bluuebunny/crossref_metadata_2025 huggingface dataset:
Cold-wall ultrahigh vacuum chemical vapor deposition of doped and undoped Si and Si1−xGex epitaxial films using SiH4 and Si2H6
Authors: Li C. , John S. , Quinones E. , Banerjee S.
Published: July 2002

Doped and undoped silicon homoepitaxy and Si1−xGex-on-Si heteroepitaxy have been achieved by cold-wall ultrahigh vacuum chemical vapor deposition using disilane (Si2H6), silane (SiH4), digermane (Ge2H6), and germane (GeH4) as the reactant gases. Boron and phosphorus doping were achieved by flowing B2H6 and PH3 dopant gases, respectively, into the reactor. The growth mechanism and film quality of intrinsic Si, B/P-doped films, and Si1−xGex alloys using SiH4 and Si2H6 are comparatively studied in this article. The crystallinity of the films was examined by Nomarski microscopy after Schimmel etching, transmission electron microscopy (TEM), and in situ reflection high energy electron diffraction (RHEED). The defect density of the intrinsic Si films grown by Si2H6 and SiH4 was found to be below the TEM detection limit (105/cm2). B-doped and P-doped single-crystal Si were deposited using Si2H6 or SiH4 with a partial pressure of 10 mTorr at substrate temperatures from 550 to 600 °C. The B- and P-doping concentrations were determined by secondary ion mass spectroscopy (SIMS). From plan-view TEM analysis, it was found that the defect density of the B- and P-doped Si films grown using Si2H6 is lower than that grown using SiH4 at even lower substrate temperatures. It was also found that the phosphine (PH3) ‘‘poisoning effect’’ for growth rate reduction and crystallinity degradation in Si2H6 chemical vapor deposition (CVD) is not as serious as in SiH4 CVD.

A model for the PH3 poisoning effect was developed to explain the growth rate reduction in SiH4 CVD with high PH3 flux. The morphology of both P-doped and B-doped Si films using Si2H6 was found to be smoother than for those using SiH4, as indicated by plan-view TEM and by RHEED analysis. Si1−xGex alloys were deposited by using various reactant gases. The thickness of the Si1−xGex alloy films and the Ge mole fraction were measured by SIMS. A 50-period Si1−xGex–Si superlattice was grown using Si2H6 and GeH4. The transition layers were found to be extremely sharp and layer thickness control using Si2H6 was found to be excellent by cross-sectional TEM analysis. In this study, Si2H6 was found to be a better Si precursor compared to SiH4 under our growth conditions. From the growth rate study, the activation energies for the Si growth rate were found to be 1.47 and 1.60 eV for Si2H6 and SiH4, respectively. The activation energies for the Ge growth rate are 0.93 and 1.0 eV using Ge2H6 and GeH4, respectively. A growth kinetic model was developed to predict the growth rate of undoped Si for various reactant gas partial pressures and substrate temperatures. The adsorption rate preexponential constant for SiH4 was found to be about twice that of Si2H6. The model can also predict the Ge mole fraction in Si1−xGex alloys and B/P doping concentrations in the Si films.
In situ polarization-sensitive laser-light-scattering method for simultaneous measurements of two-dimensional spatial size and density distributions of particles in plasmas
Authors: Shiratani Masaharu , Kawasaki Hiroharu , Fukuzawa Tsuyoshi , Watanabe Yukio
Published: July 2002

An in situ polarization-sensitive laser-light-scattering (PSLLS) method is developed to measure simultaneously two-dimensional spatial distributions of size and density of particles in plasmas, in order to reveal growth processes and behavior of particles over a discharge space. The system developed can view the whole discharge area of 50×200 mm2 illuminated by a sheet laser beam with a spatial resolution of 2×2×2 mm3 and a time resolution of 33 ms, and measure particles larger than 50 nm in size and greater than 106 cm−3 in density. Using the PSLLS method, it is found that particles formed in radio frequency silane plasmas initially appear principally in an annular region around the plasma/sheath boundary near the powered electrode. Moreover, larger particles tend to reside nearer to the powered electrode about 10 mm off the discharge-column axis. The region occupied by particles spreads axially toward the grounded electrode (downstream region) and also radially toward both the discharge-column axis and the discharge wall, and then particles flow out of the discharge space with a gas flow.
Five layer stack of nitride, oxide, and amorphous silicon on glass, analyzed with spectroscopic ellipsometry
Authors: Tompkins Harland G. , Williams Phillip H.
Published: July 2002

A stack of nitride/oxide/amorphous Si/oxide/nitride on a glass substrate was fabricated and subsequently analyzed with spectroscopic ellipsometry. The oxides and nitrides were deposited by plasma-enhanced chemical-vapor-deposition and the amorphous Si was deposited with sputter deposition. The optical constants of these materials depend on deposition conditions and hence handbook values cannot be used. The optical constants of the amorphous Si layer are modeled as a combination of Lorentz oscillators. A further complication is that the amorphous Si layer is opaque over about half of the spectral range. Drawbacks of the straight-forward analysis method are discussed and an enhanced analysis method is described and the results presented. The enhanced method improves the uncertainty in the thickness determination of two of the layers by an order of magnitude.
Static secondary ion mass spectrometry study of the decomposition of triethylgallium on GaAs (100)
Authors: Wong K. C. , Jackson M. S. , McEllistrem M. T. , Culp R. D. , Ekerdt J. G.
Published: July 2002

