bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of the phosphine plasma decomposition and its formation by ablation of red phosphorus in hydrogen plasma
Authors: Bruno G. , Losurdo M. , Capezzuto P.
Published: July 2002

Mass spectrometry and optical emission spectroscopy have been used to study the chemistry of PH3 plasma decomposition as well as its formation by ablation of red phosphorus in hydrogen plasma. It has been shown that PH3 decomposition easily equilibrates at low levels of PH3 depletion (15%–30 %), this depending mainly on the rf power. The ablation of red phosphorus in H2 plasma produces phosphine in significant amount, depending mainly on the total pressure but also on the rf power. It has also been found that H* and PH* emitting species originate not only by the dissociative excitation of H2 and PH3, respectively, but also by the direct excitation of the same species in the ground state. Considerations are developed on how to derive the H-atom and PH radical densities by actinometry, under specific experimental conditions. Besides, the linear dependence of PH3 formation rate, rPH3, on H-atom density, [H], leads to the definition of the kinetic equation rPH3=k[H], and to the hypothesis that the formation of PH radical on the surface or its desorption is the dominant mechanism for PH3 production.
X-ray photoelectron spectroscopy study of submonolayer native oxides on HF-treated Si surfaces
Authors: Yano Fumiko , Hiraoka Akiko , Itoga Toshihiko , Kojima Hisao , Kanehori Keiichi , Mitsui Yasuhiro
Published: July 2002

This article investigates, by a novel spectral analysis technique, the possibility of applying conventional x-ray photoelectron spectroscopy to characterize the initial oxidation process. Quantitative analysis of submonolayer native oxides is made possible by spectral decomposition of Si 2p into Si4+, Six+, and Si0+ based on the O 1s binding energy, and by calculation of the SiO2 and SiOx thicknesses using the decomposition results. Here, the sensitivity for oxide-thickness change is about 1/10 monolayer. Using this technique, the initial oxidation processes of HF-treated Si(111) and Si(100) are precisely characterized. The influence of the dissolved-oxygen concentration in the HF solution is also investigated.
Radiation-induced decomposition of PF3 on Ru(0001)
Authors: Tao H.-S. , Diebold U. , Chakarian V. , Shuh D. K. , Yarmoff J. A. , Shinn N. D. , Madey T. E.
Published: July 2002

Soft x-ray photoelectron spectroscopy using synchrotron radiation has been employed to study the decomposition of PF3 on Ru(0001) at 80 K induced by energetic electrons. Due to the large binding energy shifts in the P 2p core levels, the phosphorus-containing surface intermediates produced from the electron-induced decomposition of PF3 can be identified and their evolution can be followed as the fluence of electrons is changed. A stepwise decomposition of PF3 induced by energetic electrons, i.e., PF3→PF2→PF→P, is observed. The dissociation cross section for PF3→PF2 induced by 550 eV electrons is measured to be on the order of ∼1×10−16 cm2. The main channels that lead to PF3 dissociation involve the excitation of F 2s as well as valence states of PF3.
Effect of preadsorbed oxygen on the direct dissociative chemisorption of ethane on Ir(110)
Authors: Kelly D. , Hago W. , Weinberg W. H.
Published: July 2002

Molecular beam techniques were employed to determine the effect of preadsorbed oxygen on the direct dissociative chemisorption of ethane on Ir(110) at a surface temperature of 600 K. The direct dissociative chemisorption of ethane on Ir(110) has been investigated using translational beam energies of 12 to 30 kcal/mol, parametric in oxygen precoverage from the clean surface to the oxygen-saturated surface [1 monolayer (ML) of dissociatively adsorbed oxygen]. We observed that the probability of direct dissociative chemisorption decreases in the presence of dissociatively adsorbed oxygen. For all beam translational energies studied, an oxygen precoverage of 0.12 ML decreases the probability of direct dissociative chemisorption of ethane to approximately one-half the probability observed on clean Ir(110). For oxygen precoverages below 0.5 ML, the probability of direct dissociative chemisorption of ethane increases with increasing beam translational energy. However, for oxygen precoverages of 0.5 ML or greater, the probability of direct dissociative chemisorption is independent of beam translational energy. In the case of high (≥ 0.5 ML) oxygen precoverages, CO evolution is detected from the surface during the dissociative chemisorption of ethane, resulting in a transient enhancement of the probability of chemisorption prior to ultimate poisoning by carbon.
Formation of metastable epitaxial CoSix (x<2) layers by reactive codeposition on CoSi2(111)
Authors: Hong S. , Wetzel P. , Gewinner G. , Pirri C.
Published: July 2002

