bluuebunny/crossref_metadata_2025 huggingface dataset:
Transparent and conductive multicomponent oxide films prepared by magnetron sputtering
Authors: Minami Tadatsugu
Published: July 2002

Transparent and conductive thin films of multicomponent oxides composed of binary and/or ternary compounds with varied chemical compositions have been prepared by rf or dc magnetron sputtering. Transparent conducting oxide (TCO) films were prepared in multicomponent oxides composed of ZnO, SnO2, Ga2O3, or MgO combined with In2O3 or ZnO combined with SnO2, containing ternary compounds such as Zn2In2O5, In4Sn3O12, GaInO3, MgIn2O4, and ZnSnO3. In addition, the TCO films were prepared in a multicomponent oxide composed of combinations of these ternary compounds. In particular, the Zn2In2O5 and In4Sn3O12 films exhibited a resistivity of 2×10−4 Ω cm, comparable to that of indium–tin–oxide films. TCO films could always be obtained in multicomponent oxides consisting of combinations of metal oxides as long as these oxides were TCO film materials or transparent conductors; the mixture ratio of the components could be varied over all possible compositions. The electrical, optical, and chemical properties, the band-gap energy, and the work function of these transparent conducting multicomponent oxide films could be controlled by changing the composition. Consequently, transparent conducting multicomponent oxide films are suitable for specialized applications because their electrical, optical, and chemical properties as well as physical properties can be controlled by altering the chemical composition.
Influence of annealing temperature on the formation and characteristics of sol-gel prepared ZnO films
Authors: Castanedo-Pérez R. , Jiménez-Sandoval O. , Jiménez-Sandoval S. , Márquez-Marı́n J. , Mendoza-Galván A. , Torres-Delgado G. , Maldonado-Alvarez A.
Published: July 2002

ZnO thin films have been obtained by the sol-gel method from a Zn(OOCCH3)2 precursor on soda lime glass and silicon wafer substrates. The films, obtained by a single dipping procedure, were characterized by Fourier transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies, atomic force microscopy, x-ray diffraction and ellipsometry measurements. Thermally untreated and annealed (100–450 °C) films were studied in order to analyze the influence of temperature on the formation and properties of the ZnO coatings. Remarkably, these results indicate that ZnO forms at considerably lower temperatures than 450 °C, which is usually considered in the literature as a reference temperature for the formation of ZnO. Thus, a sharp absorption edge of ZnO at ∼380 nm can be easily observed in the UV-vis spectra of films annealed at 200 and 300 °C, accordingly, and the FTIR data indicate the absence of organic groups at these temperatures. The atomic force microscopy results show a uniform, void-free surface of the films, as well as larger grain sizes as the annealing temperature is increased. The x-ray diffraction patterns show that the films are polycrystalline and also show evidence of the formation of ZnO at temperatures as low as 200 °C. The refractive index values, obtained by ellipsometry, increase with annealing temperature, up to a value of 1.96 for the film fired at 450 °C.
Thickness and index measurement of transparent thin films using neural network processed reflectance data
Authors: Tabet Milad F. , McGahan William A.
Published: July 2002

Artificial neural networks and the Levenberg–Marquardt algorithm are combined to calculate the thickness and refractive index of transparent thin films from spectroscopic reflectometry data. A neural network is a set of simple, highly interconnected processing elements imitating the activity of the brain, which are capable of learning information presented to them. Reflectometry has been used by the semiconductor industry to measure thin film thickness for decades. Modeling the optical constants of a film in the visible region with a Cauchy dispersion model allows the determination of both thickness and refractive index of most transparent thin films from reflectance data. In this work, artificial neural networks are used to obtain good initial estimates for thickness and two Cauchy parameters An and Bn, these estimates are then used as the starting point for the Levenberg–Marquardt algorithm which converges to the final solution in a few iterations. This measurement program was implemented on a Nanometrics NanoSpec 8000XSE and will measure thickness and index of transparent films. The program works with a thickness range of 1000–16000 Å and index range of 1.36–2.35, and takes an average of 4 s.
Process monitoring of hemispherical-grained silicon thin films for dynamic random access memory applications
Authors: Hayzelden Clive , Bivas Albert , Ygartua Carlos L. , Chan Kin-Chung
Published: July 2002

Spectroscopic ellipsometry is employed to correlate the effective thickness of hemispherical-grained silicon (HSG-Si) films on underlying Si capacitor plates to final device capacitance. The fabrication of HSG-Si was developed to increase the storage plate surface area, and hence the capacitance, of dynamic random access memory devices. In this article, a novel combination of modeling techniques is employed to calculate the effective thickness of the HSG-Si film, together with the thickness and degree of crystallinity of the underlying Si capacitor plate. Seven HSG-Si films were fabricated using the “seed and anneal” process. By utilizing a range of seeding temperatures, the morphology and surface area enhancement of the films were deliberately varied. Using broadband spectroscopic ellipsometry, combined with a harmonic oscillator model for the HSG-Si film, a correlation of >95% is demonstrated between the effective thickness of the as-deposited HSG-Si films and the completed device capacitance enhancement. Using a Bruggeman effective medium approximation to model the underlying Si capacitor plate, the crystallinity of that layer was determined to be in the range 78.9%–82.7% for six out of the seven wafers. One misprocessed wafer with a markedly more amorphous capacitor plate was detected. All spectral analyses were performed using a single combination of models for all seven HSG-Si/Si/SiO2/crystalline Si film stacks.
Process optimization of dielectrics chemical mechanical planarization processes for ultralarge scale integration multilevel metallization
Authors: Treichel H. , Frausto R. , Srivatsan S. , Whithers B. , Meyer T. , Morishige R.
Published: July 2002