The decomposition of triethylgallium (TEGa-d0) and perdeuterated triethylgallium (TEGa-d15) on Ga-rich GaAs (100) was studied using temperature programmed static secondary ion mass spectrometry (SSIMS) and temperature programmed desorption (TPD). Isothermal and temperature programmed SSIMS spectra of the TEGa-dosed surface feature three dominant hydrocarbon ions, CH3+, C2H3+, and C2H5+, whose behavior indicates the presence of two distinct ethyl ligands. The TEGa-d15 results were equivalent to the TEGa-d0 results, with the ion masses shifted by the D and H mass differences. Both CH3+ and C2H3+ SSIMS signals exhibit the same temperature dependence, staying rather constant between 140–530 K and then decreasing rapidly between 530 and 650 K. The CH3+ and C2H3+ signals disappear over the same temperature range in which C2H4 forms and desorbs from the surface in TPD; these SSIMS signals are attributed to the surface ethyl ligands that are responsible for C2H4 formation. Ethyl ligands reacting to ethylene are likely bound to Ga atom lattice sites. The C2H3+ signal is well established at 140 K, suggesting that TEGa is dissociated at temperatures as low as 140 K. The C2H5+ SSIMS signal decays in parallel with the diethylgallium ion SSIMS signal, and it then disappears in parallel with the CH3+ and C2H3+ signals; the C2H5+ SSIMS signal is associated with both ethyl ligands bound to adsorbed triethylgallium and/or diethylgallium, and with ethyl ligands bound to lattice sites.
Surface processes occurring on TiSi2 and CoSi2 in fluorine-based plasmas. Reactive ion etching in CF4/CHF3 plasmas
Authors: Baklanov M. R. , Vanhaelemeersch S. , Storm W. , Kim Y-B. , Vandervorst W. , Maex K.
Published: July 2002

The kinetics of TiSi2 and CoSi2 etching in CF4/CHF3 plasmas are studied. X-ray photoelectron spectroscope studies show that after the reactive ion etching (RIE) etching of TiSi2 and CoSi2 with different gas composition, complex protective films, containing both CFx polymers and metal fluorides, are formed. The relative amount of metal fluoride and polymer depends on the gas composition. A phenomenological model describing the RIE of the metal silicides in the carbon–fluoride plasmas is established. It is shown that in the case of TiSi2, selective etching of SiO2 can be obtained by increasing the polymer precursor radical concentration in the plasma. Effective ways for the removal of the post-dry-etch residues from the TiSi2 and CoSi2 surfaces have been developed. It is shown that the use of a complex cleaning procedure, including both the SPM (H2SO4:H2O2=4:1) and O2–plasma treatments, provides practically clean surfaces of both the Ti and Co silicides without the metal fluorides and polymers.
Platinum etching in Ar/O2 mixed gas plasma with a thin SiO2 etching mask
Authors: Shibano Teruo , Nakamura Keisuke , Oomori Tatsuo
Published: July 2002

Experimental studies of the etching of platinum with a SiO2 etching mask in an Ar/O2 mixed gas plasma were performed. The etching selectivity of platinum to SiO2 increases with the addition of oxygen, and a high etching selectivity of more than 6 is obtained around an oxygen concentration of 10%. This high etching selectivity is caused by the difference in the adsorption of oxygen atoms between platinum and SiO2. In the etching of SiO2 by an Ar/O2 plasma, oxygen atoms are removed by sputtering by incident ions; however, these vacant sites of oxygen are filled immediately by the oxygen atoms incident from the plasma. The surface etching of SiO2 in an Ar/O2 plasma is disturbed by these replacements of the oxygen atoms. On a platinum surface incident oxygen atoms do not stay on the surface, therefore, disturbance of the etching by oxygen adsorption does not occur. This difference in the oxygen adsorption between platinum and SiO2 is confirmed by the x-ray photoelectron spectroscopy analysis of the etched surfaces. By using an Ar/O2 plasma where a high etching selectivity of Pt/SiO2 is obtained, platinum can be etched with thin SiO2 etching masks. By optimizing both the thickness of the SiO2 mask and the etching time, platinum can be etched without any residue from the redeposition of the etching products.
Ultrahigh vacuum arcjet nitrogen source for selected energy epitaxy of group III nitrides by molecular beam epitaxy
Authors: Grunthaner F. J. , Bicknell-Tassius R. , Deelman P. , Grunthaner P. J. , Bryson C. , Snyder E. , Giuliani J. L. , Apruzese J. P. , Kepple P.
Published: July 2002

The key technical challenge in the molecular beam epitaxial (MBE) growth of group III nitrides is the lack of a suitable source of incorporatable nitrogen. In contrast with the growth of the other III–V compound semiconductors by MBE, direct reaction of N2 with excess group III metal is not feasible, because of the high bond strength of dinitrogen. An incorporatable MBE nitrogen source must excite N2 forming a beam of atomic nitrogen, active nitrogen (N2*), or nitrogen ions. rf and electron cyclotron resonance sources use electron impact excitation to obtain atomic nitrogen and in the process generate a wide variety of excited ions and neutrals. Experiments have shown that ionic species in the beam degrade the morphology of the epitaxial layer and generate electrically active defects. Recent theoretical studies have predicted that ground state atomic nitrogen will successfully incorporate into the growing GaN surface, while atomic nitrogen in either of the excited doublet states will lead to etching. In this article, we report on the development of an ultrahigh vacuum-compatible arcjet source which uses an electric arc to thermally dissociate N2. The thermal excitation mechanism offers selective excitation of nitrogen and control of kinetic energy of the active species. This source has been fabricated from refractory materials and uses two stages of differential pumping to minimize the pressure in the growth chamber. The arcjet has been reliably operated at power levels of 10–300 W, with no visible degradation of the thoriated tungsten cathode after 300 h. No metal contaminant lines can be found in the optical emission spectrum. Using an Ar-seeded beam for calibration of the optical spectrum, we find that the arcjet plasma is far from local thermodynamic equilibrium, and show that the fraction of atomic nitrogen in the beam ranges from 0.3% to 9%. This corresponds to a flux of 0.1–4 monolayers per second at the MBE sample location. With an articulated Langmuir probe sampling the beam at the MBE growth position, we find a positive ion flux of less than 4×10−9 A/cm2, a maximum ion kinetic energy of 3.5 eV, a median electron energy of 1 eV, and a maximum electron energy of less than 4 eV. With increasing arcjet power, the ion and electron fluxes increase and the ion energy distribution shifts to lower energies. No change in the electron spectrum is observed. Quadrupole mass spectra of the ion flux measured on the arcjet axis show that the N+/N2+ ratio has a maximum at an arcjet power of about 35 W.
Magnetization of ultrathin Fe films deposited on Gd (0001)
Authors: Sherwood T. S. , Mishra S. R. , Popov A. P. , Pappas D. P.
Published: July 2002

