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Nov 1994

Volume 12, Issue 6, pp. 2995-3248


Unique hydride chemistry on silicon–PH3 interaction with Si(100)‐(2×1)

M. L. Colaianni, P. J. Chen, and J. T. Yates

J. Vac. Sci. Technol. A 12, 2995 (1994); http://dx.doi.org/10.1116/1.578927 (4 pages) | Cited 14 times

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The dissociative adsorption of phosphine (PH3) on Si(100)‐(2×1) and its high temperature thermal behavior have been studied by high‐resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy, and by temperature programmed desorption (TPD). Phosphine adsorbs dissociatively onto Si(100)‐(2×1) at 100 K as PH2 and H species, as revealed by vibrational bands at 1050 cm−1 [δsc(PH2)] and 2100 cm−1 [ν(Si–H)]. The PH2(a) undergoes thermal decomposition to adsorbed P and H near 650 K, as determined by HREELS. TPD measurements reveal two PH3 desorption processes at 485 and 635 K. The 635 K desorption is shown to result from PH2+H recombination, while the mechanism for the 485 K desorption cannot be definitely identified. Additionally, two H2 desorption states were observed at 685 and 770 K.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Spontaneous etching of Si(100) by XeF2: Test case for a new beam surface experiment

M. J. M. Vugts, G. J. P. Joosten, A. van Oosterum, H. A. J. Senhorst, and H. C. W. Beijerinck

J. Vac. Sci. Technol. A 12, 2999 (1994); http://dx.doi.org/10.1116/1.578928 (13 pages) | Cited 15 times

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An ultrahigh vacuum multiple‐beam setup has been designed to study surface reactions that are of importance in plasma etch processes. The setup consists mainly of five beams (reactive neutrals, ions, electrons, CFx radicals, and photons) all of which can be focused on the same sample area, and a quadrupole mass spectrometer detecting only molecules desorbing from this area. Data are reported on spontaneous etching for the Si(100)/XeF2 system. Both the incident flux of XeF2 on the sample and the desorbing fluxes of SiFx products and nonused XeF2 were measured quantitatively. The reaction of XeF2, the production of SiFx species and the accumulation of fluorine on the silicon surface were studied as a function of temperature (300–900 K) for XeF2 fluxes of 0.24 and 1.04 monolayers/s. For the reaction probability of XeF2 an exponential increase with temperature from 11% at 300 K up to 50% at 900 K was found. The main product was found to be SiF4 at 300 K gradually becoming replaced by SiF2 at temperatures higher than 600 K. A remarkable result is the accumulation of a rather thick SiFx reaction layer on the etched surface. From thermal desorption spectra the fluorine content was calculated to be 38 monolayers at 300 K decreasing rapidly for higher temperatures. This suggests that fluorine diffusion into the silicon bulk might be of importance in the etching process.
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81.65.-b Surface treatments

In situ observations of Ge(001) and Ge/Si(001) using low‐energy ion scattering

W. T. Taferner, A. Freundlich, A. Bensaoula, A. Ignatiev, Kelley Waters, Ketti Eipers‐Smith, Myriam Guehenneuc, and J. Albert Schultz

J. Vac. Sci. Technol. A 12, 3012 (1994); http://dx.doi.org/10.1116/1.578929 (6 pages) | Cited 3 times

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Low‐energy ion scattering (LEIS) angular distributions were measured on Ge(001)‐1×1‐O and Ge(001)‐2×1+1×2 surfaces. The intensity of 105° backscattered ions and neutrals from 3 keV Ar+ primary ions incident at 45° were recorded as a function of the surface azimuthal angle. The major symmetry directions of the Ge surface were observed. A 14.2 keV Na+ pulsed beam incident at 72.5° with direct recoiled atoms detected by time of flight (TOF) at an angle of 25°, was used to determine the levels of elemental contaminants on the Ge(001) surface at different stages of annealing. TOF‐LEIS of backscattered 3 keV Ne+ was used to monitor, in ‘‘real time,’’ Ge deposition on Si(001) at room temperature.  
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

CrSi2/Si(111): Growth of monotype domains by solid phase epitaxy on a vicinal surface

André Rocher, André Oustry, Marie Josée David, and Michel Caumont

J. Vac. Sci. Technol. A 12, 3018 (1994); http://dx.doi.org/10.1116/1.578930 (5 pages)

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CrSi2 layers grown by solid phase epitaxy on a nominal (111) Si surface exhibit in the same proportion two different orientation relationships, named A and B. When CrSi2 is deposited on a 8° vicinal (111) Si surface, B‐type orientation is favored with respect to the A type. This result can be explained by the fact that both the step width introduced by the miscut and the planar coincidence between {11̄00}CrSi2 and {112}Si are nearly equal to 23 Å. 60° misfit dislocations are observed at the interface with the same spacing. Their Burgers vector component along [111] can be almost exactly compensated by steps along the 〈110〉 directions, which make possible a coherent growth of the B‐type orientation.
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81.15.Np Solid phase epitaxy; growth from solid phases

Diffusion and electrical activity of indium in (Hg,Cd)Te

G. Weck and K. Wandel

J. Vac. Sci. Technol. A 12, 3023 (1994); http://dx.doi.org/10.1116/1.578931 (10 pages) | Cited 4 times

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Indium diffusion into Hg1−xCdxTe (0.2<x<0.3) was carried out in a two zone furnace in the diffusion temperature range from 240–380 °C. The second zone temperature was chosen to maintain a constant concentration of mercury vacancies if no indium is present. Typical indium profiles consist of an erfc‐like segment at higher concentration and an abrupt profile at lower concentration at the diffusion front. The depth of the latter coincides very well with the depth of the n‐type region. An electron concentration up to 5×1018 cm−3 was observed. The electrical activation decreases with higher indium concentration as was elucidated by differential Hall measurements. The chemical indium profiles are interpreted in terms of an interstitial diffusion together with two incorporation mechanisms of different net charge transfer: the Frank–Turnbull and the kick‐out mechanisms. A numerical diffusion model is outlined based on the assumption of a local equilibrium for site occupation and a linear response of the change of the defect concentration to the deviation from equilibrium. Although the profiles depend strongly on the indium surface concentration, an In‐concentration independent diffusion coefficient of interstitial indium DIn,i=(5.4/9.2) ×10−5 cm2 s−1 exp[(−922±20 meV)/kBT] fits the experiments. Large variations of the indium surface concentration are apparently caused by storage in air between wet chemical preparation and enclosure of the specimen in the ampoule.  
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61.72.uj III-V and II-VI semiconductors
66.30.J- Diffusion of impurities

