bluuebunny/crossref_metadata_2025 huggingface dataset:
Instabilities of the reactive sputtering process involving one metallic target and two reactive gases
Authors: Martin Nicolas , Rousselot Christophe
Published: July 2002

The present article considers instability phenomena during the sputtering of a single metallic target of titanium in a reactive atmosphere involving argon+oxygen+nitrogen gases. Since the process using two reactive gases is much more complex than one reactive gas, the transition zone of the reactive mode must be defined taking into account oxygen and nitrogen mass flow rates. A two-dimensional representation delimiting boundaries of the instability region and depending on both mass flows is proposed for radio frequency and direct current (dc) polarization of the titanium target. This diagram provides operating conditions favorable to deposit oxy-nitride coatings with a modulated oxygen or nitrogen composition. It is also shown that the supply of one reactive gas affects consumption and behaviors of the other gas as well as its own characteristics. A critical region is then defined in which the process is trapped in reactive mode and can not go back to elemental conditions by changing the mass flow rate of only one reactive gas. Kinetics and pollution of the titanium surface are discussed from measurements of dc potential for various operating points. It is shown that comportments of oxygen and nitrogen towards metallic or poisoned target are interdependent and a surprising evolution of the time of pollution against oxygen and nitrogen introduction is observed. These original results are supported by optical emission spectroscopy experiments. Emission intensities of nitrogen and oxygen species can also be used to monitor the state of pollution of the titanium target and so to control instabilities of the two reactive gases sputtering process.
Silicon etching in NF3/O2 remote microwave plasmas
Authors: Matsuo P. J. , Kastenmeier B. E. E. , Oehrlein G. S. , Langan J. G.
Published: July 2002

The etching of silicon in remote microwave discharges fed with NF3/O2 has been investigated. In situ ellipsometry and x-ray photoelectron spectroscopy (XPS) were used to monitor surface effects, while mass spectrometry was used to monitor the gas phase dynamics. Varying the microwave power from 600 to 1400 W has little effect, due to the near complete dissociation of the NF3, even at lower powers. For discharges containing pure NF3, the poly-Si etch rate increases linearly with NF3 flow. When a low proportion of O2 (O2/NF3=0.1) is added to the discharge, the etch rate increases quickly to its maximum of ∼700 nm/min. With further O2 addition, this etch rate decreases below that observed for pure NF3 processing. The fluorine concentration in the processing region decreases for all O2 additions by a dilution effect. For pure NF3 discharges, XPS measurements reveal 1–2 nm thick, highly fluorinated reaction layers with a gradual loss of fluorine content as the NF3 flow is increased. Specimens processed with both NF3 and O2 show much less surface fluorination that decreases with increasing O2 content in the feed gas. At the etch rate maximum, the observed N (1s) signal is also maximized. The reaction layer thickness increases with added O2 and continues to more than 10 nm at O2:NF3 ratios greater than unity. We discuss the enhanced reactivity of the modified Si surface and compare our results with the role of admixed N2 into the CF4/O2 system. We also injected NO directly into the effluent of NF3 and CF4/O2 discharges. For fluorine rich discharges, NO removes the modified surface layer on Si and provides for an enhanced etch rate. In the oxygen rich regime, NO injection can increase both the etch rate and the reaction layer thickness. We will present a mechanism for the enhanced etching of Si in the presence of fluorine, oxygen and the NO molecule.
In situ atomic force microscope observation of initial stages of corrosion at 18Cr–8Ni stainless steel
Authors: Katsuki F. , Matsuda M. , Matsumoto M. , Tomida T.
Published: July 2002

Atomic force microscope (AFM) was applied to the investigation of the initial stages of corrosion at 18Cr–8Ni stainless steel. Surfaces of electrochemically or mechanically polished specimens were in situ observed by AFM in a 0.89 M NaCl solution or a 1 M buffered Na2SO4 solution while measuring potentiostatic polarization curves. The mechanical polishing resulted in a substantial increase in corrosion rates, and a dramatic change in surface morphology to a facet structure has been observed in a 0.89 M NaCl solution during an anodic potential sweep up to 0.5 V. The electrochemical polish or the anodic polarization in 1 M buffered Na2SO4 leads to a lower corrosion rate, and the transition from passive to transpassive corrosion states has been clearly detected by AFM as well as in potentiostatic polarization curves. The detailed in situ observation has revealed that the transpassive film is formed on the surface with an oriented rectangle morphology.
New approach for the fabrication of device-quality Ge/GeO2/SiO2 interfaces using low temperature remote plasma processing
Authors: Johnson R. S. , Niimi H. , Lucovsky G.
Published: July 2002

It has been shown that low temperature (300 °C) remote plasma enhanced processing can separately and independently control interface formation and bulk oxide deposition on silicon substrates. Plasma processing is followed by a low thermal budget thermal anneal, e.g., 30 s at 900 °C. In this article, this process has been modified and applied to germanium substrates to determine if it can provide a successful pathway to device-quality Ge–dielectric interfaces. The new process also employs a three-step process: (i) an O2/He plasma-assisted, predeposition oxidation of the germanium surface to form a superficial germanium–oxide passivating film, (ii) deposition of a SiO2 bulk film by remote plasma-enhanced chemical vapor deposition from SiH4 and O2, and (iii) a postdeposition anneal for chemical and structural relaxation. The resulting interfaces are improved by the predeposition, plasma-assisted oxidation step, but are still far too defective for device applications.
Intermixing in Stranski–Krastanov germanium overlayer on Si(100)
Authors: Kahng S.-J. , Ha Y. H. , Moon D. W. , Kuk Y.
Published: July 2002

