Under-Bump Metallurgy Nickel Barrier for Electromigration
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Solution Overview
Problem
Traditional solder bump interconnect structures face issues with electromigration, leading to copper consumption and failure due to high resistance or electrical opens, especially under severe testing conditions.
Innovation Solution
Incorporating a nickel (Ni) barrier layer within the under-bump metallurgy (UBM) stack, which provides a stronger barrier resistant to electromigration by having a lower reaction rate than copper, thereby protecting the Cu seed layer from reacting with elements from the solder ball, and including additional Ni or alloying elements like titanium and cobalt to enhance barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Cu seed layer is used in the UBM stack for good electrical conductivity, then electrical performance is improved, but copper consumption and electromigration lead to reliability degradation under high current conditions
Solution Approach 1:
A nickel barrier layer is introduced as an intermediary between the solder ball and the Cu seed layer. This Ni layer acts as a mediator that prevents direct interaction between solder elements and copper, blocking electromigration of copper atoms while maintaining electrical conductivity. The Ni barrier layer thus protects the Cu seed layer from consumption without compromising the electrical performance of the interconnect structure.
Solution Approach 2:
The UBM stack is designed as a composite structure combining multiple materials (metallic adhesion layer, Cu seed layer, Ni barrier layer, and conductor layers) to achieve synergistic properties. The composite structure leverages the high conductivity of copper while using nickel's resistance to electromigration, creating a multi-functional system that simultaneously provides electrical conductivity and protection against material loss.
2Reliability
If additional barrier layers are added to the UBM stack to protect against electromigration, then reliability is improved, but device complexity increases
Solution Approach 1:
The UBM stack is segmented into distinct functional layers, each performing a specific role: the metallic adhesion layer for bonding, the Cu seed layer for electrical conductivity, the Ni barrier layer for electromigration protection, and conductor layers for current carrying. This segmentation allows each layer to be optimized for its specific function while working together as an integrated system, improving reliability without excessive complexity.
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 Ni barrier layer significantly reduces the formation of intermetallics and voids at the Cu seed layer, improving mechanical and electrical performance by preventing copper consumption and enhancing current distribution, thus increasing the reliability and durability of the interconnect.
Implementation Method 1
a nickel (Ni) barrier layer that is present in direct contact with the copper (Cu) seed layer... Metallic elements from the solder ball are obstructed from reacting with the Cu seed layer by the Ni barrier layer
Implementation Method 2
Incorporating a nickel (Ni) barrier layer within the under-bump metallurgy (UBM) stack, which provides a stronger barrier resistant to electromigration by having a lower reaction rate than copper
Data Source
AI summary
An interconnect structure that includes a substrate having an electrical component present therein, and a under-bump metallurgy (UBM) stack that is present in contact with a contact pad to the electrical component that is present in the substrate. The UBM stack includes a metallic adhesion layer that is direct contact with the contact pad to the electrical component, a copper (Cu) seed layer that is in direct contact with the metallic adhesion layer layer, a first nickel (Ni) barrier layer that is present in direct contact with copper (Cu) seed layer, and a layered structure of at least one copper (Cu) conductor layer and at least one second nickel (Ni) barrier layer present on the first nickel (Ni) barrier layer. A solder ball may be present on second nickel (Ni) barrier layer.