Interaction of hydrogen with chemical vapor deposition diamond surfaces: A thermal desorption study

Lye Hing Chua, Richard B. Jackman, John S. Foord, Paul R. Chalker, Colin Johnston, and Simon Romani

J. Vac. Sci. Technol. A 12, 3033 (1994); http://dx.doi.org/10.1116/1.578932 (7 pages) | Cited 4 times

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The interaction of hydrogen with a chemical vapor deposition (CVD) deposited polycrystalline film on Si(100), cleaned by heating to 1500 K, has been examined. No adsorption is observed unless prior activation with a hot filament is carried out. However atomic H thereby created is found to adsorb with a high sticking probability, subsequently desorbing in the temperature range 1100–1225 K. Etching of the diamond surface, producing gaseous methane and ethane is also seen. The reactivity patterns are rather similar to those observed on C(100) and C(111) surfaces, suggesting these are suitable model substrates for the study of reaction mechanisms associated with CVD diamond growth. However, a major difference is also seen in that a mixture of hydrogen, silane, and disilane, with other minority species, is seen to evolve from the surface of the CVD diamond film at 1275 K when exposed to the reacting gas and is not detected from single‐crystal diamond surfaces. The results indicate that this arises from the selective etching of Si present at grain boundaries in the deposited films.  
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Ga–CH3 bond scission by atomic H: The depletion of surface carbon from a gallium alkyl film on silicon dioxide

S. R. Lucas, W. D. Partlow, W. J. Choyke, and J. T. Yates

J. Vac. Sci. Technol. A 12, 3040 (1994); http://dx.doi.org/10.1116/1.578933 (8 pages) | Cited 3 times

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It is shown that atomic hydrogen is an effective reagent for the extraction of CH3 groups from an adsorbed monolayer produced from trimethylgallium adsorption on SiO2. The reaction is first order in CH3 surface concentration and proceeds with zero activation energy in the 100 K temperature region. The efficiency for the extraction process is about 10−2 per atomic H collision with the surface. These results show that the Ga–CH3 bond may be broken by insertion of hydrogen atoms and that either CH3 or CH4 is eliminated by the process. The results indicate that atomic hydrogen is an effective agent for removal of carbon (present as CH3) during III–V film growth processes. The extraction of CH3 by atomic H occurs on the surface, but in metalorganic chemical vapor deposition processes a similar reaction with metal alkyl species may also occur in the gas phase. Excellent agreement with the theoretical calculations of Hiraoka and Mashita for the interaction of atomic H with AlH2(CH3) molecules is found.  
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Amorphous nitrogenated carbon films: Structural modifications induced by thermal annealing

F. L. Freire, C. A. Achete, G. Mariotto, and R. Canteri

J. Vac. Sci. Technol. A 12, 3048 (1994); http://dx.doi.org/10.1116/1.578934 (6 pages) | Cited 11 times

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Hard amorphous nitrogenated carbon films [a‐C:H(N)] deposited by self‐bias glow discharge were annealed in vacuum in the temperature range of 300–800 °C. The annealing time was 30 min. The structural and compositional modifications induced by thermal annealing were followed by several analytical techniques: secondary ion mass spectrometry (SIMS), Raman spectroscopy, Rutherford backscattering spectrometry, elastic recoil detection (ERDA), and nuclear reaction analysis. The internal stress of the films was also measured. Nuclear analyses indicate that both nitrogen and hydrogen losses occur for annealing temperatures higher than 300 °C. ERDA and SIMS results suggest that hydrogen and nitrogen out‐diffusion occurs by molecular transport through an interconnect network of voids. In the same temperature range, Raman scattering reveals an increase of the number and/or the size of the graphite domains. Internal stress is compressive for the as‐deposited films and changes to tensile for samples annealed at 800 °C, indicating the progressive graphitization of films. A comparison with amorphous carbon films (a‐C:H) is also made.
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68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology

Al deposition on Fe: Formation of an iron aluminide surface alloy

Roland K. Schulze, Thomas N. Taylor, and Mark T. Paffett

J. Vac. Sci. Technol. A 12, 3054 (1994); http://dx.doi.org/10.1116/1.578935 (8 pages) | Cited 1 time

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An investigation has been made of the formation of a surface iron‐aluminum alloy through aluminum adsorption (and subsequent reaction) on Fe(100) single‐crystal and polycrystalline Fe surfaces. On the Fe(100) surface, Auger electron spectroscopy and low‐energy ion scattering spectroscopy (LEISS) studies indicate that at low Al coverages (<1 ML), and a very low Al deposition rate (<0.03 ML/min), a surface alloy grows uniformly at 25 °C to yield an aluminide with an approximate average stoichiometry of FeAl3. At higher Al exposures the surface becomes more aluminum rich. This Al enrichment is due to a kinetic limitation in the formation of the surface alloy. Heating the surface (300 °C during or after Al deposition) partially overcomes this kinetic limitation, and the topmost surface layer changes to a stable stoichiometry with some reduction in the relative aluminum concentration. Low‐energy electron diffraction observations made during the Al deposition (or subsequent heating experiments) gave no indication of long‐range order, suggesting the formation of a disordered surface alloy. LEISS experiments show that at 25 °C, the final stoichiometric configuration of the surface is highly dependent on the average arrival rate of Al at the surface. A higher deposition rate ultimately leads to a more aluminum‐rich surface than for an equivalent dose at a lower rate. This may be rationalized by noting that at higher deposition rates the Al atoms are more likely to encounter other Al atoms at the surface and may proceed to form two‐dimensional microclusters of Al instead of reacting to form a surface or subsurface aluminide alloy. The thermodynamic implications of these observations in the context of the formation of intermetallic alloy phases seen here will be discussed.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.Md Surface thermodynamics, surface energies

Depth profiling analysis of aluminum oxidation during film deposition in a conventional high vacuum system

Jongmin Kim, Jeffrey J. Weimer, Muamer Zukic, and Douglas G. Torr

J. Vac. Sci. Technol. A 12, 3062 (1994); http://dx.doi.org/10.1116/1.578936 (6 pages) | Cited 3 times

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The oxidation of aluminum thin films deposited in a conventional high vacuum chamber has been investigated using x‐ray photoelectron spectroscopy (XPS) and depth profiling. The state of the Al layer was preserved by coating it with a protective MgF2 layer in the deposition chamber. Oxygen concentrations in the film layers were determined as a function of sputter time (depth into the film). The results show that an oxidized layer is formed at the start of Al deposition and that a less extensively oxidized Al layer is deposited if the deposition rate is fast. The top surface of the Al layer oxidizes very quickly. This top oxidized layer may be thicker than has been previously reported by optical methods. Maximum oxygen concentrations measured by XPS at each Al interface are related to pressure to rate ratios determined during the Al layer deposition.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
42.79.Bh Lenses, prisms and mirrors

