Multi-Strike Copper-Aluminum Bonding for 3D Integration
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Solution Overview
Problem
The semiconductor industry faces limitations in increasing integration density due to physical constraints in two-dimensional integrated circuits, leading to increased circuit RC delay and power consumption, prompting the exploration of three-dimensional integrated circuits through wafer bonding techniques.
Innovation Solution
A multi-strike process is employed for bonding package components, where copper bumps with oxide layers strike aluminum pads, breaking the oxide layers to expose un-oxidized surfaces, followed by annealing to form an intermetallic compound bond without the need for solder or nickel layers, simplifying the bonding process and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solder bonding with nickel layers is used, then bonding reliability is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes the nickel layer from the traditional solder bonding process, extracting only the essential copper bump and solder ball components. This simplification maintains bonding reliability while reducing structural complexity and manufacturing cost by eliminating the intermediate nickel layer that requires additional deposition processes.
Solution Approach 2:
Instead of following the traditional sequence of copper bump with nickel layer then solder ball, the patent inverts the approach by using copper bumps directly bonded with solder balls without nickel intermediate layers. This inversion simplifies the bonding structure while achieving reliable electrical and mechanical connections through direct copper-solder bonding.
2Quantity of substance
If more devices are integrated into one chip, then integration density improves, but circuit RC delay and power consumption increase
Solution Approach 1:
The patent enables three-dimensional integration by stacking multiple device layers vertically through direct copper-solder bonding. This dimensional transition from 2D to 3D integration allows higher device density without proportionally increasing interconnection length, thereby controlling power consumption and RC delay despite increased integration density.
3Object-affected harmful factors
If oxide layers on copper bumps are present, then oxidation protection is provided, but bonding quality deteriorates
Solution Approach 1:
The patent applies preliminary protective measures by forming a thin barrier layer or controlling oxide formation before bonding. This preliminary action allows the copper bump to maintain oxidation protection while ensuring that the oxide layer does not interfere with subsequent solder bonding, thus preserving both oxidation protection and bonding quality.
Solution Approach 2:
The patent controls the oxidation state of copper bumps by adjusting processing parameters such as atmosphere control, timing, and temperature. By changing these parameters, the oxide layer is controlled to provide necessary oxidation protection during storage and handling while being thin enough or removable enough to allow high-quality solder 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 method enhances bonding reliability and reduces the need for chemical solutions, improving throughput and simplifying the structure formation, allowing direct bonding of copper and aluminum without additional layers, thus overcoming the limitations of two-dimensional integration.
Implementation Method 1
A multi-strike process is employed for bonding package components, where copper bumps with oxide layers strike aluminum pads, breaking the oxide layers to expose un-oxidized surfaces
Implementation Method 2
followed by annealing to form an intermetallic compound bond without the need for solder or nickel layers
Implementation Method 3
annealing to form an intermetallic compound bond
Data Source
AI summary
A method includes performing a first strike process to strike a metal bump of a first package component against a metal pad of a second package component. A first one of the metal bump and the metal pad includes copper. A second one of the metal bump and the metal pad includes aluminum. The method further includes performing a second strike process to strike the metal bump against the metal pad. An annealing is performed to bond the metal bump on the metal pad.