Cu-Cu Bonding via Galvanic Anodic Layer
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Solution Overview
Problem
Current copper-to-copper (Cu-Cu) bonding technologies face challenges with rapid oxide formation on Cu surfaces, requiring high temperatures (around 400°C) for successful bonding, which can damage materials like polymers, and have not achieved a practical solution for high-volume manufacturing, despite attempts such as acid dip bonding, insertion bonding, self-assembled monolayers, and surface activation bonding.
Innovation Solution
The formation of a galvanic couple between Cu and metals like magnesium (Mg), where Mg's porous oxide growth inhibits Cu oxidation, allowing Cu-Cu bonding at reduced temperatures (≤200°C) with reduced oxide formation, using anodic and cathodic metal layers in a semiconductor structure, providing cathodic protection and enabling faster cycle times and longer staging times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature (around 400°C) is used for Cu-Cu bonding, then bonding success is achieved, but materials like polymers are damaged and processing time increases
Solution Approach 1:
A galvanic couple structure is introduced as an intermediary system between the Cu surfaces to be bonded. The anodic metal layer (Mg, Al, Zn, or Ni) acts as a mediator that chemically inhibits Cu oxidation through galvanic protection, enabling bonding at lower temperatures without direct high-temperature exposure that would damage polymers
Solution Approach 2:
The oxidation potential parameters of the Cu surface are changed by introducing metals with higher oxidation potentials (Mg: 2.37V, Al: 1.66V, Zn: 0.76V, Ni: 0.25V) according to the galvanic series. This parameter change creates a protective electrochemical environment that allows bonding at reduced temperatures (≤200°C)
2Reliability
If high temperature bonding is used, then oxide formation is overcome, but processing speed decreases and cycle time increases
Solution Approach 1:
The anodic metal layer serves as a chemical intermediary that actively prevents Cu oxide formation through galvanic protection. This mediator creates a reducing environment at the Cu surface, eliminating the need for high-temperature oxide removal processes and enabling faster processing
Solution Approach 2:
The protective anodic metal layer is applied in advance before bonding occurs. This preliminary protective action prevents oxide formation during storage and handling, allowing components to be staged longer and processed faster without oxide-related delays
3Reliability
If special bonding measures (acid dip, insertion bonding, surface activation) are applied, then bonding reliability improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The galvanic couple approach creates a uniform, consistent protective environment across the entire Cu surface through a single standardized structure. This homogeneous solution replaces multiple different special treatments (acid dip, insertion bonding, surface activation) with one consistent galvanic protection mechanism, simplifying manufacturing
Solution Approach 2:
By changing the electrochemical parameters of the Cu surface through the galvanic couple (using metals with known oxidation potentials from the galvanic series), a predictable and controllable bonding environment is created. This parameter-based approach provides consistent results without the variability and complexity of multiple special processing steps
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 significantly reduces Cu oxide formation, enabling Cu-Cu bonding at lower temperatures without special measures, resulting in faster processing times and longer queue times, suitable for high-volume manufacturing.
Implementation Method 1
the anodic metal layer may be configured to inhibit growth of an oxide associated with the cathodic metal layer by providing cathodic protection to the cathodic metal layer
Implementation Method 2
an oxidation potential of the anodic metal layer may be greater than an oxidation potential of the cathodic metal layer
Implementation Method 3
the anodic metal layer may include a metal associated with a porous oxide and an oxidation rate of the porous oxide may be linear as a function of time
Data Source
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AI summary
Methods and apparatus are described for enabling copper-to-copper (Cu-Cu) bonding at reduced temperatures (e.g., at most 200°C) by significantly reducing Cu oxide formation. These techniques provide for faster cycle time and entail no extraordinary measures (e.g., forming gas). Such techniques may also enable longer queue (Q) or staging times. One example semiconductor structure (100) generally includes a semiconductor layer (102), an adhesion layer (104) disposed above the semiconductor layer (102), an anodic metal layer (106) disposed above the adhesion layer (104), and a cathodic metal layer (108) disposed above the anodic metal layer (106). An oxidation potential of the anodic metal layer (106) may be greater than an oxidation potential of the cathodic metal layer (108). Such a semiconductor structure (100) may be utilized in fabricating IC packages (300, 400) implementing 2.5D or 3D integration.