202 research outputs found
Diagnostic for Plasma Enhanced Chemical Vapor Deposition and Etch Systems
In order to meet NASA's requirements for the rapid development and validation of future generation electronic devices as well as associated materials and processes, enabling technologies ion the processing of semiconductor materials arising from understanding etch chemistries are being developed through a research collaboration between Stanford University and NASA-Ames Research Center, Although a great deal of laboratory-scale research has been performed on many of materials processing plasmas, little is known about the gas-phase and surface chemical reactions that are critical in many etch and deposition processes, and how these reactions are influenced by the variation in operating conditions. In addition, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. The research described involves the study of plasmas used in semiconductor processes. An inductively coupled plasma (ICP) source in place of the standard upper electrode assembly of the Gaseous Electronics Conference (GEC) radio-frequency (RF) Reference Cell is used to investigate the discharge characteristics and chemistries. This ICP source generates plasmas with higher electron densities (approximately 10(exp 12)/cu cm) and lower operating pressures (approximately 7 mTorr) than obtainable with the original parallel-plate version of the GEC Cell. This expanded operating regime is more relevant to new generations of industrial plasma systems being used by the microelectronics industry. The motivation for this study is to develop an understanding of the physical phenomena involved in plasma processing and to measure much needed fundamental parameters, such as gas-phase and surface reaction rates. species concentration, temperature, ion energy distribution, and electron number density. A wide variety of diagnostic techniques are under development through this consortium grant to measure these parameters. including molecular beam mass spectrometry (MBMS). Fourier transform infrared (FTIR) spectroscopy, broadband ultraviolet (UV) absorption spectroscopy, a compensated Langmuir probe. Additional diagnostics. Such as microwave interferometry and microwave absorption for measurements of plasma density and radical concentrations are also planned
Inverse design of plasma metamaterial devices with realistic elements
In an expansion of a previous study [1], we apply inverse design methods to
produce two-dimensional plasma metamaterial devices with realistic plasma
elements which incorporate quartz envelopes, collisionality (loss), non-uniform
density profiles, and resistance to experimental error/perturbation.
Backpropagated finite difference frequency domain simulations are used to
design waveguides and demultiplexers operating under the transverse magnetic
polarization. Optimal devices with realistic elements are compared to previous
devices with idealized elements, and several parameter initialization schemes
for the optimization algorithm are explored. Demultiplexing and waveguiding are
demonstrated for microwave-regime devices composed of plasma elements with
reasonable space-averaged plasma frequencies ~10 GHz and a collision frequency
~1 GHz, allowing for future in-situ training and experimental realization of
these designs.Comment: 9 pages, 9 figure
Inverse design and experimental realization of plasma metamaterials
We apply inverse design methods to produce two-dimensional triangular-lattice
plasma metamaterial (PMM) devices which are then constructed and demonstrated
experimentally. Finite difference frequency domain simulations are used along
with forward-mode automatic differentiation to optimize the plasma densities of
each of the plasma elements in the PMM to perform beam steering and
demultiplexing under transverse magnetic polarization. The optimal device
parameters are then used to assign plasma density values to elements that make
up an experimental version of the device. Device performance is evaluated
against both the simulated results and human-designed alternatives, showing the
benefits and disadvantages of in-silico inverse design and paving the way for
future fully in-situ optimization.Comment: 22 pages, 8 figures; submitted to Phys. Rev. Applie
Evidence of lower-hybrid rotating spoke oscillations in a direct current magnetron microdischarge
High frequency current-carrying spokes are observed propagating in the
EB direction in a neon direct current magnetron discharge. Two modes
are found with distinct frequencies and behaviors. At low discharge currents,
we see highly coherent 60 MHz fluctuations. Above a distinct current threshold,
secondary 5 - 10 MHz fluctuations emerge in addition to turbulent fluctuations
spanning the 60 - 100 MHz range. The presence of lower-hybrid waves is invoked
to explain the high frequency oscillations. We attribute the appearance of the
low frequency axial modes concomittant with the onset of the high frequency
turbulence to an inverse cascade process, as suggested by recent simulations
High-Pressure CO Dissociation with Nanosecond Pulsed Discharges
The efficiency of the conversion of CO into CO with nanosecond
repetitively pulsed discharges (NRP) is investigated in a high pressure batch
reactor. Stable discharges are obtained at up to 12~bar. By-products of CO
splitting are measured with gas chromatography. The energy efficiency is
determined for a range of processing times, pulse energy, and fill pressures.
The energy efficiency is found to be approximately 20% and is only weakly
sensitive to the plasma operating parameters, i.e., the extent of CO
conversion is almost linearly-dependent on the specific energy input. A
conversion rate of up to 14% is achieved with an energy efficiency of 23%. For
long processing times, a drop in efficiency is observed, due to the increasing
significance of recombination reactions, as described by a macroscopic kinetic
mechanism. Reaction pathways that are believed to play an important role in
nanosecond pulsed discharges are discussed. It appears that vibrational
excitation does not play a significant role in CO conversion in these types
of short-pulse discharge. Results also draw attention to the relative
importance of two particular electronic excitation reactions.Comment: 21 pages, 12 figure
Resonant electron transmission through a finite quantum spin chain
Electron transport in a finite one dimensional quantum spin chain (with
ferromagnetic exchange) is studied within an exchange Hamiltonian. Spin
transfer coefficients strongly depend on the sign of the exchange
constant. For a ferromagnetic coupling, they exhibit a novel resonant pattern,
reflecting the salient features of the combined electron-spin system. Spin-flip
processes are inelastic and feasible at finite voltage or at finite
temperature.Comment: 4 pages including 4 .eps figure
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