The requirements of gap-fill and global planarization for interlayer dielectric films obtain more and more importance as the size of the integrated circuits shrinks. Typical dimensions are 0.35 μm for gaps between 0.7 μm high aluminum interconnect lines with an aspect ratio of 2:1. The push of leading edge ultralarge scale integration manufacturing technologies toward the formation of sub 0.1 μm feature sizes places extreme performance demands on the processes and equipment used. At submicron linewidths, the depth-of-focus was limiting technology and chemical mechanical planarization (CMP) became a necessary tool for feature sizes of 0.35 μm and below. Thus, CMP emerged quickly and has become quite sophisticated [R. DeJule, Semicond. Int. 11, 15 (1996)]. Also, in order to fill the small feature sizes high-density plasma chemical vapor deposition (HDP–CVD) of insulators gained increasing attention in the semiconductor world. Due to the uniform thickness of the HDP intermetal dielectric (see Fig. 1) the polishing time is shortened, pad wear is reduced, and thus, increasing the intervals between pad dressing. An increased throughput, as well as extended CMP stability and repeatability can be achieved. A saving in processing time as compared to standard techniques up to 35% is possible. In this article we describe the major dependencies of machine parameters versus experimental results for different CMP processes.
Nanophase copper thin films deposited from a beam source
Authors: Urban F. K. , Khabari A. , Hosseini-Tehrani A. , Griffiths P. , Fernandez G.
Published: July 2002

Although thin films formed from beams of nanoparticles or clusters have been discussed since the early 1970s, the question of the usefulness of this method has remained open as few films of any significant thickness have been formed to date. Early attempts did not condense, could only condense a few “high vapor pressure” solids, or were so low rate as to make growth too slow to be of use. A new deposition system has been designed and built here at Florida International University along the lines of those of Averback and Haberland, and they appear to have the most promise. The new system was specifically designed for high rate with a high throughput intermediate pressure pump and 2 kW capable dc sputter source. Optically transparent films have been deposited from a copper source but are not yet fully understood. Films were deposited onto single crystal silicon substrates and show a small beam divergence of less than 1° total. The beam is highly nonuniform with maximum intensity on axis, which drops rapidly to zero within less than 10 mm off axis. Deposits have been made using a 1 Torr argon+helium sputtering and condensation atmosphere followed by nozzle aperture extraction. Films are affected by the amount of He and by cooling of the sputter chamber walls.
Spatially resolved fluorine actinometry
Authors: Shannon Steven , Holloway James Paul , Brake M. L.
Published: July 2002

A method has been developed to obtain spatially resolved optical emission spectra. This method is used in a diagnostic known as actinometry, where the relative concentration of fluorine can be obtained by examining the ratio of two spectral lines having similar excitation thresholds and excitation cross sections. Generally, the etch rate of silicon is correlated to the concentration of fluorine. In this modified actinometry method, radial emissivity profiles of the discharge are obtained 1 cm above the wafer surface by using a rotating stage to capture small wedges of light from the etching discharge, and analyzing these wedges using a regularized reconstruction algorithm. The relative fluorine concentration is obtained by comparing the ratio of a fluorine (703.75 nm) to argon (750.39 nm) emission line. The atomic fluorine radial profiles correlate to hard masked silicon etch radial profiles processed in a Lam TCP 9400 SE inductively coupled plasma processing tool using an SF6/Ar chemistry. Fluorine loading on the radial fluorine concentration profile over the wafer surface was investigated and found to affect the radial actinometry profile.
Fourier transform infrared spectroscopy of effluents from pulsed plasmas of 1,1,2,2-tetrafluoroethane, hexafluoropropylene oxide, and difluoromethane
Authors: Labelle Catherine B. , Karecki Simon M. , Reif Rafael , Gleason Karen K.
Published: July 2002

Gas-phase Fourier transform infrared spectroscopy (FTIR) has been used to analyze the effluents from C2H2F4, hexafluoropropylene oxide (CF3CFOCF2, HFPO), and CH2F2 pulsed plasmas. A series of reference spectra for possible effluent species was used to identify the major species in each. The major species in pulsed C2H2F4 plasmas were found to be: C2H2F4, HF, C2F4, C2HF5, CHF3, and SiF4 (formed from free fluorine). For HFPO pulsed plasmas, the major effluents are: HFPO, CF3COF3, COF2, C2F4, C2F6, CO, CF4, and C3F8, whereas for CH2F2 pulsed plasmas, the major effluents are: CH2F2, HF, SiF4, and CHF3. Reaction sets were postulated for each precursor to account for the observed effluents, and these sets were used to explain the trends of species concentrations with pulse on and pulse off time. In each case, most of the effluent concentration trends could be traced back to competition between dissociation pathways of a particular molecule. For both C2H2F4 and CH2F2, the main reactions were the competition between CF2 production and HF elimination from the original precursor. For C2H2F4 pulsed plasmas, the competition between these pathways was found to be ∼1:1, whereas for CH2F2 pulsed plasmas, the HF elimination pathway is dominant. For HFPO, the key reactions are the three dissociation pathways of CF3COF, a main product of the initial dissociation of HFPO into CF2+CF3COF. The global warming impact of each of the pulsed plasma enhanced chemical vapor deposition processes was gauged by the million metric tons of carbon equivalent (MMTCE) metric. CH2F2 pulsed plasmas were found to have the lowest MMTCE (min=2.1×106), whereas HFPO pulsed plasmas had the highest MMTCE (max=7.7×107). For all three precursors, the MMTCE impact is reduced by decreasing the exposure to plasma excitation through increasing the off time at a fixed on time.
Long term stability of dry etched magnetoresistive random access memory elements
Authors: Jung K. B. , Marburger J. , Sharifi F. , Park Y. D. , Lambers E. S. , Pearton S. J.
Published: July 2002

