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

Issue 6 • Date Nov 1998

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Displaying Results 1 - 25 of 64
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Dissociation processes in plasma enhanced chemical vapor deposition of SiO2 films using tetraethoxysilane

    Page(s): 3157 - 3163
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    Dissociations in plasma enhanced chemical vapor deposition for SiO2 deposition using tetraethoxysilane (TEOS) were investigated by means of mass spectrometry. First, we showed basic dissociation patterns of TEOS as a function of electron energy. It was shown that TEOS dissociates by electron impact at electron energies below 8 eV, removing the ethyl group (C2H5). Next, we presented dissociation patterns in TEOS/He plasma. Finally, dissociation in TEOS/O2 plasma was studied. It was shown that high molecular intermediate products containing carbon and hydrogen, such as Si(OC2H5)2H, Si(OC2H5)2OCH3, and Si(OC2H5)3OCH2, are present only in the TEOS/He plasma but not in the TEOS/O2 plasma. It was also shown that eliminated hydrocarbon gases such as C2H2, C2H4, C2H5, and OC2H5 are convert- - ed into H2O and CO2. Fourier-transformed infrared and x-ray photoelectron spectroscopy studies revealed that the degree of impurity concentration in the film decreased with increasing O2 concentration. Characteristics of metal–insulator–semiconductor devices reflected the degree of impurity concentration in the oxide films. It was found that oxygen gas plays an indispensable role for preparing high quality SiO2 films by oxidizing the intermediate dissociation products and eliminating hydrocarbon gases. © 1998 American Vacuum Society. View full abstract»

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  • Characterization of a novel lambda balanced inductive plasma source

    Page(s): 3164 - 3169
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    A preliminary study on the 1–4.5 kW power industrial scale 27.12 MHz rf lambda-resonator oxygen asher is presented. Contact probes of several types, including single Langmuir and flat wall probes, thermocouples, and optical emission spectroscopy, are mainly used to diagnose plasma in the inductive source area, downstream chamber and in the vicinity of wafers. Electron density in a 200 mm wafer asher at 2 kW rf power varies from 2×1011 in the plasma source to 5×107cm-3 in a downstream chamber 5–10 mm from a wafer. The ion density exceeds the electron density 10–60 times. The plasma space potential varies in a range of 14–22 V, while the floating potential of the bulk plasma and wall surface varies from +9 to -17 V. The minimum surface floating potential of -17 V exists at the maximum of the rf voltage standing wave distributed along the full lambda inductor. The wafer surface floating potential is in the range of 3–5 V depending on the reactor configuration and is constant within ±1 V on the 200 mm wafer. Positive ion current density on the wafer and downstream chamber surface is less than 1 μA/cm-2. The typical resist ashing nonuniformity is ≤2%–5% (range, not sigma) for both 200 and 300 mm ashers at about a 6–8 μ/min ashing rate. © 1998 American Vacuum Society. View full abstract»

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  • Synthesis of diamond using a low pressure, radio frequency, inductively coupled plasma

    Page(s): 3170 - 3174
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    Diamond was successfully synthesized using a low pressure, radio frequency (rf), inductively coupled plasma. A source mixture of methanol (CH3OH), hydrogen (H2), and water vapor (H2O) was introduced into a reaction chamber through a quartz tube of 12 mm inner diameter. A seven-turn rf coil was mounted on the quartz tube to produce high-density plasma. The Si substrate was located in a downstream region. Diamond formation was carried out with varying mixture ratio of source gases at total pressures of 70–140 mTorr. Diamond crystals exhibiting a well-defined 1332 cm-1 diamond Raman peak can be formed using CH3OH/H2/H2O mixtures at total pressures below 140 mTorr. © 1998 American Vacuum Society. View full abstract»

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  • Deposition of SiO2 films from novel alkoxysilane/O2 plasmas

