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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Issue 6 • Date Nov 2000

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Displaying Results 1 - 25 of 57
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

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  • Plasma deposition of optical films and coatings: A review

    Page(s): 2619 - 2645
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    Plasma enhanced chemical vapor deposition (PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others. © 2000 American Vacuum Society. View full abstract»

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  • Search for improved transparent conducting oxides: A fundamental investigation of CdO, Cd2SnO4, and Zn2SnO4

    Page(s): 2646 - 2660
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    The bulk of developmental work on transparent conducting oxides (TCOs) has been somewhat empirical. This statement applies both to more familiar materials such as indium tin oxide (ITO) and to less-well-known materials that have emerged in recent years. In this article, we place a greater emphasis on more fundamental research. Our eventual goal is to gain a thorough understanding of these materials, their potential for further improvement, whether or not they suggest new and potentially superior materials, and the way their properties are influenced by structural and other issues. We also hope to provide guidelines to other researchers working in this area. We have investigated films of cadmium oxide (CdO), cadmium stannate (Cd2SnO4 or CTO), and zinc stannate [Zn2SnO4 (ZTO)]. The CdO was prepared by chemical-vapor deposition, whereas the stannates were prepared by rf sputtering. In both cases, Corning 7059 glass substrates were used. However, some depositions were also made onto tin oxide, which had a profound effect on the nucleation of CdO, in particular. It is well known that a high free-carrier mobility is essential for a TCO with near-ideal electro-optical properties. Increasing the free-carrier concentration also increases the free-carrier absorbance but a higher mobility reduces it. We have achieved free-electron mobilities in CdO (Eg∼2.4 eV) of greater than 200 cm2V-1s-1, of almost 80 cm2V-1s-1 in CTO (Eg∼3.1 eV), but of only 10–15 cm2V-1s-1 in ZTO (Eg∼3.6 eV). We have characterized these materials, and will show key data, using techniques as diverse as the Nernst–Ettingshausen effect; Mössbauer, Raman, optical, and near-infrared spectroscopies; atomic-force and high-resolution electron microscopy; and x-ray diffraction. These measurements have enabled us to determine the effective mass of the free carriers and their relaxation time, the probable distributions of cations between octahedral and tetrahedral sites, the role of the deposition parameters on the carrier concentrations, and the nature of the dominant scattering mechanisms. We also consider issues relating to toxicity of cadmium and to reserves of indium. Both are of great significance to prospective large-volume manufacturers of TCO films and must be taken into account by researchers. © 2000 American Vacuum Society. View full abstract»

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  • Mechanisms for CF2 radical generation and loss on surfaces in fluorocarbon plasmas

    Page(s): 2661 - 2668
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    During fluorocarbon plasma etching, plasma-surface reactions result in the surface acting as either a source or sink for reactive species, thereby impacting the properties of the bulk plasma. For example, experiments have shown that surfaces in radio frequency (rf) capacitively coupled discharges can be either sources or sinks of CF2 depending on, among other properties, the sheath potential. The coupling of rf bulk and surface reactions, and their combined effects on the CF2 density, were investigated using an integrated plasma equipment and surface kinetics model. While CF2 sticking on surfaces led to its loss, CF2 can be generated from surfaces by energetic ion bombardment resulting in sputtering of polymeric films, or neutralization and dissociation of ions. The net effect of a surface for CF2 production depends on the relative rates of these loss and generation processes. A surface can transform from a net CF2 sink at low incident ion energies to a CF2 source at high ion energies because the CF2 yield by ion–surface interactions typically increases with increasing ion energy. The sensitivity of the model to probabilities of major surface reactions was also investigated. © 2000 American Vacuum Society. View full abstract»

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  • Transient plasma-induced emission analysis of laser-desorbed species during Cl2 plasma etching of Si

    Page(s): 2669 - 2679
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    The surface during the etching of Si in a Cl2 inductively-coupled plasma (ICP) was analyzed by laser desorption (LD), followed by detection of the desorbed species by monitoring the transient changes by plasma-induced emission (PIE). Optical emission from Si, SiCl, SiCl2, and possibly other species was detected in situ using this LD-PIE method as a function of rf power, substrate bias, and pressure. The surface coverage of chlorine was determined by normalizing the LD-PIE signal by either of two ways: by the electron density, as measured by microwave interferometry, or by using the background PIE signal. Little change in surface coverage was observed as the ion density was changed by varying the rf power supplied to the ICP, confirming the observation made using laser-induced fluorescence (LIF) detection (LD-LIF). The LD-PIE signal is related to the density of species desorbed from the surface and subsequently excited by electrons. LD-PIE analysis of the surface is more versatile than LD-LIF—sometimes it can detect the desorbed species while LD-LIF cannot. Still, it requires calibration to account for the electron collision-induced excitation of the laser-desorbed species. © 2000 American Vacuum Society. View full abstract»

