Oxide Semiconductor Transistor Copper Diffusion Barrier

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Solution Overview

Problem

Display devices with larger screens using transistors face issues with display quality due to varying voltage applied to elements caused by wiring resistance, and the use of copper films in oxide semiconductor transistors is hindered by copper diffusion into the semiconductor layer, increasing manufacturing costs and complexity.

Innovation Solution

A bottom-gate transistor design using a copper-containing metal film for wiring, where the copper film is positioned on the inner side of the first and third metal films to prevent copper diffusion into the channel formation region, with a specific layered structure and etching process to form source and drain electrodes, and an oxide insulating film to supply oxygen and reduce copper diffusion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a copper film is used for wiring to reduce resistance, then wiring resistance is reduced, but copper element diffuses into the semiconductor layer causing transistor characteristic deterioration

Engineering Contradiction:

Improvewiring resistanceVSAvoidtransistor characteristic stability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

A barrier film made of metal nitride (such as tungsten nitride, molybdenum nitride, or titanium nitride) is introduced as an intermediary layer between the copper-containing second metal film and the oxide semiconductor film. This barrier film prevents copper element diffusion into the semiconductor layer while allowing the copper film to maintain its low resistance properties for wiring

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The source electrode and drain electrode are constructed as composite structures with three metal films: a first metal film (tungsten, molybdenum, or titanium), a copper-containing second metal film, and a third metal film (aluminum, copper, or silver). This composite structure combines the advantages of different materials while mitigating their individual disadvantages through proper layering and positioning

Inventive Principle:

Principle #40Composite materials

2Reliability

If a barrier film is used to suppress copper diffusion, then copper diffusion is prevented, but the number of masks and manufacturing cost increase

Engineering Contradiction:

Improvecopper diffusion preventionVSAvoidnumber of masks and manufacturing process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The barrier film is integrated into the existing three-layer metal film structure of the source and drain electrodes, merging the diffusion prevention function with the electrode structure itself. This approach incorporates copper diffusion suppression within the already-necessary multi-layer electrode configuration, avoiding additional separate barrier film formation steps and masks

Inventive Principle:

Principle #5Merging (Combining)

3Loss of energy

If the copper film is positioned closer to the semiconductor layer to reduce resistance, then wiring resistance decreases, but copper diffusion into the channel formation region increases

Engineering Contradiction:

Improvewiring resistanceVSAvoidcopper diffusion into channel region

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The barrier film serves as a mediator positioned between the copper-containing second metal film and the oxide semiconductor film, enabling the copper film to be placed in optimal positions for low resistance while preventing harmful copper diffusion into the channel formation region through the protective barrier layer

Inventive Principle:

Principle #24Intermediary (Mediator)

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 stabilizes electric characteristics and reduces copper diffusion, enhancing the reliability and performance of oxide semiconductor transistors while minimizing manufacturing costs and complexity.

Implementation Method 1

an oxide insulating film over the oxide semiconductor film, the source electrode, and the drain electrode

Methodology Applied

Scientific EffectOxygen supply: Diffusion

Data Source

PatentUS9331207B2Oxide semiconductor device and manufacturing method therof

Publication Date: 2016.05.03 SEMICON ENERGY LAB CO LTD

AI summary

A semiconductor device includes a gate electrode; a gate insulating film over the gate electrode; an oxide semiconductor film in contact with the gate insulating film and including a channel formation region which overlaps with the gate electrode; a source electrode and a drain electrode over the oxide semiconductor film; and an oxide insulating film over the oxide semiconductor film, the source electrode, and the drain electrode. The source electrode and the drain electrode each include a first metal film having an end portion at the end of the channel formation region, a second metal film over the first metal film and containing copper, and a third metal film over the second metal film. The second metal film is formed on the inner side than the end portion of the first metal film.