The growth behaviors of Stranski–Krastanov Ge overlayers on the Si(100)-(2×1) surface were studied with a combination of scanning tunneling microscopy and medium energy ion scattering spectroscopy. At the growth temperature of 350 °C, as Ge coverage increases, the Si surface peak in the channeling spectra decreases due to the shadowing of Ge atoms and can be fitted by a simple growth model at the Ge coverage less than 4 monolayers. At Ge coverages between 4 and 8 monolayers, the Si surface peak shows a broad enhancement, which can be explained with the growth of hut pits and that of three-dimensional hut clusters at the expense of Ge wetting layers.
Characterization and performance improvement of secondary electron analyzers
Authors: Menzel E. , Brunner M.
Published: July 2002

The detection of voltage contrast in scanning electron microscopes requires the use of secondary (SE) analyzers that allow the SE spectrum shift to be determined accurately and with high signal-to-noise ratio. In order to improve the performance of a given analyzer, a characterization scheme has been developed that allows one to pinpoint critical detector parts and provides guidelines for design changes. Performance determining factors, e.g., the operation point of the analyzer, the contribution of backscattered electrons (BSE) and SEs generated by BSEs (tertiary electrons) to the background signal, and changes of the S-curve shape, are determined separately by using specially developed characterization techniques. The optimum analyzer operation point, where the signal difference between two sample voltages is a maximum, is determined by simultaneously varying the retarding voltage and the voltage at the sample. Reflecting the primary electron beam with a negatively biased electrode simulates BSEs and reveals areas of high tertiary electron generation. Replacing the sample by a low energy electron gun with a small energy spread simulates SEs. This allows a detailed energy resolution determination of the analyzer to be performed.
A large area deflection system with very low aberration
Authors: Kuo H. P. , Groves T. R.
Published: July 2002

A new deflector for electron or ion beam lithography is described. It combines the functions of focusing and deflection in a single unit. Focusing is accomplished by means of a uniform magnetic field oriented parallel with the optic axis of the system. A uniform electric field oriented perpendicular to the magnetic field provides the deflection capability. The optical properties, including the deflected spot size, are found from an exact solution to the nonrelativistic equations of motion. The third and fifth order aberrations are also derived. To third order, the aberration is identical with that of the uniform magnetic field alone, with no additional contribution from the electric field. This means that no growth of the spot occurs with deflection, and the beam size and shape are uniform over the entire deflection area. The system is telecentric, in that the beam intercepts the target plane at normal incidence. The focal surface is planar, and there is no distortion to third order. There is also no transverse chromatic aberration to this approximation. A practical implementation is proposed, based on a solenoidal field and a cylindrical deflector. The optical properties are analyzed numerically in the presence of electric and magnetic fringing fields, as occur with a conductive target plane and a system of finite length. A test case with a 20 kV beam, a 1.0 cm deflection area, and a 10 mrad aperture semiangle are considered. The maximum spot size with dynamic focus and astigmatism corrections is 0.17 μ. An energy spread of 1.0 eV is assumed, although much larger spreads are tolerable. This makes the system attractive for ion beam work. For a 1 cm square deflection area, the system offers an increase in addressable resolution elements by a factor of 50 over a more conventional electrostatic octupole deflector.
Large surface Fermi level shift in high temperature annealed metal–insulator–GaAs structures prepared in the presence of oxygen
Authors: Blanchet R. , Santinelli C. , Chave J. , Garrigues M. , Krawczyk S. , Viktorovitch P.
Published: July 2002

Experiments were conducted on two types of GaAs substrates according to the surface treatment which either resulted in oxidation of the substrate (chemical etching) or in nearly oxygen-free interface (exposure of the substrate to a hydrogen/nitrogen mixture plasma). Owing to appropriate choices of the sequences of technological steps in the preparation of MIS samples, which include substrate treatment, deposition of the insulator (alumina obtained by reactive evaporation), and high temperature anneal (around 550 °C), it is given evidence of the great importance of the high temperature annealing step, solely responsible for the observed improvement in the electrical properties of the interface (as derived from capacitance and conductance measurements).
Hydrogenic impurity states in a quantum well wire
Authors: Lee Johnson , Spector Harold N.
Published: July 2002

A variational calculation of hydrogenic impurity binding energies in quantum well wires has been performed. The binding of the hydrogenic impurity has been calculated as a function of the transverse dimensions of the wire. It is found that the binding energy of the hydrogenic impurity increases as the ratio of the Bohr radius of the impurity in a bulk semiconductor to the transverse dimension of the wire increases. To test the sensitivity of the binding energies to the trial wave function we have used in our calculations, we use a wave function of the same type to calculate the binding energy of hydrogenic impurities confined in a quasi-two-dimensional quantum well as a function of well width and compare our results for the binding energies to the results obtained by Bastard [Phys. Rev. B 24, 4714 (1981)].
Infrared laser-induced photodesorption and ultraviolet laser-induced thermal desorption of methylfluoride and carbon monoxide from polycrystalline copper
Authors: Hussla Ingo , Viswanathan R.
Published: July 2002