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  • Surface loss coefficients of CFx and F radicals on stainless steel

    Page(s): 2680 - 2684
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    The surface loss coefficients of CFx (x=1–3) and F radicals have been measured on the stainless steel walls of the differential pumping systems of a plasma reactor. This measurement is made by comparing the beam to background signal ratio of the radicals measured by appearance potential mass spectrometry. The surface loss of the radicals in the differential pumping stages of the vacuum system, in addition to the pumping of the species due to the vacuum pump, increases the beam to background signal ratio of the radical species. The measured loss coefficients are found to be lower than those reported on surfaces that have been exposed to fluorocarbon plasmas. This suggests that the loss coefficients of the species are dependent on the surface coverage of the radicals (CFx and F), which are lower on the walls in the differential pumping system. The measured loss coefficients in the differential pumping system are an order of magnitude lower than the loss coefficients measured in the afterglow of plasma chambers reported in the literature. We suggest the difference in the loss coefficients of radicals in the plasma chamber and those measured in this work are due to the differences in surface coverage in the two cases. © 2000 American Vacuum Society. View full abstract»

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  • Ion and substrate effects on surface reactions of CF2 using C2F6, C2F6/H2, and hexafluoropropylene oxide plasmas

    Page(s): 2685 - 2698
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    The surface reactivity of CF2 radicals has been characterized during plasma processing of a variety of substrates using the imaging of radicals interacting with surfaces technique. The plasma molecular beam sources are 100% C2F6, 50/50 C2F6/H2, and 100% hexafluoropropylene oxide (HFPO) gas mixtures. Simulation of spatially resolved laser-induced fluorescence images in the 100% C2F6 system shows that CF2 has a scatter value, S, ≫1.0 with SiO2, polyimide and photoresist substrates. A scatter of ≫1.0 indicates that CF2 molecules are generated at the surface during plasma processing. With the 50/50 C2F6/H2 plasma, CF2 exhibits a lower scatter value (∼0.85) on Si, SiO2, and polyimide substrates. With the HFPO plasma source, S≥1 for all continuous wave powers and substrates processed. Values of S∼0.8 are obtained for ion-free and pulsed plasmas, however, revealing ion collisions with the substrate play an important role in the surface generation of CF2. The radical-surface interaction data are correlated with data from surface characterization by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy of the substrates. The key finding is that our results suggest the surface reactivity behavior of CF2 radicals correlates well to the overall plasma process (etching or deposition). © 2000 American Vacuum Society. View full abstract»

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  • Carbon deposition by electron beam cracking of hydrocarbons on Ta2Zn3O8 thin film phosphors

    Page(s): 2699 - 2705
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    The cathodoluminescence (CL) brightness from thin film Ta2Zn3O8 has been studied as a function of vacuum and electron dose. The thin films were prepared by sputtered deposition followed by rapid thermal annealing at 1100 °C for 1 min. Under bombardment by 2 keV electrons, the films produce a blue luminescence with a dominant wavelength of 386 nm. These films were exposed to residual vacuum gas dominated by H2 and H2O at pressures ranging from 10-8 to 10-6 Torr with ≪10% loss in CL brightness for an electron dose of 23 C/cm2. However, when hydrocarbons from colloidal graphite “paint” raised the base pressure of the vacuum from 2×10-7 to 9×10-7 Torr, the CL brightness was degraded to 5% of its original value after ≈4 h at 2.7×10-4 A/cm2 (corresponding to a dose of 3.9 C/cm2). Degradation stopped when the electron beam was off or could not strike the surface. Auger analysis showed a 1000-Å-thick layer of carbon from electron beam cracked hydrocarbons. The effect of electron beam cracked carbon was concluded to be absorption of luminescent photons. The hydrocarbon contaminants were removed by long term baking of the vacuum system. © 2000 American Vacuum Society. View full abstract»

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  • Change in surface roughness with the thickness of TiO2 film grown on MgO(001) by Ar-ion beam sputtering

