bluuebunny/crossref_metadata_2025 huggingface dataset:
Ellipsometry and x-ray photoelectron spectroscopy study of SnO2 reduction at the interface with sputtered a-Si:H
Authors: Yang Y. H. , Feng G. F. , Katiyar M. , Maley N. , Abelson J. R.
Published: July 2002

Very thin layers of hydrogenated and unhydrogenated amorphous silicon have been deposited on tin oxide substrates under different temperatures and H2 partial pressures by dc magnetron sputtering. The deposition processes are monitored by real time in situ ellipsometry. We observe the reduction reaction of the SnO2 exposed to a H- or Si-containing deposition flux in the early stages of film growth by real time ellipsometry. The chemical states of Sn at the a-Si:H (or a-Si)/SnO2 interface have been studied by x-ray photoelectron spectroscopy (XPS). XPS confirms that a Si flux alone can reduce SnO2 to elemental Sn, and that this reaction is temperature dependent. However, the contribution of Si is secondary to that of H atoms in the reduction reaction.
Material properties of a ZrNx film on silicon prepared by ion-assisted deposition method
Authors: Horita Susumu , Tujikawa Tetuya , Akahori Hiroshi , Kobayashi Mituru , Hata Tomonobu
Published: July 2002

The resistivity, chemical composition, and crystalline quality of ZrNx films deposited on Si(100) substrates by an ion-assisted deposition (IAD) method were investigated as a function of deposition parameters. By this method, metallic Zr is deposited by electron-beam evaporation while simultaneously bombarding the film with nitrogen ions having energies of 400–700 eV. It was found that the crystalline quality of the film was improved by increasing the substrate temperature Ts to 820 °C and decreasing the ion energy. When Ts was 850 °C, zirconium silicide was formed easily near the interface between the film and the Si substrate. At Ts=820 °C, the chemical composition ratio of the film was hardly influenced by the arrival rate ratio N/Zr, Ra, in the range of 1.5 to 3.0 and the deposited ZrN film was almost stoichiometric. However, when Ra was more than 1.9, the film quality was degraded by radiation damage due to excess nitrogen ions in the growing film. When Ra was less than 1.5, the surface of the film was roughened and looked cloudy, probably because the nonstoichiometric film reacted with the Si substrate. Therefore, the optimum arrival rate ratio was found to be in the range of 1.5–1.9. With optimum fabrication conditions, a (100) oriented and almost stoichiometric ZrN film could be obtained with resistivity as low as 17.8 μΩ cm.
Friction properties of aluminium-based composites containing cluster diamond
Authors: Ouyang Q. , Okada K.
Published: July 2002

The friction properties of aluminium-based composites containing a cluster diamond both in air and in vacuum were studied. In both cases, the coefficients of friction tend to decrease with the increase of the cluster diamond content in the samples. The coefficient of friction in air is lower than that in vacuum. After friction tests, atomic force microscopy and lateral force microscopy were used simultaneously to observe the surface friction process of the sample. A unique phenomenon is found: at some microconvex areas, the coefficients of friction are significantly lower. Scanning electron microscopic studies reveal that wear debris are formed during friction test with samples containing a cluster diamond. One of the significant factors for the reduction of friction could be the rolling effect caused by cluster diamond ultrafine particles.
Infrared study of CO on NiO(100)
Authors: Vesecky Scott M. , Xu Xueping , Goodman D. Wayne
Published: July 2002

The nature of the interaction of CO with NiO(100) thin films (∼20–50 Å) grown on a Mo(100) substrate has been investigated with infrared reflection absorption spectroscopy. Isosteric heats of adsorption were measured for CO in a pressure range of 1×10−8 to 1 Torr and over a temperature range of 93–280 K. The average heat of adsorption was found to be approximately 10.4 kcal/mol, with the heat of adsorption decreasing slightly with increasing CO coverage. This value for the heat of adsorption agrees very well with that measured for CO on MgO(100). The CO stretching frequency was found to decrease with an increase in the CO coverage. At constant coverage, the CO stretching frequency as well as the full width at half-maximum were found to increase with increasing temperature. These results are discussed in the context of current theories of bonding between CO and oxide surfaces.
Ferromagnetic resonance in Ni films biased dc sputter deposited on MgO(001)
Authors: Maruyama Hiroko , Qiu Hong , Nakai Hisashi , Hashimoto Mituru
Published: July 2002

Ferromagnetic resonance measurement at X band is carried out at room temperature to investigate the mechanical and magnetic properties of Ni films 180 nm thick deposited on MgO(001) substrates at 280 °C by biased direct current plasma sputtering at 2.5 kV in Ar gas. A negative bias voltage Vs of 0, −80, and −140 V is applied to the substrate during the deposition. The homogeneous intrinsic stress σi induced in the films is compressive (σi<0) at any Vs and its value is independent of Vs. The magnetic anisotropies due to the anisotropic planar stress σu induced during the film formation and due to the magnetocrystalline anisotropy K1f of the epitaxial Ni crystal are mutually superimposed in the film plane. σu is very weak, i.e., ‖σu‖≪‖σi‖, to reduce nearly to zero as Vs reaches −140 V. Although the magnitude of K1f gradually increases as Vs increases, it is about 10−1 of that of K1 for bulk Ni. The g factor is evaluated at 2.11 independently of Vs.
Heteroepitaxy of lattice-matched compound semiconductors on silicon
Authors: Bachmann Klaus J. , Dietz Nikolaus , Miller Amy E. , Venables David , Kelliher James T.
Published: July 2002

