bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of temperature on the emission characteristics of liquid metal alloy ion sources
Authors: Bischoff L. , Teichert J. , Ganetsos Th. , Mair G. L. R.
Published: July 2002

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their emission characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co36Nd64 and Au77Ge14Si9. While the results of the former source were as expected, the latter displayed an entirely different dependence of its emission characteristics on temperature. The unusual results of the Au77Ge14Si9 LMAIS are explained in terms of the abnormal behavior of the surface tension of the alloy with temperature.
Nitrogen profile effects on the growth rate of gate oxides grown on nitrogen-implanted silicon
Authors: Nam In-Ho , Hong Sung In , Sim Jae Sung , Park Byung-Gook , Lee Jong Duk , Lee Seung-Woo , Kang Man-Suk , Kim Young-Wug , Suh Kwang-Pyuk , Lee Won-Seong
Published: July 2002

Nitrogen implantation effect on SiO2/Si interface roughness is analyzed and a new method for growing ultrathin gate oxide is proposed. Interface roughness is improved by nitrogen implantation; the root-mean-square values measured by atomic force microscopy are 2.72–2.79 Å, 1.7–2.12 Å, and 2.12–2.33 Å for 0, 1.0×1014/cm2, and 2.0×1014/cm2 nitrogen implantation, respectively. Initial O2 injection method is composed of O2 injection/N2 anneal/main oxidation, and the control process is composed of N2 anneal/main oxidation. The purpose of O2 injection is to form an extremely thin oxide layer that provides a Si/SiO2 interface at which nitrogen is accumulated during N2 annealing process. Time of flight secondary ion mass spectroscopy data show that the initial O2 injection method has a higher peak than that of the control process. The oxidation reduction rates of the control process were: 0.6% (15.4 Å/15.5 Å), 18.2%(26.9 Å/32.9 Å), and 16.4% (34.1 Å/37.4 Å) for the wafers of 1, 10, and 20 min oxidation time, respectively. And the rates of the initial O2 injection method were 7.6% (19.4 Å/21 Å), 25% (23.1 Å/30.8 Å), and 29.5% (28.4 Å/40.3 Å). It is clear evidence that the nitrogen profile can affect oxidation retardation effect as well as the nitrogen dosage. Metal–oxide–semiconductor capacitors with gate oxide thickness of 2 nm have been fabricated. Boron penetration prevention ability is intensified by the initial O2 injection process for the same dose of nitrogen implantation. The oxide reliability was investigated using time-zero dielectric breakdown (TZDB) measurement. The initial O2 injection method shows improved TZDB.
Effects of ZnO buffer layer on the luminous properties of thin-film phosphors deposited on ZnO/ITO/glass substrates
Authors: Kim Young Jin , Chung Sung Mook , Ho Jeong Young , Lee Yong Eui
Published: July 2002

ZnGa 2 O 4 :Mn and CaTiO3:Pr thin-film phosphors which emit green and red light, respectively, were deposited on ZnO/ITO/glass and ITO/glass substrates by a rf reactive magnetron-sputtering method. To improve photo- and cathodoluminescent properties of the thin-film phosphors, ZnO buffer layers were deposited between the thin-film phosphor and the ITO-coated glass substrate. A transparent c-axis preferentially oriented ZnO thin-film buffer layer could be obtained on the ITO film, while ITO had an amorphous-like structure. ZnGa2O4:Mn and CaTiO3:Pr thin-film phosphors were used to evaluate the effects of the ZnO buffer layer. The crystal structures of thin-film phosphors deposited on ZnO/ITO/glass substrates were developed better than those on ITO/glass, consequently, the former showed photo- and cathodoluminescent intensity at least twice as high as the latter.
Mechanism of nonideality in nearly ideal Si Schottky barriers
Authors: Maeda Keiji
Published: July 2002

The origin of nonideality in an actual nearly ideal Schottky barrier is an inhomogeneous Schottky barrier height (SBH). A high density of point defects is generated in the neighborhood of the interface by the fabrication process of the metal/Si interface. Local SBH lowering by positively ionized defects close to the interface is considered the cause of inhomogeneity based on the property of the metal-induced gap states. Results of analysis by this mechanism are in excellent agreement with ballistic electron emission microscopy (BEEM) observation of low-SBH spots. A Gaussian distribution of inhomogeneous SBH explains the BEEM spectrum, as well as the temperature dependence of both effective SBH and ideality factor, i.e., the so-called T0 anomaly. The spatial distribution of the ionized donor and its variation under applied voltage are obtained. This result indicates that the origin of the ideality factor is preferential neutralization of the donor close to the interface in equilibrium with the Fermi level. Thus, the proposed mechanism explains the various properties of nearly ideal Si Schottky barriers.
Characteristics of Pt/YMnO3/Y2O3/Si structure using a Y2O3 buffer layer grown by pulsed laser deposition
Authors: Shin Woong-Chul , Yang Jung-Hwan , Choi Kyu-Jeong , Jeon Young-Ah , Yoon Soon-Gil
Published: July 2002

