Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session QR2: Plasma Surface InteractionFocus
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Chair: Peter Ventzek, Tokyo Electron Room: 2a |
Thursday, October 13, 2016 8:30AM - 9:00AM |
QR2.00001: Hybrid molecular dynamics simulation for plasma induced damage analysis Invited Speaker: Masaaki Matsukuma In order to enable further device size reduction (also known as Moore's law) and improved power performance, the semiconductor industry is introducing new materials and device structures into the semiconductor fabrication process. Materials now include III-V compounds, germanium, cobalt, ruthenium, hafnium, and others. The device structure in both memory and logic has been evolving from planar to three dimensional (3D). One such device is the FinFET, where the transistor gate is a vertical fin made either of silicon, silicon-germanium or germanium. These changes have brought renewed interests in the structural damages caused by energetic ion bombardment of the fin sidewalls which are exposed to the ion flux from the plasma during the fin-strip off step. Better control of the physical damage of the 3D devices requires a better understanding of the damage formation mechanisms on such new materials and structures. In this study, the damage formation processes by ion bombardment have been simulated for Si and Ge substrate by Quantum Mechanics/Molecular Mechanics (QM/MM) hybrid simulations and compared to the results from the classical molecular dynamics (MD) simulations. In our QM/MM simulations, the highly reactive region in which the structural damage is created is simulated with the Density Functional based Tight Binding (DFTB) method and the region remote from the primary region is simulated using classical MD with the Stillinger-Weber and Moliere potentials. The learn on the fly method is also used to reduce the computational load. Hence our QM/MM simulation is much faster than the full QC-MD simulations and the original QM/MM simulations. The amorphous layers profile simulated with QM/MM have obvious differences in their thickness for silicon and germanium substrate. The profile of damaged structure in the germanium substrate is characterized by a deeper tail then in silicon. These traits are also observed in the results from the mass selected ion beam experiments. This observed damage profile dependence on species and substrate cannot be reproduced using classical MD simulations. While the Moliere potential is convenient to describe the interactions between halogens and other atoms, more accurate interatomic modeling such as DFTB method which takes the molecular orbitals into account should be utilized to make the simulations more realistic. Based on the simulations results, the damage formation scenario will be discussed. [Preview Abstract] |
Thursday, October 13, 2016 9:00AM - 9:15AM |
QR2.00002: Plasma Simulation in the Multiphysics Object Oriented Simulation Environment MOOSE. Steven Shannon, Alex Lindsay, David Graves, Casey Icenhour, David Peterson, scott White MOOSE is an open source multiphysics solver developed by Idaho National Laboratory that is primarily used for the simulation of fission reactor systems; the framework is also well suited for the simulation of plasma systems given the development of appropriate modules not currently developed in the framework such as electromagnetic solvers, Boltzmann solvers, etc. It is structured for user development of application specific modules and is intended for both workstation level and high performance massively parallel environments. We have begun the development of plasma modules in the MOOSE environment and carried out preliminary simulation of the plasma/liquid interface to elucidate coupling mechanisms between these states using a fully coupled multiphysics model; these results agree well with PIC simulation of the same system and show strong response of plasma parameters with respect to electron reflection at the liquid surface. These results will be presented along with an overview of MOOSE and ongoing module development to extend capabilities to a broader set of research challenges in low temperature plasmas, with particular focus on RF and pulsed RF driven systems. [Preview Abstract] |
Thursday, October 13, 2016 9:15AM - 9:30AM |
QR2.00003: Electron Emission from Nano and MicroStructured Materials for Plasma Applications Marlene Patino, Yevgeny Raitses, Richard Wirz Secondary electron emission (SEE) from plasma-confining walls can lead to adverse effects (e.g. increased plasma heat flux to the wall) in plasma devices, including plasma processing, confinement fusion, and plasma thrusters. Reduction in SEE from engineered materials with nm to mm-sized structures (grooves, pores, fibers), has been previously observed for primary electrons incident normal to the material. Here we present SEE measurements from one such engineered material, carbon velvet with microfibers (5 $\mu $m diameter, 1-2 mm length), and from a plasma-structured material, tungsten fuzz with nm fibers (35-50 nm diameter, 100-200 nm length). Additionally, dependence of SEE on incident angle was explored for tungsten fuzz. Results for carbon velvet and tungsten fuzz at normal incidence show 75{\%} and 50{\%} decrease in total yield from smooth graphite and tungsten, respectively. More notable is the independence of SEE on the incident angle for tungsten fuzz, as opposed to inverse cosine dependence for smooth materials. Hence, the reduction in SEE from tungsten fuzz is more pronounced at grazing angles. This is important for plasma-facing materials where a retarding plasma sheath leads to increased likelihood of plasma electrons impacting at grazing angles. [Preview Abstract] |
