bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoresponse probe of the space charge distribution in ferroelectric lead zirconate titanate thin film memory capacitors
Authors: Thakoor Sarita , Maserjian J.
Published: July 2002

A photoresponse study of sol-gel derived polycrystalline thin films of lead zirconate titanate (PZT) is described. Thin film ferroelectric capacitors were fabricated in a sandwich geometry with a transparent top electrode, and illuminated with ≊365 nm wavelength (PZT band gap ∼3.5 eV) light pulses. The observed photocurrent has two components: first, a transient spike coincident with the onset of the illumination pulse, and second, a steady dc photocurrent which prevails as long as the light is ‘‘ON.’’ The steady current response exhibits a weak dependence on the polarization, whereas the transient response exhibits a distinct polarization dependence. To understand the nature of this photoresponse we have studied the variation of the photoresponse as a function of the duration of the ‘‘write’’ pulse used to program the ferroelectric capacitor. The peak value of the polarization dependent transient component of the photoresponse relates to the injected space charge and the distribution of deep traps within the ferroelectric thin film. This, in turn, is modulated by the duration of the write pulse used to program the capacitor. We provide a space charge model that offers a framework for interpreting the photoresponse. The transient photoresponse thus serves as a qualitative measure of the space charge in the ferroelectric film, and to a limited extent, an indirect measure of the remanent polarization. We propose that these photoresponse effects can be applied as diagnostic probes of the space charge distribution in the ferroelectric thin film.
Inorganic pathways for biosynthesis: A molecular orbital modeling approach
Authors: Hench Larry L. , West Jon K.
Published: July 2002

Selective adherence on bioactive glass surfaces of various biological molecules associated with osteogenesis appears to be responsible for the correlation of in vitro reaction kinetics with the rate of bone bonding. Chemical interaction of organic molecules with hydrated silica is also important in osteogenesis and bone mineralization and affects, in as yet an unknown manner, extracellular bond and cartilage matrix formation. The AM-1 molecular orbital method is used to calculate the reaction pathways for bond formation between alanine and trisiloxane rings to simulate organic interactions with hydrated silica. The results show that there are low energy reaction pathways for the organic–inorganic bonding. Different types of interfacial bonds can be formed depending upon the structure and orientations of the organic or inorganic molecules. The differences in reaction pathways and binding energies for formation of –Si–O–C– linkages with the amino acids versus formation of –Si–N– bonds may account for the variety of biochemical effects observed for silicon in nature and for bioactive glass.
Investigation of selective SiO2-to-Si etching in an inductively coupled high-density plasma using fluorocarbon gases
Authors: Bell F. H. , Joubert O. , Oehrlein G. S. , Zhang Y. , Vender D.
Published: July 2002

A recent, important development in low-pressure plasma processing is the radio frequency inductively (RFI) coupled high density discharge. Its ability to create high densities of excited and charged species at low pressures (<10−3 Torr) makes it an attractive etching tool. In this work we have examined selective etching of SiO2 over Si using a home-built RFI source. CHF3, C2F4, C3F6 and their mixtures with hydrogen were examined. Without biasing of the substrate strong fluorocarbon deposition occurs over the investigated pressure range from 5 to 20 mTorr. As the pressure increases the ion current density decreases, whereas the fluorocarbon deposition rate increases. Both parameters increase roughly linearly with inductive rf power from 500 up to 1250 W. Etching was achieved by rf biasing. When the pressure is reduced from 20 to 6 mTorr, the oxide and silicon etch rates decrease less than 20% for all gases. The highest oxide etch rate of 830 nm/min at 350 W rf bias power is achieved for C3F6. Adding H2 decreases the etch rates for oxide and silicon for all gases. The drop of the silicon etch rate is considerably higher than for the oxide etch rate resulting in a better selectivity. The best selectivity of 45 is achieved for C2F4 when 30% H2 is added into the discharge. The results obtained with the RFI source are compared to results with a microwave electron cyclotron resonance discharge.
Filling of micron-sized contact holes with copper by energetic cluster impact
Authors: Haberland Hellmut , Mall Martin , Moseler Michael , Qiang You , Reiners Thomas , Thurner Yonca
Published: July 2002

A completely ionized and clustered beam of Mo or Cu is deposited with variable kinetic energy on a substrate, and the filling of micron-sized contact holes on semiconductor devices is studied. An excellent hole filling is obtained for the impact of charged copper clusters, if they contain 1000–3000 Cu atoms and impinge with a kinetic energy of about 10 eV per atom on a substrate having a temperature of 500 K. The morphology of small hole fillings by slow and energetic cluster impact is discussed.
Sharing of Auger electron spectroscopy and x-ray photoeletron spectroscopy spectral data with the c
o
m
m
o
n d
a
t
a p
r
o
c
e
s
s
i
n
g s
y
s
t
e
m
Authors: Yoshihara Kazuhiro , Yoshitake Michiko
Published: July 2002

The common data processing system (Ver. 3.0), which is software for common handling of spectral data taken on different instruments, has been constructed using Visual Basic language under MS–Windows (3.1). This software is used to convert each file format to the common format proposed as ‘‘VAMAS–SCA Standard Data Transfer Format,’’ to obtain the characteristic parameters of one’s spectrometer by using standard spectra in the system, to calibrate a spectrum with those parameters, to analyze spectral data by proposed procedures, and to obtain correction factors from the database. The common data processing system is not commercially produced but should be created by all the scientists and engineers who have an interest in promoting surface analysis. The fruits of the VAMAS–SCA activities have been made available with this software.
Auger in-depth profiling of Mo–Si multilayers
Authors: Konkol A. , Sulyok A. , Menyhard M. , Barna A.
Published: July 2002

