bluuebunny/crossref_metadata_2025 huggingface dataset:
Dry and wet etching characteristics of InN, AlN, and GaN deposited by electron cyclotron resonance metalorganic molecular beam epitaxy
Authors: Pearton S. J. , Abernathy C. R. , Ren F. , Lothian J. R. , Wisk P. W. , Katz A.
Published: July 2002

The dry etching characteristics of thin film InN, AlN, and GaN epitaxial layers deposited using metalorganic group III sources (trimethylindium, trimethylamine alane, and triethylgallium) and electron cyclotron resonance (ECR) plasma excited atomic nitrogen in a metal organic molecular beam epitaxy (MO-MBE) chamber have been examined using CCl2F2/Ar, BCl3/Ar, and CH4/H2/Ar discharges. In a hybrid ECR-rf system, the Cl-based chemistries readily etch GaN and AlN, while addition of F to the discharges dramatically reduces the etch rate of AlN. Slow, smooth etching of InN is achieved with the CH4/H2/Ar chemistry. Controlled rates of ∼200 Å min−1 are obtained for all three materials at moderate dc biases (≤−200 V), low pressure (1 mTorr), and low microwave power (200 W). The dc bias and pressure dependence of the etching have been systematically studied. GaN films can be wet chemically etched in 30–50% NaOH solutions, AlN in HF and InN in HCl:HNO3 solutions.
Role of stress relief in the hexagonal-close-packed to face-centered-cubic phase transformation in cobalt thin films
Authors: Cabral C. , Barmak K. , Gupta J. , Clevenger L. A. , Arcot B. , Smith D. A. , Harper J. M. E.
Published: July 2002

Stresses in thin films can affect phase transformation temperatures. We show, however, that stress relief and grain growth in Co thin films occur at temperatures below the hcp to fcc phase transformation. Temperature ramped (10 °C/min) in situ stress, differential scanning calorimetry, and resistivity were measured on evaporated 56–275 nm Co films, and microstructure was examined with transmission electron microscopy. As-deposited films are under tensile stress, ≊1×109 Pa, which is relieved between 120 and 275 °C. The as-deposited small grains (15–20 nm) undergo secondary grain growth at 230–350 °C, giving a mixed phase bimodal grain size distribution with the smallest grains (both hcp and fcc) 20–25 nm in diameter and the largest grains (〈0001〉 hcp) 150–200 nm in diameter. The hcp grain growth is signalled by an exothermic calorimetric peak at 282 °C with an enthalpy of 0.15±0.04 kJ/mol and a resistivity decrease. The hcp to fcc phase transformation is signaled by an endothermic calorimetric peak with an enthalpy of 0.27 ±0.07 kJ/mol at 380 °C although transmission electron microscopy reveals that the transformation is incomplete. There is no indication of a reverse transformation on cooling. Additional heat treatment to 736 °C, on the thinner 56 nm Co film on SiO2 substrates, results in agglomeration and an accompanying decomposition of SiO2 catalyzed by Co. The results indicate that as-deposited tensile stress does not control the phase transformation temperature in Co thin films.
Formation of device-quality metal–insulator–semiconductor structures with oxide–nitride–oxide dielectrics by low-temperature plasma-assisted processing, combined with high-temperature rapid thermal annealing
Authors: Ma Y. , Yasuda T. , Lucovsky G.
Published: July 2002

The formation of oxide–nitride–oxide (ONO) dielectrics on crystalline Si substrates by low-temperature plasma-assisted oxidation and remote plasma-enhanced chemical-vapor deposition (PECVD) is described. The electrical performance of the ONO dielectrics has been correlated with (i) the chemical bonding within the nitride layers, (ii) the accumulation of N atoms at the SiO2/Si interface, and (iii) the formation of oxynitride interfacial regions internal to the ONO structure. The ONO dielectrics have been studied in metal-insulator-semiconductor (MIS) devices, and their electrical properties have been examined by capacitance–voltage (C–V), and current–voltage (I–V) measurements. A post-deposition rapid thermal anneal (RTA) for 30 s at 900 °C, has been shown to reduce (i) the fixed charge at the two internal oxide/nitride (O/N) interfaces and (ii) the density of traps Dit at the SiO2/Si interface.
Electron source brightness and degeneracy from Fresnel fringes in field emission point projection microscopy
Authors: Spence J. C. H. , Qian W. , Silverman M. P.
Published: July 2002

Fresnel edge fringes observed in a lensless point projection field-emission electron microscope operating at 90 eV have been studied and found to be formally equivalent to the fringes observed in transmission electron microscopy (TEM) under weak scattering conditions at the edge of an opaque object. The tip-to-spectrum distance z1 plays the role of the objective lens defocus setting Δf in conventional TEM. The image magnification, effective source size, transverse coherence width, instrumental resolution, and source brightness are all obtained from an analysis of the fringe spacings and intensity. The quantum mechanical upper limit on source brightness, as well as relationships among beam brightness, coherence parameters, and degeneracy, are discussed, and the degeneracy measured from experimental Fresnel fringes.
Dry etching of titanium nitride thin films in CF4–O2 plasmas
Authors: Fracassi F. , d’Agostino R. , Lamendola R. , Mangieri I.
Published: July 2002

