摘要:

We have measured the distributions ofN2+ion velocity components parallel and perpendicular to the electrode in the sheath of a radio-frequency nitrogen reactive ion etching discharge, using pulsed laser-induced fluorescence. Parallel to the electrode, the ions have throughout a thermal distribution that is found to be consistent with the rotational temperature of 355 K. In the perpendicular direction, we see clearly the acceleration of the ions towards the electrode, and our results agree well with theoretical predictions although an unexpected peak of unaccelerated ions persists. We have also determined the absolute ion concentrations in the sheath, which we have calibrated by analyzing the decay in laser-induced fluorescence in the plasma bulk after discharge extinction. At 20 mTorr, the bulk concentration of1.0×1010 cm−3falls to around2×108 cm−3at 2 mm from the electrode. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364382

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article, we report values of ion energy and angular distributions measured at the grounded electrode of an inductively coupled discharge in chlorine gas. The inductive rf drive in our cell produced high plasma densities (1011/cm3electron densities) and stable plasma potentials. As a result, ion energy distributions typically consisted of a single peak well separated from zero energy. Mean ion energy varied inversely with pressure, decreasing from 13 to 9 eV as the discharge pressure increased from 20 to 60 mTorr. Half-widths of the ion angular distributions in these experiments varied from 6° to 7.5°, corresponding to transverse energies from 0.13 to 0.21 eV. During the course of the experiment, ion energies gradually decreased, probably due to the buildup of contaminants on the chamber walls. Cell wall temperature also was an important variable, with ion fluxes to the lower electrode increasing and the ion angular distribution narrowing as the cell temperature increased. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364383

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogous to the diffusive regime in neutral agglomeration. Large particles in high powered plasmas generally produce compact agglomerates of high fractal dimension, analogous to ballistic agglomeration of neutrals. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364384

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Low pressure (<10 mTorr) inductively coupled plasma sources are being developed for etching and deposition of semiconductors and metals. In models for these devices, plasma dynamics are typically coupled to the electromagnetic fields through Ohm’s law, which implies that collisional heating is the dominant power transfer mechanism. In this article, we describe an algorithm to couple plasma dynamics to electromagnetic field propagation which self-consistently includes noncollisional heating effects as well. The algorithm makes use of kinetic information available from an electron Monte Carlo simulation to compute plasma currents that are then used in computation of the electromagnetic field. Results for plasma density and electric field amplitude are presented as a function of power and pressure, and are compared to results from models that consider only collisional heating. We find that noncollisional heating effects are important at pressures of less than 10–20 mTorr, a range that depends both on gas mixture and geometry. Noncollisional heating effects allow the wave to couple more efficiently to the plasma. As a result, the electric field amplitude required to deposit a given amount of power in the plasma is smaller than that needed when only collisional heating is considered. For a constant power deposition, this generally leads to lower plasma densities. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364385

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The influence of UV illumination on the behavior of silent electrical discharge streamers (microdischarges) in dry and humid gases (nitrogen, oxygen, air, and Ar/O2mixtures) is presented. A commercial low-pressure mercury lamp, which was spectrally calibrated, provides UV light. The UV irradiance power coupled into the discharge cell is also calculated. The transferred charge per mean microdischarge (in a voltage half-cycle) was measured for a pin electrode assembly, configured to deliver either M−G+ transitions (electrons going from metal towards dielectric) or M+G− transitions (electrons going from dielectric to metal). The total transferred charge is recorded by monitoring a charge versus voltage plot (Lissajous figure). When illumination is restricted to the gas alone, both the total transferred charge and the individual-microdischarge transferred charge remain constant for either transition (M−G+ or M+G−). However, when the dielectric is illuminated, a marked decrease in the individual-microdischarge transferred charge is observed for M+G− transitions in some gases. For this case, a greater number of microdischarges must occur in a half-cycle to keep the total transferred charge constant, thereby creating more homogeneous discharge conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364386

