摘要:

The Cu atoms sputtered from the cathode and the corresponding Cu ions in an argon direct current glow discharge are described by a combination of two models: a fluid model for their overall behavior (diffusion and migration) in the entire discharge and a Monte Carlo model for the explicit transport of the Cu ions in the cathode dark space. The models are combined with other models described previously for the electrons, Ar ions, fast Ar atoms, and Ar metastables, in order to obtain an overall picture of the glow discharge. Results of the fluid model are the densities and fluxes of the Cu atoms and ions. At 100 Pa and 1000 V the Cu atom and ion densities are of the order of 1012–1013and 1010–1011cm−3, respectively. The ionization degree is hence about 1%, which is much higher than for Ar. The Cu ion to Ar ion density is about 6% and the Cu ion to Ar ion flux is about 5%. The energy distribution of the Cu ions bombarding the cathode is calculated with the Monte Carlo model and shows good agreement with experiment. It is characterized by a peak at maximum energy, in contrast to the energy distribution of Ar ions and fast atoms. Since sputtering increases with the bombarding energy, the amount of self‐sputtering is significant, although still clearly lower than the contribution of Ar ions and fast atoms. The influence of pressure, voltage, and current on all these quantities is investigated. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361023

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The plasma generated by a silicon filtered cathodic vacuum arc has been investigated using a Faraday cup and Langmuir probes. Ion energy distributions for arc currents ranging from 30 to 80 A were measured. Mean ion energies were found to range from 8 to 18 eV. The ion saturation current density varied from 0.1 to 1 mA/cm2depending on both the arc and filter coil currents. The energy distributions were fitted by a sum of Gaussians spaced according to the gas dynamic model for ion acceleration at the cathode spot. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362654

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The collisionless two‐fluid model of a plasma is applied to the drift of ions and electrons downstream from an electron cyclotron resonance source. A plasma potential drop of 20 V is found for the system parameters typical of plasma‐assisted epitaxy of the group III nitrides. This model provides a simple way to design downstream magnet coils to tune the ion acceleration, a key parameter in growth and etching processes. Compared to previous analyses, the present work makes clear the conditions under which an ion accelerating potential actually appears, in terms of the expansion that the plasma undergoes upon exiting from the source region. Published measurements of the potential profile downstream from a N2plasma source can be fit assuming an electron temperaturekTe=3.2 eV, somewhat greater than half the excitation energy of the long‐livedA 3&Sgr;+umetastable state. The analysis is consistent with the plane probe current–voltage characteristics obtained from the growth stage in a plasma‐assisted molecular‐beam epitaxy process. For a 10 W plasma used in the growth of GaN, the value of ion saturation current implies a plasma density at the source of 1010cm−3. Considering the suppression of electron current by the magnetic field, the measured ratio of ion to electron saturation current implies an electron temperature of 3.8 eV. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361024

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electromagnetic fields in a planar rf inductively coupled plasma source, of interest for materials processing, were measured using a two‐loop inductive (B‐dot) probe. The two loops were oriented to measure the time derivative of the axial and radial components of the magnetic fieldB˙zandB˙r, respectively, at various positions in ther–zplane of the cylindrically symmetric argon discharge. Maxwell’s equations were used with this data to calculate amplitudes of the rf azimuthal electric fieldE&fgr;and current densityJ&fgr;, as well as the complex permittivity &egr; of the plasma, from which the electron densitynewas calculated. The electron densities calculated using this technique were found to compare favorably to the results of measurements made with Langmuir probes. Electron drift velocities calculated fromJ&fgr;andnewere found to be comparable to electron thermal velocities in the region of highestE&fgr;and thus may contribute to local enhancement of electron impact reactions, thereby affecting process chemistry and uniformity. The peak in the drift velocity moved radially outward as the pressure increased due changes in the radial plasma density profile. This technique is applicable to chemistries where Langmuir probes are not practical. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361025

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Kinetics of the many‐stage process of particle nucleation and growth in low‐pressure rf discharge in silane SiH4–Ar is considered. The particle growth is considered in an analytical model as a chain of negative‐ion molecular reactions, stimulated by vibrational excitation. In the framework of this model, a limitation of first generation particle size is explained as well as the strong temperature effect on cluster growth. A theory of critical phenomena of cluster trapping in discharge area has been elaborated to describe the neutral particle selection by size, and the particle concentration increases during a period exceeding the residence time in plasma. Finally, an analytical model of critical phenomena of particle coagulation and its influence on plasma parameters is developed to explain the latest experimental results on supersmall 2–10 nm cluster kinetics. All theoretical results are presented in comparison with corresponding new experimental data and with results of an especially made computer simulation. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361026