The heteroepitaxial overgrowth of silicon by nearly lattice-matched compound semiconductors is reviewed in the context of the separation of the chemical problems associated with the initial sealing of the silicon surface by a contiguous epitaxial compound film from the problems associated with the generation of strain during heteroepitaxial growth. Of the mixed compound systems available dilute solid solutions of composition AlxGa1−xNyP1−y and ZnSySe1−y as well as ZnSixGe1−xP are suitable candidates for the exactly lattice-matched epitaxial overgrowth of silicon. Real-time process monitoring by nonintrusive methods is important for gaining an understanding of the epitaxial overgrowth mechanism and for controlling the film properties. A new method, p-polarized reflectance spectroscopy is introduced that provides detailed information about the growth rate per cycle, the bulk optical properties of the film and its topography. Submonolayer resolution is accomplished for thousands of Å of film growth by pulsed chemical beam epitaxy. While the cubic materials considered here generally afford easier control of the electrical and optical properties, the noncubic materials have advantages in the sealing of the silicon surface because of their anisotropic growth and the formation of metastable solid solutions that may permit the graded growth of compound films under exactly lattice-matched conditions. Therefore, no clear-cut preference in the materials selection for nearly lattice-matched overgrowth of silicon by compound semiconductors can be identified at this time.
Laser-induced dissociation of molecules during measurements of hydrogen atoms in processing plasmas using two-photon laser-induced fluorescence
Authors: Miyazaki K. , Kajiwara T. , Uchino K. , Muraoka K. , Okada T. , Maeda M.
Published: July 2002

During measurements of hydrogen atoms in discharge plasmas in silane and methane, using a two-photon excitation from the ground state to the n=3 states at 205 nm, the laser-induced dissociation of molecules was found to be the dominant process of hydrogen production, rather than that due to the discharge. Although the laser intensity was kept below the threshold of atomic hydrogen production from parent gases, some reaction products were at high density which were more easily dissociated by the laser irradiation. Quantitative discussions were made of the laser-induced dissociation, and the estimates of reaction product densities were thus made.
Electron field emission from amorphous tetrahedrally bonded carbon films
Authors: Talin A. A. , Felter T. E. , Friedmann T. A. , Sullivan J. P. , Siegal M. P.
Published: July 2002

Electron field emission from two amorphous, tetrahedrally bonded diamondlike carbon films, one with (a-tC:N), and a second without nitrogen doping (a-tC), prepared by pulsed laser deposition has been investigated using a scanning probe apparatus with micrometer spatial resolution. Electric fields of 100 V/μm (180 V/μm) were required to initiate emission from our a-tC:N (a-tC) films; however, once emission was established at a particular location, electrons could be drawn at average fields as low as 10 V/μm (60 V/μm) from the same region. The initiation of emission was concomitant with electrical discharges which were observed by video techniques. These discharges left craters with micrometer dimensions on the surfaces of otherwise smooth films.
Plasma etching with self-assembled monolayer masks for nanostructure fabrication
Authors: Lercel M. J. , Craighead H. G. , Parikh A. N. , Seshadri K. , Allara D. L.
Published: July 2002

Self-assembled monolayers of octadecylthiol on GaAs and octadecylsiloxanes on titanium, aluminum, and silicon have been used as electron beam resists for plasma etching into the substrates. An electron cyclotron resonance source was used to excite a low-pressure, high-density plasma with low ion energy to achieve high selectivity with the thin masking layers. Patterning of monolayers on GaAs usually produced a negative tone, but etching of the metal surfaces resulted in positive tone patterning. The maximum etch depth into the GaAs was ∼100 nm using the negative tone process. Lines have been etched into Ti with linewidths down to ∼20 nm. The negative tone process can be explained by the cross linking of the monolayer under high-dose electron beam exposure; however, the positive tone process must rely on contrast either from different etching characteristics of the oxides or different structural arrangements of the different SAMs.
Magnetic dichroism effect of binary alloys using a circularly polarized x ray
Authors: Wu S. Z. , Schumann F. O. , Willis R. F. , Goodman K. W. , Tobin J. G. , Carr R.
Published: July 2002

We have studied the magnetic properties of CoNi binary alloy films with various atomic compositions using the soft x-ray magnetic circular dichroism technique. The alloy films were deposited on a single Cu(100) crystal in situ using our well established epitaxial growth technique to achieve a layer-by-layer growth and a metastable face-centered-cubic structure, with all the films exhibiting an in-plane magnetic anisotropy. The high density, circularly polarized x-ray beam was supplied by the elliptically polarizing undulator at the Stanford Synchrotron Radiation Laboratory. Utilizing the element-specific ability and nanostructure magnetization sensitivity of this technique, we were able to perform the absorption measurements at L2 and L3 edges of Co and Ni atoms and we observed large dichroism signals. The extraction of spin moment and orbital moment for varying elemental stoichiometry using magneo-optical sum rules is discussed.
Analysis of the etching of silicon in an inductively coupled chlorine plasma using laser thermal desorption
Authors: Choe Jae Y. , Herman Irving P. , Donnelly Vincent M.
Published: July 2002