Preparation of highly oriented thin film of nonlinear optical material by vacuum deposition

Atsuhisa Inoue, Mariko Okamoto, Yoshiro Akagi, and Masayoshi Koba

J. Vac. Sci. Technol. A 12, 3068 (1994); http://dx.doi.org/10.1116/1.578937 (6 pages) | Cited 1 time

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Highly (001)‐oriented thin films of 4‐(N,N‐dimethylamino)‐3‐acetamidonitrobenzene were prepared on a thermally oxidized silicon substrate using vapor deposition. The degree of (001) orientation depends considerably on the substrate temperature (Ts) and deposition rate (R), which determines the kinetic energy (Ek) of the molecules in a flux. Under the optimized experimental parameters of Ts=30 °C and R=600 nm/min, we fabricated the (001)‐oriented thin film showing the full width at half‐maximum of x‐ray rocking curve of 1.6°. Surface flatness was also improved as the deposition rate increased. It became clear that kinetic energy (Ek) of the molecules in an evaporating flux strongly promoted (001) preferred orientation as could be seen by observing the surface morphology and a cross‐sectional view of the samples at their initial stage of growth.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
42.70.Jk Polymers and organics

Growth and characterization of cubic boron nitride thin films

D. J. Kester, K. S. Ailey, D. J. Lichtenwalner, and R. F. Davis

J. Vac. Sci. Technol. A 12, 3074 (1994); http://dx.doi.org/10.1116/1.578938 (8 pages) | Cited 26 times

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Boron nitride (BN) thin films have been grown on [100] oriented single crystal Si, diamond, Cu and Ni substrates by ion beam assisted deposition using electron beam evaporation of boron together with simultaneous bombardment by nitrogen and argon ions. Characterization by Fourier‐transform infrared spectroscopy and high‐resolution transmission electron microscopy showed that the films on Si and diamond consisted of initial noncubic (amorphous and hexagonal BN) layers, followed by the growth of cubic BN (c‐BN). This growth sequence was attributed primarily to increasing compressive intrinsic stress with increased film thickness. Increasing the substrate temperature above 400 °C led to the onset of c‐BN at a greater film thickness while increased ion flux resulted in earlier growth of this phase. These results may be explained by the relaxation of the intrinsic stress in the films at higher temperatures due to increased adatom mobility and to increased intrinsic stress in the films resulting from increased ion bombardment. Lower temperatures led to mixed phase growth. A minimum substrate temperature (200–300 °C) is required for nucleation and growth of single phase c‐BN by this technique. It is believed that the interstitial Ar observed in Rutherford backscattering spectrometry studies is primarily responsible for the stress generation in the films. A combination of h‐BN and c‐BN was deposited on Ni; only h‐BN was obtained on Cu substrates.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology

Composition effects in ‘‘flash’’ evaporated CuIn(SexTe1−x)2 films

M. León, R. Díaz, and F. Rueda

J. Vac. Sci. Technol. A 12, 3082 (1994); http://dx.doi.org/10.1116/1.578939 (5 pages) | Cited 6 times

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Thin films with composition around CuInSeTe and CuInSe1.5Te0.5 have been deposited by ‘‘flash’’ evaporation. The structural, electrical, optical, and surface [x‐ray photoelectron spectroscopy (XPS) measurements] properties have been determined. Chalcogen content is always lower than 50% and crystallinity is higher when Se content increases. The samples always show p‐type conduction even when the defect of chalcogen is 5% with resistivities in the 0.5–8.6 Ω cm range. The energy gap is in the 0.81–1.11 eV range. XPS measurements indicate that, after exposure to air, only the Te species presents two oxidation states preventing oxidation of the remaining elements. These properties are analyzed in terms of indium segregation at grain boundaries, anion vacancies, and cation disorder in the samples.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors

Plasma and processing effects of electrode spacing for tungsten etchback using a bipolar electrostatic wafer clamp

William F. Marx, Yunju Ra, Richard Yang, and Ching‐Hwa Chen

J. Vac. Sci. Technol. A 12, 3087 (1994); http://dx.doi.org/10.1116/1.578940 (4 pages)

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A tungsten etchback process has been developed using a bipolar electrostatic clamp (ESC) in a parallel‐plate, single wafer etcher with a 13.56 MHz power applied to the top electrode. The transfer of a SF6/N2 etchback process from a mechanically clamped to a bipolar electrostatically clamped system was not straightforward. Initially, the ESC system produced more tungsten residue and a lower etch rate than a mechanically clamped system. By optimizing the rf grounding circuit of the ESC, the residue was reduced. A Langmuir probe study demonstrated that the ion current profile varied strongly with electrode spacing for SF6 but not for gases such as Cl2 or Ar. Both the tungsten residue and the anomaly in the ion current profile were eliminated by the proper choice of electrode spacing. Energetic electrons have been proposed as the cause of the unusual ion current profile. Process results have been optimized with the new electrode spacing, allowing the fabrication of submicrometer tungsten plugs on 200 mm wafers. The tungsten plug recess, which is controllable by wafer temperature and process conditions, is typically 0.1 μm.  
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81.05.Bx Metals, semimetals, and alloys
84.32.Dd Connectors, relays, and switches

Damage and contamination in low‐temperature electron cyclotron resonance plasma etching

Ki‐Woong Whang, Seok Hyun Lee, Hyun‐Ho Doh, and Jae Seong Kim

J. Vac. Sci. Technol. A 12, 3091 (1994); http://dx.doi.org/10.1116/1.578941 (4 pages)

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An electron cyclotron resonance (ECR) plasma etching system has been built to study the damage and contamination inherent to the high density ECR etching. The temperature of the substrate can be lowered to −150 °C by the backside cooling of the substrate with the liquid‐nitrogen cooled helium. The substrate temperature during etching was monitored by a sheathed thermocouple and IR laser interference thermometry. Gate polysilicon etching by SF6 plasma had been carried out and the effect of the substrate temperature on the anisotropy, selectivity, and etch rate was examined with special emphasis on the damage and contamination incurred by the plasma etching. Secondary ion mass spectroscopy (SIMS) analysis shows that the depth of the contaminated layer decreases when the substrate temperature is lowered to −120 °C. Also, the measurement of the gate oxide breakdown voltage shows much less oxide damage when the substrate temperature is lowered during ECR etching.  
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81.65.-b Surface treatments
52.80.Pi High-frequency and RF discharges
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Investigation of selective SiO2‐to‐Si etching in an inductively coupled high‐density plasma using fluorocarbon gases