The Pt/YMnO3/Y2O3/Si structure for a metal/ferroelectric/insulator/semiconductor (MFIS) field effect transistors was fabricated and the effect of a Y2O3 layer on the properties of MFIS structure was investigated. The Y2O3 thin films on p-type Si(111) substrate growth by pulsed laser deposition were crystallized along (111) orientation irrespective of the deposition temperatures. Ferroelectric YMnO3 thin films deposited directly on p-type Si (111) by metalorganic chemical vapor deposition resulted in a Mn deficient layer between Si and YMnO3. However, YMnO3 thin films having good quality and stoichiometric composition can be obtained by adopting a Y2O3 buffer layer. The memory window of the YMnO3 thin films with a Y2O3 film is greater than that of the YMnO3 thin films without a Y2O3 film after the annealing at 850 °C in vacuum ambient (100 mTorr). The memory window is 1.3 V at the applied voltage of 5 V.
Dry etching of SrBi2Ta2O9 thin films in Cl2/NF3/O2/Ar inductively coupled plasmas
Authors: Im Y. H. , Park J. S. , Choi C. S. , Choi R. J. , Hahn Y. B. , Lee S.-H. , Lee J.-K.
Published: July 2002

A parametric study of high density plasma etching of SrBi2Ta2O9 (SBT) thin films was carried out in a planar type inductively coupled plasma (ICP) etcher with different chemistries of Cl2/Ar, Cl2/NF3/Ar, and Cl2/NF3/O2/Ar. The etch rate was a strong function of gas concentration, ICP source power, and rf chuck power. Both Cl2/NF3/Ar and Cl2/NF3/O2/Ar plasmas showed maximum etch rates of ∼1600 Å/min at 5 mTorr, 700 W ICP power, and 150 W rf chuck power. The addition of NF3 and O2 into the Cl2/Ar mixture played an important role in not only enhancing the etch rate, but also smoothing the etched surface by reducing the kinetic energy of ions. Electrical properties of the SBT films were quite dependent of plasma chemistries: Cl2/NF3/O2/Ar showed the least damage in the films and resulted in overall the best polarization-electric field hysteresis loop compared to other chemistries.
Low-temperature Si epitaxial growth on oxide patterned wafers by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition
Authors: Yuh Hwan-Kuk , Park Jin-Won , Lim Seung-Hyun , Hwang Ki-Hyun , Yoon Euijoon
Published: July 2002

Low-temperature electron cyclotron resonance hydrogen plasma cleaning was developed for low-temperature epitaxial growth of Si by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxide-patterned wafers. Defect-free undoped Si epitaxial layers could be obtained by optimizing the hydrogen ion flux and cleaning time, however, in the case of boron-doped Si epitaxial growth, Si epilayers had defect zones away from the bird’s beak along the window edges and a defect-free zone at the center of the window. Cross section transmission electron microscopy and energy dispersive spectroscopy results suggest that the defect zone formation is closely related with local oxygen contamination. Possible origins of the local oxygen contamination are discussed.
Process window extension of TiN diffusion barrier using preoxidation of Ru and RuOx film for (Ba,Sr)TiO3 dielectric film
Authors: Yoon Dong-Soo , Hong Kwon , Roh Jae Sung
Published: July 2002

The effect of a thin RuOx layer formed at the surface of the bottom electrodes by various preoxidation temperatures on the electrical properties of TiN barrier layer during two step annealing was investigated. The Ru(100 nm)/TiN/p-Si/Si contact system showed the ohmic behavior at the forward bias up to 550 °C, whereas the RuOx(100 nm)/TiN/p-Si/Si contact system exhibited the double Schottky characteristics at 400 °C, attributing to no formation of thin RuOx layer at the RuOx surface and porous amorphous microstructure. In particular, when the preoxidation time is decreased from 3 to 1 min, the electrical properties for the Ru(30 nm)/TiN/p-Si/Si contact system are improved, as compared to that for the Ru(100 nm)/TiN/p-Si/Si contact system. An oxygen incorporated at the surface of the Ru film by preoxidation plays a role in the formation of a thin RuOx layer and chemically strong Ru–O bonds, and is strongly stuffed along the grain boundaries as well as grains. It leads to the retardation for oxygen diffusion due to complex diffusion paths. In particular nonstoichiometric state, RuOx layer formed at the Ru surface is changed to the stoichiometric state, RuO2 crystalline phase after two step annealing, which can act as an oxygen sink layer. Correspondingly, we can conclude that electrical properties for the Ru/TiN/p-Si/Si contact system are better than that for the RuOx/TiN/p-Si/Si contact system.
Electric property improvement and boron penetration suppression in metal–oxide–Si capacitors by amorphous-Si gate electrode and two-step nitridation
Authors: Lee Jung Hsiang , Feng Wu Shiung , Juang Tzann-Cherng , Chang-Liao Kuei-Shu
Published: July 2002

The improvement of electric property and reduction of boron penetration in metal–oxide–Si (MOS) capacitors are clearly achieved by the combination of a gate electrode deposited using amorphous Si(a-Si) and a gate oxynitride formed by a two-step N2O nitridation. The charge-to-breakdown performance of MOS capacitors fabricated by this technique is excellent. The hot-electron induced interface traps and flatband voltage shifts are significantly reduced. This reliability improvement can be explained in terms of a mechanism based on an increase in compressive stress (macroscopic strain) in the oxynitride and relaxation of SiO2/Si interfacial strain. Also this improvement can be due to a reduction of hydrogen-related species diffused from the gate electrode, which is achieved by nitrogen pileup at the gate electrode/oxynitride interface. Boron penetration is significantly suppressed by an a-Si gate electrode because of a larger grain size and a longer dopant diffusion path. The boron penetration is also clearly reduced by a gate oxynitride formed using a two-step N2O nitridation. Boron penetration reduction for this oxynitride can be attributed to the nitrogen incorporation into the gate electrode/oxynitride interface. This approach would be useful for the processes of gate electrode and gate dielectric in the deep submicron MOS transistors.
Photoluminescence from ZnTe:Yb films grown on (100) GaAs by molecular beam epitaxy
Authors: Sadofyev Yu. G. , Konnov V. M. , Loiko N. N. , Gippius A. A.
Published: July 2002

