bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma-structure dependence of the growth mechanism of plasma-polymerized fluorocarbon films with residual radicals
Authors: Horie M.
Published: July 2002

Plasma-polymerized fluorocarbon polymer films are thought to contain a high density of residual radicals which are easily oxidized in air. The rf discharge power dependence of the oxidation rate in C3F6 plasma-polymerized films under an accelerating aging condition of 65 °C/85%RH was studied to estimate the density of residual radicals in the film. The corresponding discharge-power dependence of the plasma structure was also investigated by an effluent mass spectrometry. A critical discharge power was found where the oxidation rate and the plasma structure exhibit substantial changes. X-ray photoelectron spectra showed that the surface of the plasma-polymerized films prepared below the critical discharge power exhibited an excellent oxidation durability as a sputtered film of polytetrafluoroetylene. The films prepared above the critical power exhibited a high oxidation rate. An increase in –C– peaks in the C 1s spectra also suggested defluorination as well as oxidation. The secondary ion mass spectrum for the internal region of the aged plasma-polymerized films prepared above the critical discharge power contained oxidized CxFy species, while the spectra for the aged films prepared below the critical power contained no oxidation-related peaks. Concerning the mass spectra of the C3F6 plasma, high-mass species over 100 amu, including gas phase polymerization products such as C4F7 and C4F8, were predominant below the critical discharge power. Above the critical power, these high-mass species were rather decomposed, and the intensity decreasing with increasing discharge power. Simultaneously, the intensities of the small fragments such as CF, CF2, and CF3 increased with discharge power, causing about 50% of the total pressure increase. The films obtained under such a fragmentation predominant condition contained a higher density of residual radicals, resulting in a deterioration of the oxidation durability.
Cluster beam deposition: Optimization of the cluster beam source
Authors: Gatz P. , Hagena O. F.
Published: July 2002

Cluster beams from supersonic nozzle expansions of a vapor-inert gas mixture are being used for thin film formation of metals or refractory compounds. The cluster beam source is optimized with respect to enlarging the deposition area, given by the width of the cluster beam, and lowering the effective pumping speed for the carrier gas argon. With silver as a representative material for our source, the cluster beam diameter measured at 0.78 m downstream of the nozzle was 94 mm, corresponding to a beam angle of 6.8°, or 0.011 sr, and the deposition rate was up to 14 nm/s. The effective pumping speed of the nozzle discharge chamber could be lowered to 0.1 m3/s at 25.5 Pa. The cluster beam used for thin film formation contained up to 20% of the total silver flux out of the nozzle.
Change in refractive index and in chemical state of electron beam irradiated fluorinated polyimide films
Authors: Maruo Yasuko Yamada , Sasaki Shigekuni , Tamamura Toshiaki
Published: July 2002

The refractive index of fluorinated polyimide is increased by electron beam irradiation. The degree of refractive index change can be controlled by adjusting the dose of the electron beam. The depth of the refractive index change depends on the energy of the beam. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and surface profile measurement of electron beam irradiated fluorinated polyimide film were carried out to investigate the causes of the refractive index increase. The surface profile measurement indicated that the polyimide volume was decreased by an electron beam irradiation. The XPS and SIMS showed that electron beam irradiation decreases the fluorine content. The main cause of the refractive index increase is thought to be this decrease in fluorine content and volume.
Electronic transitions and excitations in solid C70 studied by reflection electron energy loss spectroscopy
Authors: Han Bo-ying , Hevesi K. , Yu Li-ming , Gensterblum G. , Rudolf P. , Pireaux J.-J. , Thiry P. A. , Caudano R.
Published: July 2002

The electronic transition and excitation properties of highly ordered C70 films have been studied by reflection electron energy loss spectroscopy (EELS). The EELS study revealed a total of eleven features in the energy loss range 1–40 eV. These include a prominent peak at 2.55 eV revealing the first dipole allowed transition across the band gap in C70 fullerite; a feature at 2.20 eV correlated with the electron transition between the highest-occupied-molecular-orbital- and lowest- unoccupied-molecular-orbital-derived bands; two excitonic levels corresponding to a tight-binding Frenkel exciton in C70 fullerite at 1.53 and 1.88 eV; and a doublet at 5.2 and 5.9 eV showing evidence of the π-plasmon splitting in fullerite C70. A broad hump at ∼28 eV corresponds to the excitation of the (σ+π) plasmon.
The radio frequency hollow cathode plasma jet arc for the film deposition
Authors: Baránková H. , Bárdoš L. , Berg S.
Published: July 2002

The radio frequency hollow cathode plasma jet (RPJ or RHCPJ) arc discharge is studied for an activated reactive deposition of TiN films. The presence of low content of nitrogen in argon enables reaching the arc regime at lower powers than in pure argon. The transition into the distributed arc after admission of low content of nitrogen results in an extreme enhancement of TiN deposition rate (20–30× higher than for Ti) and at the same time in an effective incorporation of nitrogen into the film. The spontaneously repeated transitions between the hollow cathode discharge and RHCPJ arc at particular parameters are studied. The time development and the character of these transitions confirm the substantial role of metastable argon atoms in the discharge. The comparison of several cathode materials is presented. The reactive deposition of TiN films at low nitrogen pressure without argon is examined.
Optical properties of GaN film grown by metalorganic chemical vapor deposition
Authors: Zhang R. , Yang K. , Qin L. H. , Shen B. , Shi H. T. , Shi Y. , Gu S. L. , Zheng Y. D. , Huang Z. C. , Chen J. C.
Published: July 2002