F. H. Bell, O. Joubert, G. S. Oehrlein, Y. Zhang, and D. Vender

J. Vac. Sci. Technol. A 12, 3095 (1994); http://dx.doi.org/10.1116/1.578942 (7 pages) | Cited 28 times

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A recent, important development in low‐pressure plasma processing is the radio frequency inductively (RFI) coupled high density discharge. Its ability to create high densities of excited and charged species at low pressures (<10−3 Torr) makes it an attractive etching tool. In this work we have examined selective etching of SiO2 over Si using a home‐built RFI source. CHF3, C2F4, C3F6 and their mixtures with hydrogen were examined. Without biasing of the substrate strong fluorocarbon deposition occurs over the investigated pressure range from 5 to 20 mTorr. As the pressure increases the ion current density decreases, whereas the fluorocarbon deposition rate increases. Both parameters increase roughly linearly with inductive rf power from 500 up to 1250 W. Etching was achieved by rf biasing. When the pressure is reduced from 20 to 6 mTorr, the oxide and silicon etch rates decrease less than 20% for all gases. The highest oxide etch rate of 830 nm/min at 350 W rf bias power is achieved for C3F6. Adding H2 decreases the etch rates for oxide and silicon for all gases. The drop of the silicon etch rate is considerably higher than for the oxide etch rate resulting in a better selectivity. The best selectivity of 45 is achieved for C2F4 when 30% H2 is added into the discharge. The results obtained with the RFI source are compared to results with a microwave electron cyclotron resonance discharge.
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81.65.-b Surface treatments
52.80.Pi High-frequency and RF discharges

Measurements of radical densities in radio‐frequency fluorocarbon plasmas using infrared absorption spectroscopy

M. Haverlag, E. Stoffels, W. W. Stoffels, G. M. W. Kroesen, and F. J. de Hoog

J. Vac. Sci. Technol. A 12, 3102 (1994); http://dx.doi.org/10.1116/1.578943 (7 pages) | Cited 41 times

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Densities of CF2 radicals, rotational temperatures, and the degree of dissociation in radio‐frequency fluorocarbon plasmas have been measured using Fourier transform infrared absorption spectroscopy and tunable diode laser infrared absorption spectroscopy. The CF2 densities obtained in CF4, CHF3, C2F6, and CF2Cl2 plasmas indicate that the partial pressure of CF2 is around 1%–5% of the total pressure. From the spatial dependence of the CF2 density it was established that at high pressure, CF2 is produced either on the rf electrode or close to the rf electrode. Furthermore, a comparison between measured absorption spectra and a simulation of the rotational distributions has revealed that the rotational temperatures of CF4, CF2, and HF are all close to room temperature. FTIR spectra indicate that in plasmas of gases with a low F/C ratio (due to the presence of H or Cl) the source gas is converted for a significant part into other species.
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52.80.Hc Glow; corona
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Characterization of H− extraction for a multipole ion source located in the tail of the magnetic field distribution: Type III

Y. Oka, A. Ando, O. Kaneko, Y. Takeiri, K. Tsumori, R. Akiyama, and T. Kawamoto

J. Vac. Sci. Technol. A 12, 3109 (1994); http://dx.doi.org/10.1116/1.578944 (6 pages) | Cited 2 times

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A magnetic multipole plasma source and the accelerator for H− ion source is installed in the distribution of the externally imposed magnetic field which is quasiuniform over the plasma electrode. As the magnetic field of the permanent magnets in this geometry works not only as a so‐called magnetic filter for electron cooling, but also as a deflection field to the accompanied beam electrons, there is a possibility for making the fabrication of the H− source simpler/easier due to no use of small magnets in the accelerator. The characteristics of the ion source such as H− extraction, optimization in the magnetic field, the plasma parameters, etc. are investigated. The integrated magnetic flux of 230–320 G cm should be determined by the condition which optimizes the volume production in the source plasma. Achievable current density of H− is 6 mA/cm2 with 15 keV at the target. Large amounts of the electrons, however, are accelerated altogether to a full energy. They can be stopped with a retarding potential. It is rather unusual that the positive‐ion saturation current profile with the probe becomes more like inhomogeneous across the magnetic field. The results (of H− and G cm) are compared with ones for the different three types of the magnet arrangement.
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52.25.Tx Emission, absorption, and scattering of particles
52.75.Di Ion and plasma propulsion

Spatial distributions of electron density and temperature in audio frequency and radio frequency magnetron glow discharges

S. P. Fusselman, H. K. Yasuda, J. B. Javedani, J. Chiang, and M. A. Prelas

J. Vac. Sci. Technol. A 12, 3115 (1994); http://dx.doi.org/10.1116/1.578945 (5 pages) | Cited 2 times

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The spatial distributions of electron density and temperature in parallel plate audio frequency (AF) (40 kHz) and radio frequency (RF) (13.56 MHz) magnetron discharges were obtained using double Langmuir probes. At 30 W and 580 mTorr argon, electron density ranged from 5×108/cm3 to 1.5×109/cm3 and electron temperature ranged from 3.4 to 4.6 eV in the AF discharge. For 30 W net power and 580 mTorr argon in the RF discharge, electron density ranged from 2×109/cm3 to 8×109/cm3 and electron temperature ranged from 2.5 to 3.6 eV. Electron temperature in the AF discharge increases as the discharge axis is approached, and is independent of axial position. In the RF discharge electron temperature increases near the electrode surface. Electron density distributions in both discharges show the influence of magnetic fields, with the maximum electron density occurring at the position where the radial component of the magnetic field (parallel to the electrode surface) is at a maximum. In the AF discharge, this influence is no longer apparent at axial distances from the electrode surface beyond 2.5 cm. In the RF discharge, radial variations in electron density characteristic of magnetic confinement are observed throughout the plasma, even at the center plane between electrodes.
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52.80.Pi High-frequency and RF discharges
52.70.Ds Electric and magnetic measurements

Fourier‐transform infrared absorption spectrometry measurements of a CF4 discharge in an electron cyclotron resonance reactor

