Publications

Quantum computing (QC) is a promising early-stage technology with the potential to provide scientific computing capabilities far beyond what is possible with even an Exascale computer in specific problems of relevance to the Office of Science. These include (but are not limited to) materials modeling, molecular dynamics, and quantum chromodynamics. However, commercial QC systems are not yet available and the technical maturity of current QC hardware, software, algorithms, and systems integration is woefully incomplete. Thus, there is a significant opportunity for DOE to define the technology building blocks, and solve the system integration issues to enable a revolutionary tool. Once realized, QC will have world changing impact on economic competitiveness, the scientific enterprise, and citizen well-being. Prior to this workshop, DOE / Office of Advanced Scientific Computing Research (ASCR) hosted a workshop in 2015 to explore QC scientific applications. The goal of that workshop was to assess the viability of QC technologies to meet the computational requirements in support of DOE’s science and energy mission and to identify the potential impact of these technologies.

This is an overview of the Quantum Testbed Stakeholder Workshop series.

Abstract not provided.

We have successfully designed, built and operated a microlaser based on a AlGaInAs multiple quantum well (MQW) semiconductor saturable absorber (SESA). Optical characterization of the semiconductor absorber, as well as, the microlaser output is presented. © 2010 Ontical Society of America.

The radial distribution of the measured voltage drop across a sheath formed between a 300 mm electrode and an argon plasma discharge is shown to depend on the excitation radio frequency, under constant power and pressure conditions. At a lower frequency of 13.56 MHz, the voltage drop across the sheath is uniform across the 300 mm electrode, while at higher frequencies of 60 and 162 MHz the voltage drop becomes radially nonuniform. The magnitude and spatial extent of the nonuniformity become greater with increasing frequency. © 2007 American Institute of Physics.

The spatial structure and temporal evolution of the electric fields in a sheath formed in a dual frequency, 300 mm capacitive argon discharge are measured as functions of relative mixing between a low frequency current and a high frequency current. It is found that the overall structure of the sheath (potential across the sheath and the thickness of the sheath) are dominated by the lower frequency component while (smaller) oscillations in these quantities are dictated by the higher frequency component. Comparisons of the measured spatial and temporal profiles are made for Lieberman's and Robiche et al sheath model and with a particle in a cell calculation. © 2007 IOP Publishing Ltd.

This report constructs simple circuit models for a hairpin shaped resonant plasma probe. Effects of the plasma sheath region surrounding the wires making up the probe are determined. Electromagnetic simulations of the probe are compared to the circuit model results. The perturbing effects of the disc cavity in which the probe operates are also found.

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Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K. © 2006 IOP Publishing Ltd.

There is much interest in scaling rf-excited capacitively coupled plasma reactors to larger sizes and to higher frequencies. As the size approaches operating wavelength, concerns arise about non-uniformity across the work piece, particularly in light of the well-documented slow-surface-wave phenomenon. We present measurements and calculations of spatial and frequency dependence of rf magnetic fields inside argon plasma in an industrially relevant, 300 mm plasma-processing chamber. The results show distinct differences in the spatial distributions and harmonic content of rf fields in the plasma at the three frequencies studied (13.56, 60 and 176 MHz). Evidence of a slow-wave structure was not apparent. The results suggest that interaction between the plasma and the rf excitation circuit may strongly influence the structures of these magnetic fields and that this interaction is frequency dependent. At the higher frequencies, wave propagation becomes extremely complex; it is controlled by the strong electrical nonlinearity of the sheath and is not explained simply by previous models. © 2006 IOP Publishing Ltd.

Nonuniformities in both sheath electric field and plasma excitation were observed around dissimilar metals placed on a rf electrode. Spatial maps of the rf sheath electric field obtained by laser-induced fluorescence-dip (LIF-dip) spectroscopy show that the sheath structure was a function of the electrode metal. In addition to the electric-field measurements, LIF, optical emission, and Langmuir probe measurements show nonuniform excitation around the dissimilar metals. The degree and spatial extent of the discharge nonuniformities were dependent on discharge conditions and the history of the metal surfaces.

Dual-frequency reactors employ source rf power supplies to generate plasma and bias supplies to extract ions. There is debate over choices for the source and bias frequencies. Higher frequencies facilitate plasma generation but their shorter wavelengths may cause spatial variations in plasma properties. Electrical nonlinearity of plasma sheaths causes harmonic generation and mixing of source and bias frequencies. These processes, and the resulting spectrum of frequencies, are as much dependent on electrical characteristics of matching networks and on chamber geometry as on plasma sheath properties. We investigated such electrical effects in a 300-mm Applied-Materials plasma reactor. Data were taken for 13.56-MHz bias frequency (chuck) and for source frequencies from 30 to 160 MHz (upper electrode). An rf-magnetic-field probe (B-dot loop) was used to measure the radial variation of fields inside the plasma. We will describe the results of this work.

