TiW Barrier and Nickel Interlayer for UBM Corrosion Prevention
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Solution Overview
Problem
The reliability of under bump metallization (UBM) structures in semiconductor devices is compromised due to the formation of brittle intermetallic compounds when copper comes into direct contact with solder bumps, affecting bond strength and wettability.
Innovation Solution
A UBM structure is fabricated with a thin copper seed layer protected by a sacrificial Cu oxide layer to prevent corrosion from the barrier layer, ensuring no blue vias form and maintaining bondability and wettability by using a titanium-tungsten (TiW) barrier layer and a nickel-base layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper is used in the UBM structure to increase bondability and wettability, then the bonding strength is improved, but copper reacts with solder bump to form brittle intermetallic compounds that compromise bonding strength
Solution Approach 1:
A nickel layer is introduced as an intermediary between the copper seed layer and the solder bump. The nickel layer prevents direct contact between copper and solder, thereby preventing the formation of brittle intermetallic compounds while allowing the copper layer to maintain its bondability and wettability functions.
Solution Approach 2:
The UBM structure is segmented into multiple functional layers: a copper seed layer for bondability and wettability, a nickel intermediate layer to prevent intermetallic formation, and a titanium-tungsten barrier layer for adhesion and diffusion barrier functions. This segmentation allows each layer to perform its specific function without interfering negatively with others.
2Reliability
If a thick copper layer is used to prevent corrosion, then the reliability is improved, but the wettability and bondability are compromised
Solution Approach 1:
The nickel layer serves as a protective intermediary that prevents corrosion of the copper seed layer from the solder bump side, eliminating the need for a thick copper layer. The copper layer can remain thin while still maintaining corrosion resistance through the protective nickel barrier.
Solution Approach 2:
The corrosion protection function is separated from the copper layer and assigned to the nickel intermediate layer. This allows the copper layer to be optimized for wettability and bondability with a thin thickness, while the nickel layer provides the necessary corrosion and intermetallic formation protection.
3Reliability
If multiple metal layers are used to protect copper from solder reaction, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The UBM structure is divided into distinct functional layers with clear roles: copper seed layer for surface properties, nickel intermediate layer for chemical protection, and titanium-tungsten barrier layer for physical barrier and adhesion functions. This segmentation provides reliability while maintaining manufacturing feasibility through established multi-layer deposition processes.
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 prevents corrosion of the copper seed layer, enhancing the reliability and integrity of the UBM structure, allowing all packages to pass quality tests and ensuring reliable chip-package interconnections.
Implementation Method 1
A metal oxide layer (e.g., CuO) is formed on the seed layer to prevent corrosion of the seed layer during the bump pattern step
Implementation Method 2
a barrier layer (e.g. TiW) is formed over the passivation layer and the bond pad and a seed layer (e.g., Cu) is formed over the barrier layer
Data Source
AI summary
Disclosed is an under bump metallization structure including a plurality of metal or metal alloy layers formed on chip bond pads with improved reliability due to a sacrificial metal oxide and the methods of making the under bump metallization structures. A barrier layer is formed over a bond pad. A seed layer is formed over the barrier layer. A bump resist pattern is formed exposing an area over the bond pad and a metal layer is electroplated on the seed layer.