The etching of silicon by a chlorine inductively coupled plasma (ICP) was studied using laser desorption laser-induced fluorescence (LD-LIF) analysis to determine the surface coverage of chlorine during steady-state etching. Laser interferometry was used to measure etch rates, and optical emission actinometry and Langmuir probe analysis were used to characterize the plasma. The ICP operated in the dim mode for radio frequency (rf) powers ≲ 350 W and in the bright mode for higher powers. Under typical operating conditions in the ICP bright mode, the ion density was about 4× 1011/cm3, the electron temperature was 2.8 eV, and about 90% of the Cl2 was dissociated. The chlorine surface coverage in the dim and bright modes was ∼2.0× that with chlorine flow and the plasma off, and increased slowly with power. This coverage ratio monotonically increased from ∼1.6× to 2.5× that with the plasma off as the ion energy was increased from 16 to 116 eV by increasing the rf substrate bias voltage during bright mode operation. Since roughly equivalent adlayer chlorine contents were measured by LD-LIF under high ion current/fast etch conditions (ICP bright mode), and low ion current/slow etch conditions [ICP dim mode and reactive ion etching mode (substrate stage powered and no ICP power)], both the adlayer chlorine content and the etch rate seem be controlled by the ion current to the wafer.
Analysis of native oxide growth process on an atomically flattened and hydrogen terminated Si (111) surface in pure water using Fourier transformed infrared reflection absorption spectroscopy
Authors: Fujimura Shuzo , Ishikawa Kenji , Ogawa Hiroki
Published: July 2002

Early stages of native oxide growth on an atomically flat and hydrogen terminated Si (111) surface in pure water was discussed on the basis of Fourier transform infrared reflection absorption spectroscopy (FT-IR-RAS) spectra of the oxide. To explain the RAS spectra change with oxidation time, we calculated the RAS spectra theoretically using a model that we named a precipitate model. In the model, we assumed that the shape of oxides formed at the surface was ellipsoid with axes of a1, a2, and a3. Oblateness of the ellipsoid was represented by a depolarization factor (L1, L2, and L3) relating to the reciprocal numbers of each axis of the ellipsoid; L1+L2+L3=1 and L1:L2:L3=1/a1:1/a2:1/a3. Thus, if L1=1, a2 and a3 are infinite, then the ellipsoid is a layer stretching toward direction of a2 and a3, and when L1=L2=L3=1/3, the oxide shape is spherical. The dielectric constant of a surface layer containing the ellipsoidal oxides was calculated using the effective media approximation. Calculated spectra were well fitted to the measured spectra. However, the depolarization factor (L1) calculated from the IR-RAS spectra did not become 1 even after 1×105 minutes oxidation, though the native oxide after 100 220 min oxidation contained more Si–O bonds than that formed by a sulfuric acid and hydrogen peroxide (SPM) solution (H2SO4/H2O2). FT-IR-RAS spectra of thermally grown oxide and chemical oxide formed in the SPM have similar shape to the calculated spectra at L1=1. Thus native oxide grew insularly and not through a layer-by-layer process in the early stages of oxidation.
Effects of nitrogen ion implantation on the thermal stability of tungsten thin films
Authors: Kim Yong Tae , Kwon Chul Soon , Kim Dong Joon , Park Jong-Wan , Lee Chang Woo
Published: July 2002

We implanted 6×1016–3×1017 nitrogen ions/cm2 into 100 nm thick tungsten thin films with acceleration energies of 20–60 KeV. As a result, the thermal stability of N+-implanted W thin films is greatly improved from 700 to 900 °C because polycrystalline W thin films change into nanostructured films after N+ implantation. The W thin film implanted at 40 KeV and 3×1017 ions/cm2 effectively prevents Cu diffusion after an annealing at 800 °C for 30 min. When the acceleration energy and dosage are higher or lower than this optimum condition, thermal stability of the N+-implanted W film is degraded due to surface damage of Si substrate and partially nanostructured W thin film.
Integration of fluorinated amorphous carbon as low-dielectric constant insulator: Effects of heating and deposition of tantalum nitride
Authors: Chang J. P. , Krautter H. W. , Zhu W. , Opila R. L. , Pai C. S.
Published: July 2002

We investigated the effects of heating and deposition of tantalum nitride on fluorinated amorphous carbon (a-C:F) thin films, deposited by a cosputtering process using polytetrafluoroethylene and graphite targets. Carbon is observed by x-ray photoelectron spectroscopy (XPS) in four distinct chemical states, C–C, C–F, C–F2, C–F3, and the relative intensity of C–Fx to C–C increases with increasing fluorine content and decreasing deposition temperature. Heat treatment of this material in vacuum up to 450 °C results in reduction of the intensities of C–Fx relative to that of C–C. The predominant desorbing masses detected by a mass spectrometer were consistent with CF3, CF, C3F5, CF2, COF, COF2, and Ar. The temperature at which desorbing CFx species are detected increases with decreasing fluorine concentration and increasing deposition temperature. This improved thermal stability is attributed to the decreasing amount of volatile, small molecular weight CFx species and more C–C crosslinking in the less fluorinated film. To integrate with copper metallization, the interface between a-C:F and tantalum nitride was studied by depositing tantalum nitride on a a-C:F films and monitoring the interfacial chemical reactions in situ using XPS. Substantial defluorination was observed upon deposition of tantalum nitride. This leads to the formation of tantalum fluoride, whose relatively high vapor pressure and susceptibility to hydrolysis could lead to delamination.
Comparative study ofa-C:H films for inertial confinement fusion prepared with various hydrocarbon precursors by radio frequency-plasma enhanced chemical vapor deposition
Authors: Theobald M. , Durand J. , Baclet P. , Legaie O.
Published: July 2002

