bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of molecular beam epitaxy of GaN on SiC (0001)
Authors: Ramachandran V. , Smith A. R. , Feenstra R. M. , Greve D. W.
Published: July 2002

High quality gallium nitride thin films have been grown on 6H-silicon carbide (0001) substrates at varying substrate temperatures using molecular beam epitaxy and characterized at low and high film thicknesses. The epitaxial layers show two regimes in temperature distinguishable by different morphology. For film thicknesses around the critical thickness, low temperature growth is two dimensional while for higher temperatures, growth is in the form of three-dimensional columnar islands. At a thickness of about 200 nm, the low temperature films show a large density of spiral growths while high temperature films show a two-dimensional morphology. X-ray peak widths are seen to decrease with increasing substrate temperature. These results have been explained in terms of a model which proposes different misfit dislocation formation mechanisms in the two temperature regimes.
Nature, growth, and stability of vanadium oxides on Pd(111)
Authors: Leisenberger F. P. , Surnev S. , Vitali L. , Ramsey M. G. , Netzer F. P.
Published: July 2002

Thin films of vanadium oxides grown on a Pd(111) single crystal surface have been studied using high resolution x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The vanadium oxides have been prepared by reactive evaporation of vanadium in pO2=2×10−7 mbar at 250 °C from submonolayer to 5 monolayer (ML) coverages. As observed on other substrates, the stoichiometry of the oxide phase varies as a function of the coverage, VO/VO2-like at low coverages to V2O3 for thicker oxide layers as indicated by XPS V 2p core level spectra and the characteristic NEXAFS fingerprints at both V 2p and O 1s edges. The V2O3 oxide phase grows epitaxially on the Pd(111) surface in the form of small three-dimensional (3D) islands as revealed by LEED and STM. The thermal stability of the oxides is also coverage dependent: the decomposition onset temperatures range from 300 °C for submonolayer coverage to ⩾500 °C for 5 ML. The V 2p XPS data indicate that the 1 ML V2O3-like oxide disproportionates into higher (4+) and lower (2+) oxidation state phases on heating to 300 °C. This surface shows a complex LEED pattern, due to the coexistence of ordered 3D V oxide islands and bare Pd patches as revealed by STM. On heating to 350 °C a simple p(2×2) LEED structure evolves, originating from a well ordered two-dimensional overlayer, which entirely wets the Pd(111) surface. At higher temperatures (400–500 °C), the vanadium oxide reduces to metallic vanadium and V/Pd alloy phases, as demonstrated by XPS.
Effect of capacitive coupling on inductively coupled fluorocarbon plasma processing
Authors: Schaepkens M. , Rueger N. R. , Beulens J. J. , Li X. , Standaert T. E. F. M. , Matsuo P. J. , Oehrlein G. S.
Published: July 2002

This article describes results obtained using various plasma and surface diagnostics in a study of inductively coupled fluorocarbon plasmas in which the amount of capacitive coupling was systematically varied. It is found that the plasma density decreases while the electron temperature increases as the amount of capacitive coupling is increased at a constant source power level. The rate at which the dielectric coupling window is eroded is found to scale with both the peak-to-peak rf voltage and the ion current density, and the dielectric window erosion is found to influence the resulting plasma gas-phase chemistry. The changes in plasma electrical and chemical characteristics have a large impact on the surface processes occurring in inductively coupled fluorocarbon plasmas such as fluorocarbon deposition, fluorocarbon etching, SiO2 etching and Si etching. Further, we show how the selective SiO2-to-Si etch process changes with varying capacitive coupling.
Measurements of rf bias effect in a dual electron cyclotron resonance-rf methane plasma using the Langmuir probe method
Authors: Hong Junegie , Granier Agnès , Leteinturier Christiane , Peignon Marie-Claude , Turban Guy
Published: July 2002

Low-pressure (0.35 Pa) methane (CH4) plasma was generated by a dual microwave electron cyclotron resonance (ECR)-radio frequency (rf) discharge. The plasma parameters and electron energy distribution functions (EEDFs) were measured using an automated cylindrical Langmuir probe. Optical emission spectroscopy was achieved as a complementary measurement to the probe results. The measured electron and ion densities increase from 109 to 1010 cm−3 as a function of the applied rf power. Plasma parameters obtained from both orbital motion limited theory and EEDF integrals show a consistent trend on the applied rf biasing. The EEDFs measured are well represented by Maxwellian distribution functions and show a significant increase in the electron temperature when rf biasing is applied. This contribution of hot electrons observed above 10 eV in the presence of rf biasing may lead to enhancement of the ionization and dissociation processes of CH4 in our dual ECR-rf discharge.
Stabilization of high-deposition-rate reactive magnetron sputtering of oxides by in situ spectroscopic ellipsometry and plasma diagnostics
Authors: Vergöhl M. , Hunsche B. , Malkomes N. , Matthée T. , Szyszka B.
Published: July 2002

