Session GT52: Plasma-surface Interactions I

Multiscale simulation on plasma-surface interaction: mitigation of leakage current at high-k metal oxide interface

The miniaturization of silicon microelectronics demands a fine interface control on a gate dielectric in the MOSFET to mitigate undesirable gate leakage currents. In this paper, a multiscale simulation approach is proposed using atomistic simulations to examine the effect of the hydrogen plasma treatment (HPT) on high-k metal oxide/silicon interface. Molecular dynamics (MD) simulations are employed to understand the changes in the processing surface from the atomistic perspective. For varying processing conditions, atomic incident energy and substrate temperature, the evolutions of surface structural features including dangling bonds are thoroughly monitored. From the obtained surface structure after the hydrogen treatment, high-k metal oxide interface is modeled. Then, the localized electronic states within the energy band of the interfaces are examined with density functional theory (DFT), and the changes of interface traps due to HPT are discussed depending on the processing conditions. The present multiscale approach offers a possible way of understanding the influence of HPT on high-k metal oxide/silicon interface in terms of both structural and electrical perspectives.   

Ion-induced secondary electron emission coefficient of metal surfaces analysed in an ion beam experiment

Electron emission of surfaces upon ion impact is one of the most fundamental plasma-surface-interactions. Many experimental (e.g [1-3]) and theoretical (e.g.[4-6]) approaches address the ion-induced secondary electron emission coefficient (SEEC=amount of released electrons per incident ion) in literature. However, the SEEC determination may remain rather indirect though, as the process of electron emissionn occurs often not isolated from all other plasma-surface-interactions. SEEC are especially important for magnetron sputtering discharges, because target conditions strongly affect electron emission of  targets and thus have an impact on the discharge itself. In reactive magnetron plasmas the impact of the SEEC is even more difficult to assess, because reactive species such as oxygen or nitrogen react also at the target surface and alter the SEEC. Data of such oxidized targets are very sparse and may even contain significant systematic errors, because they were often measured by modeling the complex behavior of plasma discharges. Using beam experiments avoids this complication and allows a precise SEEC determination. SEECs of clean, untreated (air-exposed) and intentionally oxidized copper and nickel surfaces are investigated in such a beam experiment. Metal foil and oxidized metal foils are exposed to beams of singly charged argon ions with energies of 200eV-10keV. SEECs of oxidized metal targets for a large ion energy range are determined precisely. A model for the electron emission of a partly oxidized surface is presented to explain the data. 

[1]D.Depla et al.J.Phys.D:Appl.Phys.,vol.41,p.202003,2008

[2]M.Daksha et al.Journal of Physics D:Appli.Phys.,vol.49,2016

[3]A.V.Phelps, Z.L.Petrovic,Plasma Sources Sci.Technol.,vol.8,pp.R21–R44,1999

[4]J.Schou, Phys.Rev.B,vol.22,pp.2141–2174,1980

[5]E.J.Sternglass,Phys.Rev.,vol.108,pp.1–12,1957

[6]P.H.Stoltz et al.Phys.Rev.STAccel.Beams, vol.6,p.054701,2003   

Study of plasma-surface interactions of CO2-CH4 plasma on CeO2 using in situ Infrared Transmission experiments

Increase in global temperature is mainly attributed to the greenhouse gas effect specially from carbon dioxide (CO2) and methane (CH4) emissions. Dry reforming of methane (DRM) is one the processes proposed for CO2 utilization leading to the conversion into valuable chemicals. Non-thermal plasmas (NTP) can provide the highly energetic environment needed for CO2 conversion. However, a plasma-catalysis approach could offer a significant advantage by improving conversion, selectivity and energy efficiency. Further development and optimization can be expected through greater understanding of the underlying mechanisms on a catalytic surface. In this study, we present evidence of the plasma-surface interaction of the intermediates present in CeO2 by in situ IR transmission experiments using low pressure glow discharge plasma reactor. Experimental results show the adsorption of CO2 as carbonates at room temperature further reacting with H active species generating formates under plasma conditions. Evolution of formates species is followed as function of time. Evidence of derivates of methane decomposition is observed on the surface. The CeO2 pellets used were subsequently characterized by X-Ray Diffraction (XRD), Diffuse Reflectance infrared Fourier transformed spectroscopy (DRIFTS) and Thermal Programmed Desorption (TPD) exhibiting a change in the oxidation state of ceria ions. The plasma-catalyst interactions were investigated under different concentrations and varying configurations: plasma in situ and downstream gas from plasma reaction. The elucidation of adsorbed intermediates of DRM reaction is crucial in the understanding of the mechanistic insight in CO2 conversion by plasma catalysis.   

Plasma Diagnostics on an Atmospheric Pressure DC Microplasma Discharge Intended for in situ TEM Integration

One of the most discussed topics in plasma technology is the plasma surface interaction due to its relevance for the production or modification of micro- or even nano-structured surfaces. State of the art analysis is mostly limited to the separation of plasma processing and surface analysis, since observing surface changes in real time and at nanoscale resolution during the plasma treatment is challenging. With the development of a DC microplasma discharge cell for in situ TEM integration based on the proof of principle experiments by Tai et al. [1] we aim to overcome this limitation.

Conventional (electrical measurements, optical imaging and emission spectroscopy) as well as non-conventional (calorimetry [2]) plasma diagnostics have been applied to characterize the microplasma, ensure its stability, and provide sufficient insight for a better understanding of the, till today, ex situ observed plasma-generated surface changes, which depend on the plasma parameters. The cell design and experimental results will be presented and a report on the current progress of the in situ measurements will be given.

[1] K Tai et al 2013 Scientific Reports 3 1325

[2] H Kersten et al 2001 Vacuum 63 385-431   

From the role of Ar ions in the sputter deposition of Al films to a comprehensive surface surrogate model

The interaction of heavy particles with surfaces in thin film sputter depositions is often studied by means of computer simulations. While forward sputtered particles in comparison to entrapped working gas atoms are assumed to have a predominant effect on the surface state, their individual contribution as well as correlation is scarcely clarified due to their inherent overlay. This issue is addressed in this work by comparing two case studies of sputter deposition of Al thin films in Ar working gas (i) with and (ii) without implanted Ar atoms. The surface interactions are described by a hybrid reactive molecular dynamics/force-bias Monte Carlo approach. The entrapment of Ar atoms is found to facilitate persistent Al interstitials and surface reconstructions. Finally, the results are used to train an artificial neural network (i.e., conditional variational autoencoder) to generalize the findings and propose a surface surrogate model that may be readily coupled to plasma transport simulations.