摘要:

Product analysis of microwave (MW)C2H2discharge byLi+ion attachment mass spectrometry demonstrates the unexpected formation of many unfamiliar hydrocarbon neutral products. The experiments were conducted under MW discharge conditions in which the peak intensities for the ionic species leaving the MWC2H2plasma were barely detectable which permits confirmation of these neutral compound in the gas phase. Various free radicals as well as stable polymer molecules were clearly present. The latter are classified asCn(n=4,6, and 8),CnH2(n=2,3, 4, 6, and 8),CnH4(n=2,3, 4, 6, and 8), and so on, wherenis the carbon number. Radicals such asCnH3(n=2and 4),CnH5(n=2,4, and 6),CnH7(n=3and 4), andCnH9(n=4)were detected. Some of these species, which have been observed in the interstellar space, have been identified mass spectrometrically for the first time. We believe that integrating aLi+ion attachment reactor with quadrupole mass spectrometry can create a powerful instrument for installation on spacecraft. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366093

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A one-dimensional fluid model for radio-frequency glow discharges is presented which describes silane/hydrogen discharges that are used for the deposition of amorphous silicon (a-Si:H). The model is used to investigate the relation between the external settings (such as pressure, gas inlet, applied power, and frequency) and the resulting composition of the gas and the deposition rate. In the model, discharge quantities such as the electric field, densities, and fluxes of the particles are calculated self-consistently. Look-up tables of the rates of the electron impact collisions as a function of the average electron energy are obtained by solving the Boltzmann equation in a two term approximation for a sequence of values of the reduced electric field. These tables are updated as the composition of the background neutral gas evolves under the influence of chemical reactions and pumping. Pumping configuration and gas inlet are taken into account by adding source terms in the density balance equations. The effect of pumping is represented by an average residence time. The gas inlet is represented by uniformly distributed particle sources. Also the radial transport of neutrals from the discharge volume into the discharge-free volume is important. As the fluid model is one dimensional, this radial transport is taken into account by an additional source term in the density balance equations. Plasma–wall interaction of the radicals (i.e., the growth ofa-Si:H) is included through the use of sticking coefficients. A sensitivity study has been used to find a minimum set of different particles and reactions needed to describe the discharge adequately and to reduce the computational effort. This study has also been used to identify the most important plasma-chemical processes and resulted in a minimum set of 24 species, 15 electron-neutral reactions, and 22 chemical reactions. In order to verify the model, including the chemistry used, the results are compared with data from experiments. The partial pressures of silane, hydrogen, disilane, and the growth rate of amorphous silicon are compared for various combinations of the operating pressure (10–50 Pa), the power (2.5–10 W), and the frequency (13.56–65 MHz). The model shows good agreement with the experimental data in the dust free &agr; regime. Discharges in the&ggr;′regime, where dust has a significant influence, could not be used to validate the model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366016

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Quantitative measurements ofC2(a3&Pgr;u),C3(X,1&Pgr;),andCH(X,2&Pgr;)have been made by calibrated linear laser-induced fluorescence in the plume of a dc-arcjet (Ar/H2/CH41.1:1:0.005) reactor during the chemical vapor deposition of diamond. The peak number density in the arcjet plume for CH is(3.7±0.8)×1012 molecules/cm3,forC2(3a)(3.1±1.3)×1010 cm−3,and forC3∼3×1012 cm−3with 25 Torr reactor pressure. The radial spatial distributions forC2and CH have a maximum in the center of the plume; however,C3is distributed as a hollow cylinder with a pronounced minimum at the center. The variation in number density and in spatial distribution is investigated for changes in chamber pressure, methane flow, and distance from the nozzle. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366017

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The interaction and energy transfer of a laser ablation plasma of Ti with a pulsedN2supersonic expansion are investigated using time-of-flight quadrupole mass spectroscopy and Langmuir probe techniques. The Ti ablation target and the exit nozzle of the pulsed gas source are positioned so that the plasma plume and gas pulse interact near to their respective origins, where the number density is still high, which hence results in strong coupling of the nascent plasma with the gas pulse. The timing between the gas pulse and ablation plume is shown to be critical in determining the scattering processes and the chemical nature of the films grown by this method, an example of which is presented. The degree of ionization of the plasma when crossed with the gas pulse compared to that for expansion into vacuum increases from less than10−3to0.28±0.11, which is attributed to collision-induced ionization of Ti atoms. Further increasing theN2number density quenches the ion signal. The effective bimolecular cross section for scattering of Ti with the high densityN2pulse is about 4 times larger than that with a static background of low pressureN2, while the fractional depletion of theN2pulse by the Ti plume depends on theN2number density in the pulse, indicating that at these high local pressures, collective effects prevail. We propose a simple model for the resulting evolution of the plasma based on electrostatic considerations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366018