    Page(s): 3175 - 3184
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    The deposition of SiO2 films from novel alkoxysilane/O2 rf plasmas has been investigated using tetraethoxysilane and the novel alkoxysilanes, triethoxysilane, tetramethoxysilane, and trimethoxysilane. We have demonstrated that high quality SiO2 films can be deposited from each of these alkoxysilanes under similar conditions. For all precursors, film deposition rates decrease with the addition of O2. Using 20:80 alkoxysilane/O2 plasmas, film deposition rate decreases with increasing substrate temperature and plasma power, while the SiO2 film quality increases, as determined by Fourier transform infrared spectroscopy, ellipsometry, and wet etch rates. Substrate temperature appears to be the most influential deposition parameter, significantly affecting both composition and properties of the deposited SiO2 films. Measured apparent activation energies for SiO2 deposition from alkoxysilane/O2 plasmas are negative for all precursors. This suggests an adsorption/desorption-limited deposition mechanism controls film formation in all systems. Additional data for SiO2 films deposited from the halogenated alkoxysilanes triethoxyfluorosilane and triethoxychlorosilane are also presented. © 1998 American Vacuum Society. View full abstract»

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  • Diamond synthesis in capacitively coupled 13.56 MHz radio frequency plasma using parallel plate electrodes with the addition of direct current power

    Page(s): 3185 - 3189
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    Capacitively coupled radio frequency plasmas offer some advantages over other techniques such as microwave induced plasmas with regard to the large area homogeneous deposition of thin films. Diamond films were synthesized from methane and hydrogen gas mixtures in a capacitively coupled radio frequency plasma using a standard 13.56 MHz source in a popular parallel plate electrode geometry with the addition of dc power. The rf+dc plasma is stable and homogeneous and suitable for prolonged operation. The diamond films deposited by this method were characterized by x-ray diffraction, scanning electron microscopy and Raman spectra measurements. Preliminary experiments with electrodes having a diameter of 60 mm were done to investigate the possibility of scaling up of this technology for large-area diamond deposition. © 1998 American Vacuum Society. View full abstract»

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  • Transparent barrier coatings on polyethylene terephthalate by single- and dual-frequency plasma-enhanced chemical vapor deposition

    Page(s): 3190 - 3198
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    Transparent barrier coatings on polymers are receiving much attention in industry, for pharmaceutical, food and beverage packaging applications. Plasma-enhanced chemical vapor deposition (PECVD) is among several competing techniques which can produce thin layers of inorganic glassy barrier materials. In this article we describe the performance of silicon compounds (SiO2 and Si3N4) on 13 μm polyethylene terephthalate (PET) substrates, the barrier coatings being deposited in a dual-frequency (microwave/radio frequency) pilot-scale PECVD reactor for continuously moving flexible webs up to 30 cm in width. The volatile silicon compound used for SiO2 deposition is HMDSO (C6H18Si2O), while SiH4 serves to deposit Si3N4. Coating thicknesses, d, in the range 8 nm≤d≤200 nm, are measured using a variety of techniques, namely stylus profilometry, continuous wavelength optical interferometry, x-ray fluorescence, variable angle spectroscopic ellipsometry, and transmission electron microscopy, while film compositions are determined by x-ray photoelectron spectroscopy. Oxygen transmission (OTR) and water vapor transmission (WVTR) measurements are carried out with MOCON “Oxtran” and “Permatran-W” instruments, respectively. As also reported by other workers, we typically find OTR values of about 0.5 scc/m2 day and WVTR about 0.3 g/m2 day, for barrier thicknesses exceeding a “critical” value (dc, about 15 nm), but the minimum permeation values depend upon the concentration of defect sites in the coating (mostly related to substrate microroughness). In order to confirm this correlation, we have developed a technique combining reactive ion etching through the PET, followed by optical and transmission electron microscopies, to characterize the types and number densities of coating defects. On the basis of these, we find good agreement between measured and calculated values of OTR. © 1998 American Vacuum Society. View full abstract»

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  • Silicon hydride composition of plasma-deposited hydrogenated amorphous and nanocrystalline silicon films and surfaces

    Page(s): 3199 - 3210
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    In situ attenuated total reflection Fourier transform infrared spectroscopy was used to study the H bonding on the surfaces of a-Si:H and nc-Si:H during plasma enhanced chemical vapor deposition from SiH4/H2/Ar containing discharges. Well-resolved SiHx (1≤x≤3) absorption lines that correspond to the vibrational frequencies commonly associated with surface silicon hydrides were detected. During deposition of a-Si:H films using SiH4 without H2 dilution, the surface coverage was primarily di- and trihydrides, and there are very few dangling bonds on the surface. In contrast, during deposition of nc-Si:H using SiH4 diluted with H2, the amount of di- and trihydrides on the surface is drastically reduced and monohydrides dominate the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film surfaces match well with the resonant frequencies of monohydrides on H terminated Si (111) and Si (100) surfaces. The decrease of higher hydrides on the surface upon H2 dilution is attributed to increased dissociation rate of tri- and dihydrides on the surface through reaction with dangling bonds created by increased rate of H abstraction from the surface. Results presented are consistent with SiH3 being at least one of the precursors of a-Si:H deposition. © 1998 American Vacuum Society. View full abstract»

