bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid Phase Epitaxial Regrowth of Implantation Amorphized Si0.7Ge0.3 Grown on (100) Silicon
Authors: Lee C. , Jones K. S.
Published: March 2011

The solid phase epitaxial regrowth (SPER) process of implantation amorphized Si0.7Ge0.3 layers (850± Å thick) grown on (100) Si has been studied by cross-sectional transmission electron microscopy. For amorphous layers produced by 40 Ar+ implantation highly defective three dimensional regrowth was observed in both Si0.7Ge0.3 and Si. Stacking faults were the principle defect formed of both materials during regrowth. SPER after amorphization via 73 Ge+ implantation was also investigated. It was found that the SPER velocity of the 73 Ge+ implanted Si0.7 Ge0.7 Ge0.3 was about twice the velocity of the 40 Ar+ implanted samples; for 73 Ge+ implanted Si it was about three times that of the 40Ar+ implanted samples. The activation energy for SPER in 40Ar+ and in 73 Ge+ implanted Si0.7 Geo0.3 was about 1.6 and 2.6 eV, respectively. The defect density was significantly reduced in 73 Ge+ amorphized Si but not in the 73 Ge+ amorphized Si0.7 Ge0.3. It is proposed that limited Ar solubility inhibits high quality regrowth in both SiGe and Si. Upon 73 Ge+ amorphization and solid phase epitaxy the interfacial strain between the SiGe and Si cannot be accommodated. Thus the epitaxial process is poor in these SiGe strained layers regardless of the amorphizing species.
Excimer Laser Irradiation of Metallic Films on Ceramic Substrates
Authors: Godbole M. J. , Pedraza A. J. , Lowndes D. H. , Thompson J. R.
Published: March 2011

Copper films sputter deposited on mechanically polished (optical finish) and on annealed substrates were laser-irradiated at various energy densities. The effect of the substrate condition on both the evaporation threshold and the morphology of the laser-irradiated metallic films was investigated. The energy density threshold for laser-induced evaporation of the copper films was studied using energy dispersive x-ray spectroscopy (EDS) in a scanning electron microscope (SEM). It was found that for annealed substrates the energy density threshold decreases relative to the threshold for the as-polished condition. These results are compared with predictions of a mathematical model that assumes that the near surface region of the as-polished ceramic is a highly damaged region and, thus, constitutes a thermal barrier. The film remains intact and with almost no change in morphology after laser irradiation at energy densities lower than 0.80 J/cm2 if the substrate has been previously annealed. On the other hand, copper films deposited on as-polished substrates break up during laser processing forming copper islands.
High-Resolution Transmission Electron Microscope Study of Electron-Beam Induced Damage in some Oxide Superconductors
Authors: Matsui Yoshio , Yanagisawa Kasumi
Published: March 2011

Electron-beam induced damage of some oxide superconductors is examined by high-resolution transmission electron microscopy (HRTEM), using both 1 MV high-voltage machine and conventional 200kV one. By 1 MV electron beam, both YBa2Cu4Oy and Y2Ba4Cu7Oy suffer from amorphization due to knock-on effects which is initiated at (CuO)2 double-chain sites. By 200kV beam, some of the double-chains decompose into the single-chains and precipitation of CuO crystal is induced, due to thermal heating effects. Both Bi- and Pb-based superconductors, on the other hand, suffer from amorphizations at both 1MV and 200kV. The materials relating to La2CuO4, for instance the T*-type of superconductor (Nd, Sr, Ce)2CuO4, never amorphize even by irradiations of 1000kV electron beam. These results suggest that it is possible to introduce defects or precipitates to control the microstructures of superconductors by means of electron beam irradiations.
Thermal Neutron Irradiation and Large Pinning Enhancement in Superconducting Materials
Authors: Zhao Y. J. , Liu J. R. , Meng R. L. , Hor P. H. , Chu W. K.
Published: March 2011

Up to 25 times enhancement of magnetic critical current density has been observed at 70 K and 2500 O for 3% 6Li-doped sintered YBCO sample irradiated with thermal neutrons at a dose of 1 × 1018 n/cm2. High energy reaction product of 6Li and thermal neutron, the 2.73 MeV 3H and 2.05 MeV 4He produced uniform damage throughout the bulk sample. The strong field dependence of the Jc enhancement points to the weak center nature of the radiation defects. The upper critical field of this weak center decreases with temperature, and is about 800, 300, 150 Oe at 30, 50, 70 K respectively.
Non-Linear and Time-Dependent Diffusion of Gold in Amorphous Silicon.
Authors: Wagner A. V. , Wu D. T. , Spaepen F.
Published: March 2011

By performing scaling experiments [1] and examining the evolution of the spatial second moment of the concentration profile, it was shown that the diffusion coefficient of gold in amorphous silicon is both concentration and time dependent. The second moment curves for different temperature anneals can be scaled to a master curve using a factor with an activation enthalpy of 2.0 eV.
Magnetic Field Dependence of Jc in A T1–1223 Wire; Presence of Pinning and Good Grain Boundary Connectivity.
Authors: Doi Toshiya J. , Nabatame Toshihide , Okada Michiya , Yuasa Toyotaka , Tanaka Kazuhide , Inoue Naomi , Soeta Atsuko , Aihara Katsuzo , Kamo Tomoichi , Shin-Peimatsuda
Published: March 2011

The existence of effective pinning in single T1-layer 1223 superconductors has been reported [1–3], as opposed to lower values in T1- and Bi-double layer systems, which is intimately related to their crystal structures. In order to investigate the possibility of T1–1223 being applied as a practical superconductor, tape shaped wires of the chemical composition (T10.5Pb0.51 (Sr0.8Ba0.2Ca2Cu3O9were prepared. Transport Jc of T1–1223 was measured to be 1.8 × 104 A/cm2 at 77K in the absence of a magnetic field. These results seem to imply that T1–1223 has, not only effective pinning because of having a more 3-dimensional vortex line lattice like YBa2Cu3O7, but also better grain boundary weak-link performance than YBa2Cu3O7. PresenT1y it appears that T1–1223 may be a superior choice to make better superconducting wire, because of these considerations and of the higher Tc of 120K.