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The interaction of a high-contrast, 400 fs, 5×1017W/cm2laser pulse with a preformed tantalum plasma produced in a double-pulse configuration is investigated. The x-ray emission characteristics are studied for different time delays between the two laser pulses. A time-resolved transmission grating spectrometer is used to measure the x-ray conversion efficiency and emission duration in the 0.2–1.2 keV energy range. Our results show that it is possible to increase the x-ray source conversion efficiency by an order of magnitude simply by optimizing the delay between the laser pulses. To give an overview of the performances available from such laser-plasma x-ray sources, these results are compared those obtained with a single laser pulse in different interaction regimes. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364387

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the dependence of the electro-optical properties of polymer dispersed liquid crystals (PDLC) on the ultraviolet (UV) cure of the solution of monomer and liquid crystal. The kinetics of UV polymerization and its effect on the morphology of the phase separated droplets of liquid crystal determine the switching voltage, response time, and luminance of the PDLC. Using a series of statistically designed experiments, we have mapped the dependence of these responses on the weight fraction of liquid crystal, the temperature of the cell during cure, and light intensity. Temperature and composition are strongly coupled parameters that influence switching voltage, luminance, and response times. Switching voltages are minimized at 4–5 V for an 8 &mgr;m cell gap over a large region of temperature-composition space. An abrupt transition line occurs through that space. On one side of the transition line, voltage increases linearly either as temperature increases or composition decreases, and on the other side of the line, voltage is constant. Analyses of decay times, the slower response time of the PDLC, show that the times peak along a line of points in temperature-composition space that is close to the transition line for increasing switching voltages. We present these results as contours on the same graphs and relate them to our understanding of the phase separation process in the PDLC mixture. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364388

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Using confocal microscopy, we have studied the morphology of polymer dispersed liquid crystals (PDLC) as a function of polymer/liquid crystal composition, polymer cure temperature, and ultraviolet (UV) curing power and determined how this morphology affects the electro-optical properties. The PDLC morphology consists of a spongelike texture where spherically shaped liquid crystalline domains are dispersed in a polymer matrix. These domains grow as the fraction of liquid crystal increases and as the UV curing power decreases. We observe no significant changes in domain size with changes in the curing temperature. Instead, high-temperature cures result in coalescence and the formation of elliptical-shaped liquid crystal domains. The temperature at which this coalescence starts to be observed marks a threshold temperatureTth,above which the switching properties are strongly dependent on morphology. BelowTththe switching properties are largely independent of morphology. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364447

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The magnetic domain structure of amorphous ferromagnets with nonzero magnetostriction is mainly determined by the internal stress state because of the magneto-elastic coupling. The stress and field dependence of the domain structure contains important information on the internal stresses in the material. The three-dimensional neutron depolarization technique has been used to study the stress- and field-dependence of the bulk domain structures in both as-quenched and annealed ribbons of the metallic glassFe40Ni40B20. A three-layer domain structure model corresponding to compressive and tensile internal stresses is presented to explain the measured data. The influence of surface roughness on the interpretation of neutron depolarization measurements in amorphous ribbons is discussed. Finally, the internal stress relaxation due to the annealing is explained in terms of the viscous behaviour of the glass. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.364448

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The damage to diffused-junctionn+-pInP solar cells induced by electron and proton irradiations over a wide range of energy from 0.5 to 3 MeV and 0.015 to 20 MeV, respectively, has been examined. The experimental electron and proton damage coefficients have been analyzed in terms of displacement damage dose, which is the product of the particle fluence and the calculated nonionizing energy loss [G. P. Summers, E. A. Burke, R. Shapiro, S. R. Messenger, and R. J. Walters, IEEE Trans. Nucl. Sci.40, 1300 (1993).] Degradation of InP cells due to irradiation with electrons and protons with energies of more than 0.5 MeV show a single curve as a function of displacement damage dose. Based on the deep-level transient spectroscopy analysis, damage equivalence between electron and proton irradiation is discussed. InP solar cells are confirmed to be substantially more radiation resistant than Si and GaAs-on-Ge cells. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364449

出版商:AIP    

年代:1997

数据来源: AIP