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Jul 1996

Volume 14, Issue 4, pp. 1973-2680


Particle emission debris from a KrF laser–plasma x‐ray source

R. Bobkowski and R. Fedosejevs

J. Vac. Sci. Technol. A 14, 1973 (1996); http://dx.doi.org/10.1116/1.580070 (8 pages) | Cited 9 times

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The production of plasma debris ejected from various solid targets heated and ionized by intense KrF laser pulses was studied. The plasma is produced by focusing a train of 50 ps KrF laser pulses to an 8‐μm‐diam spot on the surface of solid tape targets. The plasma conditions are those of interest for the generation of a point source of the keV and sub‐keV x rays for microlithography (Cu and Fe targets) and x‐ray microscopy (plastic targets). Experimental measurements of the amounts of debris produced, the statistical distribution of the debris size, and angular distribution in vacuum are presented. The results of similar measurements in a background gas of helium are also presented together with measurements of the stopping power of the gas. A large flux of micron and submicron size particles is generated in vacuum even when employing thin tape targets. The introduction of a background gas reduces the damaging influence of such particles dramatically but only if enough path length exists to stop the particles. Theoretical calculations have been carried out of the stopping power of the background gas based on Stokes law and the Newtonian theory of deceleration of particles in gas. © 1996 American Vacuum Society
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79.20.Ds Laser-beam impact phenomena
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Formation of polytetrafluoroethylene thin films by using CO2 laser evaporation and XeCl laser ablation

Muneto Inayoshi, Masaru Hori, Toshio Goto, Mineo Hiramatsu, Masahito Nawata, and Shuzo Hattori

J. Vac. Sci. Technol. A 14, 1981 (1996); http://dx.doi.org/10.1116/1.580071 (5 pages) | Cited 5 times

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Laser evaporation and laser ablation methods were applied to the preparation of polytetrafluoroethylene (PTFE) thin films. In the case of the laser evaporation method, PTFE targets were evaporated by a continuous wave (cw) CO2 laser (10.6 μm), and fluorocarbon thin films were formed at a deposition rate of as high as 2 μm/min for a laser power of 10 W. The chemical composition and structure of the deposited film corresponded to those of a PTFE target, which was confirmed by x‐ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy analyses. In the laser ablation method, PTFE targets were ablated by a XeCl excimer laser (308 nm). It is found that the deposited films contained a small amount of fluorine atoms on the surface. From these experiments, the successful formation of PTFE thin films was demonstrated for the first time using cw CO2 laser evaporation method. © 1996 American Vacuum Society
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81.15.Fg Pulsed laser ablation deposition
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.55.-a Thin film structure and morphology

Synthesis and deposition of silicon nitride films by laser reactive ablation of silicon in low pressure ammonia: A parametric study

I. N. Mihãilescu, Adriana Litã, V. S. Teodorescu, Eniko Gyorgy, Rodica Alexandrescu, A. Luches, M. Martino, and A. Barboricã

J. Vac. Sci. Technol. A 14, 1986 (1996); http://dx.doi.org/10.1116/1.580072 (9 pages) | Cited 6 times

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The UV laser (λ=308 nm) ablation of silicon wafers in 1 mbar ambient ammonia results in the deposition of pure and uniform film of amorphous silicon nitride. At low pressures of NH3 (of several to several tens of μbar), the deposited films are a mixture of amorphous silicon nitride, amorphous nonstoichiometric silicon nitride, and amorphous silicon. The contamination with oxygen is low and is more evident at lower pressures. At ammonia pressures 0.1–1 mbar, the films also contain a certain fraction of hydrogen. Droplets of polycrystalline Si cover the surfaces of some films. This phenomenon is more important at smaller target‐collector distances and lower pressures of ambient NH3. © 1996 American Vacuum Society
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81.15.Fg Pulsed laser ablation deposition
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.-a Thin film structure and morphology

YBa2Cu3O7−x thin film over 3 in. substrate using off‐axis excimer laser deposition

T. Nagaishi and H. Itozaki

J. Vac. Sci. Technol. A 14, 1995 (1996); http://dx.doi.org/10.1116/1.580073 (4 pages) | Cited 2 times

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A large area c‐axis oriented YBa2Cu3O7−x thin film was grown on a 3‐in. LaAlO3 substrate using off‐axis excimer laser deposition. Substrate rotation and laser beam scan on a target enabled thickness variations less than ±4% over the 3‐in. film. The superconducting transition temperature was 88.4–90.8 K and the critical current density was in excess of 106 A/cm2 at 77 K under the zero magnetic field. The surface was smooth with few outgrowths, and the density of particles was 104/cm2, which is 1/100 less than that yielded on‐axis laser deposition. © 1996 American Vacuum Society
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition

Behavior of Si atoms in a silane electron cyclotron resonance plasma at high dissociations

Y. Yamamoto, M. Hori, T. Goto, and M. Hiramatsu

J. Vac. Sci. Technol. A 14, 1999 (1996); http://dx.doi.org/10.1116/1.580074 (5 pages) | Cited 4 times

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The Si atom density at the 3p2 3P2 level in electron cyclotron resonance SiH4/H2 and SiH4/Ar plasmas was measured as a function of total pressure from 0.6 to 3.3 Pa at a microwave power of 400 W and a SiH4 flow rate of 6 sccm using ultraviolet absorption spectroscopy. Parent SiH4 molecules in SiH4/H2 and SiH4/Ar plasmas were found to be considerably dissociated using infrared diode laser absorption spectroscopy. The Si atom density in the SiH4/H2 plasma was larger than that in the SiH4/Ar plasma, which was quite different from that in the capacitively coupled rf SiH4 plasmas. Behaviors of the Si atom density are discussed on the basis of the rate equation for Si atoms. It was concluded from a comparison of the behavior of the density and generation rate of Si atoms that the diffusion loss was comparable to the reaction loss in the removal process of Si atoms in the case of H2 dilution, while the reaction loss was dominant in the case of Ar dilution. © 1996 American Vacuum Society
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52.80.Pi High-frequency and RF discharges
52.25.-b Plasma properties
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. I. O2 addition to electron cyclotron resonance plasma employing CHF3

Kunimasa Takahashi, Masaru Hori, and Toshio Goto

J. Vac. Sci. Technol. A 14, 2004 (1996); http://dx.doi.org/10.1116/1.580075 (7 pages) | Cited 26 times

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Gas phase reactions of CFx (x=1−3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma were investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding O2 to CHF3 using infrared diode laser absorption spectroscopy and actinometry, respectively. By adding a small amount of O2 to CHF3, the CF and CF2 radical densities rapidly decreased, while the CF3 radical density rapidly increased but then decreased with further addition of O2 to CHF3. These reaction mechanisms in the plasma were evaluated on the basis of measurement results of CFx (x=1−3) radical and F atom densities. Under the same conditions as the measurements of radical densities, the etching rates of Si and SiO2 were measured. Furthermore, the etched Si surfaces were also analyzed with x‐ray photoelectron spectroscopy. The etching mechanisms for Si and SiO2 in the CHF3/O2 ECR plasma were investigated by connecting these etching characteristics on Si and SiO2 with the behaviors of CFx (x=1−3) radical and F atom densities. The Si etching rate was affected primarily by the concentrations of the CF and CF2 radicals and F atoms in the plasma. © 1996 American Vacuum Society
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
81.65.Cf Surface cleaning, etching, patterning
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Fluorocarbon radicals and surface reactions in fluorocarbon high density etching plasma. II. H2 addition to electron cyclotron resonance plasma employing CHF3

Kunimasa Takahashi, Masaru Hori, and Toshio Goto

J. Vac. Sci. Technol. A 14, 2011 (1996); http://dx.doi.org/10.1116/1.580076 (9 pages) | Cited 28 times

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Gas phase reactions of CFx (x=1–3) radicals and F atoms in an electron cyclotron resonance (ECR) downstream plasma have been investigated at 300 W and a CHF3 pressure of 0.4 Pa by adding H2 to CHF3. The behaviors of CFx radical densities were measured using infrared diode laser absorption spectroscopy, while F atom density was estimated with actinometry. Furthermore, the composition of fluorocarbon films deposited on the chamber walls in the CHF3/H2 ECR plasma has been investigated with x‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. On the basis of measurement results, the correlation between the characteristics of fluorocarbon films and the behaviors of radicals in the plasma has been investigated. The CF radical density was found to be changed by the variation of the composition, in particular F/C ratio, of the films deposited on the chamber walls. Under the same conditions as the measurements of radical densities, the deposition rates of fluorocarbon films formed on the substrate set in the downstream plasma region were measured. The behavior of CF radical density followed the deposition rates, which suggested that the CF radical played an important role for the formation of carbon‐rich fluorocarbon films in the CHF3/H2 ECR plasma. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Relating electric field distribution of an electron cyclotron resonance cavity to dry etching characteristics

K. K. Ko, S. W. Pang, and M. Dahimene

J. Vac. Sci. Technol. A 14, 2020 (1996); http://dx.doi.org/10.1116/1.580077 (6 pages) | Cited 5 times

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The electric field distribution for an electron cyclotron resonance (ECR) cavity was measured using microcoaxial probes. Typically, two to three resonant modes are found for each plasma condition and longer cavity length provides a more stable plasma. A 30° periodicity is seen in the angular dependence of the electric field, and the peak right across the microwave input probe becomes more dominant at shorter cavity length. The longitudinal dependence of the electric field has a peak close to the middle of the cavity, and the measured field patterns agree well with the theoretical prediction. The resonant modes were identified by fitting the experimental measurements to linear combinations of electromagnetic resonant modes with characteristic length close to the cavity height. Using this method, all the modes in this ECR cavity were found to be multimode, and the resonant mode with the longest cavity length was found to be a mixing of TE314 and TE611 modes. Significant changes in the electric field patterns are seen when the ECR cavity is out of tune. The sensitivity of electric field distribution to ECR cavity tuning allows process control to be implemented by monitoring the changes in the electric field intensity of just a single probe position. Despite the variations in electric field distribution for different resonant modes, uniformity of photoresist etching across 15‐cm‐diam wafer is better than 5%. The good uniformity of the photoresist etching suggests that the plasma density at the wafer is uniform, probably due to the diffusion of the reactive species from the ECR source. © 1996 American Vacuum Society
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52.50.Dg Plasma sources
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
85.40.Hp Lithography, masks and pattern transfer

