PhD - Leuven | About a week ago
The dry and anisotropic patterning of metals is a bottleneck for multiple aspects of advanced CMOS nanotechnology: spintronics, memory, nano-interconnects and EUV lithography. The main purpose of dry etching is to create volatile compounds at reasonably low temperature (below ~200 ˚C). For some particular metals, the use of plasmas containing traditional halogen such as Chlorine (Cl2, BCl3) or Fluorine (CF4, SF6, NF3) does not allow to form reaction products below 350 ˚C, rendering their etching too complex and expensive. Up till now, the most successful etch attempt is based on noble gas ion beam technology, where high energetic non-reactive atoms (Ar, Xe) are used to bombard the target surface, removing its atoms by sputtering (they are ejected mechanically). Ion beam is non-selective (etches almost everything), not compatible with dense structures, lead to severe residues deposits and damage to the remaining layers. A paradigm change is therefore required: i.e. exploring innovative methods and chemistries.
The proposed PhD work will explore new approaches for etching metallic elements and compounds using chelation chemistry. The proposed research will address three important questions: what is the best surface preparation method? What are the best chelating reactants and reactions conditions? And, finally, what is the optimal patterning scheme allowing to create technology-relevant nanostructures using the proposed new etch processes? The target materials will be at start pure elements such as Ni, Co, Fe then will be extended to alloys such as CoFeB, Ni3Al (more exotic elements or alloys will be considered). The principle of atomic layer etching will be used, where the process is cyclic with time-separated steps. As possible sequence is as follows: first, pre-treatment of the surface to enhance its chemical reactivity; in a second stage the activated surface is exposed to reactive chelating species in the vapor phase, leading to energetically favorable formation of volatile (metal-organic) products. The key requirement for each step is its self-limiting nature and/or the ability to control it at the sub-nanometer level, i.e. atomic layer resolution. Self-limiting surface pre-treatment might rely on directional reactive beams (for oxidation or oxidative halogenation), with low energy and high collimation. Anisotropy will be enhanced by selective sidewall passivation (area-selective deposition).
More practically, the PhD work will be separated into four different activities: 1) in collaboration with the team of Dennis Van Dorp, pre-screening of best metal-oxidant/organic combination through wet dip into organic solutions; 2) after establishing a starting database, in collaboration with the team of Geoffrey Pourtois, the reaction paths will be theoretically modelled by ab-initio calculation coupled to thermodynamic generator over technologically relevant T and P ranges; 3) transfer of acquired knowledge to a vapor etching system enabling in-situ surface treatment and organic vapor exposure; 4) development of sidewall passivation techniques so as to enable anisotropic pattern transfer. The work will be applied to device manufacturing and involve the learning of the full nanofabrication flow of the target application(s), as well as electrical/magnetic/optical measurements of device characteristics. The work will be performed in close collaboration with device and material scientists from IMEC, as well as material and tool suppliers.
As a PhD student, you will learn to work in a highly dynamic and multicultural environment and be exposed to a large variety of analytical techniques and experimental methods. Gas-phase etching will be performed in a 300mm industrial-scale reactor; surface preparation will be performed using reactive gas exposure, plasma and ion beams approaches, all in industry-relevant 300mm systems. Surface physics will be studied by means of X-ray reflectivity, AFM and scanning electron microscopy. Surface chemistry will be studied both ex situ and post operando by x-ray photoelectron spectroscopy (XPS), but also by Secondary Ion Mass Spectroscopy (SIMS). Other complementary techniques like elastic recoil detection analysis, electrical characterization, transmission electron microscopy are available to complement your studies.
The PhD candidate must have excellent hands-on skills, have basic knowledge in organo-metallic chemistry. The PhD candidate must be open to travelling abroad to perform some experimental work.
Required background: master in chemistry or materials science, nanotechnology, physics
Type of work: 5% literature and technology study, 65% experimental work, 20% modelling, 10% article writing
Supervisor: Stefan De Gendt
Co-supervisor: Michael Kraft
Daily advisor: Jean-Francois de Marneffe, Dennis van Dorp, Geoffrey Pourtois
The reference code for this position is 2021-069. Mention this reference code on your application form.