The magnetization of Cl2/Ar etched magnetic multilayer (NiFeCo/CoFe/Cu/CoFe/NiFeCo) structures used in magnetoresistive random access memory elements was measured over a period of ∼6 months. Very stable magnetic properties were achieved, with no evidence of corrosion, provided chlorinated etch residues were removed by postetch cleaning. Several different cleaning procedures, including deionized water rinsing or in situ exposure to H2, O2 or SF6 plasmas were investigated. Some slight degradation in magnetization was observed in O2 plasma treated structures, but the other cleaning procedures produced no change in magnetic properties and excellent long-term stability.
Sputter deposition and annealing of Ta, TaSix and TaBx composite films and their application in next generation lithography masks
Authors: Racette Kenneth , Brooks Cameron , Guarnieri C. Richard , Hendy Dennis
Published: July 2002

Ta and Ta composites with other elements have been developed as low stress absorbers for x-ray mask technology. These thin films are often produced in small quantities by sputter deposition from targets of pure Ta with chips of the minor elements placed on the target to create the composites. For membrane-mask manufacturing it is important that absorber films have uniform composition, thickness, and low, uniform stress to assure that image size and pattern placement errors are minimal. Since sputtered films containing Ta often have highly compressive stress, several methods have been used to reduce the final stress, including careful control of sputtering conditions, deposition of layered films with different stresses, and thermal annealing. Much data has been reported regarding the effects of thermal annealing of Ta films but less information is available on multiple element films such as TaSix and TaBx. Previous reports on these materials have generally not discussed the behavior of these films under long term, higher volume manufacturing conditions. During the last several years IBM has been engaged in development and fabrication of refractory x-ray membrane masks using Ta composites as absorber materials. Films were sputter deposited from hot isostatically pressed powder targets of Ta, Si, and B using an S-gun magnetron cluster deposition system. This article reports on the deposition and annealing of these films and their application to membrane-mask fabrication in a manufacturing environment. The effects of deposition parameters such as dc power, argon gas pressure, and substrate composition on film stress, composition, and density are discussed. The results of nitrogen annealing on TaSix and TaBx films are presented. Absorber film quality data and its impact on image size, image placement, and defect density of some x-ray masks is presented.
Effects of a new combination of additives in electroplating solution on the properties of Cu films in ULSI applications
Authors: Hu J. C. , Chang T. C. , Wu C. W. , Chen L. J. , Hsiung C. S. , Hsieh W. Y. , Lur W. , Yew T. R.
Published: July 2002

Effects of a new combination of additives in acid electroplating solution on the properties of Cu thin films have been investigated. The electroplated Cu films exhibit an excellent superfilling behavior. 0.18 μm vias with an aspect ratio exceeding 5 were filled completely without any void or seam. Strong (111) texture was found for the electroplated Cu films. The resistivity of a 450-nm-thick Cu film was measured to be 1.84 μΩ cm.
Multizone uniformity control of a chemical mechanical polishing process utilizing a pre- and postmeasurement strategy
Authors: El Chemali Chadi , Moyne James , Khan Kareemullah , Nadeau Rock , Smith Paul , Colt John , Chapple-Sokol Jonathan , Parikh Tarun
Published: July 2002

Achieving good uniformity process control in chemical mechanical polishing (CMP) requires a representative uniformity metric and strong models relating this metric to process tunable inputs. Previous efforts in CMP uniformity control have yielded acceptable results utilizing a center-to-edge (CTE) first order nonuniformity metric. Closer analysis of post CMP process nonuniformity, however, reveals significant higher order nonuniformity components such as the center “dimple” and outer “doughnut” regions. These nonuniformity characteristics are due in part to upstream chemical vapor deposition (CVD) processing. Utilizing a multizone approach to uniformity modeling, a more accurate mathematical model of CMP uniformity has been identified. The model has been utilized to customize a thickness and uniformity multivariate run-to-run software control solution for the process. The controller is based on the generic cell controller structure, which is a proven enabler for run-to-run control for a number of processes including CMP, vapor phase epitaxy, and etch. The control algorithm is a zeroth order adjustable linear approximation two-stage algorithm with exponentially weighted moving average noise filtering. This algorithm, which supports first order linear and nonlinear models, has been demonstrated to be effective in CMP CTE and thickness multivariate control. The control solution has been enhanced to utilize both pre and post CMP process metrology along with process models to suggest process recipe modifications on a run-to-run basis. Results indicate improved control of CMP process nonuniformity qualities of interest. Further, the results quantify the significant benefit of utilizing premetrology (feedforward) information in addition to traditional postmetrology (feedback) in determining control recipe advice.
Effects of trapped charges on Hg-Schottky capacitance–voltage measurements of n-type epitaxial silicon wafers
Authors: Wang Q. , Liu D. , Virgo J. T. , Yeh J. , Hillard R. J.
Published: July 2002