Ion desorption stability in superconducting high energy physics proton colliders

William C. Turner

J. Vac. Sci. Technol. A 14, 2026 (1996); http://dx.doi.org/10.1116/1.580078 (13 pages)

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In this article we extend our previous analysis of a cold beam tube vacuum in a superconducting proton collider to include ion desorption in addition to thermal desorption and synchrotron radiation induced photodesorption. The ion desorption terms introduce the possibility of vacuum instability. This is similar to the classical room temperature case but is now modified by the inclusion of ion desorption coefficients for cryosorbed (physisorbed) molecules which can greatly exceed the coefficients for tightly bound molecules. The sojourn time concept for physisorbed H2 is generalized to include photodesorption and ion desorption as well as the usually considered thermal desorption. The ion desorption rate is density dependent and divergent so at the onset of instability the sojourn time goes to zero. Experimental data are used to evaluate the H2 sojourn time for the conditions of the Large Hadron Collider (LHC) and the situation is found to be stable. The sojourn time is dominated by photodesorption for surface density s(H2) less than a monolayer and by thermal desorption for s(H2) greater than a monolayer. For a few percent of a monolayer, characteristic of a beam screen, the photodesorption rate exceeds the ion desorption rate by more than two orders of magnitude. The photodesorption rate corresponds to a sojourn time of approximately 100 s. The article then turns to the evaluation of stability margins and the inclusion of gases heavier than H2 (CO, CO2, and CH4), where ion desorption introduces coupling between molecular species. Stability conditions are worked out for a simple cold beam tube, a cold beam tube pumped from the ends, and a cold beam tube with a coaxial perforated beam screen. In each case a simple inequality for stability of a single component is replaced by a determinant that must be greater than zero for a gas mixture. A connection with the general theory of feedback stability is made and it is shown that the gains of the diagonal uncoupled feedback loops are first order in the ion desorption coefficients whereas the gains of the off‐diagonal coupled feedback loops are second order and higher. For this reason it turns out that in practical cases stability is dominated by the uncoupled diagonal elements and the inverse of the largest first‐order closed loop gain is a useful estimate of the margin of stability. In contrast to the case of a simple cold beam tube, the stability condition for a beam screen does not contain the desorption coefficient for physisorbed molecules, even when the screen temperature is low enough that there is a finite surface density of them on the screen surface. Consequently there does not appear to be any particular advantage to operating the beam screen at a high enough temperature to avoid physisorption. Numerical estimates of ion desorption stability are given for a number of cases relevant to the LHC and all of the ones likely to be encountered were found to be stable. The most important case, a 1% transparency beam screen at ∼4.2 K, was found to have a stability safety margin of approximately 17 determined by ion desorption of CO. Ion desorption of H2 is about a factor of 75 less stringent than CO. For these estimates the beam tube surface was assumed to be chemically cleaned but otherwise untreated, for example, by a vacuum bakeout or by glow discharge cleaning. © 1996 American Vacuum Society
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07.30.Bx Degasification, residual gas
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
29.20.-c Accelerators

Diamond‐like carbon film synthesized by ion beam assisted deposition and its tribological properties

Xiaomimg He, Wenzhi Li, and Hengde Li

J. Vac. Sci. Technol. A 14, 2039 (1996); http://dx.doi.org/10.1116/1.580079 (9 pages) | Cited 8 times

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Ion beam assisted deposition offers a novel and unique process to prepare diamond‐like carbon (DLC) films at room temperature with particularly good interface adhesion. This advantage is explored to deposit highly wear resistant DLC coating on AISI 52100 steel. Various bombarding species and energy are examined to optimize the process. Infrared, Raman, Auger electron spectroscopy spectra, and hardness measurements are used to characterize the structure and properties of DLC films. The friction and wear behavior of DLC films are systematically investigated by performing extensive experiments in different testing styles. It is disclosed that by means of a dynamic mixing of atoms in interfaces, a pure metal intermediate layer can tremendously improve the tribological properties of DLC films on 52100 steel. The results are optimistic and may lead to useful applications. © 1996 American Vacuum Society
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.ub Fullerenes and related materials
81.40.Pq Friction, lubrication, and wear
68.35.Fx Diffusion; interface formation

Radio frequency matching for helicon plasma sources

J. P. Rayner, A. D. Cheetham, and G. N. French

J. Vac. Sci. Technol. A 14, 2048 (1996); http://dx.doi.org/10.1116/1.580080 (8 pages) | Cited 7 times

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A theoretical and experimental study of the matching network linking the antenna of a helicon plasma system to its rf power source is described. It is shown that the introduction of a rf step‐down transformer into the conventional L‐section network has a number of benefits. The transformer increases the reflected antenna impedance seen by the network, bringing it closer to the output resistance of the rf source. The resulting low‐Q network is shown to be insensitive to changes in the antenna impedance and the values of the matching elements. It is found that in general only one component in this broad‐band network needs to be adjusted rather than the iterative adjustment of two components in the conventional network. The importance of this simplification with respect to the automatic control of the matching network is discussed. © 1996 American Vacuum Society
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52.50.Dg Plasma sources
84.40.Ba Antennas: theory, components and accessories

Reactive ion beam assisted deposition of zirconium oxyfluoride thin films

U. J. Gibson and K. D. Cornett

J. Vac. Sci. Technol. A 14, 2056 (1996); http://dx.doi.org/10.1116/1.580081 (6 pages) | Cited 2 times

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Zirconium oxyfluoride thin films of varying composition and refractive index were made by ion beam assisted deposition and concurrent O+2 ion bombardment of thermally deposited ZrF4. The oxygen ion bombardment parameters control the index of refraction over the range 1.52–1.8. The composition of the ZrOxFy films, as determined by Rutherford backscattering and x‐ray photoelectron spectroscopy, varied from ZrO0.4F3.6 to ZrO2F1. Below 300 eV there is little change in oxygen content or refractive index, but at 600 eV the bombardment flux controls the material properties. Low loss (1 dB/cm) optical wave guides were fabricated using this technique. © 1996 American Vacuum Society
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
42.70.-a Optical materials
42.82.Et Waveguides, couplers, and arrays

Study of surface reactions during plasma enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar plasma

Sang M. Han and Eray S. Aydil

J. Vac. Sci. Technol. A 14, 2062 (1996); http://dx.doi.org/10.1116/1.580082 (9 pages) | Cited 36 times

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In situ attenuated total reflection Fourier transform infrared spectroscopy was employed in proposing possible surface reaction mechanisms during plasma enhanced chemical vapor deposition of SiO2 from a mixture of SiH4, O2, and Ar in a helical resonator plasma reactor. Infrared spectra taken during the oxide deposition revealed that the oxide surface is covered with OH when the deposition is conducted with a low SiH4 to O2 ratio (≪1). Both associated hydroxyls (SiOHassoc) and isolated hydroxyls (SiOHisol) were detected on the surface during growth. Two kinds of OH attached to Si exist on the surface: weakly bound OH that thermally desorb at 250 °C and strongly bound OH that desorb under ion bombardment. The thermal removal of weakly bound OH does not lead to SiO2 formation, but the ion‐assisted removal of strongly bound OH by Ar+ ion bombardment results in oxide growth via the reaction 2SiOH(s)+Ar+→Si–O–Si(s)+H2O(g)+Ar+. Experiments undertaken to delineate the possible heterogeneous reaction paths between surface species and gas phase reactants showed that the molecular fragments of SiH4 (SiHx, x=1, 2, or 3) react with surface hydroxyl groups and produce surface hydrides such as HSiO3, H2SiO2, and H3SiO. The silane fragments also react with Si on the surface to give silicon hydrides whose Si constituent is backbonded to other Si atoms in addition to O [e.g., HSi(SiO2), H2Si(SiO), HSi(Si2O), H3SiSi, and H2SiSi2]. The latter reactions become more important as the OH on the surface is depleted, and the surface becomes silicon and silicon hydride rich. A subsequent exposure of the silicon‐ hydride‐covered oxide surface to oxygen plasma creates SiOHassoc groups presumably by insertion of O into Si–H bonds of surface hydrides. The silicon hydrides are not observed during deposition using low SiH4 to O2 flow rate ratios (≪1): silane fragments, upon adsorbing onto the surface, are promptly oxidized by O atoms, leading to a SiOH‐covered surface at steady state conditions. Bombardment of the surface by ions such as Ar+ and O+2 assists H2O desorption from SiOH forming Si–O–Si bonds. © 1996 American Vacuum Society
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Reactor modeling for radio frequency plasma deposition of SiNxHy: Comparison between two reactor designs

H. Caquineau, G. Dupont, B. Despax, and J. P. Couderc

J. Vac. Sci. Technol. A 14, 2071 (1996); http://dx.doi.org/10.1116/1.580083 (12 pages) | Cited 3 times

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Plasma deposition processes involve complex phenomena which make the design and optimization of industrial equipments difficult. In the particular case of silane‐ammonia plasmas to produce silicon nitride (at very low silane percentage), two flow arrangements, i.e., (i) a longitudinal flow reactor and (ii) an axisymmetric showerhead electrode reactor were studied by two‐dimensional modeling of momentum and mass transport. First, a kinetic scheme which enables us to reproduce experimental results for both reactor configurations was selected enlightening an unusual behavior of Si(NH2)3 radicals. Then, the way silane is consumed and its consequences on active species production was outlined as playing the leading parts in the processes. As silane concentration decreases along the flow direction, the modeling of the longitudinal flow reactor shows a steep decrease of the deposition rate and a significant composition variation of the deposit. In the axisymmetric reactor, the film thickness and composition uniformities considerably improve due to the distributed gas feed. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
52.65.-y Plasma simulation

CFX radical generation by plasma interaction with fluorocarbon films on the reactor wall

Koji Miyata, Masaru Hori, and Toshio Goto

J. Vac. Sci. Technol. A 14, 2083 (1996); http://dx.doi.org/10.1116/1.580084 (5 pages) | Cited 24 times

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CFX (X=1–3) radicals were found to be generated from fluorocarbon films deposited on the reactor wall when the films are irradiated with plasmas. In this process, the fluorocarbon films were first formed on the reactor wall by electron cyclotron resonance (ECR) etching plasmas employing C4F8 and C4F8/H2 gases, and subsequently irradiated with an ECR‐Ar plasma. CFX radical densities were measured during the Ar plasma by infrared diode laser absorption spectroscopy. CF3 radical density in the Ar plasma was estimated to be the same order as that in the C4F8 plasma. the fluorocarbon films deposited on the reactor wall were investigated by x‐ray photoelectron spectroscopy. These results will offer valuable information for the production mechanism of CFX radicals in the etching process employing fluorocarbon gases. © 1996 American Vacuum Society
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

SiOxNy films deposited by remote plasma enhanced chemical vapor deposition using SiCl4