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  • Effect of hydrogen dilution on the remote plasma enhanced chemical vapor deposition of chlorinated SiO2 films

    Page(s): 3211 - 3217
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    Chlorinated silicon dioxide films have been prepared at low temperatures (200 °C) and high deposition rates (900–1700 Å/min) by remote plasma enhanced chemical vapor deposition using mixtures of SiCl4, O2, Ar, and H2 under various hydrogen flow rate conditions. It was found that films deposited without hydrogen grow with the highest deposition rate, however they exhibit poor properties such as high etch rate, low density, and low refractive index. These oxides are also chemically unstable and easily hydrolyzable upon exposure to ambient moisture. It is assumed that the low chlorine content (detected by Rutherford backscattering) in these samples is due to the hydration of the weak Si–Cl bonds existing in the as-deposited films, which generates desorption of HCl and forms the Si–OH bonds observed in the corresponding infrared spectra. The addition of hydrogen to the process reduces the deposition rate but improves the properties and stability of the films by reducing the amount of chlorine incorporated during growth. At hydrogen flow rates moderately higher than the SiCl4 flow, dense and stable chlorinated oxides with properties close to stoichiometric SiO2 are obtained. The composition results indicate that in order to obtain these types of oxides the chlorine concentration should be limited to a value around 2.6 at. %. © 1998 American Vacuum Society. View full abstract»

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  • Plasma-enhanced chemical vapor deposition of intrinsic microcrystalline silicon from chlorine-containing source gas

    Page(s): 3218 - 3222
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    Microcrystalline silicon (μc-Si:H) of truly intrinsic character can be deposited by plasma-enhanced chemical vapor deposition when dichlorosilane (SiH2Cl2) is added to the SiH4–H2 source gas. A dark conductivity of 5×10-8S/cm, activation energy of 0.62 eV, and photoconductivity of 1×10-5S/cm are obtained. The optical band gap for this material is approximately 1.1 eV. No special gas purification or microdoping is required. SiH2Cl2 added in small amounts has the additional effects of enhancing the crystallinity, and of reducing the oxygen incorporation by over a factor of 2. Sub-band gap absorption spectroscopy indicates a low defect density. Very high frequency deposition yields material with lower defect density and higher photoconductivity than material deposited using dc plasma excitation. Transition from amorphous to microcrystalline growth occurs during the first 100–150 nm of film growth. The oxygen content increases as the crystallinity increases. A first p-i-n solar cell with a 1.8 μm thick μc-Si:H(:Cl) i layer exhibits Voc=0.35 V, Isc=4.14 mA/cm2, and FF=55%, demonstrating device-quality material. © 1998 American Vacuum Society. View full abstract»

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  • Effects of ion pretreatments on the nucleation of silicon on silicon dioxide

    Page(s): 3223 - 3226
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    Low energy ion pretreatment of silicon dioxide (SiO2) surfaces results in a reduced incubation time (tinc) for polycrystalline silicon (poly-Si) deposition by rapid thermal chemical vapor deposition. By pretreating SiO2 surfaces with inert (He+, Ar+) and chemically active species (H+, N+), it was determined that ion pretreatments reduce tinc and increase the poly-Si nuclei density by creating nucleation sites via a physical damage mechanism, rather than a chemical process. © 1998 American Vacuum Society. View full abstract»

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  • Structure of the interfacial region between polycarbonate and plasma-deposited SiN1.3 and SiO2 optical coatings studied by ellipsometry

