Copper Pillar Bump Sidewall Protection Against Oxidation
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Solution Overview
Problem
Copper pillar bump technology in integrated circuit fabrication faces issues with copper oxidation leading to poor adhesion and interface delamination, resulting in reliability concerns and process costs, especially in fine pitch package technology.
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 undercut issues during the UBM etching process, enhancing adhesion with underfill materials and maintaining a vertical profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper pillar bump technology is used to achieve finer pitch and higher current carrying capacity, then electrical performance and thermal performance are improved, but copper oxidation occurs during manufacturing leading to poor adhesion and reliability concerns
Solution Approach 1:
A non-metal sidewall protection structure (dielectric or polymer material layer) is introduced as an intermediary between the copper pillar sidewall and the oxidizing environment. This protection layer prevents direct contact between copper and oxygen during the UBM etching process and subsequent manufacturing steps, thereby preventing oxidation while maintaining adhesion quality.
Solution Approach 2:
The non-metal sidewall protection structure is formed on the copper pillar sidewalls before the UBM etching process and other manufacturing steps that could cause oxidation. This preliminary protective action ensures that the copper surface is already protected when exposed to potentially oxidizing environments during subsequent processing.
2Object-affected harmful factors
If conventional immersion tin process is used to provide tin layer on Cu pillar sidewalls, then oxidation is prevented, but process costs increase and adhesion between Sn and underfill deteriorates
Solution Approach 1:
The non-metal sidewall protection structure uses inexpensive dielectric or polymer materials that can be easily deposited and removed. This temporary protection layer serves its purpose during critical manufacturing steps and is then eliminated, avoiding the need for expensive immersion tin plating while maintaining oxidation prevention benefits.
Solution Approach 2:
The non-metal protection layer acts as a temporary intermediary that prevents oxidation during manufacturing but does not interfere with subsequent underfill adhesion. Unlike tin layers that create adhesion problems with underfill, this organic-based protection layer can be completely removed or designed to be compatible with underfill materials.
3Manufacturing precision
If isotropic wet etching is used on UBM layer, then etching is uniform in all directions, but undercutting of UBM material occurs leading to loss of bump width and delamination
Solution Approach 1:
The non-metal sidewall protection structure serves as a mask or spacer during the UBM etching process, preventing the etchant from attacking the UBM material laterally at the copper-UBM interface. This maintains vertical sidewalls and prevents undercutting while allowing the isotropic etching process to proceed with uniform etching rates.
Solution Approach 2:
The thin non-metal protection layer conforms to the copper pillar sidewall shape and provides continuous coverage during etching. This thin film structure effectively blocks the etchant from causing undercutting while being thin enough to not interfere with the overall bump geometry or subsequent processing steps.
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, improves adhesion, reduces delamination risks, and maintains a vertical profile, addressing reliability concerns and process costs in copper pillar bump technology.
Implementation Method 1
A non-metal protective structure is formed on the copper pillar sidewalls to prevent oxidation
Implementation Method 2
An UBM generally contains an adhesion layer, a barrier layer and a wetting layer
Data Source
AI summary
A method of making a semiconductor device includes forming an under bump metallurgy (UBM) layer over a substrate, the UBM layer comprising sidewalls and a surface region. The method further includes forming a conductive pillar over the UBM layer, the conductive pillar includes sidewalls, wherein the conductive pillar exposes the surface region of the UBM layer. The method further includes forming a non-metal protective structure over the sidewalls of the conductive pillar, wherein the non-metal protective structure contacts the surface region of the UBM layer, and the non-metal protective structure exposes the sidewalls of the UBM layer.