A control system for stabilizing the reactive magnetron-sputter process is applied that is based on a combination of a short-term stabilization of the plasma and a long-term stabilization employing an in situ spectroscopic ellipsometer. For the formation of niobium pentoxide, a measurement of the reactive gas partial pressure with a λ-probe measurement was employed. It turns out that the specific deposition rate, i.e., deposition rate divided by the power density, is a suitable control parameter. Compared to the oxide mode, the deposition rate of niobium pentoxide films deposited in the transition mode could be enlarged by a factor of more than 4. The films were grown at different process parameters (oxygen partial pressure, target power, absolute pressure, midfrequency and dc technique) onto unheated substrates. In situ spectroscopic ellipsometry and ex situ spectroscopic ellipsometry at different angles of incidence and scanning electron microscopy investigations were applied to study the optical properties and the morphology of the films.
Laser Interferometer Gravitational-Wave Observatory beam tube component and module leak testing
Authors: Carpenter W. A. , Shaw P. B. , Jones L. , Weiss R.
Published: July 2002

Laser Interferometer Gravitational-Wave Observatory (LIGO) is a joint project of the California Institute of Technology and the Massachusetts Institute of Technology funded by the National Science Foundation. The project is designed to detect gravitational waves from astrophysical sources such as supernova and black holes. The LIGO project constructed observatories at two sites in the U.S. Each site includes two beam tubes (each 4 km long) joined to form an “L” shape. The beam tube is a 1.25 m diam 304 L stainless steel, ultrahigh vacuum tube that will operate at 1×10−9 Torr or better. The beam tube was manufactured using a custom spiral weld tube mill from material processed to reduce the outgassing rate in order to minimize pumping costs. The integrity of the beam tube was assured by helium mass spectrometer leak testing each component of the beam tube system prior to installation. Each 2 km long, isolatable beam tube module was then leak tested after completion.
Nondestructive one-dimensional scanning capacitance microscope dopant profile determination method and its application to three-dimensional dopant profiles
Authors: Kang Eu-Seok , Kang Jeong-Won , Hwang Ho-Jung , Lee Jun-Ha
Published: July 2002

In this article, we present a new one-dimensional (1D) dopant profile determination method, which extends to the quantitative three-dimensional (3D) dopant profile extraction. This nondestructive method, which is different from the common scanning capacitance microscopy (SCM) measurement/dopant extraction, can potentially measure real metal–oxide–semiconductor field-effect transistor devices having 3D structure. Through SCM modeling, we found that the depletion layer in silicon was of a form of a spherical capacitor with the SCM tip biased. Two-dimensional (2D) finite differential method code with a successive over relaxation (SOR) solver has been developed to model the measurements by SCM of a semiconductor wafer that contains an ion-implanted impurity region. Then, we theoretically analyzed the spherical capacitor and determined the total depleted-volume charge Q, capacitance C, and the rate of capacitance change with bias dC/dV. It is very important to observe the depleted carriers’ movement in the silicon layer by applying the bias to the tip. So, we calculated the depleted-volume charge, considering different factors such as tip size, oxide thickness, and applied bias (dc+ac), which have an influence on potential and depletion charges. Finally, we developed a 1D inversion algorithm to convert the SCM output (dC/dV) into real dopant concentration, comparing the SCM signal output with the calculated dC/dV. Using the inversion modeling, we have quantitatively extracted the 1D dopant profile from the SCM dC/dV vs V curves.
Identification and elimination of chlorofluorocarbon pump fluid contamination in a plasma etch system
Authors: Sirkin Eric R. , Powell R. D.
Published: July 2002

Residual gas analysis is used to identify chlorofluorocarbon-based contamination in the process chamber of a roots-blower-evacuated plasma etch system. The contamination is shown to result from volume migration of the corrosion resistant fluid used in a rotary vane backing pump. Injection of a regulated N2 flow between the blower and backing pump effectively eliminates the contamination.
Evaluation of single crystal LaB6 cathodes
Authors: Kato T. , Shigetomi A. , Watakabe Y. , Hagiwara H. , Hiraoka H.
Published: July 2002