M. J. Goeckner, M. A. Henderson, J. A. Meyer, and R. A. Breun

J. Vac. Sci. Technol. A 12, 3120 (1994); http://dx.doi.org/10.1116/1.578946 (6 pages) | Cited 12 times

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Knowledge of the neutral gas composition in a discharge is important for understanding the chemical processes involved in both etching and deposition environments. We have performed Fourier‐transform infrared absorption spectrometry measurements of a CF4 plasma in an electron cyclotron etching tool. Spectral bands from both CF4 and CF3 were observed. The densities of these species were calculated from the strength of the measured absorption. It was found for typical discharge powers that the CF4 density was approximately 20% of the total density and depended only on the plasma density. This data is used to show that recycling of the daughter species (C, CFx, Fx, etc.) on the chamber walls is the major source of the CF4 observed. Thus one finds that wall conditions play a very important role in determining the plasma chemistry in this high density, ≳1011 cm−3, and low neutral pressure, <10 mTorr, discharge. Additionally, it was found that the CF3 density was approximately 20% of the total density and depended on the product of the plasma density and the CF4 density. This implies that the CF3 is produced primarily through an e−+CF4→e−+CF3+F type of reaction. Finally, it was found that the upper limit of CF2 density was 1.6×1013 cm−3 over the entire parameter range explored.  
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.-b Surface treatments

Diagnostics and control of radio‐frequency glow discharge

N. Mutsukura, Y. Fukasawa, Y. Machi, and T. Kubota

J. Vac. Sci. Technol. A 12, 3126 (1994); http://dx.doi.org/10.1116/1.579225 (5 pages) | Cited 5 times

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The diagnostics of 13.56 MHz planar radio‐frequency (rf) plasma were carried out using spatially resolved optical emission spectroscopy between the parallel electrodes. Plasma sheath thickness d evaluated from the optical emission profiles depends on gas pressure P, and a relationship of Pnd=const. was obtained for CH4, CF4, and O2 plasmas with n≥1/3, and for He and Ar plasmas with n≥1/2. The etching rate and the etching profile of silicon in CF4 plasma were also examined as a function of gas pressure. A novel technique for controlling rf plasmas using the optical sheath thickness and maximum optical emission intensity is presented. This technique was applied to dry etching of silicon in CF4 plasma. When this novel control technique was used, the deviation in the etched depth for a constant etching time became smaller than that obtained using conventional power control methods.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges
81.65.-b Surface treatments

Plasma diagnostics of a direct current arcjet diamond reactor. I. Electrostatic probe analysis

S. W. Reeve and W. A. Weimer

J. Vac. Sci. Technol. A 12, 3131 (1994); http://dx.doi.org/10.1116/1.579226 (6 pages) | Cited 3 times

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Plasma parameters were determined for a direct current arcjet diamond chemical vapor deposition reactor. Electron temperatures and densities were measured using a floating double probe technique, yielding values ranging from 2.3 eV and 7×1011 cm−3 near the plasma gun nozzle to 0.4 eV and 1×109 cm−3 in the downstream and peripheral regions of the plasma. These results show that the plasma is weakly ionized, indicating that reactions involving electrons play a minor role in the macroscopic gas–phase chemistry though high energy products from these reactions may significantly affect film quality.
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52.70.Ds Electric and magnetic measurements
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Observations of particle layers levitated in a radio‐frequency sputtering plasma

G. Praburam and J. Goree

J. Vac. Sci. Technol. A 12, 3137 (1994); http://dx.doi.org/10.1116/1.579227 (9 pages) | Cited 9 times

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Submicron carbon particles are grown in an argon radio‐frequency (rf) sputtering plasma with graphite electrodes. In situ laser light scattering revealed particles levitated in the plasma in stratified layers, which were often thinner than 0.5 mm. Under some conditions, the number of layers was very large. These layers are grouped into clouds. In a pure argon plasma, there is one cloud near the sheath edge above the lower electrode, while adding SF6 results in additional particle clouds near the upper electrode and in the glow region. The different layers appear to separate particles according to size, with the heaviest in the lowest layer. During several hours of plasma operation, the layers collapsed and grew again into more stratified layers. The influence of parameters, such as gas pressure, rf power, electrode separation, and gas mixture was investigated. Scanning electron microscopy revealed that the particles were multisized spheres with a cauliflowerlike surface. Some of the particles were found to be coagulated, due to collisions within the plasma.
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52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects
81.15.Cd Deposition by sputtering

Corrosion behavior of sputtered amorphous magnetic thin films, with and without protective overlayers

John L. Wallace

J. Vac. Sci. Technol. A 12, 3146 (1994); http://dx.doi.org/10.1116/1.579228 (3 pages)

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Thin films of Fe78B13Si9, (similar in chemical composition to Metglas(R) 2605S2) and Fe81B13.5Si3.5C2 (similar to Metglas(R) 2605‐SC) with a thickness of approximately 1 μm were deposited by dc magnetron sputtering onto substrates of Si, SiO2, and GaAs. Some of the films were overcoated with approximately 500 Å of Si3N4; others were overcoated with 300 Å of Cr; and others were left uncoated. The samples were exposed to various environments ranging from an air‐conditioned laboratory to an outdoor, tropical marine ambient. The morphology, low‐frequency magnetic properties, and chemical composition of the films were measured before and after exposure.
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81.05.Bx Metals, semimetals, and alloys
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

Estimation of indium‐to‐germanium and gallium‐to‐germanium sputtering yield ratios using cosputtering deposition

D. Comedi, F. Fajardo, I. Chambouleyron, and M. Tabacniks

J. Vac. Sci. Technol. A 12, 3149 (1994); http://dx.doi.org/10.1116/1.579229 (3 pages) | Cited 3 times

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The relative concentration of In and Ga atoms incorporated to hydrogenated amorphous germanium (a‐Ge:H) films by the cosputtering of solid In and Ga sources together with a crystalline Ge target in a H‐containing Ar plasma has been measured by means of Rutherford backscattering spectrometry and particle‐induced x‐ray emission. Both the experimental In‐to‐Ge and Ga‐to‐Ge relative concentrations were found to linearly scale with the respective In/Ge and Ga/Ge sputtered area ratios. From the slopes of these linear dependencies, In‐to‐Ge and Ga‐to‐Ge sputtering yield ratios were estimated. The results were found to be consistent with published theoretical sputtering yield values, but to disagree with experimental sputtering yield results previously reported for the case of the In‐to‐Ge yield ratio. For the case of Ga, a sputtering yield value of 1.6 atoms/ion was deduced from the present results, which gives first experimental account of Ga sputtering by Ar ions.
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81.15.Cd Deposition by sputtering
61.72.uf Ge and Si