The magnetization of ultrathin (1.5–6 ML) Fe films deposited on Gd (0001) was studied using spin polarized secondary electron emission spectroscopy. An anomalously high Curie temperature (>320 K) was observed for very low coverages of Fe (1.5 ML). The anomalously high Curie temperature results in part from the strong antiferromagnetic exchange interaction between the Fe and Gd at the interface. In addition, a spin reorientation transition of the Fe magnetization from in-plane to perpendicular was observed as the temperature is increased for Fe thickness between 1.5–4 ML. The spin reorientation is attributed to the competition between the perpendicular anisotropy of the Fe overlayer and the exchange interaction with the in-plane Gd bulk magnetization. Therefore the effects of varying the thickness of the Gd and hence the bulk Curie temperature on the spin reorientation transition can be studied.
Ammonia decomposition on Ru(001) using gas-phase atomic hydrogen
Authors: Hagedorn Christopher J. , Weiss Michael J. , Weinberg W. Henry
Published: July 2002

Using temperature programmed desorption and high-resolution electron energy loss spectroscopy, we have studied the (partial) decomposition of multilayer NH3 on the hexagonally close packed surface of ruthenium, Ru(001), at 100 K using gas phase atomic hydrogen. Thermal desorption spectra have been collected at various hydrogen atom fluences in order to characterize the evolution of the surface overlayer. At steady-state, the formation of a stable surface overlayer, consisting primarily of NH3, NH, and H, as well as a small concentration of N adatoms, is observed. Thermal desorption spectra, of the steady-state overlayer, show two separate hydrogen desorption peaks. One peak can be assigned to recombinative desorption of hydrogen from the surface while the other is assigned to the reaction-limited decomposition of surface NH groups. Annealing this overlayer to 450 K leaves a relatively high nitrogen adatom surface coverage of θN=0.30.
Electron beam directed vapor deposition of thermal barrier coatings
Authors: Hass D. D. , Parrish P. A. , Wadley H. N. G.
Published: July 2002

Electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) are currently applied to gas turbine engine components to improve engine durability but, in the future, may be used to increase engine efficiency. These coatings are costly to apply in part because of the low evaporated materials utilization efficiency (a few percent) and the relatively slow rate of deposition (∼5–10 μm min−1). Here, an emerging electron beam directed vapor deposition (EB-DVD) approach is explored as a method for producing these TBCs. The EB-DVD technique combines low vacuum (10−3–10 Torr) electron beam evaporation with a carrier gas jet to rapidly create and efficiently transport evaporant to a deposition surface. Studies of the deposition of yttria partially stabilized zirconia (YSZ) and reactively formed zirconia coatings have been performed and the composition, microstructure, phase content and crystallographic texture of deposited layers are reported. The results indicate EB-DVD’s ability to form compositionally controlled YSZ and zirconia coatings, with a 50% or greater materials utilization efficiency, at a rate in excess of 50 μm min−1. The EB-DVD films have a columnar microstructure, phase content and crystalline texture similar to that of the EB-PVD coatings used for high performance gas turbine applications.
High-rate deposition of cBN films by ion-beam-assisted vapor deposition
Authors: Sueda Minoru , Kobayashi Toshiro , Rokkaku Tadashi , Ogawa Makoto , Watanabe Toshiya , Morimoto Satoshi
Published: July 2002

Cubic boron nitride (cBN) films were deposited by ion-beam-assisted vapor deposition method. Effects of the ion current density, the boron deposition rate, the composition of the supplied gas into the ion source on the cBN formation range and deposition rate at an ion energy of 0.5 keV were studied. cBN films were obtained at almost constant ratio of boron deposition rate to ion current density, depending on the composition of the supplied gas. The deposition rate of cBN films, whose maximum was 0.5 nm s−1 increased almost linearly with increasing the boron deposition rate. The grain sizes of the obtained films were increased with increasing the cBN deposition rate. The diffraction patterns from cBN (111), (220), (311), and (222) were observed on the transmission electron diffraction.
Molecular dynamics simulations of Cl2+ impacts onto a chlorinated silicon surface: Energies and angles of the reflected Cl2 and Cl fragments
Authors: Helmer B. A. , Graves D. B.
Published: July 2002