The dry etching of titanium nitride has been studied in fluorine containing glow discharges. Untreated samples are covered by an oxidized layer of titanium oxide and/or oxynitride. X-ray photoelectron spectroscopy cannot be utilized to clarify the nature of these species that strongly influence surface reactivity. In agreement with some published data, it has been found that the component of the N 1s signal at low binding energy is due to interstitial nitrogen atoms and not to substoichiometric nitrides. An analysis of the effect of temperature and bias voltage variation is reported as well as the changes of surface composition due to the plasma action. Comparisons with the reactivity of metallic titanium are also discussed.
Scattering of 3He from the NiO(001) surface
Authors: Bishop G. G. , Baker J. , Gillman E. S. , Hernández J. J. , Safron S. A. , Skofronick J. G.
Published: July 2002

A scattering experiment employing 3He as the probe has been performed in an attempt to measure the magnetic structure of the NiO(001) surface. A nozzle beam ∼5% 3He in a carrier gas of 4He was used to produce a narrow velocity spread of the incident 3He atoms, Δv/v≊3.5%. Measurements of the angular distributions (scattering intensity versus incident angle) yielded sharp Bragg peaks, indicating that a high quality NiO(001) surface had been produced by cleaving in situ. The diffraction pattern obtained with 3He is similar to that obtained with 4He. A careful examination of the angular region where Bragg peaks from the magnetic structure might be expected revealed no features. This negative result implies that the hyperfine interaction is much weaker than the nonmagnetic portion of the atom–surface potential, and is consistent with the magnitude of the hyperfine interactions found in electron spin resonance measurements. Features attributable to bound-state resonances in the He–surface potential were observed in the specular intensity as a function of incident wave vector. The energy levels calculated from these results were in good agreement with previous results from 4He scattering experiments.
Surface trimer crystallization on poly (ethylene terephthalate) studied by time-of-flight secondary ion mass spectrometry
Authors: Reichlmaier S. , Bryan S. R. , Briggs D.
Published: July 2002

The surface crystallization of cyclic trimer on poly (ethylene terephthalate) (PET) films was studied by time-of-flight secondary ion mass spectrometry. PET films synthesized from dimethyl- terephthalate or from terephthalic acid are compared in this study. Several thermal crystallization procedures and a solvent vapor initiated crystallization were compared in order to investigate differences in surface chemistry observed on the different types of PET. Thermal crystal growth with varying temperatures (120–180 °C) and treatment times (20 min–48 h) was compared with the crystals grown under methylene chloride vapor exposure for 24 h. PET manufactured from terephthalic acid showed a unique correlation of the trimer crystals with sodium, but only in thermal crystallization processes.
Low-energy Ar ion-induced and chlorine ion etching of silicon
Authors: Balooch M. , Moalem M. , Wang Wei-E. , Hamza A. V.
Published: July 2002

A nearly monoenergetic beam of argon and chlorine ions with kinetic energy from 40 to 900 eV and intensity up to 30 μA/cm2 is used to study the etching of Si. The etch rate and ion current density at the surface are simultaneously measured to obtain the etch yield. The ratio of atomic chlorine (Cl+) to molecular chlorine (Cl+2) ions striking the surface is measured by a quadrupole mass spectrometer. In the absence of any chlorine, the Ar ion sputtering of silicon at 120 eV is about 0.05 silicon atoms removed per ion and monotonically increases to 1 silicon atom per ion at 800 eV. The Ar+-induced etch yield increases by about an order of magnitude when the surface is simultaneously exposed to a neutral molecular chlorine flux sufficient to produce saturation coverages from the effusive doser. An etch yield of 0.13 silicon atoms removed per incident Ar ion is measured at an Ar+ energy of 50 eV, which also monotonically increases to 4 silicon atoms removed per incident argon ion at 700 eV. The etch yield further increases by approximately a factor of 20% as the surface is bombarded with energetic chlorine ions. The etch yield with energetic chlorine ions increases from 0.07 to ∼5 silicon atoms per incident ion with increasing kinetic energy from 40 to 900 eV.
Measurements of the tangential momentum accommodation coefficient in the transition flow regime with a spinning rotor gauge
Authors: Gabis David H. , Loyalka Sudarshan K. , Storvick Truman S.
Published: July 2002

Gas-surface interactions which are described with the accommodation coefficients play an important role in the determination of the mass, momentum, and thermal energy transport in rarefied gas flows, aerosol mechanics, and vacuum technology. While the thermal accommodation coefficient has been extensively studied, the investigations of the other coefficients have been limited, partly because of the difficulties that are associated with the available theories and control of surfaces. To further understand the tangential momentum accommodation coefficients, experimental investigations of the rotational motion of a freely suspended sphere in a variety of gases and over a range of pressures were undertaken. It was found that the experimental results are generally well described by recent theoretical works that have provided numerical solutions of the linearized Boltzmann equation. Further, the theory can be used to interpret experimental data in terms of the tangential momentum accommodation coefficient, α over the entire range of the Knudsen number. The values of α are near 1 for most of the gas types and vary only slightly with the pressure.
Characteristics of reactively sputtered Pt–SnO2 thin films for CO gas sensors
Authors: Di Giulio M. , Micocci G. , Serra A. , Tepore A. , Rella R. , Siciliano P.
Published: July 2002

SnO2 thin films were prepared by the rf reactive sputtering method from a target of the same compound in order to be used as gas sensors. Dynamic response characteristics of the electrical conductance to different CO concentrations in dry air are presented for pure films and for films activated with a suitable amount of metallic Pt deposited by sputtering onto a SnO2 surface. The sensitivity, the response, and recovery times as a function of temperature were analyzed. In particular, the Pt–SnO2 films show relatively high sensitivity to CO gas and good stability at an operating temperature of about 170 °C.
Ion-assisted Si/XeF2 etching: Temperature dependence in the range 100–1000 K
Authors: Vugts M. J. M. , Hermans L. J. F. , Beijerinck H. C. W.
Published: July 2002