Using a radio frequency remote plasma deposition process, hydrogenated amorphous carbon thin films were prepared from a variety of hydrocarbon precursors. Monomers were aliphatic chains (butane, trans-2-butene), rings (ethylcyclohexane), or aromatics (styrene, ethylbenzene), mixed with hydrogen. These films were elaborated in order to be used in inertial confinement fusion experiments with the future megajoule laser. Thickness and roughness were studied and optimized in relation of plasma parameters. Structural properties were analyzed by Fourier transform infrared, Raman diffusion, and others.
Characteristics of an advanced electrohydrodynamic ion source with additional mode of surface ionization
Authors: Okutani T. , Fukuda M. , Noda T. , Tamura H. , Watanabe H. , Shepherd C.
Published: July 2002

An electrohydrodynamic ion source composed of a reservoir with a sleeve and an emitter tip heated by electron bombardment was constructed. This ion source can produce a variety of ion species from materials including those with a high melting point or a high vapor pressure, owing to the heating method and the reservoir with the sleeve. This ion source was operated with metals such as Ga, In, Au, and Zn, and has successfully produced an intense and stable ion beam from each metal. This gun also functions in the mode of surface ionization from a point emitter when a cesium compound such as CsCl is used as a source material.
Thermodynamic aspects of molecular beam epitaxy: High temperature growth in the GaAs/Ga1−xAlxAs system
Authors: Heckingbottom R.
Published: July 2002

The thermodynamic framework is established for growth of GaAs and Ga1−xAlxAs by molecular beam epitaxy MBE, for the region where loss of gallium is significant. It is shown that the temperature dependence of gallium loss from GaAs is a function of the experimental beam pressures and not a basic property of the system. At a given temperature, gallium loss (and hence the growth rate for GaAs) is a function of arsenic pressure and in the alloys it is also a linear function of Al content. As2 is the equilibrium species used in the calculations. Comparison with experimental data is therefore limited, but it is clear that As4 dissociation is kinetically hindered when used in practice. Use of a closely controlled pressure of As2 is indicated to achieve good control of both layer thickness and alloy composition. The approach is likely to be more important in other alloy systems where lattice matching to the substrate is more critical.
Systematic design of an electrostatic optical system for ion beam lithography
Authors: Paik H. , Lewis G. N. , Kirkland E. J. , Siegel B. M.
Published: July 2002

An electrostatic optical system has been designed to produce a high resolution (10–100 nm) ion beam probe based on a very high brightness H+2 field ionization source developed in our laboratory.1 The system described here includes two electrostatic lenses, postlens octupole and quadrupole deflectors, beam blanker, stigmation and alignment deflectors. Since the resolution of this system is limited by the aberrations of the optics, a systematic approach is employed to minimize these aberrations. First, individual lenses were designed by many trial evaluations using appropriately constructed figures of merit. The scales and magnifications of both lenses then were determined simultaneously to minimize the axial aberrations of the combined lens. The deflectors were also optimized using analytical expressions of deflection aberration coefficients to achieve small deflection aberrations. The beam blanker at the beam crossover point can also give reasonably high blanking rates (10–300 MHz) for H+2 ions with small spurious deflection. This optical system is to be used in an ion beam lithography machine currently under construction. In this system, a 2 mrad beam acceptance half-angle will produce a probe size of 10 nm with a current density of 100 A/cm2 at 50 keV energy when used with the H+2 field ion source which produces a typical angular current density of 10 μA/sr.
Defects in x-ray masks: Detection and printability
Authors: Kluwe A. , Müller K.-H. , Betz H. , Oertel H.
Published: July 2002

X-ray mask defects occur mainly as particles on the mask and as random defects in the absorber. However, some of these mask defects do not generate disturbing resist defects. The theoretical investigation of the transfer mechanism shows two essential results. The x-rays penetrate completely organic particles of thicknesses up to 4 μ. The Fresnel diffraction limits the transfer of absorber defects at 0.17 μ size with a 50 μ proximity gap. Good agreement is found between the measured and the calculated size distribution of absorber pinspots, confirming the considerations concerning the defect printability. Only disturbing defects are detectable by inspecting the lithographical resist copy of the mask. The inspection itself can be performed by optical means. It has been shown by experiment with a specially designed test pattern that 0.2 μ defects in 0.5 μ structures can be detected reliably by using a white-light microscope.
Unidirectional deposition of aluminum using nozzle jet beam technique
Authors: Ramayarananan R. , Polasko K. , Skelly D. , Wong J. , Mei S.-N. , Lu T.-M.
Published: July 2002