    Page(s): 3227 - 3234
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    Fabrication of optical films on plastic substrates presents a considerable challenge due to the necessity of controlling adhesion and the optical properties of the interface. In the present work, the surface of polycarbonate (PC) substrates was pretreated in a microwave plasma in N2 and He gases, and amorphous hydrogenated silicon nitride (SiN1.3) and dioxide (SiO2) films were deposited in a dual-mode microwave/radiofrequency plasma. Using ex situ variable angle spectroscopic ellipsometry (VASE), spectrophotometry, and x-ray photoelectron spectroscopy, it was found that the plasma-treated PC contains a crosslinked surface layer which can extend to a depth of more than 50 nm, and which presents a refractive index increase of about 1%–2%. When PC is plasma treated and coated with SiN1.3 or SiO2, the interfacial region (interphase) is structured: it comprises the crosslinked layer, and a less dense transition region between the polymer and the film. The interphase may extend up to 100 nm. Some of the results suggest that the plasma pretreatment stabilizes the surface, leading to a lower thickness of the interphase. The accuracy of ex situ VASE analysis is discussed and the importance of the interface structure on the design and mechanical properties of optical systems on plastic substrates is emphasized. © 1998 American Vacuum Society. View full abstract»

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  • Positive ion species in high-density discharges containing chlorine and boron–trichloride

    Page(s): 3235 - 3239
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    We have used a quadrupole mass spectrometer to measure the positive ion species striking the wafer in a high-density plasma processing discharge containing chlorine and boron–trichloride. Since the relative transmission of our mass spectrometer versus ion mass is known, we are able to report the relative concentrations of the ion species striking the wafer. Our measurements were made in an inductively coupled Gaseous Electronics Conference Reference Cell operating at pressures between 15 and 50 mTorr and at electron densities up to 1011/cm3. The ion spectrum in these discharges is normally dominated by Cl+, Cl2+, BCl2+, and etch products. However, reactor wall or wafer surface conditions can strongly affect the ion species in the discharge. When a stainless steel “wafer” was replaced with a bare Si wafer, the dominant chlorine ion changed from Cl+ to Cl2+. A bare aluminum wafer strongly quenched both Cl+ and Cl2+ signals. © 1998 American Vacuum Society. View full abstract»

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  • Optical self-absorption technique for qualitative measurement of excited-state densities in plasma reactors

    Page(s): 3240 - 3246
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    Measurements of excited-state populations in processing plasmas can be useful because those populations often are indicators of, or participants in, chemical reactions. An optical self-absorption technique has been used to measure the relative densities of species in long-lived excited states in high-density plasma reactors. The technique is advantageous because it is simple and inexpensive compared to many laboratory diagnostic techniques, and thus it has potential for industrial manufacturing applications. The technique is useful when absorption strength and wavelength are in acceptable ranges. This paper describes the technique, compares its performance to a more sophisticated laser-absorption technique, and presents self-absorption data from a laboratory reactor and from a 300 mm production-prototype reactor. © 1998 American Vacuum Society. View full abstract»

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  • Effects of plasma conditions on the shapes of features etched in Cl2 and HBr plasmas. I. Bulk crystalline silicon etching

    Page(s): 3247 - 3258
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    We have studied the effects of source and bias powers, pressure, and feed gas composition on the shapes of SiO2-masked crystalline silicon features etched in a transformer-coupled high density plasma system. Higher etching rates were obtained at higher source and bias powers, and higher pressure. The etching rates of isolated and nested trenches, isolated lines, and holes were nearly the same, indicating a negligible pattern density dependence. We did, however, observe a very weak decrease in etch rates with increasing aspect ratio at 2 mTorr in a pure Cl2 plasma. At 10 mTorr, no aspect ratio dependence was observed, except at the highest source and bias powers. Microtrenching was observed under certain plasma conditions and could be reduced by using higher bias powers. At 10 mTorr in a pure chlorine plasma, we observed a slight taper at the bottoms of the etched features and the formation of narrow microtrenches near feature corners. At 2 mTorr, the microtrenches were broader and overlapped near the center of narrow trenches to form pyramid-shaped trench bottoms. When a HBr plasma was used instead of Cl2, the etching rate decreased by 50% but the etching profiles were more vertical and the trench bottoms were flat. Isolated lines etched in the HBr plasma, however, revealed broad but shallow microtrenches near the edges of the line, suggesting that the flat trench bottoms were a result of broad microtrenches that overlapped. Trenches of 3 μm depth and aspect ratios of 7 have been obtained using either HBr or Cl2, exhibiting similar microfeatures as observed when etching shallower trenches. © 1998 American Vacuum Society. View full abstract»