Auger in-depth profiles were measured on a Mo–Si multilayer structure, consisting of 45 periods of 3.3 nm molybdenum and 3.6 nm silicon layers, by means of Ar ion bombardment with rotated specimen and a glancing incidence ion beam probe. The relative sputtering yield of Si and Mo is determined in the ranges of 2–6 keV ion energy and 80°–87° incidence angle with respect to the surface normal. It is shown that the depth resolution depends strongly on the ion energy. The depth resolution changes immediately when the ion energy is changed. This observation is explained by the fact that the depth resolution in our experiment is limited by ion mixing and not by surface roughening. Attempts to determine the initial structure from the measured profile through application of Liau’s model on ion sputtering were not completely successful.
Gas desorption from an oxygen free high conductivity copper vacuum chamber by synchrotron radiation photons
Authors: Gröbner O. , Mathewson A. G. , Marin P. C.
Published: July 2002

An OFHC copper chamber was exposed to 3.75 keV critical energy synchrotron radiation for a total dose of of 2.7×1023 photons/m. After this dose, photodesorption yields down to 10−5 molecules/photon were reached for H2, CO, and CO2 and 10−7 mol/photon for CH4, H2O, and O2 and a total of about one monolayer of gas was desorbed. From observation of the transient behavior of the desorption at the beginning of an irradiation period after a prolonged interruption, the desorption yield was found to be proportional to the coverage and followed an exponential decay with increasing photon dose. This is in contrast with the normal behavior where the desorption yield decreases linearly with dose on a log–log scale. The observations are interpreted by a two-step process involving photons or photelectrons to create a new surface phase of molecules which subsequently desorb thermally. With the chamber heated to 70 °C, the photodesorption yields for H2O and O2 increased but the others remained relatively independent of the temperature. At the end of the irradiation period a substantial wall pumping was observed in the chamber. For CO, CO2, and O2 it was about 1160, 280, and 80 ℓ/s respectively.
Adherent carbon film deposition by cathodic arc with implantation
Authors: Gerstner E. G. , McKenzie D. R. , Puchert M. K. , Timbrell P. Y. , Zou J.
Published: July 2002

A method of improving the adhesion of carbon thin films deposited using a cathodic vacuum arc by the use of implantation at energies up to 20 keV is described. A detailed analysis of carbon films deposited onto silicon in this way is carried out using complementary techniques of transmission electron microscopy and x-ray photoelectron spectroscopy (XPS) is presented. This analysis shows that an amorphous mixing layer consisting of carbon and silicon is formed between the grown pure carbon film and the crystalline silicon substrate. In the mixing layer, it is shown that some chemical bonding occurs between carbon and silicon. Damage to the underlying crystalline silicon substrate is observed and believed to be caused by interstitial implanted carbon atoms which XPS shows are not bonded to the silicon. The effectiveness of this technique is confirmed by scratch testing and by analysis with scanning electron microscopy which shows failure of the silicon substrate occurs before delamination of the carbon film.
Gas distribution through injection manifolds in vacuum systems
Authors: Theil Jeremy A.
Published: July 2002

When injecting gas into a vacuum system, quite often the gas is distributed through a gas injection manifold. However, designs normally rely upon practical experience. By considering the manifold arrangement as a network of flow restrictions it is possible to optimize the distribution of gas throughout the manifold. The methodology for determining the flow distribution through the two simplest topologies of gas manifold, single- and double-opening manifolds from a single-gas injection point, is derived in this article. It is shown that the double-opening manifold topology tends to provide more uniform flow distribution than the single-opening manifold topology for similar conductance ratios. The results of this work include a summation formula for the single-opening manifold. In addition, guidelines for one type of tailored flow manifold are given. Finally, three basic design rules are presented: (1) use as few holes in the manifold as possible, (2) use a double opening manifold when possible, and (3) specify tube dimensions such that the tube/spray hole conductance ratio is maximized.
Effects of water partial pressure on the activated electron beam evaporation process to deposit tin-doped indium-oxide films
Authors: Shigesato Yuzo , Yasui Itaru , Hayashi Yasuo , Takaki Satoru , Oyama Takuji , Kamei Masayuki
Published: July 2002

The effects of water partial pressure (PH2O) during deposition on the structural and electrical properties of tin-doped indium-oxide (ITO) films have been investigated on an activated electron beam evaporation process using an arc plasma generator. The resistivity of the films deposited at 180 °C increased with an increase in PH2O in terms of a decrease both in Hall mobility and carrier density. X-ray diffraction and scanning electron microscope analyses showed that the ITO films deposited at higher PH2O consisted of a major portion of larger crystalline grains with smaller internal strain and a small portion of amorphous regions which is supposed to be at the interface between the film and the substrate. Plasma diagnostics by optical emission spectroscopy revealed that atomic hydrogen was generated by electron-impact dissociation of H2O and that the activation of Ar or O2 was suppressed in the higher PH2O process, which resulted in the deposition of less oxidized and lower-damaged ITO films.
Optimum beam energy for high depth resolution secondary ion mass spectrometry
Authors: Clegg J. B.
Published: July 2002