(T10.5Pb0.5)1Sr2CaCu2O7 (T1–1212) also seems to have effective pinning, as well as T1–1223, supporting the idea that shorter Cu-O plane spacing, or absence of thicker insulating region such as T12O2 or Bi2O2 double layer, are beneficial for effective pinning through facilitating a better 3D-like vortex line lattice [4, 5]. Our “1212” and “1223” samples are good counter examples to the 2D pancake-like vortex theory [6, 7].
Trapped Magnetic Field in Proton Irradiated Melt-Textured Y-Ba-Cu-O Superconductors
Authors: Chen In-Gann , Liu Jianxiong , Weinstein Roy
Published: March 2011

The trapped magnetic fields in high energy proton irradiated melt-textured Y-Ba-Cu-O (MT-Y123) high temperature superconductors (HTS) materials have been studied. Prototype of mini-magnet, about 1 cm3 which retains about 14, 200 G @ 77 K, has been made with these proton irradiated samples. Quasi-persistent magnetic field near 3 to 5 Tesla in liquid nitrogen is feasible with our current MT-Y123 samples. Two types of motors have been tested successfully by replacing metallic permanent magnet with the trapped field in MT-Y123 samples.

The trapped magnetic field mapping technique is used to study the superconducting properties of the MT-Y123 materials. Granular structures in MT-Y123 samples can be observed directly by the field mapping method. A phenomenological current model has been developed to account for the trapped field intensity and profile in HTS samples. The trapped field can be reproduced very well by this model. Remenant magnetic moment trapped by MT-Y123 samples measured by this mapping method and by standard VSM will be discussed. The effect of high energy proton (160–210 MeV) bombardment on the field trapping capability and stability will be discussed.
Irradiation Effect of Slow Neutrons on Mechanical Behaviour Related to Flux Pinning In YBa2Cu3Oy
Authors: Zhu J. S. , Li J. , Wang Y. N. , Jin J. R. , Gu M. , Ding S. Y. , Jin X. , Fung P. C. W. , Liu Z. M.
Published: March 2011

Internal friction and modulus in YBa2Cu3Oy, which are related to flux pinning, were examined by means of the vibrating reed technique before and after the slow neutron irradiation to different fluences. Both the decrease of mechanical dissipation and the increase of the modulus associated with strongly enhanced flux pinning were observed in a sample irradiated up to a suitable fluence. However, a decrease of modulus and magnetic hysteresis loop was found after further irradiation. A change in the microstructure of the irradiated material is used to explain the observed phenomena.
Orientation Dependence of Flux Pinning in a Layered Bi2Sr2 Ca1 Cu2O8 + 10% Ag Composite
Authors: Foldeaki Maria , Ledbetter Hassel
Published: March 2011

The Bi2 Sr2 Ca1 Cu2 O8 + 10% Ag specimen was grain oriented along the a(b) axis, but random in the perpendicular plane. Magnetic susceptibility and hysteresis measured along the axis of grain orientation and in the polycrystalline direction showed remarkable anisotropy. At low temperatures (below about 30 K), hysteresis curves were compatible with the strong-pinning model. The pinning force calculated from the hysteresis loop showed a higher maximum in the random direction, but decreased fast with increasing field and temperature. From the zero-field-cooled (zfc) and field-cooled (fc) susceptibility curves, the irreversibility line T*(H*) was determined. Evaluation according to the de Almeida-Thouless equation with fixed exponent n=3/2 revealed a two-phase vortex structure; one nearly isotropic with low (40-$K) zero-field irreversibility transition temperature, and one strongly anisotropic, the irreversibility transition being close to the superconducting-transition temperature.
In Situ TEM Observation of Defects and Amorphous Phase in Si Wafer During Ion Implantation
Authors: Shigenaka Naoto , Hashimoto Tuneyuki , Fuse Motomasa , Owada Nobuo , Yamaguchi Hizuru , Ozono Seiko
Published: March 2011

In situ TEM observations of defects and. the amorphous phase in Si wafer during 150 keV Ar+ ion implantation were made which elucidated their characteristic behavior in Si. Defects introduced by ion implantation were eliminated by amorphous phase formation and then new defects did not form in the amorphous phase. Microstructural evolution in Si wafers under high dose implantation (2E16 ions/cm2) of 400 keV Si* ions was also investigated at temperatures of -70, -30, 20, 100 and 200 °C using a cross-section 1 TEM observation technique. At temperature of 20 °C and above, a defect layer was formed in each specimen, and the defect density was observed to decrease as temperature increased. At temperture of -30 °C and below the amorphous phase was formed and a defect layer which made contact with this phase was also observed. After annealing of these implanted specimens at 850 °C for 20 min, the amorphous phase had crystallized and the defect layer in contact with the amorphous phase was almost eliminated. But another defect layer was formed during annealing in the region where the amorphous phase had existed.
Copper-Carbon Alloy Films by Methane Beam Assisted Epitaxial Copper Deposition
Authors: BROWN David W. , Donovan Edward P. , Cotell Catherine M. , Grabowski Kenneth S.
Published: March 2011