The room temperature optical properties of single crystal hexagonal GaN films on (0001) sapphire grown by metalorganic chemical vapor deposition are reported in this article. The energy gap of hexagonal GaN was determined as 3.39 and 3.400 eV by optical transmission and photoreflectance (PR), respectively, and refractive index of GaN film as the function of photon energy was obtained. The possible origin of the PR signal was attributed to the modulation of the surface field and line shape broadening of defects. Raman scattering spectra were employed to investigate the photon modes of the GaN film. The properties of longitudinal optical phonon-plasmon coupled modes were further studied, and the carrier concentration and damping constant were determined by line-shape fitting of the coupled modes.
Low-temperature (<450 °C), plasma-assisted deposition of poly-Si thin films on SiO2 and glass through interface engineering
Authors: Wolfe D. M. , Wang F. , Lucovsky G.
Published: July 2002

A low-temperature, two-stage process that employs interface engineering is investigated for deposition of poly-Si thin films on SiO2 and glass. In this two-stage process, film growth is separated into two regimes: (i) interface formation and (ii) bulk film growth. Interface formation (stage 1) was optimized for remote plasma enhanced chemical-vapor deposition (PECVD) of ultra thin (<100 Å) μc-Si films on the oxide. This layer acts as a seed template, providing ordered growth sites for the next stage of film growth. Bulk Si film deposition (stage 2) was then initiated on the seed template using remote PECVD process conditions shown to produce low-temperature (<450 °C), epitaxial-Si films on crystalline silicon substrates, so as to drive a transition to larger grain growth off of the seed crystals. Results showed that the seed layer had a dramatic impact on bulk film crystallinity. Films deposited without a μc-Si seed layer were amorphous, whereas films deposited using a seed layer, in conjunction with the appropriate second stage conditions, were highly oriented (220) poly-Si.
Dissociative adsorption of hydrogen sulfide on GaAs(100)-(2×4) and GaAs(100)-(4×2) surfaces
Authors: Yi Sang I. , Chung Chan-Hwa , Weinberg W. Henry
Published: July 2002

The adsorption of H2S on GaAs(100) surfaces has been studied using high-resolution electron energy-loss spectroscopy, temperature-programed desorption, Auger electron spectroscopy, and low-energy electron diffraction. Dissociative adsorption of H2S to HS and H via a molecularly adsorbed precursor has been observed on both GaAs(100)-(2×4) and GaAs(100)-(4×2) surfaces. Upon exposure of H2S at 100 K, dissociative adsorption occurs prior to adsorption of the more weakly bound, molecularly adsorbed H2S. The dissociated H2S desorbs as AsH3 and S2 at 600 K from the As-rich GaAs(100)-(2×4) surface, suggesting that As–SH bonds were formed from the dissociative adsorption of H2S, which decomposes at 600 K. On Ga-rich GaAs(100)-(4×2), desorption of AsH3 is observed over a wide range of temperatures from 200 to 550 K, although to a lesser extent than from the As-rich surface, and H2 desorption from Ga sites is observed at 500 K. Desorption of S2 was not observed on GaAs(100)-(4×2), suggesting that Ga–SH bonds were formed from the dissociative adsorption of H2S on GaAs(100)-(4×2).
High-pressure flow reactor designed for an ultrahigh vacuum analysis system
Authors: Sellmer C. , Gaussmann A. , Kruse N. , Prins R.
Published: July 2002

A novel high-pressure flow reactor designed to operate with real powder catalysts at pressures up to 10 bar and temperatures up to 400 °C is described. The gas flow is regulated by mass flow controllers, and the temperature is adjusted by a proportional integral derivative control. Using a heatable capillary along with strong differential pumping allows the gas composition to be monitored on-line. The high-pressure volume is kept small in order to ensure rapid evacuation after the reaction. All parts of the system exposed to gas pressure and temperature are made of metal or ceramic. The reactor is attached to an ultra-high-vacuum system equipped with x-ray photoelectron spectroscopy and secondary ion mass spectrometry for surface and reaction studies. The performance of the system is demonstrated by CO-hydrogenation experiments with promoted Pd/SiO2 catalysts.
Atomic step distributions on annealed periodic Si(001) gratings
Authors: Tanaka S. , Umbach C. C. , Blakely J. M. , Tromp R. M. , Mankos M.
Published: July 2002

One-dimensional (1D) and two-dimensional (2D) periodic square-wave gratings fabricated on Si(001) with repeat spacings of 4 and 5 μm and amplitudes of 0.1–0.25 μm were annealed in ultrahigh vacuum at temperatures between 900 and 1200 °C. The surface profiles of the gratings were determined by atomic force microscopy in air after cooling to room temperature. The microscopic structures of the steps and terraces of the gratings were investigated in situ using low-energy electron microscopy. The morphology of the gratings changes with annealing temperature. At 950 °C, both 1D and 2D gratings have surface profiles resembling truncated sinusoids, with large flat regions at the grating extrema. Between 1050 and 1100 °C, the flats at the minima of the 2D gratings expand whereas the flats at the maxima shrink. This asymmetry does not occur for the 1D gratings in this temperature range. At 1200 °C, the profiles of both the 1D and 2D gratings become sinusoidal, with no flats at the extrema. The different morphologies and their temperature dependence can be explained on the basis of the thermodynamics of the surface and the role of surface diffusion and evaporation.
Comparison of ohmic metallization schemes for InGaAlN
Authors: Ren F. , Vartuli C. B. , Pearton S. J. , Abernathy C. R. , Donovan S. M. , MacKenzie J. D. , Shul R. J. , Zolper J. C. , Lovejoy M. L. , Baca A. G. , Hagerott-Crawford M. , Jones K. A.
Published: July 2002