Practical secondary ion mass spectrometry depth resolution data show that decreasing beam energies lead to an enhanced resolution down to the lowest practical energy of 1 keV O+2 at near normal incidence. For B and C in Si, the resolution full width at half-maximum amounts to 3.1 and ∼1.4 nm, respectively. Using a retarded probing beam, we have shown that a useful flux of Si atoms can be sputtered with primary energies as low as 260 eV O+2 or 130 eV O+; the Si sputter yield is also shown to be weakly dependent on the probe energy. Therefore it is predicted that this low energy is the optimum to use in a depth profiling experiment using oxygen. The predicted resolution for B and C amounts to 1.8 and 0.8 nm. Such an analytical performance would easily justify the resources required to produce ultralow energy beams on a routine basis.
Thickness determination of uniform overlayers on rough substrates: A comparison of calculations for Al2O3/Al to x-ray photoelectron spectroscopy and atomic force microscopy experiments on technical aluminum foils
Authors: Gunter P. L. J. , Niemantsverdriet J. W.
Published: July 2002

Angle dependent x-ray photoelectron spectroscopy (XPS) is often used to determine the thickness of thin overlayers by means of a model assuming a perfectly flat substrate. In this article we analyze the consequences of neglecting roughness effects for a uniform Al2O3 overlayer on a rough Al substrate, through the application of a Monte Carlo algorithm to rough geometries generated by a method for simulation of random fractals. The main result is that the error in calculated thickness—which depends strongly on analyzing angle—nearly vanishes at off-axis angles close to 35°. We apply these findings to previously published XPS data on technical aluminum foils and compare the outcome with an atomic force microscopy based roughness analysis of these foils.
Origin of intrinsic stress in Y2O3 films deposited by reactive sputtering
Authors: Choi H. M. , Choi S. K.
Published: July 2002

Y2O3 thin films were deposited by reactive sputtering of an Y target in an Ar and O2 gas mixture. Intrinsic stresses and the Ar content in the films were measured by the sine square psi method of x-ray diffraction and wavelength dispersive spectrometer, respectively. At low working pressures the films had high compressive stresses. As working pressure increased, compressive stress was relaxed. Ar content was high in the film that had high compressive stress. After annealing of the films at 700 °C, the compressive stress was largely relaxed but the Ar content remained unchanged. These results clearly showed that compressive stress in Y2O3 films was not caused by Ar entrapment as an impurity but by Ar bombardment. Intrinsic stress was almost independent of the O2/Ar flow ratio, showing that O bombardment was equal to Ar bombardment in affecting the intrinsic stress in Y2O3 films. The independence of intrinsic stress with the O2/Ar flow ratio was explained by the concept of M1/2i{[Micosθ±(M2t−M2isin2 θ)1/2]/(Mi+Mt)} instead of the Mt/Mi ratio, where Mt is the atomic mass of the target material, Mi is the atomic mass of the sputtering gas, and θ is the scattering angle.
Fourier transform infrared study of rapid thermal annealing of a-Si:N:H(D) films prepared by remote plasma-enhanced chemical vapor deposition
Authors: Lu Z. , Santos-Filho P. , Stevens G. , Williams M. J. , Lucovsky G.
Published: July 2002

Fourier transform infrared spectroscopy has been used to study the behavior of bonded hydrogen and bonded deuterium in hydrogenated amorphous silicon nitride films [a-Si:N:H(D)] that were deposited by remote plasma-enhanced chemical vapor deposition (RPECVD) and had been subjected to rapid thermal annealing (RTA) from 400 to 1200 °C after film deposition. The amount of bonded hydrogen in the film and its distribution between Si–H and SiN–H bonding groups is correlated to the ratio (R) of the source gases: NH3 to SiH4. Chemical reaction pathways are proposed to account for bond dissociation and release of hydrogen from the films in the form of molecular H2 and NH3. As the bonded hydrogen population decreases with increasing RTA temperature, the Si–N bond population increases. This postdeposition bonding of nitrogen to silicon upon thermal release of hydrogen species is consistent with improvements in the electrical properties of RPECVD silicon nitride films after an RTA treatment at 900 °C.
Magnetron reactive ion etching of AlN and InN in BCl3 plasmas
Authors: McLane G. F. , Casas L. , Lareau R. T. , Eckart D. W. , Vartuli C. B. , Pearton S. J. , Abernathy C. R.
Published: July 2002

Magnetron reactive ion etching of AlN and InN in BCl3 discharges is found to produce anisotropic pattern transfer over a wide range of conditions. Maximum etch rates of ∼1250 Å min−1 for AlN and ∼1000 Å min−1 for InN were obtained for low pressures (2–12 mTorr) and low cathode self-bias voltages (≤−100 V). Auger electron spectroscopy and secondary ion mass spectrometry measurements showed the presence of <1 at. % boron and chlorine residue on as-etched AlN and InN. Dry etching appeared to produce a change in the surface region stoichiometry of InN.
Observation of surface symmetry for Si/XeF2 and Si/Cl2 system using second-harmonic generation
Authors: Haraichi Satoshi , Sasaki Fumio , Kobayashi Shunsuke , Komuro Masanori , Tani Toshiro
Published: July 2002