Yb-doped ZnTe layers grown on GaAs substrates have been obtained using molecular beam epitaxy. A study of photoluminescence of ZnTe:Yb/GaAs structures is performed. It is demonstrated that Yb can be rendered optically active in ZnTe if it is incorporated in three-component complexes which consist of ytterbium, oxygen, and some of background impurities.
Tribocharging in electrostatic beneficiation of coal: Effects of surface composition on work function as measured by x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy in air
Authors: Trigwell S. , Mazumder M. K. , Pellissier R.
Published: July 2002

The cleaning of coal by electrostatic beneficiation is based on tribocharging characteristics of pulverized coal particles with diameter smaller than 120 μm. The tribocharging process should be such that the organic coal particles must charge with a polarity opposite to that of the sulfur and the mineral containing particles so that coal can be separated from minerals by using a charge separator. However, the charge distribution of electrostatically separated coal particles indicates that coal exhibits bipolar charging. A significant fraction of the coal particles charges negatively which appears to be in conflict with expectations in that the organic coal particles should charge positively, and the mineral particles, present as impurities such as pyrite, charge negatively when tribocharged against copper. The relative work functions of the particles (coal and mineral) and that of the metal surface (copper or stainless steel) used for tribocharging predict these expected results. However, ultraviolet photoelectron spectroscopy (UPS) measurements in air on specimens of three different coal species, showed the work function to be approximately 5.4 eV, which is higher than a reported measured work function of 3.93 eV. Studies by UPS and x-ray photoelectron spectroscopy on copper, stainless steel, aluminum, and other commonly used tribocharging materials such as nylon and polytetrafluorethylene, as well as pure pyrite, showed that the work function varied considerably as a function of surface composition. Therefore, the reason for the bipolar charging of the coal particles may be the too small differences in work functions between coal powder and copper used as the charging material. The choice of a material for impaction triboelectric charging for coal or mineral separation should therefore depend upon the actual work function as modified by the ambient conditions such as moisture content and the oxidation of the surface.
Molecular-beam epitaxy growth of Ga(In)NAs/GaAs heterostructures for photodiodes
Authors: Gotthold David , Govindaraju Sridhar , Reifsnider Jason , Kinsey Geoff , Campbell Joe , Holmes Archie
Published: July 2002

The incorporation of nitrogen into GaInAs/GaAs heterostructures has received intense interest recently due to the large negative bowing parameter of the resultant alloy. This change in the band gap for GaInAsN makes it useful for near-infrared optoelectronic devices on the GaAs substrate. However, the effect of adding nitrogen into GaInAs is an important issue in the use of these alloys. This article focuses on the growth of GaInNAs/GaAs alloys for use in photodiodes. Under our growth conditions, we show that the incorporation of nitrogen into GaAs and Ga0.8In0.2As is linear with nitrogen in the growth chemistry up to approximately 3.5%. Photodiodes using GaNAs absorption regions show low dark currents and high quantum efficiencies with nitrogen values up to 1.75%.
Chemical and structural characterization of V2O5/TiO2 catalysts
Authors: Rodella C. B. , Nascente P. A. P. , Mastelaro V. R. , Zucchi M. R. , Franco R. W. A. , Magon C. J. , Donoso P. , Florentino A. O.
Published: July 2002

A series of V2O5/TiO2 samples was synthesized by sol–gel and impregnation methods with different contents of vanadia. These samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and electronic paramagnetic resonance (EPR). XRD detected rutile as the predominant phase for pure TiO2 prepared by the sol–gel method. The structure changed to anatase when the vanadia loading was increased. Also, anatase was the predominant phase for samples obtained by the impregnation method. Raman measurements identified two species of surface vanadium: monomeric vanadyl (V4+) and polymeric vanadates (V5+). XPS results indicated that Ti ions were in octahedral position surrounded by oxygen ions. The V/Ti atomic ratios showed that V ions were highly dispersed on the vanadia/titania surface obtained by the sol–gel method. EPR analysis detected three V4+ ion types: two of them were located in axially symmetric sites substituting for Ti4+ ions in the rutile structure, and the third one was characterized by magnetically interacting V4+ ions in the form of pairs or clusters. A partial oxidation of V4+ to V5+ was evident from EPR analysis for materials with higher concentrations of vanadium.
Characterization of bis(tertiary-butylamino)silane-based low-pressure chemical vapor deposition silicate glass films
Authors: Park Byeongju , Conti Richard , Economikos Laertis , Chakravarti Ashima , Ellenberger James
Published: July 2002