O. Sanchez, M. A. Aguilar, C. Falcony, J. M. Martinez‐Duart, and J. M. Albella

J. Vac. Sci. Technol. A 14, 2088 (1996); http://dx.doi.org/10.1116/1.580085 (6 pages) | Cited 3 times

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Silicon oxynitride films have been deposited by remote‐plasma enhanced chemical vapor deposition using SiCl4 as a silicon source at a substrate temperature of 250 °C. Different mixtures of O2 and NH3 were used to obtain different oxynitride compositions ranging from SiO2 to a stoichiometry close to that of silicon nitride. Also the effect of a hydrogen flow added during the deposition process on the structural characteristics of the deposited films was studied. The behavior of the IR absorption spectra as well as the refractive index measured by ellipsometry were used to estimate the stoichiometry of the films as well as the effect of the different deposition parameters. It was found that the IR spectra show a shift of the characteristic peak associated with the stretching vibration mode of the Si–O–Si bonds toward lower wave numbers as the relative concentration of ammonia was increased with respect to oxygen. No double peaks associated with silicon oxide and silicon nitride were observed, indicating the formation of a homogeneous alloy. The IR absorption spectra for these films did not show any presence of O–H or Si–H related peaks. Atomic force microscopy measurements on these films show that the hydrogen flow added during deposition results in a reduction of the film roughness. © 1996 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Electron‐beam controlled radio frequency discharges for plasma processing

Mark J. Kushner, Wenli Z. Collison, and David N. Ruzic

J. Vac. Sci. Technol. A 14, 2094 (1996); http://dx.doi.org/10.1116/1.580086 (8 pages) | Cited 11 times

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During plasma etching and deposition of semiconductor materials, it is desirable to have separate control over the magnitude and energy of the ion flux onto the substrate. This control is difficult to achieve in reactive ion etching discharges since the radio frequency (rf) voltage applied to the substrate both generates the ions and accelerates the ions into the substrate. High plasma density devices such as electron cyclotron resonance and inductively coupled plasma reactors achieve this control by having separate power sources for ionization and ion acceleration. In this article, we present results from a computational study of an electron beam controlled rf discharge in which the production and acceleration of ions are similarly separately controlled. Ionization is dominantly produced by injection of an electron beam into the reactor. Ion acceleration is determined by a separate rf bias applied to the substrate. The limits of e‐beam voltage, current, and rf bias voltage for which this separate control can be achieved will be discussed. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
52.40.Mj Particle beam interactions in plasmas
52.65.-y Plasma simulation

Vacuum ultraviolet emission from radio frequency plasmas of SF6 and CF4

Jan Li and J. W. McConkey

J. Vac. Sci. Technol. A 14, 2102 (1996); http://dx.doi.org/10.1116/1.580087 (4 pages) | Cited 1 time

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The vacuum ultraviolet and ultraviolet emission (115 nm<λ<300 nm) from radio frequency (rf) discharges through CF4 and SF6 have been investigated as a function of source pressure and rf power. Prominent features of the spectra arise from dissociative excitation of the parent species. Other significant emissions are impurity bands from CO (CF4) or SO (SF6) caused largely by oxygen release from the walls of the discharge tube and subsequent discharge chemistry and excitation. Minor emissions from excited CF+4, CF3, and/or CF2 were obtained from CF4 discharges. © 1996 American Vacuum Society
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Probe for measuring ion beam angular distribution

J. R. Kahn, H. R. Kaufman, C. A. Phillips, and R. S. Robinson

J. Vac. Sci. Technol. A 14, 2106 (1996); http://dx.doi.org/10.1116/1.580088 (7 pages) | Cited 4 times

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A new type of ion beam probe is described that measures the angular distribution of energetic ions and, through their sputtering effects, energetic neutrals as well. This probe does not require either complicated motion actuators or very sensitive electrical measurements in the adverse environment of an ion beam, but instead performs the measurement through the sputter etching of a multilayer sample with contrasting metal colors. This probe was tested and found to provide a half‐width at half‐maximum reproducibility of about ±0.3 deg. After use, the probe sample provides a permanent record of the angular distribution of the ion beam at the target location tested. Because no electrical contacts are required, the probe can even be attached to a moving stage to measure the effective angular distribution of an ion beam while being carried through a complicated planetary pattern. Using this probe, the low divergence and paraxial beam from an ion source with 30 cm flat graphite grids were documented. This probe, in conjunction with profiles obtained with a Faraday probe, allows full global and internal ion beam characterization. It is significant that the minimum divergences obtained in this investigation were 40–60 percent lower than the minimum divergences obtained from earlier tests with small arrays of apertures. © 1996 American Vacuum Society
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07.77.Ka Charged-particle beam sources and detectors
41.75.-i Charged-particle beams
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Cf Surface cleaning, etching, patterning

Spatial distributions of electron density and electron temperature in direct current glow discharge

W. H. Tao, M. A. Prelas, and H. K. Yasuda

J. Vac. Sci. Technol. A 14, 2113 (1996); http://dx.doi.org/10.1116/1.580089 (9 pages) | Cited 11 times

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The spatial distributions of electron temperature and density in a dc glow discharge that is created by a pair of planar electrodes were studied using double Langmuir probes. The measurement was carried out on the horizontal center plane across vertically placed circular planar parallel plate electrodes. One electrode with magnetic enhancement (magnetron) was paired with a nonmagnetron in the two possible combinations. The measurements were carried out for the following three modes: (nonmagnetron) cathode/(nonmagnetron) anode (C–A), cathode magnetron/(nonmagnetron) anode (CM–A), and (nonmagnetron) cathode/anode magnetron (C–AM). In the C–A mode, electrons gain energy from the imposed electric field, and the electron temperature (Te) rises very sharply from the cathode to the leading edge of the negative glow where Te reaches the maximum. In this region, the number of electrons (Ne) is relatively small and does not increase much. The accelerated electrons lose energy by ionizing gas atoms, and Te decreases rapidly to the plateau value, which is reached near the midpoint between two electrodes and extends to the anode. In this region, Ne increases sharply. As electrons are pulled towards the anode, a steep increase of Ne was found towards the anode and then Ne drops sharply very near the anode as electrons are captured by the anode. The value of Te increases slightly towards the edge of the cathode and the anode (radial position), and the minimum Te was found at the center. There is a clear trend that Te and Ne are inversely related (Te×Ne=constant). This trend was also found in cases in which a magnetron is used as the cathode (CM–A) or as the anode (C–AM) paired with a planar nonmagnetron electrode. In the (CM–A) mode, the magnetic entrapment of electrons is seen in the sharp increase of Ne near the cathode surface. The characteristic toroidal glow near the magnetron cathode is associated with the Ne peak, and the Te peak is found inside the circular toroidal glow where Ne is small. In the (C–AM) mode, a large Ne peak was found near the anode in the center, and the Te peak was found in the center near the cathode. A funnel shaped glow that expands from the center of the anode is distinctively different from the toroidal glow observed for the cathode magnetron glow discharge. © 1996 American Vacuum Society
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52.80.Hc Glow; corona
52.70.Ds Electric and magnetic measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Analysis of pulse‐time modulated high‐density discharges

M. Meyyappan

J. Vac. Sci. Technol. A 14, 2122 (1996); http://dx.doi.org/10.1116/1.580090 (5 pages) | Cited 13 times

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Time modulation of the input power has been used recently to improve processing rates and etch selectivity in high‐density discharges. Plasma characteristics of a pulse‐time modulated high‐density discharge is investigated here with the aid of a spatially averaged model. The model consists of mass and energy conservation equations for neutral and ionic species. Results are presented for chlorine and CF4 discharges for a range of pulse periods and duty ratios. © 1996 American Vacuum Society
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52.65.Kj Magnetohydrodynamic and fluid equation
52.80.Pi High-frequency and RF discharges

Fluorocarbon high density plasmas. VII. Investigation of selective SiO2‐to‐Si3N4 high density plasma etch processes

Ying Zhang, Gottlieb S. Oehrlein, and Ferdinand H. Bell

J. Vac. Sci. Technol. A 14, 2127 (1996); http://dx.doi.org/10.1116/1.580091 (11 pages) | Cited 23 times

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A comparison of the plasma etching characteristics of SiO2 and Si3N4 in high‐density fluorocarbon discharges with the goal of identifying an etching chemistry with a very high SiO2‐to‐Si3N4 etch selectivity has been initiated. High‐density plasmas were excited in an electron cyclotron resonance apparatus equipped with a cooled rf powered electrostatic chuck. Gas mixtures of either CF4/H2, CHF3/H2 (low carbon/fluorine ratio fluorocarbon gases), or C2F4/H2, C2F6/H2, and C3F6/H2 (high C/F ratio) were used in this work. We will show that a carbon‐rich fluorocarbon gas like C2F4 and a modest amount of H2 are useful in achieving high SiO2/Si3N4 etch selectivity (≳28). On the other hand, hydrogen‐rich fluorocarbon gas mixtures which contain less carbon, e.g., CHF3/H2, are not useful for achieving SiO2 over Si3N4 etch selectivity although they will enable SiO2/Si etch selectivity. The gas phase and surface chemical aspects of the different gas mixtures were studied by optical emission spectrometry and line of sight mass spectrometry and by post plasma x‐ray photoelectron spectroscopy. The results of these measurements can explain the etch rate data by selective deposition of fluorocarbon films on Si3N4 and Si surfaces. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Ion‐assisted Si/XeF2‐etching: Influence of ion/neutral flux ratio and ion energy

M. J. M. Vugts, L. J. F. Hermans, and H. C. W. Beijerinck

J. Vac. Sci. Technol. A 14, 2138 (1996); http://dx.doi.org/10.1116/1.580038 (13 pages) | Cited 10 times

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The Ar+ ion‐enhanced Si(100)/XeF2 reaction at 300 K is studied quantitatively in a molecular beam setup. Measurements are done for XeF2‐fluxes from 0.1 up to 3.4 monolayer/s, Ar+‐fluxes from 8×10−4 up to 8×10−2 monolayers/s and Ar+‐energies of 500, 1000 en 2000 eV. Both the XeF2 consumption and the SiFx production are measured by mass spectrometry. It is concluded that physical and chemical sputtering are the only significant ion‐induced mechanisms: damage‐enhanced etching and enhanced spontaneous etching can be neglected. The flux dependence of the etch process is found to be solely determined by the ratio of the ion over the neutral flux. This behavior is described by a simple kinetic model. From the energy dependence it is concluded that both the physical and the chemical sputtering contributions scale with the square root of the ion energy. The ion‐enhanced Si/XeF2 reaction is most efficient for ion/neutral ratios of 0.1 and higher: 80% of the XeF2 is then consumed in the reaction process versus 10% during spontaneous etching. It is concluded from the mass spectrometer signals that under these conditions between 35% and 61% of the SiFx products are released by physical sputtering and the remainder desorbs by chemical sputtering. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Role of nitrogen in the downstream etching of silicon nitride

