Dewetting of compounds studied by isotope labeling

Significance 

During high temperature treatments, thin solid films with submicron thicknesses have a tendency to break up into islands in a bid to lower the resultant free energy. Generally, this phenomenon is referred to as “agglomeration” or “dewetting”. Research has revealed that the said phenomenon is usually driven by the minimization of the total energy, including the film surface energy, the substrate-surface energy and the film-substrate interfacial energy. These thin films have a large surface area to volume ratio which induces a high driving force for agglomeration making such films more susceptible to agglomerate. With all factors considered, it can be agreed that dewetting/agglomeration is a vital process in material science since it controls the stability of thin films or can be used for film nano-structuration by formation of islands.

Models developed for dewetting usually assume diffusion at the interface and/or at the surface but no direct evidence of such diffusion has so far been demonstrated. Worse off, majority of such models mainly deal with elemental materials and not with compounds in which several elements can diffuse. To sum it up, till now the mechanism responsible for agglomeration of polycrystalline compound thin films is yet to be fully understood.

In a recent publication, IM2NP Research Institute scientists Dr. Ting Luo and Pr. Christophe Girardeaux together with Pr. Hartmut Bracht at University of Münster and Dr. Dominique Mangelinck from CNRS, Aix-Marseille University investigated the mechanism of agglomeration for the Ni monosilicide using silicon isotope multilayers and atom probe tomography (APT). They focused on revealing the agglomeration mechanism behind nickel monosilicide (NiSi), a binary compound largely used as contacts for advanced devices. Their work is currently published in the research journal, Acta Materialia.

To begin with, the research team started by employing APT to determine the redistribution of the silicon (Si) isotopes, both in NiSi and in the Si substrate in a bid to map out the distribution of atoms in three dimensions (3D) and distinguish between different isotopes with an atomic resolution. Next, they engaged in a direct experimental approach whose aim was to offer evidence for Si diffusion along the NiSi/Si interface, which, as a result, would give an access to the agglomeration mechanism of NiSi thin films. Models to establish diffusion paths during the agglomeration process were also developed.

The authors chiefly reported on the diffusion of Si, the less mobile species in NiSi. In particular, this diffusion at the NiSi/Si interface was demonstrated through comparison between the three-dimension redistribution of the Si isotopes determined by APT and models taking into account grooving and agglomeration. Additionally, they also reported that the multilayer structure was maintained in some regions of NiSi showing a limited diffusion of Si in NiSi.

In summary, the study determined the 3D redistribution of Si isotopes using APT for an agglomerated film of NiSi obtained by the reaction between a 15nm nickel film and the Si isotope multilayers. Generally, the study demonstrated that diffusion of the less mobile species is of crucial importance for agglomeration of compounds. Indeed, quantitative prediction of dewetted shapes necessitates improved models and simulations of dewetting through the knowledge of the mechanism. Altogether, results reported the associated model provide a new way for simulations of dewetting and thus for producing complex structures

About the author

Dr. Ting Luo received a bachelor’s degree of material chemistry from Central South University in Changsha, China in 2012. After that, she studied in Institute of metal research (IMR), Chinese Academy of Sciences in Shenyang, China for three years and got a master’s degree of material science and processing in July 2015. From October 2015, she conducted her PhD study in Aix-Marseille University and IM2NP (Marseille, France) under the supervision of Director de chercher Dominique Mangelinck and Professor Christophe Girardeaux. She investigated formation mechanisms of Ni-silicides by atom probe tomography and isotope diffusion and she received a doctor degree of material science and physics in November 2018.

Currently, she is a postdoc fellow in Max-Planck-Institut für Eisenforschung GmbH in Düsseldorf, Germany. Her research interests include reactive diffusion, characterization of materials at atomic scale using atom probe tomography (APT), semiconductor and thermoelectric materials.

About the author

Christophe Girardeaux is a chemist of materials science who worked, from 1990 to 1993, as a PhD student for the IBM laboratories of Corbeil-Essonnes (France). He obtained his Ph.D. from the Diderot University (Paris 7, France) in 1993. From 1994 to 1996, he has been a postdoctoral fellow in the LISE laboratory of the Notre Dame de la Paix faculty in Namur (Belgium). In 1997 he has been working as a CNRS research scientist at the L2MP laboratory in Marseille (France) and then, since 2004 he is a research professor at the IM2NP institute in Marseille (France).

He is currently Deputy Director of the IM2NP Research Institute. The research throughout his career has been mainly devoted to the investigation of matter transport at the nanoscale.

About the author

Hartmut Bracht received his Ph.D. degree from the University of Münster in 1993. He was awarded with the Feodor-Lynen Fellowship of the Alexander von Humboldt Foundation and with the Heisenberg Fellowship of the Deutsche Forschungsgemeinschaft and was research fellow at the Lawrence Berkeley National Laboratory and the University of California at Berkeley (USA). Presently he is Professor at the Institute of Materials Physics at the University of Muenster in Germany.

His research interest concerns experimental and theoretical studies on atomic and heat transport in semiconductors to characterize diffusion and defect reactions and heat flow in semiconductor materials.

He has authored/coauthored more than 170 scientific publications in various international journals and conferences. In his career, he presented more than 240 scientific talks at various national and international conferences and seminars across the world, more than 70 of which were invited talks. Prof. Dr. Bracht has supervised 19 PhD and 41 physics diploma, masters and bachelor students.

About the author

Dominique Mangelinck is research director in CNRS at the institute Materials Microelectronics Nanosciences of Provence (IM2NP). He has received the bronze medal from CNRS in 2003. He has obtained in 1995 a Ph.D. in Materials Science that was on the alloy effect on the formation, the epitaxy and stress of nickel silicide. From 1996 to 1997, he held a postdoctoral position at the Royal Institute of Technology of Stockholm (Sweden) to study the redistribution of dopant in silicide and in SiGe, and the formation and electrical properties on alloyed Fe silicide. From 1998 to 2000, he has been research fellow in the Institute of Materials Research and Engineering (Singapore) to develop the integration of the Ni monosilicide in microelectronics through the salicide process. Since 2000, he is CNRS researcher in IM2NP .

His research is mainly devoted to diffusion and phase transformation in nanometric materials. He used in-situ experiments and other analysis such as APT to understand the fundamental mechanisms of diffusion and reaction and to develop industrial processes for metallurgy, aeronautics and mainly microelectronics. He has published more than 170 scientific papers, holds 4 patents and was involved in more than 60 invited talks and more than 170 communications in conferences.

Reference

T. Luo, C. Girardeaux, H. Bracht, D. Mangelinck. Role of the slow diffusion species in the dewetting of compounds: The case of NiSi on a Si isotope multilayer studied by atom probe tomography. Acta Materialia, volume 165 (2019), page 192-202.

Go To Acta Materialia

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