patterns closer to the substrate have different thicknesses compared to those farther away, creating localized structural variations that compensate for the cumulative effect of oblique walls in tall stacks, thereby maintaining pillar orthogonality without requiring uniform thickness throughout the entire device

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent implements parameter changes by deliberately modifying the thickness parameter of repeating layer patterns. By changing the thickness of specific layer patterns based on their position in the stack (closer to or farther from the substrate), the invention compensates for deviations from orthogonality that accumulate over many stacked cells, thus maintaining manufacturing precision in complex multi-cell structures

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If uniform thickness repeating layer patterns are used, then device complexity is reduced, but reliability deteriorates due to variations in current drive characteristics

Engineering Contradiction:

Improvelayer pattern uniformityVSAvoidcurrent drive consistency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies local quality by varying the thickness of repeating layer patterns at different positions within the stack. Specifically, layer patterns closer to the substrate have different thicknesses compared to those farther away, creating localized structural variations that compensate for the cumulative effect of oblique walls in tall stacks, thereby maintaining pillar orthogonality without requiring uniform thickness throughout the entire device

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent implements parameter changes by deliberately modifying the thickness parameter of repeating layer patterns. By changing the thickness of specific layer patterns based on their position in the stack (closer to or farther from the substrate), the invention compensates for deviations from orthogonality that accumulate over many stacked cells, thus maintaining manufacturing precision in complex multi-cell structures

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8952438B2Three-dimensional microelectronic devices including horizontal and vertical patterns

Publication Date: 2015.02.10 SAMSUNG ELECTRONICS CO LTD

AI summary

A vertical NAND flash memory device includes a substrate having a face and a string of serially connected flash memory cells on the substrate. A first flash memory cell is adjacent the face, and a last flash memory cell is remote from the face. The flash memory cells include repeating layer patterns that are stacked on the face, and a pillar that extends through the series of repeating layer patterns. The pillar includes at least one oblique wall. At least two of the series of repeating layer patterns in the string are of different thicknesses. Other vertical microelectronic devices and related fabrication methods are also described.