Copper-carbon alloy films containing between 7 and 40 at.% carbon, as measured with 6.2 MeV He++ scattering, were deposited by ion beam assisted deposition (IBAD) on pure epitaxial Cu(100) films on Si(100) substrates. The IBAD process involved simultaneous deposition of evaporated copper (0.3 to 2.0 nm/s) and bombardment with 400 eV ions (340 μA/cm2 on target) from a Kaufman ion source fed with methane. Transmission electron microscopy (TEM) showed that an IBAD layer with 15 at.%C was epitaxial with the underlying pure Cu(100) layer. X-ray diffraction (XRD) indicated that the IBAD films were epitaxial at low carbon concentration but polycrystalline at high concentration. The small range of carbon ions in copper and the evidence of sputtering suggest that this loss of epitaxy resulted from increased surface carbon interfering with epitaxy. Although carbon and copper are immiscible, TEM and XRD have revealed no evidence of carbon precipitation, indicating that the carbon may be in solution and that such IBAD layers may be suitable for diamond formation by laser annealing.
Influence of Energy Deposited by Energetic Particle Bombardment on Thin Film Characteristics
Authors: Winters Harold F. , Eckstein W. , Coufal H. J.
Published: March 2011

It has been recognized since the 1960's that bombardment of a growing thin film by energetic particles strongly influences film properties. Particle bombardment has generally been accomplished by accelerating ions into the growing film. However, it has also been recognized since the 1960's that energetic particles reflected from the target influence the characteristics of films grown by physical sputtering and many experiments have been interpreted on this basis. A systematic study of the energy reflected from the surface by normally incident, singly charged noble-gas ions on five substrates of different masses has recently been published. This data along with sputter yields from the literature allow estimates to be made which were previously unavailable. The energy reflected from the target is carried away by electrons, sputtered particles and reflected ions (neutrals). The purpose of this paper is to provide basic information which will allow thin film scientists to estimate the influence of various experimental parameters on the amount of energy arriving at the growing film. The energy reflected from the target per sputtered atom will be given as a function of ion mass, target mass, and ion energy. TRIM.SP Monte Carlo calculations will be used to estimate the ratio of the energy carried away by sputtered atoms to that carried away by reflected ions. Calculations will also be used to estimate the average energy of the sputtered atoms as a function of ion mass, substrate mass and ion energy. It will be shown how this information can be used to guide the adjustment of experimental parameters in sputtering environments so as to control film characteristics.
Simulations of Low-Energy Ion Bombardment and Epitaxial Growth
Authors: Chason E. , Bedrossian P. , Tsao J. Y. , Dodson B. W. , Picraux S. T.
Published: March 2011

We have performed computer simulations of epitaxial growth and low-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) mesurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this work, we focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simultaneous ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large.
In Situ Observation of Growing Process of Particles in Silane Plasmas and Their Effects on Amorphous Silicon Deposition
Authors: Shiratani Masaharu , Watanabe Yukio
Published: March 2011

In rf silane plasmas, growing process and behavior of dust particles and presence of negative ions are studied by square-wave-amplitude-modulating an rf discharge voltage. By combining the rf modulation method with Mie scattering methods, particle behavior together with temporal evolutions of particle size and density is revealed. While the rf modulation is effective for the suppression of particle growth, small particles are found to exist still in the discharge space for a larger duty cycle. Further, particles seem to be suspended around an rf electrode by counter balance between an electrostatic force due to time-averaged sheath electric field and a force increasing with particle size. The development of particle growth also affects the rf discharge itself, resulting in inhomogeneity of film properties. Negative ion detection is carried out as a first step for studying whether they cause the particle formation. It is found that negative ions are formed in rf silane discharges even for a low concentration of 0.5%SiH4 and their formation is due to attachment to dissociated radicals rather than dissociative attachment of SiH4.
Low Temperature Silicon Oxidation With Electron Cyclotron Resonance Oxygen Plasma
Authors: Sung K. T. , Pang S. W.
Published: March 2011

Silicon was oxidized at low temperature with an oxygen plasma generated by an electron cyclotron resonance (ECR) source. The ECR source utilized a multicusp magnetic field formed by permanent magnets. Microwave power at 2.45 GHz was applied to the source and if power at 13.56 MHz was applied to the sample stage. Si oxidation was studied as a function of source distance, pressure, microwave power, and rf power. The oxide thickness increases with microwave and rf power but decreases with source distance. The oxidation rate increases with pressure up to 12 mTorr, men decreases at higher pressure. The relative emission intensities in the plasma monitored using optical emission spectroscopy showed similar dependence on the source distance and microwave power. Oxidation temperature was estimated to be <100°C. Using ellipsometry and X-ray photoelectron spectroscopy, the oxidized films were found to be close to that of thermal oxide with refractive index at 1.45 and oxygen to silicon ratio of 2. From the current-voltage and capacitance-voltage measurements, the breakdown fields of these oxide films were 6.3 MV/cm and the fixed charge densities were 7×1010 cm−2.
Characterization of High Temperature Superconducting Thin Film Grown by Laser Ablation Method
Authors: Shimizu K. , Nobumasa H. , Nagai N. , Matsunobe T. , Kawai T.
Published: March 2011

