AVS1997 Session TF2-ThA: Energetic Depositions

Thursday, October 23, 1997 2:00 PM in Room B1/2

Thursday Afternoon

Start	Invited?	Item
2:00 PM		TF2-ThA-1 A Phase-Space Compressed, Guided Ion Beam Instrument for Mass-Selected Ion Beam Deposition A. Lapicki, K.J. Boyd, M. Aizawa, S.L. Anderson (University of Utah) A new approach to acheiving high ion deposition current densities is presented. A gas-filled, tapered quadrupole ion guide is used to collect iond from the source. Collisional cooling reduces the kinetic and internal energy distributions of the ions, and the quadrupole compresses the beam radius as well. The resulting compression of the ions' phase-space distribution results in a beam with greatly improved focusability. The ions are mass selected by a variable bandpass filter, consisting of two quadrupole ion guides, operated in highpass and lowpass guiding modes, respectively. The ions are guided continuously from the source to the sample, and the guiding fields prevent beam expansion from space charge. Ion-surface collisions take place in a UHV system housing STM, XPS, and HREELS hardware for characterization of the deposited films.
2:20 PM		TF2-ThA-2 Plume Development and Evolution during Low Fluence UV Laser Ablation of Transparent Materials D.R. Ermer (Washington State University); J.J. Shin (National Taiwan University, Republic of China); S.C. Langford, J.T. Dickinson (Washington State University) A critical aspect of thin film growth by pulsed laser deposition methods is the mixture of atomic and molecular neutral species accompanied by high densities of energetic electrons and ions. These species are incident upon substrates with varied kinetic energy as well as temporal and density distributions. After a brief introduction into the characterization of these features on laser irradiated dielectrics, we examine plasma generation from laser interactions with surfaces under conditions where inverse bremstrahlung (normally proposed to explain plasma formation) is not possible due to insufficient photon and electron densities. We present new measurements addressing the interaction between the emitted particles in the near surface region from exposure to pulsed laser irradiation of surfaces of ionic crystals. These emissions include photoelectrons, energetic positive ions, and neutral atoms. We first establish experimentally, in vacuum, that there is overlap in space and time of portions of the distributions in the near surface region. We then present a new model for the collected motion of these particles including proof of negative velocities (particles returning to the target). We show that as laser fluence is increased, sufficient densities, overlap, and kinetic energies are available to explain the onset of plume formation. The features examined include excitation of neutral atoms to generate plume fluorescence and ionization of neutral species at fluences far below breakdown. These studies aid our understanding and possible control of energetic and reactive species desired for efficient and directed thin film growth. This work was supported by the Department of Energy under Contract DE-FG06-92ER14252.
2:40 PM	Invited	TF2-ThA-3 Synergetic Effects in Ion Beam Energy and Substrate Temperature During Energetic Film Deposition J.W. Rabalais (University of Houston) Synergestic effects between ion beam energy and substrate temperature will be discussed for the cases of energetic film deposition and chemical reactions between energetic particles and surfaces. A mass-selected, low-energy, ultra-high vacuum dual ion beam system with well-defined ion energy (E) is used to study these interactions. The films and reacted surfaces are studied by means of in situ RHEED and AES and ex situ RBS, SIMS, XPS, and TEM. Direct ion beam deposition of ²⁸Si⁺ ions for homoepitaxial film growth on Si(100) over the range 8 - 80 eV in the low temperature range of 100 - 500 C will be used as an example of Si homoepitaxy. The growth mode, crystalline quality, and number of defects in the films as a function of ion energy and substrate temperature will be discussed. An optimum ion energy window for ion beam enhanced Si epitaxy has been found for 20 ± 10 eV at 160 C. The synergy between ion energy and substrate temperature will be shown to facilitate low temperature cleaning of Si and InP surfaces. A semiquantitative subplantation model has been developed to describe these low energy ion-surface interactions. Two of the most important phenomena involved which affect film growth are the ion penetration into subsurface layers and defect production rates. It will be shown that this model is capable of interpreting a large array of energetic ion-surface experimental data, including low temperature epitaxy, diamond-like film growth, and surface nitridation reactions.