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  • Surface reaction mechanisms of trifluoroacetylacetone on clean and pre-oxidized Ni(110): An example where etching chemistry does not follow volatility trends

    Page(s): 3259 - 3265
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    Ni contamination is an increasing problem in the fabrication of thin microelectronic films. In previous work, we examined nickel removal using oxygen and 1,1,1,5,5,5-hexafluoro2,4-pentanedione (Hhfac) or 2,4-pentanedione (Hacac) and oxygen. In both cases, Ni was etched cleanly by the precursors under net oxidizing conditions. Decomposition pathways were prevalent, however, under reducing conditions. In the results reported in this article, we used temperature-programmed desorption to examine the use of another β-diketone, 1,1,1-trifluoro-2,4-pentanedione, and oxygen in the same process. Ni was etched on the oxidized surface by the desorption of Ni(CF3COCHCOCH3)2 between 260 and 430 K. Etching ceased as decomposition products formed. The structures of decomposition products on both surfaces indicates the promotion of β-bond scission by Ni, predominantly at C-CF3, C-CH3 and C-CH/C-CH2. In the hexafluoropentanedione and pentanedione studies, β scission was also the decomposition pathway. However, with trifluoropentanedione, the pathways produced many more species than with either the unfluorinated or the fully fluorinated analog. This observation was unexpected. Another unexpected observation was that some maximum desorption rate temperatures do not follow expectations based on volatility: Instead, Ni(CF3COCHCOCH3)2 desorbed at nearly the same temperature as Ni(CH3COCHCOCH3)2 and much lower than Ni(CF3COCHCOCF3)2. Another trend that does - - not follow predictions based on volatility is the desorption of the intact precursor from the monolayer on the pre-oxidized surface: Molecular CH3COCH2COCH3 desorbed at a lower temperature than either the CF3COCH2COCF or CH3COCH2COCH3. At present, it is unclear why the results disagree with the volatility trends. © 1998 American Vacuum Society. View full abstract»

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  • Laser-induced thermal desorption analysis of the surface during Ge etching in a Cl2 inductively coupled plasma

    Page(s): 3266 - 3273
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    Laser desorption laser-induced fluorescence (LD-LIF) detection of GeCl was used to determine in situ the surface coverage of chlorine during the etching of germanium by Cl2 in an inductively coupled plasma (ICP) reactor. The ICP operated in the dim mode for radio frequency (rf) power >~350 W and in the bright mode for higher powers. The etch rate was 3.5 μm/min with 540 W rf power and -40 V substrate bias. The chlorine surface coverage was about 2× that with chlorine flow only and the plasma off, both with dim- and bright-mode operation, and was independent of rf power within each mode for laser repetition rates of 0.2, 5, and 15 Hz. Similarly, the chlorination of the adlayer did not change when the ion energy was increased from 16 to 116 eV by increasing the substrate bias voltage, both with dim- and bright-mode operation. This was confirmed by x-ray photoelectron spectroscopy measurements in a similar high density reactor, where it was found that the surface density of chlorine was ∼2.6×1015Cl/cm2. As the ion energy increases from 16 to 116 eV, the etch yield of ions increases from 1 to 3 atoms/ion. “Wait and probe” measurements show that the GeClx adlayer is quite stable. Since the same adlayer chlorine content was measured by LD-LIF under high ion current/fast etch conditions (bright mode) and low ion current/slow etch conditions (dim mode), both the adlayer chlorine content and the etch rate seem to be controlled by the ion current to the wafer. Previously reported work in Si etching in this ICP [J. Vac. Sci. Technol. A 15, 3024 (1997)] showed a similar independence of adlayer chlorination with rf power, but much slower chlorination and an increasing chlorination of the adlayer with increasing ion energy. © 1998 American Vac- - uum Society. View full abstract»

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  • Comparison of two-dimensional and three-dimensional models for profile simulation of poly-Si etching of finite length trenches

