/Physics of dielectric breakdown revealed by low-frequency noise spectroscopy

Physics of dielectric breakdown revealed by low-frequency noise spectroscopy

PhD - Leuven | More than two weeks ago

Developing non-destructive testing methodologies for BEOL and MOL dielectrics

​Time dependent dielectric breakdown (TDDB) measurements are commonly used to assess the reliability of back-end-of-line (BEOL) and middle-of-line (MOL) insulators. Dielectric breakdown is one of the main causes of failure for interconnect systems, posing a serious threat to the functionality of electronic components expected to operate for at least 10 years under nominal operating conditions.

To estimate the perspective lifetime of a dielectric material, an accelerated, but still time consuming, test procedure is normally used: TDDB measurements are performed at higher fields and temperatures compared to nominal operating conditions. TDDB measurements are also a destructive technique since a constant stress voltage is applied until dielectric breakdown occurs. The inferred time-to-failure (TTF) is then used to extrapolate the lifetime at nominal operating conditions using one of the several models that have been developed over time predominantly based on empirical observations and physical modelling of dielectrics (Power Law Model, E-Model, 1/E Model, etc). Moreover, as the thickness of BEOL and ML dielectrics is being decreased with each new technology node, it has become evident that TDDB are not sufficient to fully understand the underlying physical mechanisms of dielectric failure. For example, surface/interface defectivity has been found to play a key role in metal drift-induced dielectric breakdown.

The objective of this PhD project is to investigate the potentiality of low-frequency noise (LFN) spectroscopy technique in revealing essential features of dielectric breakdown in thin insulating films. The LFN methodology relies on studying the statistical distribution of current fluctuations measured in a dielectric under constant stress voltage. LFN is a non-destructive technique and could provide meaningful insights about surface and bulk defectivity as well as the dominant conduction mechanism(s) as well as their evolution resulting in the breakdown event.

In more details, the main goal of the PhD student is to perform LFN measurements on BEOL and MOL stacks:

  • to study the impact of stress conditions (stress level, stress duration and temperature) on defects distribution within the dielectric(s). LFN data will then compared and validated by means of other defects characterization techniques, e.g. IPE, photoconductivity, and dielectric trap spectroscopy;
  • to improve the understanding of failure mechanisms by focusing on the role played by metal/dielectric and dielectric/dielectric interfaces;
  • to develop a lifetime prediction model based on non-destructive test approach based on LFN measurements. The model should cover both intrinsic dielectric breakdown as well as metal drift-induced dielectric breakdown. The model will then be calibrated using standard measurements techniques (e.g. TDDB).

Required background: Semiconductor Physics, Material Science, Engineering Technology, Mathematics

Type of work: 40% Experimental, 20% Interpretation, 20% Literature, 20% Modelling

Supervisor: Valeri Afanasiev, co-supervisor Kristof Croes

Daily advisor: Davide Tierno

The reference code for this position is 2022-118. Mention this reference code on your application form.