The reaction of Co deposited at 350 °C on epitaxial CoSi2 is investigated by means of low-energy electron diffraction, core-level and angle-resolved valence-band photoemission, and ion scattering spectroscopy. Co is deposited onto ∼100-Å-thick CoSi2(111) films epitaxially grown on Si(111) which exhibit a Si-rich surface. For one Co monolayer equivalent, the Si-rich surface labeled CoSi2(111)–Si is converted into a bulklike terminated one, labeled CoSi2(111). The latter is characterized by a specific surface state located at ∼2.8 eV binding energy at the center of the surface Brillouin zone, which derives from dangling bonds on Co and Si in the topmost planes. Upon increasing the amount of Co, the latter is found to react with the silicide layer up to much larger depths comparable to the photoelectron mean free path (15–20 Å). A thin metastable epitaxial CoSix (x≤2) overlayer with a cubic structure is formed for Co amounts up to the equivalent of 15 monolayers, typically. The electronic as well as crystallographic structure of this thin metastable CoSix layer is compared to that of recently discovered metastable CoSix layers, epitaxially grown on Si(111) by codeposition and found to be closely related. The data strongly suggest a simple picture where the additional Co merely diffuses into the initial CaF2-type CoSi2 layer and occupies part of the interstitial octahedral sites of the face centered cubic Co sublattice. Moreover, it is shown that upon reaction of 6–8 Co monolayers the surface state observed on the ideal-bulk–CoSi2(111) termination still persists but is shifted toward higher binding energies due to changes in the composition of the silicide underneath. This indicates that the surface structure of the CoSix (x≤2) layer is also similar to that of bulk-terminated CoSi2(111). For higher Co coverages, an epitaxial ε-CoSi layer with the stable B20 type structure is achieved, as attested by a ∛×∛ R30° low-energy electron diffraction pattern and specific valence-band features.
Trapping-mediated dissociative chemisorption of propane on Ir(110)
Authors: Kelly D. , Weinberg W. H.
Published: July 2002

We have employed molecular beam techniques to investigate the molecular trapping and trapping-mediated dissociative chemisorption of propane on Ir(110) at low beam translational energies, Ei≤5 kcal/mol, and a wide range of surface temperatures, Ts, from 85 to 1200 K. At Ei=1.6 kcal/mol and Ts=85 K, molecular propane is physically adsorbed on Ir(110) with a trapping probability of 0.94. At Ei=5 kcal/mol and Ts=85 K the trapping probability drops to 0.86. For Ts≳150 K propane is dissociatively chemisorbed, with initial probabilities of dissociative chemisorption decreasing with increasing surface temperature from 150 to approximately 700 K. At surface temperatures from 700 to 1200 K, the initial probability of dissociative chemisorption maintains the essentially constant value of 0.16. These observations are explained within the context of a kinetic model which includes both C–H and C–C bond cleavage. Below 500 K propane chemisorption on Ir(110) arises essentially solely from C–H bond cleavage, an unactivated mechanism (with respect to a gas-phase energy zero) for this adsorption system, which accounts for the decrease in initial probabilities of chemisorption with Ts. With increasing Ts, however, C–C bond cleavage, the activation energy of which is greater than the desorption energy of physically adsorbed propane, increasingly contributes to the measured probability of dissociative chemisorption. The activation energies, referenced to the bottom of the physically adsorbed molecular well, for C–H and C–C bond cleavage for C3H8 on Ir(110) are found to be Er,CH=5.3±0.3 kcal/mol and Er,CC=9.9±0.6 kcal/mol, respectively, while the desorption activation energy of propane from Ir(110) is approximately 9.5 kcal/mol. These activation energies are compared to activation energies determined recently for ethane and propane adsorption on Ir(111), and ethane activation on Ir(110).
Low temperature growth of AlN(0001) on Al(111) using hydrazoic acid (HN3)
Authors: Russell John N. , Bermudez Victor M. , Leming Andrés
Published: July 2002

Thin films of AlN(0001) were grown by reacting hydrazoic acid (HN3) with an Al(111) substrate at temperatures below 800 K. The resulting films were characterized with Auger electron spectroscopy, low energy electron diffraction (LEED), and infrared reflection-absorption spectroscopy (IRRAS). The energies and line shapes of the Al LVV and N KLL Auger transitions were consistent with those of AlN. A hexagonal LEED pattern, in registry with that of the Al(111) substrate, was observed for the fully nitrided film and was consistent with a single-domain, AlN(0001) surface. Only the A1 LO phonon mode of AlN, at 886 cm−1, was observed in IRRAS, indicating a wurtzite-structured film with the c axis normal to the surface plane.
Dual-plasma reactor for low temperature deposition of wide band-gap silicon alloys
Authors: Etemadi R. , Godet C. , Perrin J. , Drévillon B. , Huc J. , Parey J. Y. , Rostaing J. C. , Coeuret F.
Published: July 2002

A dual-plasma [surface wave-coupled microwave (MW) at 2.45 GHz and capacitively coupled radio frequency (rf) at 13.56 MHz] reactor called MORFAX was developed for the deposition of amorphous wide band-gap alloys (a-SiOx:H, a-SiNy:H) at high growth rates and at low temperatures compatible with usual polymer substrates. These optical thin films may be used as components of multilayer coatings, such as index gradient devices or transparent interferential filters, to protect optical polymers. The dual-plasma MORFAX reactor was designed to provide three advantages: a high reactive species density (MW), a chemical selectivity due to the separation of the MW plasma and the rf plasma regions, and a variable ion bombardment energy due to the rf plasma dc polarization. Using O2, NH3, or N2 gases diluted in He–Ar mixtures in the microwave plasma while silane was injected in the postdischarge region, we have obtained the following information. (i) Optical emission spectroscopy shows the changes in the electron energy distribution function for single- and dual-plasma modes as a function of the (He–Ar) mixture composition, that in turn provides a means to control the reactive gas processes. (ii) In the single MW mode, the decomposition of O2 (diluted in He–Ar) is very efficient, producing an atomic oxygen density of [O]≈1014cm−3; due to low wall recombination, a high density of atomic O is transported in the flowing afterglow where silane is very strongly decomposed by O atoms. (iii) In the dual-plasma mode, atomic oxygen produced in the MW plasma and electrons due to the rf plasma both participate in the silane decomposition. Cooperative effects between the MW postdischarge and the rf plasma were observed, in particular on the deposition rate of silicon oxide films. (iv) As compared to oxide growth rates (up to 5 nm s−1 limited by the silane depletion), the lower growth rate of silicon nitride films is attributed to the small reactive dissociation coefficient of SiH4 by N and NH2 radicals. (v) In situ and ex situvibrational spectroscopy and spectroscopic ellipsometry show that the ion energy can be effectively used to increase the density of the oxide films. At 70 °C, good control of the stoichiometry and porosity of a-SiOx:H films was obtained over the full composition range (0⩽x⩽2.2). Water molecules are reversibly adsorbed upon exposure of the porous oxide films to the ambient and are desorbed under vacuum at room temperature.
Effect of H2 addition on surface reactions during CF4/H2 plasma etching of silicon and silicon dioxide films
Authors: Marra Denise C. , Aydil Eray S.
Published: July 2002