M. G. Blain, T. L. Meisenheimer, and J. E. Stevens

J. Vac. Sci. Technol. A 14, 2151 (1996); http://dx.doi.org/10.1116/1.580039 (7 pages) | Cited 20 times

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Chemical downstream etching of silicon nitride (Si3N4) requires the addition of nitrogen to the discharge for obtaining efficient etch rates. A 10% addition of N2 to a CF4/O2 discharge (CF4/O2 = 1.2, 0.525 Torr) causes a factor of 6 increase in the Si3N4 etch rate and a 8% decrease in the silicon dioxide etch rate. The result is selectivities approaching 9:1. Importantly, the conversion of CF4 to F and F‐containing reactive species by the discharge decreases or remains constant as nitrogen is added to the discharge mix, indicating that the etching reaction is not limited by delivery of these species to the substrate. By measuring the amount of NO and NO2 in the etch chamber, it is found that the NO concentration increases by a factor of 6 as N2 is added, while the amount of NO2 remains small and constant. The NO signal is significantly reduced during nitride etching compared to the signal observed during a discharge with an empty etch chamber, implying that the increase in Si3N4 etch rate is related to the formation of NO in the discharge. This view is consistent with the observation that an NF3 plasma in a quartz discharge tube results in a nitride etch rate which is a factor of 2 higher than for the same discharge in a sapphire tube. The conclusion is that the oxygen liberated by erosion of the quartz tube allows the formation of NO. That NO is a key Si3N4 etch reactant was confirmed by performing a series of experiments in which N2, NO, NO2, and N2O were injected into the discharge and then downstream in the reaction chamber during a CF4/O2 discharge. Nitride etch rates increased significantly upon injection of NO into both discharge and etch chamber as compared to injection of the other NxOy species. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Negative ion density in inductively coupled chlorine plasmas

G. A. Hebner

J. Vac. Sci. Technol. A 14, 2158 (1996); http://dx.doi.org/10.1116/1.580040 (5 pages) | Cited 36 times

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Laser photodetachment spectroscopy has been used to infer the density of chlorine negative ions in an inductively coupled chlorine plasma. Time dependent, excess electron density produced by photodetaching electrons from Cl− was detected by a microwave interferometer operating at 80 GHz. By focusing the microwave probe beam through the center of the discharge, negative ion density measurements could be performed in a small, 1.5 cm3, volume. As the rf power into the plasma increased from 155 to 340 W at 20 mTorr, the Cl− density in the center of the bulk plasma increased from 3.4 to 5.2×1011 cm−3. As the pressure was increased from 15 to 50 mTorr at 240 W, the Cl− density increased from 3.5 to 5×1011 cm3. Over this parameter space, the negative ion density equaled the electron density to within a factor of 2. The negative ion radial distribution was relatively constant, with a 20% decrease in the center of the plasma for some operating conditions. When the surface of the bias electrode was changed from stainless steel to silicon, the electron density remained constant but the Cl− density decreased by a factor of 2 to 3. © 1996 American Vacuum Society
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Characterization of helicon wave plasma designed for direct current sputtering

J. Q. Zhang, Y. Setsuhara, T. Ariyasu, and S. Miyake

J. Vac. Sci. Technol. A 14, 2163 (1996); http://dx.doi.org/10.1116/1.580041 (6 pages) | Cited 5 times

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The rf plasma produced in a helicon wave frequency range was studied using helical antennas and its application to dc sputtering at low Ar pressures was reported. A dense plasma of the order of 1012–1013 cm−3 could be obtained at a pressure around 0.1 Pa by using the antennas with azimuthal mode number of m=±1 or m=0. The measurement of the axial magnetic component Bz of the rf field in the plasma showed evidence of the excitation of helicon wave. A sputtering apparatus has been developed by means of the helicon wave plasma excited with a m=0 mode two‐turn antenna. It was found that the characteristics of the rf plasma enhanced sputtering discharge were dominated by the properties of the rf plasma sustained at pressures as low as 3×10−2 Pa. A target current as high as 2 A at a pressure of 0.4 Pa was achieved, and sputtering of the Al target indicated that a deposition rate of 1 μm/min could be obtained under this condition. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.70.Ds Electric and magnetic measurements
81.15.Cd Deposition by sputtering

Origin of stresses in sputtered elemental and alloy thin films

C. Hudson and R. E. Somekh

J. Vac. Sci. Technol. A 14, 2169 (1996); http://dx.doi.org/10.1116/1.580042 (6 pages) | Cited 5 times

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The properties of a sputtered film are strongly influenced by the deposition conditions. In this article we try to develop an understanding of the way in which the many parameters associated with sputtering process combine together to give only a few parameters which ultimately determine the film properties. In particular we consider the stresses in films and consider the conditions required to produce films with neutral stress, a state often required in films made in routine production. It is apparent that the product of the sputtering gas pressure and the substrate–target distance is a major factor in controlling the film stress, but also of relevance are the sputtering voltage and the substrate temperature. Many elemental and alloy films have been investigated, using variable argon pressures and substrate–target distances, at a low power and therefore a deposition temperature of approximately 20–40 °C. Detailed analyses have shown that a model of the total energy flux of particles bombarding the film is required to explain the results fully. In this article, the origin of film stress is ascribed to the total energy flux to the substrate per deposited atom, which in sputtering comes from both the arriving film atoms and the reflected neutrals. © 1996 American Vacuum Society
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68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys

Electrostatic scattering of ionic species in low pressure sputtering of Ti and TiN

C. J. Backhouse, K. Robbie, J. Parks, J. N. Broughton, S. Dew, G. Este, and M. J. Brett

J. Vac. Sci. Technol. A 14, 2175 (1996); http://dx.doi.org/10.1116/1.580043 (7 pages) | Cited 1 time

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A technique of sputtering with low pressures and large substrate to target distances (long throw) has been studied with a view of applying the technique to the deposition of titanium and titanium nitride on high aspect ratio topographies. The angular distributions of the sputtered species produced by most sputtering systems are broad and therefore unsuitable for application to via filling in ultralarge scale integration or even to lift‐off patterning in very‐large scale integration. In our work, progressive reduction in the pressure to 0.013 Pa (0.1 m Torr) while reducing the size of the planar magnetron (to 50 mm diam), was made possible by injecting electrons and ionized Ar by means of a secondary hollow cathode source. These reductions in pressure and magnetron size have greatly narrowed the incident angular distribution of the sputtered species at the substrate. However, we believe that a component of the sputtered species is electrostatically scattered near the substrate. This is important because many of the applications of sputtering at low pressures will involve insulating substrate structures that are expected to be particularly susceptible to this effect (for instance lift‐off deposition on, or via filling in, insulators). In addition, we believe that our findings will be applicable to several related deposition techniques of current interest in the literature such as electron cyclotron resonance, ionized sputtering (i.e., ionizing the sputtered flux and directing it towards the substrate) and conventional magnetron sputtering. © 1996 American Vacuum Society
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

Discharge characteristics of a facing target sputtering device using unbalanced magnetrons

G. K. Muralidhar, J. Musil, and S. Kadlec

J. Vac. Sci. Technol. A 14, 2182 (1996); http://dx.doi.org/10.1116/1.580044 (5 pages) | Cited 2 times

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This article presents the details of our investigations on the characteristics of a facing target sputter discharge using two highly efficient unbalanced magnetrons with electromagnetic coils. The variation of ignition and extinction pressures has been studied as a function of the current in the coils (I1 and I2) in both the magnetrons at two intertarget distances 290 and 125 mm, respectively. These studies have been carried out in closed as well as cusp field configurations and the results are compared. A negative resistance region has been observed in the discharge characteristic in the cusp field at longer intertarget distances (290 mm), which has been explained on the basis of electron trapping efficiency. Although the closed field has been found to be advantageous in achieving the lower pressure operation possible (0.01 Pa), deposition rates are relatively higher (about 20%) in the cusp field. © 1996 American Vacuum Society
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Cd Deposition by sputtering

High‐rate magnetron sputtering

J. Musil, A. Rajský, A. J. Bell, J. Matouš, M. Čepera, and J. Zeman

J. Vac. Sci. Technol. A 14, 2187 (1996); http://dx.doi.org/10.1116/1.580045 (5 pages) | Cited 5 times

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This article reports on the process of high‐rate magnetron sputtering of solid materials using an unbalanced magnetron with extremely high target power densities of up to 150 W cm−2. Particular attention is devoted to a comparison of sputtering in the 10−1 Pa range, low pressure sputtering (<10−1 Pa), and self‐sputtering. The advantages and drawbacks of the sputtering process at different pressures are critically analyzed. The extinction pressure measured as a function of the magnetron discharge current for the magnetron discharge of Cu, Ag, and Ti targets is given. Deposition rates and selected properties of Ti and Cu films are also reported. © 1996 American Vacuum Society
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Cd Deposition by sputtering

Oxidation‐enhanced roughening of thin Co films during sputtering by O+2 ions

B. Mohadjeri, M. Petravić, and B. G. Svensson

J. Vac. Sci. Technol. A 14, 2192 (1996); http://dx.doi.org/10.1116/1.580046 (10 pages)

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Substantial variations in the erosion rate during low energy (5.5–10.5 keV) O+2 sputtering of polycrystalline Co thin films are demonstrated by crater depth measurements as a function of sputtering time. At normal incidence the erosion rate is constant, while for oblique angles (≤55°, with respect to surface normal) the rate is between ∼30% and 75% higher at the surface compared to that in the ‘‘bulk.’’ A clear relationship between the width of the preequilibrium region and the sputtering‐induced roughness is shown, as revealed by surface stylus profilometry and atomic force microscopy measurements. Sputtering by Ar+ ions, where no chemical compounds form, results in significantly smoother craters and the erosion rate is constant. The development of the preequilibrium region during O+2 sputtering of Co is attributed to oxidation‐induced roughening of Co. A model is proposed for the oxidation‐enhanced roughening, which is further supported by results obtained from Rutherford backscattering spectrometry measurements of oxygen incorporation during O+2 bombardment and Ar+ sputtering combined with oxygen flooding. © 1996 American Vacuum Society
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
81.70.Jb Chemical composition analysis, chemical depth and dopant profiling

