Dual Metal Source Drain Contact Structure for Semiconductor Reliability

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Solution Overview

Problem

Traditional tungsten-based contact structures in semiconductor devices face challenges with high aspect ratio gap fill issues, leading to seams or keyholes, while copper-based structures exhibit low electrical resistance but are susceptible to electromigration, causing leakage in Field Effect Transistors.

Innovation Solution

A dual metal source/drain contact structure is implemented, where a first contact conductor portion with high electromigration resistance, such as tungsten, is formed at the bottom of the contact trench to contact the source/drain region, and a second contact conductor portion with lower resistance, like copper or copper alloys, is deposited on top, separated by a non-copper containing layer to prevent diffusion and enhance conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If tungsten is used for contact structures, then electromigration resistance is improved, but electrical resistance increases and gap fill becomes difficult

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidgap fill quality

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The contact structure is divided into two distinct segments: a tungsten-based first contact conductor portion at the bottom for electromigration resistance, and a copper-based second contact conductor portion at the top for low electrical resistance. This segmentation allows each material to perform its optimal function without the drawbacks of using either material alone throughout the entire structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining two different metals (tungsten and copper) in a single contact structure. The tungsten portion provides electromigration resistance while the copper portion provides low electrical resistance, creating a composite material system that achieves properties superior to either individual material.

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If copper is used for contact structures, then electrical resistance decreases, but electromigration resistance worsens causing leakage

Engineering Contradiction:

Improveelectrical resistanceVSAvoidelectromigration resistance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A barrier layer is introduced as an intermediary between the copper second contact conductor portion and the source/drain region. This barrier layer prevents copper diffusion into the semiconductor region, eliminating the electromigration problem associated with copper while preserving its low electrical resistance benefit.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If high aspect ratio contact structures are formed, then device density increases, but gap fill issues worsen with seams or keyholes

Engineering Contradiction:

Improvedevice densityVSAvoidgap fill quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The contact trench is filled in two stages: first with tungsten to a partial depth (leaving the top portion unfilled), then with copper to complete the fill. This partial filling approach allows each material to be deposited optimally without attempting to fill the entire high aspect ratio trench with a single material, avoiding seam and keyhole formation.

Inventive Principle:

Principle #16Partial or excessive action

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 configuration reduces contact resistance and mitigates electromigration issues by using copper's high conductivity while preventing copper diffusion into the source/drain regions, thereby improving the performance and reliability of Field Effect Transistors.

Implementation Method 1

a non-Cu containing first contact conductor portion, the risk of electromigration caused by Cu diffusion is prevented

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

a second contact conductor portion comprising a highly conductive metal such as Cu or a Cu alloy is formed over the first contact conductor portion

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS10340355B2Method of forming a dual metal interconnect structure

Publication Date: 2019.07.02 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A method of forming source/drain contact structures that exhibit low contact resistance and improved electromigration properties is provided. After forming a first contact conductor portion composed of a metal having a high resistance to electromigration, such as, for example, tungsten, at a bottom portion of source/drain contact trench to form direct contact with a source/drain region of a field effect transistor, a second contact conductor portion composed of a highly conductive metal, such as, for example, copper or a copper alloy, is formed over the first contact conductor portion.