3D Memory Double-Width Staircase Regions Stress Distribution

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Solution Overview

Problem

Current three-dimensional memory devices face challenges in distributing mechanical stress evenly during the replacement of sacrificial material layers with electrically conductive layers, leading to substrate distortion and reduced process windows for lithography steps due to unidirectional stress and deposition of by-products in backside trenches.

Innovation Solution

The use of discrete backside openings instead of elongated backside trenches for replacing sacrificial material layers with electrically conductive layers, which distributes stress omnidirectionally and reduces unidirectional stress, thereby minimizing substrate distortion and improving the process window.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If backside trenches are used for replacing sacrificial material layers with electrically conductive layers, then the replacement process can be performed, but unidirectional stress is generated causing substrate distortion and reduced process windows

Engineering Contradiction:

Improvereplacement process capabilityVSAvoidsubstrate distortion

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent divides the continuous backside trench into multiple discrete backside openings arranged in a pattern. This segmentation distributes the stress generation into multiple smaller sources rather than one large continuous source, transforming the stress distribution from unidirectional to more omnidirectional, thereby reducing substrate distortion while maintaining the replacement functionality

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces different structural characteristics at different locations by creating a pattern of discrete openings with specific spacing and size variations. This allows local stress distribution to be optimized at different regions of the substrate, preventing uniform unidirectional stress accumulation that causes global substrate distortion

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If backside trenches are used for replacing sacrificial material layers, then the replacement can be achieved, but deposition of by-products occurs reducing process window

Engineering Contradiction:

Improvereplacement process capabilityVSAvoidby-product deposition

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

By segmenting the backside trench into discrete openings, the surface area available for by-product deposition is reduced. The isotropic etchant can access sacrificial material through multiple distributed openings rather than one large trench, minimizing the total interface where by-products accumulate and reducing their harmful effects on the process window

Inventive Principle:

Principle #1Segmentation

3Manufacturing precision

If discrete backside openings are used instead of elongated backside trenches, then stress is distributed omnidirectionally reducing substrate distortion, but the structural complexity increases

Engineering Contradiction:

Improvesubstrate distortionVSAvoidopening pattern structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent combines multiple functions into the discrete opening pattern: stress distribution, isotropic etchant access, and by-product minimization are all achieved through the same structural feature. This merging reduces the need for additional separate structures or processes, offsetting the apparent complexity with functional integration

Inventive Principle:

Principle #5Merging (Combining)

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 allows for more even mechanical stress distribution, reducing substrate distortion and enhancing the process window for subsequent lithography steps, leading to improved fabrication efficiency and accuracy in three-dimensional memory devices.

Implementation Method 1

replacing remaining portions of the sacrificial material layers with electrically conductive layers by introducing an isotropic etchant that etches the remaining portions of the sacrificial material layers through the backside openings

Methodology Applied

Scientific EffectIsotropic etching:

Data Source

PatentUS10615172B2Three-dimensional memory device having double-width staircase regions and methods of manufacturing the same

Publication Date: 2020.04.07 SANDISK TECHNOLOGIES LLC

AI summary

Memory openings and backside openings are formed through an alternating stack of insulating layers and sacrificial material layers with patterned stepped surfaces and an overlying retro-stepped dielectric material portion. The backside openings may be formed in rows with shape modifications in staircase regions to provide more lateral elongation in areas with lesser layers of the alternating stack. Non-circular horizontal cross-sectional shapes for the backside openings in the staircase regions allow formation of the backside opening with less shape distortion. Memory opening fill structures are formed in the memory openings, and the sacrificial material layers are replaced with electrically conductive layers using the backside openings as conduits for an etchant and for a deposition precursor material. The electrically conductive layers are isotropically recessed around each backside opening to form width-modulated cavities, which is filled with width-modulated insulating wall structures.