The effects of surface charge in the oxide layer for Hg-Schottky capacitance–voltage (C–V) measurements have been discussed in detail. The accumulation of majority carriers at the Si surface has been identified as a major factor controlling the stability and accuracy of the Hg-Schottky C–V measurement. For n-type wafers, the fixed oxide charge in Si oxide layer induces electron accumulation at the oxide/Si interface. This electron accumulation cannot be dissipated until a depleting voltage as high as −5.0 V is applied depending on the preparation of the oxide layer. It has been found that introducing Cu during the growth of the oxide layer can produce a deep trap level in the oxide. Pre-electrical-field stress at 5 MV/cm for 5 s can fill these traps and eliminate electron accumulation, resulting in a stable and accurate C–V measurement. Our results on p-type wafers show that the fixed oxide charge in the oxide layer can establish a surface depletion condition and produce a stable and accurate C–V measurement. With these experimental results, we propose that Si oxide layer can improve the stability and accuracy of the Hg-Schottky C–V measurement for both n- and p-type wafers. For n-type wafers, pre-electrical stress and a Si oxide layer with deep electron trap level are necessary; for p-type wafers, only the fixed oxide charge is needed.
The adsorption and desorption of CO on the W(111) surface
Authors: Lee S. Y. , Kim Y.-D. , Yang T. S. , Boo J.-H. , Park S. C. , Lee S. B. , Park C. Y. , Kwak H. T.
Published: July 2002

The adsorption and desorption of CO have been studied on the W(111) surface in the temperature range of 300 and 1100 K by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and thermal desorption spectroscopy. Saturation adsorption of CO at 300 K reveals four desorption states at 410, 850, 1000, and 1150 K, called α, β1, β2, and β3 states, respectively. The desorption kinetic order of CO in the β3 state is followed by the first order, indicating that CO in the β3 state seems to be nondissociative, rather than dissociative. The inequalities of XPS and UPS obtained following adsorption of CO and O2 under the same condition support a nondissociative adsorption of CO in the β3 state. Based on calculations for CO adsorbed on W43 cluster models using atom-position and electron delocalization molecular orbit, the changes in binding energy and in intensity of XPS and UPS can be attributed to a lying-down species of nondissociatively adsorbed CO in the β3 state. As a result, the binding energies of O(1s) and C(1s) for adsorbed CO in the α state is characterized by 529.8 and 282.7 eV, respectively, whereas those for nondissociatively adsorbed CO in the β3 state is characterized by 530.1 and 282.4 eV, respectively.
Effect of HCl catalyst in the formation of flat structures of Ta2O5 thin films by sol-gel technique
Authors: Cantalini C. , Pelino M. , Phani R. A. , Passacantando M. , Picozzi P. , Santucci S.
Published: July 2002

Ta 2 O 5 thin films have been prepared from tantalum ethoxide solutions [Ta(C2H5O)5] by sol-gel spin coating technique on Si (100) substrates and annealed at different temperatures ranging from 500 to 800 °C for 1 h. The physical, chemical and morphological characteristics of both fine powders and thin films have been characterized by bulk techniques like N2 adsorption and He porosimetry, thermogravimetry, differential thermal analysis and surface techniques like x-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), and x-ray photelectron spectroscopy (XPS). Additions of acid catalyst (HCl) and proper thermal treatment enable the formation of highly dense flat like films of Ta2O5, as observed by AFM observations. Films prepared from neutral precursor solutions show a micrometer-range porous network and a strongly marked rough polycrystalline surface structure. HCl catalyst resulted in a decrease of the crystallization temperature to 630 °C, with respect to a crystallization temperature of 732 °C found for the neutral prepared films. The evolution of dense structures upon HCl treatment has been confirmed by surface area and density measurements on the fine powders. XPS measurements have confirmed the formation of stoichiometric Ta2O5 for the HCl prepared films. The pH of the precursor solution as well as the annealing thermal treatment have resulted in the key process parameters for controlling the microstructural characteristics of the deposited films.
In-situ characterization of thin films by the focused ion beam
Authors: Choi S. H. , Li R. , Pak M. , Wang K. L. , Leung M. S. , Stupian G. W. , Presser N.
Published: July 2002

In this article, we report silicon-based multilayered nanometer-size wires for vertical metal oxide semiconductor field effect transistor (MOSFET) and the ohmic contact of gallium nitride (GaN) field effect transistor (FET) were milled to produce trenches with a micron-scale rectangular area for a subsequent inspection by the field emission scanning electron microscope (FESEM). The cross-sectioning view by the FESEM enabled the investigation of individual film thickness and morphology as well as a depth profiling of elements by a subsequent Auger analysis. Monte Carlo simulation was done to estimate the penetration range of gallium ions into silicon and GaN at high energy.
Measurement of axial pressure distribution on a rotor of a helical grooved molecular drag pump
Authors: Sawada T. , Sugiyama W. , Takano K.
Published: July 2002

