AVS2001 Session TF-FrM: Diamond and Related Materials

Friday, November 2, 2001 8:20 AM in Room 123

Friday Morning

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8:20 AM		TF-FrM-1 Synthesis and Characterization of Highly Conducting Nitrogen Doped Ultrananocrystalline Diamond Films J. Birrell, O. Auciello, S. Bhattacharyya, J.A. Carlisle, L.A. Curtiss, A.N. Goyette, D.M. Gruen, J. Schlueter, A.V. Sumant, P. Zapol (Argonne National Laboratory) Diamond has many superior materials properties, yet its application in electronic devices is severely limited due to the difficulty of producing n-type thin films of sufficiently high conductivity. In this work ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma enhanced chemical vapor deposition (MPCVD) method using a CH₄ (1%)/Ar gas mixture with 1-20% nitrogen gas added. CN and C₂ radicals are identified in the plasma and both their relative and absolute concentrations change as N₂ gas is added. The morphology and transport properties of the films are both greatly affected by the presence of CN. High-resolution TEM data indicated that the grain size and GB width increase with the addition of more than 5% N₂ in the plasma. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω^-1 cm^-1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films, in which nitrogen segregates to the grain-boundaries and promotes sp² bonding and the introduction of more states into the fundamental gap, leading to enhanced electron transport. Work supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract W-31-109-ENG-38.
8:40 AM		TF-FrM-2 Probing Surface Species on a Diamond C(111) Surface During the Chemical Vapour Deposition of Diamond A. Heerwagen, M.T. Strobel, M. Himmelhaus (University of Heidelberg, Germany); M. Buck (University of St Andrews, Scotland) The bottleneck in the accurate modeling of the diamond growth by chemical vapour deposition (CVD) is the lack of knowledge of the surface species and chemistry. In contrast to the gas phase, there is a deficit in experiment data for chemical species and reactions associated with the surface of a growing diamond film. The reason for this striking imbalance between experimental data on the gas phase and the surface lies in the diffculty to probe surface species in situ under the conditions of diamond CVD. Under these conditions, which are prohibitive for other surface science techniques we have applied IR-visible sum frequency generation (SFG) to probe the surface of a natural diamond during the CVD process, using a hot filament (HF) reactor and a gas mixture of hydrogen and methane. Monitoring the range of the C-H stretching vibrations, a single band reflecting a monohydrogen termination of the diamond substrate surface is observed under conditions which yield high quality diamond films. A decrease of the filament temperature from 2000Â°C to 1850Â°C leads to a decrease in intensity of this peak appearing around 2820 cm-1. At filament temperatures below 1800Â°C a new band at 2809 cm-1 emerges while the peak at 2820 cm-1 vanishes. Lowering the substrate temperature has a minor influence on this spectral feature but, instead, a new band at 2855 cm-1 appears. Changing the composition of the gas phase causes the intensity and frequency of the monohydrogen band to vary significantly. In particular, in a pure hydrogen atmosphere it blue-shifts to 2830 cm-1 while a pronounced increase in intensity is detected. Comparison of these results with previous SFG data obtained under ultra high vacuum reveals pronounced similarities. Furthermore, the identification of the species and surface structure associated with the peak at 2855 cm-1 seems to be vital for improving the quality of CVD diamond films grown at lower temperatures.
9:00 AM		TF-FrM-3 Structural, Mechanical and Electrical Properties of DLC Films Deposited by DC Magnetron Sputtering E. Broitman (College of William and Mary); Zs. Czigáni, L. Hultman (Linköping University, Sweden); B.C. Holloway (College of William and Mary) The microstructure, morphology, growth rate, surface roughness, surface energy, electrical and mechanical properties of diamond-like carbon (DLC) films deposited by direct current (d.c.) magnetron sputtering on Si substrates at room temperature were investigated. Film properties were found to vary markedly with the pressure (P_Ar), bias voltage (V_B), and discharge current (I_T). Plan-views HRTEM revealed an amorphous microstructure, however cross-sectional SEM shows a columnar structure at the higher V_B. Film stresses were found to be compressive in all cases, increasing from 0.5 GPa for grounded substrates to 3.5 GPa for films deposited at V_B = - 90 V and I_T = 0.3 A. Film stress was not affected by V_B at I_T = 0.9 A. The hardness (H), Young's moduli (E) and elastic recovery (R) increased with V_B to maximum values of H = 27 GPa, E = 250 GPa, and R = 68 %. With an increase in the negative bias, the resistivity ρ went through a maximum of 2.2 Ωcm at potentials around the floating potential U, while ρ decreased with the increase of pressure or discharge current. Langmuir probe measurements of the local electron temperature, density, and plasma potential as a function of Ar pressure and target current were also made at the substrate location. The properties of the films have been correlated in terms of differences in the deposition and plasma parameters.