    Page(s): 3274 - 3280
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    The development of two-dimensional (2D) profile simulators for fabrication of microelectronics features has significantly progressed during the past few years and now enables modeling of etch profile evolution for many different plasma processing conditions. Increasingly complex devices which have three-dimensional (3D) (that is, asymmetric) structures are now being designed. These structures require improved dimensionality in profile simulators to capture their most important features. Under many conditions, such as circular via etching, two-dimensional profile simulators can be used to address 3D structures. A legitimate issue is to what degree these 2D approaches can indeed be applied to truly 3D structures. In this article, we present results from a 3D profile simulator for the purpose of comparing profiles for innately 3D features to results obtained from a 2D profile simulation. It has been found that profiles obtained from the 3D simulators exhibit greater sidewall sloping in three-plane corners than predicted by the 2D simulator. The implication to process design is that a greater degree of overetching will be required to clear these corners than predicted by the 2D simulators. Asymmetries as well as the angular spread of the ion flux distribution are examined to determine their role in 3D profile evolution. © 1998 American Vacuum Society. View full abstract»

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  • Selective SiO2-to-Si3N4 etching in inductively coupled fluorocarbon plasmas: Angular dependence of SiO2 and Si3N4 etching rates

    Page(s): 3281 - 3286
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    In the fabrication of microstructures in SiO2, etch selectivity of SiO2 to masking, etch stop, and underlayer materials need to be maintained at corners and inclined surfaces. The angular dependence of the SiO2-to-Si3N4 etch selectivity mechanism in a high density fluorocarbon plasma has been studied using V-groove structures. The SiO2 etch rate on 54.7° inclined surfaces is lower than on flat surfaces, while the SiO2 etch yield (atoms/ion) is a factor of 1.33 higher. The results are consistent with a chemical sputtering mechanism. The Si3N4 etch yield is greater by a factor of 2.8 for 54.7° inclined surfaces than for flat surfaces. This large enhancement is explained by a fluorocarbon surface passivation mechanism that controls Si3N4 etching. The fluorocarbon deposition is decreased at 54.7° whereas the fluorocarbon etching rate is increased at 54.7°. This produces a thinner steady-state fluorocarbon film on the inclined Si3N4 surface, and results in a large enhancement of the Si3N4 etch yield. © 1998 American Vacuum Society. View full abstract»

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  • High-rate deposition of cBN films by ion-beam-assisted vapor deposition

    Page(s): 3287 - 3294
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    Cubic boron nitride (cBN) films were deposited by ion-beam-assisted vapor deposition method. Effects of the ion current density, the boron deposition rate, the composition of the supplied gas into the ion source on the cBN formation range and deposition rate at an ion energy of 0.5 keV were studied. cBN films were obtained at almost constant ratio of boron deposition rate to ion current density, depending on the composition of the supplied gas. The deposition rate of cBN films, whose maximum was 0.5 nm s-1 increased almost linearly with increasing the boron deposition rate. The grain sizes of the obtained films were increased with increasing the cBN deposition rate. The diffraction patterns from cBN (111), (220), (311), and (222) were observed on the transmission electron diffraction. © 1998 American Vacuum Society. View full abstract»

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  • Preparation of gold thin films by epitaxial growth on mica and the effect of flame annealing

    Page(s): 3295 - 3300
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    Highly crystalline thin films of gold were grown on scratch-free mica. Epitaxial growth was accomplished by heating a fleshly cleaved 8 mm×8 mm piece of mica to 380 °C for 12 h at 1.9×10-7Torr, followed by gold deposition at 1 Å/s and 380 °C until 100 nm was deposited. After flame annealing, these gold films are observed to have grains that are on average 6300 Å in width with a peak to peak topography of a few atomic layers. Adhesion of gold to mica was accomplished by controlling the temperature and length of bakeout in addition to the temperature of deposition. Films prepared in this manner exhibited excellent adhesion when immersed in all solvents except water. The nearly universally [111] terminated gold films were characterized by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). STM imaging showed that the gold surfaces exhibit the 22×√3 reconstruction. Flame annealing of films removes contaminants and increases the flat surface area by a factor of 25 relative to the unannealed films as was indicated by both STM and TEM. © 1998 American Vacuum Society. View full abstract»

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  • Formation of nanocrystalline NiCr–N films by reactive dc magnetron sputtering