The Ar+-ion enhanced Si(100)/XeF2 reaction is studied in a multiple beam setup for silicon temperatures from 100 K up to 1000 K. The XeF2 flux is 2.7 monolayers/s and the Ar+ flux 0.033 monolayers/s at an energy of 1000 eV. Both the XeF2 consumption and the SiFx production are measured by mass spectrometry. The enhancement of the etch rate peaks around 250 K as is observed in both the XeF2 and SiFx signals. The gradual decline above 250 K is attributed to a diminished surface fluorination and XeF2 precursor concentration. The dropoff below 250 K is presumably caused by sputtering of the XeF2 precursor, as is concluded from the temperature dependence of the XeF+/XeF2+ signal ratio. Around 175 K this decrease is so strong that the ions seem to no longer enhance, but rather reduce, the etch rate. Below 150 K the ions are driving the etch process. In this range the spontaneous process is blocked by XeF2 condensation, but the ion-assisted process continues due to sputtering or dissociation of the condensate.
Thermovoltage in scanning tunneling microscopy
Authors: Hoffmann D. , Haas A. , Kunstmann T. , Seifritz J. , Möller R.
Published: July 2002

The thermovoltage which will be discussed arises if the tunneling tip and the sample are at different temperatures. For zero external bias voltage the difference of the Fermi distribution for both electrodes will lead to a thermally driven current since, in general, the balance between forward and backward tunneling of electrons will be disturbed. If the external current is zero a bias voltage is found leading to a tunneling current of the same magnitude but opposite direction. This voltage will be referred to as thermovoltage. It provides an analytical tool with excellent lateral resolution which is very sensitive to minor variations of the local electronic density of states of tip and sample in the vicinity of the Fermi level. The investigation of the (111) surfaces of the noble metals reveals several details of the electronic structure. Au(111) shows a local variation with atomic periodicity. For the first time, this provides evidence that the energy dependence of the electronic density of states varies between a position right above an atom or in between atoms of a metallic surface. The thermovoltage may also be used for the investigation of chemically heterogeneous surfaces. As an example the growth of Ag on Au(111) is analyzed. It demonstrates that the measurement of the thermovoltage should be especially useful for the study of alloying processes.
Epitaxial growth of ultrathin films of chromium and its oxides on Pt(111)
Authors: Zhang Lanping , Kuhn Markus , Diebold Ulrike
Published: July 2002

The growth of vapor-deposited Cr and chromium oxide on Pt(111) has been studied by ion scattering spectroscopy, x-ray photoelectron spectroscopy, low energy electron diffraction, and scanning tunneling microscopy. Both metal Cr film and its oxide nucleate at Pt(111) step edges, and grow in a step-flow mode. The metal Cr film is pseudomorphic to the Pt(111) substrate within the first two monolayers. At higher coverages, the chromium overlayer adopts a bcc(110) surface structure and forms three-dimensional elongated islands oriented along the three close-packed directions of the Pt(111) surface. For the chromium oxide, a well ordered p(2×2) structure is observed within the first two monolayers and attributed to the epitaxial growth of metastable Cr3O4. At higher coverages, a (√3×√3)R30° structure appears, due to the formation of the stable Cr2O3 phase.
Preparation and optical studies on flash evaporated Sb2S3 thin films
Authors: Mahanty S. , Merino J. M. , León M.
Published: July 2002

Thin films of Sb2S3 were prepared by flash evaporation. As-deposited films were found to be amorphous and highly resistive (R>106Ω) in nature. An amorphous-crystalline phase transition occurs at 498 K on subsequent annealing in nitrogen atmosphere. The fundamental optical transition is direct in nature and the optical band gaps (Eg) lie in the region 1.70–2.07 and 1.42–1.65 eV for amorphous and crystalline films, respectively. A near-linear decrease in Eg with decreasing S/Sb ratio was observed suggesting the dependence of the band gap on film composition.
Electrical properties of metal–insulator–semiconductor structures with silicon nitride dielectrics deposited by low temperature plasma enhanced chemical vapor deposition distributed electron cyclotron resonance
Authors: Hugon M. C. , Delmotte F. , Agius B. , Courant J. L.
Published: July 2002

The present article reports a study of current–voltage (J–E) and capacitance–voltage (C–V) measurements on metal–insulator–semiconductor diodes, using SiNx:H as an insulator layer and Si or InP as semiconductors. We have deposited SiNx:H films by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition at floating temperature, with physical properties similar to films prepared at 800 °C by low pressure chemical vapor deposition. Silane and nitrogen were used as the reactive gases. The experimental results show that the resistivity (ρ) and the critical field (EC) are a strong function of the dielectric composition. For films deposited under optimum conditions, ρ was equal to 1016 Ω cm and EC reached 3.65 or 4.5 MV/cm for Al/SiNx:H/Si and Al/SiNx:H/InP diodes, respectively. The dominant mode of electronic conduction appears to be the Poole–Frenkel emission. The postmetallization annealing (PMA) has no significant effect on these bulk properties (ρ, EC and electronic conduction). On the contrary, PMA has been shown to mainly affect the properties of both SiNx:H/Si and SiNx:H/InP interfaces. The optimized Al/SiNx:H/Si fabrication procedure induced a midgap interface state density (Dit) of 6×1010 eV−1 cm−2 evaluated by high frequency and quasistatic C–V characteristics. In the case of Al/SiNx:H/InP diodes, we have found that the carrier trapping by direct tunneling near the SiNx:H/InP interface is dominant.
Corrosion resistance of titanium nitride and mixed titanium/titanium nitride coatings on iron in humid SO2-containing atmospheres
Authors: Agudelo A. C. , Gancedo J. R. , Marco J. F. , Hanžel Darko
Published: July 2002

