Copper Pillar Sidewall Protection for Fine Pitch Packaging

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Solution Overview

Problem

Copper pillar bumps in integrated circuit fabrication are prone to oxidation, leading to poor adhesion and reliability issues, particularly in fine pitch package technology, due to high process costs and interface delamination concerns with conventional immersion tin processes.

Innovation Solution

A non-metal sidewall protection structure, such as a dielectric or polymer material layer, is applied to the copper pillar sidewalls to prevent oxidation and enhance adhesion with underfill materials, reducing the risk of underfill cracking and improving solder wetting during the reflow process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional immersion tin process is used to provide tin layer on Cu pillar sidewalls, then copper oxidation is prevented, but process costs increase and adhesion issues occur

Engineering Contradiction:

ImproveadhesionVSAvoidprocess cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

A non-metallic sidewall protection layer (silicon oxide, silicon nitride, or silicon oxynitride) is introduced as an intermediary between the copper pillar and the external environment. This layer prevents copper oxidation without requiring immersion tin processing, thereby eliminating the associated cost increases and adhesion problems while maintaining reliable protection.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the material parameter of the sidewall protection layer from metallic (tin) to non-metallic (silicon-based dielectric materials). This parameter change enables oxidation protection through deposition processes rather than immersion plating, reducing process complexity and cost while avoiding tin-related adhesion issues.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If copper pillar bumps are used in fine pitch package technology, then higher current carrying capacity and better thermal performance are achieved, but oxidation leads to poor adhesion and reliability issues

Engineering Contradiction:

ImproveadhesionVSAvoidoxidation

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The non-metallic sidewall protection layer is applied in advance to the copper pillar sidewalls before any oxidation can occur. This preliminary protective action prevents the harmful oxidation effect from taking place, ensuring that the copper remains adherent and reliable throughout subsequent processing and underfill operations.

Inventive Principle:

Principle #9Preliminary anti-action

3Ease of manufacture

If conventional methods are used without sidewall protection, then process costs are reduced, but underfill cracking occurs along the interface of underfill and copper pillars

Engineering Contradiction:

Improveprocess costVSAvoidadhesion strength

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The non-metallic sidewall protection layer serves as a mediator between the copper pillar and the underfill material. It provides a stable, non-oxidized surface that prevents direct harmful interaction between underfill chemicals and copper, thereby preventing underfill cracking while adding minimal process steps.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If immersion tin process is used, then copper oxidation is prevented, but solder wetting issues occur on sidewalls

Engineering Contradiction:

Improveoxidation preventionVSAvoidsolder wetting

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

By changing the sidewall material from metallic tin to non-metallic silicon-based dielectric, the surface properties are fundamentally altered. This parameter change prevents solder from wetting the sidewalls, as the dielectric materials are inherently solder-resistant, while still providing effective oxidation protection during manufacturing.

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

The non-metal sidewall protection structure effectively prevents copper oxidation, enhances adhesion between the copper pillar and underfill, and reduces solder wetting issues, thereby improving the reliability and performance of copper pillar bump technology in fine pitch packaging.

Implementation Method 1

copper has a tendency to be oxidized during the manufacturing process. Oxidized copper pillars may lead to poor adhesion of an electronic component to a substrate

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Implementation Method 2

enhances adhesion with underfill materials, reducing the risk of underfill cracking

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS11257714B2Method of making a pillar structure having a non-metal sidewall protection structure and integrated circuit including the same

Publication Date: 2022.02.22 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

An integrated circuit device includes a semiconductor substrate; and a pad region over the semiconductor substrate. The integrated circuit device further includes an under-bump-metallurgy (UBM) layer over the pad region. The integrated circuit device further includes a conductive pillar on the UBM layer, wherein the conductive pillar has a sidewall surface and a top surface. The integrated circuit device further includes a protection structure over the sidewall surface of the conductive pillar, wherein sidewalls of the UBM layer are substantially free of the protection structure, and the protection structure is a non-metal material.