The magnitude and structure of the ion wakefield potential below a single negatively-charged dust particle levitated in the plasma sheath region was calculated and measured. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy collisions between different mass particles in a well-defined electrostatic potential.

Plasma and sheath structure around a rf excited stepped electrode is investigated. Laser-induced fluorescence dip spectroscopy is used to spatially resolve sheath fields in an argon discharge while optical emission and laser-induced fluorescence are used to measure the spatial structure of the surrounding discharge for various discharge conditions and step-junction configurations. The presence of the step perturbs the spatial structure of the fields around the step as well as the excitation in the region above the step.

Two-dimensional maps of the sheath electric fields formed around a metal-dielectric interface were measured in a radio frequency (rf) argon plasma using laser-induced fluorescence-dip spectroscopy. Experimentally determined Stark shifts of the argon Rydberg 13d[3/2]1 state were used to quantify the electric fields in the sheath as functions of the rf cycle, voltage, and pressure. Both the structure of the sheath fields and the discharge characteristics in the region above the electrode depend on the discharge conditions and the configuration of the surface. Dissimilar materials placed adjacent to each other result in electric fields with a component parallel to the electrode surface.

Laser-induced fluorescence-dip spectroscopy was used to measure two-dimensional (2-D) maps of the electric field present in an argon discharge above a ratio frequency-powered, nonuniform surface. Electric fields were obtained from experimentally measured Stark shifts of the energy of argon Rydberg states. The 2-D maps of the electric fields demonstrated that nonuniformities present on an electrode have long-range effects on the structure of the sheath.

The magnitude and structure of the attractive ion wakefield potential below a negatively charged dust particle levitated in the plasma sheath region was measured as a function of the interparticle spacing. The ion wakefield force field generated by an upper lighter target dust particle was determined by colliding it with a heavier probe dust particle levitated at a lower height. The interaction potentials were obtained from the particle's position and velocity by numerically inverting the Newtonian equations of motion. A transition from repulsive, nonvertically aligned pairs, to attractive vertically aligned pairs, and then back to nonvertically aligned pairs, was observed as the vertical spacing between the particles was increased.

Abstract not provided.

The magnitude and the structure of the ion-wakefield potential below a negatively charged dust particle levitated in the plasma-sheath region have been determined. Attractive and repulsive components of the interaction force were extracted from a trajectory analysis of low-energy dust collisions in a well-defined electrostatic potential, which constrained the dynamics of the collisions to be one dimensional. The peak attraction was on the order of 100 fN. The structure of the ion-wakefield-induced attractive potential was significantly different from a screened-Coulomb repulsive potential.

This report documents measurements in inductively driven plasmas containing SF{sub 6}/Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF{sub 6} based processing of materials and to validate models of the gas and surface processes.

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Laser induced fluorescence was used to measure the spatially resolved CF, CF2, and SiF radical density in inductively driven discharges containing fluorocarbon gases. Measurements of the spatially resolved CF density were performed in C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition on a silicon substrate. In addition, CF rotational temperatures were calculated, assuming saturated spectra. Measurements of the spatially resolved CF2 and SiF density were performed in C4F8, C2F6, and CHF3 containing discharges as functions of inductive power, pressure and bias condition. SiF rotational temperatures were also estimated. As the induction coil power was increased, the SiF density in the center (r = 0 cm) increased while the CF2 density decreased and the CF density slightly decreased. In all cases, the radical density in the center of the glow increased with pressure changes from 5 to 30 mTorr while changes in the bias power had little influence on any of the measured radical densities. The spatial distribution of the CF and SiF density peaked in the center of the discharge. The CF2 density had a local maximum in the center of the plasma with a decreasing density at the edge of the glow. However, the CF2 density outside the glow region was a factor of 2-6 higher than the density inside the glow region, depending on the gas. CF and SiF rotational temperatures were between 450 and 750 K. © 2001 American Institute of Physics.

In-situ optical diagnostics and ion beam diagnostics for plasma-etch and reactive-ion-beam etch (RIBE) tools have been developed and implemented on etch tools in the Compound Semiconductor Research Laboratory (CSRL). The optical diagnostics provide real-time end-point detection during plasma etching of complex thin-film layered structures that require precision etching to stop on a particular layer in the structure. The Monoetch real-time display and analysis program developed with this LDRD displays raw and filtered reflectance signals that enable an etch system operator to stop an etch at the desired depth within the desired layer. The ion beam diagnostics developed with this LDRD will permit routine analysis of critical ion-beam profile characteristics that determine etch uniformity and reproducibility on the RIBE tool.