The theory in regard to the pumping performance of a helical grooved molecular drag pump proposed by the authors has been employed successfully as a design and evaluation tool. However, some researchers presented results different from the authors’ using the direct simulation Monte Carlo method. Their method included the inlet effect and the secondary flow in grooves, both of which were neglected in the authors’ theory. This study was planned to examine the validity of the authors’ theory precisely. A helical grooved cylindrical rotor was located concentrically in a smooth sleeve. In order to obtain the pressure distribution on the rotor, several taps were installed on the sleeve along the axial direction. The taps led to one side of a differential pressure gauge via valves and the inlet side of the rotor was connected to the other side of the gauge. The pressure was measured by switching the valves in turn. The measurements show that (a) the pressure in the free molecule flow regime increases exponentially from the inlet to outlet, (b) the pressure increases almost linearly from the inlet to outlet in the slip and viscous flow regime, and (c) the inlet effect becomes remarkable in the turbulent flow regime. The validity of the theory has been proved from the free molecule to viscous flow regimes, but the theory needs modification so as to include the inlet effect in the turbulent flow regime.
Carburizing of tantalum by radio-frequency plasma assisted chemical vapor deposition
Authors: Rubinshtein A. , Shneck R. , Raveh A. , Klemberg-Sapieha J. E. , Martinu L.
Published: July 2002

Tantalum carbide (TaC) has great potential as an alternative to tantalum and tantalum oxide for applications requiring thermal stability and corrosion resistance. In this study TaC layers were produced by inductive rf plasma-assisted chemical vapor deposition that combines diffusion with chemical vapor deposition. The maximum temperature of the tantalum substrates measured during a 6 h processing time was 900 °C using Ar–CH4 or Ar–CH4–H2 gas mixtures. The microstructure of the layers was characterized by X-ray diffraction and Auger electron spectroscopy, and the mechanical properties were studied by micro- and nanoindentation and by microscratch techniques. A close correlation among the carburizing parameters, the microstructure, the mechanical behavior of the layers, and the corrosion resistance was found. The best performing films, several μm thick, consisting of TaC phase with the highest hardness (∼25 GPa), were obtained under the following conditions: input power of 1400 W, pressure of 40–60 mbar, and substrate located at the center of the rf coil. The effect of gas composition, gas pressure, and substrate temperature on the layer composition, the TaC/Ta2C phase ratio, and the mechanical characteristics and chemical stability is presented and discussed. A mechanism of carburizing of tantalum in an inductive rf plasma is proposed.
Subnanometer scale tribological properties of nitrogen containing carbon coatings used in magnetic storage devices
Authors: Wienss A. , Persch-Schuy G. , Hartmann R. , Joeris P. , Hartmann U.
Published: July 2002

Ultrathin carbon coatings are used in the magnetic storage industry to protect sensitive sensor heads and magnetic media against corrosion and mechanical damage. Such damage can be modeled by artificially generated scratches using scanning force microscope techniques. Loading forces in the μN range are applied, resulting in scratches with residual depths of only a few Å. A special image subtraction technique is used which allows careful analysis of tiny grooves even on rough surfaces. The scratching resistance of various CNx films, magnetron sputtered on hard disks with a thickness of about 12 nm, was determined and found to improve with an increased nitrogen content (6–16 at.%). This behavior, together with a linear downward shift of the Raman G-peak position from 1569 to 1564 cm−1, supports the assumption that the incorporation of nitrogen increases the fraction of sp3 bonds.
Air bearing collision dynamics
Authors: Stupp Steven E. , Blanco Richard J. , Strom Brian D. , Chen Li
Published: July 2002

The dynamic response of sliders with different air bearing designs, following a controlled collision with an asperity, is reported. Systematic differences are found between air bearings with continuous positive pressure bearing surfaces running from the leading to trailing edge of the slider (so-called continuous rail designs) and some of those with separate positive pressure bearing features at the leading and trailing edges of the slider (so-called island-type designs). Particular island-type designs are found to be more susceptible to flying height modulation during the collision and, under certain conditions, appear to exhibit at least one additional head-disk contact after the slider has moved past the asperity. The results have consequences for reliability, especially in systems where the slider flies below the disk glide height.
Ultrahigh vacuum compatible matrix assisted laser desorption/ionization time-of-flight mass spectrometer
Authors: Porter T. L. , Hermann S.
Published: July 2002

The technique of matrix assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (MS) allows for the mass determination of single oligomeric species that suffer from fragmentation effects using conventional MS techniques. Using MALDI, the sample to be analyzed is combined with a strong ultraviolet (UV) absorbing “matrix,” such as 3-hydroxypicolinic acid or 2,5-dihydroxybenzoic acid. Short UV laser pulses desorb the matrix plus sample material from the topmost sample surface, while simultaneously gently ionizing the sample material. The ionized species are then ejected into a time-of-flight analyzer for mass determination. The gentle ionization process allows oligomers on surfaces that would normally suffer from fragmentation effects to be detected intact. In this article, we describe an ultrahigh-vacuum MALDI instrument that has been constructed from primarily off-the-shelf components at minimal cost. This instrument may be used to detect the presence of picomole concentrations of material with atomic weights from a few hundred to over 100 000.
Site preferences of oxygen and boron atoms during dissociative reaction of HBO2 molecules onto the Si(111)-7×7 surface
Authors: Kaikoh T. , Miyake K. , Li Y. J. , Morita R. , Yamashita M. , Shigekawa H.
Published: July 2002