In situ multiple internal reflection Fourier transform infrared spectroscopy and spectroscopic ellipsometry are used to study the surfaces of Si and SiO2 films during etching with CF4/H2 plasmas. At sufficiently low H2 concentration, a thin fluorocarbon film forms on both Si and SiO2 surfaces during etching, but Si and SiO2 removal continues despite the existence of such a layer. The structure of this film depends on the H2 concentration in the feed gas. Above a critical H2 concentration, the fluorocarbon film becomes more crosslinked, fluorine deficient, and amorphous carbonlike. Formation and subsequent growth of this fluorinated amorphous carbon (a-C:F) film stops etching of both Si and SiO2. In the absence of energetic ion bombardment, the critical concentration at which etching is arrested and a-C:F growth begins is the same for both Si and SiO2 films indicating that whether this film forms or not is determined by the fluxes of reactive species arriving at the surface from the gas phase rather than by the nature of the surface. In particular, H abstraction of F from the fluorocarbon film is shown to be responsible for the formation of fluorine deficient amorphous carbonlike film. In the presence of energetic ion bombardment this critical H2 concentration is increased but at different amounts for Si and SiO2 films. The film formed on SiO2 is more easily sputtered than that which forms on Si due to the higher number of C–O bonds in the film formed on SiO2. The difference in the structure of the inhibiting layers formed on Si versus SiO2 enables the selective etching of SiO2 over Si.
Multicomponent surface analysis system combined with high pressure reaction cells for studying metal oxide model catalysts
Authors: Weiss W. , Ritter M. , Zscherpel D. , Swoboda M. , Schlögl R.
Published: July 2002

A three chamber ultrahigh vacuum (UHV) surface analysis system combined with high pressure reaction cells has been designed. It can be used for the preparation and characterization of ordered metal oxide model catalyst surfaces and for the investigation of heterogeneous catalytic reactions there on also under high pressures. The reaction cells are completely separated from the UHV analysis chambers. They can be used for oxidation treatments and reaction studies at total pressures up to 1 bar. A new sample transfer mechanism together with sapphire sample holders and sample heating–cooling stations on the analysis chamber manipulators provides electron beam and resistive sample heating, liquid nitrogen sample cooling, and precise thermocouple temperature control. First experimental results obtained on single crystalline iron oxide dehydrogenation films grown onto Pt(111) substrates are presented. These results demonstrate the capability of the system for in situ investigation of a sample surface using scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, photoelectron emission microscopy, and temperature programmed desorption before and after catalytic reactions at high pressures. This single crystal surface science approach provides new insight into the atomic scale surface chemistry of metal oxides under real catalysis conditions.
Measurement and error evaluation of electrical parameters at plasma relevant frequencies and impedances
Authors: Garvin C. , Grimard D. , Grizzle J. , Gilchrist Brian E.
Published: July 2002

The errors present in electrical measurements at frequencies and impedances relevant to plasma processing in the semiconductor industry are studied. A theoretical bound on calculated delivered power error as a function of measured electrical values is derived. The derivation shows that for constant measurement error, power error is a linear function of load impedance expressed in terms of voltage standing wave ratio. This bound is supported by experimental data taken with both a directional coupler and a voltage- and current-based probe. Linear and nonlinear model based sensing methods are implemented which reduce power error by a factor of 5 over a standard calibration. Published results are cited which indicate that the voltage standing wave ratio of typical plasma processing and experimental regimes is high enough to cause small measurement errors to result in large calculated power errors.
Characterization of the etch rate non-uniformity in a magnetically enhanced reactive ion etcher
Authors: Buie M. J. , Pender J. T. P. , Dahimene M.
Published: July 2002

A constant concern in semiconductor manufacturing is plasma induced damage. A non-uniform etching plasma can induce a dc current at the wafer surface that can damage the film and therefore the device. The magnetic field in an Applied Materials magnetically enhanced reactive ion etch chamber has been enhanced to provide minimal self-bias non-uniformity. The objective of this article is to characterize the magnetic field through a comparison of experimental etch data and modeling. Both analytical and empirical modeling have been used to gain a better understanding of the particular magnetic field configuration under investigation. At low pressure the etch rate pattern correlated well with the calculated stationary magnetic field gradient. For higher pressure this model failed to predict the etch rate uniformity behavior because of contributions from other effects in the plasma. In order to characterize these effects, experiments were conducted for both stationary and rotating magnetic fields. This was done to aid process optimization with respect to the potential for damage.
Plasma cleaning and nitridation of sapphire substrates for AlxGa1−xN epitaxy as studied by x-ray photoelectron diffraction
Authors: Seelmann-Eggebert M. , Zimmermann H. , Obloh H. , Niebuhr R. , Wachtendorf B.
Published: July 2002