We describe the energy and angle distributions of reflected Cl2 molecules and Cl atom fragments obtained from molecular dynamics (MD) simulations of Cl2+ ion impacts onto a chlorinated silicon surface. We simulated Cl2+ ion impacts onto a silicon surface with 1 monolayer (ML) of adsorbed Cl atoms. The ion incident energies Ei were 20, 50, and 100 eV. We varied the ion incident angles θi from 0° to 85° from the surface normal. We report the Cl2 dissociation probability, as well as the scattering probabilities for both the Cl2 molecules and the Cl atom fragments. The effects of Ei and θi on these quantities are discussed. For the 100 eV Cl2+ impacts with θi⩾75°, we describe the distributions of energies Er and angles (polar θr and azimuthal φr) for the reflected Cl2 molecules and Cl atom fragments. In addition, we compare the average energies of the reflected molecules and atoms with the predictions of two simple models based on the binary collision approximation.
Low-temperature large-grain poly-Si direct deposition by microwave plasma enhanced chemical vapor deposition using SiH4/Xe
Authors: Shindo Wataru , Sakai Shigefumi , Tanaka Hiroaki , Zhong Chuan Jie , Ohmi Tadahiro
Published: July 2002

Polycrystalline silicon is grown at a temperature of 300 °C by microwave-excited plasma enhanced chemical vapor deposition using SiH4/Xe. The grain size measured by x-ray diffraction is about 25 nm. High-density (>1012 cm−3) plasma having very low electron temperature (<1 eV) is excited by microwave irradiation using radial line slot antenna. We present the implementation of this system for the growth of poly-Si. Low-energy (3 eV), high-flux ion bombardment utilizing xenon ion on a growing film surface activates the film surface and successfully enhances surface reaction/migration of silicon, resulting in high quality film formation at low temperatures.
Modeling and characterization of logarithmic complementary metal–oxide–semiconductor active pixel sensors
Authors: Tabet Muahel , Tu Nick , Hornsey Richard
Published: July 2002

We present a detailed analysis of logarithmic active pixel sensors (log-APS) to be used in complementary metal–oxide–semiconductor (CMOS) imagers for real-time on-chip motion detection. Based on an equivalent circuit model for CMOS-compatible photodiodes, an HSPICE simulation has been used to characterize different configurations of these sensors under various conditions of light intensities and switching speeds. These investigations are supported by the experimental results obtained from the chip fabricated with standard 0.5 μm CMOS technology. It is concluded that more robust on-chip motion detection in CMOS imagers can be achieved with careful design of its log-APS photocircuits that considers the issues discussed here.
Design and performance of an x-ray lithography beam line at a storage ring
Authors: Haelbich R. P. , Silverman J. P. , Grobman W. D. , Maldonado J. R. , Warlaumont J. M.
Published: July 2002

A beam line for x-ray lithography using synchrotron radiation (SR) has been built at the VUV storage ring of the National Synchrotron Light Source and is now in operation. The high intensity and good collimation of SR overcome the problems of low throughput and resolution-limiting penumbra associated with using conventional x-ray sources. The design of a beam line for SR has to deal with two problems. First, the beam line must meet the ultrahigh vacuum standards of the storage ring, and second, the emitted radiation is horizontally uniform but very nonuniform vertically. The beam line optics consist of an oscillating cylindrical mirror that scans the reflected light vertically over the exposure area and collimates the incident radiation horizontally, thus increasing the intensity by a factor of 3. We will describe the vacuum system, the beryllium window that separates the exposure chamber from the beam line, and the vacuum protection of the ring. We will show the measured uniformity of illumination. The energy density incident onto the resist as well as the energy absorbed in the resist have been determined and will be compared with the calculated power distribution. First exposures show that features down to 0.25 μm can be copied into PMMA with an aspect ratio of 10 to 1 using a 40 μm mask-to-wafer separation.
Lithographic evaluation and processing of chlorinated polymethylstyrene
Authors: Hartney M. A. , Tarascon R. G. , Novembre A. E.
Published: July 2002

Chlorinated polymethylstyrene has been shown to behave as a negative resist upon electron beam exposure. Polymethylstyrene was prepared by both anionic and free radical techniques and chlorinated to produce a series of polymers with a range from 0 to 2.5 chlorine atoms per polymer repeat unit (0 to 42.5 wt. % chlorine). Sensitivity and contrast were found to be a function of chlorine content, molecular weight, and polydispersity. Sensitivity was maximum for materials with 0.6 to 0.9 chlorine atoms per repeat unit, depending on the chlorination technique chosen. Nearly monodisperse polymers exhibited much higher contrast than broader molecular weight materials and showed improved resolution. Thermogravimetric analysis was employed to study solvent removal from spun films and to determine prebaking and postbaking conditions. A chlorinated polymethylstyrene (0.92 chlorines/monomer unit) with a molecular weight of 70 000 and polydispersity of 1.06 had a sensitivity of 2.0 μC/cm2 and contrast of 2.0. This material demonstrated half-micron resolution for line and space patterns in both single level and trilevel processing.
Proximity effect reduction in high voltage electron-beam lithography by bias exposure method
Authors: Nishimura E. , Takigawa T. , Abe T. , Katoh Y.
Published: July 2002