We have measured the complex dielectric function of BizSr2Ca1Cu2Ox samples in the near infrared region directly by spectroellipsometry. As for both single crystal and thin film, superconducting samples have a zero point in the real part (ε1) of the complex dielectric function (ε*) and a clear peak of the imaginary part of the inverse ε* at almost the same frequency. On the other hand, non-superconducting samples have no such ei zero point, and the peak height of (-Im(1/ε*)) becomes small. Then we can determine the superconductivity of samples by this spectroellipsometry measurement at room temperature.
In SituCharacterization of the Pulsed Laser Deposition of Magnetic Thin Films
Authors: Paul A. J. , Bonnell D. W. , Hastie J. W. , Schenck P. K. , Shull R. D. , Ritter J. J.
Published: March 2011

Pulsed Laser Deposition (PLD) has been proven as an effective means of depositing films from refractory targets. In our earlier work, either Nd/YAG or excimer lasers, interacting directly with target surfaces, were used to deposit thin films of high Tcsuperconductors, high dielectric constant BaTiO3and ferroelectric PbZr0.53Ti0.47Os3(PZT). Time-resolved molecular beam mass spectrometry and optical emission spectroscopic techniques have been developed to characterize the vapor plumes responsible for film formation. More recently, this work has been extended to the PLD of magnetic thin films of Ag-Fe3O4nanocomposites using excimer (ArF*, 193 nm) laser excitation. Optical emission spectra of the excited vapor phase species, formed during the plume generation and material deposition process, indicate that physically compressed powdered metal targets have inadequate homogeneity for film production, compared to targets that are chemically produced. Anin situLaser-induced Vaporization Mass Spectrometry (LVMS) technique utilizing a Nd/YAG (1064 nm) laser has been used to determine Time-of-Arrival (TOA) profiles of the atomic, molecular, and ionic species produced in the plumes of Ag-Fe3O4The neutral species TOA profiles indicate velocity distributions that are multimodal and not Maxwellian. These observations are in contrast to the TOA profiles observed from one-component targets (Ag or Fe3O4), where a single Maxwellian velocity distribution is found. Mossbauer effect measurements of the thin films have been made for correlation with the gas phase studies.
Photophysics of Polyatomic Species Ejection Following UV Laser Ablation of Single Crystal Bi2Sr2Ca1Cu2O8
Authors: Wiedeman Lawrence , Kim Hyun-Sook , Helvajian Henry
Published: March 2011

A series of experiments have been conducted which probe the origin of the polyatomic ions (e.g., Sr2O+, BiCu+) measured following the low fluence, pulsed UV laser irradiation of crystalline Bi2Sr2CaCu2O8 (BiSrCaCuO). The photoejection of polyatomic species presents a problem for the pulsed laser deposition (PLD) technique. The deposition of polyatomic products could limit epitaxial growth during thin film material processing. Our results indicate that the polyatomic species are not the consequence of a gas phase recombination, but are in fact directly produced. All experiments are done at laser fluences below that required for above surface plasma formation. As such, our results do not address the formation of large clusters within the dense plume in high fluence laser ablation.
Surface Studies of Laser Processing of W on GaAs from WF6
Authors: Tabbal M. , Lecours A. , Izquierdo R. , Meunier M. , Yelon A.
Published: March 2011

Laser Chemical Vapor Deposition of tungsten on GaAs from WF6 using a focused cw scanning argon-ion laser beam has been investigated. Lines have been produced using different mixtures of WF6:H2 and WF6:SiH4 and in some cases, without any reducing gas. Depositions are found to occur within a narrow process window, and are difficult to reproduce. In order to understand this process, we have performed surface analysis on GaAs samples exposed to WF6. X-Ray Photoelectron Spectroscopy studies on the interaction between WF6 and GaAs in the absence of laser illumination show that fluorinated tungsten compounds are present on the GaAs surface. Furthermore, the existence of a chemical reaction leading to the formation of GaF3 at the surface and to a loss of the stoichiometry of the substrate surface is detected. Possible mechanisms, and the effects of these reactions on the deposition process are discussed.
Enhancement of Photoresist Etch Rates by Argon Metastables in a Plasma Afterglow Reactor
Authors: Koretsky Milo D. , Reimer Jeffrey A.
Published: March 2011

The etching of a novolak-based positive photoresist was studied downstream of O2/CF4 and Ar/O2/CF4 plasmas. Gas phase electron resonance was used to quantitatively track the two primary etchant species, atomic oxygen and atomic fluorine. These species were then correlated to etch rates as determined by laser interferometry. In addition to being industrially relevant, the downstream reactor allows the influence of neutral chemistry and surface activation to be deconvoluted from that of ion bombardment and strong electric fields, which traditionally make processes occurring in the body of the plasma so difficult to understand. The maximum in etch rate with respect to CF4 addition to an oxygen plasma yields an optimum ratio of O/F of 20 at 150 °C. The addition of argon to the O2/CF4 gas mixture unexpectedly leads to an increase in etch rate by a factor of at least two. Moreover, the optimum O/F ratio decreases by a factor of three and, correspondingly, the optimum CF4 mole fraction decieases. Analysis of oxygen and fluorine densities suggests argon metastables alter the homogeneous chemistry for fluorine atom production as well as the heterogeneous chemistry of photoresist chain scission. Overall activation energies are 10.6, 10.8, 4.1 and 0.7 kcal/mole for O2, Ar/O2, O2/CF4 and Ar/O2/CF4 mixtures, respectively. The optimal CF4 mole fraction increases with increasing substrate temperature. A Hougen-Watson model for the heterogeneous chemistry on the wafer surface reproduces the data very well.
Evaluation of Semiconductor Lattice Damage Using a Newly-Developed Photodisplacement Laser Probe
Authors: Sumie S. , Takamatsu H. , Tsunaki H. , Nishimoto Y. , Nakai Y
Published: March 2011

