/Directional Etching of Metals and Alloys by Plasma Enhanced Vapor Etch (PEVE)

Directional Etching of Metals and Alloys by Plasma Enhanced Vapor Etch (PEVE)

Leuven | More than two weeks ago

You will explore a new film removal technique which combines surface preparation by plasma followed by selective gaseous reactions

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The downscaling of nanoelectronics devices is leading the digital transition, a revolution enabled by the improvement of the performance at lower power and cost. A breakthrough in the field is the extent of the devices’ geometry from two to three dimensions to increase the number of transistors per volume. It has been first done through vertical channel (FinFETs), and in the future by stacking NMOS and PMOS devices on top of each other (CFET). Performance gain is also enabled by stacking chips on top of each other. Going from 2D (planar technology) to 3D (CFET + chip stacking) is a paradigm shift which require the introduction of new processes and materials, as the conventional ones such as Si, SiO₂ or Cu are reaching their properties limits.

3d transition metals and metallic alloys (3d-MAs) are very promising candidates towards better interconnects (improve electrical conductivity at the nanoscale), better memory (magnetoresistive RAM-MRAM), new spin logic (spin torque majority gates-STMG) and higher printing resolution (mask adsorbers for EUV lithography). Depending on the application, the 3d-MAs of interest are selected based on the following factors (i) Their estimated conductivity at the nanoscale (film thickness <10nm) (ii) Their n and k value at EUV wavelength (13.6 nm) (iii) Their ferromagnetic properties at the nanoscale (film thickness <1.5nm). Among the many candidates, Co-based alloys are considered as most promising for all above-mentioned applications. Another element of revived interest is Cu, which is used for 3D chip stacking (Through Silicon Vias, Redistribution layers) and poses several integration challenges.

New materials come along with new challenges in developing nanofabrication methods. So far, the most prominent one for the 3d-MAs is their anisotropic etching: preferably removing some materials in a vertical direction. Etching directionality is a mandatory requirement for developing devices in 3D, as it allows the different structure composing the devices to be placed closer each from the others (contrary to isotropic etching). Conventional anisotropic (dry) etching process mainly relies on halogen-based plasma (F, Cl, Br), but 3d-MAs are not volatile in the temperature range acceptable for CMOS devices when reacting with halogens alone. That is why the development of new etching processes is needed, to enable gains in computing performance.

Exploring a different chemical removal pathway is necessary, enabling removal at nanoscale, low temperature and halogen-free (more environmentally friendly). These requirements translate into the need for a cyclic process called atomic layer etching (ALE) forming volatile organo-metallic compounds. The ALE is composed of two main steps, described as: a first surface preparation step (increase of oxidation level of the outer metallic layer), followed by a second removal step, where organic molecules attach to the surface, forming stable organo-metallic bonds. Ultimately, volatile organo-metallic molecules are formed, which can desorb under small energy input (thermal, chemical or kinetic) leading to desorption and etching.

The objective of this doctoral work is to achieve a directional etching, meaning that one of the two steps of the ALE recipe must be anisotropic. Therefore, a directional plasma (halides, oxygen, nitrogen, or mixtures) assisted by substrate bias and sidewall passivation will be used to achieve a preferential surface modification on the horizontal plane, i.e. the bottom of the structures. After surface preparation, when exposed to gaseous organic precursor, volatile 3d organo-metallic compound will be formed with the modified surface, i.e. only the horizontal surface, resulting in an anisotropic etching.

The research work will take place in imec's FABs and LAB facilities but might also require travelling abroad for short periods, in order to run experiments in associated labs. As a doctoral student, you will be trained to use a wide range of tools in multiple labs, analyze and interpret data, interact with various scientists and engineers at imec and in associated academic labs. You will present (part) of your work at international conferences and publish scientific papers. Your background consists preferably in a master's in chemistry or physics. You need to demonstrate extensive lab experience, rigorous organization and problem-solving skills. You are gifted for good and soft communication and can adapt in a multicultural work environment.

Required background: Master in chemistry, master in physics

Type of work: 50% experimental, 30% data analysis and interpretation, 20% literature

Supervisor: Stefan De Gendt

Co-supervisor: Jean-Francois de Marneffe

Daily advisor: Jean-Francois de Marneffe, Dennis van Dorp, Alexis Franquet

The reference code for this position is 2025-055. Mention this reference code on your application form.

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