Abstract : Tetraethyl orthosilicate (TEOS) was used as a silicon source to grow SiO2 films in a modulated electron beam generated plasma enhanced chemical vapor deposition (PECVD) arrangement. Process parameters investigated were: substrate temperature, gas composition, duty factor, and incident ion energy. At high temperatures (>150 C), film compositions were less sensitive to the process parameters, while at lower temperatures, the film chemistries varied greatly. Activation energies of -0.122 eV and -0.020 eV were determined for the films grown in these respective temperature ranges. Below 250 C, preferred growth conditions (> 20 nm/min) were found at small flow percentages of TEOS in argon/oxygen mixtures (2:48:50) with increased ion energies. The trade-off between substrate temperature and incident ion energy demonstrated a process viability not previously seen in scalable PECVD systems.

A method is described for measuring ion energy distributions using a commercially available, combined energy analyzer/mass spectrometer. The distributions were measured at an electrode located adjacent to pulsed, electron beam-generated plasmas produced in argon. The method uses energy-dependent tuning and was tested for various plasma conditions. The results indicate an improved collection efficiency of low-energy ions when compared to conventional approaches in measuring ion energy distributions.

Plasmas generated from moderate energy (2–5keV) electron beams (e-beam) have unique, attractive characteristics that are ideal for materials processing applications. These plasmas possess low electron temperatures (<0.5eV), variable plasma densities (109–1012cm−3) with an improved control of plasma species generation, and perhaps most importantly, a direct scalability to processing areas exceeding one square meter. These characteristics are due to the plasma ionization being driven by the e-beam instead of an external electromagnetic field as used in conventional processing plasma sources. Theoretical and experimental system details are discussed in terms of plasma operating conditions applied to three different surface modification approaches: metal nitriding, negative ion etching, and polymer surface energy tailoring.

A modulated, electron-beam generated plasma processing system was used to study plasma-polymer interactions for 193 and 248nm photoresists (PRs) that differed significantly in polymer structure. Because of the low plasma potential of the electron-beam generated plasma, the authors were able to study plasma etching and surface roughening of the photoresists at very low ion energies (<5eV) without sacrificing high ion flux (>1014cm−2). Typical conditions in the experiments were 2kV∕4ms electron-beam pulses with a 20ms period. The effects of ion bombardment energy, chemically assisted etching using fluorine, and the presence of a thin fluorocarbon overlayer on surface roughness formation during PR etching were examined. Gas mixtures containing SF6 resulted in much higher etch rates and an increased surface roughness relative to values measured in pure Ar plasmas. However, the rms roughness per nanometer of photoresist removed was greater for pure Ar plasmas. Overall the 248nm PR showed less surface roughness than 193nm PR after identical treatments, which was explained by a higher etching rate of the 193nm photoresist material. Finally, it was found in a pure argon plasma that the thickness of a fluorocarbon overlayer determined the roughness of the underlying photoresist; specifically, thicker layers resulted in smoother PR surfaces after plasma exposure.

A high-quality Ge epilayer on Si has emerged as a viable method to integrate III-V optoelectronics and to achieve high carrier mobility than conventional Si-based CMOS devices. The epilayer quality is often measured by the density of threading dislocations that adversely impact the carrier transport. A number of strategies have been developed in recent years to reduce the threading dislocation density in Ge epilayers grown on Si. These strategies include multiple post-growth annealing, liquid-phase epitaxy, epitaxial necking, and graded SiGe layers. In search of a relatively simple and low-temperature growth technique, we have previously demonstrated Ge "touchdown" on Si, where high-quality Ge is grown epitaxially on Si covered with a thin layer (~ 1.2 nm) of chemically grown SiO2. Herein, we focus on the unique surface chemistry involving Ge, SiO2, and Si that gives rise to the formation of approximately 7-nm-wide windows in the SiO2 layer and selective growth of Ge on exposed Si rather than on SiO2

Abstract : Pulsed hollow cathode discharges, used to generate kilovolt electron beams for the production of plasmas, were studied in low pressure (50-70 mTorr) backgrounds of argon, oxygen, nitrogen, SF sub 6 and mixtures thereof. Cathode currents were measured as a function of cathode voltage, duty factor, and relative gas concentration. The cathode current was found to have a dependence on all variables, with the greatest impact being operating gas for all voltages and duty factors. The ambient gas is thought to influence the production of secondary electrons at the cathode surface thereby impacting the operation of the hollow cathode discharge and electron beam production.

A hybrid plasma enhanced physical vapor deposition (PEPVD) system consisting of an unbalanced dc magnetron and a pulsed electron beam-produced plasma was used to deposit reactively Sputtered titanium nitride thin films. The system allowed for control of the magnitudes of the ion and neutral flux, in addition to the type of nitrogen ions (atomic or molecular) that comprised the flux. For all deposition experiments, the magnitude of the ion flux incident on the substrate was held constant, but the composition of the total flux was varied. X-ray diffraction and atomic force microscopy showed that crystallographic texture and surface morphology of the films were affected by the plasma flux composition during growth.

Time-resolved ion flux and energy distributions were measured at an electrode located adjacent to a pulsed, electron beam-generated plasma produced in argon. A Langmuir probe was also used to determine time-dependent electron temperature and plasma density. Temporal variations in the incident Ar/sup +/ and Ar/sup +2/ ion energy and flux were correlated to changes in the electron temperature and plasma density. The evolution of the plasma density and ion flux is understood by considering the loss mechanisms of each ion species.

ing System) was invented in NRL's Plasma Physics Division and Materials Science and Technology Direc-torate. It uses a 2-5 keV electron beam to ionize and dissociate gas molecules, species that are then used to modify the surface properties of various materials. Th novel approach to plasma generation provides a direct scalability of the system and higher control over reac-tive chemical species compared to conventional plasma processing systems used in the semiconductor and coatings industries. Th e scalability is simply dictated by the dimensions of the electron beam, allowing unprecedented surface areas to be treated uniformly. Th e process/chemical control is provided by electron beam/molecule interactions, which ensures that all chemical reaction pathways are accessible, as opposed to conventional plasma systems. Th e ability to increase the hardness of a mate rial while preserving its intrinsic properties provides tremendous advantages in choosing materials for demanding applications. Th in layers of well-known hard coatings are frequently used, but adhesion prob-lems (lattice and temperature coeffi cient matching) limit their utility. For metals, incorporating nitrogen into the surface's lattice (surface nitriding) is highly desirable because the nitrided layer is physically part of, yet significantly harder than, the bulk material. Equally important in surface nitriding is maintaining suffi ciently low temperatures to preserve the properties of the bulk material.

An electron beam generated plasma processing system was characterized with in situ diagnostics and employed for a series of low energy (350 eV) stainless steel nitriding experiments in the temperature range of 325–462 °C. Plasma characterization yielded quantitative ion specie fluxes to the stainless steel workpiece in an argon–nitrogen plasma, with a significant fraction of the flux comprised of N+ ions. The nitriding rates were as high as 20 μm h−1/2 with surface layers exhibiting hardness values of approximately 15.5 GPa for specimens processed at all temperatures. X-ray diffraction analysis revealed nitrogen concentrations of approximately 30 at.% in all samples processed below 460 °C. The process activation energy was comparable to that in nitriding systems with higher ion fluxes, suggesting favorable plasma chemistry with respect to plasma nitriding applications.