Microstructure of radio frequency sputtered Ag1−xSix alloys

K. D. Leedy and J. M. Rigsbee

J. Vac. Sci. Technol. A 14, 2202 (1996); http://dx.doi.org/10.1116/1.580047 (5 pages) | Cited 1 time

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A series of thin film Ag1−xSix alloys were fabricated using radio frequency sputter deposition with composite Ag+Si sputter targets and water‐cooled and liquid nitrogen–cooled substrate holders. The microstructures of the films were analyzed using x‐ray diffraction and transmission electron microscopy. As‐deposited films contained fcc Ag and amorphous Si. The Ag grain size decreased as the Si content increased. Films deposited on the liquid nitrogen–cooled substrate holder exhibited grain sizes smaller than films deposited on the water‐cooled substrate holder. Despite the negligible Ag and Si mutual solid solubilities, the metastable Ag3Si hcp silver silicide phase was observed in addition to fcc Ag and amorphous Si in a 12 at. % Si alloy deposited on the liquid nitrogen–cooled substrate holder. The Ag3Si phase observed by x‐ray diffraction in 5000‐Å‐thick films was not found in the 250‐Å‐thick TEM films, suggesting a thickness dependence of stability. During vacuum anneals above 100 °C, the Ag3Si phase partially decomposed. © 1996 American Vacuum Society
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys

Reactive sputter‐deposition and characterization of lead oxide films

Y. Pauleau and E. Harry

J. Vac. Sci. Technol. A 14, 2207 (1996); http://dx.doi.org/10.1116/1.580048 (8 pages) | Cited 1 time

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Lead and lead oxide containing films have been deposited on various substrates by radio frequency sputtering of a lead target in pure argon and argon–oxygen discharges. The sputter‐deposited films were characterized by Rutherford backscattering spectroscopy, nuclear reaction analyses, and the x‐ray diffraction technique. The composition, deposition rate, and crystalline structure of films were investigated as functions of the oxygen content (1.5%–50%) in the gas phase and sputtering power (50–200 W). The O/Pb atom number ratio increased rapidly up to one as the oxygen content in the discharge was varied from 1.5% to 6%. The films deposited under these conditions were composed of metallic lead, yellow orthorhombic β‐PbO and PbO1.57 phases in variable proportions. Amorphous and noncataloged lead oxide phases were also formed for oxygen contents in the discharge higher than 6%. The effect of the composition of the deposited material on the residual stresses developed in the films was determined and related to the morphology of films examined by scanning electron microscopy. The friction properties of lead and lead oxide containing films deposited on stainless steel disks were determined by alumina ball‐on‐disk tribological tests conducted in air at a sliding speed of 3 cm s−1 under a load of 2 N. The friction coefficient was investigated as a function of the sliding distance, film thickness, and surface roughness of tribological disks and test temperature. © 1996 American Vacuum Society
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81.15.Cd Deposition by sputtering
81.40.Pq Friction, lubrication, and wear
68.55.-a Thin film structure and morphology

Characteristics of reactively sputtered Pt–SnO2 thin films for CO gas sensors

M. Di Giulio, G. Micocci, A. Serra, A. Tepore, R. Rella, and P. Siciliano

J. Vac. Sci. Technol. A 14, 2215 (1996); http://dx.doi.org/10.1116/1.580049 (5 pages) | Cited 6 times

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SnO2 thin films were prepared by the rf reactive sputtering method from a target of the same compound in order to be used as gas sensors. Dynamic response characteristics of the electrical conductance to different CO concentrations in dry air are presented for pure films and for films activated with a suitable amount of metallic Pt deposited by sputtering onto a SnO2 surface. The sensitivity, the response, and recovery times as a function of temperature were analyzed. In particular, the Pt–SnO2 films show relatively high sensitivity to CO gas and good stability at an operating temperature of about 170 °C. © 1996 American Vacuum Society
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81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Postdeposition annealing of radio frequency magnetron sputtered ZnO films

M. K. Puchert, P. Y. Timbrell, and R. N. Lamb

J. Vac. Sci. Technol. A 14, 2220 (1996); http://dx.doi.org/10.1116/1.580050 (11 pages) | Cited 28 times

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Zinc oxide (ZnO) films have been deposited on 1 μm SiO2/Si (100) substrates by rf magnetron sputtering. Using a sputtering gas of pure oxygen, a pressure regime is found in which the ZnO films grow on room temperature substrates with a single (0001) orientation, small grains (crystallite sizes ∼10–15 nm), and high intrinsic biaxial compressive stress (∼6 GPa). The effects of post‐deposition annealing these films in air was investigated over a range of temperatures (200–1000 °C) and durations (2–2000 min). Annealing resulted in lower biaxial compressive stresses and increased average crystallite sizes in all films. Additional ZnO grain orientations were detected only after annealing above 500 °C for longer than 90 min, and the results are interpreted in terms of film recrystallization. Consequently, a relatively rapid thermal anneal at 1000 °C for 5 min caused grain recovery without recrystallization, resulting in maximum stress reduction (90%–100% of stress was relieved and average crystallized size tripled) while maintaining the original film orientation. The film surface area—measured by atomic force microscopy—decreased by up to 25% during annealing. X‐ray photoelectron spectroscopy results indicate that although the surfaces of as‐deposited films have a slight excess of oxygen, annealing as low as 200 °C results in a stoichiometric ZnO surface. High values of electrical resistivity (∼105 Ω cm) measured across the thickness of unannealed oriented films indicate low levels of elemental zinc clusters in the film bulk. © 1996 American Vacuum Society
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68.60.Dv Thermal stability; thermal effects
81.05.Hd Other semiconductors
81.15.Cd Deposition by sputtering
73.61.Le Other inorganic semiconductors

Computational modeling of reactive gas modulation in radio frequency reactive sputtering

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

J. Vac. Sci. Technol. A 14, 2231 (1996); http://dx.doi.org/10.1116/1.580051 (4 pages) | Cited 6 times

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Computer simulation of reactive sputtering was carried out to explain the enhancement of the deposition rate of complete oxide film using reactive gas flow modulation. The model dealt with the preparation of TiO2 film with a titanium target and oxygen in rf reactive sputtering. The computed results showed good agreements with the experimental data obtained in our previous work. The effects of the flow modulation were elucidated with the calculated timewise variations for partial oxygen pressure and target coverage. The effects of modulation patterns were also evaluated using the simulation. © 1996 American Vacuum Society
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81.15.Cd Deposition by sputtering

Compact‐heating stage for use in sputtering in active oxygen gas environments

Y. Igarashi, Y. Fujino, and T. Takahashi

J. Vac. Sci. Technol. A 14, 2235 (1996); http://dx.doi.org/10.1116/1.580052 (3 pages)

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An easily movable compact heating stage for heating substrates in an oxidizing atmosphere up to a temperature of about 700 °C is described. A resistive heating element of Kanthal (72.5Fe‐22Cr‐5.5A1 wt %) wire is used. The heating element is mounted inside a stainless steel vessel to isolate it from active oxygen gas environments. The vessel is assembled in air of one atmospheric pressure at room temperature. Substrates are contacted for heating on the top plane of the vessel with a stainless steel substrate holder. In order to show the performance of the heating stage, the resistive transition property of a single crystal YBa2Cu3O7–x thin film formed by rf magnetron sputtering on a MgO (100) substrate heated by this stage is demonstrated. © 1996 American Vacuum Society
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07.20.-n Thermal instruments and apparatus
81.15.Cd Deposition by sputtering
74.78.-w Superconducting films and low-dimensional structures

Low‐temperature growth of aluminum nitride thin films on silicon by reactive radio frequency magnetron sputtering∗

Chien‐Chuan Cheng, Ying‐Chung Chen, Horng‐Jwo Wang, and Wen‐Rong Chen

J. Vac. Sci. Technol. A 14, 2238 (1996); http://dx.doi.org/10.1116/1.580053 (5 pages) | Cited 10 times

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Low‐temperature growth of c‐axis oriented aluminum nitride (AlN) thin films on silicon (Si) substrates by reactive rf magnetron sputtering was investigated. The structural and morphological characterizations determined by x‐ray diffraction (XRD) measurement and scanning electron microscopy (SEM) were found to be sensitive to the deposition conditions, such as sputtering pressure, rf power, substrate temperature, and N2 concentration. A strong AlN (002) preferred orientation perpendicular to the substrate surface was identified at substrate temperatures as low as 150 °C by XRD and a densely pebble‐like surface texture of c‐axis oriented AlN thin films was observed by SEM. The cross‐sectional SEM photograph of AlN thin film showed a high degree of alignment of the columnar structure with c‐axis preferred orientation. The selected‐area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. © 1996 American Vacuum Society
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81.15.Cd Deposition by sputtering
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.-a Thin film structure and morphology

Physical properties and chemical states of rf sputter deposited SiWOx films

Itaru Shibata, Toshikazu Nishide, and Toshinori Hasegawa

J. Vac. Sci. Technol. A 14, 2243 (1996); http://dx.doi.org/10.1116/1.580054 (4 pages) | Cited 3 times

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Tungsten oxide films containing silicon oxide (SiWOx) as solar control materials were deposited by rf sputtering using Si10W90 and Si50W50 targets. The resistivity and transmittance in the near‐infrared region of all the films increased as the O2/Ar ratio increased. Resistivities from 0.86 Ω cm to 2.27×104 Ω cm were obtained depending on the target used and O2/Ar ratio. The oxidation states of tungsten in the films were estimated by curve fitting XPS spectra. When the films were deposited using a target with a smaller amount of Si (Si10W90), the chemical state of W was similar to that in WOx films. However, lower and novel chemical states of W (W5+, W4+, and W3+) were present when the films were deposited using a target with a larger amount of Si (Si50W50). © 1996 American Vacuum Society
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Cd Deposition by sputtering
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.61.-r Electrical properties of specific thin films

Formation of high temperature phases in sputter deposited Ti‐based films below 100 °C

J. Musil, A. J. Bell, J. Vlček, and T. Hurkmans

J. Vac. Sci. Technol. A 14, 2247 (1996); http://dx.doi.org/10.1116/1.580055 (4 pages)

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This article reports on the sputtering of pure Ti and Ti‐based alloy films onto substrates where the temperature Ts was kept below 100 °C, using the magnetron sputter ion plating process. It was found that while the pure Ti film is a hexagonal low‐temperature phase film (h–αTi), the Ti–Cr, and Ti–Fe alloy films, containing a relatively small amount of Cr or Fe of about 10 wt %, are cubic high‐temperature beta phase Ti alloy films [c‐βTi(Cr) or c‐βTi(Fe)]. This finding is of immense importance both scientifically and practically. The conditions under which high‐temperature phases are formed in alloy films sputtered at substrate temperatures below 100 °C, which is much lower than the temperature necessary to form these high‐temperature phases (Thtp) according to the equilibrium phase diagram, will be discussed in detail. X‐ray diffraction analyses of these films will also be presented. © 1996 American Vacuum Society
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68.55.Nq Composition and phase identification
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys

Cu (In,Ga)Se2 thin films and solar cells prepared by selenization of metallic precursors