The corrosion behavior in humid SO2-polluted atmospheres of three different TiN coatings on iron [single layer TiN (1000 nm), bilayer Ti(100 nm)/TiN(1000 nm) and multilayer Ti(100 nm)/TiN(100 nm)/Ti(100 nm)/TiN(100 nm)] have been investigated by means of x-ray photoelectron spectroscopy. Only the single layer coating shows some degradation in low concentration (0.001% v/v) SO2 atmospheres after 14 days of exposure, the other two coatings remaining stable. Exposure to higher SO2 concentration (0.04% v/v) for 7 days results in the total degradation of the single layer coating. Exposure to this latter atmosphere for 14 days brings about a considerable degradation of the bilayer and multilayer coatings, the results showing that the multilayer coating, even with the lowest total thickness, presents the highest resistance against these corrosion conditions. Corrosion of the TiN coatings results in the formation of TiO2 and several N species [probably of the type (NH4)2SO4 and species containing N–O bonds]. The degradation of the coatings results in the corrosion of the underlying iron. Fe2+ sulphates and sulphites, as well as FeOOH, are the main iron corrosion products.
Kinetic modeling of the charging of nonconducting walls in a low pressure radio frequency inductively coupled plasma
Authors: Kortshagen U.
Published: July 2002

This article investigates the overall charging of a nonconducting, plane wall (for instance a wafer) in a low pressure inductively coupled plasma. The problem is addressed using a two-dimensional kinetic model for a low pressure inductive discharge. Comparisons to experimental results show good agreement with the charging profiles predicted by the model. It is pointed out that the surface charge profile on a nonconducting wall is determined by the plasma homogeneity and the high energy part of the electron distribution function. An interpretation of the radial profiles of the sheath potential drop and of the surface charge potential in terms of the differential temperature of the electron distribution function in different energy ranges is presented.
Metal bonding during sputter film deposition
Authors: Shimatsu T. , Mollema R. H. , Monsma D. , Keim E. G. , Lodder J. C.
Published: July 2002

We studied the bonding between two flat Si substrates with thin metal films. The bonding was accomplished during thin film sputter deposition on contamination free surfaces of metal films. In this work we used Ti and Pt. Successful bonding of these metal films (each having a thickness of 10–20 nm) occurred at room temperature over the entire bonded area (12 mm×12 mm). Self-diffusion, particularly at grain boundaries and film surface, was the mechanism for bonding. Suitable metal bonding only occurred if the film surface roughness is sufficiently smaller than the self-diffusion length of metals. Particularly in the bonding of Ti to Ti films, transmission electron microscope observation revealed that complete crystalline grains had been formed across the former interface between the single thin Ti films. The interfaceless bonding can be explained by recrystallization of the Ti lattice due to the high self-diffusion coefficient of Ti. This technique would be applied to bonding of wafers to fabricate thin film devices or microsystems. Moreover, this bonding technology can be used with many different thin film materials and various semiconductor substrates.
Molecular beam epitaxial growth of AlN single crystalline films on Si (111) using radio-frequency plasma assisted nitrogen radical source
Authors: Yasutake K. , Takeuchi A. , Kakiuchi H. , Yoshii K.
Published: July 2002

We have grown AlN films on Si (111) using a molecular beam epitaxy (MBE) approach in which reactive nitrogen species are generated in a remote 13.56 MHz radio-frequency plasma discharge, nitrogen radical source. Effects of the Al/Si (111) γ-phase on epitaxial growth of AlN on Si (111) has been studied. Successive processes of forming stable Al/Si (111) γ-phase at 800 °C followed by MBE growth without interrupting Al beam exposure was effective to prevent amorphous SiNx formation on Si substrate. The Al/Si (111) γ-phase was found effective to fix the orientation relationship between AlN and Si for epitaxial growth of single crystal AlN. Single crystal AlN was grown on the Al/Si (111) γ-phase at the temperature as low as 400 °C. By optimizing growth conditions (substrate temperature, V/III ratio and plasma conditions), growth of single crystal AlN films in a quasi-layer-by-layer fashion was observed for the thickness up to 60 nm. The optimized value on the growth temperature was 800 °C and that on the V/III ratio was 440. The surface of the AlN film grown under the optimized condition was quite smooth with a root mean square roughness of 0.3 nm. The resistivity of the film was about 2×109 Ω cm.
Optical and electronic properties of sputtered TiNx thin films
Authors: Schmid Philippe E. , Sato Sunaga Masako , Lévy Francis
Published: July 2002