Preliminary results of CO2 laser-induced photodesorption and KrF excimer laser-induced thermal desorption of methylfluoride from mixtures with carbon monoxide coadsorbed on polycrystalline copper surfaces are reported. The data indicate that selective desorption of CH3F in the presence of CO-coadsorbate is feasible by thermal desorption using a KrF pulse laser, due to differences in absorbed laser power density desorption threshold of the coadsorbate components. Photodesorption of CH3F is accomplished by vibrational excitation of the ν3 mode of adsorbed CH3F, while simultaneous desorption of CO is not observed.
O2 plasma-converted spin-on-glass for planarization
Authors: Butherus A. D. , Hou T. W. , Mogab C. J. , Schonhorn H.
Published: July 2002

So-called ‘‘spin-on-Glass’’ materials (herein abbreviated as SOG) have generated a considerable amount of interest in the field of microelectronic materials and processing. The materials have been used for some time as doping sources, and have recently been investigated for use as dielectric layers, planarizing layers, RIE etch stops in multilevel lithography processes, and as final passivation layers. We report here the use of a commercially available SOG, Owens-Illinois GR-650 as a planarizing layer. Additionally we report a process by which this material can be converted from the as-deposited organic polysiloxane material to an inorganic SiO2. This conversion is effected at low (≤100 °C) temperatures by an rf-generated oxygen plasma. This process is particularly attractive for fabricating devices when the higher temperatures of plasma deposited SiO2 (>250 °C) or thermally converted SOG (≊500 °C) cannot be tolerated.
Summary Abstract: Surface morphology of oxidized and ion-etched silicon by scanning tunneling microscopy
Authors: Feenstra R. M. , Oehrlein G. S.
Published: July 2002

Topographical changes induced by low-energy (<1 keV) ion beams are difficult to observe with conventional techniques such as scanning electron microscopy (SEM). However, such topographical changes can drastically alter the electrical properties of structures built on these surfaces, e.g., due to local changes in electric field distribution [D. J. DiMaria and D. R. Kerr, Appl. Phys. Lett. 27, 505 (1975)], and are an area of concern. We have used scanning tunneling microscopy (STM) to study the morphology of silicon (100) surfaces which have been subjected to low-energy argon-ion bombardment. The technique of STM as developed by Binnig and co-workers has recently proven to be a very valuable tool for measuring surface morphology on an atomic scale. We have obtained high resolution (0.5 Å vertical, and 10 Å lateral) topographic images which show roughening of the bombarded surfaces relative to unbombarded (control) samples. The bombarded samples display characteristic hillocks typically 50 Å in diameter and about 10 Å high.
Electron beam proximity printing: Complementary-mask and level-to-level overlay with high accuracy
Authors: Nehmiz P. , Zapka W. , Behringer U. , Kallmeyer M. , Bohlen H.
Published: July 2002

Electron-beam proximity printing (EBP) is a promising candidate for submicron lithography because it meets the stringent requirements for resolution, throughput, and image fidelity (here defined as registration and overlay). Registration and level-to-level overlay capabilities of EBP are reported in this paper. Two levels of a chip were exposed and processed subsequently, these levels represented by two different patterns in the same mask. Distortions of both patterns relative to each other, amounting up to several hundred nanometers, were detected. These distortions could be automatically compensated for during exposure to yield an average overlay better than 50 nm. Together with the low data scatter of 3σ<170 nm, this indicates high performance of the EBP registration and distortion compensation procedure.
Overlay measurements for x-ray lithography
Authors: Müller K.-H. , Burghause H.
Published: July 2002

The metrology in submicron lithography is an increasingly difficult task. Especially the control of the stability of the x-ray masks, which needs resolution better than 0.1 μm over a large area, supplies a lot of problems. Some of them can be investigated by double exposures evaluated with overlay measurement methods. We use a method that needs a minimum of process steps. Both exposures are made within the same resist. The resist patterns are measured directly. No additional processing step other than lithography and resist developing are necessary. We built an experimental alignment system for x-ray lithography in a vacuum chamber, so we can expose in vacuum or in a He atmosphere. A swivel-mounted microscope allows the observation of the alignment marks on the mask and on the wafer. With six motordriven screws we can adjust wafer to mask. With another setup it is possible to make tilted exposures. After the double exposure we measure the relative position of special metrology marks with light optics on an accuracy of 30 nm (3δ value). The assembly consists of a LEITZ linewidth measuring microscope, a high precision motordriven x-y-z table, and a microcomputer. The automatic measuring procedure is performed under the control of the computer. With these measuring and evaluation methods we could measure the alignment accuracy, and changes of the x-ray masks due to heating by the synchrotron radiation. It is also possible to compare the accuracy of two x-ray masks and to control the stability of the exposure system.
An improved trilevel resist system for submicron optical lithography
Authors: Gellrich N. , Beneking H. , Arden W.
Published: July 2002