9:20 AM		TF-FrM-4 Electron Transmission in Thin B-doped CVD Diamond Films J.E. Yater, A. Shih, J.E. Butler, P.E. Pehrsson (Naval Research Laboratory) Diamond is a promising cold emitter material for vacuum electron devices because of the negative electron affinity (NEA) observed at specific surfaces. While the NEA properties have been studied extensively, the cold emission process in diamond has not been well characterized. In this study, we inject electrons into thin CVD diamond films using a 0-20 keV electron gun, and we examine the transport and emission of low-energy secondary electrons in transmission measurements. In particular, we measure the intensity and energy distribution of transmitted electrons as a function of incident beam parameters (energy, current) and material properties (film thickness, doping concentration). A series of B-doped CVD diamond films has been grown with thickness between 1 and 7 microns, with the first sample being a lightly-doped, 2.5-micron-thick film with a NEA emitting surface (as indicated by yield measurements of ~20). For beam energies above 13 keV, the transmitted intensity is sharply peaked ~0.60 eV above the emission onset with a FWHM of ~0.60 eV. At constant beam energy (or current), the peak width, position, and emission onset remain constant as the beam current (or energy) is increased, and the peak is very similar to that obtained in reflection measurements. At beam energies below 13 keV, the transmission peak is much broader and less intense. It is possible that the light B doping impacts the transport of electrons to the front surface since a sharp peak was observed at all energies in a previous study of a more conductive 2-micron-thick film. Our ongoing studies continue to examine the role of doping and film thickness on the transmission properties of diamond films.
9:40 AM		TF-FrM-5 Influence of Nitrogen and Temperature on the Deposition of Fluorinated Amorphous Carbon Films L. Valentini, E. Braca, J. Kenny (Universita di Perugia, Italy); R.M. Montereali (Dip. Innovazione ENEA C.R. Frascati, Italy); L. Lozzi, S. Santucci (Universita dell'Aquila, Italy) Plasma deposited hydrogenated amorphous (a-C:H) carbon and fluorinated amorphous carbon films (a-C:H:F) are among the potential candidates considered for the low dielectric constant (k) interconnects. Incorporation of the low-k materials in ULSI integrated structures imposes a lot of requirements to be satisfied, among them stability at the processing temperature of 400Â°C. As deposited a-C:H:F films may be thermally stabilised, in terms of dimensional stability and material loss, by nitrogen incorporation. In this work the effect of nitrogen addition on the properties of a-C:H:F films produced by radio-frequency plasma enhanced chemical vapor deposition has been investigated. The films were studied as a function of nitrogen content and deposition temperature. The structural and optical properties were investigated by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-VIS transmittance and ellipsometry measurements. The dependence of both fluorine and nitrogen incorporation in the carbon matrix on deposition temperature has been analysed. It was found that the main effect of progressive nitrogen incorporation is a decrease of transmittance and optical band gap of the samples grown at room temperature and at 400Â°C. Raman spectra evidence that for films deposited at 400Â°C a sudden loss of sp3 carbon bonding occurs. In particular, at fixed plasma composition the decrease of the optical band gap is interpreted as a clustering of the existing sp2 carbon sites. The ellipsometry characterization indicates that nitrogen incorporation for the room temperature deposited samples induces an increase of the refractive index and suggested that carrying out a deposition at 400Â°C the films undergo a reduction of the refractive index; this has been correlated to changes in the graphitic cluster size of the network. In particular the increase in the deposition temperature produces an increase in the size of the graphitic clusters.