The bis(tertiary-butylamino)silane-based low-pressure chemical vapor deposition (LPCVD) undoped silicate glass and phospho-silicate glass (PSG) processes were investigated to study film composition, etch rate, and step coverage. Through the addition of phosphorous doping, LPCVD PSG processing offers an attractive low temperature option. Enhanced deposition rate for the PSG process enables the lowering of the deposition temperature to the 400–500 °C range, thereby minimizing the thermal cycle and offering compatibility with many back-end-of-line processes. Many properties of these films are similar to those of the tetraethoxysilane (TEOS)-based LPCVD oxide. Differences in the film properties compared with the TEOS-based LPCVD oxide films can be traced to the composition of these films and the reaction mechanism.
Comparative investigation of interface effect on transmission function of electrons and holes in InAs/AlSb-based heterostructures
Authors: Ichizli V. M. , Droba M. , Mutamba K. , Sigurdardóttir A. , Hartnagel H. L.
Published: July 2002

The influence of interface types in InAs/AlSb based heterostructures are considered for both electrons and holes. First calculations based on the transfer matrix method and including AlAs, InSb interface types or some of their combinations show the existence of more quantized energy hole levels than can be expected in the case when no interface effects are considered. The consideration is simplified by assuming the interfaces as individual intermediate layers formed between the InAs–quantum well and AlSb barriers. While for electrons such an intermediate layer of AlAs modifies the designed barriers or quantum wells of the heterostructure, it creates narrow barriers for holes leading to the appearance of a miniband type of energy levels.
Study on the characteristics of TiAlN thin film deposited by atomic layer deposition method
Authors: Koo Jaehyoung , Lee June-Woo , Doh Taehan , Kim Yangdo , Kim Young-Do , Jeon Hyeongtag
Published: July 2002

The microstructural characteristics and electrical and chemical properties of TiAlN films deposited by the atomic layer deposition (ALD) method were investigated. The growth rate of TiAlN film was measured to be 1.67 Å/cycle. TiAlN film deposited by ALD has a B1(NaCl) structure with a lattice parameter of 4.20 Å. The chlorine content in TiAlN film was below the detection limit of Auger electron spectroscopy. TiAlN film showed the columnar structure with a resistivity of about 400 μΩ cm. The sheet resistance increased abruptly after annealing at 650 °C due to the formation of a high resistivity Cu-silicide phase at the interface between the TiAlN and Si substrate. The failure of the ALD TiAlN barrier layer was observed by an etch-pit test after annealing at 600 °C for 1 h. TiAlN films deposited by the ALD method exhibited excellent film properties and improved barrier characteristics compared to other chemical vapor deposition methods.
Patterning processes for fabricating sub-100 nm pseudo-spin valve structures
Authors: Vögeli Bernhard , Smith Henry I. , Castaño Fernando J. , Haratani Susumu , Hao Yaowu , Ross C. A.
Published: July 2002

Interference lithography (IL) was used to pattern sputtered Co/Cu/NiFe layers into large-area arrays of pseudo-spin valve (PSV) elements. In order to precisely control size, aspect ratio, and shape uniformity of the elements, three methods of increasing complexity were developed. Pattern transfer was achieved by reactive-ion etching and ion milling, and was found to maintain the multilayered structure of the PSV film. The switching field of the PSV elements, and the remanent state, varied with the aspect ratio as expected. Furthermore, IL was employed to fabricate magnetic random access memory-type structures. Both sense and word lines were conductive, and the buried PSV elements had similar magnetic properties to PSV elements patterned in large-area arrays.
Electrostatic self assembly of nanocomposite polymers in grating structures
Authors: Cheng Xing , Guo L. Jay
Published: July 2002

Electrostatic self-assembly (ESA) is a layer-by-layer approach to synthesize nanocomposite materials with desired functionalities. Thin films with nonlinear optical properties can be deposited by ESA. Although ESA is a versatile technique, it involves laborious and time-consuming deposition steps for practical device applications. We explored the ESA of nanocomposite polymers with nonlinear optical properties in grating structures to create thick films suitable for photonic device applications. We have achieved uniform growth of ESA on the sidewalls of the oxide grating. We proposed an electro-optic modulator configuration based on the Mach–Zehnder interferometer that can make use of the developed method. For nanofabrication, the lateral growth of ESA film on the pattern sidewalls is also potentially useful for creating nanoscale feature sizes with molecular level control.
Observation of speckle patterns in extreme ultraviolet imaging
Authors: Solak H. H. , Yang Y. , Cerrina F.
Published: July 2002

Light scattered by multilayer coated extreme ultraviolet (EUV) optics is a cause of concern in EUV lithography due to its contribution to flare. Because of the extremely small wavelength of light, even subnanometer roughness on mirror surfaces can cause significant scattering. Flare is usually assumed to be an incoherent additive background, which reduces intensity modulation in the image. However, this is not universally true since flare can add coherently under certain conditions depending on the illumination coherence and mirror roughness properties. Coherent addition of flare can lead to speckle-like fluctuations in the image causing undesirable artifacts in a lithography system such as linewidth variation and line edge roughness. We experimentally observed this phenomenon in the recorded images of a pinhole using a Schwarzchild objective based EUV microscope. These images reveal a high contrast speckle pattern in the scattered halo around the specularly reflected beam. The overall distribution of scattered light is directly related to the power spectral density of roughness on the mirror surfaces. In order to better understand the potential influence of this in a lithography system, we simulated imaging of various object patterns by “rough optics.” Simulation results indicate that the speckle effect is not likely to cause appreciable image degradation if current design goals for EUV lithography systems which call for sub-0.5 nm roughness on mirror surfaces are met.
Three-dimensional carrier concentration profiles and ionization energy plots for low-temperature GaAs
Authors: Halder N. C. , Krishnan V. , Baker Bradley
Published: July 2002