W, WSi0.44, and Ti/Al contacts were examined on n+In0.65Ga0.35N, InN, and In0.75Al0.25N. W was found to produce low specific contact resistance (ǫc∼10−7 Ω cm2) ohmic contacts to InGaN, while WSix showed an as-deposited ǫc of 4×10−7 Ω cm2 but this degraded significantly with subsequent annealing, reaching 10−5 Ω cm2 at 700 °C. Ti/Al contacts on InGaN were stable to ∼600 °C (ǫc∼4×10−7 Ω cm2 at ⩽600 °C). InN contacted with W and Ti/Al produced ohmic contacts with ǫc∼10−7 Ω cm2 and for WSix ǫc∼10−6 Ω cm2 and all three metallization schemes retained values ⩽10−6 Ω cm2 up to 600 °C. The contact resistances for all of the metals were ⩾10−4 Ω cm2 on InAlN, and degraded with subsequent annealing. WSix contacts on InN grown graded from In0.6Al0.4N were also examined. The specific contact resistance was an order of magnitude lower (ǫc∼10−5 Ω cm2) after 500 °C anneal than that measured for WSix deposited directly on In0.6Al0.4N. Measurements of the temperature dependence of these contact structures showed that field emission was generally the most important conduction mechanism.
Ion-scattering spectroscopy during InGaAs molecular beam epitaxy: Reduction of sputtering using glancing-angle Ar ions
Authors: Labanda J. G. C. , Barnett S. A.
Published: July 2002

An ion scattering spectroscopy (ISS) geometry is described that minimizes sputtering and ion damage. The key feature is the use of a glancing-incidence-angle Ar ion beam: Ar ions provide better mass resolution than He while the glancing angle minimizes sputtering. The GaAs(001) sputtering rate, measured via reflection high energy electron diffraction oscillation periods, decreased rapidly with decreasing ion impingement angle φ. For example, the sputtering rate of 3 keV Ar ions decreased from 0.122 to 0.013 ML/s (corresponding to a sputtering yield reduction for ∼3.4 to ∼0.5 atoms/ion) as φ was reduced from 15° to 3°. No sputtering was detected for E=1 keV and φ⩽9°. ISS measurements of 1-ML-thick InAs films on GaAs(001) were made using 1.1 keV Ar ions at φ=3° and a 56° scattering angle. No change in the In peak was observed after 20 min of continuous ISS scans corresponding to a dose of ∼1.6×1016 ions cm−2 (estimated yield < 0.004 atoms/ion). In segregation was observed by ISS during subsequent GaAs overlayer growth.
Nickel doping of boron–carbon alloy films and corresponding Fermi level shifts
Authors: Hwang Seong-Don , Remmes N. , Dowben P. A. , McIlroy D. N.
Published: July 2002

We have grown nickel doped boron–carbon alloy films by the technique of plasma enhanced chemical vapor deposition. The source gas closo-1,2-dicarbadodecaborane (orthocarborane) was used to grow the boron–carbon alloy, while nickelocene [Ni(C5H5)2] was used as the dopant source for nickel. With sufficient levels of Ni doping, diodes with characteristic tunnel diode behavior can be fabricated. The doping of nickel transformed a B5C p-type material, relative to lightly doped n-type silicon, to a strongly n-type material. In order to gain insight into the shift of the Fermi level of the Ni-doped material, we have examined the changes in the electronic structure of sodium doped films of the precursor molecule orthocarborane which has an icosahedral structure similar to that of boron–carbon materials. The establishment of unoccupied states at the Fermi level with Na doping of the orthocarborane films is consistent with the transformation of the p-type B5C to an n-type material with Ni doping.
Semiquantitative subplantation model for low energy ion interactions with surfaces. II. Ion beam deposition of carbon and carbon nitride
Authors: Marton D. , Boyd K. J. , Rabalais J. W. , Lifshitz Y.
Published: July 2002

The semiquantitative subplantation model developed in article I of this series [J. Vac. Sci. Technol. A 16, 444 (1998)] is applied to model experimental data for the systems of C+ and N+ ion interactions with graphite, the deposition of diamondlike carbon (DLC) films from C+ ions, and the deposition of carbon nitride (CxNy) films from C+ and N+ ions. The success of the model is based on its ability to provide semiquantitative interpretations of the physical phenomena underlying experimental data from several sources that had previously been interpreted only qualitatively. These phenomena include the effects of ion kinetic energy, ion beam fluence, substrate temperature, radiation enhanced diffusion, penetration thresholds, displacement thresholds, substrate density, and bonding sites. The model allows one to draw previously unexpected conclusions about the interaction mechanisms and to establish quantitative estimates for some previously unknown physical parameters. The results indicate that there is a value of the C+ and N+ ion penetration threshold, ∼7 to 8 eV, which is applicable to graphite, CxNy, and DLC surfaces. The production of sp3 bonded structures is determined by a balance between the beneficial effects (subsurface deposition, enhanced diffusion, densification) and the deleterious effects (damage) of energetic particle beams.
X-ray photoelectron spectroscopy study of TiN films produced with tetrakis(dimethylamido)titanium and selected N-containing precursors on SiO2
Authors: Endle J. P. , Sun Y.-M. , White J. M. , Ekerdt J. G.
Published: July 2002