A highly sensitive laser probe for photo-acoustic displacement(PAD) has been developed and applied to the monitoring of low-level lattice damage in semiconductors. Since a photodisplacement laser probe with the sensitivity of 0.1 picometers is employed in this measurement, lower density damage for instance, formed by 50 keV B+ implantation with a dose of 5X109 ions/cm2 can be detected. Correlation of the PAD with damage density was obtained in B+ implantation. Therefore, quantitative damage density can be obtained from the relation for lightly damaged layers, such as formed by chemomechanical polishing and by electron cyclotron resonance plasma etching. This technique is useful-for monitoring of low damage density surface.
Ion Beam Etching System for Mercury Cadmium Telluride and III-V Compound Semiconductors
Authors: Reeves Geoffrey K. , Leech Patrick. W. , Bond Patrick
Published: March 2011

This paper describes a laboratory built ion beam etching system and its performance when used for etching Hg1-xCdxTe, GaAs and InP. The etching system provides a means for forming device mesas on a wide range of semiconductors without having to resort to wet chemical etches. The system uses a Kaufmann ion source, a rotating platform and two flow controllers to allow the variation of gas ratios and flows.
Laser-Induced Desorption of in and Ga from Si(100) and Adsorbate Enhanced Surface Damage
Authors: Strupp Paul G. , Alstrin April L. , Korte Brenda J. , Leone Stephen R.
Published: March 2011

Laser-induced desorption (LID) of In and Ga from Si(100) under ultra-high vacuum conditions is investigated. The frequency doubled 532 nm, 2-6 ns output of a Nd:YAG laser is focussed to 0. 14±0.03 J/cm2 on the Si surface to induce desorption. Desorbed In or Ga atoms are detected by laser-induced fluorescence initiated by a pulsed dye laser propagating in front of the surface. LID occurs by thermal desorption with approximate desorption energies and pre-exponential factors in agreement with literature values from previous isothermal desorption measurements. Experiments at higher coverages suggest that desorption occurs predominantly from the two-dimensional (2D) adsorbate layer with little desorption occurring directly from adsorbate islands. The 2D layer is resupplied by either diffusion out of adsorbate islands or by diffusion of incorporated adsorbate out of the bulk. Adsorbate-enhanced laser-induced surface damage is also observed; only 0.2 monolayer of In reduces the number of laser pulses required to observe damage by greater than a factor of 30.
Epitaxy and Chemical Reactions During Thin Film Formation from Low Energy Ions New Kinetic Pathways, New Phases and New Properties
Authors: Herbots Nicole , Hellman O.C. , Vancauwenberghe O.
Published: March 2011

Three important effects of low energy direct Ion Beam Deposition (IBD) are the athermal incorporation of material into a substrate, the enhancement of atomic mobility in the subsurface, and the modification of growth kinetics it creates. All lead to a significant lowering of the temperature necessary to induce epitaxial growth and chemical reactions. The fundamental understanding and new applications of low temperature kinetics induced by low energy ions in thin film growth and surface processing of semiconductors are reviewed. It is shown that the mechanism of IBD growth can be understood and computed quantitatively using a simple model including ion induced defect generation and sputtering, elastic recombination, thermal diffusion, chemical reactivity, and desorption The energy, temperature and dose dependence of growth rate, epitaxy, and chemical reaction during IBD is found to be controlled by the net recombination rate of interstitials at the surface in the case of epitaxy and unreacted films, and by the balance between ion beam decomposition and phase formation induced by ion beam generated defects in the case of compound thin films. Recent systematic experiments on the formation of oxides and nitrides on Si, Ge/Si(100), heteroepitaxial SixGe1−x/Si(100) and GaAs(100) illustrate applications of this mechanism using IBD in the form of Ion Beam Nitridation (IBN), Ion Beam Oxidation (IBO) and Combined Ion and Molecular beam Deposition (CIMD). It is shown that these techniques enable (1) the formation of conventional phases in conditions never used before, (2) the control and creation of properties via new degrees of freedom such as ion energy and lowered substrate temperatures, and (3) the formation of new metastable heterostructures that cannot be grown by pure thermal means.
Atomic Oxygen Plasma Effects on Cvd Deposited Diamond-Like Carbon Films
Authors: Hale Jeffrey S. , Synowicki R.A. , Nafis S. , Woollam John A.
Published: March 2011

