Impact of thermal gradients on the reliability of nano-wires, 3D-TSVs and heaters

Leuven - PhD
More than two weeks ago

Solving a head-breaking reliability problem


Recent developments in advanced on-chip and 3D-TSV interconnects lead to the introduction of thermal gradients during chip operation and reliability testing. Also, metal or Si-heaters for Si photonics applications require high currents leading to thermal gradients.

Interconnects reliability is classically tested using constant current stresses at elevated temperatures. The interconnect failure mechanism triggered by these tests is called electromigration and the lifetime model used in this case is the classical Black's law. Unfortunately, this model is only valid if the Joule heating induced by the stress current in the metal line is limited. If this condition is not fulfilled, the parameters extracted with this model are meaningless.

While electromigration tests on nowadays interconnects fulfill the absence of Joule heating requirement, this is not the case in advanced on-chip and 3D-TSV interconnects (see figure). Obviously, for metal or Si-heaters for Si photonics thermal gradients need to be properly considered during reliability testing as well. As a result, a new approach to electromigration testing is needed.

3D-TSV interconnects


The goal of this PhD is to investigate and study the reliability of advanced interconnects when thermal gradients are present. The study should lead to the following achievements:
  • Gaining a deeper understanding of the electromigration failure mechanism when a thermal gradient is present in the line under test;
  • Building a reliability model calibrated and validated with experimental data measured on suitable test structures, which would allow lifetime predictions in function of the line dimensions and in presence of a thermal gradient;
  • Identifying by the model the suitable line dimensions, stress gradient and thermal gradient properties which guarantees the respect of the lifetime specs for the interconnections.


The following activities are foreseen: 

  • Deep understanding of the physics of electromigration;
  • Reliability characterization of advanced interconnects by electrical measurements and failure analyses to identify the failure modes and their localizations;
  • Design of test structures;
  • Statistical data analysis of reliability data extracted from electrical characterizations;
  • Building of analytical/computer models for interconnects lifetime predictions;
  • Interaction with process integration engineers to provide them feedback on the reliability characterization results.


Required background: Physics or Electrical engineering

Type of work: 10% Literature. 30% Modeling, 10% Test structure, 50% Experimental

Supervisor: Ingrid De Wolf

Daily advisor: Kristof Croes

The reference code for this position is 2020-031. Mention this reference code on your application form.
Chinese nationals who wish to apply for the CSC scholarship, should use the following code when applying for this topic: CSC2020-15.


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