PhD - Leuven | More than two weeks ago
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:
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.