We have observed completely nonconformal Al step coverage using nozzle jet expansion deposition technique. In this technique, pure Al was evaporated in a graphite crucible at a temperature up to 1600 °C. The vapor was then ejected through a small nozzle into a vacuum region of 10−6 Torr. The ejected beam was subsequently ionized by electron bombardment and a potential up to several kilovolts was applied to the beam. The SEM micrographs showed no evidence of sidewall coating for vias (1 μm feature size) with almost vertical steps. Liftoff structures were formed using a combination of contrast enhancing material (CEM) and AZ1470. No Al was observed on the photoresist sidewall all across the 3 in. wafer; after liftoff, 0.4 μm clean isolated openings were observed in the Al layer. Metallized contacts 0.3 μm apart and 1 μm in width devoid of ‘‘flags’’ were also obtained. Our computer simulation study indicated that the angular extent of the jet beam source is smaller than a typical electron-beam evaporation source.
An alignment system for synchrotron radiation x-ray lithography
Authors: Itoh Junji , Kanayama Toshihiko , Atoda Nobufumi , Hoh Koichiro
Published: July 2002

We have developed an alignment exposure system for synchrotron radiation (SR) x-ray lithography. The present system consists of vertical mask and wafer stages, optics for mask-to-wafer displacement detection, a feedback control system, and an aluminum chamber containing them. The chamber is filled with He gas in atmospheric pressure and separated by a 25-μm-thick Be window from the SR beam line in ultrahigh vacuum. The alignment method is based on an optical-heterodyne displacement detection using three diffraction gratings. With 1.0-μm-period gratings and a He–Ne transverse-mode Zeeman laser (wavelength=0.6328 μm), alignment precision better than 0.01 μm was achieved. Features and performance of the system are described.
Electron-beam inspection technology for x-ray masks
Authors: Takeuchi S. , Moriizumi K. , Saitoh K. , Yoshioka N. , Kato T.
Published: July 2002

An electron-beam inspection system with a capability of detecting quarter-micron defects has been developed and is applied to the inspection of the x-ray mask itself. The accuracy of this system is measured and discussed. The distortion of the electron-beam deflection is 0.08 μm (root-mean-square error) within 70×90 μm area in the scan field of 100 μm2. A sample x-ray mask has Au absorption patterns with the thickness of 0.8 μm on a 2.0-μm-thick SiN membrane. An accelerating voltage of 3 kV was found to give a stable signal with a minimum of charging effects. The inspection is performed by means of die-to-die comparison scheme. Detection of 0.3 μm defects was demonstrated, indicating the potential of electron-beam technology for x-ray mask inspection.
Plasma focus x-ray source for lithography
Authors: Kato Yasuo , Ochiai Isao , Watanabe Yoshio , Murayama Seiichi
Published: July 2002

A bright and reliable x-ray source for lithography has been developed using plasma focus. Discharge with constant pressure gas, one of the features of plasma focus, makes the x-ray source system simple and lengthens lifetime. A fine ceramic insulator made of alumina in place of a conventional Pyrex glass insulator improves system reliability. The system operates for more than 105 discharges without maintenance. The lifetime of the system is ten times longer than that of a conventional plasma focus device. The resolution of a pattern printed by multishot exposure depends not only on the diameter of pinched plasma but also on the variation of source position. A new spherical electrode surrounding the plasma-focusing space is added to stabilize the location of the spot on the axis by eddy currents which exert the Lorentz force on the plasma. The spot position deviation has become negligibly small as compared with the pinched plasma diameter. The x-ray source size for neon is 1 mm in diameter and 10 mm in length. Consequently, 0.4-μm fine pattern has been printed with this source. Neon radiates intense x rays in opposite voltage polarity to that of a conventional plasma focus. Polarity inversion enables a very thin beryllium window to be located on the axis with the assistance of magnetic deflector and plasma stop. An x-ray intensity of 5 mJ/cm2/shot 25 cm from the source with an irradiance of 10 mW/cm2 at the 2-Hz repetition rate has been obtained. The plasma focus is a promising x-ray source for lithography from the viewpoint of intensity, resolution, and lifetime.
Characteristics of optical components for soft x-ray microscopy and x-ray holography using an undulator radiation optical system
Authors: Kakuchi M. , Yoshihara H. , Tamamura T. , Maezawa H. , Kagoshima Y. , Ando M.
Published: July 2002

X-ray optical components, including Fresnel zone plates and transmission gratings, have been fabricated using finely focused electron beam lithography and Ta-on-SiN x-ray mask fabrication technology. The optical components for x-ray microscopy and x-ray holography were evaluated in an undulator radiation optical system.
Detection of dry etching product species with i
n s
i
t
u Fourier transform infrared spectroscopy
Authors: Cleland T. A. , Hess D. W.
Published: July 2002

I n situ Fourier transform infrared (FTIR) spectroscopy has been utilized to detect gas-phase product species resulting from the dry etching of aluminum and heavily doped n-type polycrystalline silicon (n+ poly-Si) in Cl2 . The products of aluminum etching in Cl2 were investigated in the presence and absence of a plasma. With the plasma off, Al2 Cl6 was the only infrared-active etch product detected at both low (50 °C) and high (>120 °C) sample temperatures. With the discharge on, the spectrum was more complex, indicating partial fragmentation of the dimer etch product in the plasma forming AlCl3 and, perhaps, AlCl. Silicon tetrachloride was the only infrared-absorbing product detected during the Cl2 plasma etching of n+ poly-Si. Unsaturated silicon chlorides (SiClx , x=1–3) were not present at detectable levels. These results are compared with those of ultrahigh vacuum (UHV) beam studies; in comparing UHV results with those obtained in a processing plasma, allowances must be made for the considerable difference in pressure, and therefore, in species’ fluxes in these two experimental environments. Unlike UHV studies, in situ FTIR measurements permit detection of etch products under typical processing conditions. When interpreting the results, however, the possibility that the products leaving the sample surface react further upon entering the plasma must be considered.
I
n s
i
t
u monitoring of selective etch of III–V compound semiconductor heterostructures
Authors: Hase I. , Taira K. , Kawai H. , Kaneko K. , Watanabe N.
Published: July 2002

