Flip Chip Under-Bump Metallurgy for Oxidation Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Aluminum interconnect structures in integrated circuits face signal propagation delays and challenges in depositing conductive materials in smaller openings, while copper interconnects offer better conductivity but require additional processing steps and are prone to oxidation, making flip-chip solder bump formation complex and costly.
Innovation Solution
The method involves forming a first conductive pad on a semiconductor substrate, a passivation layer with an opening to expose the pad, a second conductive pad within the opening, an under-bump metallurgical structure on the exposed surfaces, and a solder bump over the metallurgical structure, eliminating the need for a final passivation layer and improving step coverage and electromigration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper interconnects are used instead of aluminum, then conductivity and electromigration resistance are improved, but processing complexity and oxidation susceptibility increase
Solution Approach 1:
The invention segments the pad structure into multiple functional layers: aluminum bond pad, tungsten cap, and solder bump. This segmentation allows each layer to perform its specific function optimally - aluminum for bonding, tungsten for oxidation resistance and conductivity, and solder for interconnection - thereby achieving copper-like reliability without the processing complexity of full copper interconnects.
Solution Approach 2:
The tungsten cap serves as an intermediary layer between the aluminum bond pad and the solder bump. It mediates the interaction by providing oxidation resistance and improved electromigration properties while maintaining compatibility with both aluminum and solder materials, thus achieving the benefits of copper interconnects without requiring copper deposition processes.
2Productivity
If flip-chip solder bump formation is implemented, then connection density and electrical performance are improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention performs preliminary actions by forming the tungsten cap and under-bump metallurgy structures before solder bump deposition. This preliminary preparation ensures proper wetting, adhesion, and electrical connection are established in advance, simplifying the subsequent solder bump formation process and reducing manufacturing complexity while maintaining high connection density.
Solution Approach 2:
The tungsten cap and under-bump metallurgy structures provide self-service functions by automatically ensuring proper solder wetting and adhesion without requiring additional complex processing steps. The materials and structures are designed to self-organize and self-adjust during solder bump formation, reducing the need for precise external control and simplifying manufacturing.
3Reliability
If aluminum bond pads are exposed to contaminants, then oxidation and degradation occur, but encapsulation increases processing steps
Solution Approach 1:
The tungsten cap acts as an intermediary protective layer between the aluminum bond pad and the external environment. It provides oxidation resistance and contamination protection while maintaining electrical conductivity and mechanical integrity, thereby protecting the aluminum pad without requiring additional complex encapsulation layers.
Solution Approach 2:
The invention uses composite material structure combining aluminum, tungsten, and solder materials in a multi-layer configuration. Each material contributes its specific properties - aluminum for bonding, tungsten for oxidation resistance, and solder for connection - creating a composite structure that provides protection and functionality without requiring separate encapsulation layers.
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 approach reduces processing costs, improves cycle time, and enhances wafer yield by encapsulating aluminum pads with under-bump metallurgical structures, reducing exposure to contaminants and improving mechanical and metallurgical interfaces, thus addressing the challenges of copper interconnects and flip-chip solder bump formation.
Implementation Method 1
improving electromigration resistance and protecting the aluminum pad from oxidation and contaminants
Implementation Method 2
forming an under-bump metallurgical structure and a solder bump over the metallurgical structure
Data Source
AI summary
A solder bump structure and an under bump metallurgical structure. An upper surface of a semiconductor substrate comprises a first conductive pad (200) disposed thereon. A passivation layer (202) overlies the upper surface. A second conductive pad (212) is disposed in an opening (204) in the passivation layer and in contact with the first conductive pad. The under bump metallurgical structure (300) encapsulates the second conductive pad, covering an upper surface and sidewalls surfaces of the second conductive pad, protecting both the first and the second conductive pads from environmental and processing effects. According to the present invention, the conventional second passivation layer is not required. Methods for forming the various structures are also presented.