Conductive Bump with Pd-Pt Barrier Layer for Micro-Interconnects
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Solution Overview
Problem
In three-dimensional integrated circuits, micro bumps with diameters of 20 μm or less face challenges in forming a reliable connection due to the diffusion of base metals into the Au or Ag layer, and conventional electroless Pt plating baths are unstable, leading to poor connection reliability and plating bath instability.
Innovation Solution
A conductive bump structure comprising a base conductive layer, a Pd layer, and a Pt layer, with the Pt layer directly contacting the Pd layer, and an electroless Pt plating bath containing a water-soluble platinum compound, a reducing agent, a buffer agent, and ammonium chloride, which enhances the stability and coverage of the Pt layer, preventing base metal diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Pt layer is formed directly on the base conductive layer to prevent metal diffusion, then connection reliability is improved, but the electroless Pt plating bath becomes unstable and Pt particles are deposited
Solution Approach 1:
A Pd layer is introduced as an intermediary between the base conductive layer and the Pt layer. This Pd intermediate layer serves as a stable substrate for Pt deposition, preventing direct contact between Pt and the base metal while maintaining plating bath stability and preventing Pt particle precipitation.
Solution Approach 2:
The invention modifies the plating bath composition by adding specific agents (citric acid, tartaric acid, or malic acid along with ammonia or ammonium salts) to change the chemical parameters of the bath, thereby stabilizing it and preventing unwanted Pt particle deposition while still enabling effective Pt layer formation.
2Area of moving object
If the bump diameter is reduced to 20 μm or less for high-density interconnection, then integration density is improved, but the Pt layer cannot be effectively formed and connection reliability deteriorates
Solution Approach 1:
The Pd layer acts as an intermediary that enables effective Pt deposition on micro-scale substrates (20 μm or less). The Pd intermediate layer provides a suitable surface for Pt nucleation and growth, allowing uniform Pt layer formation even on very small bump structures where direct Pt deposition would fail.
Solution Approach 2:
The plating bath composition is specifically optimized with pH control agents (ammonia or ammonium salts combined with organic acids) to maintain stable deposition conditions at micro-scale dimensions, enabling reliable Pt layer formation on 20 μm or smaller bumps.
3Device complexity
If the base metal layer is used directly without intermediate layers to reduce structure complexity, then manufacturing simplicity is improved, but metal diffusion occurs into the Au or Ag layer under high-temperature thermal history
Solution Approach 1:
A Pd layer is introduced as a diffusion barrier intermediary between the base conductive layer and the Au or Ag layer. This intermediate layer effectively blocks metal diffusion under high-temperature conditions while adding minimal structural complexity.
Solution Approach 2:
The invention creates a composite multi-layer structure (base conductive layer + Pd layer + Pt layer + Au/Ag layer) where each layer serves a specific function. The Pd and Pt layers work together as a composite barrier system to prevent diffusion, providing superior protection compared to single-layer structures.
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 proposed solution effectively prevents base metal diffusion into the Au or Ag layer, improving connection reliability and stabilizing the electroless Pt plating bath, even under high-temperature thermal history, while maintaining thin layer thickness for compact integrated circuits.
Implementation Method 1
an electroless Pt plating bath for forming the Pt layer
Implementation Method 2
the electroless Pt plating bath comprises a water-soluble platinum compound, a reducing agent, a buffer agent and ammonium chloride
Data Source
AI summary
The present invention provides a bump that can prevent diffusion of a metal used as a base conductive layer of the bump into a surface of an Au layer or an Ag layer. A conductive bump of the present invention is a conductive bump formed on a substrate. The conductive bump comprises, at least in order from the substrate:a base conductive layer;a Pd layer;a Pt layer; andan Au layer or an Ag layer having directly contact with the Pd layer, wherein a diameter of the conductive bump is 20 μm or less.