CVD deposited diamond-like carbon (DLC) films have been studied for possible use as a secondary standard for Low Earth Orbit materials degradation. Samples of various thicknesses have been exposed to a simulated Low Earth Orbit atomic oxygen (AO) environment using a plasma asher. Mass loss measurements indicate that DLC degrades at a rate of 0.7 mg/hr which is two to three times the rate of currently used Kapton samples which degrade at a rate of.3 mg/hr. Thickness measurements show that DLC thins at a rate of 77 Angstroms/min. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights. Adhesion of DLC films to both fused silica and crystalline silicon substrates has been studied under thermal cycling conditions. Film adhesion to fused silica can be enhanced by sputtering a thin layer of silicon dioxide onto the substrate prior to deposition. In addition to the above, the index of refraction and extinction coefficient of various thicknesses of DLC films has been characterized by Variable Angle Spectroscopic Ellipsometry.
Growth and High Resolution Tem Characterization of GexSi1−x/Si Hetero-Structures by Remote Plasma-Enhanced Chemical Vapor Deposition
Authors: Qian R. , Chung I. , Kinosky D. , Hsu T. , Irby J. , Mahajan A. , Thomas S. , Banerjee S. , Tasch A.
Published: March 2011

Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been used to grow GexSi1−x/Si heteroepitaxial thin films at low temperatures (∼450°C). In situ RHEED has been used to confirm that smooth, single crystal heteroepitaxial films can be grown by RPCVD. Plan-view and cross-sectional TEM have been employed to study the microstructure of the heteroepitaxial films. Lattice imaging high resolution TEM (HRTEM) has shown perfect epitaxial lattice alignment at the heterojunction interfaces. GexSi1−x/Si films which exceed their CLT's appreciably show dense Moiré fringes under plan-view TEM. The spacings between the fringes have been used to estimate the relaxed lattice constants. In addition to the inhomogeneous strain observed in XTEM, Selected Area electron Diffraction (SAD) analysis of the interfaces displays two split patterns. The spacings between the diffraction spots have been used to calculate the lattice constants in the epitaxial films in different crystal directions, which agree very well with the prediction by Vegard's law as well as the estimate from planview TEM analysis. HRTEM analysis also reveals the crystallographic nature of the interfacial misfit dislocations in the relaxed films.
Pulsed Laser Planarization of Metals for IC Interconnect
Authors: Baseman Robert J. , Kuan Tung-Sheng , Aboelfotoh M. Osama , Andreshak Joseph C. , Turene Frank E. , Previti-Kelly Rosemary A. , Ryan James G.
Published: March 2011

We consider the feasibility of using an excimer laser to planarize copper deposited over polyimide. Even though the polyimide is thermally sensitive, a 2.8 µn thick copper film, deposited over polyimide, was planarized with 248 nm, 25 ns, laser fluences from 1.7 to 2.6 J/cm2. Although planar surfaces were readily produced, a variety of defects were observed in the underlying structures. The defects observed include stress induced fractures of the interconnect structure, polyimide surface roughening, and changes in the electrical characteristics of the polyimide. We also describe cross sectional TEM images of cavities formed in interlayer contacts during laser planarization that support recent descriptions of the surface tension driven flow.
Excimer Laser Induced Modification of Teflon Surface into Silicon Carbide-Like
Authors: Okoshi M. , Toyoda K. , Murahara M.
Published: March 2011

A silicon carbide-like layer was produced in the near-surface region of teflon by irradiating with an ArF excimer laser in a SiH4 and B(CH3)3 mixed gas atmosphere. The pure photochemical reaction was employed in the modification process, and the defluorination of the surface was performed with boron atoms which were photodissociated from B(CH3)3. The CH3 radicals, also photodissociated, induced the dehydrogenation of SiH4 gas; which followed the production of SiHx radicals. The SiHx radicals and CH3 radicals which could not have induced the dehydrogenation of SiH4 were substituted for fluorine atoms of the surface. As a result, the surface was photomodified into silicon carbide. Chemical composition of the photomodified surface was inspected by the XPS and the ATR-FT-IR spectra measurement, and the bonding of the Si-CH3 radicals which traded off the reduction of the fluorine atoms was comfirmed. The Si/C composition ratio of the photomodified surface was 0.7.
Excimer Laser-Induced Decomposition of Aluminum Nitride
Authors: Esrom H. , Zhang J-Y , Pedraza A.J.
Published: March 2011

A thin film of aluminum, detected by x-ray photoelectron spectroscopy, is left at the surface of aluminum nitride (AIN) substrates exposed to a high intensity excimer laser beam of UV radiation. Due to the presence of this film, there is a decrease in the surface resistivity of the substrate with increasing number of laser pulses. In addition, line profilometry shows a decrease of the surface roughness with the number of pulses.

The thermal decomposition of AIN is assumed to take place in two stages. In the first, liquid aluminum is produced together with the evolution of gaseous nitrogen, and in the second, aluminum evaporates. Using a computer model to simulate the laser heating cycle, it is shown that the thickness of the aluminum film saturates at a given laser energy density. The saturation thickness is a strong function of the substrate absorption and reflectivity and, therefore, of the laser light frequency. The influence of the substrate roughness on the electrical resistivity of the aluminum film is discussed.