The influence of plasma and thermal treatments on the structure and composition of sapphire (00.1) surfaces has been studied by hemispherically recorded x-ray photoelectron spectroscopy and diffraction (XPD) to better understand the surface conditioning during the growth initiation procedure for the epitaxy of GaN. A treatment involving an O2 plasma generated by electron cyclotron resonance is shown to efficiently remove surface contamination and to produce well-ordered surfaces. After a thermal treatment in vacuum the sapphire (00.1) surface becomes terminated by Al atoms. AlN films with good short-range order are obtained by a simple high temperature nitridation step in the metal organic chemical vapor deposition reactor. A novel direct crystallographic method termed CHRISDA is employed for the analysis of the XPD data. By analysis of the XPD patterns the crystal structure of sapphire is found to extend into the probed near surface region without significant perturbations. The AlN layers formed by thermal nitridation were found to crystallize in the hexagonal phase and to be terminated by nitrogen atoms.
High growth rate GaN films using a modified electron cyclotron resonance plasma source
Authors: Berishev I. , Kim E. , Bensaoula A.
Published: July 2002

GaN thin films were deposited by reactive molecular beam epitaxy method with a modified ASTeX®  compact electron cyclotron resonance (ECR) plasma source of nitrogen. The effect of different ECR exit apertures on the growth rate and photoluminescence properties of GaN films was investigated. An aperture with a matrix of 1.6 mm holes allowed for GaN films with good optical properties at growth rates up to 1 μm/h. Apertures of larger diameter resulted in semi-insulating films. Room temperature photoluminescence for both undoped and Si-doped GaN films with full width at half maximum less than 100 meV has been obtained at the highest growth rates. We suggest that such an aperture effectively blocks the energetic ions from reaching the substrate thus reducing ion damage, resputtering, and increasing the Ga surface population. It also creates a higher pressure inside the ECR resonator, and therefore, provides a higher flux of active species. While further optimization will result in better GaN film quality, our results suggest that the growth rate in Ga-rich condition is limited by the microwave power available in the ASTeX compact ECR source.
Application of pulsed-laser deposition technique for cleaning a GaAs surface and for epitaxial ZnSe film growth
Authors: Ryu Y. R. , Zhu S. , Han S. W. , White H. W.
Published: July 2002

A new method is described whereby a pulsed ArF excimer laser can be used to clean GaAs substrates prior to thin film deposition by pulsed-laser deposition (PLD). The laser is used to create excited hydrogen, which effectively removes contaminants from the GaAs surface. The cleaning process involves hydrogen, photoelectrons, and photons, and is termed HEP to reflect the involvement of these three types of particles. ZnSe films have been epitaxically deposited by PLD on GaAs substrates cleaned by the HEP process. X-ray diffraction data show that GaAs substrates treated by excited hydrogen are very good for epitaxial growth of ZnSe. ZnSe films were synthesized at 320 °C under different Ar pressures to understand the effects of ambient gas pressure on film quality and morphology. Introduction of an ambient gas (Ar) improved film quality and morphology. The full width at half maximum of the x-ray theta rocking for the (004)-ZnSe peak for the best film grown, at 20 mTorr and 320 °C, was 0.04°. X-ray and atomic force microscopy results are reported for several ZnSe films deposited on GaAs substrates cleaned by the HEP process. The results are compared with those of ZnSe films synthesized on GaAs substrates that were thermally treated, but were not treated by the HEP process.
Low damage reactive ion etching for photovoltaic applications
Authors: Schaefer Sebastian , Lüdemann Ralf
Published: July 2002

New concepts in silicon solar cell design require dry processing technologies. For this reason two reactive ion etching (RIE) processes have been developed: one for surface cleaning and one for the removal of phosphorous glass (PSG). However, damage is induced in silicon during reactive ion etching which deteriorates solar cell performance. Damage caused by SF6 RIE cleaning has been investigated by means of secondary ion mass spectroscopy, positron annihilation, and minority charge carrier lifetime measurements. Particles contained in the etch gas can be detected up to a depth of 50–80 nm in the silicon sample. A two layer model of vacancy distribution has been established: A layer of high vacancy concentration (1019 cm−3) up to a depth of 20 nm is followed by a second layer that extends over a depth of 1 μm with a vacancy concentration of 1016 cm−3. Effective minority charge carrier lifetimes decrease to about 10% of the lifetime of the wet etched control during RIE. If a heavily damaged layer of 20 nm is being removed by anodic oxidation, lifetimes return to the initial value. Under certain etching conditions it is possible to anneal plasma induced damage at 400 °C. The influence of RIE induced damage on solar cells is quantified by open circuit voltage analysis: Long process times, addition of oxygen to the etch gas, and high rf power or self-induced dc bias result in a significant decrease in open circuit voltage. Nearly damage free RIE processes have been developed for surface cleaning as well as PSG removal. Dry processed solar cells thus show the same performance as wet etched cells.
Reduced carbon contaminant, low-temperature silicon substrate preparation for “defect-free” homoepitaxy
Authors: Taylor Patrick J. , Jesser W. A. , Martinka M. , Singley K. M. , Dinan J. H. , Lareau R. T. , Wood M. C. , Clark W. W.
Published: July 2002