Observation of surface symmetry change with etching reaction for the Si(111)/XeF2 and Si(111)/Cl2 systems has been demonstrated using second-harmonic generation (SHG) is reported. SHG output decays quickly with spontaneous XeF2 etching because of the formation of a SiFx reaction layer. Surface symmetry is broken by 1–2 langmuir exposure to XeF2 and recovered by ohmic heating to 800 °C. SHG output also decays quickly with exposure to Cl2. However, surface symmetry seems to remain after 20 langmuir exposure to Cl2 and SHG output is recovered by ohmic heating to 1000 °C.
Synergistic sputtering effects during ion bombardment with two ion species
Authors: Berg S. , Katardjiev I. V.
Published: July 2002

The modification of the sputtering yield during ion bombardment with two ion species of different masses is studied with the dynamic Monte Carlo code T−DYN. Specifically, the sputtering yield of low mass targets with low to medium mass primary ions is substantially enhanced when a second ion species of higher mass is introduced. This enhancement is due to the incorporation of the heavier ion species into the target material thus changing significantly the collision cascade behavior of the primary ions. As a result, the energy deposited at the surface is increased and hence the sputtering yield is also increased. This sputter yield enhancement is found to be a function of the ion energy, angle of incidence, masses and atomic densities of the two ion species, steady state concentration of the secondary ion species at the surface (primary to secondary ion ratio), etc. The effect is found to be most pronounced at low energies where the sputter yield enhancement is predicted to increase by a factor of 2 or more. The mechanisms of the sputter yield enhancement as well as the modification of the energy deposition function are discussed in detail.
Solid-state reaction of Ti and Ni thin films with aluminum nitride
Authors: He Xiangjun , Tao Kun , Fan Yudian
Published: July 2002

Pure bulk AlN substrates were prepared by hot pressing to eliminate the influence of an aid-sintering substance on the interface reactions. AlN thin films were deposited on Si(111) substrates to decrease the influence of charging on the analyses of metal/AlN interfaces with x-ray photoelectron spectroscopy (XPS). Thin films of titanium and nickel were deposited on bulk AlN substrates by e-gun evaporation and ion-beam assisted deposition (IBAD) and deposited on AlN films in situ by e-gun evaporation. The samples of the evaporated Ti films on bulk AlN and Ni films on bulk AlN were annealed at temperatures from 600 to 800 °C and from 600 to 850 °C for 1 h, respectively. Solid-state reaction products between the metal films and bulk AlN substrates under annealing and IBAD were investigated by x-ray diffraction (XRD) and Ruthford backscattering spectroscopy (RBS). TiAl3, TiN, and Ti4N3−x including Ti2N were found at the interface between the Ti films and AlN substrates for the annealed samples and IBAD sample. No interaction phase was detected for the sample as-deposited by evaporation. However, XPS depth profile of the Ti/AlN/Si sample showed that Ti–N bonding existed at the interface between the AlN film and Ti film. In the Ni/bulk AlN system, NiAl3 and Ni3N were formed at the interface between the Ni thin film and bulk AlN substrate for the samples annealed above 600 °C for 1 h. No interaction phase was detected by XRD and RBS for as-deposited samples and no evidence for Ni–N or Ni–Al bonding was obtained by XPS depth profile of Ni/AlN/Si.
Infrared diode laser absorption spectroscopy measurements of CFX (X=1–3) radical densities in electron cyclotron resonance plasmas employing C4F8, C2F6, CF4, and CHF3 gases
Authors: Miyata Koji , Hori Masaru , Goto Toshio
Published: July 2002

Infrared diode laser absorption spectroscopy was used for measuring CFX (X=1–3) radical densities in electron cyclotron resonance plasmas employing C4F8, C2F6, CF4, and CHF3 gases commonly used for the plasma etching of silicon dioxide. CFX (X=1–3) radical densities in these plasmas were measured systematically together with CHF3 and CF4 molecular densities as a function of microwave power and as a function of H2 dilution. Furthermore, variations of F atom densities in these plasmas were also investigated by the actinometry technique. The differences in the radical and atomic densities according to fluorocarbon feed gases are discussed based on their molecular structures and atomic component ratios (carbon/fluorine and hydrogen/fluorine).
Impurity back diffusion through an ultrahigh vacuum turbomolecular pump under large gas throughput
Authors: Konishi Nobuhiro , Shibata Tadashi , Ohmi Tadahiro
Published: July 2002

Impurity back diffusion through a main UHV turbomolecular pump to a reduced-gas-pressure processing chamber has been experimentally studied. A large throughput of process gases severely degrades the capability of a UHV main pump in dragging impurities, resulting in the back diffusion of impurities to the processing chamber. Such degradation is greatly influenced by the pumping speed of the low-vacuum backing pump. However, we have found for the first time that the impurity level in the chamber can be made even lower than that for the best performance of the main pump under UHV operation when the gas flow rate is optimized for the system. It is shown that the optimized gas flow rate corresponds to the flow rate at which the effective pumping speed of a UHV main pump begins to decrease. The back diffusion levels are largely dependent upon the mass of impurity gas molecules and less back diffusion occurs for heavier gas molecules. The guidelines for designing a vacuum pumping system for use in reduced-gas-pressure processing are presented.
Simulation and experimental study of re-emission during sputter deposition of Ti–W films
Authors: Rogers B. R. , Cale T. S. , Chang Y. K.
Published: July 2002