Bülent M. Başol, Vijay K. Kapur, Arvind Halani, Craig R. Leidholm, Jon Sharp, James R. Sites, Amy Swartzlander, Richard Matson, and Harin Ullal

J. Vac. Sci. Technol. A 14, 2251 (1996); http://dx.doi.org/10.1116/1.580056 (6 pages) | Cited 4 times

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CuIn(1−x)GaxSe2 (CIGS) thin films with Ga ratio, x, ranging from 0.55 to 0.75 were grown on Mo/glass substrates by the selenization of metallic precursors in a H2Se atmosphere. Without a postdeposition annealing step the films were found to have a highly graded composition that became Ga rich near the absorber/Mo interface. A high‐temperature annealing step promoted diffusion of Ga to the surface region of the films. These absorbers were used to fabricate glass/Mo/CIGS/CdS/ZnO thin‐film solar cells with open‐circuit voltages ranging from 0.4 to 0.74 V and efficiencies approaching 12%. Devices, as well as the absorber layers, were characterized. © 1996 American Vacuum Society
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84.60.Jt Photoelectric conversion
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Hd Other semiconductors

Analysis of aluminum nitride epitaxial growth by low pressure metal organic chemical vapor deposition

R. C. Buggeln, M. Meyyappan, and S. J. Shamroth

J. Vac. Sci. Technol. A 14, 2257 (1996); http://dx.doi.org/10.1116/1.580057 (6 pages) | Cited 1 time

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Epitaxial growth of aluminum nitride films by low pressure metal organic chemical vapor deposition is modeled. The feed gas mixture consists of trimethyl aluminum, ammonia, and hydrogen. The governing fluid flow, energy, and species conservation equations are solved numerically in two dimensions. The effects of process variables on growth characteristics is investigated in the mass transport limited regime. Results are presented in terms of flow patterns, species distributions, and growth parameters for various reactor pressures and growth temperatures. In the low pressure regime (50–150 Torr) the growth rate is nearly independent of temperatures between 600 and 1200 °C. The growth rate increases approximately linearly with pressure at 1200 °C. © 1996 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Preparation and characterization of a well‐ordered surface on a Si(001) substrate with a buried metal layer for application of infrared reflection spectroscopy

Yoshihiro Kobayashi, Koji Sumitomo, Kuniyil Prabhakaran, and Toshio Ogino

J. Vac. Sci. Technol. A 14, 2263 (1996); http://dx.doi.org/10.1116/1.580058 (6 pages) | Cited 2 times

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The preparation and characterization of an atomically flat and well‐ordered surface on the Si(001) substrate with a buried metal layer (BML) are reported. The BML substrate was formed by implantation of Co+ ion and subsequent annealing. After molecular beam epitaxy growth of the Si overlayer on the cleaned BML sample in ultrahigh vacuum, clear 2×1 patterned and ordered steps with regular terrace width were observed by reflection high energy electron diffraction and atomic force microscopy. No contamination, including Co, was observed in the spectra of Auger electron spectroscopy and x‐ray photoelectron spectroscopy. Ultraviolet photoelectron spectra showed a distinct surface peak that originated from surface dangling bonds and is characteristic of a clean and ordered surface. The surface atomic structure, including stress and damage caused by ion implantation, was characterized by medium energy ion scattering (MEIS). Very low χmin (1.7% with 300 keV H+) and a dip pattern in blocking profile in the MEIS spectra indicate that surface crystal quality is comparable to that of a homoepitaxially grown Si layer on normal Si substrate without BML. These results show that the BML substrate obtained by the procedure is quite useful for the structural investigation of surface species on Si by infrared (IR) reflection spectroscopy. Typical examples of IR spectra qualifying the BML substrate for surface studies are also presented. © 1996 American Vacuum Society
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.60.Dp Adsorbed layers and thin films
78.30.Am Elemental semiconductors and insulators

Investigation of deep levels in ZnSe:Cl films grown by molecular beam epitaxy

L. Hernández, O. de Melo, M. Meléndez‐Lira, Z. Rivera‐Alvarez, and I. Hernández‐Calderón

J. Vac. Sci. Technol. A 14, 2269 (1996); http://dx.doi.org/10.1116/1.580059 (6 pages) | Cited 4 times

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Using ZnCl2 as a doping source, we have grown epitaxial layers of Cl‐doped ZnSe onto GaAs(100) substrates at a temperature of 285 °C by molecular beam epitaxy. The carrier concentration was controlled by the ZnCl2 source temperature. The maximum carrier concentration obtained was 1.2×1019 cm−3 with a resistivity of 2.7×10−3 Ω cm. Higher doses of Cl atoms tend to decrease free carrier concentration and introduce additional defects; this effect was consistent with an increase of deep‐level photoluminescence emission. From deep‐level transient spectroscopy measurements we determined the presence of four traps with energy levels Ec around 0.50, 0.68, 0.74, and 1.20 eV. The last three traps have not been previously reported. One of them, Ec∼0.74 eV, presents a clear dependence with Cl concentration and thus can affect the performance of ZnSe:Cl‐based devices. The microscopic nature of these traps is discussed in terms of Zn vacancies (VZn) and VZn–Cl complexes. © 1996 American Vacuum Society  
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71.55.Gs II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors

Surface‐extended x‐ray absorption fine structure study of silicon deposited onto GaAs(110)

M. L. Hasnaoui, A. M. Flank, M. Pompa, and P. Lagarde

J. Vac. Sci. Technol. A 14, 2275 (1996); http://dx.doi.org/10.1116/1.580060 (7 pages)

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The system Si/GaAs(110) was studied by surface extended x‐ray absorption fine structure at the silicon K edge, starting from a 0.5 monolayer (ML) coverage up to 3 ML. At very low coverages, the first adsorption site of the silicon has been determined to be above the center of the triangle formed by two arsenic and one gallium surface atoms. The growth mode of silicon on this surface obeys a modified version of the Stranski–Krastanov model: the formation of three‐dimensional clusters appears at 2.5 ML and involves all the deposited silicon atoms. © 1996 American Vacuum Society
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
68.35.Ct Interface structure and roughness

Adsorption controlled Si(1−x)Gex growth during chemical vapor deposition

H. Kühne, A. Fischer, Th. Morgenstern, and P. Zaumseil

J. Vac. Sci. Technol. A 14, 2282 (1996); http://dx.doi.org/10.1116/1.580061 (7 pages) | Cited 1 time

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The present investigation concerns Si(1−x)Gex thin film growth that, at certain deposition conditions, is characterized by nonlinearity in the partial growth rate of germanium versus the increase of the germane (GeH4) content in the reaction gas mixture. A linear increase had previously been understood as caused by a reaction rate limited growth mechanism. The nonlinear increase of the partial growth rate of germanium versus the GeH4 partial pressure will be explained by means of an adsorption controlled growth mechanism based on competitive adsorption of both silane and germane. Transition from one to the other growth mechanism is possible as shown by the discussion of corresponding experimental growth results. © 1996 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Visualization of a buried organic interface by imaging time‐of‐flight secondary ion mass spectrometry and scanning Auger microprobe of an ion‐beam crater edge

Patrick C. Schamberger, Gary L. Jones, Joseph A. Gardella, Patrick J. McKeown, and Larry E. Davis

J. Vac. Sci. Technol. A 14, 2289 (1996); http://dx.doi.org/10.1116/1.580062 (14 pages) | Cited 2 times

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A method has been developed for chemically imaging a buried organic interface of thickness similar to that of a biological conditioning film. Using an ion beam to form a sputter crater, elemental analysis of the edge of the crater is performed using Auger electron spectroscopy and chemical imaging of the edge is performed by time‐of‐flight secondary ion mass spectrometry. The crater edge that is formed due to the shape of the ion beam and geometry of the spectrometer has the ability to magnify the interfaces by 1000×. Samples mimicking titanium bone implant protheses were analyzed to demonstrate the feasibility of the method. © 1996 American Vacuum Society
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87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Cleaning thin‐film diamond surfaces for device fabrication: An Auger electron spectroscopic study

Bhaswar Baral, Simon S. M. Chan, and Richard B. Jackman

J. Vac. Sci. Technol. A 14, 2303 (1996); http://dx.doi.org/10.1116/1.580063 (5 pages) | Cited 17 times

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Auger electron spectroscopy was used to analyze polycrystalline thin‐film diamond surfaces following the use of differing methods for the removal of unwanted nondiamond carbon. Exposing the film to a hydrogen plasma at the termination of the growth process is effective for producing a surface that gives an Auger spectrum typical of diamond with little contamination. Strongly oxidizing solutions involving sulfuric acid generate low concentrations of surface sulfur together with an oxide phase. However, in the case of an ammonium persulfate–sulfuric acid etchant solution, the Auger features associated with the diamond more closely resemble those of single crystal material suggesting that this treatment may offer better performance when used during the fabrication of thin‐film diamond electronic devices. © 1996 American Vacuum Society
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81.65.Cf Surface cleaning, etching, patterning
81.05.ub Fullerenes and related materials
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Isothermal hydrogen desorption from the diamond (100)2×1 surface

M. McGonigal, M. L. Kempel, M. S. Hammond, and K. D. Jamison

J. Vac. Sci. Technol. A 14, 2308 (1996); http://dx.doi.org/10.1116/1.580064 (7 pages) | Cited 3 times

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Isothermal desorption experiments to study the kinetics of the desorption of hydrogen from the diamond (100)2×1 surface are described. The surface hydrogen concentrations are measured using direct recoil spectroscopy, an ion spectroscopy in which ions and neutral species recoiled from the surface are detected by time‐of‐flight measurements. Results indicate that the desorption of hydrogen from diamond (100) is zeroth order at temperatures below 800 °C and changes to first order above 825 °C. In the first‐order region, the measured activation barrier is 39 kcal/mol and the pre‐exponential factor is 3.2×105 s−1. © 1996 American Vacuum Society
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Time‐resolved mass spectrometry in rough vacuum environment

J. Laimer, O. Schnabl, C. G. Schwärzler, and H. Störi

J. Vac. Sci. Technol. A 14, 2315 (1996); http://dx.doi.org/10.1116/1.580065 (10 pages) | Cited 1 time

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A specially constructed helium flushed probe system was developed in order to ensure a quick transport of species extracted from a process gas at a few tens of mbar to a quadrupole mass spectrometer. The amount of extracted process gas can be adjusted by the setting of the helium gas flow. The time response of the probe system was simulated and compared with measurements performed on a pulsed hydrogen‐deuterium discharge. The probe system is characterized by a delay time of a few tens of ms depending on the process pressure and a time resolution of about 20 ms. A decrease of the time resolution to values well below 10 ms is possible. © 1996 American Vacuum Society
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
07.75.+h Mass spectrometers
52.70.Nc Particle measurements