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Quantitative high resolution electron microscopy (HREM) was employed to study the crystallography of a zirconia‐alumina transformation‐toughening nanolaminate. The nanolaminate consisted of alternating layers of polycrystalline zirconia and amorphous alumina. The zirconia layer thickness was scaled to insure unity volume fraction of the metastable tetragonal phase at the growth temperature, as predicted by an end‐point thermodynamics model and verified by x‐ray diffraction. In the microscopy sample, phase identification was achieved from precise measurements of lattice spacings using digital diffractograms of individual nanocrystallites. Of the nanocrystallites analyzed, (22±6)% were monoclinic in a distinct crystallographic relationship with their tetragonal neighbors. The following plane and direction relationships were identified:m(100)//t(100) andm[001]//t[001]. The observed structure is the result of a stress‐induced transformation from the tetragonal phase. This transformation was localized to nanosized regions within the individual zirconia layers. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361027

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have studied the effect of ion‐irradiation on porous Si formation, microstructure, and optical properties. Porous Si was first self‐implanted and then fabricated by anodization. With increasing implantation dose, the photoluminescence (PL) intensity decreased, and the PL spectra were also red shifted. Porous Si formed from crystal Si emitted light, while that from preamorphized Si did not. Porous Si luminescent patterns with a resolution of 2 &mgr;m features were formed by selective ion implantation. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361028

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The structural and chemical properties of hydrogenated amorphous silicon carbide (a‐Si1−xCx:H) thin films, deposited by plasma‐enhanced chemical‐vapor deposition, were determined by extended x‐ray absorption fine structure (EXAFS), x‐ray‐absorption near‐edge spectroscopy (XANES), small‐angle x‐ray scattering, Fourier transform infrared (FTIR) spectroscopy, Auger electron spectroscopy, and visible spectrometry. The EXAFS and XANES results show the crucial influence of the ‘‘starving’’ plasma deposition conditions on the structural properties of wide‐gapa‐Si1−xCx:H films and are consistent with the FTIR and optical‐absorption data. The first‐neighbors distance for alloys with smaller carbon content or deposited at higher silane flow are very close to the mean Si–Si distance obtained fora‐Si:H. On the other hand, the EXAFS spectra of films with higher carbon content (x≳50 at. %) and deposited under ‘‘starving’’ plasma regime show Si–C distances similar to crystalline SiC (c‐SiC). The presence of a typicalc‐SiC resonance in the XANES spectra of the same samples is evidence that the material has a chemical order close to that ofc‐SiC. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361029

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Rietveld analysis of neutron‐diffraction data from Nd3Fe29−xTx(T=Ti, Cr, and Mn) has been used to determine the location of the substitutional atoms and the magnetic moments. Reanalysis of the T=Ti data confirms that the space groupA2/mis a better choice thanP21/c, which had previously been used to describe the structure. The Ti atom locations and concentrations remain unaffected in the two space groups, but for the other substituents the refined concentrations are well behaved inA2/m, whereas inP21/cthe refinements were unstable due to the symmetry relations between certain substituted sites. The site occupancies are analyzed in terms of steric and environment effects. A possible explanation for the high Curie temperature of the Cr compound is proposed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361030

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Copper in Si was shown to be strongly bound at cavities formed by He ion implantation and annealing. Evolution of this system during heating was observed by Rutherford backscattering spectrometry and transmission electron microscopy. Results were mathematically modeled to characterize quantitatively the binding of Cu in the cavities and, for comparison, in precipitates of the equilibrium silicide, &eegr;‐Cu3Si. Binding of Cu to cavities occurred by chemisorption on the walls, and the binding energy was determined to be 2.2±0.2 eV relative to solution in Si. The heat of solution from the silicide was found to be 1.7 eV, consistent with the published phase diagram. These findings suggest the use of cavities for metal‐impurity gettering in Si devices. Hydrogen in solution in equilibrium with external H2gas displaced Cu atoms from cavity walls, a mechanistically illuminating effect that is also of practical concern for gettering applications.

ISSN:0021-8979    

DOI:10.1063/1.361031

出版商:AIP    

年代:1996

数据来源: AIP