Low pressure chemical vapor deposition TiN films were produced on SiO2 by codosing tetrakis(dimethylamido)titanium (TDMAT) with selected N-containing precursors. The films were grown at total pressures ranging from 10−4 to 10−3 Torr and temperatures between 523 and 773 K. Film composition and chemical states were determined, without exposure to ambient pressure, using x-ray photoelectron spectroscopy (XPS). Our primary goal was to evaluate how precursor ligands affect C and N incorporation into TiN films. To this end, methylhydrazine (MH), dimethylhydrazine (DMH), and 1-aminopiperidine (AP) were chosen for their steric differences, and t-butylamine (TBA) and aniline allowed us to assess how C and N incorporation are affected by the C–N bond in the aminolike compounds versus the N–N bond in the hydrazinelike compounds. At all growth temperatures, a decrease in the carbon concentration and an increase in the N concentration were observed for the MH and DMH cases when compared to TDMAT alone, while C content increased for aniline. AP caused only a slight reduction of C at temperatures of 673 K and above. Growth temperature affected film composition and the chemical states of C, N, and Ti. At 623 K, DMH and MH reduced the C/Ti ratio from 1.0 with TDMAT alone to 0.2, while aniline increased C/Ti to 2.0 and AP and TBA had little effect. The addition of the N-containing precursors causes the XPS C 1s peak to broaden and shift to higher binding energy; the N 1s peak also broadened, suggesting that, compared to TDMAT alone, more C–N bonds are formed. Furthermore, the Ti 2p peak shifted to higher binding energy and became broader upon codosing, suggesting the incomplete conversion of Ti (IV) to Ti (III) in the TiN film. Postdosing with MH and DMH supports the conclusion that surface reactions occur between TDMAT and the hydrazinelike precursors.
Determination of metal vapor ion concentration in an argon/copper plasma for ionized physical vapor deposition
Authors: Foster J. E. , Wendt A. E. , Wang W. W. , Booske J. H.
Published: July 2002

An important characterization parameter associated with ionized physical vapor deposition systems is the amount of metal vapor that is actually ionized. In such systems, metal ions, in this case copper, formed by passing sputtered metal vapor through a high density plasma are used for ion plating applications. Here, a Langmuir probe technique is utilized which takes advantage of changes in the ratio of the ion saturation current to the electron saturation current to determine the variations in both copper and argon ion concentrations as a function of sputter power. The data indicate that at fixed rf power, the copper ion concentration increases rapidly with increasing sputter rate, eventually overtaking argon as the dominant ion species in the discharge. These findings also suggest that the fraction of electrons with sufficient energy to ionize argon neutrals decreases as a function of magnetron power. Optical emission spectra collected as a function of magnetron sputter power provide supporting evidence that the electron population in the tail of the electron energy distribution function is depleted by the introduction of the copper vapor. This quenching is attributed to inelastic collisions with copper associated with the low threshold energies and large excitation and ionization cross sections as compared to argon, and the resulting reduction in the measured plasma potential.
Ultralarge scale integrated metallization and interconnects
Authors: Whitman Christine , Moslehi Mehrdad M. , Paranjpe Ajit , Velo Lino , Omstead Tom
Published: July 2002

The use of copper interconnects enables higher speed, enhanced electromigration lifetime reliability, reduced power consumption, and ultimately reduced manufacturing cost for silicon integrated circuits. The formation of planarized inlaid copper interconnects requires sequential deposition of a continuous diffusion barrier layer followed by copper seed/fill deposition and chemical-mechanical polishing (CMP). In this article we present a vacuum-integrated cluster tool technology for deposition of a TaN barrier and copper seed/fill layers using metalorganic chemical vapor deposition (MOCVD). The MOCVD-based TaN layers deposited at substrate temperatures below 430 °C are highly conformal, have 800–1000 μΩ cm resistivity, have satisfactory adhesion to silicon dioxide, and provide superior diffusion barrier properties compared to Ta and TaN layers deposited by physical vapor deposition. The cluster MOCVD-Cu process is capable of depositing conformal and low-resistivity copper seed layers with satisfactory adhesion for subsequent copper filling by either electrochemical deposition or MOCVD. The cluster MOCVD technology has been used to fabricate inlaid copper metallization lines and plugs based on CMP damascene processing. The combination of MOCVD TaN and MOCVD copper is expected to provide an extendable multigenerational copper metallization solution for 0.18–0.10 μm technology nodes and beyond.
Gate oxide damage: Testing approaches and methodologies
Authors: Gabriel Calvin T.
Published: July 2002

The main types of gate oxide damage measurement techniques are examined and compared, leading to a selection of “application-specific” damage measurement techniques. Each technique has strengths and weaknesses, so no single measurement can completely characterize damage. Instead, a combination of measurement approaches is needed, each one targeted to provide a piece of the damage puzzle. It is helpful to understand the different damage mechanisms when selecting a measurement technique, so a survey of mechanisms is given. Damage proceeds by either direct exposure of the gate oxide (through ion bombardment or ultraviolet radiation) or by indirect exposure (by charging from a nonuniform plasma or from the presence of high aspect ratio structures on the wafer). The relative importance of each mechanism depends on process technology and other factors. The most useful combination of damage measurement techniques includes surface potential measurement, electrically erasable read-only memory transistors, direct measurement of charging, antenna transistors, and passive voltage contrast. Damage measurements should be calibrated to device performance parameters such as yield or reliability.
Evaluation of charging damage test structures for ion implantation processes
Authors: Goeckner M. J. , Felch S. B. , Weeman J. , Mehta S. , Reedholm J. S.
Published: July 2002