Thermal stability of photochemical native oxide films on Hg1−xCdxTe

G. H. Winton, N. Warrington, and L. Faraone

J. Vac. Sci. Technol. A 14, 2325 (1996); http://dx.doi.org/10.1116/1.580017 (6 pages) | Cited 1 time

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Heat treatments were carried out on native oxide films grown on Hg1−xCdxTe by a photochemical process. The thermal stability of such layers was assessed by monitoring changes in depth profiles obtained from x‐ray photoelectron spectroscopy in conjunction with argon ion sputtering. After annealing, photochemical oxides grown in N2O showed a large change in the oxide/Hg1−xCdxTe interface width and a movement of the Cd and Te interfaces towards the oxide surface. These results are comparable to previous studies carried out on anodically grown oxides by other workers. For photochemical oxides grown in an O2 ambient at slightly higher temperatures, the oxide/Hg1−xCdxTe interface was observed to be very stable under the same annealing conditions, with no observable change in the oxide/Hg1−xCdxTe interface width and no movement of the individual element interfaces. For both the N2O and O2 grown oxides, there was a significant loss of Hg from the oxide for extended annealing at 250 °C in a vacuum of 10−5 Torr. © 1996 American Vacuum Society
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68.60.Dv Thermal stability; thermal effects
81.65.Rv Passivation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Numerical ellipsometry: Applications of a new algorithm for real‐time, in situ film growth monitoring

Frank K. Urban and John Craig Comfort

J. Vac. Sci. Technol. A 14, 2331 (1996); http://dx.doi.org/10.1116/1.580018 (6 pages)

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The equations associated with the popular models of film deposition of a material on a substrate tend not to be invertible in practical situations. Thus development of numerical techniques for obtaining approximate solutions to these equations has become necessary. At present, real‐time, in situ thin film growth ellipsometry data are limited to a single angle of incidence due to the deposition system windows. The 2C algorithm, developed by the authors, represents a new approach to solve this problem. This algorithm is fast enough for reliable real‐time solutions without requiring either accurate initial estimates or any off‐line processing. Algorithm 2C employs the techniques of dynamic step adjustment, overrelaxation, and reduction in dimension, as well as curve following and curve intersection location techniques developed by the authors. The algorithm was originally developed for nickel deposited on BK7 glass, and in this article it is applied to silver, silicon, and gold depositions on BK7 glass. Gold films could be solved readily with no changes, while problems with convergence were encountered with some silver measurements and silicon data required changes in the ‘‘standard’’ initial estimate. © 1996 American Vacuum Society
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78.20.Bh Theory, models, and numerical simulation
78.66.Bz Metals and metallic alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Molecular beam sampling to analyze the reaction mechanism of chemical vapor deposition

Y. Tsutsumi, M. Ikegawa, T. Usui, Y. Ichikawa, K. Watanabe, and J. Kobayashi

J. Vac. Sci. Technol. A 14, 2337 (1996); http://dx.doi.org/10.1116/1.580019 (6 pages) | Cited 2 times

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In order to understand the chemical vapor deposition (CVD) reaction mechanism, forming a thin film from the gas phase, it is important to identify the intermediate chemical active species (radicals) for each reaction. Radicals generally have very short lifetimes; therefore, it is very difficult to detect them. Molecular beam sampling (MBS) is a method that can extract radicals in the gas phase using free jet expansion. A vacuum system using a MBS method was designed to analyze the CVD reaction mechanism in the gas phase near the surface of the wafer. The system consists of a thermal flow‐through type CVD reactor and three differential pumping vacuum chambers with a quadrupole mass analyzer. The performance of the MBS system was tested with various gases. The system was applied to detect radicals produced in the region near the wafer in a thermal TEOS/O3 (tetraethylorthosilicate) CVD reaction to deposit SiO2 thin films. It is proved that the radicals, from which ethoxy bases of TEOS are extracted, are formed in the gas phase and can play an important role in the thermal TEOS/O3 CVD reaction. © 1996 American Vacuum Society
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37.20.+j Atomic and molecular beam sources and techniques
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Infrared diode laser absorption spectroscopy measurements of CFX (X=1–3) radical densities in electron cyclotron resonance plasmas employing C4F8, C2F6, CF4, and CHF3 gases

Koji Miyata, Masaru Hori, and Toshio Goto

J. Vac. Sci. Technol. A 14, 2343 (1996); http://dx.doi.org/10.1116/1.580020 (8 pages) | Cited 30 times

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Infrared diode laser absorption spectroscopy was used for measuring CFX (X=1–3) radical densities in electron cyclotron resonance plasmas employing C4F8, C2F6, CF4, and CHF3 gases commonly used for the plasma etching of silicon dioxide. CFX (X=1–3) radical densities in these plasmas were measured systematically together with CHF3 and CF4 molecular densities as a function of microwave power and as a function of H2 dilution. Furthermore, variations of F atom densities in these plasmas were also investigated by the actinometry technique. The differences in the radical and atomic densities according to fluorocarbon feed gases are discussed based on their molecular structures and atomic component ratios (carbon/fluorine and hydrogen/fluorine). © 1996 American Vacuum Society
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
81.65.Cf Surface cleaning, etching, patterning
52.80.Pi High-frequency and RF discharges

Atomic force microscopy of amorphous hydrogenated carbon–nitrogen films deposited by radio‐frequency‐plasma decomposition of methane–ammonia gas mixtures

R. Prioli, S. I. Zanette, A. O. Caride, D. F. Franceschini, and F. L. Freire

J. Vac. Sci. Technol. A 14, 2351 (1996); http://dx.doi.org/10.1116/1.580021 (5 pages) | Cited 11 times

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Atomic force microscopy was used for the surface characterization of hard amorphous hydrogenated carbon–nitrogen films deposited by plasma enhanced chemical vapor deposition. The films were deposited onto silicon substrates by rf‐plasma decomposition of methane–ammonia mixtures. The film roughness and the friction coefficient between the silicon nitride tip and the film surface were determined. The results indicate that the surface roughness increases with the amount of nitrogen incorporated in the film. The friction coefficients, measured in air, are almost constant for nitrogen incorporation up to 11 at. %. © 1996 American Vacuum Society
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

In situ wafer temperature monitoring of silicon etching using diffuse reflectance spectroscopy

J. L. Booth, B. T. Beard, J. E. Stevens, M. G. Blain, and T. L. Meisenheimer

J. Vac. Sci. Technol. A 14, 2356 (1996); http://dx.doi.org/10.1116/1.580022 (5 pages) | Cited 2 times

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Real time, in situ temperature measurements during chemical downstream etching of silicon wafers have been performed using a diffuse reflectance spectroscopy based sensor [Weilmeier et al., Can. J. Phys. 69, 422 (1991)]. The spectrometer has a spatial resolution of 1 cm2, updates the temperature every 2 s, and has a temperature resolution of better than 1 °C. The thermal time constant the wafers and the thermally regulated electrostatic chuck (10 °C<T<90 °C) varied between 7 and 30 s depending on clamping and backside gas pressure. The exothermic etch process is accompanied by increases in the silicon wafer temperature consistent with the thermal conductivity conditions and with the etch chemistry. The temperature uniformity across the wafers was better than 2 °C during the entire etch process. © 1996 American Vacuum Society
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07.20.Dt Thermometers
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.Cf Surface cleaning, etching, patterning

Relative sensitivity factors of B related to SiGe alloy composition on secondary ion mass spectrometry with an oxygen primary ion beam

Kiyohisa Fujinaga

J. Vac. Sci. Technol. A 14, 2361 (1996); http://dx.doi.org/10.1116/1.580023 (5 pages)

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This paper describes the useful yields of positive 11B, 28Si, and 70Ge ions produced from the surface of B‐doped Si1−xGex alloys when the surface is irradiated by an 8 keV positive O2 ion beam. Boron doping into alloys was done by implanting 11B ions with an energy of 30 keV at a dose of 1×1015 cm−2. The reactive sensitivity factors (RSFs) of 11B to the matrix isotopes of 28Si or 70Ge are determined using the useful yields, and the relationships between the RSFs and the alloy compositions are shown. Also described are the RSFs of 11B estimated from the local thermal equilibrium model with two internal standard elements of Si and Ge. The theoretical RSFs were a factor of 3–4 greater than the experimental RSFs. © 1996 American Vacuum Society
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.up Other materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Surface chemical reaction between polycarbonate and kilo‐electron‐volt energy Ar+ ion in oxygen environment

Won‐Kook Choi, Seok‐Keun Koh, and Hyung‐Jin Jung

J. Vac. Sci. Technol. A 14, 2366 (1996); http://dx.doi.org/10.1116/1.580024 (6 pages) | Cited 4 times

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In order to improve wettability of polycarbonate to triple distilled water, an Ar+ ion and an oxygen ion were irradiated on a polycarbonate (PC) surface under various oxygen flow rates. Doses of ions were changed from 5×1014 to 5×1016 ion/cm2 in a range from 500 eV to 1.5 keV energy by a broad ion beam source. Wetting angle of PC was not reduced much with only Ar+ irradiation, but the wetting angle was significantly decreased by Ar+ ion irradiation with flowing oxygen gas and had a minimum of 12° by 1 keV Ar+ ion irradiation at oxygen flow rate of 4 sccm. Change in wettability by O+2 ion irradiation shows the similar feature as compared with those of Ar+ ion irradiation. In atomic force microscopy study, root mean square of surface roughness was changed from 14 to 22–27 Å by Ar+ ion irradiation, to 26–30 Å by Ar+ ion irradiation with the oxygen flow, but did not depend on amounts of ion fluence which indicates that the wetting angle change was not influenced by surface morphology. Improved wettability of modified polymer surface is explained in terms of a two‐step process. Formation of hydrophilic groups on the polymer was identified by Fourier transform infrared and by the increase of carbonyl oxygen peak in O 1s x‐ray photoemission spectroscopy spectra of PC in the sample modified by Ar+ ion irradiation with the oxygen flow. © 1996 American Vacuum Society
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
34.35.+a Interactions of atoms and molecules with surfaces
68.08.Bc Wetting

Interaction of water with clean and gallium precovered Fe(111) surfaces

P. Jiang, M. W. Zappone, Steven L. Bernasek, and A. Robertson

J. Vac. Sci. Technol. A 14, 2372 (1996); http://dx.doi.org/10.1116/1.580025 (6 pages)

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The interaction of water with the clean Fe(111) surface and that surface modified by small coverages of Ga has been investigated. Both thermal energy atom scattering and Auger electron spectroscopy have been used to probe this interaction. Water adsorption occurs via a molecular precursor state on these surfaces, and a passivated overlayer is formed on the clean surface exposed to water at 423 K. Small amounts of Ga precoverage, from the decomposition of triethyl gallium, strongly affect the subsequent water adsorption. Preadsorbed gallium reduces the molecular water sticking coefficient and inhibits water dissociation. This effect is proportional to the Ga precoverage. Electron beam irradiation during Auger measurement also strongly affects the water adsorption on the clean and Ga modified surface, and this effect is discussed. © 1996 American Vacuum Society
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.50.Kx Processes caused by X-rays or γ-rays