10:00 AM		TF-FrM-6 Investigation of Nitrogen Bonding in Amorphous Carbon Nitride W.J. Gammon (College of William & Mary); O. Kraft (Max-Planck-Institut für Metallforschung, Germany); R.L. Vold, G. Houtson, A.S. Reilly, B.C. Holloway (College of William & Mary) Previous x-ray photoelectron spectroscopy (XPS) work has shown that the N(1s) spectra of highly elastic amorphous carbon nitride (CN_x) can be resolved into two peaks positioned at ~ 398.5 and 401 eV.¹ Furthermore, the exact location and intensity of the two peaks is directly correlated to the mechanical properties of the film.² Based on XPS data and theoretical calculations, earlier work suggests that the N(1s) peak at 398.5 eV in hard and elastic CN_x, is due to nitrogen bonded to sp³ hybridized carbon.² ^- ³ This interpretation supports the phenomenological model that the mechanical properties of hard CN_x are due to the cross-linking of graphitic planes through sp³ bonded carbon.² However, we present XPS data that suggest the low binding energy N(1s) peak may be due to sp² coordinated nitrogen to carbon in an aromatic ring. Also, our data show that the N(1s) peak exhibits bonding over the whole range of possible hybridization. In fact, XPS is not sensitive enough to make unambiguous peak assignments in CN_x, and XPS exhibits no resolvable chemical shift between sp² and sp³ bonded carbon to carbon. However, nuclear magnetic resonance spectroscopy (NMR) provides better discrimination to these bonding types. Therefore, the purpose of this study is to clarify the dependence of chemical bonding on mechanical properties by using NMR data to remove the ambiguity of proposed XPS peak assignments. In this work, we present ¹³C and ¹⁵N NMR, XPS, and FTIR data on CN_x. These films were deposited on a heated Si(001) substrate by DC magnetron sputtering, and nanoindentation was used to quantify the mechanical properties. NMR results are shown for both the hard and elastic phase (deposited at temperatures > 300 ° C) and mechanically poor phase (deposited at ambient temperature). In addition, computational models will be developed concurrently from experimental data to investigate the stability of carbon/nitrogen structures. ¹ B.C. Holloway, O. Kraft, D.K. Shuh, M.A. Kelley, W.D. Nix, P. Pianetta, and S. Hagström, Appl. Phys. Lett., 74, 3290 (1999). ² N. Hellgren, M.P. Johansson, E. Broitman, L. Hultman, and J. Sundren, Phys. Rev. B, 59, 5162, (1999). ³ Å. Johansson and S. Stafström, J. Che. Phys., 111, 3203, (1999).
10:20 AM		TF-FrM-7 Structural and Physical Properties of Carbon Nitride Films with High Nitrogen Content Synthesized by Reactive Pulsed Laser Deposition J.P. Zhao, Z.Y. Chen, T. Yano, T. Ooie (National Institute of Advanced Industrial Science and Technology, Japan) Carbon nitride films with high nitrogen content were prepared by reactive pulsed laser deposition in nitrogen atmosphere. The fourth harmonic from a Q-switch Nd:YAG laser with wavelength of 266 nm and pulse duration of 10 ns was focused onto a high purity (99.99%) highly-oriented-pyrolytic-graphite (HOPG) target for producing carbon plume. The laser was pulsed at a rate of 10 Hz. Laser fluence was kept around 12.7 J/cm² during deposition. Base pressure of the deposition chamber was lower than 3x10^-7 Torr. Nitrogen gas of 99.999% purity was admitted into the chamber during deposition, with pressure varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increasing the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at.% at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning on the core level and valence band structures. With adding the nitrogen incorporation, both the binding energy and peak intensity of the core level and valence band spectra vary systematically as a function of nitrogen content in the films. Structural and physical properties were also studied by using glancing angle X-ray diffractionmeter (XRD), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, and UV-visible spectrophotometer. Some fingerprint information that show the role of nitrogen in controlling the electronic structure and physical properties of carbon nitride film were found based on these studies.