The application of this process to direct laser writing in high density hybrid circuits is illustrated. During hole drilling by excimer laser, a thin aluminum film is continuously produced at the hole walls. This process can also be employed for substrate planarization.
Dynamics of Graphite Photoablation
Authors: Murray P. T. , Peeler D.T. , Dempsey D. V.
Published: March 2011

Speed distributions were determined for the ions, ground state and electronicallyexcited neutrals ejected from a graphite target by 248 nm laser ablation. Mass distributions were measured for the laser-ejected ions. The measurements were carried out normal to the graphite target as well as at an angle of 45°. Significant differences were observed in both the speed and mass distributions at the two angles.
Processing of Y1Ba2Cu3O7-x Superconducting Thin Films on GaAs Substrates with Double Buffer Layers
Authors: Lee Sang Yeol , Jia Quanxi , Anderson Wayne A. , Shaw David T.
Published: March 2011

High temperature superconducting Y1Ba2Cu3O7-x(YBCO) thin films have been grown on GaAs substrates by in situ laser deposition with a double buffer layer of yttrium-stabilized ZrO2 (YSZ)/Si3N4. A barrier layer using a combination of YSZ/Si3N4 was used to grow high quality YBCO thin films without the degradation of the GaAs during YBCO film deposition. Strongly c-axis oriented superconducting YBCO thin films with a zero resistance temperature of 85.5 K and a critical current density of 1.9x103 A/cm2 at 77 K have been obtained. The electrical properties of the YBCO thin films were mainly dependent on YSZ buffer layer deposition condition.
Ambient Gas Effects on Debris Formed During KrF Laser Ablation of Polyimide
Authors: Küper Stephan , Brannon James
Published: March 2011

The surface debris that results from KrF excimer laser ablation of polyimide has been investigated as a function of the pressure. and atomic or molecular weight of several ambient gases: H2, He. Ne, air, Ar, Kr, and Xe. A linear relation between the measured debris radius and the inverse third root of the ambient pressure was found to exist, consistent with the predictions of blast wave theory. No measureable debris could be observed using helium or hydrogen gases up to 1 atm. similar to previous reports on helium. The derived value of the blast energy. equal to about 5% of the incident pulse energy, was used to estimate a nascent blast pressure of approximately 150 atm. By making the assumption that surface debris will form if the ablation fragments are confined in a “small” volume for a “sufficient” time, then conclusions from blast wave theory suggest how to decrease the amount of generated debris.
Photoinduced Selective Deposition of Aluminium Thin Film Using Dimethylaluminum Hydride
Authors: Hanabusa Mitsugu , Ouchi Hideki , Ishida Kenji , Kawasaki Masahiro , Shogen Satoshi
Published: March 2011

Aluminum thin film was deposited via a photochemical surface reaction of dimethylaluminum hydride (DMAH) using a deuterium lamp. The period required to initiate the film growth differed with substrate, and making use of this result the film could be grown preferentially on silicon nitride and silicon oxide layers rather than on wet-etched silicon. On the basis of an x-ray photoelectron spectroscopy the observed dependence of photodeposition on substrate surfaces can be attributed to how DMAH is chemisorbed initially.
Laser Assisted Chemical Vapor Deposition of Cu from a New Cu Organometallic Complex
Authors: Han Jaesung , Jensen Klavs F. , Norman John A.T.
Published: March 2011

We describe pyrolytic laser assisted chemical vapor deposition (LCVD) of copper onto silicon using a copper(I) hexafluoroacetylacetonate trimethylvinylsilane organometallic complex with 514.5 nm radiation from an Ar+ laser. Growth rates of 0.4-40 μm/min were obtained and at intermediate laser powers, the Cu lines had a resistivity comparable to that of bulk Cu. The line shape and morphology was strongly dependent upon laser power with volcano shapes appearing at higher powers. The growth was sensitive to the nature of the substrate suggesting that film nucleation was a critical element in the writing process.
Coarsening in Two-Dimensional Soap Froths and the Large-Q Potts Model
Authors: Grest Gary S. , Glaziers James A. , Anderson Michael P. , Holm Elizabeth A. , Srolovitz David J.
Published: March 2011

A detailed comparison between the experimental evolution of a two-dimensional soap froth and the large Q state Potts model is presented. The pattern evolution starting from identical initial conditions will be compared as well as a variety of distribution functions and correlations of the two systems. Simulations on different lattices show that the discrete lattice of the Potts model causes deviations from universal domain growth by weakening the vertex angle boundary conditions that form the basis of von Neumann's law. We show that the anisotropy inherent in a discrete lattice simulation, which masks the underlying ‘universal’ grain growth, can be overcome by increasing the range of the interaction between spins or increasing the temperature. Excellent overall agreement between the kinetics, topological distributions and domain size distributions between the low lattice anisotropy Potts-model simulations and the soap froth suggests that the Potts model is useful for studying domain growth in a wide variety of physical systems.
Kinetics of Facet Formation During Growth and Etching of Crystals
Authors: Vlachos D. G. , Schmidt L. D. , Aris R.
Published: March 2011

Morphological instabilities of surfaces with respect to faceting in deposition of microelectronic materials and etching of semiconductors and catalysts are of great technological importance. Macroscopic theories fail in predicting correctly the time and size dependence of microstructures observed.

