Underbump Metallization Passivation Stress Management

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The use of under bump metallization (UBM) with different materials having varying coefficients of thermal expansion (CTE) leads to stress-induced delamination during temperature changes, particularly when low-k or extremely low-k dielectrics are used, causing yield and productivity issues.

Innovation Solution

A system and method where the UBM is formed with a passivation layer interposed between its contact portions and the contact pad, creating openings through the passivation layer to absorb thermal expansion stresses, thereby preventing delamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If UBM is formed with materials having different CTE to achieve electrical connection, then electrical connectivity is improved, but thermal stress-induced delamination occurs during temperature changes

Engineering Contradiction:

Improveelectrical connectivityVSAvoidbond strength between UBM and contact pad

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent introduces a passivation layer as an intermediary between the UBM and the contact pad. This passivation layer acts as a stress-absorbing intermediary that decouples the thermal expansion stresses from the UBM-contact pad interface, preventing delamination while maintaining electrical connectivity through the structured openings in the passivation layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the physical and structural parameters of the interface region by creating a passivation layer with specific openings. This modifies the stress distribution parameters and thermal expansion characteristics at the interface, allowing the structure to accommodate CTE differences without delamination while preserving electrical connection functionality.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If low-k or extremely low-k dielectric materials are used for dielectric layers to improve signal performance, then signal transmission quality is improved, but stress-induced delamination is exacerbated due to CTE mismatch

Engineering Contradiction:

Improvesignal transmission qualityVSAvoidthermal stress and delamination

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The passivation layer serves as a protective intermediary between the low-k dielectric layers and the UBM structure. It absorbs and isolates the thermal stresses generated by the low-k materials during temperature cycling, preventing these stresses from propagating to critical interfaces and causing delamination, thereby enabling the use of low-k dielectrics without compromising structural integrity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If UBM extends directly through passivation layer to contact pad to reduce manufacturing complexity, then manufacturing process is simplified, but peeling and shear stresses build up at interfaces during reflow processing

Engineering Contradiction:

ImproveUBM formation processVSAvoidpeeling stress and shear stress at interfaces

Core Design Contradiction:

Ease of manufactureVSStress or pressure

Solution Approach 1:

The patent modifies the structural parameters of the UBM assembly by introducing a passivation layer with controlled openings. This structural parameter change creates a stress-management architecture that accommodates thermal expansion differences during reflow processing, reducing peeling and shear stresses at critical interfaces while maintaining a relatively simple manufacturing process.

Inventive Principle:

Principle #35Parameter changes

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 reduces peeling and shear stresses, enhancing the yield and reliability of semiconductor devices by absorbing thermal expansion stresses within the passivation layer, rather than transmitting them to the underlying structure.

Implementation Method 1

stresses caused by differences in materials' coefficient of thermal expansion are absorbed by the passivation layer

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS9859235B2Underbump metallization structure

Publication Date: 2018.01.02 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A system and method for forming an underbump metallization (UBM) is presented. A preferred embodiment includes a raised UBM which extends through a passivation layer so as to make contact with a contact pad while retaining enough of the passivation layer between the contact pad and the UBM to adequately handle the peeling and shear stress that results from CTE mismatch and subsequent thermal processing. The UBM contact is preferably formed in either an octagonal ring shape or an array of contacts.