3D NAND Sacrificial Layer Removal with Two-Step Trench Isolation

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Solution Overview

Problem

In 3D NAND memory device manufacturing, the removal of sacrificial layers in high-aspect-ratio trenches is challenging due to the risk of sulfuric acid etchant flowing from the stair step area to the core area, potentially removing sacrificial layers in the core area, leading to structural instability and increased manufacturing costs.

Innovation Solution

A method involving the formation of a stack with alternating insulating and sacrificial layers, where trenches are created to expose lateral sides, and a liner is deposited to protect the sacrificial layers. The liner is selectively removed in different areas to prevent etchant flow, allowing for controlled removal of sacrificial layers in two steps, using etchants like sulfuric acid and TMAH, and filling spaces with conductive materials to form word line layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If existing methods are used to remove sacrificial layers, then sacrificial layers can be removed, but unintended etching of sacrificial layers in adjacent areas occurs and manufacturing complexity increases

Engineering Contradiction:

Improveselective removal of sacrificial layersVSAvoidmanufacturing process complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent divides the gate line trench into two distinct regions: a first region where the sacrificial layer is removed, and a second region where the sacrificial layer is retained. This segmentation is achieved by forming a liner that extends into the trench and using a trench filler material that is selectively removed only from the first region. The segmentation allows precise control over which sacrificial layers are removed and which are retained, eliminating unintended etching in adjacent areas while simplifying the manufacturing process by avoiding complex multi-step procedures.

Inventive Principle:

Principle #1Segmentation

2Shape

If high aspect ratio gate line trenches are used, then vertical structure is achieved, but etchant exposure causes unintended etching in adjacent areas

Engineering Contradiction:

Improvevertical trench structureVSAvoidunintended etching of sacrificial layers

Core Design Contradiction:

ShapeVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a liner as an intermediary element that extends into the gate line trench and a trench filler material that selectively fills portions of the trench. The trench filler material acts as a mediator that prevents etchant from reaching the sacrificial layer in the second region while allowing etchant to access and remove the sacrificial layer in the first region. This intermediary structure enables the maintenance of high aspect ratio vertical trenches without causing unintended etching in adjacent areas, as the trench filler material provides localized protection where needed.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 method simplifies the 3D NAND process flow, reduces manufacturing costs, and ensures precise removal of sacrificial layers without structural collapse, enhancing the stability and efficiency of the 3D NAND memory device production.

Implementation Method 1

forming a liner to cover the exposed lateral sides of the insulating layers and the sacrificial layers in the trenches

Methodology Applied

Scientific EffectPhysical barrier protection:

Implementation Method 2

removing the sacrificial layers of the stack within the first area

Methodology Applied

Scientific EffectChemical etching:

Implementation Method 3

A method involving the formation of a liner resistant to etchants, followed by selective removal of sacrificial layers in two distinct areas using trench filler materials and etchants

Methodology Applied

Scientific EffectPhysical isolation:

Data Source

PatentUS20240172437A1Method for removing sacrificial layers of a stack of a three-dimensional semiconductor structure in two steps

Publication Date: 2024.05.23 YANGTZE MEMORY TECH CO LTD

AI summary

A method includes forming a stack of alternating insulating layers and sacrificial layers over a substrate; forming a trench through the stack to uncover the substrate to expose lateral sides of the insulating layers and the sacrificial layers, the trench extending from a core area to a stair step area of the stack; forming a liner to cover the exposed lateral sides; removing the liner in the trenches within a first area of the core area and the stair step area to expose the lateral sides of the sacrificial layers of the stack within the first area; removing the sacrificial layers within the first area; removing the liner in the trenches within a second area of the core area and the stair step area to expose the lateral sides of the sacrificial layers of the stack within the second area; and removing the sacrificial layers within the second area.