Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session FT2: Inductively Coupled Plasmas |
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Chair: Earl Scime, West Virginia University Room: 308 AB |
Tuesday, October 13, 2015 1:30PM - 1:45PM |
FT2.00001: Student Award Finalist: Negative Power Absorption in Low-Pressure Inductive Discharges Jan Trieschmann, Martin Lapke, Ralf Peter Brinkmann, Thomas Mussenbrock Inductively coupled radio-frequency plasmas for technological applications are frequently operated at relatively low gas pressures (below 10 Pa). One specific feature of this regime is that collisions of electrons with atoms or molecules of the neutral background gas are infrequent. Under these conditions the discharges are operated in the nonlocal regime, i.e., the relation between the high frequency current density and the electric field is nonlocal. To describe this specific situation, Maxwell's equations have to be coupled self-consistently to Boltzmann's equation. In this paper we present an analytical, self-consistent solution to the one-dimensional problem of a plane wave propagating from one half-space (vacuum) into the other filled with a bounded homogeneous plasma. We particularly discuss the anomalous skin effect, negative power absorption, and phase mixing. The results from the analytical model are finally compared with results from self-consistent Particle-In-Cell simulations. [Preview Abstract] |
Tuesday, October 13, 2015 1:45PM - 2:00PM |
FT2.00002: 3D-PIC simulation of an inductively coupled ion source Robert Henrich, Nina Sarah Muehlich, Michael Becker, Christian Heiliger Inductively coupled ion sources are applied to a wide range of plasma applications, especially surface modifications. The knowledge of the behavior and precise information of the plasma parameters are of main importance. These values are tedious to measure without influencing the discharge. By applying our fully three-dimensional PlasmaPIC tool we are able to reach these plasma parameters with a spatial and temporal resolution which is quite hard to achieve experimentally. PlasmaPIC is used for modeling discharges in arbitrary geometries without limitations to any symmetry. By this means we are able to demonstrate that the plasma density has an irrotational character. Furthermore, we will show the dependence of the plasma parameters of different working conditions. We will show that for gridded inductively coupled ion sources the neutral gas pressure inside the discharge chamber depends on the extraction of ions. This effect is considered in PlasmaPIC by a self-consistent coupling of the neutral gas simulation and the plasma simulation whereas the neutral gas distribution is calculated using the direct simulation Monte Carlo method (DSMC). [Preview Abstract] |
Tuesday, October 13, 2015 2:00PM - 2:15PM |
FT2.00003: Vibrational kinetics in Cl$_{2}$ and O$_{2}$ low-pressure inductively-coupled plasmas Jean-Paul Booth, Mickael Foucher, Daniil Marinov, Pascal Chabert, Anna Annusova, Vasco Guerra, Ankur Agarwal, Shahid Rauf Low energy electron interactions with molecules via resonances can cause vibrational excitation (affecting chemical kinetics), electron energy loss and modification of the EEDF. However, with the exception of N$_{2}$ and H$_{2}$ plasmas, very little attention has been paid to this subject. We have implemented a novel high-sensitivity ultra-broadband UV absorption bench, allowing spectra to be recorded with noise as low as 2x10$^{-5}$ over a 250nm wavelength range, and recording of complete vibronic bands. We applied this to radiofrequency inductively-coupled plasmas in low pressure (5-50 mTorr) pure O$_{2}$ and pure Cl$_{2}$. In O$_{2}$ plasmas we surprisingly observe highly vibrationally excited O$_{2}$ (v'' up to 18) via B-X Schumann-Runge bands. Cl$_{2}$ molecules show a broad UV absorption spectrum in the region 250-400nm, with distinctly different absorption spectra for vibrationally excited molecules. However, only a small fraction of the Cl$_{2}$ molecules were observed in vibrationally excited states and the vibrational temperature is close to equilibrium with the local gas translational temperature (up to 1000K), in contrast to O$_{2}$. We are currently working on global models with vibrational kinetics to explain these results. [Preview Abstract] |
Tuesday, October 13, 2015 2:15PM - 2:30PM |
FT2.00004: Characterization of Inductively Coupled Plasmas in High Power, High Pressure Regime Jun-Chieh Wang, Jason Kenney, Ankur Agarwal, Michael Nichols, James Rogers, Shahid Rauf Inductively coupled plasmas (ICP) are widely used in the microelectronic industry for thin film etching. ICPs have typically been operated at low gas pressures (\textless 50 mTorr) and they have been well-characterized in this regime. Several applications requiring high etch rates (e.g., vertical NAND etch) have recently extended the use of ICPs to the high power (\textgreater 4000 W) and high pressure (\textgreater 100 mTorr) regime. ICP operation in this high-power, high-pressure regime imposes a tremendous challenge of achieving good plasma uniformity over large substrates. This necessitates a good theoretical understanding of the underlying physics, thorough experimental characterization, and more accurate numerical models for hardware design guidance. In this study, we will focus on the characterization of ICP in the high-power, high-pressure regime. Computational modeling is done using CRTRS, our in-house 2D/3D plasma model. The fluid plasma model is coupled to a circuit model to self-consistently account for the capacitive coupling from the coils that is expected to dominate in this operating regime. Properties of Ar plasma will be discussed and compared with experiments. The impact of critical operating parameters such as ICP power, pressure, flow rate, and current ratio (in multi-coil antenna structures) on plasma characteristics will be examined. Results in relevant processing gases will also be discussed. [Preview Abstract] |
Tuesday, October 13, 2015 2:30PM - 2:45PM |