    Page(s): 2706 - 2708
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    The surface roughness, Ra, and the crystallinity are studied for the rutile-type TiO2 films at their thickness, d, above 10 nm deposited on the air-cleaved MgO(001) held at 630 °C at 3.1×10-3 Pa in the partial pressure of O2 by sputtering the Ti target by Ar-ion beam accelerated with 1.2 kV. The amount of Ra estimated by observing the surface morphology with an AFM is the order of nanometers and changes with d according to d1/2. The linear relationship between the intensity ratio of the (110) peak for the TiO2 to the (004) peak for the MgO in x-ray diffraction pattern and d2 is also confirmed which is evidence of little change in the film crystallinity during growth. These mean that the surface morphology of the TiO2 films at d≫10 nm keeping their crystallinity is determined from the statistical fluctuation in the impinging vapor flux. © 2000 American Vacuum Society. View full abstract»

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  • A conductance model (approach) for kinetic studies: The Ti–Ta–Si system

    Page(s): 2709 - 2714
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    Electrical resistance measurements provide a convenient way to study the kinetics of transformations in isothermally annealed thin films. The measured resistance and the amount of a new phase formed during some sort of reaction in a transformation process are often related by a linear function. This simple relationship between the measured resistance and the fraction of the new phase formed is not always valid and the reliability of the results might be questionable. In this communication, a different approach is suggested, which is based on conductance. The validity of the model is tested by experimental data for the Ti–Ta–Si system. The suggested and the linear resistance models are compared, and it seems that it is more appropriate in certain cases to use the conductance approach for kinetic purposes. An effective activation energy can be derived from the results by defining the time needed at each temperature to obtain either a constant resistance, or alternatively, a certain fraction of the new phase. The activation energy derived for the end phase, i. e. (Ti,Ta)Si2 formation from the experimental data in the example (Ti–Ta–Si) considered is ∼2.6 eV. © 2000 American Vacuum Society. View full abstract»

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  • Microwave plasma nitriding of a low-alloy steel

    Page(s): 2715 - 2721
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    A low-alloy steel was nitrided in the downstream zone of an electron cyclotron resonance (ECR) discharge at low pressure (0.15–0.25 Pa). Structure and properties of the nitrided surfaces were primarily controlled by the substrate temperature Ts (300–550 °C), the nitrogen–hydrogen–argon gas mixture composition, and the substrate bias voltage Ub (-1000 to +40 V) at a typical value of the incident microwave power Pi=900 W, the distance of the substrate from output aperture of the ECR source was d=250 mm, and the nitriding time t=2 h. Optical emission spectroscopy was used to study the behavior of significant atomic and molecular species, such as N2, N2+, NH, H, Fe, Ar, and Ar+, in front of the nitrided sample. It has been found that due to a high plasma reactivity, nitriding is effective at substrate temperatures Ts≥500 °C, when the surface hardness is about 1200 HV0.05 and a diffusion layer thickness up to 120 μm has been achieved for t=2 h. The presence of 10%–30% H2 in a nitrogen–hydrogen gas mixture enhances the efficiency of nitriding in comparison with treatment in pure nitrogen under the same conditions. For Ts≥500 °C, the process is effective even for substrates at positive potential (Ub=+30 V) and for a lower amount of N2 (10%–30%- - ) in a nitrogen–hydrogen–argon gas mixture, for which no compound layer is formed on the nitrided surface. However, the negative substrate bias voltage Ub enhances considerably the efficiency of nitriding only at lower substrate temperatures (Ts≈400 °C), when the nitriding is relatively weak. © 2000 American Vacuum Society. View full abstract»

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  • Measurement of beam-gas scattering lifetime in Pohang light source

    Page(s): 2722 - 2727
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    The beam-gas scattering lifetime of the Pohang light source (PLS) storage ring was studied. To eliminate the dominant Touschek effect for measurements of the beam-gas scattering lifetime, two methods were used separately: vacuum pressure increase by helium injection and very low electron beam density. Then two vertical beam scrapers were used to investigate the dependence of the Coulomb lifetime on the acceptance limiting aperture size. It was possible to obtain the separate ranges of Coulomb and bremsstrahlung lifetimes in the pressure range of normal operation. The results indicate that the vacuum is still an important factor for PLS, especially when small gap undulators are installed. © 2000 American Vacuum Society. View full abstract»

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  • Estimation of the TEOS dissociation coefficient by electron impact