Thin titanium nitride films were deposited by rf reactive sputtering. The N/Ti ratio varied between 0.88 and 1.12. The optical constants have been determined by ellipsometric measurements between 1.5 and 5 eV. The normal reflectivity was measured between 0.5 and 5.5 eV. The results have been fitted by a model dielectric function based on a set of Drude–Lorentz oscillators. In this way the contributions due to free carriers and to interband transitions could be unambiguously sorted out. The analysis of the optical properties sheds light on the nature of the stoichiometry-related defects of TiNx. It is shown that TiN contains one conduction electron per TiN unit, and that in TiNx the square of the plasma frequency varies in a manner indicating a loss of about one electron to each nitrogen interstitial and a gain of about one conduction electron for each nitrogen vacancy. In substoichiometric material the most significant defect is the nitrogen vacancy and in nitrogen-rich TiNx excess nitrogen behaves like an interstitial defect. The occasional presence of titanium defects is also detected.
Model of interfacial thermal resistance of diamond composites
Authors: Jagannadham K.
Published: July 2002

The effective thermal conductivity of diamond and aluminum nitride layered composites was analyzed for three different types of interfaces. A sharp interface with a stepwise discontinuity, a graded interface with a linear variation and a diffused interface with a minimum or a maximum in thermal conductivity across the interface were considered. The results of the modeling analysis were used to explain the experimental results described in the literature of improved heat spreader characteristics of diamond and aluminum nitride composites.
Development of a triplasmatron ion source for the generation of SF5+ and F− primary ion beams on an ion microscope secondary ion mass spectrometry instrument
Authors: Gillen Greg , King R. Lance , Chmara Frank
Published: July 2002

A hot filament duoplasmatron ion source operating with argon has been modified by the addition of an enclosed expansion cup mounted to the extraction side of the duoplasmatron anode. Using sulfur hexafluoride (SF6) as a feed gas, this triplasmatron ion source has been used to generate SF5+ and F− primary ion beams for secondary ion mass spectrometry (SIMS). For positive primary ions, the current extracted from the source is composed of a series of SFx+ cluster ions (x=1–5) with the SF5+ ion being the most intense. SF5+ currents of ∼ 10–20 nA with a maximum of 40 nA are obtained at an extraction voltage of 10 kV. By applying a positive bias to the expansion cup, a localized secondary arc discharge is initiated giving 200 nA–300 nA of SF5+ with a current density of 0.5 mA/cm2. Depending on the operating parameters of the source, lifetimes of greater than 70 h have been achieved. For negative primary ions (with the cup removed), the current extracted from the source is primarily composed of F− ions with a maximum current of 3 μA. The source can be briefly dosed with SF6 and will generate F- beams for 1–2 days without any additional gas being added. Evaluation of the SF5+ and F− ion beams for common SIMS applications demonstrates that these novel primary beams offer significant advantages for depth profiling, organic surface characterization and imaging.
Real-time monitoring of structure and stress evolution of boron films grown on Si(100) by ultrahigh vacuum chemical vapor deposition
Authors: Nesting David C. , Kouvetakis J. , Hearne Sean , Chason E. , Tsong I. S. T.
Published: July 2002

The morphology and biaxial stress of amorphous boron films grown on silicon at 630 °C have been determined in situ and in real time using energy dispersive x-ray reflectivity and multiple-beam optical stress sensor techniques. The capability to determine the morphology and stress of light-element thin films in situ and in real time provides a unique opportunity to optimize the parameters of thin film deposition under chemical vapor deposition conditions.
Influence of an electrical field on the macroparticle size distribution in a vacuum arc
Authors: Keidar M. , Aharonov R. , Beilis I. I.
Published: July 2002

The results of experimental study of macroparticle distribution in a vacuum arc presented for Cu, Ti, Zr, and Cr cathodes. We have studied the macroparticle contamination of the films deposited on the substrate having floating potential and biased up to −1000 V with respect to the anode. It has been found that the macroparticle number significantly decreases (by a factor of 3–4) with substrate biasing for all examined cathode materials. A model of macroparticle motion in the quasineutral plasma and near-substrate sheath was proposed. The model bases on analyses of the macroparticle charging and motion in the quasineutral plasma and near substrate sheath. The model can qualitatively explain the macroparticle reduction in the coating due to negatively charged macroparticle reflection in an electric field.
Electrical characterization of metal–oxide–semiconductor capacitors with anodic and plasma-nitrided oxides
Authors: Landsberger L. M. , Ghayour R. , Sayedi M. , Kahrizi M. , Landheer D. , Bardwell J. A. , Riopel Y. , Jean C. , Logiudice V.
Published: July 2002

We have studied two novel techniques that should inherently be more uniform than current mainstream processes used to produce silicon dioxide or nitrided-oxide gate insulators. Anodic films were fabricated by anodizing Si wafers in HCl solutions, and thermal oxide films were nitrided in N2O plasmas produced with an electron-cyclotron resonance source. Using typical polysilicon-gate test structures, the electrical characteristics are obtained and compared to thermal oxides. Both techniques can produce thin films (<15 nm thick) with interface state densities and leakage currents initially comparable to their thermal oxide counterparts, if the films are subjected to rapid thermal annealing at temperatures of 950 °C. The annealed films are subjected to high-field (⩾8 MV/cm) Fowler–Nordheim stress and the buildup of trapped charge is monitored as a function of time. Anodic films are found to have moderately higher bulk and interface trap generation rates than the thermal control. Thinner anodic oxides, which were grown at slower rates, had better properties than thicker anodic oxides, suggesting that even slower growth rates could yield anodic oxides with improved electrical properties.
Study of the effects of discharge conditions and substrate temperature on Si epitaxial deposition using sputtering-type electron cyclotron resonance plasma
Authors: Gao Junsi , Wang Junli , Sakai Naofumi , Iwanaga Kanako , Muraoka Katsunori , Nakashima Hiroshi , Gao Dawei , Furukawa Katsuhiko
Published: July 2002