Microtribological studies of unlubricated and lubricated surfaces using atomic force/friction force microscopy

Vilas N. Koinkar and Bharat Bhushan

J. Vac. Sci. Technol. A 14, 2378 (1996); http://dx.doi.org/10.1116/1.580026 (14 pages) | Cited 24 times

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Microtribological studies were performed on unlubricated and lubricated (Z‐15 and Z‐DOL with hydroxyl end groups) silicon, double grafted C18 layer, Langmuir–Blodgett (LB) film, gold film and mica samples in ambient, dry nitrogen and dry air environments using atomic force/friction force microscopy (AFM/FFM). A sharp tip of AFM/FFM sliding on a surface simulates a single asperity contact. The silicon samples lubricated with Z‐15 and Z‐DOL lubricant films exhibit lower coefficient of microfriction than that of the unlubricated silicon sample. Microfriction values are lower than that of the macrofriction. Ploughing contribution is responsible for the higher macrofriction values. The microfriction experiments on bare silicon and lubricated with Z‐15 and Z‐DOL carried out in dry nitrogen and dry air exhibit lower coefficient of microfriction values than those in ambient atmosphere measurements. Dewetting of the liquid film in a humid environment is believed to be responsible for higher microfriction. The dependence of scanning velocity on microfriction was studied and it was found that the friction force decreases with an increase in the scanning velocity for the liquid‐lubricated samples in the humid environment and it is relatively insensitive to scanning velocity in dry environments. Alignment of liquid molecules (shear thinning) is believed to be responsible for the drop in microfriction at high scanning velocities. Micro‐ and nanowear tests reveal that the chemically bonded Z‐DOL lubricant is more durable than the Z‐15, double grafted C18, LB and gold films. © 1996 American Vacuum Society  
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81.40.Pq Friction, lubrication, and wear
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Comparison of submicron particle analysis by Auger electron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and secondary electron microscopy with energy dispersive x‐ray spectroscopy

Kenton D. Childs, David Narum, Lori A. LaVanier, Patricia M. Lindley, Bruno W. Schueler, George Mulholland, and Alain C. Diebold

J. Vac. Sci. Technol. A 14, 2392 (1996); http://dx.doi.org/10.1116/1.580027 (13 pages) | Cited 6 times

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Particulate contamination can result in a significant yield loss during semiconductor device fabrication. As device design rule dimensions decrease the critical defect size also decreases, resulting in the need to analyze smaller defects. Current manufacturing requirements include analysis of sub‐0.5‐μm defects, with analysis of sub‐0.1‐μm defects expected in the near future. This article investigates the particle analysis capabilities of Auger electron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and energy dispersive x‐ray spectroscopy during scanning electron microscopy (SEM/EDS). In order to evaluate each method carefully, a standard set of samples was prepared and analyzed. These samples consist of 0.5‐, 0.3‐, and 0.1‐μm Al and Al2O3 deposited on 1‐in. Si wafers. Although all the methods observed an Al signal, a semiquantitative gauge of capability based on the relative strengths of particle versus substrate signal is provided. The dependence of the sample‐to‐substrate signal on primary electron energy is examined for both EDS and Auger analyses. The ability to distinguish metallic Al particles from Al oxide particles for the three techniques is also discussed. © 1996 American Vacuum Society
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82.80.-d Chemical analysis and related physical methods of analysis
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Recoil spectrometry of thin film reactions in the Pd/InP system

Leif Persson, Mohamed El Bouanani, Mikael Hult, Patrik Jönsson, Harry J. Whitlow, Margaretha Andersson, Kristina Georgsson, Ian F. Bubb, Peter N. Johnston, Scott R. Walker, David D. Cohen, Nick Dytlewski, Carina Zaring, and Mikael Östling

J. Vac. Sci. Technol. A 14, 2405 (1996); http://dx.doi.org/10.1116/1.580028 (9 pages) | Cited 1 time

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Interfacial reactions between (100) InP and Pd were investigated as part of a systematic study aimed at investigating the stability of planar nonalloyed metallizations to InP. A 50‐nm‐thick Pd film was deposited on an InP substrate, and parts of it were subsequently thermally treated for 30 min at temperatures varying from 100 to 500 °C in steps of 50 °C. Separate characterizations of the Pd, In, and P depth distributions were obtained using mass and energy dispersive recoil spectrometry. The different phases were determined using x‐ray diffraction, and scanning electron microscopy was used to study the surface topography. It is assumed that the interaction starts in the as‐deposited sample, and definite formation of a ternary phase with the suggested composition Pd5In2P2 starts at an annealing temperature of 100 °C. At 250 °C all Pd is chemically reacted. Preferential outdiffusion of P leads to a loss of P from the surface at 500 °C, and the only phase observed in the x‐ray diffraction spectrum from the surface is PdIn. © 1996 American Vacuum Society
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
82.80.-d Chemical analysis and related physical methods of analysis

Focusing glass capillary array molecular beam inlet for a high sensitivity mass spectrometer system

Y. Ma, B. Y. H. Liu, H. S. Lee, K. Mauersberger, and J. Morton

J. Vac. Sci. Technol. A 14, 2414 (1996); http://dx.doi.org/10.1116/1.580029 (4 pages) | Cited 4 times

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A molecular beam is formed using a focusing glass capillary array to serve as the gas inlet of a mass spectrometer beam system. The glass disk has a diameter of 13 mm. The number of pores in the capillary array is about a half‐million. The pore diameter is 10 μm and the pore length is 0.5 mm. The focal length of the glass capillary array is 9.5 cm. Results show that within the 0–30 mTorr input range, the molecular beam intensity is proportional to the inlet pressure. High sample transmission is obtained for low pressure gas input. Beyond this range, the beam intensity levels off rapidly. As opposed to the orifice beam formation, a relatively narrow operational window exists which limited the ability of the capillary array to obtain high sample transmission efficiency for high pressure gas input applications. © 1996 American Vacuum Society
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07.77.Gx Atomic and molecular beam sources and detectors
07.75.+h Mass spectrometers

Physical properties of diamondlike carbon films deposited in mixed atmospheres of C2H4–Ar, C2H4–H2, and C2H4–N2

Masatoshi Nakayama, Yasuhiro Matsuba, Junichi Shimamura, Yasuyuki Yamamoto, Hiroshi Chihara, Hideo Kato, Kazunori Maruyama, and Kiichiro Kamata

J. Vac. Sci. Technol. A 14, 2418 (1996); http://dx.doi.org/10.1116/1.580030 (9 pages) | Cited 2 times

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Diamondlike carbon films were deposited in a pure C2H4 atmosphere and in mixed atmospheres of C2H4–Ar, C2H4–H2, and C2H4–N2 by radio frequency plasma chemical vapor deposition. The partial pressures of Ar, H2, and N2 were 25%, 50%, and 66.7%, respectively. The films were deposited with a high negative bias of −610 V. The hardness, the density, and the internal stress of the films decrease and the amount of gas evolution increases with increasing partial pressures of N2 and H2, while they do not depend on the partial pressure of Ar. These results show that N2 and H2 react with carbon in the films and decrease the degree of the crosslinking in the network structure, while Ar does not change the degree of crosslinking. The surface is very flat and the roughness (Rmax) is below 1 nm. The hardness is 40 GPa for the films deposited in atmospheres of pure C2H4 and mixed C2H4–Ar with a bias of −610 V. © 1996 American Vacuum Society
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Conductance and leakage in superconducting tunnel junctions

M. S. Goodchild, Z. H. Barber, and M. G. Blamire

J. Vac. Sci. Technol. A 14, 2427 (1996); http://dx.doi.org/10.1116/1.580031 (6 pages) | Cited 2 times

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We report an analysis of data from Nb/AlOx/Nb tunnel junctions. We show that both conductance and subgap leakage follow simple scaling laws as a function of oxidation conditions. The leakage effects are discussed in terms of a simple physical model of tunnel barrier inhomogeneity that is also applicable to directly deposited barriers on NbN. We demonstrate that an improvement in barrier properties can be achieved by the use of a buffer layer overlying the barrier, and that this improvement is consistent with a model based on resputtering effects. © 1996 American Vacuum Society
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85.25.Am Superconducting device characterization, design, and modeling
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Schottky barrier at the Au/Gap (110) interface

M. Fanfoni, C. Goletti, P. Chiaradia, W. Ng, F. Cerrina, Y. Hwu, A. Terrasi, and G. Margaritondo

J. Vac. Sci. Technol. A 14, 2433 (1996); http://dx.doi.org/10.1116/1.580032 (4 pages)

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The Schottky‐barrier formation of the Au/GaP (110) interface has been investigated by photoemission, in the presence of large surface photovoltage effects induced by the intense photon beam of a synchrotron‐radiation source. The surface photovoltage has been measured with a Kelvin probe. The largest surface photovoltage shift observed in the photoemission spectra was almost 1 eV. The Schottky barrier appears to be fully established at about 8 Å, while the surface photovoltage does not disappear until about 16 Å. The Schottky‐barrier height is 1.35±0.1 eV. The Kelvin‐probe results demonstrate directly that the photoemission data must be corrected for the surface photovoltage during the formation of the barrier but are insensitive to it once full coverage is obtained. © 1996 American Vacuum Society
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.Dp Adsorbed layers and thin films

Characterization of as‐grown and annealed thin SiO2 films formed in 0.1 M HCl

E. M. Allegretto and J. A. Bardwell

J. Vac. Sci. Technol. A 14, 2437 (1996); http://dx.doi.org/10.1116/1.580033 (6 pages) | Cited 3 times

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Anodic oxidation at constant voltage has been used to produce oxide films of thickness 10–440 Å on Si(100). The electrolyte was 0.1 M HCl. Both annealed and as‐grown samples were characterized by ellipsometry and Fourier transform infrared spectroscopy (FTIR), as well as by etch rate measurements in dilute HF. For as‐grown samples, the voltage dependence of the thickness was determined. FTIR results for the as‐grown films showed that the properties were dependent on the oxide thickness and not directly on the formation voltage. These results also provided a basis of comparison for the annealed samples. Demonstrably higher quality oxide films were characteristic of the annealed samples in comparison to the as‐grown samples. The higher quality of the annealed samples was confirmed by measurement of the etch rate.