Control of charging damage is a critical issue in both current and future ion implantation systems. The development of sub-0.18 μm devices will make control of wafer charging more difficult and more important. In addition, sub-0.18 μm devices will require novel doping technologies such as ultralow energy ion implanters or plasma doping, PLAD. Here, we examine the efficacy of two, very distinct, charging monitors. They are Varian Research Center’s, VRC, antenna-MOS devices, and CHARM-2 devices. Some of the limitations and advantages of each test device are examined. In addition, results from implantations using both PLAD and a traditional beamline system are reported. It is found that the results from the VRC devices are consistent with production results while correlations with CHARM-2 results are less clear. It is shown in this article that these differences are due to the fundamental nature of the CHARM technique combined with how modern ion implanters operate. It is also noted that CHARM is well suited for examining charging damage in steady state processes, but these same concerns for the reliability of predictions based on CHARM-2 data will arise for any ion/plasma process in which the current to the surface undergoes rapid variations.
Scanning tunneling microscope studies of boron-doped Si(001)
Authors: Nielsen J.-F. , Im H.-J , Pelz J. P. , Krueger M. , Borovsky B. , Ganz E.
Published: July 2002

We have used scanning tunneling microscopy (STM) and Auger electron spectroscopy to characterize B/Si(001) surface structures and the dependence of their density and location on high-temperature annealing. While annealing of heavily B-doped Si(001) surfaces is known to result in periodic SB step “fingers” whose density depends strongly on temperature, we have found that, on the time scale of formation of the step fingers, the atomic-scale properties of these surfaces are not altered significantly by high-temperature processing. B structures were found to decorate SA step edges. Hot STM was used to study the dynamics of finger formation and the interaction between atomic-scale B/Si(001) structures and fluctuating dimer rows.
Effects of grid bias on ZnO/α-Al2O3(0001) heteroepitaxy
Authors: Doh S. J. , Park S. I. , Cho T. S. , Je Jung Ho
Published: July 2002

We studied grid-bias effects on the microstructure of epitaxial ZnO/α-Al2O3(0001) films using synchrotron x-ray scattering and atomic force microscopy. ZnO films were grown by radio frequency magnetron sputtering, applying positive or negative bias on a grid that was set-up 2 cm from the substrate. We found that the epitaxial quality of the ZnO films was greatly dependent on the bias voltage; as the bias increased from 0 to +100 V, the mosaic distribution of the ZnO(0002) planes and the surface roughness continually improved. But a further increase in bias led to a falling off of the epitaxial quality. Meanwhile, negative biases deteriorated the epitaxial quality significantly. We attribute the best epitaxial quality at an optimum bias to the great flux reduction of energetic oxygen anions bombarding the film surface, thereby significantly suppressing the resputtering phenomenon. We suggest that a biased grid may be very useful for enhancing the epitaxial quality of ZnO films in sputter deposition.
Epitaxial growth of Zn2Y ferrite films by pulsed laser deposition
Authors: Kim H. , Horwitz J. S. , Piqué A. , Newman H. S. , Lubitz P. , Miller M. M. , Knies D. L. , Chrisey D. B.
Published: July 2002

Oriented and single phase Ba2Zn2Fe12O22 (Zn2Y) thin films (∼5000 Å thick) have been grown using pulsed laser deposition (ArF, 193 nm) on single-crystal (0001) sapphire substrates. A single phase polycrystalline Zn2Y target was used to deposit films. The composition, structure, and morphology of the films were determined using Rutherford backscattering spectrometry, x-ray diffraction (XRD), and scanning electron microscopy. As a function of substrate temperature (>700 °C), films deposited in 200 mTorr of oxygen pressure were found to be deficient in Zn. The Zn deficiency increased with increasing substrate deposition temperature (<900 °C). Analysis of the XRD patterns indicated that films deposited from stoichiometric targets were primarily BaFe12O19 (BaM). Compensation of the target with excess Zn changed the structure of the film from BaM to a mixture of phases, i.e., BaM and Zn2Y. Highly oriented and single phase Zn2Y films could be achieved by depositing Zn2Y film onto ZnO (∼400 Å) buffered sapphire substrates. Deposited films exhibit an epitaxial relationship of (001)Zn2Y//(001)ZnO//(001)Al2O3. The ferromagnetic resonance derivative linewidth of the Zn2Y film for an in-plane applied field was ∼310 Oe, which is larger than expected for bulk single crystals.
Secondary ion coincidence in highly charged ion based secondary ion mass spectroscopy for process characterization
Authors: Hamza Alex V. , Schenkel Thomas , Barnes Alan V. , Schneider Dieter H.
Published: July 2002

Coincidence counting in highly charged ion based secondary ion mass spectroscopy has been applied to the characterization of selective tungsten deposition via disilane reduction of tungsten hexafluoride on a patterned SiO2/Si wafer. The high secondary ion yield and the secondary ion emission from a small area produced by highly charged ions make the coincidence technique very powerful.
Consideration of local shadowing and ion beam voltage effects in the prediction of a surface evolving under ion milling
Authors: Klein Eric J. , Ramirez W. Fred
Published: July 2002

Ion milling applications in the micro-electronics industry are becoming more challenging due to decreasing feature sizes and increasing aspect ratios. A simulation of the milling problem which is capable of predicting surface evolution in the presence of high aspect ratios where local shadowing of the substrate surface becomes an important issue is described. A method of characteristics solution based on surface inclination angles is derived for a three-dimensional surface evolution model. An algorithm is developed to account for local shadowing effects, where raised areas of the substrate surface (i.e., the photomask) prevent the ion beam from reaching hidden or shadowed portions of the surface. The yield (sputtering) function is modified to account for beam voltage as well as the angle of beam incidence. Yield function parameters are determined experimentally for Al2O3, Ti, permalloy (83/17 wt % Ni–Fe) and postbaked AZ P4400 photoresist. Model predictions are in good agreement with experimental results for the surface evolution of a photopatterned Al2O3 substrate.
Growth of GaNAs by molecular beam expitaxy using a N2/Ar rf plasma
Authors: Gotthold David W. , Govindaraju Sridhar , Mattord Terry , Holmes Archie L. , Streetman Ben G.
Published: July 2002