    Page(s): 3301 - 3304
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    The article reports on structure and hardness of NiCr–N films prepared by dc reactive magnetron sputtering of NiCr (80/20 wt. %) target in a mixture of Ar and N2 on glass and 15 330 steel substrates at room temperature using a round planar magnetron of diameter 75 mm. It was found that while pure NiCr films are polycrystalline, an addition of nitrogen into the film reduces a grain size d and makes it possible to form nanocrystalline NiCr–N films. The hardness HV of the NiCr–N film increases with decreasing grain size d but only down to about 7 nm. For grains smaller than 7 nm the hardness HV decreases. © 1998 American Vacuum Society. View full abstract»

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  • Structural, optical and electrical characteristics of yttrium oxide films deposited by laser ablation

    Page(s): 3305 - 3310
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    Yttrium oxide films deposited by laser ablation on Si(100) substrates have been evaluated for possible application as high dielectric constant insulator layers. The structural, optical and electrical characteristics of these films have been determined by means of x-ray diffraction, atomic force microscopy, Auger electron spectroscopy, ellipsometry, infrared transmittance, and capacitance and current versus voltage (C-V and I-V) as a function of the deposition parameters. It has been found that the crystallinity of these films is strongly dependent on the substrate temperature during the deposition. At low deposition temperatures (350 °C) the films present an amorphous component and a polycrystalline part that is highly oriented in the (100) direction perpendicular to the surface of the film. As the deposition temperature is increased up to 650 °C, the amorphous part of the films is reduced drastically and the dominant orientation of the polycrystalline part becomes the (111) orientation. The refractive index at 630 nm was found to be in the range between 1.91 and 1.95, having its maximum value for films deposited at 450 °C. Similar behavior was observed for the dielectric constant κ, measured from the high frequency capacitance measurements, with a maximum value of 15 obtained for the above mentioned deposition temperature as well. The average roughness of the films decreases with substrate temperature from ∼30 Å to less than 5 Å in the range of temperatures studied. © 1998 American Vacuum Society. View full abstract»

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  • Surface modification of α-Al2O3(0001) by N2+ ion irradiation

    Page(s): 3311 - 3313
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    The surface of sapphire most widely used as a substrate for III-V nitride growth was modified by N2+ ion irradiation with ion-beam energies from 100 to 1000 eV. As the ion-beam energy increased from 100 to 500 eV, the root-mean-square roughness of the surface morphology decreased. However no significant change in surface roughness at energy higher than 500 eV was observed. From the N 1s x-ray photoelectron spectroscopy core-level spectra, no peak related to a nitrogen bond could be found in the samples irradiated with ion energy below 500 eV. An AlON peak began to appear in the samples irradiated with 600–900 eV N2+ ions, and two peaks corresponding to AlON and AlN were distinctively observed in the sample irradiated at 1 keV. © 1998 American Vacuum Society. View full abstract»

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  • Modeling surface kinetics and morphology during 3C, 2H, 4H, and 6H–SiC (111) step-flow growth

    Page(s): 3314 - 3327
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    A Monte Carlo surface kinetics model has been developed to predict growth rate, morphology, and the atomic content of thin films of various SiC polytypes (3C, 2H, 4H, 6H). The model represents the crystal lattice on a structured mesh which retains fixed atom positions and bond partners indicative of a perfect crystal lattice. Specified events occurring at different rates and probabilities change the configuration and the atomic content of the lattice. Events in the model include precursor transport to surface, adatom adsorption, diffusion, and desorption from surface, growth and etching reactions between adatoms and lattice atoms, and evaporation. The initial validation of the model for SiC consists of replicating trends seen when experimentally growing polytypes of SiC (111) on circular mesas and on off-axis vicinal planes. The model can predict the (111) plane faceting seen in β-SiC and the hexagonal structures seen when growing on α-SiC. Also, step flow growth rates which change with flow direction are predicted by the model. Step flow growth on a (111) plane in <112¯0> directions is faster than growth in <11¯00> directions. The model is used to investigate step bunching. Step bunching is shown to be due in part to the growth rate variability of <11¯00> directions and the hexagonal stacking content in the α-SiC polytype. The chemical variation of the step risers in the step bunch could lead to reaction rate limited growth of some steps over others leading to further bunching. The model is used to predict growth rate differences between the Si and C face of SiC. The face growth rate differences are a function of the SiH4 and CH4 surface reaction probabilities. © 1998 American Vacuum Society. View full abstract»

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G. Lucovsky
North Carolina State University