Laser Diode Contact Pad UBM for Reflow-Stable Ohmic Junctions

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Solution Overview

Problem

Existing semiconductor devices face challenges in maintaining ohmic junctions and preventing metal inter-diffusion during the reflow process of conductive connectors, which affects the electrical connections and reliability of laser diodes.

Innovation Solution

The formation of underbump metallurgies (UBMs) between contact pads and conductive connectors, using materials with different work functions to prevent metal inter-diffusion, and the use of passivation features to maintain ohmic properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conductive connectors are directly bonded to contact pads, then electrical connection is achieved, but metal inter-diffusion occurs during reflow process

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidmetal inter-diffusion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

An underbump metallurgy (UBM) layer is introduced as an intermediary between the conductive connector and the contact pad. This UBM layer acts as a diffusion barrier that prevents metal inter-diffusion during the reflow process while maintaining electrical connectivity. The UBM layer is formed with specific material composition and thickness to simultaneously provide electrical conductivity and diffusion barrier properties.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrical connection structure uses composite materials with different properties: the contact pad is made of a conductive material (such as aluminum or copper), the UBM layer is made of a diffusion barrier material (such as titanium, tungsten, or tantalum), and the conductive connector is made of a solder material. This composite structure combines the advantages of each material to achieve both electrical connectivity and diffusion prevention.

Inventive Principle:

Principle #40Composite materials

2Strength

If reflow process is performed to bond conductive connectors, then electrical connection strength is improved, but ohmic junction properties deteriorate due to metal inter-diffusion

Engineering Contradiction:

Improveelectrical connection strengthVSAvoidohmic junction property

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The UBM layer serves as a protective intermediary that allows the reflow process to be performed at high temperatures to strengthen the bond between the conductive connector and the UBM, while preventing the contact pad material from diffusing into the connector. This enables the reflow process to achieve strong mechanical and electrical bonding without degrading the ohmic junction properties of the contact pad.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If contact pads are made highly conductive, then electrical connection quality is improved, but susceptibility to metal inter-diffusion increases

Engineering Contradiction:

Improveelectrical connection qualityVSAvoidmetal inter-diffusion susceptibility

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The electrical connection system uses a composite structure where the contact pad is made of a highly conductive material to ensure low resistance electrical connection, while the adjacent UBM layer is made of a diffusion barrier material to prevent inter-diffusion. This composite approach allows the contact pad to be optimized for conductivity without compromising to diffusion resistance.

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 approach ensures that the metal-semiconductor junctions retain their ohmic properties, reducing contact resistance and enhancing the reliability and quality of electrical connections in laser diodes.

Implementation Method 1

The formation of underbump metallurgies (UBMs) between contact pads and conductive connectors, using materials with different work functions to prevent metal inter-diffusion

Methodology Applied

Scientific EffectDiffusion barrier: Diffusion Barrier

Implementation Method 2

the reflow process of conductive connectors

Methodology Applied

Scientific EffectReflow:

Data Source

PatentUS20250309608A1Semiconductor Device and Method

Publication Date: 2025.10.02 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

In some embodiments, laser devices having contact pads are formed. The laser diodes are formed from a doped semiconductive material. The contact pads and semiconductive material share an ohmic junction. Underbump metallurgies are formed on the contact pads. Conductive connectors are electrically coupled to the laser devices. The underbump metallurgies help prevent metal inter-diffusion between the contact pads and conductive connectors. As such, when reflowing the conductive connectors, the junction of the contact pads and semiconductive material may retain its ohmic properties.