Erbium‐doped indium oxide films prepared by radio frequency sputtering

Hong Koo Kim, Cheng Chung Li, and Pedro Jose Barrios

J. Vac. Sci. Technol. A 12, 3152 (1994); http://dx.doi.org/10.1116/1.579230 (5 pages) | Cited 2 times

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Er doping of conducting oxide films has been investigated. Erbium‐doped indium oxide films were prepared by rf magnetron sputtering. The deposited films were characterized in terms of electrical, optical, and structural properties. The Er‐doped indium oxide films are highly (222)‐oriented normal to the substrate surface and show a resistivity in the range of 10−3–103 Ω cm. The Er‐doped conducting (or semiconducting) oxide films are optically active, i.e., show a clear room‐temperature photoluminescence at 1.54 μm, corresponding to intratransitions in Er3+ ions. Compared with the undoped indium oxide films, the erbium doping is found to have the effect of increasing the resistivity (up to two orders of magnitude) of the films, mainly via a reduction of carrier concentration. Post‐deposition annealing in air ambient significantly enhances both the Er3+ luminescence and Hall mobility (up to 60 cm2/V s), and reduces the carrier concentration. The enhancement of Hall mobility is attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by the x‐ray diffraction measurement results. Post‐deposition annealing in reducing ambient (N2/H2) decreases the resistivity dramatically, mainly via an increase of carrier concentration (up to 1020 cm−3), and also enhances the Er3+ luminescence.
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors

Intrinsic resputtering during film deposition investigated by Monte Carlo simulation

Wolfgang Bauer, Gerhard Betz, Herwig Bangert, Anton Bergauer, and Christoph Eisenmenger‐Sittner

J. Vac. Sci. Technol. A 12, 3157 (1994); http://dx.doi.org/10.1116/1.579231 (8 pages) | Cited 8 times

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In sputter deposition intrinsic resputtering is caused by energetic neutral particles which result from the primary sputter events at the target. These energetic particles are target material atoms, known to have energies up to tens of electron volts and sputter gas neutrals backscattered from the target with energies of up to hundreds of electron volts. The yield for each kind of sputter event depends on the mass of the impinging particle and the mass and surface binding energy of the sputtered atom. Therefore, the composition of a binary alloy film with strongly different surface binding energies and masses of the atoms involved in the deposition process varies due to their individual amount of resputter events. To explore the intrinsic resputtering we chose the Cu–Pb system. The gas phase transport of energetic particles from a Cu 2.05 at. % Pb target to a cylindrical substrate and the resputtering effects from the chamber walls as well as the substrate were calculated using the Monte Carlo technique. We observe a Pb concentration of the growing film from zero up to a value six times higher than the target concentration depending on the working gas pressure and the vacuum chamber geometry. Good qualitative agreement between simulations and experiments was observed for several geometries and pressures.
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81.15.Cd Deposition by sputtering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Comparative study of Ni ultrathin film grown on Pt(110)‐(1×1) and ‐(1×2) at 130 K

J. S. Tsay, Tsu‐yi Fu, P. S. Tsai, and C. S. Shern

J. Vac. Sci. Technol. A 12, 3165 (1994); http://dx.doi.org/10.1116/1.579232 (4 pages)

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The growth mode of a nickel thin film on Pt(110)‐(1×1) and Pt(110)‐(1×2) surfaces was studied by low‐energy electron diffraction (LEED) and Auger electron spectroscopy at a temperature of 130 K. From the results of Auger uptake curves and the intensity profiles of LEED spots, we conclude that the growth of Ni on the Pt(110)‐(1×1) surface follows the Volmer–Weber mode, while the Pt(110)‐(1×2) surface follows the Stranski–Krastanov mode. The mechanism of the different growth behaviors is discussed.
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68.55.-a Thin film structure and morphology

Directed sputter deposition of AlCu: Film microstructure and microchemistry

Y.‐W. Kim, J. Moser, I. Petrov, J. E. Greene, and S. M. Rossnagel

J. Vac. Sci. Technol. A 12, 3169 (1994); http://dx.doi.org/10.1116/1.579233 (7 pages) | Cited 6 times

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The microstructure and microchemistry of AlCu films deposited onto unheated oxidized Si(001) substrates by two recently developed directional sputtering techniques, collimated magnetron sputter deposition (CMSD) and ionized magnetron sputter deposition (IMSD), have been investigated using Rutherford backscattering spectroscopy, x‐ray diffraction (XRD), plan‐view transmission electron microscopy (TEM), cross‐sectional TEM (XTEM), and scanning TEM (STEM). Both sets of films had essentially the same average compositions as the alloy targets while exhibiting dense columnar microstructures with (111) preferred orientation, relatively abrupt film/ substrate interfaces, and no indication of surface faceting. Microstructure evolution pathways, however, were quite different. IMSD layers exhibited competitive column growth resulting in a degree of (111) orientation which was more than an order of magnitude larger than that found in corresponding CMSD films and, for thicker layers (≳1 μm), larger average column sizes. The IMSD films also had a much smaller spread in the azimuthal distribution of (111)‐oriented columns. XRD line broadening analyses and TEM/XTEM examinations revealed that IMSD layers contained inhomogeneous strain due to residual ion‐irradiation‐induced defects and, in the upper near‐surface region, Al2Cu precipitates while CMSD layers appeared defect‐free in TEM/XTEM images. The IMSD films were slightly tensile (+0.13±0.01 GPa) and the CMSD films were slightly compressive (−0.18±0.06 GPa).
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81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Enhancement of the deposition rate of TiO2 film in radio frequency reactive sputtering

Hidetoshi Sekiguchi, Atsushi Kanzawa, Takahiro Imai, and Takuya Honda

J. Vac. Sci. Technol. A 12, 3176 (1994); http://dx.doi.org/10.1116/1.579234 (4 pages) | Cited 5 times

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Titanium oxide thin films were prepared using rf reactive sputtering in which a titanium target was sputtered in a mixture of Ar and reactive O2 gas. The flow modulation of reactive gas was proposed to enhance the deposition rate of the film which is generally low in continuous flow reactive sputtering. The experimental results indicated that the deposition rate could be enhanced maintaining the film stoichiometric ratio of TiO2. The enhancement occurred because the modulated flow appeared to reduce the formation of compounds on the target surface which inhibit sputtering under continuous flow conditions. The effects of the flow modulation were understood by adapting a reactive sputtering theoretical model.
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81.15.Cd Deposition by sputtering
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Characteristics of polyimide films deposited by ionized cluster beam