The intensity of an AsCl2 signal obtained from a mass spectrometer showed the most remarkable increase during etching of GaAs with CCI2 F2 /He. It was shown that etching of GaAs/AlGaAs/GaAs and GaAs/InAs(3 monolayers)/GaAs could be precisely monitored with the signal intensity of AsCl2. Even etch-stop on the 3 monolayers InAs was directly observed, showing that precise control of the etching on a monolayer scale is possible. The technique can be used to selectively etch III–V compound semiconductor heterostructures which contain As.
Surface oxide effects on tunneling spectroscopy measured with a cryogenic scanning tunneling microscope
Authors: Wilkins R. , Amman M. , Ben-Jacob E. , Jaklevic R. C.
Published: July 2002

We describe a simple, versatile cryogenic (∼4.2 K) scanning tunneling microscope (CSTM) system optimized for spectroscopic studies. We find that spectroscopic data obtained at low temperatures are a function of the local surface characteristics of both the tip probe and sample. The superconducting density of states of lead is masked for tips with a heavy surface oxide (etched tungsten, stainless steel), yet easily observed with nonoxidized tips (gold, platinum). We show direct evidence that small metallic inclusions embedded in some oxides can produce single electron capacitive charging effects that dominate current-voltage characteristics.
Cs adsorption on the Si(100)2×1 surfaces
Authors: Hashizume Tomi , Sumita I. , Murata Y. , Hyodo S. , Sakurai T.
Published: July 2002

Cs adsorption on the Si(100)2×1 surface was investigated by the field ion-scanning tunneling microscope. It was found that Cs atoms occupy the off-centered valley bridge site at the initial coverage. The result, together with Li/K adsorption, can be understood well based on the strong interaction between the directional dangling bonds and active alkali metal atoms.
First x-ray stepper in IBM advanced lithography facility
Authors: Chen A. C. , Progler C. J. , Couch F. F. , Gunther T. A. , Fair R. H. , Cooper K. A.
Published: July 2002

This article describes the first commercially available state-of-the-art x-ray stepper, the Karl Suss XRS200/3, installed at the IBM Advanced Lithography Facility (ALF) at the end of 1991. ALF was built for the development of x-ray lithography for future generations of electronics devices [G. Lesoine, K. Kukkanen, and J. Leavey, Proc. SPIE 1263, 131 (1990)]. This stepper is attached to the first lithography beamline in ALF [J. Oberschmidt, R. Rippstein, R. Ruckel, A. Chen, J. Grandlund, and A. Palumbo, Proc. SPIE 1671, 324 (1992)]. The architecture of the tool and its two main improvements, (a) kinematic mask handling and (b) alignment system, will be discussed. Then the qualification test methodology and resulting data on key lithographic properties and throughput will be presented.
Nanolithography and its prospects as a manufacturing technology
Authors: Pease R. F. W.
Published: July 2002

The resolution requirements for nanolithography can be satisfied; both devices and small-scale circuits with features well below 100 nm have been fabricated. However other requirements such as adequate throughput (about 1 cm2/s) and a precision on feature edge placement of the order of 10 nm over 20 mm remain as serious challenges. Evolving technology may allow us to extend present-day technology such as deep ultraviolet lithography towards 100 nm feature sizes. But to go below that size radically new approaches will probably be needed. Examples include x-ray printing and some form of adaptive alignment in which relative distortion between mask and wafer is tracked.
Physical properties of the x-ray membrane materials
Authors: El Khakani M. A. , Chaker M.
Published: July 2002

Over the last ten years, the materials most used for x-ray membrane applications have been boron nitride, silicon, silicon nitride, silicon carbide, and diamond. This work presents a review of the macroscopic properties (roughness, biaxial Young’s modulus, optical transmission, fracture strength, and radiation hardness) of these materials. From an examination of the overall criteria, it can be concluded that silicon carbide and diamond continue to be the potential material candidates, even if few properties of diamond membranes have still to be improved. On the other hand, to optimize the physical properties of the membrane material, one has to understand the relationship between the macroscopic characteristics of the membrane and its microstructure. To this aim, we have studied two types of SiC membrane materials, namely, (i) plasma enhanced chemical vapor deposited a-SiC:H and (ii) laser ablation deposited a-SiC. The microstructural characterizations were carried out by means of x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and elastic recoil detection analysis techniques. We were thus able to (i) point out the role of C–H and Si–H hydrogenated bonds and Si–C bonds in the stress evolution, from compressive to tensile, (ii) demonstrate the linear dependence of the biaxial Young’s modulus upon the Si–C bond density and (iii) show the effect of dangling bonds on the optical transmission.
End-point detection using absorbed current, secondary electron, and secondary ion signals during milling of multilayer structures by focused ion beam
Authors: Davies S. T. , Khamsehpour B.
Published: July 2002

