Electroless Copper Bond Pad Structure for Void Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The semiconductor industry faces challenges with copper-metallized integrated circuits due to the formation of thin copper(I)oxide films, which inhibit reliable bonding and are susceptible to corrosion, and existing solutions like aluminum caps or nickel-palladium-gold layers encounter issues with adhesion, corrosion, and void formation.
Innovation Solution
A metal structure for contact pads with a first copper layer under an insulating overcoat, where a second copper layer with a transition zone is deposited, followed by a nickel layer and a noble metal layer, using electroless plating and palladium chloride activation to ensure controlled thickness and adhesion, reducing void formation and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a layer of aluminum is formed as a cap over the copper bond pad, then reliable bonding is achieved, but added cost and risk of scratching or smearing causing electrical shorts occur
Solution Approach 1:
The patent replaces expensive and problematic aluminum cap layers with a cost-effective electroless plating process using nickel and palladium layers. This disposable-like approach uses thin, controlled layers that are applied only where needed and removed or covered subsequently, eliminating the need for expensive aluminum capping while maintaining bonding reliability.
Solution Approach 2:
The patent changes the chemical and physical parameters of the bond pad surface through electroless plating, transforming the copper surface into a nickel-palladium-gold composite structure. This parameter change enables reliable bonding without requiring aluminum capping, thus resolving the contradiction between bonding reliability and process complexity.
2Reliability
If layers of nickel, palladium, and gold are deposited on the copper, then reliable bonding is achieved, but adhesion problems, corrosion, and void formation occur
Solution Approach 1:
The patent applies preliminary electroless plating of nickel and palladium layers onto the copper bond pad before final gold deposition. This preliminary action creates a stable, adherent base layer that prevents subsequent adhesion problems and corrosion, ensuring long-term stability of the multi-layer structure.
Solution Approach 2:
The patent uses a composite material structure of nickel-palladium-gold layers deposited electrolessly on copper. This composite approach combines the advantages of each material: nickel for adhesion, palladium for corrosion resistance, and gold for bonding reliability, while eliminating the individual problems of each layer through synergistic combination.
3Reliability
If electroless plating is used to deposit nickel and palladium on bare copper, then bonding reliability is improved, but void formation and undercut corrosion occur
Solution Approach 1:
The patent changes the surface parameters of the copper bond pad through controlled electroless plating, creating a uniform nickel layer that serves as a stable base for subsequent palladium and gold deposition. This parameter control prevents void formation and undercut corrosion by ensuring even layer distribution and proper adhesion.
Solution Approach 2:
The electroless plating process inherently provides feedback control through its chemical mechanism, where the deposition rate is self-regulating based on surface conditions. This feedback ensures uniform layer thickness and prevents defects such as voids and undercuts, maintaining manufacturing precision while achieving reliable bonding.
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 provides a low-cost, reliable bond pad structure with reduced void formation and corrosion, enabling uniform copper surfaces and controlled nickel layer thickness, enhancing production efficiency and yield while protecting against moisture and delamination.
Implementation Method 1
A layer of second copper of second thickness covers conformally the exposed first copper layer... deposited on the exposed portion of the first copper layer by an electroless plating technique
Implementation Method 2
The second copper is activated by exposing it to an acetic palladium chloride solution so that a controlled portion of the second copper is substituted by palladium
Implementation Method 3
A layer of nickel is on the second copper layer... providing a barrier and adhesion layer
Data Source
AI summary
A metal structure (100) for a contact pad of a semiconductor, which has interconnecting traces of a first copper layer (102). The substrate is protected by an insulating overcoat (104). The first copper layer of first thickness and first crystallite size is selectively exposed by a window (110) in the insulating overcoat. A second copper layer (105) of second thickness covers conformably the exposed first copper layer. The second layer is deposited by an electroless process and consists of a transition zone, adjoining the first layer and having copper crystallites of a second size, and a main zone having crystallites of the first size. The distance a void can migrate from the second layer is smaller than the combined thicknesses of the first and second layers. A nickel layer (106) is on the second copper layer, and a noble metal layer (107) is on the nickel layer.