A number of spin-on glasses (SOG) have been investigated with respect to their suitability for submicron pattern generation in a trilevel process for optical lithography. Some of them can be significantly improved so as to permit baking of both the bottom polymer and SOG at temperatures below 200 °C without the formation of cracks and allowing the use of inorganic developers. A trilevel resist system has been used in combination with a high numerical aperture lens (Zeiss lens 10-78-02, NA=0.42, λ=436 nm) for generation of 0.5 μm lines and spaces over 1 μm SiO2 and aluminum steps.
Characteristics of maskless ion beam assisted etching of silicon using focused ion beams
Authors: Ochiai Yukinori , Shihoyama Kazuhiko , Shiokawa Takao , Toyoda Koichi , Masuyama Akio , Gamo Kenji , Namba Susumu
Published: July 2002

Characteristics of ion beam assisted etching (IBAE) for Si have been investigated by bombarding focused ion beams (FIB’s) in Cl2 gas ambient. The etched surface was analyzed by Auger electron spectroscopy (AES). It was observed that the etching rate increased with increasing the Cl2 gas pressure at low gas pressure and decreased with further increase of the Cl2 introduction. It was also observed that the etching rate depends on the scan speed of the (FIB) and decreased rapidly at a high scan speed above 500 μm/s.
A new metallization technique for very large scale integrated structures: Experiments and computer simulation
Authors: Bader H. P. , Lardon M. A.
Published: July 2002

A new metallization process was developed. Grooves and holes with an aspect ratio of up to 1 were completely filled and partially planarized by the combination of high vacuum evaporation and sputter etching in a multiple cycle alternating process. Excellent agreement between experimental and computer simulated groove and hole profiles was achieved.
Oxidation of InAs(110) and correlated changes of electronic surface properties
Authors: Baier H.-U. , Koenders L. , Mönch W.
Published: July 2002

The adsorption of unexcited, molecular oxygen at clean, cleaved InAs(110) surfaces at room temperature was monitored by AES, EELS, UPS, and a Kelvin probe under the same experimental conditions. The main oxygen uptake was found to set in at some 106 L of O2 and to proceed in two subsequent stages, T1 and T2, which are activated and immobile adsorption followed by field-aided oxide-film growth (Cabrera–Mott mechanism). The oxygen is incorporated in the top layer rather than adsorbed on it since the unchanged ionization energy indicates the absence of adsorption dipoles with moment components normal to the surface. With increasing oxygen uptake, As(3d) and In(4d) energy losses chemically shifted by 3 and 0.6 eV as well as an O(2p)-related energy loss of 6.8 eV and a O(2p)-related valence-band feature are observed to grow to the same extent as the O(510 eV) Auger line. Already at very low exposures, which result in no oxygen uptake detectable by AES, a surface band-bending builds up which saturates at some 104 L of O2. The Fermi level is then pinned at 0.13 eV above the bottom of the conduction band. Above 108 L of O2, i.e., in adsorption stage T2, the work function was found to decrease again.
Surface passivation by adding fluorocarbons and chlorofluorocarbons into an Al dry etch reactor
Authors: Maa Jer-shen
Published: July 2002

Adding fluorocarbon or chlorofluorocarbon compounds into an Al etch reactor can alter the induction time, change the Al etch rate, and inhibit the Al etching from the grounded electrode and chamber wall. These phenomena are explained by a surface passivation mechanism. During an etching process, the aluminum can react with chlorine-containing radicals and fluorine-containing radicals simultaneously to form either a volatile aluminum chloride or a stable passivation layer. The important parameters which control the etch and passivation rates, for a given system geometry, are the gas flow rate, the fluorine atomic concentration, and the bias voltage of the bottom electrode.
Fabrication of 30-nm-scale structures for electron transport studies using a polymethylmethacrylate bilayer resist
Authors: Rooks M. J. , Wind S. , McEuen P. , Prober D. E.
Published: July 2002

We describe a polymethylmethacrylate (PMMA) bilayer system which provides a simple high-resolution resist for the research and development of structures smaller than ∼0.2 μm. Intermixing between the two resist layers is avoided by the use of a weak solvent, xylene, as the solvent of the upper PMMA layer. Metal lines as narrow as 30 nm have been fabricated for electron-transport studies. Much larger features can be produced with deep-ultraviolet exposure, which facilitates electrical contact to the ultrasmall structures.
Barium fluoride and strontium fluoride negative electron beam resists
Authors: Scherer A. , Craighead H. G.
Published: July 2002

The suitability of strontium and barium fluoride as electron beam resist materials has been studied. Their sensitivity to high energy electron beams was measured, and the exposure mechanisms were described using scanning transmission electron microscopy. The effect of crystallite size and film composition on the exposure and development conditions of these inorganic resist systems were investigated. Finally, these resists were directly used as etch masks on gallium arsenide, and their performance was evaluated. Both barium and strontium fluoride were found to be sensitive negative resists, requiring exposure doses of 25–100 μC/cm2. The resolution of pure strontium and barium fluoride is limited by the grain size of the original fluoride deposits. The resolution and development conditions were improved by deposition of a mixture of barium and strontium fluoride (of approximately 50 at. % BaF2 in SrF2), which yielded line resolutions of better than 100 nm. All of these fluorides are extremely resistant to reactive ion etching with halogen containing gases and can be used as etch masks to pattern GaAs.
Laser-direct-writing processes: Metal deposition, etching, and applications to microcircuits
Authors: Black Jerry G. , Ehrlich Daniel J. , Rothschild Mordechai , Doran Scott P. , Sedlacek Jan H. C.
Published: July 2002