Using scanning tunneling microscopy (STM), we succeeded in observing the initial process of the HBO molecule on the Si(111)-7×7 surface for the first time. Since HBO2 molecules are commonly used as the B source in the molecular beam epitaxy system, and the dominant flux from the HBO2 source in the ordinary condition is the form of HBO, analysis of the HBO reaction process is highly important. When the substrate temperature was kept at room temperature during the molecular irradiation, the adsorbed HBO molecules remained on the surface without dissociation. With the substrate temperature being increased, the dissociation process was activated, and the oxygen- and boron-related adatoms were produced at the corner and center adatom sites in the 7×7 units, respectively. The site dependence was well determined by the bias voltage dependent STM. The selective reaction site of oxygen atoms was comprehensively explained by their electronegativity and charge distribution in the Si(111)-7×7 surface adatoms. On the other hand, regarding the selectivity for the boron atoms, introduction of the surface strain effect was found to be essential.
Band-gap engineering via graded gap, superlattice, and periodic doping structures: Applications to novel photodetectors and other devices
Authors: Capasso Federico
Published: July 2002

Recent new multilayer structures and their device applications are reviewed. These new concepts allow one to radically modify the conventional energy band diagram of a pn junction and thus tailor the high field transport properties to an unprecedented degree (band-gap engineering). This approach has been used to propose and implement a new class of avalanche photodiodes with enhanced ionization rates ratio and the solid state analog of a photomultiplier (staircase detector). Other device applications such as repeated velocity overshoot structures are also discussed.
EL-3 application to 0.5 μm semiconductor lithography
Authors: Davis D. E. , Gillespie S. J. , Silverman S. L. , Stickel W. , Wilson A. D.
Published: July 2002

The application of IBM’s 3rd generation direct write electron beam lithography tool EL-3 has been extended into the submicron region. This was accomplished with tool modifications in conjunction with suitable process adjustments. EL-3 is presently being used in both development and manufacturing for the exposure of wafers and masks. It was designed as a high current, high throughput tool to cover lithography requirements down to 1 μm minimum dimensions. To move into the 0.5 μm realm, no basic architecture changes were made, but the beam current, deflection speeds, and maximum spot and field sizes were reduced to make the trade-offs against throughput that were necessary and acceptable for the system’s application to technology development. A single layer resist process was devised to demonstrate fully the performance capability of the tool. The process uses top surface imaging which allows one to analyze tool performance without excessive distortions. Spot-to-spot butting and illumination consistency were monitored using this process. Linewidth tolerance and overlay results obtained with the new tool/process configuration will be reported. Top surface imaging, whether in a single or multilayer resist process, represents the most viable approach for submicron electron-beam lithography.
The effect of low pressure plasma on Si–SiO2 structures and GaAs substrates
Authors: Chung Y. , Chen C. Y. , Langer D. W. , Park Y. S.
Published: July 2002

The degradation of insulating films and GaAs substrates by exposure to low pressure plasma is investigated. In Si–SiO2 structures, the increased density of fast surface states and the nonuniform storage of positive trapped charges within the oxide layer is responsible for the degradation of MOS devices exposed to low pressure plasma. The charge carrier reduction due to the creation of compensating defects during the hydrogen plasma treatment of n-GaAs is reported.
An improved technique for resist-profile control in holographic lithography
Authors: Lezec Henri J. , Anderson Erik H. , Smith Henry I.
Published: July 2002

Undercut profiles are achieved in holographically exposed resist when the maximum of the orthogonal standing wave is placed at the resist–substrate interface. We demonstrate that this condition can be achieved by tilting the substrate normal out of the plane of the interferometer. The condition of maximum interface intensity is detected by determining when there is maximum optical coupling into a test film of 10 nm-thick photoresist. Exposure of the test film is detected by diffraction.
Reactive-ion etching of 0.2 μm period gratings in tungsten and molybdenum using CBrF3
Authors: Schattenburg M. L. , Plotnik I. , Smith Henry I.
Published: July 2002

X-ray spectroscopy and imaging over a broad spectral range (0.1–20 nm) require transmission diffraction gratings and zone plates of high Z (atomic number) materials with narrow linewidths and large height-to-width ratios, often ≥10 to 1. Such structures have been achieved in gold and silver by electroplating into PMMA molds produced by x-ray lithography. Calculations of the x-ray attenuation and phase shift as a function of wavelength and Z show the value of expanding beyond Au and Ag the range of materials that can be used in diffraction gratings and zone plates. We present the result of calculations showing the effectiveness of W and Mo as substitutes for Au and Ag, respectively, and demonstrate reactive-ion etching of gratings in W and Mo with ∼80 nm wide slots, 0.4–0.7 μm deep. The etch gas CBrF3 was used which allowed us to achieve vertical sidewall structures, while comparative studies using CF4 and SF6 demonstrated excessive undercut. The W films were deposited by CVD and the Mo films by rf sputtering. This work is directed toward generating improved diffraction gratings for future x-ray astronomy missions, as well as improved x-ray masks for submicrometer lithography.
The effects of local electric fields and specimen geometry on voltage contrast in the scanning electron microscope
Authors: Wager William E. , Wolf Edward D.
Published: July 2002