A low-temperature cleaning technique incorporating an ultraviolet light–ozone treatment with conventional hydrogen-passivation techniques is shown to yield a low concentration of surface contaminants: 0.01 monolayer. An additional advantage is that no ultrahigh vacuum prebaking treatments are required for substrates receiving this treatment prior to epitaxy. Epitaxial silicon layers deposited onto substrates receiving the present technique are characterized by a threading dislocation density on the order of 104/cm2, which is considerably lower than the 105/cm2–106/cm2 order measured for films receiving more conventional preparation techniques. The results of this study suggest that aqueous solutions are a significant source of surface carbon and that residual carbon on the silicon surface before epitaxy contributes to the generation of threading dislocations in Si homoepitaxial films.
Enhanced electrical performance of Au/n-GaN Schottky diodes by novel processing
Authors: He L. , Wang X. J. , Zhang R.
Published: July 2002

Au/n-GaN Schottky diodes with the Au electrode deposited at low temperature (LT) (77 K) and at room temperature were compared. Photoluminescence and x-ray rocking curve measurements were performed prior to device fabrication. The best LT Schottky diodes exhibited excellent performances with leakage current densities as low at 2.55×10−11 A cm−2 at −2.5 V. By using the commonly used effective Richardson constant value, typical zero-biased barrier heights of ΦB0=1.08 eV and zero electric field barrier heights of ΦBF=1.32 eV we obtained, with the best values of ΦB0=1.22 eV, ΦBF=1.88 eV for the LT diode. A possible model to interpret this high barrier height was proposed. It was found that great differences existed between the saturated reverse current and that extrapolated from the linear region of the forward I-V curve. A deep state-assisted tunnel mechanism was proposed to qualitatively explain this feature for diodes with low leakage currents. The obvious enhancement in electrical performance makes LT processing a very promising technique for GaN device application although details of the conduction mechanism for LT Au/n-GaN Schottky diodes are still under investigation.
Growth kinetics of GaN and effects of flux ratio on the properties of GaN films grown by plasma-assisted molecular beam epitaxy
Authors: Myoung J. M. , Gluschenkov O. , Kim K. , Kim S.
Published: July 2002

The kinetic processes of GaN growth using plasma-assisted molecular beam epitaxy (PAMBE) have been investigated employing a precursor-mediated model. Using the highly efficient radio-frequency (rf) plasma source which produces sufficient atomic nitrogen with a low density of ions having low kinetic energy, significant ion-induced desorption is not observed, and the growth kinetics are determined by the flux ratio between Ga and N, JGa/JN. It is found that the growth rates obtained by the precursor-mediated model fit well with the experimental results, implying that the growth kinetics are effective in describing the film growth by PAMBE. Also, it is found that the flux ratio JGa/JN is one of the most important factors which determine the growth mode, degree of crystallinity, and electrical and optical properties of GaN films. Although the growth rate is high (∼680 nm/h), the surface morphology and crystalline quality of the films grown at a higher Ga flux are found to be significantly improved due to the two-dimensional layer-by-layer growth mode [root-mean-square (rms) roughness ≈1 nm]. Their electrical and optical properties are also discussed.
Selected energy epitaxial deposition of GaN and AlN on SiC(0001) using seeded supersonic free jets of NH3 in helium
Authors: Torres V. M. , Doak R. B. , Wilkens B. J. , Smith D. J. , Tsong I. S. T.
Published: July 2002

By expanding a gas mixture into vacuum through a supersonic nozzle, a heavy “seed” species in a light diluent gas can be aerodynamically accelerated to suprathermal translational energies. Such beams are intense, directional, easily tuneable in energy, and narrowly distributed in energy. They thereby offer the means of selectively promoting activated gas-surface reactions. We report the use of 10% NH3 in He seeded beams to grow GaN and AlN epitaxially on 6H–SiC(0001) and to grow GaN on AlN buffer layers deposited on SiC(0001). The III–N films were grown under a variety of incident energies and angles of the NH3 beam, with the III metal species supplied from an effusive evaporator source. Film thickness and morphology were characterized ex situ with Rutherford backscattering spectroscopy, Auger spectroscopy, transmission electron microscopy, and atomic force microscopy. Of particular relevance to the III–N growth are the following results: (1) Selected energy epitaxial growth was observed, evidently via a direct reaction channel over a barrier of 0.25±0.1 eV. A comparison of films grown at 0° (normal) and 30° angles of NH3 incidence indicated total energy scaling of this chemisorption process. (2) A low energy reaction channel (<0.10 eV) was explicitly confirmed. The mechanism by which this might occur is discussed.
Interface analysis of naphthyl-substituted benzidine derivative and tris-8-(hydroxyquinoline) aluminum using ultraviolet and x-ray photoemission spectroscopy
Authors: Forsythe E. W. , Choong V.-E. , Le T. Q. , Gao Yongli
Published: July 2002

