Al Pad Barrier Layer Prevents Purple Plague

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Solution Overview

Problem

The reaction between aluminum (Al) pads and gold (Au) interconnection layers in semiconductor devices leads to increased electric resistance due to the formation of intermetallic compounds, known as 'purple plague,' which is exacerbated by high temperatures and mechanical stress during wire bonding, causing reliability issues in high-power semiconductor applications.

Innovation Solution

A semiconductor device design featuring an Al pad with an interconnection portion outside the bonding area, an Au interconnection layer electrically connected to the pad, and a barrier layer between the interconnection portion and the Au layer, preventing direct contact and reaction between Al and Au by forming the Al pad and Au interconnection layer with a barrier layer, such as TiN or TiWN, to maintain electrical connectivity without intermetallic compound formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a barrier layer is formed between the Al pad and Au interconnection layer, then the reaction between Al and Au is prevented, but the electric resistance increases due to the barrier layer itself

Engineering Contradiction:

Improveprevention of intermetallic compound formationVSAvoidelectric resistance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

A barrier layer made of TiN or TiWN is inserted between the Al pad and Au interconnection layer to prevent direct contact and reaction between Al and Au, eliminating the purple plague phenomenon while maintaining electrical connectivity through the barrier layer's conductive properties

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The pad structure uses composite material stacking (Al pad + TiN/TiWN barrier layer + Au interconnection layer) to combine the advantages of each material: Al for low resistivity and wire bonding compatibility, TiN/TiWN for barrier properties and adhesion, and Au for high conductivity and oxidation resistance

Inventive Principle:

Principle #40Composite materials

2Manufacturing precision

If the Al pad is formed directly on the Au interconnection layer without a barrier layer, then the electrical resistance is low, but the reaction between Al and Au forms intermetallic compounds increasing resistance

Engineering Contradiction:

Improveelectric resistanceVSAvoidstability at high temperature

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The TiN or TiWN barrier layer serves as an intermediary that prevents direct Al-Au contact and intermetallic compound formation, while maintaining sufficient electrical conductivity to keep overall resistance low, and providing thermal stability at operating temperatures up to 200°C

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The barrier layer thickness is optimized to balance two competing requirements: thick enough to prevent Al diffusion and intermetallic formation, but thin enough to maintain low electrical resistance, typically in the range of 5-50 nm

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the barrier layer is made thicker to prevent Al-Au reaction, then the reaction prevention is improved, but the electric resistance increases

Engineering Contradiction:

Improveprevention of reactionVSAvoidelectric resistance

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The barrier layer thickness is precisely controlled within an optimal range (5-50 nm) to achieve sufficient reaction prevention while maintaining low electrical resistance, avoiding both thinness that allows diffusion and thickness that increases resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The barrier layer properties are optimized locally at the Al-Au interface where reaction prevention is most critical, while maintaining overall pad structure design that balances reaction prevention and electrical conductivity requirements

Inventive Principle:

Principle #3Local quality

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 design effectively prevents the formation of intermetallic compounds, maintaining low electrical resistance and reliability at temperatures up to 200°C, ensuring high bond strength and preventing damage to the barrier layer during wire bonding, thus enhancing the semiconductor device's performance and longevity in high-power applications.

Implementation Method 1

a barrier layer that is provided between the interconnection portion and the interconnection layer

Methodology Applied

Scientific EffectPhysical barrier: Physical Containment

Implementation Method 2

an interconnection layer that contains Au and is electrically connected to the interconnection portion of the pad

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS8222736B2Semiconductor device with Al pad

Publication Date: 2012.07.17 SUMITOMO ELECTRIC DEVICE INNOVATIONS

AI summary

A semiconductor device includes: a pad that is formed on a semiconductor layer, contains Al, and has an interconnection portion that is formed outside a bonding area; an interconnection layer that contains Au and is electrically connected to the interconnection portion of the pad, an edge of the interconnection layer being formed outside of the bonding area; and a barrier layer that is provided between the interconnection portion and the interconnection layer.