It was found that epitaxial Si films could be deposited on Si substrates by using a sputtering-type electron cyclotron resonance plasma that had a conventional base pressure of 5×10−7 Torr. The effects of discharge conditions and substrate temperature were studied systematically in order to understand the necessary conditions for epitaxial growth. It was found that discharge gas pressure, target power for sputtering, and substrate temperature play crucial roles in the epitaxial deposition. The implications of the changes of the three parameters are discussed in detail.
Etching characteristics of SrBi2Ta2O9 film with Ar/CHF3 plasma
Authors: Seo Jung-Woo , Lee Do-Haing , Lee Won-Jae , Yu Byoung-Gon , Kwon Kwang-Ho , Yeom Geun-Young , Chang Eui-Goo , Kim Chang-Il
Published: July 2002

Among the ferroelectric thin films that have been widely investigated for ferroelectric random access memory (FRAM) applications, the SrBi2Ta2O9 (SBT) thin film is appropriate as a memory capacitor material due to its excellent fatigue endurance. However, very few studies on the etch properties of SBT thin films have been reported, even though dry etching is an area that demands a great deal of attention in the very-large-scale integration of ferroelectric thin-film capacitors for FRAM applications. In this study, SrBi2Ta2O9 thin films were etched using a magnetically enhanced inductively coupled Ar/CHF3 plasma. Etch properties, such as etch rate, selectivity, and profile, were measured for different gas mixing ratios of CHF3/(Ar+CHF3), while the other process conditions were fixed at rf power of 600 W, dc-bias voltage of −150 V, and chamber pressure of 5 mTorr. The maximum etch rate of SBT thin films was 1650 Å/min under CHF3/(Ar+CHF3) of 0.1. Selectivities of SBT to Pt and photoresist masks were 1.35 and 0.94, respectively. The chemical reaction and compositional change of the etched surfaces were investigated by x-ray photoelectron spectroscopy analysis. The Sr and Ta atoms of SBT films react with fluorine; Sr–F and Ta–F are then removed by physical sputtering by Ar ions. The surface of a SBT film etched with CHF3/(Ar+CHF3)=0.1 was analyzed using secondary ion mass spectrometry. Scanning electron microscopy was used to examine etched profiles of SBT thin films. The wall angle of a SBT film etched using CHF3/(Ar+CHF3)=0.1 was approximately 85°.
Growth of SiC thin films on graphite for oxidation-protective coating
Authors: Boo J.-H. , Kim M. C. , Lee S.-B. , Park S.-J. , Han J.-G.
Published: July 2002

We have deposited thick SiC thin films on graphite substrates in the temperature range of 700–850 °C using single-molecular precursors by both thermal metal–organic chemical-vapor deposition (MOCVD) and plasma-enhanced MOCVD (PEMOCVD) methods for oxidation-protection wear and tribological coating. Hexamethyldisilane (HMDS), (CH3)3Si–Si(CH3)3, was used as a single-source precursor, and hydrogen and Ar were used as a bubbler and carrier gas. A highly oriented polyerystalline cubic SiC layer in the [111] direction was successfully deposited on graphite at temperatures as low as 800 °C with HMDS by PEMOCVD. For thermal MOCVD, on the other hand, only amorphous SiC layers were obtained at 850 °C. From this study, we confirmed that PEMOCVD was a highly effective process in improving the characteristics of the SiC layers compared to those grown by thermal MOCVD. The mechanical and oxidation-resistant properties have been assessed. The optimum SiC film was obtained at 850 °C and rf power of 200 W. The maximum deposition rate and microhardness are 2 μm/h and 4336 kg/mm2 Hv, respectively. The hardness was strongly influenced by the composition ratio of the SiC protective layers.
Etching of organic low dielectric constant material SiLK™ on the Lam Research Corporation 4520XLE™
Authors: Janowiak C. , Ellingboe S. , Morey I.
Published: July 2002

Various processes were investigated to etch the low κ dielectric material SiLK™. Because SiLK is a polymeric material, the two main process options are either an oxidizing or a reducing etch gas mixture which uses either oxygen or hydrogen as the main etchant gas, respectively. Hydrogen-based etch processes were found to have a large process window but slow etch rates and minimal profile control. When oxygen was used as the primary etch gas, a hydrocarbon was added for sidewall passivation. These oxygen-based processes demonstrated higher etch rates, and the addition of ethylene provided more control of the etch profile. The oxygen to ethylene flow ratio was found to be the dominant factor controlling the etch profile. Reduced hardmask faceting was achieved for both the hydrogen-based and oxygen-based processes by running with low rf power. Significant changes in etch rate, profile angle, and hardmask faceting were observed as the photoresist was cleared from the hardmask during the etch. These changes are caused by the changing etch chemistry as a result of the dramatic reduction in the area of organic film exposed to the plasma. Finally, the transfer of the final process to another organic film, FLARE™ was demonstrated.
The dependence of Al Schottky barrier height on surface conditions of GaAs and AlAs grown by molecular beam epitaxy
Authors: Wang W. I.
Published: July 2002