A high efficiency nitrogen rf plasma source has been used to grow GaNAs by diluting the N2 gas with Ar. This source (an EPI UniBulb™ source) was originally designed for use in the growth of pure nitrides at high growth rates. For growth of As-rich GaNAs, high concentrations of active nitrogen lead to the growth of GaN instead of a random alloy. In this work we demonstrate that a dilute N2/Ar mixture leads to GaNAs films where the amount of nitrogen incorporation varies directly with the percentage of N2 in the gas mixture. Films with high structural quality were grown, thus validating the use of this approach.
GaInAs–AlInAs heterostructures for optical devices grown by MBE
Authors: Welch D. F. , Wicks G. W. , Woodard D. W. , Eastman L. F.
Published: July 2002

The band gap of Ga0.47In0.53As corresponds to an emission wavelength of ∼1.65 μm. Lasers have been produced with Al0.48In0.52As as cladding layers operating at room temperature. The peak emission of Ga0.47In0.53As can be continuously varied from 1.65 to 1.2 μm by the use of the multiquantum well structures. This range of wavelengths covers the minimum loss and dispersion in optical fibers and will be applicable to integrated optics. Double heterostructure broad area lasers have been fabricated using AlInAs as cladding layers to the GaInAs active layer. Room temperature threshold current densities of 4.3 kA/cm2 have been obtained for lasers with a 4500 Å active regions. The first data on GaInAs/AlInAs quantum well emitters will be presented. 4 K photoluminescence from quantum well layers of 100, 150, and 180 Å with 150 Å AlInAs barrier layers produced emission at 1.27, 1.35, and 1.41 μm, respectively. Ga0.47In0.52As quantum well LED’s have also been produced which emit at 1.34 μm.
n-i-p-i doping superlattices—metastable semiconductors with tunable properties
Authors: Döhler Gottfried H.
Published: July 2002

Semiconductors, modulated by periodic n and p doping, possibly with intrinsic regions in-between (‘‘n-i-p-i crystals’’) represent a new class of semiconductors, because of their tunable electronic properties. A large number of intriguing phenomena, predicted by the theory, have been observed recently on GaAs doping superlattices grown by molecular beam epitaxy. In this paper we summarize the theory and experimental results with special emphasis on the aspects of the metastability of large deviations of the carrier concentrations from thermal equilibrium. Approximate analytical expressions for the lifetime enhancement, its dependence of the ‘‘design parameters’’ and on the state of excitation are derived. A brief outlook on possible extensions of the original concept is given.
Two-stage arsenic cracking source with integral getter pump for MBE growth
Authors: Krusor B. S. , Bachrach R. Z.
Published: July 2002

The design is described for a two-stage arsenic evaporation and cracking source that incorporates an integral getter pump which effectively converts As4 to As2 as well as reduces arsenic oxides. The results show that the conversion efficiency from As4 to As2 is approximately 85% at 700 °C and the in beam background As–O is reduced during growth by a factor of 6 for our system to approximately 1×10−10 Torr. We have measured the room temperature As2 sticking coefficient on GaAs and find that it increases from near zero for As4 to 0.5 for As2. The effect of the cracking has been evaluated by measurements on layers and devices grown with this arsenic source.
Optical properties of GaSb–AlSb superlattices
Authors: Mendez E. E. , Chang C.-A. , Takaoka H. , Chang L. L. , Esaki L.
Published: July 2002

The formation of a GaSb–AlSb superlattice grown by molecular beam epitaxy has been demonstrated metallurgically from x-ray diffraction and optically from electroreflectance and photoluminescence measurements. The luminescence spectra exhibit emission peaks associated with interband transitions between quantum states as well as acceptor impurities.
Initial growth of Al on GaAs(001) and electrical characterization of the interface
Authors: Andersson Thorwald G. , Svensson Stefan P. , Landgren Gunnar
Published: July 2002

The formation of the interface between GaAs(001) and Al was studied by reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). All growth was performed by molecular beam epitaxy. Two surface reconstructions defined the native surface: c(2×8) and (4×6). In the studied temperature interval, 268 to 673 K, two temperature ranges were found. Above 550 K no nucleation was observed. At lower temperatures the growth of the first monolayer (ML) was detected as a linear (temperature independent) increase of the Auger signal with coverage. In the coverage range between 1 ML and the point of nucleation the Auger signal became more nonlinear. Both the Al and Ga Auger energies shifted toward metallic states. This shift, however, decreased with substrate temperature. The event of nucleation as observed by RHEED had a clear temperature dependence only when starting the growth from the c(2×8) surface. Evidence was found by both AES and electrical characterization that increasing temperature caused an intermixing at the interface. Electrical characterization of the interface was made by capacitance-voltage (C-V) and current-voltage (I-V) techniques. Averaging over a large number of diodes gave the Schottky-barrier height φb ≊0.75 eV for both techniques. No dependence on the initial surface reconstruction was found but excess Ga gave a larger barrier while excess As typically gave a lower barrier. Annealing the interface usually increased the Schottky barrier and increased the ideality factor above ∼1.05.
Ga(As,P) strained-layer superlattices: A ternary semiconductor with independently adjustable band gap and lattice constant
Authors: Gourley P. L. , Biefeld R. M.
Published: July 2002