A high resolution voltage contrast test system was implemented in a scanning electron microscope using a planar grid retarding field spectrometer. Samples were constructed which simulate the geometries for both present and future integrated circuits. The operation of the system was characterized as were the effects of local electric fields. Two secondary electron (SE) loss mechanisms were identified which explain some of the inconsistencies in the operation of this type of spectrometer, and a system parameter was introduced which controls the SE losses. The system was sensitive to voltage changes as small as 10 mV, and measurements were made on aluminum lines as narrow as 0.5 μ. Errors as large as 0.5 V were introduced by local electric fields on certain specimen geometries when operating in a 5 V range. It was shown that the ‘‘potential barrier’’ model for local electric field effects was inadequate to explain the observed effects. Instead, a model for secondary electron deflection was used.
Nucleation and growth processes in thin film formation
Authors: Venables J. A.
Published: July 2002

The mechanisms of nucleation and growth of thin films are briefly reviewed. A kinetic theory of the nucleation and growth of two-dimensional clusters is outlined. Calculations of the nucleation density in a pair binding model are presented and applied to layer plus island Ag deposition systems on W(110), Mo(100), and Si(100) and (111). The behavior at low supersaturation is discussed, and it is shown that explicit treatment of surface vibrations is required to obtain self-consistent results in this region. Atomic parameters deduced for these Ag deposition systems are tabulated.
Electronic structure of molecular beam epitaxy grown CaF2 on Si(111)
Authors: Karlsson U. O. , Himpsel F. J. , Morar J. F. , Rieger D. , Yarmoff J. A.
Published: July 2002

High resolution core level spectroscopy, polarization-dependent near edge x-ray absorption fine structure and angle-resolved photoemission have been used to study CaF2 grown by molecular beam epitaxy on Si(111). It is found that both Ca and F bond to Si at the interface and that both Ca and F-derived interface states are created. A new radiation induced ordered structure is also reported.
An x-ray photoelectron spectroscopy study of sulfur hexafluoride etchant residue on silicon and silicon dioxide
Authors: Thomas J. H. , Hammer L. H.
Published: July 2002

X-ray photoelectron spectroscopy has been used to characterize sulfur hexafluoride radio frequency (rf) plasma exposure in a reactive ion configuration. Reactive ion etched silicon is coated with a thin layer of SiFx similar to that observed on CF4 reactive ion etched silicon. A similar thin layer is observed on SiO2. When the surface is inadvertently contaminated (in this instance with nickel), sulfur, not observed on a clean surface, is present. In addition, silicon becomes roughened. Dilution of SF6 in argon gas does not significantly change the surface residue chemistry but does greatly decrease the etch rate of silicon. Increasing the power density from 0.2 to 1.2 W/cm2 increases the etch rate by a factor of ∼20. At the highest power densities, surface contamination is observed in the form of nickel and sulfur residues. Finally, as in the case of CF4 reactive ion etched silicon, the surface is observed to be crystalline at the lower power densities due to lack of ion bombardment damage effects and becomes amorphous as the power density is increased. At an equivalent power density, the self-bias generated in an SF6 plasma was measured to be significantly less than that in a CF4 plasma. High silicon etch rates are achieved at very low power densities as compared with CF4 reactive ion etching confirming the findings reported in literature references. This study leads to the conclusion that CF4 may be a better etchant system than SF6 for contact cleaning.
Application of diazonaphthoquinone compounds and a diazonium salt to contrast enhanced lithography
Authors: Kaifu Katsuaki , Itoh Toshio , Kosuge Maki , Yamashita Yoshio , Ohno Seigo , Asano Takateru , Kobayashi Kenji , Nagamatsu Gentaro
Published: July 2002

New photobleachable materials, two kinds of diazonaphthoquinone compounds and a diazonium salt, have been developed for contrast enhanced lithography. These materials are quite soluble in nonpolar solvents and are stable even in solution. Therefore, they can be directly coated on a bottom resist layer and removed without attacking it. Their films have strong absorption bands in the UV region involving g-, h-, and i-lines. They are uniformly bleached by UV exposure. When these materials employ as contrast enhancement layers, 1.0 μm line and space patterns are clearly resolved by using a mirror projection aligner and 0.55 μm line and space patterns are clearly resolved by using an i-line reduction projection aligner.
EBES4: A new electron-beam exposure system
Authors: Alles D. S. , Biddick C. J. , Bruning J. H. , Clemens J. T. , Collier R. J. , Gere E. A. , Harriott L. R. , Leone F. , Liu R. , Mulrooney T. J. , Nielsen R. J. , Paras N. , Richman R. M. , Rose C. M. , Rosenfeld D. P. , Smith D. E. A. , Thomson M. G. R.
Published: July 2002