The laser-directed discretionary deposition of metal films broadens the scope of electronics fabrication and provides new capabilities for building and restructuring microelectronic devices. When such depositions are combined with local laser-guided etching processes, multilevel modifications are enabled. This mode of processing allows the modification of individual circuits on a micrometer scale, as well as permitting the interconnection of larger circuits composed of multiple devices, both on a single substrate (‘‘wafer-scale’’ integration) and in multichip hybrid configurations. In this paper, recent advances in the interconnect deposition processes useful for these applications are described, as well as some principal demonstrations on functioning circuits.
Microporous GaAs/GaAlAs superlattices
Authors: Deckman H. W. , Moustakas T. D.
Published: July 2002

By using the layer of molecular-beam epitaxially grown GaAs/GaAlAs superlattices as a self-organized etching template, we create two-dimensional slots which can have critical dimensions as small as ∼10 Å. Width of slot structure is determined by layer thickness in the deposited superlattice and selectivity of the etchant used to create slot structures. Durability of these molecular sized pore structures is not limited by layer buckling when aspect ratios of slot walls are <5:1. As such, these materials can be used as molecular sieves with no significant long-term stability problems.
Mechanical characterization of membranes for x-ray lithography masks
Authors: Uzoh C. E. , Maldonado J. R. , Dana S. S. , Acosta R. , Babich I. , Vladimirsky O.
Published: July 2002

This paper presents experimental results on the mechanical properties of x-ray mask substrates. Relevant mechanical properties were determined using an automatic system which plots membrane deformation versus applied differential pressure. In the system, the substrate is held in a leak-tight chuck, and a differential pressure is applied across the membrane by compressed nitrogen. The resulting bulging of the membrane is measured with a laser gauge. The results obtained allow determination of the Young’s modulus, mechanical hysteresis, tension, and fracture strength of x-ray lithography mask membranes. Relatively thin (1–7 μm) membranes of different geometries, and of several materials including B-doped Si and boro–hydro–nitride were characterized. In addition, data that shed light on the role of polyimide coatings on the mechanical integrity of the membranes are presented.
Monte Carlo calculation of low-energy electron emission from surfaces
Authors: Allen T. E. , Kunz R. R. , Mayer T. M.
Published: July 2002

Monte Carlo calculations were carried out to estimate the spatial distribution of low-energy secondary and backscattered electrons emitted from Si bombarded by low-energy (<4 keV) electron beams. The calculation includes Mott scattering cross sections for elastic scattering, experimental and calculated electron inelastic mean free paths, the Streitwolf excitation function for production of secondary electrons, a simple cascade for transport of secondaries, and a surface refraction condition for emission. The spatial distribution of emitted secondary electrons was observed to be directly related to that of backscattered electrons in peripheral areas. The role of low-energy electron emission in the efficiency and resolution of direct write electron beam processes is discussed and results of the calculation are presented.
Temperature dependence of GaAs metal–semiconductor field effect transistor threshold voltage
Authors: Liang C. L. , Wong H. , Mutikainen R. H. , Fourkas R. M. , Cheung N. W. , Sokolich M. , Kwok S. P. , Cheung S. K.
Published: July 2002

We have investigated the temperature dependence of threshold voltage (Vth) of n-channel GaAs metal–semiconductor field effect transistors with different gate materials and structures. It is found that Vth increases by 0.3–0.4 V as temperature decreases from 350 to 80 K. The Vth versus temperature relationship is approximately linear. The amount of Vth shift is independent of channel length from 0.8 to 3 μm and it does not strongly depend on the gate material used. Similar Vth increases are observed for different channel doping methods, such as ion implantation and molecular-beam epitaxy growth. Different GaAs substrates only show a small effect on the Vth temperature dependence. Calculations show that Fermi-level shift and energy-gap expansion with decreasing temperature account for only a fraction of the observed change in Vth. Our measurements indicate that the extra Vth shift is not mainly due to deep-level traps within the channel. Results from C–V measurements on metal/GaAs diodes suggest that build-in voltage changes with temperature are principally responsible for the Vth shift.
Lateral-surface-superlattice and quasi-one-dimensional GaAs/GaAlAs modulation-doped field-effect transistors fabricated using x-ray and deep- ultraviolet lithography
Authors: Ismail K. , Chu W. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We have fabricated and tested lateral-surface-superlattice (LSSL) and quasi-one-dimensional (Q1D) devices on a modulation-doped GaAs/GaAlAs heterostructure. The LSSL consists of a 0.2-μm-period (0.1-μm nominal linewidth) Ti/Au grating or grid on top of the GaAlAs layer, forming a Schottky barrier which presents a tunable periodic potential modulation to the electrons traveling from source to drain. The grating gate was fabricated using x-ray lithography to define the grating lines in poly(methylmethacrylate), and deep-UV lithography to expose gate contact pads, followed by lift-off of Ti/Au. Plots of the source–drain current as a function of the grating-gate bias showed distinct plateaulike features at 4.2 K, providing evidence of a superlattice effect, that is, electron backdiffraction. Minor modifications of the fabrication process permitted Q1D and grid-gate devices to be made. These also showed the expected structure in the conductance.
Radiation damage study of bipolar devices in x-ray lithography
Authors: Hsia L. C. , Magdo I.
Published: July 2002