A systematic study of the Al Schottky barrier height on clean GaAs(100) and AlAs(100) as a function of initial arsenic surface coverage has been performed. Two new surface phases on AlAs(100) have been observed. Al Schottky barrier height showed a steady decrease with increasing arsenic coverage on GaAs, and showed steady increase with increasing arsenic coverage on AlAs. The results are compared with current models of Schottky barrier formation.
High resolution measurement of the step distribution at the Si/SiO2 interface
Authors: Henzler M. , Marienhoff P.
Published: July 2002

With a recently developed high resolution LEED instrument spot profiles of the 00–beam of Si/SiO2 interfaces have been taken after the removal of the oxide. It is demonstrated, that beyond the half-width the full profile down to a hundredth of peak intensity gives valuable information. The distribution of terraces up to more than 50 nm contribute essentially to a sharp central spike, which is only visible with a high resolution system. Whereas with usual LEED optics only terraces up to about 20 nm are evaluated from spot profile, the present data for the first time allow an evaluation in an extended range of terrace widths besides step atom density. Model calculations show the influence of instrument response and of details of the terrace width distribution on the spot profile.
Chlorine surface interaction and laser-induced surface etching reactions
Authors: Sesselmann W. , Chuang T. J.
Published: July 2002

Surface reaction and radiation-enhanced desorption of product species are basic surface processes in laser-induced chemical etching of solids. These processes have been studied in Cl2-Si and a number of metal systems which depending on the reaction behavior are divided into three classes, namely, the spontaneous etching, the passive, and the diffusive reaction systems. Various gaseous and surface analyses including XPS, AES, time-resolved mass spectrometry, and quartz-crystal microbalance measurements are performed in conjunction with surface irradiation by UV and visible laser pulses. The surface chlorination reactions and the effects of laser irradiation, in particular, the nonthermal radiation effects are discussed.
Normal (unenhanced) Raman spectroscopy of molecules adsorbed on surfaces
Authors: Campion Alan
Published: July 2002

Design considerations for a surface Raman spectrometer are reviewed. The behavior of the electromagnetic field near a conducting surface dictates the excitation and observation conditions for surface Raman spectroscopy; multichannel detection results in sufficient sensitivity to detect submonolayer quantities of material adsorbed on single crystal metal and semiconductor surfaces. Several examples, which illustrate the versatility of the technique, are presented.
Simulation of resonant-tunneling heterostructure devices
Authors: Frensley William R.
Published: July 2002

The resonant-tunneling quantum-well diode is studied by numerical evaluation of the quantum-mechanical density matrix. This approach addresses such aspects of the tunneling problem as the effect of temperature, the transient response of a tunneling device, and the effects of dissipative interactions. The density matrix contains the spatial distribution of electrons and by calculating the time evolution of the density matrix the evolution of the electron density is observed. The density matrix is represented on a finite-difference basis in real space. Its time evolution is obtained by numerically integrating the quantum Liouville equation. To incorporate dissipative effects a simple relaxation term was added to Liouville equation. The boundary conditions were formulated so as to simulate the effects of Ohmic contacts. For the resonant-tunneling diode the simulations show a significant electron density in the quantum well, which builds up in a time on the order of 100 fs, when the structure is biased at resonance. For biases below the resonant value, the electron density in the well remains negligible.
Surface emitting laser diode with AlxGa1−xAs /GaAs multilayered heterostructure
Authors: Ogura Mutsuo , Yao Takafumi
Published: July 2002

We realize the first distributed feedback surface emitting laser diode with Al0.3Ga0.7As/GaAs multilayered heterostructure both by optical pumping and current injection. Sharp stimulated emission is observed at the selected wavelength determined by the optical cavity. Lateral p–n junction is formed by a selective Zn diffusion. The threshold current is 120 mA at 150 K with the active layer thickness of 6 μm and width of 3 μm. The temperature coefficient of the lasing wavelength is equal to a conventioal DFB laser diode. Anomalous mixing is found in the course of Zn diffusion and succeeding thermal treatment.
Dependence on ionicity of the (110) surface relaxations of zinc-blende semiconductors
Authors: Kasowski R. V. , Tsai M.-H. , Dow John D.
Published: July 2002

It is argued that the surface relaxation angle ω of zinc-blende (110) surfaces should depend on ionicity or on longitudinal effective charge Z approximately as ω=ω0−ω1 Z2e2/εaL, with ω1≂6°/eV.
Kinetic processes in atomic-layer epitaxy of GaAs and AlAs using a pulsed vapor-phase method
Authors: Ozeki M. , Mochizuki K. , Ohtsuka N. , Kodama K.
Published: July 2002

Atomic-layer epitaxy (ALE) has been developed for GaAs and AlAs using a pulsed vapor-phase method using metal-organic compounds and hydride. Growth rate has been investigated in detail as a function of various growth parameters. When arsine gas-pulse duration is increased, the growth rate decreases drastically once a film thickness [1 monolayer (ML) for GaAs(100), (110), and (111)B, 2 ML for AlAs(100) and (111)B, and 3 ML for AlAs(110)] has been reached. A model has been suggested to explain the result.
Soft x-ray projection lithography using an x-ray reduction camera
Authors: Hawryluk Andrew M. , Seppala Lynn G.
Published: July 2002

Soft x-ray projection lithography can now be realized with recent developments in x-ray optics. Using new x-ray optical components and spherical imaging optics, we have designed an x-ray reduction camera which is capable of projecting with soft x-ray radiation, a 5× demagnified image of a mask onto a resist coated wafer. The resolution of this design is ∼100 nm with a depth of focus of ±5.6 μm and a 0.5-cm-diam image field. We use x-ray reflecting masks (patterned x-ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free. Our design uses a laser produced plasma for the x-ray source. Better resolution and/or larger areas are possible with improvements in optic figures and source characteristics.
Novel Monte Carlo simulation of space-charge-induced energy broadening in laser irradiated cathodes
Authors: Allee D. R. , Pehoushek J. D. , Pease R. F. W.
Published: July 2002