We have measured both the lattice constant and the optical transitions in GaP/GaAsxP1−x strained-layer superlattices (SLSs) as a function of composition x from x=0 to 0.6. By comparing these results to those for the alloys GaAsx̄P1−x̄ where x̄=x/2 corresponds to the same average compositions as the SLSs, we demonstrate for the first time in a ternary system, a semiconductor crystal with a band gap that can be varied independently of its lattice constant.
Improvement of electrostatic lenses for ion beam lithography
Authors: Szilagyi M.
Published: July 2002

A systematic investigation of a large number of practically feasible axial potential distributions was carried out with a subsequent reconstruction of the electrode systems producing such distributions. By using parametrized analytical functions and different curve-fitting techniques we were able to find many potential distributions with both small spherical and chromatic aberrations. A cubic spline curve-fitting algorithm proved to be especially effective. The reconstruction of the electrode systems resulted in several new electrostatic ion lenses with excellent optical properties. As an example, a four-electrode electrostatic lens is presented with a voltage ratio of Vmax/Vmin =9, spherical aberration coefficient Cs0/f0 =0.92 and chromatic aberration coefficient Cc0/f0 =0.55 (both coefficients are referred to the object, related to the object side focal length and calculated for the case of infinite magnification). With an acceptance angle α0=5 mrad and magnification M=2.58 a 10.5 nm aberration disk diameter can be achieved. If α0=2 mrad, the disk diameter is 3 nm.
Elevated temperature low energy ion cleaning of GaAs
Authors: Oelhafen P. , Freeouf J. L. , Pettit G. D. , Woodall J. M.
Published: July 2002

We have studied various cleaning procedures for obtaining atomically clean, well-ordered surfaces of GaAs(100) and (110). We have evaluated the resulting surfaces by angle resolved ultraviolet photoelectron spectroscopy (ARUPS), x-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). We report results for thermally cleaned, ion bombarded and annealed, and ion bombardment at elevated temperature cleaning procedures. The most reproducible results, giving the best, lowest background LEED patterns and the sharpest ARUPS results, were obtained from the elevated temperature ion bombardment cleaned samples. Our thermally cleaned samples, while showing low impurity concentrations to XPS studies, had a relatively high background LEED pattern. The ARUPS results were not indicative of a high degree of surface order; the normal emission spectra more resemble angle integrated UPS results. The room temperature ion bombarded samples, followed by anneals of 30 min at temperatures up to 520 °C, yielded a high quality 1×1 pattern on a GaAs(100) surface, but no higher order reconstruction could be obtained. The ion bombardment typically used in this work was 200 eV Ar ions. Substrate temperature during bombardment were varied from 300 to 800 K. Post anneals were also examined. Temperatures of 300 °C were quite adequate to obtain a high quality 1×1 LEED pattern on both (100) and (110) surfaces. Post anneals at 520 °C yielded a low background (8×2) Ga surface.
Chemical deposition of SiO2 on InP
Authors: Bertrand P. A. , Fleischauer P. D.
Published: July 2002

Chemical deposition experiments were performed to determine how surface preparation and film deposition conditions influence the resulting insulator–semiconductor interface composition and chemical structure. Silicon dioxide layers were chemically deposited on indium phosphide by hydrolyzing silicon orthopropoxide. On unoxidized, etched surfaces, coverage was always patchy. On InP with approximately one monolayer of chemisorbed oxygen in a hydrated-phosphatelike environment, a continuous, ∼60-Å-thick SiO2 film was formed at room temperature. SiO2 attached to the substrate through about one monolayer of Si–O–P bonds. Heating to 50 °C during hydrolysis resulted in a mixed Si–In–P oxide, owing to simultaneous hydrolysis and oxidation processes.
The use of pulsed laser irradiation in silicon molecular beam epitaxy: A comparative low energy electron diffraction study
Authors: de Jong T. , Douma W. A. S. , Smit L. , Korablev V. V. , Saris F. W.
Published: July 2002

We present a low energy electron diffraction (LEED) study of the initial stages of epitaxial growth of silicon on silicon with emphasis on the growth mechanisms involved. Silicon is evaporated under ultrahigh vacuum conditions. We used pulsed laser irradiation and thermal annealing for surface preparation and show that epitaxial growth can take place on surfaces, prepared by either procedure. We determined the epitaxial temperature (defined with electron diffraction) for Si(111) and Si(100) substrates. We also used 4.0° vicinal oriented Si(111) to determine the influence of a large number of misorientation steps on the growth mechanism. The (100) epitaxial temperature equals 470 K, much lower than that of Si(111) which is found to be 870 K. The use of vicinal (111) surfaces lowers the epitaxial temperature to 770 K. Pulsed laser irradiation was not only used to prepare clean and ordered substrate surfaces, but also as a means to prepare the metastable Si(111) surface, exhibiting a (1×1) LEED pattern. The initial stages of epitaxial growth on this surface were studied. Room temperature depositions of Si on Si(100) are shown to be partly ordered. Three differently prepared (100) substrates were used to determine the influence of substrate surface preparation on the structure of the overlayer.
Very low threshold current GaAs–AlGaAs GRIN-SCH lasers grown by MBE for OEIC applications
Authors: Fujii T. , Yamakoshi S. , Nanbu K. , Wada O. , Hiyamizu S.
Published: July 2002

