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/Job opportunities/Characterization of IMC (intermetallic compound) properties used at 3D stacking high density interconnects

Characterization of IMC (intermetallic compound) properties used at 3D stacking high density interconnects

PhD - Leuven | More than two weeks ago

As PhD researcher in the 3D system integration group, you will be involved in the fabrication, 3D bonding, electrical test and characterization of IMC material properties, using state-of-the-art facilities at imec.

To improve the performance and functionality of electronics devices, beside scaling transistor gate length and high mobility transistors, 3D stacking of Si chips and wafers lowers the interconnect length, allows to combine different technologies and nodes to finally obtain a high-performance device.

Interconnects in 3D staking are made by direct metal to metal bonding or solder-based bonding. Solder based bonding offers a fast and high throughput solution for bonding two different chips which may have been made from different technologies, different die sizes and different functionalities. The increasing density and scaling of devices on the chips also require an increasing density of the solder bonds, and thus a decrease in their size down to a few microns. . During solder bonding a brittle IMC layer is made which may have reliability concerns especially when the size of connections and joints become small.



The goal of this PhD thesis is to study the properties of IMC layers when bump sizes are in the few microns range and to propose a good working system for high density interconnects.  



The properties to be studied include:

  • IMC growth rate at solid state and molten phases
  • IMC grain evolution with scaling bump dimension
  • Electrical and mechanical properties of IMCs for decreasing bump diameters
  • Reliability properties of such small bumps, such as electromigration and mechanical robustness

These properties will be studied using in-situ electrical measurements at different temperatures on dedicated test samples; X-ray CT analysis (if possible also in-situ) of the solder and of the IMC shape and evolution, and of bonded stacks (voids, delamination, solder volume distribution); and cross-sectional SEM/EBSD analysis of the solder bumps, Additional analysis techniques such as AFM to study roughness, XPS and Auger to study material composition,  and contact angle measurements to study wettability will also be applied (by the PhD student or in collaboration with tool experts). To understand the IMC phase evolution and wettability, phase field and molecular dynamic simulations might be needed as well.


The PhD candidate has preferably a materials engineering background. Know-how of electrical measurements and different analyses techniques such as SEM, XPS, Auger, contact angle measurements, TEM, AFM, XCT and EBSD is an advantage.

Required background: material science, electrical engineering, physics

Type of work: 50% experimental, 30% simulation, 20% literature and analysis of data

Supervisor: Ingrid De Wolf

Daily advisor: Jaber Derakhshandeh

The reference code for this position is 2021-028. Mention this reference code on your application form.