The radiation damage of bipolar transistors has been investigated using the vacuum ultraviolet (VUV) storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The bipolar devices under investigation were exposed to the x-ray radiation in the range of 1–2 keV. The device parameters were measured before and after irradiation, and were measured again after the devices were annealed in forming gas at 400 °C for 30 min. The study shows that x-ray radiation degrades the common emitter current gain. At small collector currents, the current gain is reduced by about 20%. This change is primarily due to the interface states generated by irradiation at the interface between Si and SiO2 in the base region. Upon annealing, current gain recovers its initial value. The C–V (capacitance–voltage) measurements on MOS capacitors indicate that x-ray radiation increases interface state density from its initial order of magnitude of 1010/cm2 eV to 1012/cm2 eV. The C–V curves also clearly indicate the generation of positive trapped charges in the silicon oxide. Upon annealing, the interface state density is reduced back to its initial value.
Silicon oxide deposition from tetraethoxysilane in a radio frequency downstream reactor: Mechanisms and step coverage
Authors: Selamoglu Nur , Mucha John A. , Ibbotson Dale E. , Flamm Daniel L.
Published: July 2002

Isotopic labeling and step coverage studies of silicon oxide deposited from tetraethoxysilane (TEOS) have been carried out by introducing TEOS(16O) downstream from an 18O2 discharge. Rutherford backscattering (RBS) data on films deposited near 440 °C show that, on average, one Si–O bond in the original TEOS molecule is preserved in the process, while mass spectrometric results indicate only H216O and C18O16O as gaseous products of the cleavage of the remaining three Si–O bonds. Infrared analyses of films deposited at room temperature show large amounts of Si–OH in a gel-like material, and the presence of a C■O species. The results suggest a mechanism dominated by diffusion and condensation of Si–OH species that form extensive chains and preserve an Si–16O bond from the original precursor. This is followed by cross-linking to form the final silicate network; however, Si–O bond cleavage is apparently occurring at potential cross-linking sites via a carbonate intermediate that promotes isotopic scrambling. Step coverage is shown to be better under conditions (high temperature, low TEOS flow) that favor a low concentration of surface precursors during film growth. This is consistent with the proposed mechanism since second-order condensation reactions of surface species under these conditions would be kinetically limited allowing effective mean free paths to increase dramatically. Experimental parameters and techniques, such as modulated chemical feeds to enhance the role of surface migration also lead to improved step coverage. However, we also conclude that perfectly conformal coverage based on similar mechanisms will inevitably lead to void formation in high-aspect-ratio topography because of transport limitations.
Chemically modified GaAs Schottky barrier variation
Authors: Schmidt M. T. , Ma Q. Y. , Podlesnik D. V. , Osgood R. M. , Yang E. S.
Published: July 2002

Chemical modification of GaAs surfaces with and without photoenhancement can produce large variations in the Schottky barrier for metals which are subsequently deposited. Deep ultraviolet light enhanced oxidation of the GaAs surface produces barrier variation toward the ideal Schottky limit, however, there is no evidence that the number of interface states is reduced. A calculation suggests that this can be explained by the interface state energy distribution being altered to shift the states toward the band gap edges, possibly by a photochemical reaction of oxygen. This allows a wider range of Fermi level movement. Different procedures to introduce oxygen at the metal/GaAs interface without photoenhancement result in different barrier variation. Therefore, altered interface chemistry, as well as the mere presence of a species at the interface, is shown to be important for Schottky barrier formation.
Antimony on indium phosphide: Electrical barriers, defects, and induced gap states
Authors: Williams R. H. , Zahn D. R. T. , Esser N. , Richter W.
Published: July 2002

We describe an investigation of an unreactive interface, namely Sb on InP(110) clean cleaved surfaces. Transport techniques (I–V, C–V), Raman spectroscopy, and soft x-ray photoelectron spectroscopy have been used to study the Schottky barrier heights, overlayer structure, and interface interactions for Sb layers deposited on substrates held at room and low temperatures. The evolution of the overlayer structure at room temperature is complex, with an amorphous Sb layer growing on top of an ordered monolayer, until a thickness of ∼10 monolayers (ML), when the layer crystallizes. The evolution of the Schottky barrier is also complex but for thick layers we observe the lowest barriers on n-InP and the highest ever observed on p-InP. Possible mechanisms for the fact that the Fermi level appears pinned close to the conduction band are discussed.
Molecular-beam epitaxy grown Fabry–Perot multiple quantum well reflection modulator
Authors: Simes R. J. , Yan R. H. , English J. H. , Coldren L. A. , Gossard A. C.
Published: July 2002