EBES4 is an electron-beam exposure machine designed for accurate submicron lithography with good throughput. It can write on optical and x-ray mask substrates and directly on semiconductor substrates. Standard pattern data are preprocessed using a special purpose processor to remove overlap and to reverse the tone if required. The address size can be varied from 1/16 to 1/8 μm. Patterns are written by first breaking them into microfigures which can be rectangles, parallelograms, or 45° triangles with a maximum size of 16×16 addresses. Each microfigure is positioned on the continuously moving substrate using magnetic and electrostatic deflection systems. They are written by stepping in a raster with a 1/8 μm spot using an additional very high speed electrostatic deflection system. The coordinate system can be distorted by digital hardware to correct for mechanical errors or to register with another lithography level. The electron-beam column with its thermal-field-emission gun, the hydraulic stage, the mask-handling robot, the control system, and the pattern data flow are all described. The system is highly automated, and the pattern data flow, electron-beam column setup, vacuum system switching, and cassette handling are all under the control of a VAXTM 11/780. Distributed processors are used for lower level control tasks. Resists of up to 8 μC cm−2 can be exposed at a rate of one 4 in. mask (containing 109 microfigures) every 30 min at 1/8 μm address size, while resists requiring 20 μC cm−2 can be exposed at a rate of one every 50 min. No damaging heating effects have been observed.
Electron velocity overshoot in sub-100-nm channel length metal–oxide–semiconductor field-effect transistors at 77 and 300 K
Authors: Shahidi G. G. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We have reported previously on the fabrication, using x-ray lithography, of Si metal–oxide–semiconductor field-effect transistors (MOSFET’s) having channel lengths ranging from 60 nm to 5 μm. Devices with channel lengths of 75 nm showed electron velocity overshoot at 4.2 K. We have improved the mobility of the short-channel MOSFET’s by implanting with B and then growing the gate oxide rapidly such that the concentration in the inversion layer is about 2×1016 cm−3 rather than the 5×1017 cm−3 used previously. A peak concentration of 2.2×1017 cm−3 occurs at a depth of 0.19 μm, where it prevents punchthrough by screening the field lines from the drain. With devices having channel lengths shorter than 100 nm we measured mean electron velocities at 300 and 77 K that exceeded 107 and 1.3×107 cm/s, the bulk saturation velocities at these two temperatures. The highest mean velocity measured at 77 K was 2.3×107 cm/s.
Thin titanium dioxide films as interlayers in trilayer-resist structures
Authors: Stillwagon L. E. , Kornblit A. , Taylor G. N.
Published: July 2002

The use of thin titanium dioxide (TiO2 ) films as interlayers in trilayer-resist structures was investigated in this paper. TiO2 layers, 30–200 Å thick, were formed on the surface of thick positive photoresist films by the reaction of titanium tetrachloride (TiCl4 ) with water adsorbed on the surface of the films. The TiCl4 -treated films served as the bottom two layers in trilayer-resist structures. Using a thin TiO2 interlayer that acted as the mask in the final reactive ion etching pattern transfer step, 0.5-μm features were transferred from a top imaging layer to a 1.2-μm-thick bottom layer with ∼0.05-μm linewidth loss. Processing variables that affect the thickness of the TiO2 films were investigated. We discuss these variables, etching techniques for transfer of the resist pattern from the top imaging layer to the TiO2 interlayer and pinhole defects in the TiO2 films.
Applications of microfabrication technology to x-ray laser cavities
Authors: Hawryluk Andrew M. , Ceglio Natale M. , Stearns Daniel G.
Published: July 2002

We have fabricated new, efficient x-ray optical components (x-ray mirrors, beamsplitters, and highly dispersive multilayer mirrors) and have used them to build an x-ray laser cavity. With our laser cavity, we have demonstrated multipass amplification of soft x rays with significant enhancement (>20×) of the x-ray laser emission. This is an important first step in the ultimate conversion of x-ray amplifier media into true x-ray lasers with optimized coherence and divergence properties. We used advanced microfabrication techniques to fabricate the key laser cavity components which require precise layering of alternating materials, thin-film membrane technology, and precise patterning. The x-ray laser requirements, fabrication details, and characterization results for these cavity components are discussed.
Dry etching: From plasma ashing to quantum dots
Authors: Lehmann Hans W.
Published: July 2002

First applications of plasma etching in very large scale integration were reported in the literature 20 years ago. After reviewing the early days of dry etching, applications of this technique to high-resolution pattern transfer are illustrated by the fabrication of deep square-wave gratings with micron dimensions used in diffractive structures as well as submicron structures with large aspect ratio, both etched into SiO2 in CHF3 plasmas. The importance of pattern distortion by faceting effects, redeposition of sputtered material, and undercutting by isotropic etching is discussed. Modern developments like etching of deep trenches into Si and the fabrication of quantum dots are briefly outlined.
Organometallic chemical vapor deposition of cobalt and formation of cobalt disilicide
Authors: Gross M. E. , Schnoes Kranz K. , Brasen D. , Luftman H.
Published: July 2002

The deposition of Co thin films by organometallic chemical vapor deposition is reported. Co is of interest in very large scale integration technology as a catalyst for electroless plating of other metals and as a precursor to formation of CoSi2. High purity, conformal films of Co are deposited by pyrolysis of Co2(CO)8 at 200 °C in vacuum. These films exhibit electrical resistivities of 5–10 μΩ cm and excellent adhesion to Si and SiO2. CoSi2 is formed by heating the samples at 700 °C. The CoSi2 films resulting from reaction of the Co films with the Si substrate contain larger grains than the starting film and exhibit electrical resistivities of ∼13–37 μΩ cm. Selective formation of CoSi2 on patterned test wafers shows similar attributes.