We have investigated the carrier concentration profiles in molecular-beam epitaxy-grown, Si-implanted, low-temperature (LT) GaAs. The samples were grown at 300 °C and the Schottky diodes were fabricated using Au contacts. The capacitance voltage measurements were made in the temperature range 100–350 K at an interval of 2 K. From the field-effect transient spectroscopy experiments, data were collected for the peak positions and peak energy of the trap levels. The effective carrier concentration increased with temperature showing a saturation around 350 °C. The ionization energy of the carriers indicated a linear relationship. The overall results indicate that the carrier concentration in three-dimensional mapping is a reliable indicator of the sample quality and of the Schottky diode characteristics. Additionally, one should be specific about the temperature and the reverse bias voltage before selecting the value of the carrier concentration when determining the deep trap concentration in semiconductors, specifically, in LT GaAs.
Simulations of field emission from a semiconducting (10,0) carbon nanotube
Authors: Mayer A. , Miskovsky N. M. , Cutler P. H.
Published: July 2002

We present three-dimensional simulations of field emission from an ideal open (10,0) carbon nanotube without adsorption, by using a transfer-matrix methodology. By introducing pseudopotentials for the representation of carbon atoms and by repeating periodically a basic unit of the nanotube, band-structure effects are manifested in the distribution of energies. The total-energy distributions of both the incident and field-emitted electrons present features, which are related to the gap of the semiconducting (10,0) nanotube, to a van Hove singularity, and to stationary waves in the structure. The transmission through the middle of the gap is exponentially decreasing, with each basic unit of the nanotube associated with a reduction of the current density at this particular energy value by a factor of 5.4. Except for the contribution associated with the van Hove singularity, all peaks are displaced to lower energies when the extraction field is increased.
Calibration and validation of projection lithography focusing by fluorescence detection of latent photoacid images in chemically amplified resist
Authors: Feke G. D. , Grober R. D. , Pohlers G. , Cameron J. F.
Published: July 2002

We dope the commercial resist UVIII with the pH sensitive dye coumarin 6 (C6) to demonstrate a fluorescence microscopy technique for detecting latent photoacid images in exposed chemically amplified resist films. The spectroscopic properties of C6 in the resist matrix are investigated in order to select spectroscopic filters which optimize the fluorescence image contrast of exposed patterns. We apply this technique to focus calibration of a projection lithography system and show a significant correlation of the results to scanning electron microscope analysis of developed features. Hence, we demonstrate the utility of this technique as a fabrication line diagnostic for focus calibration and validation (i.e., proof of focus) prior to postexposure processing of the resist film.
Suppressing boron penetration and cobalt silicide agglomeration in deep submicron p-channel metal–oxide–semiconductor devices
Authors: Kamal A. H. M. , Obeidat A. T. , Budri T.
Published: July 2002

Two discrete processing techniques have been combined for the doping and silicidation of thin (∼125 nm) amorphous silicon (a-Si) film. One technique uses an implantation barrier consisting of a stack of low temperature cobalt silicide (CoSi) and a-Si. The other technique incorporates nitrogen (N2+) to suppress CoSi2 agglomeration. When combined, the implantation barriers consisting of the CoSi/a-Si stack or a-Si films reduce boron penetration in p-channel metal–oxide–semiconductor devices and the implanted N2+ hinders cobalt silicide agglomeration. The two processing approaches presented here differ only in the implantation sequence. TRIM (transport of ions in matter) simulation has been used to predetermine the approximate doses and energies of implantation species. Sheet resistances are measured to assess the silicide thickness and quality of the resulting films. Depth profiles for boron, nitrogen, fluorine and cobalt have been extracted analytically by secondary ion mass spectroscopy. Transmission electron microscopy micrographs have been included to show the silicide/Si interface and also to manifest that there is no grain boundary grooving in the resulting cobalt silicide film.
In situ trench etching and releasing technique of high aspect ratio beams using magnetically enhanced reactive ion etching
Authors: Kok Kitt Wai , Yoo Won Jong , Sooriakumar K.
Published: July 2002

This article describes an in situ trench etching and releasing technique to fabricate high aspect-ratio beams for high performance microelectromechanical systems (MEMS) accelerometers using magnetically enhanced reactive ion etching (MERIE) technique. In the conventional process, lateral encroachment due to the release etching is severe underneath the SiO2 etching mask. In this process, the sidewall of the beams was passivated by inhibiting layers formed during the HBr/SiF4/O2 trench etching, and the beams were not attacked by the subsequent SF6 release etching. Auger electron spectroscopy showed the etch inhibiting layer to consist mostly of Si and O. This was also confirmed by x-ray photoelectron spectroscopy as SiOx (1<x<2) was detected as a predominant species. The in situ process eliminated (1) sidewall deposition step and (2) floor etching step of the conventional process. In addition, the dependency of MERIE etching rates on open ratio and pattern size was studied for high aspect-ratio MEMS structures. The MERIE etching rates of Si substrate were insensitive to the open ratio in the range of from 10% to 50%, in contrast to inductively coupled plasma etching. The capacitance and yield results from MEMS accelerometers made by the in situ process were acceptable to replace the conventional process.
Two-dimensional modeling of long-term transients in inductively coupled plasmas using moderate computational parallelism. I. Ar pulsed plasmas
Authors: Subramonium Pramod , Kushner Mark J.
Published: July 2002