Very highly efficient GaAs–AlGaAs GRIN–SCH lasers were grown on an n-GaAs substrate as well as on a semi-insulating GaAs substrate by MBE. The threshold current density Jth of the lasers was found to be minimum when the thickness of the GaAs quantum well active layer is 6 nm. The lowest Jth of 260 A/cm2 was achieved for the broad-area Fabry–Perot laser (the Al composition of the cladding layer x=0.7, the cavity length L=400 μm). A ridge-waveguide (5 μm wide stripe) GaAs–AlGaAs GRIN–SCH laser, which is monolithically integrated with GaAs MESFET’s on a semi-insulating GaAs substrate, exhibited cw operation with a threshold current as low as 19 mA at room temperature.
Nonuniform surface potentials and their observation by surface sensitive techniques
Authors: Tang J. Y.-F. , Freeouf J. L.
Published: July 2002

Various models of Schottky barrier formation have been proposed in the last few years which involve metallurgical interactions at the metal–semiconductor interface. Most of these models involve nonuniform lateral variations in the surface potential. For metallic clusters and/or anion clusters, these variations involve a relatively large size scale (tens to hundreds of angstroms). For interface defect formation, the suggestion of cluster formation energy as the driving force for defect formation could also lead to a nonuniform distribution of pinning sites on a similar size scale. We have studied the effects of various spatial distributions of pinning sites (e.g., surface defects, clusters of anions and/or adsorbed metal atoms) and variations of their energy levels upon surface potentials and their depth distribution via a two-dimensional finite difference program that integrates Poisson’s equation. Our results suggest that surface sensitive spectroscopies provide a less than exact measure of pinning levels in many such cases. For example, for 1018 n-GaAs and pinning site separation of 100 Å, our calculations imply a Kelvin probe band-bending result for the surface potential of ≊0.15 V less than the ‘‘pinning’’ value (for pinning values of 0.8 and 0.6). Furthermore, such nonuniform distributions alter the effect of probe depth. The surface potential determined via e.g., UPS, with a 20 Å mean free path, would differ from the ‘‘true’’ surface averaged value by ≊0.09 eV for a uniform 0.8 V surface; while this difference is ≊0.07 for 100 Å separations, and ≊0.05 for 400 Å separations, the ratio of this λ dependent term to the total measured band bending increases as the distance between pinning sites increases. Note that a pinning level 0.8 eV below the conduction band minimum leads (under the assumptions of 100 Å between sites, probe depth ≊20 Å, and 1018 cm−3 bulk doping) to a ‘‘measured’’ surface potential within 0.6 eV of the conduction band minimum. These results should impact the interpretation of surface dependent studies of Schottky barrier formation, especially for specific models of such formation.
Structure and properties of rapidly thermal annealed Ta/Si multilayers
Authors: Natan Menachem , Shatas Steven C.
Published: July 2002

The microstructure, chemistry, and phases in thin Ta/Si multilayers of various stoichiometry reacted by rapid thermal annealing (RTA) were investigated with cross-sectional transmission electron microscopy (X-TEM), Auger electron spectroscopy (AES), and glancing angle x-ray diffraction (XRD). The nucleation and growth processes of TaSi2, the only silicide formed, are illustrated and discussed. The growth kinetics are affected by contamination. In contrast to reactions between Ta films and crystalline Si substrates where Si is diffusing and Ta is stationary, both species appear to be diffusing in thin amorphous multilayers. A thin Ta oxide forms on the surface when the material in contact with the annealing atmosphere (0.999 99 Ar) is Ta, but not when it is Si or TaSi2. The resistivity is stoichiometry and temperature dependent, and is always higher in silicide-on-SiO2 than in polycide structures, indicating that polysilicon substrates shunt some of the current during measurement.
Quantum model of dephasing-enhanced laser desorption: Master equation approach
Authors: Lin Jui-teng , Huang Xi-Yi , George Thomas F.
Published: July 2002

A new model for laser-induced desorption is proposed based on a master equation for the photon population in a closely coupled subsystem involving the relevant degrees of freedom. The validity of approximations such as the Born and Markovian approximations is discussed in terms of the laser pulse duration and multiple time scales of the adspecies-surface system. The desorption rate is numerically calculated from the photon population and the threshold number of photons absorbed by the adspecies. The effects of anharmonicity, dephasing and laser detuning on the desorption rate are examined. The mechanism of dephasing and the possible direct and indirect desorption channels are discussed.
Heterojunction band discontinuity growth sequence variation at compound semiconductor-germanium (110) interfaces: Possible role of antiphase disorder
Authors: Grant R. W. , Waldrop J. R. , Kowalczyk S. P. , Kraut E. A.
Published: July 2002

The valence-band discontinuity (ΔEv) at heterojunctions formed by growing GaAs epitaxially on Ge(110) substrates has been studied by using x-ray photoelectron spectroscopy. The GaAs grown on Ge (110) interface is observed to exhibit a time dependent variation in ΔEv that is as much as ∼0.2 eV. For GaAs/Ge(110) heterojunctions grown at 350 °C and kept at room temperature for >100 h, ΔEv∼0.3 eV; this is ∼0.25 eV less than the ΔEv measured for the stable interface formed by growing Ge epitaxially on GaAs (110). It is observed that ΔEv for growth of a lattice matched compound semiconductor (AB) on Ge(110) is substantially smaller than for the reverse growth sequence, i.e., ΔEv [AB/Ge(110)]<ΔEv[Ge/AB(110)]. A possible mechanism for this growth sequence effect which involves antiphase disorder at AB/Ge(110) interfaces is suggested.