The proximity effect reduction was achieved by electron beam (EB) uniform exposure (bias exposure) on the target covered with PMMA resist of 1 μm in addition to conventional high voltage EB writing. At an acceleration voltage of 50 kV and a dosage of 50 μC/cm2, a pattern size error of 0.5 μm pattern due to the proximity effect amounted to 0.25 μm, which was improved to 0.12 μm by bias exposure. When dosage was large, the pattern size error was further improved by bias exposure. For 50 kV and 140 μC/cm2 writing, 0.25 μm pattern including isolated window, line and window, and isolated line was formed with an accuracy of ±0.025 μm. The pattern size error for conventional EB writing was almost independent of dosage. For 20 kV and 20 μC/cm2 writing, the pattern size error was hardly improved by bias exposure.
Study of heteroepitaxial interfaces by atomic resolution electron microscopy
Authors: Otsuka N. , Choi C. , Kolodziejski L. A. , Gunshor R. L. , Fischer R. , Peng C. K. , Morkoç H. , Nakamura Y. , Nagakura S.
Published: July 2002

Two heteroepitaxial interfaces, GaAs/Si and CdTe/GaAs, have been studied with a 1 MV ultrahigh vacuum, high voltage electron microscope. High resolution images have shown the presence of two types of misfit dislocations in the GaAs/Si interface. One has a Burgers vector parallel to the interface, and the other a Burgers vector inclined from the interface. The slight tilting of the substrate surface from the (100) plane significantly affects the distribution of the two types of misfit dislocations in the interface. The mechanism of the dramatic reduction of the density of threading dislocations in the GaAs epilayer by tilting the substrate surface is explained based on this observation. The atomic structure in the interface between the (111) CdTe epilayer and the (100) GaAs substrate has been investigated with high resolution images taken along two different orientations. High resolution images of the CdTe epilayer which were taken along the [011̄] direction have shown asymmetrical images of Cd and Te pairs. Image calculations have been carried out in order to determine the polarity of the epilayer from these observed images.
Ion and neutral atomic and cluster sputtering yields of molybdenum
Authors: Pellin M. J. , Husinsky W. , Calaway W. F. , Burnett J. W. , Schweitzer E. L. , Young C. E. , Jo/rgensen B. , Gruen D. M.
Published: July 2002

The yield of neutral and ionized Mo, Mo2, and Mo3 sputtered from a Mo target by 4-keV Ar+ has been measured in the surface analysis by resonance ionization of sputtered atoms (SARISA) machine. Ionization spectroscopy combined with time-of-flight (TOF) secondary ion mass spectrometry (SIMS) allowed us to obtain for the first time absolute sputtering yields and ionization fractions of sputtered atoms and metal clusters. Unlike sputtered atomic species, Mo clusters have been found to be sputtered with large ion fractions. The sputtering yield of Mo clusters is very sensitive to oxygen on the surface, i.e., even small amounts of oxygen on the surface identified by Mo+ and MoO+ peaks in the SIMS spectrum, reduce the cluster yield substantially. A broad structureless absorption band was observed for sputtered Mo2 molecules indicating substantial rovibronic excitation as predicted by theoretical models.
Damage to resist structures during scanning electron microscope inspection
Authors: Erasmus S. J.
Published: July 2002

In order to obtain a high resolution scanning electron microscope (SEM) image of a resist pattern, it is necessary to use a relatively large electron dose, but many resists change in size and shape when irradiated. The dimensional stability of several common resists as a function of electron dose and electron energy has been investigated. An optimum dose, which is a compromise between resolution and radiation damage can be chosen. It is shown that the optimum dose should be used when inspecting radiation sensitive materials, because a micrograph taken at too high a dose will be distorted, but may not exhibit obvious signs of damage.
Imaging microanalysis of surfaces with a focused gallium probe
Authors: Chabala J. M. , Levi-Setti R. , Wang Y. L.
Published: July 2002

A focused gallium scanning ion probe is used, in conjunction with an efficient secondary ion mass spectrometry system, to obtain high lateral resolution mass-resolved images of specimen surfaces. The Ga+ beam, extracted from a liquid metal ion source, is accelerated to 40 keV and focused to a spot with a minimum diameter of ∼20 nm (ultimate resolution). The secondary ion handling system is briefly discussed; the secondary ion detection efficiency is 0.2%. Applications relevant to integrated circuit inspection and evaluation are presented, including high signal statistics elemental images of the metallizations and substrate of submicrometer devices, and examples of the detection of circuit flaws.
The angular dependence of the emission characteristics for a Pd2As liquid-alloy ion source
Authors: Rao S. , Bell A. E. , Schwind G. A. , Swanson L. W.
Published: July 2002

An extensive study of the Pd2As liquid-alloy ion source (LAIS) as a function of angle has been carried out. The main goal of this investigation was to gain a better understanding of the mechanism of ion formation and the emission characteristics of the Pd2As LAIS. A point of interest was the calculation of the angular dependence of the As+++ and As++ intensities. These results could then be used in connection with the post-ionization theory to predict the angular dependence of the electric field. The investigation showed that up to angles of 20°–30°, the cluster species of PdAs and the monomer Pd and As ions exhibited little variations in intensity with angle at a current of 10 μA. Beyond these angles, they showed a rapid falloff in intensity. The emission from the source was quite stable at temperatures of 1080–1160 K, lasting for around 40–60 h at a maximum current of 20 μA. The amount of As which was emitted in the form of different species ranged from 24% at 4 μA to about 26% at 20 μA. The total composition for each ion species was obtained by summing the ion current increments at each angle over the total hemispherical emission region up to the maximum angle measured.
Disintegration of TiSi2 on narrow poly-Si lines at high temperatures
Authors: Norström H. , Maex K. , Vandenabeele P.
Published: July 2002