Quantifying transient phenomena such as pulsed operation is important for optimizing plasma materials processing. These long-term phenomena are difficult to resolve in multidimensional plasma equipment models due to the large computational burden. Hybrid models, which sequentially execute modules addressing different phenomena, may not be adequate to resolve the physics of transients due to their inherent iterative nature. In this article, a different modeling approach is described in which a moderately parallel implementation of a two-dimensional plasma equipment model is used to investigate long-term transients. The computational algorithms are validated by comparing the plasma properties for sequential and parallel execution for a steady state case. The physics model is validated by comparison to experiments. Results from the model were used to investigate the transient behavior of pulsed inductively coupled plasmas sustained in Ar. The consequences of varying pulse repetition frequency, duty cycle, power, and pressure on plasma properties are quantified. We found that the electron density, temperature, and source function, and plasma potential, peak beneath the coils during avalanche at the beginning of a pulse, finally attaining a diffusion dominated profile with a small off axis peak. As the pulse repetition frequency decreases, a more pronounced local maximum in plasma potential and electron temperature occurs.
Investigation of breakdown characteristic of a novel plasma display panel discharge cell with rotationally symmetric structure
Authors: Tu Yan , Zhang Xiong , Wang BaoPing , Yin Hanchun , Tong Linsu
Published: July 2002

Breakdown characteristic of a novel plasma display panel discharge cell with rotationally symmetric structure has been investigated by simulation. The corresponding formulas are given in this article. The electric field and particle density distribution are obtained from the simulation at different times, as well as the variation of average density of particles. The simulation results show that our novel structure has many advantages, such as lower ignition voltage, lower power consumption, higher luminous efficiency, and enhanced response frequency. Without application of energy recovery circuit a luminous efficacy of 0.8–0.9 lm/w is obtained.
Gap-filling capability and adhesion strength of the electroless-plated copper for submicron interconnect metallization
Authors: Lin Jian-Hong , Hsieh Wei-Jen , Hsu Jyh-Wei , Liu Xein-Wien , Chen Uei-Shin , Shih Han C.
Published: July 2002

The major goal of this study is to combine the plasma immersion ion implantation (PIII) to implant Pd catalyst onto a TaN diffusion barrier layer and the electroless plated Cu to accomplish the ultralarge scale integrated interconnection metallization. Both patterned and nonpatterned wafers were employed using Pd as a catalyst by PIII after which copper was electroless plated onto a TaN/FSG/Si multilayer structure. The Pd atoms were sputtered from a negatively biased target and ionized in an argon inductively coupled plasma. The Pd ions were adequately implanted into the substrate with a highly pulsed negative bias (∼4000 V). Characterized by field enhanced scanning electron microscopic (FESEM) cross-section images of FESEM, and under the circumstances of higher substrate bias voltage and plasma ionization, the electroless copper grows upward from the bottom of the vias (width: 0.25 μm, aspect ratio: 7), with an excellent gap filling ability. The result of this process, by employing the mechanical pull-up tests, showed that higher substrate bias and higher plasma ionization can effectively enhance the adhesion strength between the copper film and the TaN layer.
Electrochemical behavior of copper chemical mechanical polishing in KIO3 slurry
Authors: Hsu Jyh-Wei , Chiu Shao-Yu , Tsai Ming-Shih , Dai Bau-Tong , Feng Ming-Shiann , Shih Han-C.
Published: July 2002

The electrochemical behavior of polishing copper with colloidal silica abrasive slurry formulated with KIO3 oxidizer has been investigated. For planarization of the surface morphology, the control of the surface passivation of Cu is critical during polishing. KIO3 is not only an oxidizer but also a passivator for copper in an acidic slurry by forming a CuI layer on the surface. With alkaline slurry, Cu2O is the primary corrosion product on the Cu surface. The copper corrosion rate and removal rate can be decreased dramatically with increasing slurry pH. The low corrosion resistance or high corrosion susceptibility of Cu as determined by electrochemical measurements is the basis for the high removal rates. The copper removal rate is reduced from 4600 to 650 Å/min when the slurry pH is increased from 2 to 5; and the copper removal rate levels off at pH 7 with a steady-state removal rate of 200 Å/min.
Effect of thermal diffusion on a membrane-mask-distortion correction and compensation method
Authors: Murooka Ken-ichi , Lim Michael H. , Smith Henry I.
Published: July 2002

The idea of correcting x-ray mask distortion through differential heating of the membrane (i.e., projecting a heat pattern onto the membrane that introduces a correcting distortion which cancels the original undesired distortion) was first proposed by Feldman [J. Vac. Sci. Technol. B 17, 3407 (1999)]. Because this correction strategy relies on a precise heat pattern, one must account for how thermal diffusion would blur the edges of the pattern. Here, we numerically analyze how thermal diffusion affects this correction strategy and find that no compensation is necessary if the blurred regions are smaller than the spatial frequency of the distortion correction. We also devise compensation techniques to correct for the temperature distribution effects of thermal diffusion. Our results show how one might construct a real-time correction of arbitrary in-plane distortion through local heating.
Reemission of Ionically Pumped H2 and He from a Stainless Steel Surface
Authors: Martin G. , Lewin G.
Published: July 2002

H 2 and He discharges in a stellarator produce copious wall bombardment by the plasma ions. The reemission rate of the gas was measured for times of 0.06 to 105 see after bombardment. The rate was approximately proportional to t−0.6 for He and t−0.75 for H2. The reemission is also calculated assuming diffusion of the gas in the solid and taking into account the finite nonuniform initial distribution. It follows from the analysis that the rate is proportional to t−n where n approaches 0.5 or 1.5 as the ratio of reemission to bombarding time approaches zero or infinity.
Enhancement of Noble Gas Pumping for a Sputter-Ion Pump
Authors: Komiya Souji , Yagi Nobuaki
Published: July 2002