    Page(s): 2728 - 2732
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    SiO2-like films are deposited in a low-pressure rf helicon reactor using oxygen-rich O2/TEOS (tetraethoxysilane) mixtures. A model based on the deposition rate variation with the distance to the TEOS injection is used to estimate the TEOS electron-impact dissociation coefficient ke and the effective sticking coefficient of reactive fragments s. In the helicon diffusion chamber where the electron temperature and density are about 4 eV and 1010cm-3, respectively, ke and s are found to be 1.82×10-7cm3 s-1 and 0.035, respectively. Under these low-pressure plasma conditions, the TEOS dissociation by electron impact is dominant over dissociation by oxygen atoms. © 2000 American Vacuum Society. View full abstract»

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  • Studies on plasma-nitrided iron by scanning electron microscopy, glancing angle x-ray diffraction, and x-ray photoelectron spectroscopy

    Page(s): 2733 - 2737
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    The tribological and mechanical properties of several iron alloys are improved by nitriding processes. In this work the plasma process was employed because it offers various advantages as compared to other methods used in surface modifications. For example, it is a nonpollutant method and the nitriding times are reduced. Four samples were prepared by nitriding the iron substrates in a gas mixture of 80% of H2 and 20% of N2 under a pressure of 900 Pa, discharge frequency of 10 kHz and temperature of 500 °C, for 1, 2, 4, and 6 h. The samples were analyzed by optical microscopy, scanning electron microscopy (SEM), microhardness technique, glancing angle x-ray diffraction (GXRD), and x-ray photoelectron spectroscopy (XPS). SEM and GXRD results showed the presence of γ-Fe4N and a small amount of Є-Fe3N phase. XPS was employed in order to obtain the chemical-state and quantitative informations on the plasma-nitrided iron surfaces. The surface N/Fe atomic ratios obtained by XPS were close to the ideal value of 0.25 for Fe4N. The nitrogen concentration close to the surface is lower than that found in the bulk for all samples. This effect is explained by the presence of H2 in the gas mixture, which not only cleans the surface but also removes nitrogen by sputtering. © 2000 American Vacuum Society. View full abstract»

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  • Scanning tunneling microscopy study of the Er/Ge(111) c(2×8) interface

    Page(s): 2738 - 2741
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    Scanning tunneling microscopy (STM) is used to study the Er interaction on the Ge(111) substrate reconstructed c(2×8). In the submonolayer range, a homogeneous two-dimensional (2D) (1×1) reconstructed island distribution is observed for an Er deposit at room temperature with an additional annealing at 500 °C. However, when Er is deposited on substrate held at 500 °C, a significant modification in the surface morphology has been observed: 2D islands are accumulated at the step edges due to the high Ge and Er atom mobility. Moreover, for temperature under 500 °C, STM images have revealed the presence of metastable rod-shaped islands. Above 1 ML Er deposit, the interface displays a thin film reconstructed √3×√3R30° with a layer-by-layer growth mode. © 2000 American Vacuum Society. View full abstract»

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  • Etching of xerogel in high-density fluorocarbon plasmas

    Page(s): 2742 - 2748
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    The etching of various xerogel films has been studied in high-density fluorocarbon plasmas. The xerogel etch rate is in part enhanced by the porosity. In discharges resulting in low surface polymerization, such as CF4 or oxygen-rich fluorocarbon plasmas, an additional enhancement up to 60% is observed. When the polymerization of the discharge is increased, this additional enhancement disappears and the xerogel etch rate becomes more suppressed. The suppression is more pronounced for xerogel films with a higher porosity and a larger pore size. X-ray photoelectron spectroscopy analysis on partially etched samples shows that the suppression in etch rate is accompanied by an increasing amount of fluorocarbon material at the xerogel surface, especially in the pores of the xerogel structure. Finally, a 30% porous xerogel film was patterned using CHF3 as an etching gas. Slight bowing of the sidewalls was observed. © 2000 American Vacuum Society. View full abstract»

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  • High density plasma oxide etching using nitrogen trifluoride and acetylene