Many applications of focused ion beam micromachining of multilayer structures require the ability to accurately and unambiguously signal the transition from one layer to the next during milling. Instances where this may be critical include most microcircuit sectioning, reconfiguring, or repair operations. Here we compare absorbed specimen current with secondary electron and secondary ion signals and contrast their effectiveness in providing an indication of end-point. A number of thin film and multilayer samples have been investigated including thin films of Au and W (thickness 0.1 μm) deposited on Si, and Al (thickness 1.0 μm) deposited on thermally grown SiO2 (thickness 1.0 μm) on Si.
Quantum well GaAs/AlGaAs shallow-donor far-infrared photoconductors grown by molecular-beam epitaxy
Authors: Goodhue W. D. , Mueller E. R. , Larsen D. M. , Waldman J. , Chai Y. H. , Lai S. C. , Johnson G. D.
Published: July 2002

Photoconductors utilizing planar-doped silicon shallow donors in GaAs quantum wells formed with AlGaAs barriers have been fabricated and measured to have far-infrared (FIR) resonant-wavelength responsivities of ∼1 V W−1, with noise equivalent power values of ∼1×10−7 W Hz−1/2 at 4 K. The technology makes possible the use of FIR photoconductive magnetospectroscopy to measure the well position of sheet-doped silicon ions when incorporated at doping levels below 1×1016 cm−3. A comparison of the measured position of the ions with the intended position reveals a discrepancy that can be linked to the growth parameters used to produce the structure.
Theory of electron emission in high fields from atomically sharp emitters: Validity of the Fowler–Nordheim equation
Authors: Cutler P. H. , He Jun , Miskovsky N. M. , Sullivan T. E. , Weiss B.
Published: July 2002

Field emission from metallic emitters is generally described by the Fowler–Nordheim (FN) theory, which is based on a planar model of the tip with a classical image correction. Within the free-electron model and the Wentzel–Kramers–Brillouin approximation, the planar tip model leads to the well-known FN equation. The form of this equation predicts that a plot of log J/F2 versus 1/F, where J is the current density and F is the field, should be a straight line within the rather narrow region of field strengths of typical field emission experiments, 3–5 V/nm. This has been experimentally confirmed for conventional emitters, (i.e., electrolytically etched tips with radii ≳50 nm). However, field emitters fabricated with today’s new techniques are much sharper with radii of curvature of the order of nanometers or even the size of a single atom. Hence, the local geometry of the tip may become an important factor in the electron emission process. To investigate the effects of the shape and/or size on emission, the authors, in a recent series of papers, studied the dependence of the current–voltage characteristics on the local geometry of pointed emitters. It was found that the calculated results, plotted as log J/V2 versus 1/V, do not exhibit the straight line behavior predicted by the FN theory. In addition, there is a dramatic increase in the tunneling current for a fixed external bias, V, relative to the FN result for a planar model of the tip with the same bias voltage. Using the exact current integral additional results have been obtained exhibiting the effects of emitter curvature on electron emission in high fields and temperatures. These results continue to differ with the predictions of the β-modified FN equation. Therefore, the adequacy of a β factor in the conventional planar model FN equation to account for emitter curvature is examined. It is demonstrated that even the use of β-modified FN equation is not valid when applied to sharp emitters (rt≤10 nm) and will lead to spurious results when extracting information such as field values or emitting area from experimental FN curves. The explanation for this is discussed.
Vacuum emission of hot electrons from insulating and semiconducting films
Authors: Fitting H.-J.
Published: July 2002

Monte Carlo calculations and vacuum emission experiments have been shown to be powerful tools to investigate the high field electronic transport in metal–insulator–semiconductor and metal–semiconductor–insulator–semiconductor layer devices. Direct proof of hot-electron acceleration in semiconducting ZnS:Mn electroluminescent layers by means of vacuum emission and energy analysis in a spherical grid analyzer has been given as it was earlier for insulating a layer of SiO2. The energy distributions show strong peaking in the low-energy region around 3 eV as well as a high-energy tail exceeding even 20 eV. The enhanced emission of low-energy electrons with increasing field F indicates impact valence band excitation and direct avalanching in thin insulating and semiconducting films of sufficient thickness, than it has been predicted by strong acoustic phonon coupling and intervalley scattering.
Electrostatic removal of lithium fluoride from field-emitter tips at elevated temperatures
Authors: Panitz J. A.
Published: July 2002

The electrostatic removal of lithium fluoride (LiF) from field-emitter tips has been visualized at elevated temperatures in the transmission electron microscope (TEM). The apex of a field-emitter tip coated with ∼1500 Å of LiF provides a unique substrate for observing the removal process in the TEM in real time, and its curvature generates the required electrostatic field strength. The influence of the imaging electron beam on coating morphology has been visually assessed. A LiF coating can tolerate an electron dose of ∼2000 e−/Å2 at room temperature without visible damage (at a resolution of 5 Å). At elevated temperatures a higher dose can be tolerated before visible damage is observed. Removal of LiF coatings at room temperature occurs at 18 MV/cm. At 800 °C piecewise removal of the coating occurs at 9 MV/cm. Synergistic effects of the electron beam and the electrostatic field on the removal of the coating were not observed. The removal of LiF at any temperature is attributed to field-induced fatigue stress of the coating. Field desorption does not appear to play a significant role in the removal process. Implications for the production of ions from lithium fluoride thin films exposed to high electric fields (in laboratory experiments and in particle beam fusion accelerators such as PBFA II) are discussed.
Energy and angle distributions of ions striking the spherical target* in plasma source ion implantation
Authors: Wang Dezhen , Ma Tengcai , Deng Xinlu
Published: July 2002