We have studied the interface between naphthyl-substituted benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum (Alq3). Ultraviolet photoemission and x-ray photoemission spectroscopy (UPS, XPS) are used to distinguish contributions from NPB and Alq3 and reveal an interface formation region of approximately one to two monolayers. The UPS results show the highest occupied molecular orbital (HOMO) level offset is 0.3 eV, whereas the lowest unoccupied molecular orbitial offset is 0.8 eV, which confines electrons in the emissive Alq3 layer of the heterostructure. From the UPS difference spectrum, the gradual modification of the HOMO levels are revealed. Within the interface region, the energy levels bend by more than 0.3 eV. The Alq3 and NPB HOMO level increases are consistent with the vacuum level shift as well as the observed core level shifts from XPS. Further, the XPS and UPS results show no chemical interactions or wave function overlap at the interface.
Growth habit of rhombohedral Bi thin films on zinc-blende CdTe substrates with various orientations
Authors: Kim Yunki , Cho Sunglae , DiVenere Antonio , Wong George K. , Ketterson John B.
Published: July 2002

Rhombohedral Bi thin films have been grown on zinc-blende (111), (211) and (100) CdTe substrates by molecular beam epitaxy. Reflection high-energy electron diffraction patterns showed that Bi grew layer-by-layer on the CdTe substrates without any reconstruction. X-ray diffraction θ−2θ scans revealed that the Bi films grown on (111) CdTe are (00.l) oriented and that the Bi films on (100) CdTe are (10.4) oriented. X-ray pole figures from the Bi films and the CdTe substrates indicated that Bi (00.l) on (211) CdTe grew along the CdTe (111) direction, like in the case of the Bi films on (111) CdTe. Most Bi grains on (100) CdTe select one particular direction out of the four possible directions in the presence of an off-axis tilt relative to the (100) substrate surface normal.
Detailed simulation of mass spectra for quadrupole mass spectrometer systems
Authors: Gibson J. R. , Taylor S. , Leck J. H.
Published: July 2002

A method of computation to determine the trajectories of large numbers of ions in quadrupole mass spectrometers has been developed. The computer program produces simulated mass scans with over 105 ions injected into the quadrupole model at each point on the mass scale. The computation method has been combined with an improved representation of an ion source to predict the behavior of complete quadrupole systems; the results obtained are shown to reproduce most features of experimentally observed mass scans. The calculations show that the shape and height of mass peaks depend strongly on the properties of the ion source. However, ion source properties have a relatively small effect on the resolution of the mass spectrometer and an alternative to the common method of presenting the resolution of a quadrupole is proposed. This alternative better indicates the performance of the instrument as it is less sensitive to effects of the ion source. Results are also presented which indicate that peak splitting, closely matching experimental observations, can be produced by small changes in the exit aperture of the quadrupole.
Infrared characterization of GaN and GaN/AlGaN molecular beam epitaxial layers
Authors: Bardwell J. A. , Dharma-Wardana M. W. C. , Tang H. , Webb J. B.
Published: July 2002

An infrared reflection technique has been developed for the characterization of GaN and GaN/AlGaN epitaxial layers and multilayers. The infrared light is brought to the III-nitride surface with a KRS-5 internal reflection crystal. The technique is complimentary to Raman measurements and provides information on the longitudinal and transverse optical (LO) modes of GaN and AlN. For thin GaN layers, the modes of the thin, 22-nm-thick AlN nucleation layer can be clearly observed in the spectra. The free carrier concentration of the GaN can be characterized by analyzing the LO phonon-plasmon coupled mode present in doped samples. Because the light is multiply reflected in the GaN layer, the technique can potentially detect impurities (such as H or C) in the GaN. The application of this technique to characterize high quality molecular beam epitaxial layers is discussed.
Diagnostic studies of aluminum etching in an inductively coupled plasma system: Determination of electron temperatures and connections to plasma-induced damage
Authors: Malyshev M. V. , Donnelly V. M. , Downey S. W. , Colonell J. I. , Layadi N.
Published: July 2002

Using trace rare gases-optical emission spectroscopy (TRG-OES) and Langmuir probe measurements, electron temperatures (Te) were obtained in Cl2/BCl3/N2 plasmas in an inductively coupled plasma system, under typical processing conditions for metal etching. A small amount (1.7% each) of the five rare gases was added to the plasma and emission spectra were recorded. TRG-OES Tes corresponding to the high-energy tail of the electron energy distribution function were derived from the best match between the observed and computed rare gas emission intensities. Te was determined as a function of total pressure, source power, fraction of BCl3 added to Cl2 and substrate material (SiO2, Al, and photoresist). Positive ion densities and relative electron densities were also measured for some of these conditions. At source and bias powers of 1000 and 100 W, TRG-OES Tes in Cl2/BCl3/N2/rare gas plasmas increased from 1.4 eV at 40 mTorr to 2.3 eV at 3 mTorr, about 15% lower than values computed from a global model and ∼1.4 times lower than those measured with a Langmuir probe. Reduced plasma induced damage to the gate oxide at higher pressures (18 vs 10 mTorr) correlates with a drop in both Te (1.7 vs 1.9 eV) and plasma density (1.0×1011 vs 1.3×1011 cm−3), but is due mostly to the lower Te.
Evolution of the corrosion process on thin-film media
Authors: Ying JiFeng , Anoikin Tatiana , Martner Cecilia
Published: July 2002