We used experiments and physically based process simulations to study the re-emission of Ti and W during sputter deposition of Ti–W films and Ti during the sputter deposition of Ti films. Ti–W thin films have previously been shown to become Ti rich in geometrically confined areas, such as in features of a microelectronic device, compared to unconfined areas. This spatial composition variation was attributed to re-emission of Ti during the deposition process. Re-emission during Ti–W sputter deposition was confirmed by depositing a Ti–W film onto test structures with large areas with no direct line-of-sight to the target. Transmission electron microscopy was used to image the film deposited on all areas of the structure and Auger electron spectroscopy was used to determine the composition of the film. EVOLVE, a physically based process simulator, was used along with the experimental data to estimate the effective sticking coefficients of Ti and W during Ti–W deposition. Simulation results indicate the effective sticking factors of Ti and W to be 0.30 and 0.74, respectively. The Ti to W effective sticking factor ratio determined in this study, 0.40, was in good agreement with that previously reported, 0.38. In comparison, sputter deposition of Ti onto these test structures showed little re-emission. Process simulation of Ti sputter deposition indicated the Ti effective sticking factor to be essentially unity.
Characterization of a low temperature, low pressure plasma enhanced chemical vapor deposition tetraethylorthosilicate oxide deposition process
Authors: Arias, Jr. Louie J. , Selbrede Steve C. , Weise Mark T. , Carl Daniel A.
Published: July 2002

A low temperature (180 °C) and pressure (⩽750 mTorr) tetraethylorthosilicate (TEOS) oxide deposition process was developed and characterized in a commercially available plasma enhanced chemical vapor deposition reactor. The reactor uses a dual frequency, capacitively coupled, parallel plate electrode design, which employs multistation sequential deposition to enhance throughput and uniformity. Deposition rate, within wafer film thickness uniformity, and film stress were characterized as a function of process pressure, gas composition, rf power, and temperature. Production quality oxide films were deposited using low TEOS flow rate (45 sccm), high oxygen flow rate (4000 sccm), and low pressure (500 mTorr). Deposition rate increased linearly with TEOS flow rate and decreases with oxygen flow rate. Deposition rate was weakly dependent on high frequency power and independent of pressure in this low pressure regime. Film thickness uniformity across a 200 mm wafer improved with decreasing TEOS flow rate and pressure. Uniformity was a weak function of oxygen flow rate and high frequency power. Film stress became more compressive with decreasing TEOS flow rate and was a weak function of oxygen flow rate, high and low frequency power, and pressure. A high quality TEOS oxide was deposited in this new processing regime, suitable for integrated circuit applications.
Characterization of chemical interaction of asbestos surfaces during culturing with lung cells
Authors: Seal Sudipta , Barr Tery L. , Krezoski Sue , Petering David H. , Antholine W.
Published: July 2002

The pathogenic nature of asbestos has become an established fact in environmental science. This is particularly true for the injury of epithelial cells. Although speculation exists as to the involvement of the fibrous nature of asbestos silicates, and/or the adverse oxidative properties of any ferrous components, as of yet, no concrete mechanism has been discerned for this pathogenic interaction. It should be apparent, however, that since the silicates are apparently altering the chemical and structural properties of the cells, stoichiometry requires some type of corresponding chemical alteration in the properties of the asbestoses. In the present case, we report on a variety of interesting results centered around the latter “reverse mechanism.” In these studies, x-ray photoelectron spectroscopy or electron speetroscopy for chemical analysis, atomic absorption spectroscopy, and electron spin resonance were employed to track the behavior and alterations of the chrysotile silicates immersed in select cell cultures. In this regard, a unique mechanism is hypothesized involving (1) selective chemical attachment of the cellular bodies to the tetrahedral silicate layer of the asbestos, (2) followed by progressive extraction of some of the Mg, and then (3) any Fe that may be present is partially drawn out of the octahedral layers, and (4) eventually the latter species are found to lodge in the cells where chemical involvement with oxidants produced in the life cycle (such as H2O2) may generate peroxides through a fenton-type mechanism.
Extracting more chemical information from X-ray photoelectron spectroscopy by using monochromatic X rays
Authors: Sherwood Peter M. A.
Published: July 2002

Monochromatized X-ray sources have been available for use in commercial X-ray Photoelectron spectrometers for more than 20 years. Nevertheless most X-ray photoelectron spectroscopic (XPS) data are collected using achromatic radiation. The advantages of using monochromatized XPS combined with high resolution data collection for the study of core and valence band XPS are discussed, with a focus on the latter region. Examples discussed include studies of metals and oxides. The importance of eliminating X-ray satellite features in obtaining lead oxide valence band spectra is illustrated, and the resulting valence band spectra are shown to be able to distinguish between the oxides. While the valence band region can be well understood by using a cluster model for oxides, the importance of using a band structure model is illustrated for graphite and molybdenum spectra. Possible band structure effects are reported in oxide valence band spectra.
Study of shallow silicon trench etch process using planar inductively coupled plasmas
Authors: Lee Ju-Hoon , Yeom Geun-Young , Lee Ju-Wook , Lee Jung-Yong
Published: July 2002