K. W. Kim, C. E. Hong, S. C. Choi, S. J. Cho, C. N. Whang, T. E. Shim, and D. H. Lee

J. Vac. Sci. Technol. A 12, 3180 (1994); http://dx.doi.org/10.1116/1.579235 (6 pages) | Cited 3 times

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Ionized cluster beam deposition (ICBD) technique has been employed to fabricate high‐purity crystalline polyimide (PI) film. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were co‐deposited using dual ICB sources to form a polyamic acid film, which was subsequently thermally cured to form a PI film. Fourier transform infrared spectroscopy (FTIR), x‐ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) studies show that the bulk and surface chemical properties and the crystalline structure are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage. At optimum ICBD conditions, the PI films have a maximum imidization, negligible impurities (∼1% isoimide), and a good crystalline structure probably due to the high surface migration energy, and surface cleaning effect. The weight average molecular weight as determined by quasielastic light scattering was found to be ∼45 000. These characteristics are superior to those of films deposited by other techniques such as solvent cast, vapor deposition, or sputtering techniques.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.-a Thin film structure and morphology

Outgassing characteristics and surface analysis of pure aluminum plates under electron beam irradiation

Tsutomu Ohi and Osamu Konno

J. Vac. Sci. Technol. A 12, 3186 (1994); http://dx.doi.org/10.1116/1.579236 (6 pages) | Cited 1 time

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In order to develop aluminum with suitable surface properties for use in beam lines and scattering chambers, where ultrahigh vacuum is required; tests were carried out on aluminum samples with two different surface preparations. For one sample (specimen N) the surface was milled with a diamond cutter while in an atmosphere of dry nitrogen; for the other (specimen EP), the surface was electropolished. The surface properties and the outgassing of each sample were studied, after the samples had been irradiated with a flux of 60 MeV electrons. The outgassing from specimen N was found to be the lower. The surface composition was studied using x‐ray photoelectron spectroscopy, and indicated that the surface hydration of specimen N was lower than for specimen EP; this was true both before and after irradiation. It is shown that, before irradiation, both specimens had surface layers of a mixture of Al2O3(H2O) and Al2O33(H2O); after irradiation the surface of specimen N contained only Al2O3(H2O) while the surface of specimen EP contained a mixture of Al2O3(H2O) and Al2O33(H2O). Not only does the proportion of Al2O33(H2O) on the surface change after irradiation, but so does the thickness of the hydroxide layer. The dissociation of water from the hydroxide layer by the electron beam irradiation would appear to be a significant source of gas desorption. Thus the indications are that surface preparation as with specimen N (machining in dry nitrogen) is preferable if the aluminum is to be used in a high‐vacuum situation.
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81.05.Bx Metals, semimetals, and alloys
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
07.30.-t Vacuum apparatus
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Computer simulation of the ion beam deposition of binary thin films: Carbon nitride and boron carbide

S. S. Todorov, D. Marton, K. J. Boyd, A. H. Al‐Bayati, and J. W. Rabalais

J. Vac. Sci. Technol. A 12, 3192 (1994); http://dx.doi.org/10.1116/1.579237 (8 pages) | Cited 25 times

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A dynamic trim‐based computer simulation program that includes treatment of post‐cascade atomic motion has been used to model the ion beam deposition of carbon nitride and boron carbide thin films at energies below 100 eV. Simulations of chemically enhanced phenomena are based on describing the motion of the atoms as a sequence of ballistic steps followed by a chemically guided step. In the case of B–C films, a satisfactory description of the experimental results is achieved by including only ballistic effects in the simulation. For C–N, agreement between experiment and simulation requires the inclusion of a mechanism of preferential nitrogen re‐emission into the program. This mechanism is modeled by the formation of nitrogen‐containing dimers which are considered volatile and are readily released through the surface. The probability of dimer formation depends on the local N concentration. The simulation reproduces well both as‐deposited composition measurements and Auger sputter depth profiling. The model represents a possible implementation of chemical sputtering.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating

Existence of structural inhomogeneity in ion‐beam‐modified polyimide films

X. L. Xu, D. Xu, H. L. Xu, R. Wang, S. C. Zou, G. D. Du, and G. Q. Xia

J. Vac. Sci. Technol. A 12, 3200 (1994); http://dx.doi.org/10.1116/1.579238 (5 pages) | Cited 2 times

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Pyromellitic dianhydride and oxydianiline polyimide films turn electrically conductive upon irradiation with energetic ions. Raman spectroscopy shows an initial dissociation of the molecular structure at low irradiation doses ranging from 1×1014 to 1×1015 B+/cm2, followed by the appearance, at a high dose of 1×1016 B+/cm2, of structures similar to those observed in amorphous graphite. Comparing the reduced Raman spectra of materials irradiated up to a dose as high as 1×1016 B+/cm2 with the one‐phonon density of states of amorphous graphite, one finds that this structural similarity to graphite only exists within a short range. Meanwhile, an ion‐beam‐induced aggregation of aromatic rings in irradiated polyimide films is indicated by ultraviolet‐visible spectroscopy. In view of the structural information from resonant Raman spectroscopy, the existence of structural inhomogeneity is proposed for the high‐dose irradiated polyimide. From perspectives of the model of heterogeneous media, the structural similarity to graphite within a short range is attributed to the existence of the second phase composed of broken functionalities of irradiated polyimide and the sp3‐bonded carbon atoms.
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73.61.Ph Polymers; organic compounds
61.80.Jh Ion radiation effects
68.55.-a Thin film structure and morphology

Influence of the composition of the altered layer on the ripple formation

K. Elst and W. Vandervorst

J. Vac. Sci. Technol. A 12, 3205 (1994); http://dx.doi.org/10.1116/1.579239 (12 pages) | Cited 15 times

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The ripple formation on Si under oxygen bombardment is studied in detail. The influences of temperature, oxygen flooding, primary ion, and the flux of the primary beam are explored and the results are compared with the existing models. As none of the models is capable of explaining all features consistently, a new mechanism is proposed that uses the heterogeneity of the altered layer. The model takes the history of the primary ion incorporation into account and it is implemented into a simulation program. Comparisons between experimental results and simulations using the new model are presented and good overall agreement is found.
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61.80.Jh Ion radiation effects
68.35.B- Structure of clean surfaces (and surface reconstruction)

Experimental and analytical studies on mechanical behavior of knife‐edge‐type metal‐seal flange for fusion vacuum sealing

