The dry and anisotropic patterning of metals is a bottleneck for multiple aspects of advanced CMOS nanotechnology, spintronics, cryogenic electronics, quantum computing and EUV lithography. The main requirement is the need to create volatile compounds, in order to avoid the presence of non-volatile residues contaminating some part of the wafer and the chamber walls. Up till now, most attempts used low temperature continuous plasmas or noble gas ion beam technology. The pure plasma approach suffers from low etch rate, poor selectivity, and poor volatility of the formed compound; the ion beam approach is not compatible with tight pitch and lead to severe residues deposits and damage to the remaining layers. A paradigm change is required: i.e. exploring innovative methods and chemistries.
The proposed PhD work will explore new approaches for etching metallic elements and compounds using chelating chemistries. 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 reactivity with the next step; in a second stage the activated surface is exposed to reactive 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).
The PhD work will explore the different reactions paths and options for this technique. The PhD work will be separated into four different activities: 1) pre-screening of best metal-oxidant/organic combination through wet dip into organic solutions; 2) after establishing a starting database, 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.
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 pysics, chemistry, nanotechnology (Science or Engineering)_
Type of work: 70% experimental, 20% modeling, 10% literature
Supervisor: Stefan De Gendt
Daily advisor: Jean-Francois de Marneffe, Geoffrey Pourtois
The reference code for this position is 2020-059. Mention this reference code on your application form.