We have examined the temporal and spatial evolution of unstable interfaces in zero net flux, growth, and etching of crystals as functions of temperature and degree of irreversibility using the Monte Carlo method. In addition to faceting, thermal or kinetic roughening transitions are also observed under some conditions. We have found that the type of transition and the surface structures depend strongly on the irreversibility of the process and the surface temperature. It is demonstrated that surface diffusion has a profound influence on the transitions and surface morphologies.
Structure of Au-Al2O3 Granular Metal Films
Authors: Abeles B. , Zhang Q. , Hung H. H. , Liang K. S. , Ohtani H. , Behal S. K. , Disko M. M. , Lanford W. A. , Gadenne M. , Gadenne P.
Published: March 2011

We have investigated the structural properties of sputter deposited granular AU-Al2O3 films. The films exhibit an abrupt percolation transition from insulating to metallic behavior at the composition of xc-40 vol.% Au. STM measurements yield images of individual grains and clusters of grains consistent with the TEM images. The surface roughness increases abruptly from 30Å to 50Å as the Au concentration increases from 35 to 45 vol.%. The roughening of the films in the metallic regime is consistent with behavior of the X-ray reflectivity.
Epitaxial Growth and Recovery: an Analytic Approach
Authors: Zangwillt A. , Luset C. N. , Vvedensky D. D. , Wilby M. R.
Published: March 2011

Most detailed studies of morphological evolution during epitaxial growth and recovery make use of computer-based simulation techniques. In this paper, we discuss an alternative, analytic approach to this problem which takes explicit account of the atomistically random processes of deposition and surface diffusion. Beginning with a master equation representation of the dynamics of a solid-on-solid model of epitaxial growth, we derive a discrete, stochastic equation of motion for the surface profile. This Langevin equation is appropriate for growth studies. In particular, we are able to provide a microscopic justification for a non-linear continuum equation of motion proposed for this problem by others on the basis of heuristic arguments. During recovery, the deposition flux and its associated shot noise are absent. We analyze this process with a completely deterministic equation of motion obtained by performing a statistical average of the original stochastic equation. Results using the latter compare favorably with full Monte Carlo simulations of the original model for the case of the decay of sinusoidally modulated initial surfaces.
The Evolution of Periodic Step Arrays on Si by Surface Diffusion
Authors: Keeffe Mary E. , Umbach C. C. , Blakely Jack M.
Published: March 2011

Periodic step arrays on Si(001) surfaces have been produced using photolithography, reactive ion etching and vacuum annealing. These have been studied by optical diffraction, low energy electron diffraction(LEED), and scanning tunneling microscopy (STM). The periodically varying step density on these arrays has been examined by STM. For small deviations from (100) along the [110] zone, single atomic steps dominate, while at larger angles biatomic steps are the most common; at intermediate angles the steps are of mixed character and there is some evidence for a range of unstable orientations. Interesting differences in the ratio of the areas of the two types of terrace (2×1) reconstructions are observed for the minima and maxima of the quasi- sinusoidal surfaces; these differences may be due to stresses produced by the step arrays or to differences in the line tensions associated with the two different types of steps on reconstructed Si(001) surfaces. The observations will be compared to the predictions of capillarity theory for isotropie materials. At high temperatures surface diffusion leads to a decay in amplitude of these surface gratings probably by mutual annihilation of atomic steps at the extrema. The overall rate of this process has been followed by monitoring the change in the distribution of intensity in the diffraction pattern from the grating using a He-Ne laser while the sample is annealed in UHV. With some simplifying assumptions, the intensity distribution can be directly related to the grating amplitude. The experiments are being performed for a range of grating spacings (to allow identification of the dominant transport process from scaling laws) and for a range of temperatures. The relationship between the ‘macroscopic’ observations of the shape development and the STM results will be explored.
Molecular Dynamics Studies of Impurity Segregation and Trapping.
Authors: Gilmer G. H. , Roland Christopher , Karunasiri R. P. U.
Published: March 2011

The ability to make highly doped δ-layers in semiconductors depends on the rate of interchange of atoms between layers at the crystal surface. We have simulated molecular beam epitaxy on a silicon (100) surface covered with a monolayer of impurity atoms. The kinetics of impurity segregation to the surface was examined for various growth conditions and segregation energies. We find that segregation is facilitated by appreciable inter-layer diffusion of atoms in the top several layers. The amount of diffusion is much greater during deposition than it is when the beam is off.
Cluster Size Distributions in Different Temperature Regimes: The System Ga on GaAs(001)
Authors: Ren Y. , Zinke-Allmang M. , Feldman L. C. , Van Saarloos W.
Published: March 2011

In this paper we discuss results for the clustering of Ga on GaAs(001). The dominant dynamic process which drives this system toward this three dimensional equilibrium changes from Ostwald ripening at low deposition rates to coalescence at higher deposition rates. The experimental data allow us to test several theoretical predictions for cluster size distributions based on a detailed study of the microscopic processes. These include, at higher deposition rates, the observation of local ripening effects and diffusion limited growth.
Molecular Dynamics Simulation of A Langmuir Monolayer
Authors: Bareman James P. , Klein Michael L.
Published: March 2011

Molecular dynamics calculations were carried out for a Langmuir monolayer at high density. A model was employed in which the motions of both the amphiphiles and the water are allowed, enabling investigation of the details of the water-monolayer interaction and the structure of the interface. Results are presented for the density profiles of the water and the amphiphiles and for the distribution ofgauchedefects.
The Many Facets of Interface Motion.
Authors: Cahn John W.
Published: March 2011

Many dynamic growth processes are shown to involve changes in more than one of the nine geometric variable that describe the geometry of a planar interface between crystals. Even simple examples illustrating changes in each one of the nine are found to involve some of the others. A generalized concept of crystal-crystal interface motion, using all nine variables, is suggested.
Low Energy Electron Microscopy
Authors: Tromp R. M. , Reuter M. C.
Published: March 2011

- We have designed and built a Low Energy Electron Microscope for surface and interface studies in Ultra High Vacuum. In this paper we present major features of the design, and some of our results on surfactant mediated Ge growth on Si(001).