Multilayer Metal Source Drain Structure for FET Interface Stability

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Solution Overview

Problem

Existing semiconductor-based field-effect transistors (FETs) face challenges in achieving low resistance and high chemical stability at the metal-semiconductor interfaces, particularly for n-channel FETs, where low-workfunction metals tend to react and form barriers, and for p-channel FETs, where high-workfunction metals may not be suitable due to thermal resistance issues.

Innovation Solution

A multilayer metal source/drain structure is implemented, where a first metal layer with low chemical stability is capped with a second metal layer that exhibits superior chemical stability and lower resistivity, ensuring minimal reaction and optimal interface characteristics for both n-channel and p-channel FETs, potentially including a third metal layer for enhanced thermal management.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a low-workfunction metal is used for n-channel FET source/drain to minimize potential barrier, then carrier flow into channel is improved, but chemical stability deteriorates due to metal reaction with semiconductor

Engineering Contradiction:

Improvecarrier flow efficiencyVSAvoidchemical stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The source/drain structure is segmented into multiple metal layers with distinct functions: the first metal layer (low-workfunction) provides optimal carrier injection into the channel, while the second metal layer (high chemical stability) protects the interface and provides structural stability. This segmentation allows each layer to optimize for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite metal structure where two different metals are combined in a layered configuration. The composite structure integrates the beneficial properties of both metals: low effective workfunction for carrier injection and high chemical stability for interface protection, resolving the contradiction between these two requirements.

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If a high-workfunction metal is used for p-channel FET source/drain to achieve thermal stability, then chemical stability is improved, but electrical resistance increases due to higher resistivity

Engineering Contradiction:

Improvechemical stabilityVSAvoidelectrical resistance

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The source/drain is segmented into functional layers: the first metal layer provides low electrical resistivity for efficient current conduction, while the second metal layer provides chemical stability and thermal management. This segmentation allows optimization of electrical and chemical properties independently.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The layered composite metal structure combines metals with complementary properties, where one metal contributes low resistivity for electrical performance and the other contributes chemical stability and thermal properties, resolving the contradiction between electrical resistance and chemical stability.

Inventive Principle:

Principle #40Composite materials

3Device complexity

If a single metal layer is used for source/drain to simplify structure, then device complexity is reduced, but interface reaction and potential barrier formation increase

Engineering Contradiction:

Improvestructure simplicityVSAvoidinterface stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The source/drain interface is segmented into multiple metal layers, each performing a specific function: carrier injection, chemical protection, and thermal management. This segmentation improves interface stability and reduces unwanted reactions while maintaining reasonable structural complexity through systematic layering.

Inventive Principle:

Principle #1Segmentation

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 multilayer metal structure reduces potential barriers, enhances chemical stability, and lowers electrical and thermal resistivity, improving the performance and reliability of FETs by optimizing the effective workfunction and thermal dissipation across both n-channel and p-channel transistors.

Implementation Method 1

a first layer of a first metal is deposited to form a first metal layer of the source/drain

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Implementation Method 2

a second layer of a second metal is deposited to form a second metal layer over the first metal layer

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Data Source

PatentUS8658523B2Method for making semiconductor insulated-gate field-effect transistor having multilayer deposited metal source(s) and/or drain(s)

Publication Date: 2014.02.25 ACORN SEMI LLC

AI summary

A metal source/drain field effect transistor is fabricated such that the source/drain regions are deposited, multilayer structures, with at least a second metal deposited on exposed surfaces of a first metal.