Laser irradiation is one alternative to the use of a Wehnelt for confining the area of emission of an electron gun. The absence of the retarding Wehnelt electrode allows the direct acceleration of the electrons to the anode, reducing space-charge-induced energy broadening in several ways. Fewer crossovers are necessary to achieve a given spot size, and the space-charge density and total current near the source are reduced. A novel Monte Carlo algorithm has been developed to simulate for the first time the space-charge interactions in this type of gun for thermionic and photonic emission from various source materials. A novel data structure incorporating a linear ordering of the particles in each of three dimensions allows an efficient determination of particle neighbors. The central processing unit time is proportional to n1.4 instead of n2, where n is the number of particles. This provides a savings in the cost of a simulation or allows more particles to be simulated. The simulation results indicate that, for source current densities up to 20 A/cm2, energy broadening can be practically eliminated by reducing the emission spot size. The predicted energy broadening is significantly less than that reported by Pfeiffer for traditional thermionic electron guns with Wehnelt electrodes. The advantages of a short electron beam lithography column for high-resolution mask fabrication that incorporates a laser irradiated thermionic source are discussed.
Effect of ammonia plasma treatment on plasma deposited silicon nitride films/silicon interface characteristics
Authors: Arai Hitoshi , Tanaka Keiji , Kohda Shigeto
Published: July 2002

The properties of silicon nitride film obtained by plasma-assisted chemical vapor deposition (plasma CVD) are studied along with the effect of NH3 plasma treatment on plasma CVD silicon nitride/silicon interface characteristics. With this NH3 plasma treatment of the silicon surface before silicon nitride film deposition, the interface state densities of the silicon nitride/silicon interface are reduced to about 1010 cm−2  eV−1 and the hysteresis voltage of the capacitance–voltage (C–V) curve is reduced to 0.1 V. These improvements are most pronounced when there is a large H concentration in the silicon nitride film. However, no effect is observed when N2 or H2 plasma was used instead of NH3 plasma. Auger electron spectroscopy analysis of the silicon surface after NH3 plasma treatment shows that nitrogen is incorporated in the near surface region of the silicon substrate. This implies that nitridation of the silicon surface occurs due to NH3 plasma treatment and the interface characteristics are improved because the silicon nitride/silicon interface is made inside the silicon substrate due to this nitridation.
Sub-20-nm-wide line fabrication in poly(methylmethacrylate) using a Ga+ microprobe
Authors: Kubena R. L. , Stratton F. P. , Ward J. W. , Atkinson G. M. , Joyce R. J.
Published: July 2002

A 50 keV focused Ga+ microprobe has been formed with a full width at half-maximum of 15 nm and a 800 nm diameter at 10−5 below the peak current density. This probe was used to expose patterns in both positive and negative resist films. Features as small as 12 nm on sub-100-nm periods were delineated in thin poly(methylmethacrylate) (PMMA) resist on thick GaAs substrates. Although only about 25 ions irradiated each pixel, these features exhibited smooth edges. Using the ion beam exposed PMMA patterns as a mask, Al lines 50 nm wide on 85 nm periods were successfully fabricated using a lift-off procedure.
Simulation of electron beam exposure of submicron patterns
Authors: McMillan Jo A. , Johnson Sylvester , MacDonald Noel C.
Published: July 2002

Analytical and Monte Carlo electron beam radial exposure distributions (REDs) are compared for accuracy in predicting proximity effects in submicron lithographic patterns. A proximity effect simulation tool (PRESTO) has been developed to convolve the desired pattern with the RED obtained from a companion Monte Carlo program for the simulation of electron energy loss (SEEL) or an empirical RED which is an analytical fit to experimental results. Together, SEEL and PRESTO are shown to simulate the electron beam exposure of submicron size patterns using a focused Gaussian electron beam system. PRESTO generates the electron distribution for the pattern by simulating the exposure of the resist for each pixel. Once the energy distribution has been determined equienergy density contours for the exposure of a given shape can be plotted. The ability of PRESTO and SEEL to accurately simulate the exposure of patterns with 0.25 μm design rules is demonstrated. Comparisons are made of the simulation results obtained when double Gaussian, triple Gaussian and SEEL approximations are used for the REDs. We also show that these two programs can be used to evaluate the sensitivity of the radial exposure distribution and proximity effects for multilevel substrates, for varying topography, and for different exposure conditions.
Multilayer reflectors by molecular-beam epitaxy for resonance enhanced absorption in thin high-speed detectors
Authors: Chin Albert , Chang T. Y.
Published: July 2002

The spectral responses of resonantly enhanced photodiodes are analyzed theoretically and verified experimentally. The quantum efficiency of a Schottky photodiode with a 50-nm AlInAs Schottky contact layer and a 475-nm GaInAs absorbing layer can be enhanced 1.5-fold by using a 16-layer quarter wave stack (QWS) of alternating Al0.17Ga0.30In0.53As and Al0.48In0.52As. The enhancement can be further improved if more periods of QWS are incorporated, or the substrate is selectively removed. The resonance width is approximately 60 nm. This type of structure should be very valuable for very small size ultrafast photodiodes and for optoelectronic integration.