C4 Under Bump Metallization Etch Masking

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Solution Overview

Problem

Conventional methods for forming solder connections on semiconductor devices often result in undercut corrosion, which reduces the integrity of the bump attachment and is problematic as devices become smaller, as the undercut can significantly degrade device performance.

Innovation Solution

A method involving the deposition of metal layers and patterning with resist to control the size and shape of solder connections, using electroplating and reactive ion etching to prevent undercut, with a pad metal layer acting as a mask during etching, and forming a passivation layer to preserve dimensional integrity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If wet etching is used to remove underlying films after C4 plating, then the etching process can be completed, but undercut corrosion occurs that reduces BLM footprint and bump attachment integrity

Engineering Contradiction:

Improveetching process completionVSAvoidBLM footprint dimension

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

A first metal containing layer (such as tantalum, titanium, or titanium-tungsten alloy) is deposited onto the passivation layer before forming the copper layer and solder bump. This preliminary layer serves as an etch mask that protects the underlying structure during wet etching, preventing undercut corrosion and preserving the BLM footprint dimensions while allowing the etching process to complete successfully.

Inventive Principle:

Principle #10Preliminary action

2Volume of moving object

If device size is reduced to create smaller solder connections, then device scaling is achieved, but undercut becomes a greater threat to C4 structure integrity

Engineering Contradiction:

Improvesolder connection sizeVSAvoidC4 structure integrity

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The first metal containing layer is deposited in advance as a protective etch mask before subsequent processing steps. This preliminary protective layer prevents undercut corrosion during wet etching, which is particularly critical for smaller devices where even minor undercut can significantly compromise the integrity of the C4 structure.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If copper layer is used as top layer of BLM, then electroplating of Ni is enhanced, but Cu reacts with Sn-based solder to form intermetallic barrier layer that may affect reliability

Engineering Contradiction:

Improveelectroplating enhancementVSAvoidbump connection reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

A first metal containing layer (such as tantalum, titanium, or titanium-tungsten alloy) is introduced as an intermediary barrier between the copper layer and the tin-based solder. This intermediate layer prevents direct reaction between Cu and Sn, avoiding the formation of unreliable intermetallic compounds while still allowing the copper layer to serve its function of enhancing nickel electroplating.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 method reduces or eliminates undercut corrosion, maintaining the dimensional integrity of solder connections and enhancing the reliability of semiconductor devices by controlling the size and shape of under bump metallization layers, particularly beneficial for smaller devices.

Implementation Method 1

The first metal containing layer is deposited by physical vapor deposition

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 2

At least a pad metal containing layer is formed within the at least one opening (preferably by electroplating processes)

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 3

The resist and the first metal layer, underlying the resist, are etched (with the second metal layer acting as a mask, in embodiments)

Methodology Applied

Scientific EffectWet etching:

Implementation Method 4

The method includes flowing solder material within the trench and on pad metal containing layer after the etching process

Methodology Applied

Scientific EffectSoldering: Soldering

Data Source

PatentUS8164188B2Methods of forming solder connections and structure thereof

Publication Date: 2012.04.24 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method comprises depositing a first metal containing layer into a trench structure, which contacts a metalized area of a semiconductor structure. The method further includes patterning at least one opening in a resist to the first metal containing layer. The opening should be in alignment with the trench structure. At least a pad metal containing layer is formed within the at least one opening (preferably by electroplating processes). The resist and the first metal layer underlying the resist are then etched (with the second metal layer acting as a mask, in embodiments). The method includes flowing solder material within the trench and on pad metal containing layer after the etching process. The structure is a controlled collapse chip connection (C4) structure comprising at least one electroplated metal layer formed in a resist pattern to form at least one ball limiting metallurgical layer. The structure further includes an underlying metal layer devoid of undercuts.