Enhancement of noble gas pumping has been observed for cathodes of different configuration and material. On the basis of the fact that erosion proceeds at the central portion of a cathode exposed to a Penning discharge, while sputtered material piles up at the circumferential area of the cathode, the ratio of the number of sputtered atoms per unit time to the number of impinging gas ions per unit time has been considered to be the controlling factor. A multiholed tantalum plate combined with conventional flat titanium cathode gives a pumping speed for argon about 40% as large as the pumping speed for nitrogen. With a flat tantalum cathode in one side and a flat titanium cathode in the opposite, the pumping speed for argon was about 27% of that for nitrogen. Both pumps, however, showed some 20% to 25% less speed for nitrogen compared with a conventional pump having a pair of flat titanium cathodes. A pump equipped with multiholed copper plates instead of multiholed tantalum plates was also tested, which did show an argon pumping speed twice as large as that of a conventional pump. During a long test run for the so-called argon instability, the multiholed tantalum pump did not show an appreciable pressure pulse at least for 700 h at 2×10−5 Torr with a constant throughput of argon.
Ion milling (ion-beam etching), 1954–1975: A bibliography
Authors: Hawkins Donald T.
Published: July 2002

The ion milling process is briefly described as an introduction to the extensive bibliography presented on this process and its varied applications. (AIP)
The structure of co−sputtered tungsten−aluminum oxide granular films
Authors: Pinch H. L.
Published: July 2002

Tungsten−aluminum oxide granular films with metal volume fraction, x, varying from 0.9 to 0.15 were prepared by an rf sputtering technique in which the entire compositional range was simultaneously deposited. At the metal−rich end the tungsten particles are mainly in the normal bcc form (α−W). As x decreases, the amount of tungsten in the β phase (A−15 structure) increases. At x∠0.3 the tungsten is all β−W. In the as−prepared films the particle size, as determined by x−ray line broadening, varies from ∠65 Å to ∠25 Å as x varies from 0.9 to 0.15. Annealing the films results in particle growth and an increase in the amount of α phase. The β phase persists in these granular films to much higher temperatures than reported elsewhere. It is proposed that the metastable β−W phase is stabilized by the very small crystallite size.
Valence−band structure in the Auger spectrum of aluminum
Authors: Houston J. E.
Published: July 2002

Previous work on the valence−band structure for the aluminum L2,3 VV transition has suffered from an arbitrary correction for the secondary electron background contribution. In the present paper this contribution is accurately assessed through the application of dynamic background subtraction and the resulting structure is shown to be a step−like function. This behavior is attributed to loss processes involving the escaping Auger electrons and is taken into account by deconvoluting the Auger spectrum using the inelastic backscatter data taken with an incident electron energy of 70 eV. The resulting Auger valence−band structure is very similar in shape to the calculated spectrum but slightly narrower. Additional data will be presented which indicate that this narrowing is a result of the surface sensitivity of the Auger technique.
Superconducting transition temperatures of reactively sputtered films of tantalum nitride and tungsten nitride
Authors: Kilbane F. M. , Habig P. S.
Published: July 2002

Superconducting tantalum nitride and tungsten nitride films have been prepared by reactively sputtering the pure metals in argon−nitrogen gas mixtures. X−ray diffraction and Auger electron spectroscopy were used to characterize the deposited compounds. For fcc TaN a maximum Tc of 8.15 K was measured. The high Tc is attributed to achieving a nitrogen content close to the stoichiometric composition. In the tungsten−nitrogen system, a mononitride was not produced. However, superconductivity was found for films in the 5−20 at.% nitrogen range. The maximum Tc of 4.85 K occurred in a compound close to the phase boundary between β−W and W2N.
Study of the N–Cu(100) system
Authors: Burkstrand J. M. , Kleiman G. G. , Tibbetts G. G. , Tracy J. C.
Published: July 2002

The reaction of a clean Cu(100) surface with atomic N has been studied with low energy electron diffraction (LEED), Auger electron spectroscopy, ultraviolet photoemission spectroscopy (UPS), and x-ray photoemission spectroscopy (XPS). Atomic nitrogen, formed by electron dissociation of N2 forms a c(2×2) overlayer on the Cu(100) surface. An analysis of LEED intensity profiles averaged over constant momentum transfer indicates that the N binds in a fourfold symmetric site, 0.145 nm above the first layer of Cu atoms. UPS data reveal small adsorbate-induced electronic levels at 1.3 and 5.8 eV below the Fermi level, in addition to rather complex changes in the Cu d band. XPS measurements yield 397.3 eV for the binding energy of the N 1s electrons with respect to the Fermi level. Our UPS and Auger data on Cu(100)/N in terms of N-induced states is shown to be plausible.
Evaluation of surface roughness of metal films by transmission electron microscopy and ellipsometry
Authors: Chan E. C. , Marton J. P. , Brown J. D.
Published: July 2002

