Metal Gate Diffusion Barrier for Threshold-Stable FETs

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Solution Overview

Problem

The challenge of threshold voltage shift due to metal diffusion between closely spaced FETs in integrated circuits, particularly with aluminum-containing work function adjustment layers, leads to degradation of FET properties and performance issues.

Innovation Solution

Incorporation of an aluminum diffusion barrier layer at the surface of work function adjustment layers to prevent metal diffusion and protect underlying layers from aluminum contamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If aluminum-containing work function adjustment layers are used in closely spaced FETs, then device performance is improved, but threshold voltage shift occurs due to metal diffusion

Engineering Contradiction:

ImproveFET performance stabilityVSAvoidmetal diffusion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A diffusion barrier layer is introduced as an intermediary between the aluminum-containing work function adjustment layer and adjacent FET structures. This barrier layer (comprising materials such as titanium nitride, tantalum nitride, or tungsten nitride) prevents aluminum atoms from diffusing into neighboring devices, thereby eliminating the harmful metal diffusion effect while preserving the electrical performance benefits of the aluminum-containing layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The gate structure is segmented into multiple functional layers: the aluminum-containing work function adjustment layer is separated from adjacent devices by the diffusion barrier layer. This segmentation isolates the aluminum source, preventing its harmful diffusion effects while maintaining its beneficial role in work function adjustment within the intended device region.

Inventive Principle:

Principle #1Segmentation

2Productivity

If work function adjustment layers are placed close to adjacent devices, then integration density is improved, but aluminum diffusion contaminates underlying layers

Engineering Contradiction:

Improveintegration densityVSAvoidaluminum contamination

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The diffusion barrier layer serves as a protective intermediary positioned between the aluminum-containing work function adjustment layer and the underlying channel region. This barrier prevents aluminum contamination of the channel while allowing the work function adjustment layer to remain in close proximity to adjacent devices, thereby maintaining high integration density without suffering from aluminum diffusion effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If diffusion barrier layer is added to prevent metal diffusion, then threshold voltage stability is improved, but device complexity increases

Engineering Contradiction:

Improvethreshold voltage stabilityVSAvoidgate structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The diffusion barrier layer is designed with optimized thickness parameters (typically 1-10 nm) and specific material compositions (titanium nitride, tantalum nitride, or tungsten nitride) that provide effective aluminum diffusion blocking while minimizing the additional structural complexity. By carefully controlling these parameters, the barrier layer achieves its protective function with minimal impact on overall device complexity.

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

The solution effectively prevents threshold voltage shifts and maintains FET performance by isolating aluminum-containing layers from adjacent devices, ensuring stable operation and improved device reliability.

Implementation Method 1

a diffusion barrier layer at least at one of a bottom surface region and a top surface region of the aluminum containing layer

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Data Source

PatentUS20250324722A1Method of manufacturing semiconductor devices and semiconductor devices

Publication Date: 2025.10.16 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device includes a gate structure disposed over a channel region and a source/drain region. The gate structure includes a gate dielectric layer over the channel region, one or more work function adjustment material layers over the gate dielectric layer, and a metal gate electrode layer over the one or more work function adjustment material layers. The one or more work function adjustment layers includes an aluminum containing layer, and a diffusion barrier layer is disposed at at least one of a bottom portion and a top portion of the aluminum containing layer. The diffusion barrier layer is one or more of a Ti-rich layer, a Ti-doped layer, a Ta-rich layer, a Ta-doped layer and a Si-doped layer.