K. Kitamura, K. Itoh, T. Uchida, M. Kondoh, K. Obara, K. Nakamura, and Y. Murakami

J. Vac. Sci. Technol. A 12, 3217 (1994); http://dx.doi.org/10.1116/1.579240 (7 pages)

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Mechanical behavior of a knife‐edge‐type metal‐seal flange system was examined on the variations of the displacement between the flanges and reaction forces of the tightening bolts during load steps such as tightening the bolts, setting up a transverse weight load on the flange surface and 300 °C baking and cool down. These were compared with a thermo‐elasto‐plastic finite element method structural analysis. Good agreement was obtained for both the flange deformation and reaction forces of the bolts and copper gasket between experimental and analytical results. Effects of the transverse load by a dummy weight mounted at the flange surface on the changes of reaction force of the bolts and on gasket deformation were considered to be negligibly small in the view of vacuum seal characteristics. The application of Inconel Belleville spring washers between bolt heads and flange surface was confirmed to be quite effective for the suppression of the bolt force looseness and gasket relaxation due to cyclic heating and cooling of the knife‐edge‐type metal‐seal flange system.  
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28.52.Lf Components and instrumentation
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Test results for a sputter‐ion pump with a new cell structure

Yusuke Suetsugu

J. Vac. Sci. Technol. A 12, 3224 (1994); http://dx.doi.org/10.1116/1.579241 (4 pages)

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A test model of a sputter‐ion pump using a new cell structure was fabricated, where the magnets reside within the Penning cell assembly. The magnetic field intensity in the cell, pressure (P) dependence of discharge current, and pumping speed are measured. An axial magnetic field larger than 700 G is created inside the cells using commercial magnets with a remanent magnetism of 12 kG. The discharge current (I) is proportional to P1.0–P1.6 in the measured pressure range from 7.5×10 −9 to 1×10−6 Torr. Pumping speed for nitrogen is proportional to P0.6 on the average in the pressure range from 2×10−8 to 1×10−6 Torr and can be written as 0.05 I/P for P≥1×10−7 Torr. The test model is almost less than a half, in both volume and weight, compared to conventional ion pumps with almost the same nominal pumping speeds. It was confirmed experimentally that the new cell structure has the possibility of becoming a compact and light ion pump. The problem remains to optimize the cell sizes to moderate the pressure dependence of the discharge current, i.e., the pumping speed.
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07.30.Cy Vacuum pumps

Capillary arrays with variable channel density: An improved gas injection system

D. A. Scheinowitz, K. Werner, and S. Radelaar

J. Vac. Sci. Technol. A 12, 3228 (1994); http://dx.doi.org/10.1116/1.579242 (5 pages) | Cited 1 time

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A new design concept has been studied for capillary array collimators used for the injection of gases, e.g., in gas source molecular‐beam epitaxy. So far, the conventional designs suffer from either poor uniformity or low efficiency in precursor consumption (ratio of flux impinging on substrate to total emitted flux). The key feature of our new design is that the surface channel density is not homogeneous across the array but radius dependent instead, with the density of channels increasing towards the source array edge. In this way the steep decrease of the flux away from the beam center, which is a characteristic feature of conventionally designed arrays, is compensated. The numerical analysis shows that with the improved design, a high degree of uniformity (≳99%) can be achieved while at the same time the efficiency is increased by more than one order of magnitude compared to conventional capillary arrays.
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07.30.-t Vacuum apparatus
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Performance of an ionization gauge with a large‐angle ion deflector. I. Total pressure measurement in extreme high vacuum

C. Oshima and A. Otuka

J. Vac. Sci. Technol. A 12, 3233 (1994); http://dx.doi.org/10.1116/1.579243 (6 pages) | Cited 2 times

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Performance of the ionization gauge with a large‐angle ion deflector (254.6°) has been examined in extreme high vacuum. We have estimated 4×10−13 Pa to be the lowest measurable limit of the gauge due to soft x‐ray noise (1‐min period of measurement) and to be less than 2×10−13 Pa for electron stimulated desorption ion noise. The sensitivity of the gauge was 0.018 Pa−1 for hydrogen. By use of a channeltron multiplier for ion detection, the sensitivity of the gauge is improved: hence, a pressure of ∼3×10−11 Pa is easily measured at an emission current <0.1 mA. Deviation from the linear relation of ion current versus emission, allows outgassing from the gauge to be detected.
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07.30.Dz Vacuum gauges

Coupling of radio‐frequency bias power to substrates without direct contact, for application to film deposition with substrate transport

Donald L. Smith and Andrew S. Alimonda

J. Vac. Sci. Technol. A 12, 3239 (1994); http://dx.doi.org/10.1116/1.579244 (3 pages)

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We have demonstrated the coupling of 13.56 MHz rf bias power to an electrically floating substrate platform during aluminum sputter deposition by using an rf‐driven electrode spaced 3 mm away from the back of the platform. This electrode gap and the sputtering plasma sheath in series with it form a capacitive voltage divider, so that the peak rf voltage on the platform is 350 V when that on the electrode is 750 V. This amount of coupling produced enough ion bombardment on the aluminum to result in 23% resputtering and an improvement in film sidewall coverage from 10% to 100%. This noncontact, ‘‘proximity’’ method of substrate biasing should greatly facilitate the coupling of rf power into moving substrates in transport‐type deposition processes.
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81.15.Cd Deposition by sputtering

Monte Carlo simulation of ion transport through radio frequency collisional sheaths

M. Ardehali

J. Vac. Sci. Technol. A 12, 3242 (1994); http://dx.doi.org/10.1116/1.579245 (3 pages) | Cited 1 time

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Ion transport in collisional sheaths is simulated with a Monte Carlo method. The simulation results indicate that the length scale over which the horizontal component of the electric field is significant scales with the trench width. Thus the degree of ion deflection by the horizontal component of the electric field at the trench opening does not depend on the trench width.
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52.40.Hf Plasma-material interactions; boundary layer effects
81.65.-b Surface treatments
52.25.Fi Transport properties

Simple source of Li metal for evaporators in ultrahigh vacuum (UHV) applications

F. J. Esposto, K. Griffiths, P. R. Norton, and R. S. Timsit

J. Vac. Sci. Technol. A 12, 3245 (1994); http://dx.doi.org/10.1116/1.579246 (3 pages) | Cited 1 time

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Abstract Unavailable
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Erratum: ‘‘Optical emission spectroscopy of zinc sulfide etch’’ [J. Vac. Sci. Technol. A 10, 3065 (1992)]

Glennis J. Orloff

J. Vac. Sci. Technol. A 12, 3248 (1994); http://dx.doi.org/10.1116/1.579247 (1 page)

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Abstract Unavailable
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81.65.-b Surface treatments
78.66.Hf II-VI semiconductors
99.10.Cd Errata
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