Rough metallic films sputtered onto smooth pyrex glass substrates were analyzed by ellipsometry and electron microscopy. The ellipsometric data was interpreted in terms of a pair of roughness parameters through the use of generalized Maxwell–Garnett theory and the anisotropic Fresnel equations. The surfaces of all the samples were replicated and examined by transmission electron microscopy. The micrographs obtained were compared with the ellipsometer results. Qualitative agreement was found between the results obtained from ellipsometry and electron microscopy.
Substrate surface contamination from dark-space shielding during sputter cleaning
Authors: Kominiak G. J. , Uhl J. E.
Published: July 2002

Soft x-ray appearance spectroscopy is used to monitor nickel contamination levels in an iron substate during glow discharge sputter cleaning, most severe surface contamination is introduced from an electrically floatting stainless steel shield during dc sputter cleaning. Grounding the shield minimizes the contamination and rf sputtering virttually eliminates it.(AIP)
Performance of the modified orbitron pump
Authors: Naik Pramod K. , Verma S. L.
Published: July 2002

The conventional orbitron pump is modified to improve the speeds for inert gases. Pumping speed measurements were made on the modified orbitron pump by using the two-gauge calibrated conductance method for helium, argon, and xenon with the temperatures of the pump body at 288 K (15 °C), 323 K (50 °C), and 418 K (145 °C). Improvements in the maximum speed in comparison with the conventional orbitron pump are by factors varying from 1.15 to 1.88. Increase in speed for helium with pressure is attributed to the concentration of helium atoms at some trapping sites in titanium films. Increase in speed for helium at 323 K (50 °C) temperature indicates that the pumping of helium is governed by a diffusion-controlled process before the entrapment. Deterioration in the speeds for argon and xenon at 323 K (50 °C) and for helium at 418 K (145 °C) is believed to be due to thermal release of the trapped gas.
Photoemission and band-structure studies of the GaAs(110) surface
Authors: Pandey K. C. , Freeouf J. L. , Eastman D. E.
Published: July 2002

We have studied the electronic and geometrical structure of the cleaved GaAs(110) surface, using experimental ultraviolet photoemission spectroscopy (UPS) of both filled and empty surface states together with tight-binding calculations. We have considered several different types of structural models, including the relaxation model in which surface Ga atoms move into, and As atoms move out of, the surface by an amount such that the plane through the nearest-neighbor Ga and As atoms makes a tilt angle, ϑT, with the corresponding plane in the ideal surface while bond lengths remain constant. We show that this model with a tilt angle ϑT∠19° in contrast with ϑT∠35° as previously concluded from (LEED) low-energy electron-diffraction analysis adequately accounts for the photoemission spectroscopy data. A description of the nature of surface states including the local s- and p-orbital densities of states and dispersion relations is given for this relaxation model.
Space Shuttle−A personal view
Authors: Mark Hans
Published: July 2002

The history of the Space Shuttle is reviewed and its principal features and uses are summarized. A personal viewpoint is adopted through several anaswers to the question: ’’What experiments would I do as a Space Shuttle passenger–user?’’
Physical vapor deposition of chromium and iron
Authors: Weston William F. , Baker Thomas C. , Smith Carl J. , Chavez Abraham L. , Grotzky Virgil K. , Capes James F.
Published: July 2002

Chromium and iron films of 10–50μm thickness were deposited on beryllium substrates by electron-beam evaporation. Deposition rates varied from 35 to 425 Å/s. Substrate temperatures ranged from 300° to 650°C. The relationships between coatings characteristics and substrate temperatures, deposition rate, and angle of vapor incidence were studied. A columnar grain structure is achieved under these conditions with the chromium films having less than theoretical density. The chromium films become denser and less porous as substrate temperatures increases. The lack of full density in the chromium can be ascribed to discontinuities between grains. The iron coatings are denser, exhibiting very large columnar grains, approaching equi-axed, at the higher substrate temperatures. Deposition rates above about 300 Å/s lead to splattering of the evaporant and conelike defects in the films. Vapor deposition at oblique angles leads to less dense coatings, with grain growth occurring radially toward the source. Coatings microstructures were not disturbed by multiple, interrupted deposition. Burnishing or sanding the chromium films tends to densify and crush the coating.
Surface cleaning by low-temperature bombardment with hydrogen particles: An AES investigation on copper and Fe–Cr–Ni steel surfaces
Authors: Bouwman R. , van Mechelen J. B. , Holscher A. A.
Published: July 2002

Hydrogen has been used at a pressure of 5×10−5 Torr (6.6×10−3 Pa) and at room temperature in an ’’ion-etching beam mode’’ for cleaning solid surfaces. Two systems, viz. solvent-cleaned and atmosphere-exposed copper and heat-resistant Fe–Cr–Ni steel, were analyzed in Auger spectroscopy before and after bombardment with hydrogen particles produced in a conventional ion gun. Copper is almost completely cleaned of carbon, sulfur, and oxygen within 30 min. A bulk-carbon-containing steel is completely freed from surface carbon while the bulk carbon is preserved in the subsurface zone at a satisfactory level. The proposed cleaning method seems to be very surface specific and nondestructive to subsurface layers.
Plasma diagnostics with electric probes
Authors: Clements R. M.
Published: July 2002

The use of Langmuir or electric probes in collisionless plasmas which are of interest in sputter coating is briefly reviewed. The analysis of the probe current–voltage characteristic, especially that from double floating probes, to yield the plasma parameters, the electron temperature, and the ionization density, is considered in some detail. This paper is intended to be of use to the experimentalist who wishes to use Langmuir probes as a diagnostic tool but does not really want to become an expert in all aspects of probe theory and operation.