The thermal stability of TiSi2/poly-Si structures with narrow lines has been studied as a function of the dopants introduced into the poly-Si (i.e. boron or arsenic) in the temperature range from 700 °C to 950 °C. The silicide layer was formed by rapid thermal processing (RTP) in nitrogen via a solid–solid reaction between titanium and poly-Si. The integrity, upon heat treatment, of the TiSi2 film on large areas was investigated by Rutherford backscattering spectroscopy (RBS) analysis, plan-view scanning electron microscopy (SEM), and cross-sectional SEM studies. Electrical information about the thermal stability of the bilayer was obtained from sheet resistance measurements on Van der Pauw structures in combination with linewidth measurements of bridge resistors with a nominal width between 0.8 and 1.5 μm. To provide for statistical variation about one hundred measurements were collected for each linewidth and temperature setting. The results clearly show that the thermal stability of the bilayer is a function of the amount and type of dopants in the polysilicon, favoring the use of high levels of arsenic. Moreover, the thermal stability was observed to be affected by the linewidth, since at the temperature for onset of degradation (above 900 °C), narrow lines were found to disintegrate at a much higher rate than wider ones. Cross-sectional SEM and TEM micrographs of the polycide lines clearly reveal the TiSi2/poly-Si interface to suffer from bowing. The effect was observed to be more pronounced on narrow undoped and boron-doped polycide lines. Both the narrow line disintegration and the bowing effect of polycide structures can have important implications for submicron very large scale integrated (VLSI) technologies.
Radio frequency plasma etching of Si/SiO2 by Cl2/O2 : Improvements resulting from the time modulation of the processing gases
Authors: McNevin S. C.
Published: July 2002

The etching of poly-Si and its selectivity over gate oxide SiO2 were measured for both Cl2 and Cl2/O2 plasmas and the experimental data indicate that modulation of the processing gases increases the Si/SiO2 selectivity while decreasing the unwanted deposition. The best results to date have been Si etch rates of ∼1000 Å/min and Si/SiO2 selectivities of ∼50, and it has been demonstrated that the Si/SiO2 selectivity is critically related to the presence of photoresist. A qualitative model for these results is proposed which appears to fit these observations. In this model, hydrocarbon fragments from sputtered photoresist reduces the SiO2 to Si, with a corresponding decrease in the Si/SiO2 etching selectivity. This carbonaceous material can be removed by the oxygen before it causes etching damage to the SiO2. Oxygen, unfortunately, can also react with the etching reaction products (e.g., SiCl4 ) to form SiO2 and the Si oxy-chlorides (Si2OCl6, Si3OCl8 ) which deposit on the wafer. The experimental evidence indicates, however, that this unwanted deposition can be minimized by alternating the Cl2 and O2 gases, rather than by running them both at a constant pressure as is typically done. Of most immediate interest is the fact that this modulation improvement can be achieved on time scales (≳1 s) which are attainable with the fairly slow residence times available in present generation hex etchers.
State-resolved laser probing of As2 in a molecular-beam epitaxy reactor
Authors: Smilgys Russell V. , Leone Stephen R.
Published: July 2002

Results are presented on the first state-resolved optical detection of As2 in a molecular-beam epitaxy (MBE) reactor. Using the technique of laser induced fluorescence (LIF) on the A 1∑+u–X 1∑+g transition, the gas phase populations of vibrational and rotational states of As2 emanating from a commercial As4 oven-cracker source are probed. A Boltzmann fit of the populations of the first four vibrations indicates that these states are thermalized to the source temperature (source: 1050±25 K; vibrations: 1020±100 K). Likewise, the rotational manifold of each vibration is consistent with thermalization at the same temperature. The sensitivity of the LIF technique is sufficient to characterize a flux of 3×1014 As2 cm−2 s−1. Therefore, the method is capable of being an in situ real-time MBE diagnostic. Optical detection may provide complementary information to reflection high-energy electron diffraction (RHEED) that would not otherwise be available. Future applications of this technique may lead to new insights into epitaxial growth processes.
Scanning tunneling microscope–laser fabrication of nanostructures
Authors: Yau S.-T. , Saltz D. , Nayfeh M. H.
Published: July 2002

We have developed a technique to write nanometer-scale features on surfaces. The technique combines two of the most advanced technologies: the laser and the scanning tunneling microscope (STM). Laser radiation is used to break the chemical bonds of trimethylaluminum to free aluminum atoms in the region of the tunneling gap of the STM. The atoms are subsequently selectively excited and ionized. The ions are then driven softly toward the surface where they are deposited by the field in the tunneling gap of the microscope. Since the field of the tip can be confined to a few nanometers, the writing can be controlled with such resolution. The technique is also capable of filling holes and addressable nondestructive erasing.
Semiconductor characterization by scanning force microscope surface photovoltage microscopy
Authors: Weaver J. M. R. , Wickramasinghe H. K.
Published: July 2002

A technique is described for the measurement of surface photovoltage (SPV) on semiconducting samples using the attractive-mode scanning force microscope. The use of SFM potentiometry1 permits microscopic measurement of surface photovoltage to be made in air with a spatial resolution of a few tens of nm and voltage resolution of better than 1 mV. Thus, with a spatial resolution only 1 order of magnitude worse than scanning tunneling microscopy measurements,2 atomic force microscopy (AFM) is seen to be a good choice in measurements on devices or other structures where measurement under ambient is desirable or tolerable. Historically, SPV has permitted the observation of a wide range of features in semiconducting samples, including mapping of dopant concentration, sodium accumulation, local charge, dislocations, precipitates, stacking faults, grain boundaries and microcracks, local resistivity, recombination time, band gap shifts (for instance in heterostructures), and stress.3 Experimental results will be presented which demonstrate the application of AFM/SPV to microcracking, dopant profiling and dislocation structure.
Negative resistance characteristics in tunneling experiments on metallic samples
Authors: García Ricardo
Published: July 2002

