Cameron A. Moore

Optical and RF electrical characteristics of atmospheric pressure open-air hollow slot microplasmas and application to bacterial inactivation

We report electrical properties of radio frequency (RF)-driven hollow slot microplasmas operating in open air but with uniform luminous discharges at RF current densities of the order of A cm −2 . We employ interelectrode separations of 100–600 µm to achieve this open-air operation but because the linear slot dimension of our electrode designs are of extended length, we can achieve, for example, open-air slot shaped plasmas 30 cm in length. This creates a linear plasma source for wide area plasma driven surface treatment applications. RF voltages at frequencies of 4–60 MHz are applied to an interior electrode to both ignite and sustain the plasma between electrodes. The outer slotted electrode is grounded. Illustrative absolute emission of optical spectra from this source is presented in the region from 100 to 400 nm as well as total oxygen radical fluxes from the source. We present both RF breakdown and sustaining voltage measurements as well as impedance values measured for the microplasmas, which use flowing rare gas in the interelectrode region exiting into open air. The requirement for rare gas flow is necessary to get uniform plasmas of dimensions over 30 cm, but is a practical disadvantage. In one mode of operation we create an out-flowing afterglow plasma plume, which extends 1–3 mm from the grounded open slot allowing for treatment of work pieces placed millimetres away from the grounded electrode. This afterglow configuration also allows for lower gas temperatures impinging on substrates, than the use of active plasmas. Work pieces are not required to be part of any electrical circuit, bringing additional practical advantages. We present a crude lumped parameter equivalent circuit model to analyse the effects of changing RF sheaths with frequency of excitation and applied RF current to better understand the relative roles of sheath and bulk plasma behaviour observed in electrical characteristics. Estimates of the bulk plasma densities are also provided. Finally, we present results of afterglow plasma based bacteria inactivation studies (Escherichia coli, Bacillus atrophaeus and B. atrophaeus spores) in which we employ the flowing afterglow plume from a hollow slot microplasma device rather than the active plasma itself, which is fully contained between electrodes. (Some figures in this article are in colour only in the electronic version)

Laser Photolytic Deposition of Thin Films

An excimer laser is used to photochemically deposit thin films of silicon dioxide, silicon nitride, aluminum oxide, and zinc oxide at low temperatures (100–350deg;C). Deposition rates in excess of 3000 A/min and conformal coverage over vertical walled steps were demonstrated. The films exhibit low defect density and high breakdown voltage and have been characterized using IR spectrophotometry, AES, and C-V analysis. Device compatibility has been studied by using photodeposited films as interlayer dielectrics, diffusion masks, and passivation layers in production CMOS devices. Additionally, we have deposited metallic films of Al, Mo, W, and Cr over large (>5 cm 2 ) areas using UV photodissociation of trimethylaluminum and the refractory metal hexacarbonyls. Both shiny metallic films as well as black particulate films were obtained depending on the deposition geometry. The black films are shown to grow in columnar grains. The depositions were made at room temperature over pyrex and quartz plates as well as silicon wafers. We have examined the resistivity, adhesion, stress and step coverage of these films. The films exhibited resistivities at most ∼20 times that of the bulk materials and tensile stress no higher than 7 × 10 9 dynes/cm 2

Large area electron beam annealing

We have achieved wide area (38 cm2) electron beam annealing of ion implanted silicon wafers using a glow discharge electron beam with electron energies between 3 and 7 keV. A continuous beam 7 cm in diameter with a power density up 90 W/cm2 was used to anneal the 7‐cm‐diam central portion of boron‐implanted (30 keV, 5×1015 atoms/cm2) n‐type 〈100〉 silicon wafers 10 cm in diameter. Annealing was obtained without redistribution of the original dopant profile using a 15‐selectron beam exposure. Due to the high electron beam power density achieved over a large area, one can uniformly anneal an entire wafer in a single exposure without sample or beam scanning.

Titanium disilicide formation by wide‐area electron beam irradiation

We describe the use of a wide‐area (38 cm2) electron beam as a heat source to interdiffuse 400‐A‐thick sputter‐deposited titanium films into 3–6‐Ω cm〈100〉 n‐type silicon wafers. Isochronal exposures of 30 s with electron beam of current densities greater than 250 mA/cm2 reduced the as‐deposited sheet resistance by a factor of 10, while exposures at half this current caused the sheet resistance to increase by a factor of 2.5. Compositional depth profiles obtained from a combination of ion beam sputtering and Auger electron spectroscopy show that this resistivity increase is caused by diffusion of oxygen into the titanium film induced by the electron beam heating. At exposures to beam intensities sufficient to induce complete silicide formation, oxygen is segregated at the surface by the advancing silicon. We conclude that the silicide self‐cleanses itself of oxygen during formation.

