Copper Pillar Bump Adhesion via In-Situ Protective Layer
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Solution Overview
Problem
The existing copper pillar bump technology faces issues with interfacial delamination between the conductive layer and the under bump metallurgy (UBM) layer due to copper diffusion and adhesion problems, leading to reliability and bonding strength concerns in integrated circuit packaging.
Innovation Solution
An in-situ deposited protective conductive layer is used over the conductive layer to prevent oxidation and improve adhesion, allowing for the omission of the lower UBM layer and enhancing the bonding between the copper pillar bump and the substrate, thereby reducing delamination risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper pillar bump technology is used to achieve finer pitches and reduce capacitance load, then manufacturing precision and electrical performance are improved, but interfacial delamination between conductive layer and UBM layer occurs due to copper diffusion and adhesion problems
Solution Approach 1:
A protective conductive layer is introduced as an intermediary between the base conductive layer and the UBM layer. This protective layer prevents copper diffusion to the UBM layer while maintaining electrical conductivity, thereby eliminating interfacial delamination issues and improving bonding reliability without sacrificing manufacturing precision
Solution Approach 2:
The conductive structure is designed as a composite system with multiple layers including base conductive layer, protective conductive layer, and UBM layer. Each layer serves specific functions: the protective conductive layer combines copper's high conductivity with barrier properties, creating a composite structure that simultaneously achieves fine pitch precision and interfacial bonding reliability
2Ease of manufacture
If conventional copper pillar bump structure is used, then manufacturing process is simplified, but adhesion problems occur leading to delamination between conductive layer and UBM layer
Solution Approach 1:
The conductive structure is segmented into distinct functional layers: base conductive layer for electrical connection, protective conductive layer for diffusion prevention and adhesion enhancement, and UBM layer for bonding. This segmentation allows each layer to be optimized independently while maintaining overall manufacturing simplicity and enhancing interfacial bonding strength
3Device complexity
If copper diffusion is allowed to occur, then manufacturing process is simpler, but adhesion between conductive layer and UBM layer deteriorates causing delamination
Solution Approach 1:
The protective conductive layer serves as a diffusion barrier intermediary that physically separates the base conductive layer from the UBM layer, preventing copper diffusion while maintaining electrical connectivity. This intermediary layer eliminates adhesion deterioration without significantly increasing structural complexity
Solution Approach 2:
The protective conductive layer creates an inert environment between the copper-containing base layer and the UBM layer, preventing harmful chemical interactions and diffusion. This inert barrier protects the interface from degradation while maintaining overall structural simplicity and enhancing adhesion reliability
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 solution effectively improves the adhesion quality between the conductive layer and the UBM layer, reducing interfacial delamination and enhancing the reliability and bonding strength of the copper pillar bump structure in integrated circuit packaging.
Implementation Method 1
The protective conductive layer and the base conductive layer are deposited in a vacuum without exposing the substrate to air or water, thereby preventing oxidation of the base conductive layer
Implementation Method 2
the copper pillar bump adheres to the protective conductive layer, thereby eliminating the need for the lower UBM layer
Data Source
AI summary
The mechanism of forming a metal bump structure described above resolves the delamination issues between a conductive layer on a substrate and a metal bump connected to the conductive layer. The conductive layer can be a metal pad, a post passivation interconnect (PPI) layer, or a top metal layer. By performing an in-situ deposition of a protective conductive layer over the conductive layer (or base conductive layer), the under bump metallurgy (UBM) layer of the metal bump adheres better to the conductive layer and reduces the occurrence of interfacial delamination. In some embodiments, a copper diffusion barrier sub-layer in the UBM layer can be removed. In some other embodiments, the UBM layer is not needed if the metal bump is deposited by a non-plating process and the metal bump is not made of copper.