SiC Solderable Contact with Gap and Barrier

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Solution Overview

Problem

Silicon carbide (SiC) devices face challenges in forming reliable solderable connections due to poor adhesion of metal electrodes like aluminum to solder, which can lead to silver ion electromigration and dendrite formation, damaging the passivation layer and reducing device reliability.

Innovation Solution

A solderable contact with a silver-containing trimetal stack is formed with a gap between the contact and the amorphous silicon passivation layer, allowing the solder to cover the entire surface and prevent silver ion migration, while a second insulating passivation layer further contains the solder and enhances reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a solderable contact containing silver is formed directly on the electrode surface to enable solder-based connections, then electrical and mechanical connection reliability is improved, but silver ions can migrate under electric fields and moisture to form dendrites that damage the passivation layer

Engineering Contradiction:

Improveconnection reliabilityVSAvoidsilver ion electromigration

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A barrier layer is introduced between the silver-containing solderable contact and the passivation layer to prevent silver ion migration. This intermediary layer blocks the harmful interaction between the solderable contact and the passivation layer while maintaining the electrical connection function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The structure is segmented into distinct functional layers: the electrode, solderable contact, barrier layer, and passivation layer. This segmentation isolates the silver-containing contact from the passivation layer, preventing dendrite formation while preserving connection reliability.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the passivation layer overlaps the edges of the electrodes to provide insulation, then electrical insulation is improved, but the passivation layer may contact and conceal portions of the solderable contact, preventing complete solder coverage and creating migration sources

Engineering Contradiction:

Improveelectrical insulationVSAvoidsolder coverage completeness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The barrier layer serves as an intermediary that allows the passivation layer to extend close to or overlap the electrode edges for insulation while preventing direct contact with the solderable contact. This ensures complete solder coverage is achieved without creating concealed migration sources.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If aluminum electrodes are used for their electrical conductivity, then electrical performance is improved, but adhesion to solder is poor requiring additional solderable contacts

Engineering Contradiction:

Improveelectrical conductivityVSAvoidsolder adhesion

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

A composite structure is created by depositing a solderable contact layer (containing silver or other solder-compatible metals) over the aluminum electrode. This composite structure combines the high electrical conductivity of aluminum with the solder adhesion properties of the contact layer.

Inventive Principle:

Principle #40Composite materials

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 ensures reliable connections by preventing silver ion electromigration and dendrite formation, maintaining the integrity of the passivation layer and enhancing the reliability of SiC devices under electric fields and moisture exposure.

Implementation Method 1

the solder will typically dissolve the exposed silver along the surfaces of the contact, forming a solder alloy

Methodology Applied

Scientific EffectDissolution:

Implementation Method 2

a semi insulating passivation layer that overlies the outer peripheral edge, for example, of the power electrode

Methodology Applied

Scientific EffectElectrical insulation:

Data Source

PatentUS9496421B2Solderable top metal for silicon carbide semiconductor devices

Publication Date: 2016.11.15 SILICONIX TECH C V

AI summary

A silicon carbide device includes at least one power electrode on a surface thereof, a solderable contract formed on the power electrode, and at least one passivation layer that surrounds the solderable contact but is spaced from the solderable contract, thereby forming a gap.