Silicon shallow trenches applied to the shallow trench isolation of integrated circuits were etched using planar inductively coupled Cl2 and HBr/Cl2 plasmas and the effects of process parameters such as gas combination, inductive power, and bias voltage on etch rates, selectivities, and etch profiles of silicon trenches were investigated. Also, the physical damages on the trench bottom and sidewall in Cl2 and HBr/Cl2 plasmas were studied using cross-sectional high resolution transmission electron microscopy (HRTEM). The increase of inductive power and bias voltage in Cl2 and HBr/Cl2 plasmas increased polysilicon etch rates in general, but reduced the etch selectivity over nitride. In case of Cl2 plasmas, low inductive power and high bias voltage showed an anisotropic trench etch profile, and the addition of oxygen or nitrogen to chlorine also increased the etch anisotropy. The use of pure HBr plasmas showed a positively angled etch profile and the addition of Cl2 to HBr improved the etch profile more vertically. HRTEM study showed defects formed near the sidewall, bottom, and bottom edge of the silicon trenches etched in Cl2/N2 plasmas, and more dense defects in HBr/Cl2 plasmas possibly due to the penetration of hydrogen in HBr. No defects were found for the trenches etched in pure Cl2 or Cl2/O2 plasmas.
Aspect ratio effects in submicron contact hole plasma etching investigated by quantitative x-ray photoelectron spectroscopy
Authors: Le Goff C. , Peignon M. C. , Turban G. , Bilhant R.
Published: July 2002

The submicron contact hole etching process using CHF3–CF4–Ar plasma was performed in a commercial parallel plate reactive ion etching reactor (LAM 4520). Response surface methodology was employed to correlate input parameters with etching results. For the aspect ratio investigations, a special test pattern consisting of line/space and contact/space arrays of various dimensions (1 and 0.6 μm) was used. Aspect ratio dependent etching effects were observed. The bottom surface chemistry of SiO2/Si patterned structures after plasma etching have been investigated by using quantitative x-ray photoelectron spectroscopy (XPS). After the SiO2 etching treatments, the silicon surface of the contact (or trench) bottom presents modifications similar to that observed on unpatterned SiO2/Si samples. These modifications are described by a two-layer model involving a fluorocarbon overlayer and an interfacial oxide layer. The fluorocarbon layer thickness strongly increases when the surface area of silicon substrate exposed to the plasma decreases whereas, as unexpected, the fluorine density of the fluorocarbon film decreases. A refluorination mechanism depending on the diffusion of the fluorine atoms from the plasma through the fluorocarbon overlayer is proposed. This work points out the interest of XPS surface analysis in improving the contact hole etching process.
Hole-size dependent highly selective SiO2 etching with a hexthode-type wide-gap plasma etcher
Authors: Hosomi Shinichi , Omori Nobuhiko
Published: July 2002

We carry out contact-hole etching of SiO2 with a high selectivity over the underlying Si using a hexthode-type wide-gap plasma etcher. In spite of the low power density in the plasma, heavy fluorocarbon deposition was observed. The amount of deposition is thought to depend on the bias voltage near the surface of the wafer. Selectivity is low in smaller holes (<∅0.8 μm), since the deposition radicals are shaded and cannot reach the bottom of the holes. In larger holes (>∅0.8 μm), however, selectivity is very high (>50), and almost infinite in a hole of ∅2.0 μm in diameter. Moreover, sidewall deposition is enough to prevent retardation of the resist even in smaller holes. As a result, quite unique hole-size dependent etching characteristics were obtained, such as tapered etching for smaller holes and high selectivity etching for larger holes. This oxide etcher is applicable when large shallow holes and small deep holes must be etched at the same time.
Sheath thickness in very-high-frequency plasma chemical vapor deposition of hydrogenated amorphous silicon
Authors: van Sark W. G. J. H. M. , Meiling H. , Hamers E. A. G. , Bezemer J. , van der Weg W. F.
Published: July 2002

When very-high-frequency (VHF) glow discharges are used to obtain homogeneous hydrogenated amorphous silicon films on glass substrates, an optimum combination of process pressure and excitation frequency is required. With frequencies in the range of 30 to 80 MHz pressures from 0.65 to 0.35 mbar are used. It was suggested that the sheath thickness plays an important role in this. We use two recently developed experimental methods to determine the sheath thickness, i.e., gap-induced inhomogeneity and in situ energy-resolved mass spectrometry. The gap-induced inhomogeneity method (GI method) is based on the observation of a reduced deposition rate, if a gap exists between the glass substrate and the metal substrate electrode. The reduction scales with gap thickness and, more importantly, with the sheath thickness. In situ energy-resolved mass spectrometry is employed to measure the ion-energy distributions (IEDs) at the grounded electrode. From the observed charge-exchange peaks in the IEDs in silane plasmas we are able to deduce the sheath thickness (IED method). Both methods are employed to determine the sheath thickness in VHF silane/hydrogen glow discharges. For the optimum frequency-pressure combinations it appears that all sheath thicknesses are about equal and amount to about 4 mm (GI method), while the IED method shows a decreasing sheath thickness with frequency. The total integrated IEDs of all ions, i.e., the total energy dose, is constant for these conditions, which correlates well with the fact that material properties are similar for the optimum frequency-pressure combinations.
Design of a scanning tunneling microscope for in situ topographic and spectroscopic measurements within a commercial molecular beam epitaxy machine
Authors: Ventrice, Jr. C. A. , LaBella V. P. , Schowalter L. J.
Published: July 2002