10:40 AM		TF-FrM-8 Structure and Properties of Carbon Nitride Thin Films Synthesized by Nitrogen-Ion-BeamAssisted Pulsed Laser Ablation Z.Y. Chen, J.P. Zhao, T. Yano, T. Ooie (National Institute of Advanced Industrial Science and Technology, Japan) Carbon nitride films were deposited by pulsed KrF excimer laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and four-probe resistance. The irradiation effect of the nitrogen ion beam with various ion currents on the synthesis of carbon nitride films was investigated. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the nitrogen irradiation with different ion currents during deposition. The carbon-nitrogen bonding of C-N and C=N was observed in the films. High nitrogen ion current was proposed to promote the desired sp³-hybridized carbon and the C₃N₄ phase. In addition, the tribological properties of the carbon nitride films deposited on TiN coated stainless steel substrates were also studied in both dry and oil environments, which exhibited a low friction coefficient and low wear compared to hard TiN film and commercial stainless steel.
11:00 AM		TF-FrM-9 On the Preparation of Silicon Carbonitride Compounds H. Lutz, M. Bruns (Forschungszentrum Karlsruhe, Germany); E. Theodossiu, H. Baumann (Universitaet Frankfurt/Main, Germany) Carbonitride as well as Silicon Carbonitride thin films have been the subject of great interest in recent years due to the expected improvement of surface properties for a lot of applications. Various precursor based techniques have been employed to synthezise the pure materials. However, most of these efforts result in amorphous films or tiny crystals embedded in amorphous matrices of deficient nitrogen content and considerable hydrogen and oxygen content, respectively. Very promising approaches to Si-C-N synthesis are R.F. magnetron sputtering and ion implantation providing tailored stoichiometries at high purity. Silicon carbonitrides were reactively sputtered using ¹⁵N enriched N₂/Ar sputter gas and co-sputter targets with different Si/C areas resulting in defined and reproducible Si/C ratios at constant nitrogen concentrations. Alternatively, surface modification by sequential high fluence implantation of C and N ions into silicon allows for tuning the atomic fraction of all elements over a wide range. Both techniques enable us to synthezise ternary systems of more than 52 at.% nitrogen content, which are stable up to 1000°C. The chemical composition of the Si-C-N films was characterized by means of X-ray photoelectron spectroscopy. In case of the buried implanted layers chemical binding states were attainable after sputter etching using 300 eV Ar ions of a projected range minimized to a negligible part of the XPS information depth. In addition, Auger electron spectroscopy, FTIR spectroscopy, and Raman spectroscopy were used to achieve a comprehensive characterization. For quantification XPS and AES data were calibrated with absolute concentration values from non-Rutherford backscattering spectrometry. Furthermore, both preparation techniques have the advantage that ¹⁵N and ¹³C isotopes can be introduced into the layers enabling non-destructive nuclear reaction analysis for depth profiling.
11:20 AM		TF-FrM-10 The Investigation of Homogeneity of a-SiC:H Thin Films B.G. Budaguan, A.A. Sherchenkov, E.I. Artemov (Moscow Inst. of Electronic Technology, Russian Federation) Hydrogenated amorphous silicon-carbon alloy (a-SiC:H)is an important material for device applications because of the possibility to control the optical bandgap by changing the carbon concentration. The physical properties and stability of a-SiC:H as well as device quality strongly depend on material's structural properties and, particularly, on its structural homogeneity. In this paper we determine the local chemical environment of the Si-H bond and the forms of carbon incorporation by analysing with use of chemical induction model the dependence of the Si-H stretching frequency shift on the alloy composition r=[C]/[Si]. a-SiC:H thin films were prepared by decomposition in the low frequency (55 kHz) glow-discharge plasma the gases mixture of silane and methane with varying methane fraction at substrate temperature of 320°C. Si and C atoms can be backbonded to Si-H bond in four possible ways to form HSiSi_3-nC_n configurations with n=0-3. So we decomposed the IR absorption band between 1840 and 2300 cm^-1 attributed to the Si-H stretching vibrations in monohydride SiH group into four subbands with Gauss distributions. Using the chemical induction model we calculated the dependencies of frequencies for each of four peaks both on the local environments of the Si-H group, and on the medium. In order to estimate the validity of frequency evaluations we calculated the probabilities of HSiSi_3-nC_n structures as the functions of r assuming the homogeneous film and random bonding. We observed two slopes on the dependence of the Si-H stretching mode peak position on r. At r<0.16 only two structural configurations HSiSi_3-nC_n with n=0 & 1 dominate in a-SiC:H. For r>0.16 the inhomogeneity in medium is due to carbon clustering in the forms of mentioned above structures with n=2 & 3. The influence of structural configurations on optical properties was discussed.