    Page(s): 2749 - 2758
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    The use of nitrogen trifluoride (NF3) and acetylene (C2H2) in the presence of helium has been examined for oxide etching in an inductively coupled, high density plasma etch tool. Oxide etch rates have been measured for blanket films and for patterned wafers with features of 0.6, 0.45, and 0.35 μm nominal critical dimension, while process performance has been assessed with cross-sectional scanning electron microscopy. Optical emission spectroscopy has been employed in situ to characterize the species present in the plasma, and quadrupole mass spectrometry has been used to analyze process effluent sampled between the chamber outlet and the turbo pump inlet. Polymer film deposited on the surface of the oxide layer has been studied with time-of-flight secondary ion mass spectrometry. Global warming emissions for a range of process conditions have been quantified using Fourier transform infrared spectroscopy, and are compared to emissions from more typical oxide etch processes on the same tool type. Results indicate that the NF3/C2H2 chemistry is capable of etching oxide anisotropically, while offering a significantly lower global warming impact than current oxide etch chemistries. © 2000 American Vacuum Society. View full abstract»

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  • Reaction layer dynamics in ion-assisted Si/XeF2 etching: Temperature dependence

    Page(s): 2759 - 2769
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    We study the dynamics of the reaction layer during Ar+ ion-assisted Si etching by XeF2 in the temperature range T=150–800 K. Depending on temperature, the etch rate can be enhanced a factor of 8 by ion bombardment. The dynamics are studied with ion-pulse measurements on a time scale of 1–100 s in a molecular beam setup. A reaction layer with a submonolayer fluorine coverage and dangling bonds is found to be formed on the Si(100) surface during ion bombardment. The dangling bond concentration increases with ion flux and is independent of temperature in the range 150–600 K. Chemisorption on these dangling bonds results in a higher reaction probability of XeF2. The temperature dependence of the reaction probability of XeF2 is fully determined by the temperature dependence of the XeF2 precursor state. A simple model gives a very good description of the reaction probability as a function of both temperature and ion flux. The model description of the behavior of the precursor concentration as a function of ion flux and temperature is confirmed by ion pulse measurements on a time scale of 1 s. Further, it is concluded that the mechanisms for enhanced SiF4 formation during ion bombardment are the same over the temperature range studied. © 2000 American Vacuum Society. View full abstract»

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  • Etching chemistry of benzocyclobutene (BCB) low-k dielectric films in F2+O2 and Cl2+O2 high density plasmas

    Page(s): 2770 - 2778
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    The etching chemistry of benzocyclobutene (BCB) low-k dielectric films was studied in a high density plasma etcher using F2+O2 and Cl2+O2 plasmas. The etching rate in F2+O2 plasmas exceeded 1.2 μm/min with selectivity over oxide and nitride of 16 and 32, respectively. The etching rate in Cl2+O2 plasmas exceeded 0.6 μm/min with selectivity over oxide and nitride of 40 and 80, respectively. BCB films do not etch in pure Cl2 or pure O2 plasmas without ion bombardment, but etching rates of 1000 Å/min were observed using F2 plasmas without ion bombardment. The ion flux in F2+O2 plasmas is primarily O2+ and O+, whereas in Cl2+O2 the dominant ion is ClO+. BCB etching yields in F2+O2 plasmas were measured with a plasma beam/quartz crystal microbalance system. The etching yields suggest that the neutral fluxes and surface chemistry control the etching rates under these conditions, not the ion flux. Using x-ray photoelectron spectroscopy, it was determined that oxygen plasmas preferentially remove the carbon content of BCB, leaving behind a silicon oxide surface. Chlorine plasmas preferentially remove the silicon, leaving behind a carbon surface. F2+O2 plasmas etch BCB th- - rough a fluorocarbon film layer, the thickness of which increases with increasing fluorine concentration in the plasma. © 2000 American Vacuum Society. View full abstract»

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  • Codeposition on diamond film surface during reactive ion etching in SF6 and O2 plasmas

    Page(s): 2779 - 2784
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    The surface of polycrystalline diamond films during reactive ion etching in electron cyclotron resonance SF6 and O2 plasmas has been examined by scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. A SF6 plasma required a high voltage in negative substrate biasing in order to achieve an equivalent etching rate to an O2 plasma. This was ascribed to the codeposition effects and the low mean energy of ions upon impact in a SF6 plasma. The elemental composition of the amorphous layer formed at the etched film surface in the two plasmas was almost equivalent and mainly composed of carbon and oxygen, except a low concentration (≤1%) of sulfur and fluorine in the case of a SF6 plasma. The significant codeposition on diamond surface was the most likely the result of plasma–wall interactions induced by the fragments from SF6, and highly responsible for suppressing the ratio of lateral to vertical etching rate leading to anisotropic etching in a SF6 plasma, in contrast with the little or no codeposition leading to isotropic etching in an O2 plasma. The results give the substantial implications for the etching process in practical SF6/O2 plasmas utilized in device fabrication. © 2000 American Vacuum Society. View full abstract»