FT2.00005: Ignition Delay in a Pulsed Inductively Coupled Plasma (ICP) in Tandem with an Auxiliary ICP Vincent M. Donnelly, Lei Liu, Shyam Sridhar, Demetre J. Economou Plasma ignition delays were observed in a ``main'' ICP, in tandem with an ``auxiliary'' ICP. The Faraday-shielded ICPs were separated by a grounded metal grid. Power (13.56 MHz) to the main ICP was pulsed with a frequency of 1 kHz, while the auxiliary ICP was operated in continuous wave (cw) mode. In chlorine plasmas, ignition delay was observed for duty cycles greater than 60{\%} and, in contrast to expectation, the delay was longer with increasing duty cycle up to $\sim$ 99.5{\%}. The ignition delay could be manipulated by changing the auxiliary and/or main ICP power. Langmuir probe measurements provided the temporal evolution of electron temperature, and electron and positive ion ($n_{+})$ densities. These measurements revealed that the plasma was re-ignited shortly after the decaying $n_{+}$ in the main ICP reached the density ($n_{+,aux})$ measured when only the auxiliary ICP was powered. At that time, the depressed electron density increased sharply resulting in plasma re-ignition. Plasma ignition delay occurred when the afterglow of the pulsed plasma was not long enough for $n_{+}$ to reach $n_{+,aux}$ during the afterglow. Besides Cl$_{2}$, plasma ignition delays were also observed in other electronegative gases (SF$_{6}$, CF$_{4}$/O$_{2}$ and O$_{2})$ but not in an electropositive gas (Ar). [Preview Abstract] |
Tuesday, October 13, 2015 2:45PM - 3:00PM |
FT2.00006: Producing ion waves from acoustic pressure waves in pulsed ICP: Modeling vs. Experiments Emilie Despiau-Pujo, Gilles Cunge, Maxime Darnon, Nader Sadeghi, Nicholas Braithwaite Neutral depletion is an important phenomenon in CW high-density plasmas, mostly caused by gas heating - with a small contribution due to electron pressure Pe - under typical material processing conditions. In pulsed ICP, neutral depletion plays an important role on radical transport in the afterglow. At the beginning of the afterglow, Pe drops rapidly (10$\mu$s) by electron cooling and the gas cools down as well. It generates a neutral pressure gradient between the plasma bulk and the reactor walls, which in turn forces the cold surrounding gas to move rapidly towards the center, thus launching an acoustic wave in the reactor. Fast gas displacement is evidenced by measuring Al atoms drift velocity in the early afterglow of a Cl2/Ar discharge by time-resolved LIF, the acoustic wave in the chamber being observed by mass spectrometry. 2D fluid simulations of Cl2 pulsed ICP predict similar results. These phenomena are further studied during both the plasma ignition and afterglow using modeling and experiments. Strong oscillations are observed both on the Cl2 neutral densities and on the ion flux. As neutrals are pushed towards (or outwards) the chamber walls by the pressure gradient, ions are also pushed in that direction through collisions, as well captured by our ion flux probe. [Preview Abstract] |
Tuesday, October 13, 2015 3:00PM - 3:15PM |
FT2.00007: Electronegative Plasma Instabilities in Pulsed Plasmas Patrick Pribyl, Walter Gekelman Modern inductively coupled plasma reactors can all be operated in unstable configurations, although in many cases normal precautions result in quiescent stable operation. However, electronegative gases that are important for etch processes have a series of instabilities that occur at process relevant conditions. These have been studied since the 1990s, but are becoming a much more important today as plasma reactors are being pushed to produce ever finer features, and tight control of the etch process is becoming crucial. A device at UCLA was designed to simulate industrial reactors used in semiconductor processing. Various gas mixtures are programmable (Ar, SF6, O2). ICP coils in different configurations are driven by pulsed RF generators operating separately from 400 kHz to 40 MHz. A stainless steel ``chuck'' assembly can be positioned at a variable height, either with a wafer and RF bias, or with direct DC bias to directly program sheath voltage. A computer controlled automated probe drive can access the entire volume above the substrate. The probe can be a Langmuir probe, a ``Bdot'' probe, or an emissive probe the latter used for more accurate determination of plasma potential. A microwave interferometer is available to measure line-averaged electron density. Optical emission can be diagnosed using a half or 1 meter spectrometer. We describe work with electronegative gases to characterize and potentially stabilize the plasma against ionization instabilities using pulsed plasmas. [Preview Abstract] |
Tuesday, October 13, 2015 3:15PM - 3:30PM |
FT2.00008: Characterization of inductively coupled Ar and Ar/CH4 plasma using tuned single Langmuir probe and fluid simulation Ju-Hong Cha, Moon-Ki Han, Kwon-Sang Seo, Dong-Hyun Kim, Hae June Lee, Ho-Jun Lee An inductively coupled plasma source driven by 13.56MHz was prepared for the deposition of a-C:H and hydro-fluorocarbon thin film. Properties of the plasma source are investigated by fluid simulation including Navier-Stokes equations and home-made tuned single Langmuir probe. Signal attenuation ratios of the Langmuir probe at first and second harmonic frequency were 49dB and 46dB respectively. Dependencies of plasma parameters on process parameters were well agreed with simulation results. It was found that gas flow field significantly affect spatial distribution of electron density and temperature even in inert gas feeding case. Higher electron density and lower temperature was observed near the gas inlet area. Ar/CH4 plasma simulation results shown that hydrocarbon radical densities have their lowest value at the vicinity of gas feeding line due to high flow velocity. For input power density of 0.07W/cm3, CH radical density follows electron density distribution. On the other hand, central region of the chamber become deficient in CH3 radical due to high dissociation rate accompanied with high electron density. The result suggest that optimization of discharge power is important for controlling deposition film quality in high density plasma sources. [Preview Abstract] |
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