Scanning tunneling microscopy experiments on specific semiconducting samples show negative resistance characteristics. It is predicted that similar behavior can be achieved on metallic samples. The requirement for those samples is the existence of a bulk band gap for electron momentum perpendicular to sample surface. Calculations for a tip-vacuum-Ni(100) junction have been performed. In this system, negative resistance characteristics arise due to the presence of localized surface barrier states. Another property of those systems is that negative resistance disappears with increasing temperature.
Scanning tunneling microscopy of photoexcited carriers at the Si(001) surface
Authors: Cahill David G. , Hamers R. J.
Published: July 2002

A scanning tunneling microscope is used to probe changes in the surface potential created by photoexcited carriers. At small tunneling currents, the dependence of surface photovoltage on laser intensity agrees with a model based on the transport of majority carriers through the depletion layer. At larger values of the tunneling current, charging of the surface by the current modifies the surface photovoltage because of changes in band bending near the probe tip. Spatial variations in the surface photovoltage are observed on a length scale comparable to the width of the depletion layer. Variations on an atomic scale are also observed and are interpreted as an increase in surface charging at specific defects on the Si(001) surface.
Resist stripping in an O2+H2O plasma downstream
Authors: Fujimura Shuzo , Shinagawa Keisuke , Suzuki Miki T. , Nakamura Moritaka
Published: July 2002

Characteristics are reported for a resist stripping process downstream of an oxygen plasma to which water vapor is added. The effects of additive water vapor are an increase in atomic oxygen concentration in the plasma, a decrease in activation energy of ashing reaction, and protection of semiconductor devices from the sodium contamination from the resist. The atomic oxygen concentration was approximately doubled by mixing 10% H2O into the oxygen plasma. The activation energy of the ashing reaction to the resist made from novolak resin decreased from about 0.5 to 0.39 eV by the addition of water vapor of more than 1%. The activation energy of hydrogen abstraction from hydrocarbon molecules by an OH radical was lower than that by a ground state oxygen atom [O(3P)], which was the dominant ashing species in the oxygen plasma downstream, and that by an atomic hydrogen was higher than that by the ground state oxygen atom. Moreover, the activation energy in the downstream ashing of the oxygen plasma added to which was 1% water vapor was lower than that of the oxygen plasma to which 3% hydrogen was added, even though the relative concentration of atomic hydrogen in each plasma was equal. Therefore the decrease in the activation energy was probably due to the OH radical generated in the plasma and the downstream. Sodium atoms in the resist were blocked from entering into the semiconductor devices in the stripping process by use of the O2+H2O plasma downstream. Thus sodium was not removed and remained on the wafer surface after resist stripping. Also, by adding N2 or CF4 to the O2+H2O plasma, we can increase the ashing rate without losing the above characteristics.
Performance measurements of a 1-keV electron-beam microcolumn
Authors: Muray L. P. , Staufer U. , Kern D. P. , Chang T. H. P.
Published: July 2002

A complete 1-keV electron-beam microcolumn, measuring only 2.5 mm in length, has been assembled and tested. The microcolumn combines a scanning tunneling microscope aligned field-emission source with a miniaturized octupole scanner and a microfabricated einzel lens. Expected performance of this configuration, at a working distance of 1 mm and semiconvergent angle of 2.5 mrad, has been calculated to be a probe size of 8 nm with current density exceeding 104 A/cm2. The microcolumn has been successfully operated at 1 keV in scanning transmission mode using a 1-μm grid sample. Images were acquired with scan fields ranging from 10 to 100 μm and preliminary resolution measurements indicated Gaussian beam diameter of 200 nm. Significant improvements are expected in the near term.
Properties of borophosphosilicate glass films deposited by different chemical vapor deposition techniques
Authors: Rojas S. , Gomarasca R. , Zanotti L. , Borghesi A. , Sassella A. , Ottaviani G. , Moro L. , Lazzeri P.
Published: July 2002

Borophosphosilicate glass films prepared by chemical vapor deposition techniques based on atmospheric pressure, low pressure with liquid and gaseous sources, and low pressure plasma enhanced processes in the temperature range of 390–680 °C have been studied. Films with low B (1.5 wt %) and high P (9.0 wt %) content were used for this study. To evaluate the effect of different thermal treatments, the films were annealed in a horizontal furnace at 920 °C for 30 min in three different ambients, i.e., N2, N2/O2, and H2/O2 and with rapid thermal annealing at 1050 °C for 10 s in a N2 ambient. The main properties of the as-deposited and annealed samples such as elemental content, thickness uniformity, shrinkage, density, refractive index, wet etch rate, stress, step coverage, and reflow are reported. Infrared absorption measurements were performed to study the water and Si–OH group presence in the films and P=O, B–O, Si–O bond behavior and interactions. The best physical and chemical film properties were obtained using liquid sources in a low pressure system. These films were tested as the interlevel dielectric in 1 Mbit erasable programmable read-only memory devices and good electrical performances were obtained, comparable with atmospheric pressure deposited films.
Fabrication and carrier transport phenomena of one-dimensional quantum wires of p-type silicon
Authors: Iwano H. , Zaima S. , Koide Y. , Yasuda Y.
Published: July 2002

