Pulse-Laser Bonding for Through-Silicon-Via Interconnects
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Solution Overview
Problem
Existing bonding methods for through-silicon-via (TSV) based 3D die-stacking, such as diffusion bonding, soldering, and adhesive bonding, face challenges in achieving reliable and cost-effective connections while maintaining high component density and small form factor in electronic devices, with issues like high temperature requirements, reflow reliability concerns, and low bonding strength.
Innovation Solution
A pulse-laser based bonding method that forms intermetallic compounds by aligning metal plugs in TSVs and applying a controlled pulse of laser energy, using metals like Au, Cu, Sn, In, Ag, Ni, and W, with optional adhesion and isolation layers, to create strong and reliable bonds between semiconductor components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diffusion bonding is used to bond semiconductor components, then good bond quality and reliability are achieved, but high bonding temperature and requirement for very good coplanarity make the method difficult and expensive to implement
Solution Approach 1:
The patent applies periodic pulsed laser heating instead of continuous high-temperature heating. The laser delivers energy in short pulses (e.g., 10-1000 microseconds duration) to locally heat the metal bonding layers at the via interfaces, allowing bonding to occur at lower overall temperatures while maintaining good bond quality through repeated thermal cycles that promote diffusion without requiring sustained high temperatures.
Solution Approach 2:
The patent uses localized laser heating concentrated at the via locations where metal bonding layers are present. The laser beam is focused to a small spot size (e.g., 10-50 micrometers) to heat only the specific areas requiring bonding, rather than heating the entire wafer surface. This local heating approach reduces the overall temperature requirement while achieving effective bonding at the critical interfaces.
2Reliability
If soldering is used to bond semiconductor components, then good reliable bond is produced at lower temperatures, but the soldering process causes reflow of previously created solder joints when new components are added to the stack
Solution Approach 1:
The pulsed laser bonding process allows for staged, incremental bonding of multiple components. Each component can be bonded separately using controlled laser pulses, and the previously bonded joints remain stable because the laser energy is localized to the current bonding interface. This periodic, localized heating prevents thermal reflow of existing joints while enabling continuous stacking of multiple components.
Solution Approach 2:
The localized nature of laser heating at specific via locations means that only the immediate bonding interface is heated to bonding temperature. Previously bonded joints at other locations are not significantly heated, preventing reflow. This spatially selective heating enables multi-layer stacking where each layer can be bonded independently without affecting the stability of previously created bonds.
3Ease of manufacture
If adhesive bonding is used to bond semiconductor components, then low cost and ease of manufacture are achieved, but bonding strength is low and it is not suitable for high current use
Solution Approach 1:
The patent replaces mechanical/adhesive bonding with laser-induced diffusion bonding. Instead of relying on adhesive materials and their associated manufacturing processes, the invention uses pulsed laser energy to directly bond metal layers through diffusion. This substitution eliminates the need for adhesive materials while achieving superior bond strength capable of handling high current applications, though the equipment complexity increases.
Solution Approach 2:
The patent changes the bonding mechanism from chemical adhesion to thermal diffusion bonding. By controlling laser parameters (pulse duration, energy density, wavelength) to achieve specific temperature profiles, the metal bonding layers are heated to temperatures that promote atomic diffusion and metallurgical bonding. This parameter-controlled approach transforms the bonding process from low-strength adhesive bonding to high-strength diffusion 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 provides high bond quality with medium temperatures, allows for multiple chip stacking, and reduces thermal stress, enabling efficient and cost-effective manufacturing with high throughput and reliability.
Implementation Method 1
the two metal bonding layers diffuse into each other to form the bond
Implementation Method 2
applying a pulse of laser energy to form a bond between said metal plugs
Data Source
AI summary
There is described a method of forming a through-silicon-via to form an interconnect between two stacked semiconductor components using pulsed laser energy. A hole is formed in each component, and each hole is filled with a plug formed of a first metal. One component is then stacked on another component such that the holes are in alignment, and a pulse of laser energy is applied to form a bond between the metal plugs.