Confined Geometry Interactions of Downstream RF-Excited Atmospheric Plasma Wires

We report on the generation and propagation of plasma by-products via the electrical excitation of argon gas flowing in an insulating millimeter-sized tube at excitation frequencies of 13.56-25 MHz. An electrode on the outer surface of the tube acted to capacitively couple excitation RF energy (<1 W to tens of watts) into the plasma, resulting in a plume that extends into open air for millimeter distances that are far beyond the main plasma excitation volume (ldquoplasma wiresrdquo). By using identical tubes with flowing argon but with the external electrode grounded, we demonstrate the plasma plume propagation between multiple tubes. Contrary to prior work, the open-air plasma wires propagate opposite the gas flow direction.

Cold Cathode Electron Beam Recrystallization of Soi Films

A cold cathode line source electron beam system for forming SOI (Silicon-om-Insulator) films by zone melt recrystallization is described. Possible advantages gained from using a cold cathode electron beam include the controllability of the beam profile and power level, as well as straight-forward scaling to 6 or 8 inch wafers. A computer-based melt width control procedure incorporating feedback to the line intensity from optical observation of the molten zone is also described. This technique allows direct control and adjustment of the melt zone over widths typically from 1 to 3 mm. 5 figs.

Radio frequency driven slot micro-discharges operating in open air

Microdischarges are formed between a grounded hollow slot electrode and a radio frequency driven recessed wedge electrode. At low current, the discharges are uniform nonequilibrium glows, while for higher currents, the discharges transition to arcs. For certain operating conditions, patterned striations are produced in the discharge.

9 – Laser and Electron Beam Assisted Processing

Publisher Summary This chapter discusses recent progress in the application of photon beams and electron beams to semiconductor device fabrication. Specifically, it examines photon and electron beam assisted chemical vapor deposition (CVD) of microelectronic films, electron beam induced annealing of ion implantation damage and associated dopant activation. It also examines electron beam induced alloying of silicide structures, self-developing electron beam proximity lithography of submicron features and traveling-melt photon, and electron beam recrystallization of deposited polycrystalline silicon films on SiO2. Thermal CVD relies on high substrate temperatures and catalytic reactions between donor molecules and substrate surfaces to achieve the dissociation of feedstock gases with binding energies in the 1 to 3 eV range. One improvement over conventional thermal CVD techniques is plasma-enhanced chemical vapor deposition (PECVD). The chapter compares laser and electron beam induced traveling-melt recrystallization of polysilicon deposited on four inch wafers. This purely thermal process consists of locally melting an area of the deposited polysilicon film followed by propagation of this melt front across the entire wafer surface.

NMOS device characteristics in electron-beam-recrystallized SOI

Characteristics of n-channel MOSFETs fabricated in cold-cathode electron-beam-recrystallized silicon-on-oxide layers have been examined. Assorted crystallographic defects exist in the recrystallized silicon layer, ranging from highly branched subgrain boundaries to widely spaced parallel subgrains and rows of threading dislocations. Some of these MOSFET transistors have characteristics approaching those fabricated in bulk silicon including approximately=828 cm/sup 2//V-s electron surface mobilities and 130 mV/decade inverse subthreshold slopes. However, many of the devices tested exhibited leakage currents up to 10/sup -6/ A/ mu m, resulting in high inverse subthreshold slopes and reduced threshold voltages. Some effects of crystal imperfections on device behavior are discussed. >

Bulk direct band gap MoS 2 by plasma induced layer decoupling

We report a robust method for engineering the optoelectronic properties of many-layer MoS2 using low energy oxygen plasma treatment. Gas phase treatment of MoS2 with oxygen radicals generated in an upstream N2-O2 plasma is shown to enhance the photoluminescence (PL) of many-layer, mechanically exfoliated MoS2 flakes by up to 20 times, without reducing the layer thickness of the material. A blue shift in the photoluminescence spectra and narrowing of linewidth is consistent with a transition of MoS2 from indirect to direct band gap material. Atomic force microscopy and Raman spectra reveal that the flake thickness actually increases as a result of the plasma treatment, indicating an increase in the interlayer separation in MoS2. Ab-initio calculations reveal that the increased interlayer separation is sufficient to decouple the electronic states in individual layers, leading to a transition from an indirect to direct gap semiconductor. With optimized plasma treatment parameters, we observed enhanced PL signals for 32 out of 35 many-layer MoS2 flakes (2-15 layers) tested, indicating this method is robust and scalable. Monolayer MoS2, while direct band gap, has a small optical density, which limits its potential use in practical devices. The results presented here provide a material with the direct band gap of monolayer MoS2, without reducing sample thickness, and hence optical density.