Plasma source ion implantation is a process in which a target is immersed in a plasma and a series of large negative-voltage pulses are applied to it to extract ions from the plasma and implant them into the target. A Monte Carlo simulation model is developed to study the energy and angle distributions of ions striking the spherical target for high pressures of the neutral gas. The charge exchange and momentum transfer sections of ion-neutral that depend on the ion energy are taken into account precisely. The energy and angle distributions of A+r at the spherical target during the sheath edge evolution for the different pressures are investigated in detail.
Structure and wear behavior of nitrogen-implanted aluminum alloys*
Authors: Xia Lifang , Wang Rizhi , Ma Xinxin , Sun Yue
Published: July 2002

Aluminum alloys L2, LD2, LF12, LY12, and Al-4% Cu were implanted at room temperature with nitrogen ions at an energy of 80 keV and dose range of 1×1016–8.3×1017 N+ cm−2. The surface structure and chemical state of the implanted surface layer was investigated by x-ray photoelectron spectroscopy, transmission electron microscopy and transmission electron diffraction. Hardness measurements were made using a Vickers microhardness tester, and wear tests were carried out using a pin-on-disk wear testing machine. The results reveal that implanted nitrogen combines with aluminum to form AlN precipitates at room temperature and nitrogen implantation accelerates the aging process of Al-4% Cu alloys. The results also reveal that nitrogen implantation increases the hardness and sliding wear resistance of aluminum alloys. The improvements are mainly attributed to the formation of AlN precipitates.
Reduced effects of laser illumination on field emission due to the finite duration of quantum tunneling
Authors: Hagmann Mark J.
Published: July 2002

Laser illumination of a field emitting tip modulates the barrier by superimposing the electric field of light. Numerical simulations suggest that the dependence of tunneling current on the frequency of this modulation can serve as a basis for determining the duration of barrier traversal. Modulation increases the emitted current at low frequencies, but this effect disappears at modulation frequencies much greater than the reciprocal of the traversal time.
Proposal to study the thermopower produced by a vacuum-tunneling junction
Authors: Xu J. , Koslowski B. , Möller R. , Läuger K. , Dransfeld K. , Wilson I. H.
Published: July 2002

This paper elaborates on the idea of using the scanning tunneling microscope in new experiments on thermopower generation by a vacuum-tunneling junction. We first introduce the subject of thermopower generation in metals in the presence of a temperature gradient, emphasizing the physical origins of the thermopower. Then we discuss a thermopower produced in a homogeneous metallic chain containing a tunneling junction. This thermopower is sufficiently large to be measured. Finally, we describe an arrangement to measure the thermopower, especially with the help of the scanning tunneling potentiometry.
Accounting for the stiffnesses of the probe and sample in scanning probe microscopy*
Authors: Burnham N. A.
Published: July 2002

The elements of a scanning probe microscope are modeled as a set of springs in series. For a single-component sample, that is, a sample consisting of only one material, the detected feature height in variable force (force microscopy) or variable current (tunneling microscopy) modes is a function of the total system stiffness and the stiffness of the detector. For a multicomponent sample, the data in both variable force (current) and constant force (current) modes are modified by the set-point force, the detector stiffness, and the relative stiffnesses of the components of the sample. A detection scheme for reducing this compliance effect is proposed.
Cost estimates for commercial plasma source ion implantation
Authors: Rej Donald J. , Alexander Ralph B.
Published: July 2002

A semiempirical model for the cost of a commercial plasma source ion implantation (PSII) facility is presented. Amortized capital and operating expenses are estimated as functions of the surface area throughput T. The impact of secondary electron emission and batch processing time is considered. Treatment costs are found to decrease monotonically with T until they saturate at large T when capital equipment payback and space rental dominate the expense. A reasonably sized PSII treatment facility should be able to treat a surface area of 104 m2 per year at a cost of $0.01 per cm2.
Mechanisms of strained island formation in molecular-beam epitaxy of InAs on GaAs(100)
Authors: Chen P. , Xie Q. , Madhukar A. , Chen Li , Konkar A.
Published: July 2002

Results of a systematic examination of InAs island formation on GaAs(100) as a function of deposition conditions and thickness are presented. A non-Arrhenius dependence of the island density on substrate temperature and a decrease in the island density with increasing As4 pressure at lower substrate temperatures is observed, indicating that currently popular frameworks of compound semiconductor molecular-beam epitaxical growth and island formation mechanism(s) need to be enlarged. Plan-view transmission electron microscopy (TEM) and use of the behavior of Moiré fringes provides the island size distribution and demarcation between coherent and incoherent islands. Photoluminescence (PL) behavior is shown to vary significantly with the growth conditions and to correlate to the attendant structural nature revealed by TEM. The issue of lateral quantum confinement (i.e., three-dimensional islands as quantum boxes) is shown to be subtle and complex, calling for caution in interpreting PL behavior. The results suggest that a regular array of ‘‘quantum boxes’’ made of coherently strained volumes of uniform size may be achieved via growth on prepatterned mesas.