Epitaxial Monocrystalline Channel for 3D Memory Storage Transistors

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Solution Overview

Problem

Polysilicon channel regions in thin-film storage transistors exhibit low conducting transistor current, high temperature sensitivity, high dopant diffusivity, high leakage currents, and variability in threshold voltages due to grain boundaries, which hinder the formation of high-quality tunneling oxide and introduce variability in thin-film storage transistors.

Innovation Solution

The formation of single-crystal epitaxial silicon channel regions is achieved by providing a semiconductor substrate with a planar surface, depositing oxide isolation layers, creating deep trenches, and using selective epitaxial silicon growth to fill cavities with single-crystal silicon, thereby replacing polysilicon channel regions with monocrystalline silicon.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polysilicon channel regions are used in thin-film storage transistors, then the manufacturing process is simpler and cost-effective, but the transistor current is low and temperature sensitivity is high due to grain boundaries

Engineering Contradiction:

Improvemanufacturing process simplicityVSAvoidtransistor current stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the material parameter from polysilicon to single-crystal silicon for the channel region. This fundamental material parameter change eliminates grain boundaries while maintaining compatibility with existing semiconductor manufacturing processes, thereby improving transistor current stability and reducing temperature sensitivity without completely abandoning conventional fabrication approaches

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure where single-crystal silicon is integrated into the thin-film transistor architecture. The channel region uses single-crystal silicon while other portions of the device may retain polysilicon or other materials, creating a composite device that combines the manufacturing advantages of polysilicon processes with the electrical performance benefits of single-crystal silicon

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If polysilicon channel regions are used, then the fabrication process is easier, but dopant diffusivity is high and leakage currents are high

Engineering Contradiction:

Improvefabrication process easeVSAvoidleakage currents

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent changes the crystal structure parameter from polycrystalline to single-crystal silicon in the channel region. This parameter change fundamentally reduces dopant diffusivity and leakage currents by eliminating grain boundary pathways, while the overall fabrication process remains compatible with standard semiconductor manufacturing through selective epitaxial growth techniques

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If polysilicon channel regions are used, then the device structure is simpler to fabricate, but threshold voltage variability is high due to grain boundaries

Engineering Contradiction:

Improvedevice structure simplicityVSAvoidthreshold voltage control

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent changes the material parameter from polysilicon to single-crystal silicon for the channel region. This parameter change eliminates grain boundary-induced variability in threshold voltage, enabling more precise control over device characteristics while maintaining a fabrication process that builds upon conventional semiconductor manufacturing techniques

Inventive Principle:

Principle #35Parameter changes

4Ease of manufacture

If polysilicon channel regions are used, then the manufacturing cost is lower, but the quality of tunnel oxide formation is poor

Engineering Contradiction:

Improvemanufacturing costVSAvoidtunnel oxide quality

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent changes the material parameter from polysilicon to single-crystal silicon in the channel region. This parameter change provides a superior substrate for tunnel oxide formation, enabling higher quality dielectric layers to be deposited. The process remains cost-effective by using selective epitaxial growth and integrating with existing fabrication workflows

Inventive Principle:

Principle #35Parameter changes

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 enhances electron mobility, reduces leakage currents, allows for in situ formation of clean source and drain junctions, and improves the quality of tunnel oxide formation, resulting in more stable and efficient thin-film storage transistors with reduced variability.

Implementation Method 1

selective epitaxial silicon growth to fill cavities with single-crystal silicon

Methodology Applied

Scientific EffectEpitaxial growth: Epitaxy

Data Source

PatentUS11557606B2Epitaxial monocrystalline channel for storage transistors in 3-dimensional memory structures and methods for formation thereof

Publication Date: 2023.01.17 SUNRISE MEMORY CORP

AI summary

A thin-film storage transistor includes (a) first and second semiconductor regions comprising polysilicon of a first conductivity; and (b) a channel region between the first and second semiconductor regions, the channel region comprising single-crystal epitaxial grown silicon, and wherein the thin-film storage transistor is formed above a monocrystalline semiconductor substrate.