A scanning tunneling microscope that performs scanning tunneling microscopy, scanning tunneling spectroscopy, and ballistic electron emission microscopy measurements on 2-in. wafers has been designed and constructed. The instrument is incorporated into the Si preparation chamber of a cryo-pumped Fisons V90H Si/III-V molecular beam epitaxy machine. Its design uses two commercial Burleigh inchworms: one for performing scanning tunneling microscopy measurements and a second for making a front contact which is necessary for the ballistic electron emission microscopy measurements. The substrate holder for the V90H system is designed to handle wafers up to 6 in. in diameter. Therefore, a custom 6-in.-diam. holder has been constructed which supports two 2-in. holders: one for performing reflection high energy electron diffraction measurements and a second which allows transfer of the wafer to the scanning tunneling microscope and also incorporates a removable shadow mask for growing metal/semiconductor Schottky diodes. Although the chamber vibrations generated by the cryopump and its compressor are quite severe, atomic-resolution images have been obtained with all of the system’s pumps in operation. The enhanced stability of our design is attributed to our unique support system of the inchworm and wafer which are both manufactured from machinable ceramic, the use of Be–Cu springs with an extension length of 16 in. for vibration isolation, and the use of silicone O-rings for vibration damping.
Spinning rotor gauge in the range from 10−4 to atmospheric pressure
Authors: Boffito C. , Moraja M. , Pastore G.
Published: July 2002

Many industrial applications require measuring pump down pressure trends over several orders of magnitude, in various sensor positions. The SAES Vacuum Gauge (SVG1) senses from 10−4 Pa to atmospheric pressure with orientation-independent positioning. A temperature sensor was added to the conventional spinning rotor gauge to compensate for the thermal response; new magnets were added to stabilize the levitation. A nonlinear data processing algorithm was developed to stabilize the gauge over the expanded pressure range. The SVG1 range is larger than a traditional spinning rotor gauge (10−4–1 Pa), and capacitance manometers (1–105 Pa).
Temperature dependence of reflection high-energy electron diffraction intensity from Si(111)-7×7 superlattice
Authors: Yamaguchi K. , Mitsui H. , Shigeta Y.
Published: July 2002

Rocking curves of reflection high-energy electron diffraction (RHEED) were observed from Si(111)-(7×7) surface at temperature of 293, 523, and 653 K by a RHEED apparatus with a magnetic deflector to change the glancing angle. The temperature dependence of RHEED intensity was calculated with change of the real and imaginary part of the potential corresponding to the thermal diffuse scattering arising from a thermal vibration of atoms, which was obtained by the way proposed by Dudarev et al. [Surf. Sci. 330, 86 (1995)]. We assumed that the amplitude of the thermal vibration (Debye parameter) increases with temperature according to the Einstein model. By comparing with the experimental results, the atomic positions of the (7×7) structure satisfying the observed RHEED rocking curves in this temperature range is determined. The positions of the surface atoms are almost coincident with the results obtained by using ab initio molecular-dynamics scheme (Brommer et al. [Phys. Rev. Lett. 68, 1355 (1992)]) within the difference of 0.01 nm.
Characterization of wall conditions in DIII-D
Authors: Holtrop K. L. , Jackson G. L. , Kellman A. G. , Lee R. L. , West W. P. , Wood R. D. , Whyte D. G.
Published: July 2002

Wall conditioning in DIII-D is one of the most important factors in achieving reproducible high confinement discharges. For example, the very high confinement mode (VH-mode) was only discovered after boronization, a chemical vapor deposition technique to deposit a thin boron film over the entire surface of the tokamak. In order to evaluate wall conditions and provide a data base to correlate these wall conditions with tokamak discharge performance, a series of nominally identical reference VH-mode discharges (1.6 MA, 2.1 T, double null diverted) were taken at various times during a series of experimental campaigns with evolving wall conditions. These reference discharges have allowed a quantitative determination of how the wall conditions have evolved. For instance, core carbon and oxygen levels in the VH-mode phase remained at historically low levels during the 1995 run year and there was also a steady decrease in the oxygen levels at plasma initiation during this period. We will discuss the long term changes in low Z impurities and the effect of wall conditioning techniques such as boronization and baking on these impurities. In addition, the evolution of the deuterium recycling rates will be discussed.
Performance of different etch chemistries on titanium nitride antireflective coating layers and related selectivity and microloading improvements for submicron geometries obtained with a high-density metal etcher
Authors: Abraham S. C. , Gabriel C. T. , Zheng J.
Published: July 2002

Different chemistries were evaluated in a metal etcher with a high-density plasma source that was used to etch a titanium nitride antireflective coating (ARC). A composite film structure consisting of aluminum (with 0.5%–1% Cu) as the underlying layer, a titanium nitride ARC layer, and titanium nitride as the barrier layer were used for the standard stack, while titanium nitride and aluminum layers alone were used for the initial characterizations of the process. Conventional BCl3/Cl2 chemistry was used initially to etch both the titanium nitride ARC layer and the underlying aluminum layer. The performance of BCl3/Cl2 chemistry on the titanium nitride ARC layer as well as on the composite stack was evaluated. Partial etch measurements were taken to calculate the composite microloading and resist selectivity values. Different etch chemistries were then employed for the ARC layer while keeping conventional BCl3/Cl2 chemistry for the aluminum layer, and the difference in process performances were evaluated. Fluorine additives along with chlorine as the main etchant gave very high etch rate values for the titanium nitride layer. CHF3 was added as the fluorine source for the current study. When the titanium nitride layer was etched with chemistries having faster etch rates, CHF3 added chemistries in the current study, a remarkable improvement in the composite microloading was observed, compared to the microloading values obtained with conventional chemistry. An improved etch rate uniformity was another noticeable performance improvement. Possible mechanisms for these trends are explained in this article. The experimental portion of this article will provide details relating to the etcher and the film structure used for the study. The results and discussion section will give details of the process performance and a comparative evaluation of different titanium nitride chemistries, as well as possible mechanism for the trends observed.
Reactive-sputtering of titanium oxide thin films
Authors: Guerin D. , Shah S. Ismat
Published: July 2002