3:20 PM		TF2-ThA-5 Seeded Pulsed Supersonic Molecular Beam Growth of Silicon Carbide Thin Films K.D. Jamison, M.D. Kempel (Systems & Processes Engineering Corp.); V.W. Ballarotto, M.E. Kordesch (Ohio University) SiC thin films have been grown on Si and SiC substrates using a dual pulsed supersonic molecular beam system. Silane and hydrocarbon precursors were seeded into helium and hydrogen molecular beams to increase the translational kinetic energy of the arriving reactants. Energies between 2 and 5 eV were used for the C source. Pulsed solenoid beam valves (without skimmers) allow reduction of the gas load during growth relative to continuous beam sources and fine control of the reaction process. High quality, single polytype homoepitaxial films were grown on 6H SiC at 1530 K; 3C SiC films with large domains (5 um) were grown on silicon substrates at 1400 K. The various advantages of helium and hydrogen as carrier gasses, different hydrocarbon sources and the possibility for polytype determination with emission microscopy will be discussed. Work supported by BMDO contract DSWA01-96-C-0113.
3:40 PM		TF2-ThA-6 Formation of Carbon Nitride Thin Films by Charge Balanced Dual Ion Beam Deposition Y.H. Kim, D.J. Choi, D.W. Han, H.K. Baik (Yonsei University, Korea) Carbon nitride thin films have been deposited by dual beam impingement of 60-160eV C^- and 75-175eV N⁺ or N₂⁺ ions upon (100) oriented Si substrate. The influence of ion energy have been studied at the highest value of J_N+/J_C- within the limited deposition condition. The critical J_N+/J_C- ratio is 1.1 and the typical beam current density was 25.5µA/cm² for N⁺. The films were characterized by Raman spectroscopy, XPS, AES and XRD. Nitrogen content of up to 35 at.%, 0.544 maximum sp³ ratio of hybridized CN and 1.086 N/C ratio of CN have been measured by XPS. Visible transparent films which is mainly affected by carbon ion energy were formed in the range of 60-120eV C^- ion energy. Factor analysis of this work for kinetic energy effect of carbon nitride characteristics by energetic carbon and nitrogen beams are discussed.
4:00 PM		TF2-ThA-7 Cubic Boron Nitride Thin Film Deposition by Unbalanced Magnetron Sputtering and dc Pulse Substrate Biasing W. Otaño-Rivera, R. Messier, L.J. Pilione (Pennsylvania State University) Boron nitride thin films were deposited by unbalanced magnetron sputtering. An asymmetric bipolar dc power supply was used to bias the substrate. This power supply imparts a dc pulse to the substrate whose frequency and duty cycle can be adjusted. It eliminates the buildup of charge in the insulating material being deposited and allows the control of the bias voltage at the substrate. For the BN films it was found experimentally that the best excitation frequency is about 218 kHz. At this low frequency the ions respond to the maximum potential across the plasma sheath. This maximum negative voltage is comparable with the dc component of the bias rf signals commonly used by other groups. Films where deposited at different bias voltages and pressures with over 80% of the cubic phase obtained as measured by FTIR. A linear relation was found between the negative substrate bias voltage necessary for the stabilization of the cubic phase and the product of deposition pressure and sheath thickness. It was determined that the average particle bombarding energy depends on the bias potential and on the depositing pressure. A model is proposed that allows one to know the average bombarding energy as a function of bias voltage and pressure. Using this model it is then possible to calculate the momentum per arriving boron atom imparted to the growing film. These results and the implications for the stabilization of cBN will be presented. It will be also shown how the use of different substrates change the properties of the deposited films. For example, several films were deposited on AlN and diamond thin films previously deposited on silicon. A three-fold reduction of the FWHM was observed for cBN deposited on the diamond/Si substrates.
4:20 PM		TF2-ThA-8 Growth of GaN and AlN on 6H-SiC(0001) using Supersonic He Beams Seeded with NH₃ V.M. Torres, M. Stevens, J.L. Edwards, David J. Smith, R.B. Doak, I.S.T. Tsong (Arizona State University) The growth of group III nitride films has been subject of intensive research over the last decade due to their exceptional thermal, optical and electrical properties. The film quality is strongly dependent on the growth temperature, and for MBE growth of GaN the upper limit is determined by the decomposition temperature ~ 800°C. Consequently, in low pressure growth processes, it is desireable to explore the use of monoenergetic beams for deposition to increase the energetics of the growth system without increasing the substrate temperature. Supersonic He beams seeded with the desired molecules provide a means of tunning the energy of the flux species for deposition. We have grown smooth, stoichiometric, epitaxial AlN and GaN layers on 4° off-axis 6H-SiC(0001) substrates using supersonic He beams seeded with NH₃ in conjunction with evaporated Ga and Al. The AlN films, which served as buffer layers for subsequent GaN growth, were deposited at 900°C with a NH₃ kinetic energy of 0.22 eV. The GaN films were grown at at 800°C with a NH₃ kinetic energy of 0.40 eV. The films were characterized by RBS, SEM, TEM, TED and electron channeling patterns. The TEM micrographs show that : (a) the AlN/SiC interface was clean and coherent revealing an excellent epitaxial relationship, and (b) the GaN films grown on the AlN buffer layers, with a thickness of ~ 105 nm, were well ordered and contained a defect density of ~ 2x10¹⁰ cm^-2. Work supported by the Office of Naval Research (N00014-95-1-0122).