Thursday, October 13, 2016 9:30AM - 9:45AM |
QR2.00004: Effects of Gas and Surface Temperatures during Cryogenic Etching of silicon with SF$_{\mathrm{6}}$/O$_{\mathrm{2}}$ Stefan Tinck, Erik Neyts, Thomas Tillocher, Remi Dussart, Annemie Bogaerts Cryogenic deep reactive ion etching (DRIE) of silicon and SiO2 used for creating vias is investigated. The wafer is cooled to about $-$100 \textdegree C and a SF$_{\mathrm{6}}$/O$_{\mathrm{2}}$ mixture is applied. During cryogenic DRIE, a SiF$_{\mathrm{x}}$O$_{\mathrm{y}}$ passivation layer is formed which prevents isotropic etching and the diffusion of F atoms into the Si or SiO2 material. When the wafer is brought back to room temperature, this passivation layer desorbs naturally, leaving a clean trench with no scalloping. The primary issue with cryogenic DRIE is the high sensitivity to oxygen content and substrate or gas temperature. Both effects are investigated here. We believe that understanding the temperature dependent surface behavior of the O and F atoms to etch silicon is a primary step in obtaining full insight in the mechanisms of the SiFxOy passivation layer formation and automatic desorption. For this purpose, we apply a self-consistent model that covers both the bulk plasma characteristics as well as the surface processes during etching. Molecular Dynamics (MD) simulations are also performed to obtain insight in the surface reaction mechanisms. For validation of the modeling results, the etch rates are also experimentally obtained with reflectometry and Scanning Electron Microscopy (SEM) pictures. [Preview Abstract] |
Thursday, October 13, 2016 9:45AM - 10:00AM |
QR2.00005: Spectral Emission of fast non-Maxwellian Atoms at metallic Surfaces in low density Plasmas Sven Dickheuer, Oleksandr Marchuk, Christian Brandt, Albrecht Pospieszczyk We have observed Doppler shifted components of the Balmer-lines emitted by fast non-Maxwellian atoms using different targets in a linear magnetized plasma in the PSI-2 device. In a pure hydrogen plasma the Doppler shifted components of the Balmer emission lines cannot be detected above the signal-to-noise-ratio (C. Brandt et al. O3.J107, EPS Conference (2015)). However, in a mixed H/Ar plasma with composition of 1:1 the Doppler red- and blue-shifted components can be clearly observed. The Balmer-lines are analyzed by optical emission spectroscopy at observations angles of 35$^\circ$ and 90$^\circ$. For target materials we use Ag, Pd, Fe and C. An acceleration potential can be applied to the target to change the kinetic energy of the incoming ions between 40 and 200 eV enabling the observation of the Doppler shifted components. The emission mechanism is discussed in details and is probably due to excitation transfer from metastable argon atoms to the fast hydrogen atoms. The Doppler shifted signal can be used to determine the properties of the surfaces, e.g., the energy and angular distribution of reflected atoms. Also the spectral reflectance of the target surface can be obtained and tested against the reference data and measurements with light calibration sources. [Preview Abstract] |
Thursday, October 13, 2016 10:00AM - 10:30AM |
QR2.00006: Atomic Precision Plasma Processing -- Modeling Investigations Invited Speaker: Shahid Rauf Sub-nanometer precision is increasingly being required of many critical plasma processes in the semiconductor industry. Some of these critical processes include atomic layer etch and plasma enhanced atomic layer deposition. Accurate control over ion energy and ion / radical composition is needed during plasma processing to meet the demanding atomic-precision requirements. While improvements in mainstream inductively and capacitively coupled plasmas can help achieve some of these goals, newer plasma technologies can expand the breadth of problems addressable by plasma processing. Computational modeling is used to examine issues relevant to atomic precision plasma processing in this paper. First, a molecular dynamics model is used to investigate atomic layer etch of Si and SiO$_{\mathrm{2}}$ in Cl$_{\mathrm{2}}$ and fluorocarbon plasmas. Both planar surfaces and nanoscale structures are considered. It is shown that accurate control of ion energy in the sub-50 eV range is necessary for atomic scale precision. In particular, if the ion energy is greater than 10 eV during plasma processing, several atomic layers get damaged near the surface. Low electron temperature ($T_{e})$ plasmas are particularly attractive for atomic precision plasma processing due to their low plasma potential. One of the most attractive options in this regard is energetic-electron beam generated plasma, where $T_{e}$ \textless 0.5 eV has been achieved in plasmas of molecular gases. These low $T_{e}$ plasmas are computationally examined in this paper using a hybrid fluid-kinetic model. It is shown that such plasmas not only allow for sub-5 eV ion energies, but also enable wider range of ion / radical composition. Coauthors: Jun-Chieh Wang, Jason Kenney, Ankur Agarwal, Leonid Dorf, and Ken Collins [Preview Abstract] |
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