Electrically-tunable Fabry–Perot structures have been shown to work well as intensity modulators. We describe the growth of these structures by molecular-beam epitaxy. A sensitivity analysis was performed. For some applications, deviations of >0.1%–0.2% in layer thicknesses from the desired thicknesses can degrade the modulation performance. Such tolerances offer continued challenges to crystal growers regarding control of layer thickness, composition, and uniformity.
Superlattice gate and graded superlattice buffer for microwave power metal–semiconductor field effect transistor grown by molecular-beam epitaxy
Authors: Liu W. C. , Chang C. Y. , Hsu W. C. , Lour W. S. , Wang R. L.
Published: July 2002

A new power metal–semiconductor field effect transistor (MESFET) with employing the superlattice structure in the gate and buffer has been fabricated successfully by molecular-beam epitaxy. The use of undoped GaAs–Al0.3Ga0.7As superlattice gate insulator results in much smaller gate to source parasitic capacitance (Cgs) and leakage current and higher gate to drain breakdown voltage (25–30 V) than conventional MESFET’s. Furthermore, the existence of graded superlattice buffer provides higher saturation current and much smaller velocity degradation region than those of AlGaAs buffer MESFET’s. By the improvement of Cgs and transconductance, the cutoff frequency is expected to be higher. Due to the increasing of gate breakdown voltage and saturation current, the output power drivability is improved. In summary, the demonstrated superlattice gate and graded superlattice buffer structure is suitable for low-noise, high-frequency, and high-power application.
Study of GaSb(001) substrate chemical etching for molecular-beam epitaxy
Authors: Da Silva F. W. O. , Silga M. , Raisin C. , Lassabatere L.
Published: July 2002

In this paper we present and discuss the surface properties of GaSb substrates correlated to the cleaning procedure. Different etchants were tested and the resulting surfaces were studied by Auger spectroscopy, then by reflection high-energy electron diffraction and finally annealed under an Sb4 flux in order to get a suitable substrate for molecular-beam epitaxy. From the comparison of the surface properties we show that one of the tested etchants, which associates HCl, HBr, CH3COOH, and HNO3 gives the best results: the etch rate can easily be controlled, the cleaned surfaces are smooth (i.e., free of etch pits) and the surface stoichiometry is the least disturbed by the cleaning procedure.
Optical properties of one-dimensional electron gas in semiconductor quantum wires
Authors: Weiner J. S. , Danan G. , Pinczuk A. , Valladares J. , Pfeiffer L. N. , West K.
Published: July 2002

In optical experiments with laterally patterned modulation-doped GaAs/AlGaAs quantum wells, we observe spatially separate confinement of electrons and holes to one-dimensional quantum wires. We determine the one-dimensional subband spacing and Fermi energy from inelastic light scattering and photoluminescence spectra. From these measurements we directly determine the one-dimensional electron density.
Metal/GaAs interface chemical and electronic properties: GaAs orientation dependence
Authors: Chang S. , Brillson L. J. , Rioux D. F. , Kime Y. J. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

Synchrotron radiation photoemission results for metals on intentionally misoriented molecular-beam epitaxy GaAs(100) surfaces reveal an orientation-dependent interfacial chemistry and Schottky barrier heights at low temperature (90 K). Previous measurements for different metals on aligned GaAs(100) surfaces show a Fermi stabilization energy range of 0.95 eV. However, for Au and Al on 2° misoriented specimens, narrower ranges are observed: 0.65 eV for GaAs surfaces cut towards [110] and 0.45 eV for surfaces cut towards [111] with either Ga or As dangling bonds perpendicular to the step edges. The decrease in the range of the Fermi level stabilization energies is mainly due to the increase in Schottky barrier heights for Al contacts on misoriented specimens, where a more pronounced interface reaction is observed. Our results indicate that the observed degree of chemical reaction and diffusion increases in the order of GaAs(100) surfaces tilted toward [110], [111]A, and [111]B. Our bonding results emphasize the importance of interfacial chemistry and the perfection of the substrate GaAs in the metal/GaAs junction electronic properties.
Adhesion enhancement of Ni films on polyimide using ion processing. II. 84Kr+ implantation
Authors: Galuska A. A.
Published: July 2002

The influence of 84 Kr+ ion implantation on the interfacial chemistry and adhesion of 30 nm Ni films on poly[N,N-(p,p’-oxydiphenylene) pyromellitimide] polyimide (PI) substrates was examined. The Ni/PI specimens were held at temperatures below 100°C and implanted with 170 keV 84 Kr+ at doses of either 5×1015 , 1×1016 , or 5×1016 Kr/cm2 . At low doses, the topography of the specimens remained smooth. However, after implantation with 5×1016 Kr/cm2 , the Ni films were largely destroyed by island formation. The as-deposited films formed sharp interfaces with the PI substrates. After implantation, the interfaces remain sharp, but large quantities of C had been transferred from the PI substrates into the Ni films. An average film stoichiometry of approximately nickel carbide (Ni3 C) resulted after both the 5×1015 and the 1×1016 Kr/cm2 implants. X-ray photoelectron spectroscopy analyses showed (Ni3 C) formation at the interfaces of both the as-deposited and ion implanted Ni/Pl specimens. Although the Ni3C formation extended more deeply into the ion implanted Ni films, the chemical bonding at the Ni/PI interfaces was not greatly affected by the ion implantation. Adhesion evaluations, performed using a scratch test in conjunction with scanning electron microscopy and Auger electron spectroscopy analysis, showed an adhesion enhancement of greater than a factor of 3 for the specimens implanted with either 5×1015 or 1×1016 Kr/cm2 . This adhesion enhancement was attributed primarily to the mechanical interlocking (interfacial mixing) of the Ni films and the PI substrates. While this adhesion enhancement is significant, it is much less than the factor of 20 enhancement previously observed after 28 Si+ implantation.
Demonstration of a low threshold quantum well double-heterostructure optoelectronic switch
Authors: Cooke P. , Taylor G. W. , Claisse P. , Chang T. Y.
Published: July 2002