Fabrication of p-type Si quantum wires in n-type substrates has been performed by selective implantation of focused ion beams of Ga. It has been confirmed that this method and associated device structure have the advantage of being able to control the diameter of quantum wires. This is accomplished by applying a reverse substrate bias to change the depletion width of the pn junctions. The conductance shows a distinctive temperature dependence of ln(σ)∝T−1/2, which coincides with the characteristic of one-dimensional (1D) hopping conductance. At 4.2 K, we have observed electrical properties characteristic of 1D systems, such as conductance dips in the wire-conductance versus substrate-bias characteristics and a positive magnetoconductance in the magnetic field range up to 5 T.
Recombination lifetime in InAs–Ga1−xInxSb superlattices
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Miles R. H. , Chow D. H.
Published: July 2002

We report an experimental investigation of Shockley–Read and Auger lifetimes in InAs–Ga1−xInxSb and InAs–GaSb superlattices, based on measurements of the photoconductive response to excitation by a frequency-doubled CO2 laser (4.63 μm) at intensities up to 100 kW/cm2. Results at 77 K for low excitation levels yield Shockley–Read lifetimes between 0.13 and 6 ns. The scaling of the lifetime with carrier concentration also provides the first determinations of Auger coefficients in narrow-gap type II superlattices: γ3≊8×10−25 cm6/s at 300 K and γ3≊1.3×10−27 cm6/s at 77 K. The observed Auger lifetime at 77 K is two orders of magnitude longer than that in Hg1−xCdxTe with the same energy gap, which has highly favorable implications for InAs–Ga1−xInxSb superlattices in both IR detector and nonlinear optical applications.
Gas source molecular beam epitaxy growth of ZnSe on novel buffer layers
Authors: Lu K. , Fisher P. A. , House J. L. , Ho E. , Coronado C. A. , Petrich G. S. , Kolodziejski L. A. , Hua G.-C. , Otsuka N.
Published: July 2002

Thin films of ZnSe on pseudomorphic and partially relaxed (In,Ga)P buffer layers (on GaAs) have been examined; both epilayers were grown by gas source molecular beam epitaxy. The ZnSe layers were grown using elemental Zn and thermally decomposed H2Se. The II–VI nucleation occurred following an ex situ transfer in air of the As-passivated (In,Ga)P buffer layers, grown using In, Ga, and cracked PH3. Microstructural characterization of the II–VI/III–V heterostructures was performed with high-resolution x-ray diffraction and transmission electron microscopy. The (511) reflection of the x-ray rocking curves was used to measure the residual strain in the ZnSe/(In,Ga)P/GaAs structures, and to determine the alloy composition of the (In,Ga)P. The (400) reflection of the x-ray diffraction rocking curves indicated peaks having full width at half-maximum of 130 and 18 arcsec for the relaxed ZnSe on thin (1 μm) pseudomorphic (In,Ga)P buffer layers, respectively. Transmission electron microscopy confirmed the relaxed or pseudomorphic nature of each heterolayer. Thicker (≳4 μm) In0.52Ga0.48P buffer layers were still not completely relaxed, and exhibited a residual lattice mismatch of approximately 0.11% between the ZnSe layer and the In0.52Ga0.48P buffer layer. Relatively thick (1–2 μm) ZnSe films had surface morphologies that were featureless when examined by Nomarski microscopy and scanning electron microscopy. Low-temperature photoluminescence spectra originating from the ZnSe films on the partially relaxed (In,Ga)P buffer layers were dominated by donor-bound and free-excitonic features with each exhibiting nearly the same intensity. Luminescence from extended defects (the Y0 and Iv transitions) within the ZnSe layer, and luminescence originating from the (In,Ga)P buffer layers, were also observed.
Integration of materials and processes for reliable silicon interconnections*
Authors: Paraszczak J.
Published: July 2002

As device densities in integrated circuits have grown, the number of connections between them has followed, resulting in larger chips with increased numbers of layers of metal wiring. Traditionally these layers of wiring were fabricated using aluminum and its alloys for the conductor and silicon oxide as the dielectric and insulator. New combinations of dielectrics and metals promise improved performance and increased reliability, which can require alternative methods of fabrication.
Modification of Al/GaAs(001) Schottky barriers by means of heterovalent interface layers
Authors: Cantile M. , Sorba L. , Faraci P. , Yildirim S. , Biasiol G. , Bratina G. , Franciosi A. , Miller T. J. , Nathan M. I. , Tapfer L.
Published: July 2002

The Schottky barrier height in Al/Si/GaAs(001) junctions grown by molecular-beam epitaxy was determined in situ by means of x-ray photoemission spectroscopy and ex situ through current–voltage and capacitance–voltage measurements. We found that the barrier height can be tuned from a minimum value of 0.2 eV to a maximum of 1.1 eV provided that a sufficiently high As or Al flux is employed during the growth of the Si interface layer. The minimum and maximum values of the barrier are already established for Si layer thicknesses in the 1–2 monolayer range. We propose that the changes in barrier height derive from the establishment of a Si-induced local interface dipole. The magnitude and orientation of the dipole reflects the detail of the atomic reconstruction achieved at the interface in the different growth conditions.
High temperature deposition of SiN films using low pressure chemical vapor deposition system for x-ray mask application
Authors: Ohta Tsuneaki , Kumar Rakesh , Yamashita Yoshio , Hoga Hirosi
Published: July 2002

SiN films for x-ray mask membranes were prepared using a low pressure chemical vapor deposition system designed for high temperature deposition and low impurity incorporation. The physical and optical properties of the films such as stress, uniformity, optical transmittance, and absorption were investigated. Film composition and impurities were also evaluated. The SiN film deposited at a substrate temperature of 1000 °C showed suitable properties for x-ray mask membrane, such as well controlled tensile stress of about 5×107 Pa, high optical transmittance over 95% at 500 to 800 nm, and low impurity concentration.