ChemEng.Upatras Seminars 2022 - Nikolaos Cheimarios

Abstract

Chemical vapor deposition (CVD) process is one of the basic processes for the production of thin solid films. It is carried out in reactors equipped with special surfaces, the wafers, where chemical reactions and the deposition of the film occurs. The produced films are used in semiconductor devices, micro- or nano-electromechanical systems, nano-electronic devices and integrated circuits.

Nowadays, the size of these devices or systems shrinks to lower scales and the specifications of the films refer to properties in micro- or nano-scale. The evolution of the physical/chemical phenomena at the micro-/nano-scales - which determine the properties of the films - depends on the (macroscopic) operating conditions of the reactor. Thus, the single scale conventional CVD modeling methods are not adequate and more advanced, multiscale modeling, methods are needed for studying the phenomena in the co-existing (multiple) scales. Two computational frameworks will be presented for simulating multiple spatial scales in CVD processes. The first concerns the coupling of the macro-scale (order of cm) of the gas phase of a CVD reactor with a predefined micro-topography (order of μm) on the surface of the wafer and the second links the gas phase of a CVD reactor with the nano-morphology (of order nm) of the growing film.

For the numerical solution of the governing equations describing transport phenomena, the use of commercial CFD software has become standard. Although, this software are integrated systems with state-of-the-art physics and chemistry models, solution algorithms and easy-to-use graphical environments – which make them robust, reliable and highly flexible - commercial CFD codes are practically unable to perform systematic detection and tracing of multiple solutions, to circumvent turning point singularities along solution branches and to compute unstable steady-state solutions. Therefore, they fail to provide all the ``pieces of the puzzle'' i.e. of the dependence of solutions of nonlinear problems on key parameters. These missing pieces may hide crucial information about the limits of stability of solutions as well as entire branches of solutions which might be suggestive of advantageous operating ``windows'' of the process of concern. Two computational frameworks applied as outer computational shells around widely used commercial CFD software will be presented. The main purpose of these frameworks is to enable the CFD software to trace solution branches of nonlinear problems that have multiple solutions in a systematic and efficient way, and even induce convergence on unstable steady states.

Speakers Short CV

Dr. Nikolaos (Nikos) Cheimarios is a Chemical Engineer with a MEng in Chemical Engineering (2006) from the University of Patras, Department of Chemical Engineering, a MSc in “Computational Mechanics” (2008) and a PhD in Chemical Engineering both from the National Technical University of Athens (NTUA) (2012). After his PhD, he worked as a postdoctoral researcher in NTUA and Ostram Opto Semiconductor GmbH, Regensburg, Germany (2013) working on the systemic analysis of CVD processes. After his postdoctoral work he joined Scienomics SARL, Paris France, as a research scientist where he designed and developed Chameleon; a generalized connectivity altering Monte Carlo based software for tackling properties of realistic polymer systems. Then he joined the R&D department of BIOEMTECH, Athens, Greece, as senior research scientist working on the software for the in vivo molecular screening of nuclear compounds in small animals. He then got a fellowship from the State Scholarships Foundation (IKY) to work on the multiscale modeling of novel copper precursors (2021). The last 2 years is a senior research scientist in NovaMechanics Ltd Nicosia, Cyprus, working on the development of various models and software concerning physical/chemical processes. From a broad perspective, his research combines different models from multiple scales (PDEs, ballistic, MC/kMC, MD, ab initio) in an effort to understand how the physical/chemical phenomena - including their non-linear character - in engineering processes affect materials properties. Another pilar of his research is scientific software development in combination with high performance computing (HPC) in CPU/GPU. Currently he designs and is the lead developer of Apothesis, a kinetic Monte Carlo software for deposition processes. He has co—authored 21 journal publications and 3 book chapters. He has received the Best Doctoral Thesis Award in NTUA by the Sarafis foundation (2017), awarded the Best Doctoral Thesis in Computational mechanics (CFD) by the Greek Association of Computational Mechanics (GRACM) (2013) and nominated for the Best Doctoral Thesis Award by the European Community on Computational Methods in Applied Sciences (ECCOMAS) (2013).