Titanium oxide thin films are useful for applications such as catalysis, optical coatings, gas sensors, and other electronic devices. We have sputtered titanium in atmospheres of varying amounts of oxygen and argon; the resulting films were studied with x-ray photoelectron spectroscopy and x-ray diffraction in order to determine the changes in chemical composition. In addition, the thicknesses were measured for the purpose of finding the film growth rate versus oxygen content. We found that the films were composed of combinations of metallic titanium and three oxides. Metallic titanium and stoichiometric titanium oxide coexisted only in films grown with decreasing oxygen flow rates. Also, the highest stoichiometric TiO2 content in high-deposition rate films was obtained in the region of decreasing oxygen flow.
Sputtered Cu/Co films for giant magnetoresistance: Effect of plasma gas and annealing treatment
Authors: Maya L. , Paranthaman M. , List F. A. , Warmack R. J.
Published: July 2002

Sputtered Co/Cu films were deposited on silicon either directly, using an argon plasma, or through an intermediate step involving the deposition of CoN/Cu3N by reactive sputtering in a nitrogen plasma. The nitride composite was pyrolyzed to release the nitrogen. The effect of preparation route and different annealing treatments on the resistivity of these films as a function of magnetic field and temperature was established. As in previous studies particle size is of primary importance in determining the giant magnetoresistance (GMR) characteristics of a film; thus optimizing the magnitude of the GMR effect requires close control of the duration and temperature of annealing treatments. The microstructure of these films was examined by means of atomic force microscopy. The intermediate nitride step produced a film in which the GMR effect was degraded apparently through the inclusion of voids that are not eliminated in the pyrolysis stage.
Comparison of magnetic linear dichroism in 4f photoemission and 4d–4f photoemission from Gd on Y(0001)
Authors: Gammon W. J. , Mishra S. R. , Pappas D. P. , Goodman K. W. , Tobin J. G. , Schumann F. O. , Willis R. , Denlinger J. D. , Rotenberg E. , Warwick A. , Smith N. V.
Published: July 2002

Magnetic linear dichroism (MLD) in 4d–4f resonant and 4f nonresonant photoemission (PE) is studied from thin epitaxial gadolinium films. In an angle resolved and high-energy resolution mode, experiments were conducted with the electric-field vector of the incident light perpendicular to the sample magnetization. Our results show a significant difference in behavior of MLD in resonant PE as compared to that in nonresonant PE. Off-resonance, the MLD signal is dominated by a negative feature at the low binding energy side of the peak. Near the 4d–4f resonance maximum, the MLD displays a plus–minus shape, with a negative signal at the low binding energy side of the 4f peak and a positive signal at the high binding energy side. Analysis of MLD in 4d–4f resonant PE may provide insight into interactions of the 4d core hole with the 4f core level in the intermediate state.
Approach for a three-dimensional on-chip quantification by secondary-ion mass spectrometry analysis
Authors: Gnaser Hubert
Published: July 2002

An attempt to perform a three-dimensional (3D) quantitative evaluation of the complete sample volume sputter removed in a secondary-ion mass spectrometry analysis is described. Using a focused (∼3 μm) 7 keV Cs+ primary-ion beam and detecting sputtered MCs+ ions (M stands for any sample element), a vertical Si–metal–oxide–semiconductor transistor structure (with a lateral size of ∼40 μm and a total vertical dimension of ∼3 μm) was analyzed by image depth profiling. Elemental concentrations of these micrographs were derived from relative sensitivity factors and the pertinent depth information in the 3D sample (data) volume could be estimated by utilizing these factors and an approximation of the atomic densities. The specimen’s surface topography both in the pristine state and upon completion of the sputter depth profile was recorded by two-dimensional stylus profilometry. By these means, a reconstruction of the sample volume eroded during the analysis appears feasible at a lateral resolution of a few μm and an in-depth resolution of about 10 nm.
X-ray photoelectron spectroscopy study of the chemical interaction between BN and Ti/TiN
Authors: Seal Sudipta , Barr Tery L. , Sobczak Natalie , Benko Ewa
Published: July 2002

Many nitrides, particularly BN and TiN, have stimulated commercial interest because of their extreme hardness, wear and corrosion resistance, and thermal and electrical properties. All of these features are enhanced by the resulting structures and the large degree of covalency exhibited by the metal–nitride bonds. Coatings of select nitrides with films of related materials may particularly influence these properties in critical surface and interface regions. Materials of interest include the deposition by plasma vapor deposition of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Resulting structural and morphological features have been investigated with electron microscopy and x-ray diffraction. Critical importance is also attributed to the chemical behavior of species deposited and grown at the resulting interfaces. Detailed x-ray photoelectron spectroscopy has, therefore, been rendered of these interfaces using cross-sectional display and sputter etching. Movement of nitridation and interference from oxidation and carbide formation are of particular concern.