Thin-film hard disks were exposed to elevated temperature/humidity, and dilute acidic vapor environment. These tests are designed to simulate possible galvanic corrosion, which, for the thin-film media, is characterized by the formation of Co and Ni containing corrosion nodules. The evolution of the corrosion process was elucidated by inducing different degrees of corrosion on the media, and these distinct corrosion stages were characterized morphologically by Scanning electron microscopy and chemically by Auger electron spectroscopy compositional analysis. In addition, an x-ray photoelectron spectroscopy chemical state study on the reactivity of Co, Cr, and Ni to ambient and chlorinated environments was conducted. A probable galvanic corrosion mechanism is proposed to understand the chemistry observed during the evolution of the corrosion process. In particular, the effects of ionic contaminants as corrosion accelerators and the role of the Cr underlayer as a corrosion-preventing barrier layer are discussed.
Periodic magnetic microstructures by glancing angle deposition
Authors: Dick B. , Brett M. J. , Smy T. J. , Freeman M. R. , Malac M. , Egerton R. F.
Published: July 2002

An advanced deposition technique known as glancing angle deposition (GLAD) [K. Robbie, J. C. Sit, and M. J. Brett, J. Vac. Sci. Technol. B 16, 1115 (1998); K. Robbie and M. J. Brett, U.S. Patent No. 5,866,204 (filed 1999)] has been used to fabricate periodic arrays of magnetic pillars and randomly seeded magnetic helices, posts, and chevrons. Because of the nature of initial film nucleation, the GLAD process normally distributes posts randomly on the substrate surface. We can grow periodic arrays of GLAD microstructures by suppressing the randomness inherent within the initial nucleation stage of film growth. Shadowing sites were fabricated by pre-patterning a thin titanium layer on silicon substrates into a square array using electron beam lithography. These sites shadow regions of the substrate from incident flux during film deposition and act as preferred nucleation sites for film growth. Using this process, we have fabricated periodic arrays of cobalt posts with a regular elemental period of 600 nm and post diameters and heights of 300 and 400 nm, respectively. Randomly seeded posts, helices, and chevrons were also fabricated. The mean separation for the randomly seeded posts was 350 nm with individual post diameters of 100–150 nm, while the separations for the helices and chevrons were less than 100 nm. X-ray diffraction, transmission electron microscopy, and a dc superconducting quantum interference device magnetometer were used to analyze the magnetic and crystal properties of both the periodic and randomly seeded arrays. A newly developed three-dimensional ballistic deposition simulator was used to simulate the growth of the periodic post arrays in order to better understand the growth mechanisms.
Atom-probe study of the early stage of silicide formation. I. W–Si system
Authors: Nishikawa Osamu , Tsunashima Yoshitaka , Nomura Eiichi , Horie Shiro , Wada Minoru , Shibata Mezame , Yoshimura Toshihiko , Uemori Ryuji
Published: July 2002

The early stage of silicide formation was studied by depositing Si on W tip specimens of the FIM and the atom probe. The optimum temperature for W silicide formation was found to be 900–1000 K and its composition was WSi2. The observed FIM image of the silicide agreed well with the computer-simulated image which was composed of the W atoms of the tetragonal C11b structure. The silicide often grew independently on each W{001} plane because the W lattice constant of these planes matches well with that of the basal plane of the silicide. The boundary between the independently grown silicides was also observed along the expected areas from the simulated image.
Simulation models of the crystal–vapor interface
Authors: Gilmer George H. , Broughton Jeremy Q.
Published: July 2002

The atomic structures of crystal–vapor surfaces have been studied using Monte Carlo simulations of the Ising model and molecular dynamics simulations of a system of Lennard-Jones particles. The roughening transition and its effects on the kinetics of growth and the crystal structure are discussed together with some implications for the growth of composition modulated crystals. Growth by two-dimensional nucleation and an impurity mechanism are discussed. Atomic positions at close-packed crystal–vapor surfaces are obtained from the molecular dynamics model. The atomic mobility in the surface region and the possibility of a surface melting transition are discussed.
Practical aspects of microfabrication in the 100 nm regime
Authors: Kern D. P. , Houzego P. J. , Coane P. J. , Chang T. H. P.
Published: July 2002

The fabrication of microstructures with minimum dimensions below 100 nm introduces several additional problems not normally associated with electron-beam lithography at the 1/2 to 1 μm level. The quality of a 100 nm resist image, when defined by an electron beam pattern generator, depends strongly upon the exposure conditions such as beam energy and dose. Another important factor is the substrate, since it greatly influences the range and amount of backscattered electrons and, hence, the exposure contrast achievable in a given resist system. There is generally a big difference in energy deposited in the resist whether the exposure is performed on a thin membrane, on bulk silicon, or on a thick layer of a heavy metal, and also whether a single thin layer of resist or thick two or three-layer systems are used. The characteristics of the resist and the development process itself are important aspects, too. In addition to controlling the resist image, one must also consider the properties and requirements of the subsequent transfer process to the working material such as lift-off, plating, ion milling, and reactive ion etching. The specific process is often dictated by the materials and the geometry of the particular structure to be fabricated. So, as many of the conditions interact, it is impossible to define a single process that would be suitable for the wide range of applications that structures of this size are intended for. Using examples of x-ray zone plates and FET gate definition, we discuss the merits of some of the processes used together with the techniques and problems associated with the evaluation of process performance at these dimensions.
Investigations of x-ray exposure using plane scanning mirrors
Authors: Bieber M. , Scheunemann H.-U , Betz H. , Heuberger A.
Published: July 2002