The double-heterostructure optoelectronic switch (DOES) has been adapted to incorporate a graded index waveguide and a single quantum well active region. The structure was grown using molecular-beam epitaxy (MBE). Broad area devices, fabricating using thermally evaporated contacts and wet chemical etching to define the devices, exhibited ideal switching characteristics with a 7:1.8 V contrast between the on and off-states. As a laser, the best threshold current density obtained was 580 A/cm2 for a 560 μm long device. Variation of efficiency and threshold with cavity length yielded optical losses of 11 cm−1 and an internal efficiency of 43%.
Scattering matrix analysis of electron transport in disordered Aharonov–Bohm interferometers and ballistic constrictions
Authors: Cahay M. , Bandyopadhyay S. , Frohne H. R.
Published: July 2002

We present a fully quantum-mechanical analysis of phase-coherent electron transport in disordered semiconductor nanostructures. The analysis is based on a scattering matrix formalism which allows us to simulate the effects of interface roughness scattering, as well as scattering from point defects and defect clusters. Using this technique, we have studied quantum conduction in electrostatic Aharonov–Bohm interferometers and narrow ballistic constrictions of submicron dimensions.
A study of proximity effects at high electron-beam voltages for x-ray mask fabrication. I. Additive mask processes
Authors: Rosenfield M. G. , Rishton S. A. , Kern D. P. , Seeger D. E. , Whiting C. A.
Published: July 2002

Proximity effects can be reduced when exposing x-ray mask membranes by increasing the electron-beam accelerating voltage. Forward scattering in the resist is reduced and exposure due to backscattered electrons is also reduced since the more energetic electrons are able to pass through the electroplating base and thin mask membrane. In this article, a detailed study of the proximity effect at high electron-beam voltages for additive process x-ray mask fabrication will be discussed. The main contributors to the proximity effect at high beam voltages were found to be backscattering from the x-ray mask membrane, fast secondary electron production by the incident beam, backscattering from the Au/Cr plating base, and finite beam size. The proximity effect was found to still be significant at 75 kV; but, greatly reduced compared to the measured effect at 50 kV. A Monte Carlo simulation program which included the effects of fast secondary electron production was used to analyze the experimental results. Simulated radial absorbed energy distributions were found to agree well with experimental data from x-ray mask structures. The use of proximity correction parameters, determined from the Monte Carlo data, in a proximity correction program predicted that correction will be necessary at 75 and 100 kV. The reduction in proximity effect gained by using 100 kV was found to be quite small compared to the reduction gained by using 75 instead of 50 kV.
Energy density function determination in very-high-resolution electron-beam lithography
Authors: Gentili M. , Grella L. , Lucchesini A. , Luciani L. , Mastrogiacomo L. , Musumeci P.
Published: July 2002

A proximity effect correction algorithm requires an accurate knowledge of the energy density function (EDF) deposited in the electron resist layer. In case of high-resolution electron-beam lithography (EBL), whenever the required resolution is below 0.5 μm, forward and large-angle backward scattering contribution has to be carefully analyzed. In this paper, we compare Monte Carlo (MC) simulation data with experimental point exposure measurements over different substrates and with different beam energy (range 20–40 kV). The substrates we analyze are silicon and silicon nitride membranes (2 μm thick), indium phosphide, and gold. A good correlation between MC data and experiments is proved. Experiments and MC data suggest that the usual double Gaussian fit applied to the distribution is not suitable for the application of high-resolution lithography or with high-Z materials. These data indicate that the recently proposed triple Gaussian fit can be considered as a particular case of a more complex multi Gaussian function. Experimental high-resolution resist profiles are then simulated successfully using MC EDFs in a cell development model.
Scanning tunneling microscopy/scanning tunneling spectroscopy of the organic superconductors (TMTSF)2-PF6 and (TMTSF)2-ClO4
Authors: Fainchtein R. , Murphy J. C.
Published: July 2002

Direct observations of the organic superconductors (tetramethyltetraselenafulvalene) (TMTSF)2-PF6 and (TMTSF)2-ClO4 were made in air at room temperature. The samples consisted of single crystals electrochemically grown. Images revealing the molecular structural arrangement along different crystallographic orientations will be presented as well as spectroscopic data related to the electronic density of states. The images reveal a structure made up of flat molecules that stack on top of one another to form columns and are responsible for the quasi-one-dimensional nature of the electrical conductivity. Although both materials have similar crystal structure the differences in the symmetry and orientation of the counter anions are not resolved. Tunneling spectroscopy data at room temperature shows no apparent difference in the electronic density of states of both materials.