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Models capturing the periodic steady-state behavior of rf capacitively coupled discharges are now commonplace. New plasma sources have been motivated by selectivity, charge-damage mitigation, and general process control needs in plasma processing of electronic materials. These new sources require models that can accurately capture the transient behavior of the plasma source.Such models are not commonplacebecause the behavior of transport parameters in transients is still not well understood and because the problem is inherently stiff, i.e., widely disparate time scales are important. In this paper, we present the results of an investigation of the simplest type of transient, known as a step disturbance, in a 2 cm gap parallel-plate argon discharge at 1 Torr. As examples, two classes of step transients are considered: step increases in the peak-to-peak (pp) applied voltage (300 to up to 450 V pp) and step decreases (300 to as low as 150 V pp). The resulting transients are interpreted in terms of time scales representative of electron and ion motion in the sheath, ionization dynamics, and neutral transport processes. The possibility of using these transients as a means of process identification is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366019

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dust particle transport in low-temperature plasmas has recently received considerable attention due to the desire to minimize contamination of wafers during plasma processing of microelectronics devices. Laser light scattering observations of dust particles near wafers in reactive-ion-etching (RIE) radio frequency (rf) discharges have revealed clouds which display collective behavior. These observations have motivated experimental studies of the Coulomb liquid and solid properties of these systems. In this paper, we present results from a two-dimensional model for dust particle transport in RIE rf discharges in which we include particle-particle Coulomb interactions. We predict the formation of Coulomb liquids and solids. These predictions are based both on values of&Ggr;>2(liquid) and&Ggr;>170(solid), where &Ggr; is the ratio of electrostatic potential energy to thermal energy, and on crystal-like structure in the pair correlation function. We find that Coulomb liquids and solids composed of trapped dust particles in RIE discharges are preferentially formed with increasing gas pressure, decreasing particle size, and decreasing rf power. We also observe the ejection of particles from dust crystals which completely fill trapping sites, as well as lattice disordering followed by annealing and refreezing. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366020

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In a balanced magnetron sputtering system the thermal power at a substrate has been determined from the temperature change of the substrate when the plasma is switched on. Using the temperature as a function of the potential of a probe, the calorimeter has been calibrated absolutely. A heat input equivalent of about 10 eV per electron has been determined for a dc discharge. The results for the total thermal power at the substrate are compared with values published by other groups for similar discharge systems. The contributions of different kinds of particles are discussed. For the dc discharge at a discharge power of 50 W and a pressure of 0.8 Pa, a thermal power of 15.6mW cm−2has been found which is mainly produced by particles other than the plasma ions. It can be concluded from the increase of the thermal power with decreasing pressure that bombardment by particles originating from the target is the main source of the substrate heating. In an rf discharge the ion energy is two times and the flux density is nearly three times higher than in a dc discharge. Here the dependence of the thermal power on pressure is only weak and mainly the plasma ions transport the power to the substrate. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366092

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In inertial confinement fusion (ICF) experiments, irradiation uniformity is improved by passing laser beams through distributed phase plates (DPPs), which produce focused intensity profiles with well-controlled, reproducible envelopes modulated by fine random speckle. [C. B. Burckhardt, Appl. Opt.9, 695 (1970); Y. Kato and K. Mima, Appl. Phys. B29, 186 (1982); Y. Kato &etal;, Phys. Rev. Lett.53, 1057 (1984); Laboratory for Laser Energetics LLE Review 33, NTIS Document No. DOE/DP/40200-65, 1987 (unpublished), p. 1; Laboratory for Laser Energetics LLE Review 63, NTIS Document No. DOE/SF/19460-91, 1995 (unpublished), p. 1.] A uniformly ablating plasma atmosphere acts to reduce the contribution of the speckle to the time-averaged irradiation nonuniformity by causing the intensity distribution to move relative to the absorption layer of the plasma. This occurs most directly as the absorption layer in the plasma moves with the ablation-driven flow, but it is shown that the effect of the accumulating ablated plasma on the phase of the laser light also makes a quantitatively significant contribution. Analytical results are obtained using the paraxial approximation applied to the beam propagation, and a simple statistical model is assumed for the properties of DPPs. The reduction in the time-averaged spatial spectrum of the speckle due to these effects is shown to be quantitatively significant within time intervals characteristic of atmospheric hydrodynamics under typical ICF irradiation intensities. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366021

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366276

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electrical breakdown of plane parallel steel electrodes (10 cm diam) is studied in a Pyrex-walled vacuum chamber (minimum pressure less than8×10−6Torr). For clean gases, H2and D2, and with electrode gaps from 0.5 to 8 cm, the breakdown at pressures from 0.3 to 0.5 Torr is consistent with a secondary process of electron release by ion bombardment. The breakdown curves for the two gases, when scaled on both axes, overlap to a considerable extent. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366278

出版商:AIP    

年代:1997

数据来源: AIP