One of the essential processing problems in x-ray lithography using synchrotron radiation is the relatively small vertical divergence of the radiation. A possible method to enlarge the small exposure field is the application of scanning x-ray mirrors in the grazing incidence region with a reflectivity of about 90% at wavelengths around 10 Å. The theoretical values of the absorbed energy in the x-ray resist as a function of the glancing angle, in the case of a plane mirror, have been compared with experimental results. In order to obtain a homogeneous exposure when scanning the mirror, the velocity profile of the mirror movement has to be adjusted to the change in the reflectivity. Another important aspect in the application of the mirror is the degradation of its surface, due to cracked hydrocarbon products under the influence of synchrotron radiation. Initial experimental results show that this problem is not as severe as previously expected. The investigations show that the application of x-ray mirrors is in fact a useful way to enlarge the exposable area in the case of synchrotron radiation, since the loss in intensity is acceptable and the mirror lifetime is satisfactory.
Overview of coating technologies for large scale metallurgical, optical, and electronic applications
Authors: Bunshah R. F.
Published: July 2002

There are hardly any high technology applications which do not involve composite materials with a coating of specific properties on a substrate with another set of properties. This overview is concerned with the various coating methods for a variety of substrates for metallurgical, optical, and electronic applications. Selection criteria for process/apparatus for large scale applications are presented. Economic considerations are discussed.
Hot jet etching of GaAs and Si
Authors: Geis M. W. , Efremow N. N. , Lincoln G. A.
Published: July 2002

This paper contains a description of a new anisotropic dry etching technique (hot jet etching) which does not require ions or plasmas. The anisotropic etching is obtained from a directed flux of chemically reactive species. The reactive species are obtained by thermally decomposing comparatively unreactive feed gases in a resistively heated tube. Using Cl2, CF3Br, or SF6, Si and GaAs have been etched. Etch rates as high as 5 μm min−1 have been obtained with Cl2 and GaAs samples. High differential etch rates have been obtained, since there is no sputtering component to the etching. The anisotropic ratio of the etch depth to the undercutting distance is approximately 5 for GaAs with a feed gas of Cl2. The hot jet technique may make possible a new class of chemical etchants.
Expitaxial metal–semiconductor structures and their properties
Authors: Tung R. T. , Levi A. F. J. , Gibson J. M.
Published: July 2002

Recent development of epitaxial silicide technology has allowed structurally perfect metal–semiconductor interfaces to be fabricated. The atomic structure at these abrupt silicide–silicon interfaces has been modeled and electron transport across Schottky barriers with homogeneous interface structure have been studied for the first time. In addition, high quality multilayered structures of epitaxial metals and semiconductors have been fabricated, opening up possibilities for very high speed device applications. This paper reviews the state-of-the-art growth techniques, and the novel structures and properties of single crystal silicide thin films and multilayers.
The thermal and ion-assisted reactions of GaAs(100) with molecular chlorine
Authors: Balooch M. , Olander D. R. , Siekhaus W. J.
Published: July 2002

Reaction of single-crystal GaAs with molecular chlorine was studied with and without simultaneous bombardment by energetic argon ions. The reaction was detected by an in situ mass spectrometer; reflected chlorine and reaction product signals were measured as functions of crystal temperature. A modulated molecular beam of intensity 1×1017 cm−2 s−1 was used for the purely thermal reaction tests. At temperatures greater than 550 K, the monochlorides of Ga and As were observed in equal quantities. At lower temperatures, only the trichlorides were observed. A maximum reaction probability for trichloride production of 0.3 was observed at 450 K. The effect of modulated ion bombardment with a steady Cl2 beam was also examined. The shapes of the waveforms of the desorbed products observed in this experiment suggested that the gallium-chloride-producing reaction was stimulated by ion bombardment. In the absence of ion-assisted desorption, the gallium chloride surface builds up to a saturation coverage of ∼1015 Ga atoms/cm2. This layer prevents reaction of the substrate GaAs with the Cl2 beam. A quantitative model of the ion-assisted reaction was proposed and compared with the data.
High-resolution electron-energy-loss spectroscopy studies of GaAs (100) surfaces
Authors: Frankel D. J. , Yu C. , Harbison J. P. , Farrell H. H.
Published: July 2002

High-resolution electron-energy-loss spectroscopy (HREELS) has been used to study the vibrational spectra of chemisorbed atomic H on the GaAs(100)c(2×8), (4×6), (4×1), and c(8×2) surface structures. Our results show that both As–H and Ga–H species are present on the GaAs(100)c(2×8) surfaces even at very low exposures. This result is notable because it indicates that the c(2×8) structure is terminated with less than a full monolayer of As atoms. Furthermore, HREELS results indicate that a wide range of surface stoichiometries exists for this surface with the Ga–H mode actually slightly stronger than the As–H mode at the higher annealing temperatures. On the c(8×2) structure the HREELS data show almost exclusively Ga–H with little or no As–H. Strong similarities are observed between the (4×1) and the c(8×2) surfaces, particularly after sufficient annealing, which minimizes the presence of the more As-rich (1×6) domains that often accompanies the (4×1) structure. Several model structures incorporating dimer vacancies are discussed in relation to the HREELS data.