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  • Ion fluxes and energies in inductively coupled radio-frequency discharges containing C2F6 and c-C4F8

    Page(s): 2785 - 2790
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    We report ion energy distributions (IEDs), relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference (GEC) radio-frequency (rf) reference cell for discharges generated in pure C2F6, c-C4F8, and in mixtures of each gas with Ar. These discharges contain several ions of significant intensity, with the dominant ion seldom that expected from direct ionization of the feed gas. Neither the C2F6 nor the c-C4F8 fraction in the Ar mixtures significantly influences the reactive ion composition. IEDs vary from single peaked to bimodal, the latter indicating rf modulation of the ions’ energy as they traverse the plasma sheath. Elevated gas pressures and higher fractions of either C2F6 or c-C4F8 all result in comparatively broader and more bimodal IEDs. IEDs in pure c-C4F8 discharges, compared to C2F6 discharges, generally exhibit more pronounced broadening and bimodality. View full abstract»

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  • Angular dependence of SiO2 etching in a fluorocarbon plasma

    Page(s): 2791 - 2798
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    SiO2 etch rates in a CF4 plasma were obtained at various surface angles using a Faraday cage with pinholes on the upper plane through which ions are incident on the substrate fixed at various angles inside the cage. The reactive ion etching experiments were performed at 5 mTorr in a wide bias-voltage range from -100 to -800 V. The normalized etch-yield curves showed virtually the same angular dependence regardless of the ion incident energy. The curve shape was similar to that of physical sputtering except that the ratio of the maximum yield to that at 0° was as low as about 1.3. This is the deviation from the cosine dependence characteristic of chemical sputtering, which is the main mechanism of SiO2 etching in a fluorocarbon plasma. This deviation is partly attributed to the fluorocarbon polymer film, which existed as a few monolayers-thick film on the substrate surface at low angles near 0° but as a submonolayer at high angles between 45° and 75°. The effect of the film-coverage difference on the deviation is explained in terms of reactant chemisorption, product desorption, energy deposited by ions causing the collision cascade, and incorporation of projectiles and recoils leading to the mixing effect. The deviation is also attributed to physical sputtering, which became comparable to chemical sputtering as the ion energy increased. Both factors, i.e., the formation of the thin fluorocarbon polymer film and physical sputtering, are supposed to contribute to the curve deviation, although their relative importance changed with the ion incident energy. © 2000 American Vacuum Society. View full abstract»

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  • Tantalum etching with a nonthermal atmospheric-pressure plasma

    Page(s): 2799 - 2805
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    Tantalum was etched in a downstream, atmospheric-pressure plasma. In this process, etching occurred without significant ion bombardment. An etching rate of 6.0±0.5 μm/min was achieved using 14.8 Torr oxygen, 22.4 Torr carbon tetrafluoride, 720±5 Torr helium, 685 W radio frequency power at 13.56 MHz, and a film temperature of 300 °C. The etching rate increased with the applied power, carbon tetrafluoride pressure, oxygen pressure, and residence time of the gas between the electrodes, indicating that the surface reaction depends on the density of reactive fluorine species generated in the plasma. X-ray photoemission spectroscopy revealed that the etched surface was covered with tantalum fluoride and to a lesser extent, tantalum oxide. Based on these observations, a mechanism for tantalum etching is proposed which involves the reaction between fluorine atoms and the adsorbed tantalum fluoride. © 2000 American Vacuum Society. View full abstract»

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  • Control of the radio-frequency wave form at the chuck of an industrial oxide-etch reactor

    Page(s): 2806 - 2814
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    Radio frequency (rf) power is commonly applied to the chuck of a high-density plasma reactor in order to extract ions and to control the energy of the ions used for the fabrication of microelectronic devices. In many cases, the temporal shape of the rf wave form largely determines the shape of the spectrum of those extracted ions, thereby strongly affecting feature evolution. Using auxiliary rf circuits, we successfully made major changes to the rf-potential wave form at the chuck of an Applied Materials 5300 HDP Omega reactor without affecting the normal functioning of the reactor’s control systems. This work established the practical feasibility of techniques for modifying the ion energy distribution functions of industrial reactors. © 2000 American Vacuum Society. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology A is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
G. Lucovsky
North Carolina State University