Noncontact thermocompression bonding: suppressing shrinkage at CU nanowire interconnection interfaces

A laser-induced thermocompression bonding technique developed by researchers at Wuhan University enables the bonding of Cu nanowires with a diameter of 200 nm to Au pads.

Published in the International Journal of Extreme Manufacturing, this work introduces a noncontact nanojoining method to expand interconnecting interfaces between heterogeneous materials, creating significant opportunities for the integration and packaging of nanodevices.

Expanding Nanojoining Interfaces for Enhanced Device Performance

"The interconnect interface of the nanostructure is an important factor in determining device performance and reliability," said Chengqun Gui, corresponding author on the paper and Distinguished Professor at the Institute of Technological Sciences, Wuhan University, "The contact thermocompression bonding method is an efficient way to expand heterogeneous interconnect interfaces, but it is difficult to realize at the nanoscale. Here, we present a laser-induced thermocompression bonding strategy, which may address this problem."

Encountering Interfacial Shrinkage in Nanojoining

Interfacial shrinkage due to surface tension is an important factor in reducing nanojoining interfaces.

Due to the surface tension generated by thermal melting, it is difficult to suppress the shrinkage problem at the interconnect interface when using nanojoining strategies that rely on thermal effects. The small contact area between heterogeneous nanomaterials leads to high contact resistance and poor reliability, thereby reducing the performance and reliability of the device.

Overcoming the Shrinkage with Laser-Induced Bonding

To address this challenge, researchers employ a laser-induced approach to manipulate the interfacial properties of the nanowires. When a metal nanowire is illuminated, part of the incident light is scattered in the surroundings, while the other part gets absorbed and ultimately dissipated into heat. Light can exert force because it carries momentum, and a change in momentum is always coupled with the application of force.

By adjusting the laser intensity and polarization direction, the scattering force acting on the nanowire can be controlled. When the ratio of scattering force to gravity of the exposed nanowires exceeds 3,600, the Cu nanowires are thermocompressively bonded to the Au pad by the laser beam instead of shrinking into the nanosphere. Comparative analysis reveals that the Cu-Au interface area after thermalcompression bonding is enlarged by a factor of four, which significantly improves the contact resistance.

Exploring Next-Generation Devices with Low Damage and High Efficiency

"The noncontact thermocompression bonding technology provides significant possibilities for the interconnect packaging and integration of nanodevices." said co-corresponding author Sheng Liu, Distinguished Professor in the school.

The researchers are continuing this work and aim to further improve the integration and performance of the micro-nano devices. They also want to ensure that this noncontact nanojoining method offers the advantages of low damage and high efficiency, which are crucial for device reliability and industrialization.

About IJEM:

International Journal of Extreme Manufacturing (IF: 16.1, consecutive 1st in the Engineering, Manufacturing category) is a multidisciplinary and double-anonymous peer-reviewed journal uniquely publishing original articles and reviews of the highest quality and impact in the areas related to extreme manufacturing, ranging from fundamentals to process, measurement, and systems, as well as materials, structures, and devices with extreme functionalities.

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