The emission characteristics of single crystal LaB6 tips with 〈100〉, 〈110〉, and 〈210〉 orientations as a cathode for electron beam lithography systems have been evaluated. The tip with 〈100〉 orientation shows stable emission behavior after about 400 h of operation at 1430 °C, 5×10−7 Torr, because the faceting planes are formed and the shape of the tip stabilizes. The tips with 〈110〉 and 〈210〉 orientations also show better stability after early stage operation than do those with 〈100〉 orientation, as faceting planes have already appeared on the tips after 200 h of operation. As one of the applications, a 〈100〉 LaB6 cathode has been operated over 4000 h with high stability in a manufacturing electron beam lithography system (EeBES40).
Annealing of Ar sputter-etch-damaged Si by a Q-switched ruby laser
Authors: Lawson E. M. , Scott M. D. , Rose A.
Published: July 2002

Argon sputter etching of single crystal Si results in damage of the surface and entrapment of the sputtering gas. In a 6-kV dc sputtering system these effects have been observed and characterized by Rutherford backscattering. Irradiation by a Q-switched ruby laser was found to restore the crystal quality and to release the entrapped gas.
Space charge effects in focused ion beams
Authors: Yau Y. W. , Groves T. R. , Pease R. F. W.
Published: July 2002

Focused ion beams have significant advantages (over other directed energy beams) in terms of resist response and direct materials processing. However, the low value of q/m raises questions about space charge effects—particularly the stochastic effects which limit high throughput e-beam systems. We have modified the space charge simulation program originally set up for electrons to allow for a greater number of particles and the effect of energy spreading in the source accelerating region. Beams of 50 keV Ga ions suffer serious spreading at currents above 1 nA (α=2 mrad); 50 keV protons suffer similar spreading at currents above 50 nA.
Influence of dopants and deposition temperatures on the properties of TaSi2/polysilicon films and their thermal oxides
Authors: Gant H. , Boetticher H. , Deppe H. R.
Published: July 2002

Tantalum silicide films were prepared by sputtering from compound targets. The influence of various deposition and process parameters on the TaSi2/poly-Si film properties and on the quality of thermal oxides grown by dry and steam oxidation on top of the polycide was investigated. In particular, the cleaning procedure of the poly-Si surface prior to TaSix-sputtering was varied and elevated substrate temperatures were adjusted during deposition. Furthermore, As- or P-implantations were inserted at various stages of the process sequence to study the properties of oxidized polycide structures present within actual devices. The polycide films were characterized by measurements of the sheet resistivity as well as by x-ray microprobe analysis and x-ray diffraction, while the thermal oxides were investigated by cross-sectional TEM and breakdown strength measurements. At the elevated substrate temperatures during TaSix-deposition, the sheet resistivity of the as-deposited and the sintered films decreases and the quality of the thermal oxides increases. At the maximum temperature of 400 °C, best results were obtained for the oxidized polycide structures. The preferential orientation of the TaSi2 crystallites within the polycrystalline layer depends on the process stage of the implantation. These implantations cause an increase of the quality of the thermal oxides on top of the polycides. Best oxides with mean breakdown fields of up to 5 MV/cm—even better than for oxides grown on polysilicon—were obtained by an As implantation process after sintering. Finally, the results were compared with those for TaSi2/poly-Si films prepared by cosputtering.
Spatial dependence of the optical emission intensities from CF4+O2 plasmas
Authors: Kawata H. , Murata K. , Nagami K.
Published: July 2002

Optical emission intensities from CF4+O2 plasmas are measured at various positions in a rf parallel plate reactor. Since the emission intensities are measured at two different positions between the anode and the cathode electrodes simultaneously, the intensity at either position can be used as a reference to check fluctuations of plasma conditions. Though the raw measured emission intensities depend strongly on the position, the emission intensities normalized to Ar emission vary less than 15%. Although the generation rates of plasma species may depend on the position, the spatial distributions of the plasma species densities are nearly uniform because of diffusion. However, effects of the generation rate and/or the gas flow must also be considered when the spatial dependencies of the plasma species are examined in detail.
A novel four-terminal device grown by molecular beam epitaxy
Authors: Lo Y. H. , Hong J. M. , Wang S.
Published: July 2002

A novel four-terminal device TBGFET (top-back-gate field-effect transistor) grown by MBE is fabricated. An n+ Sn-doped GaAs buried contact layer is grown on a Cr-doped semi-insulating substrate first, and an undoped Al0.4Ga0.6As insulating layer and Sn-doped GaAs channel are grown subsequently. Nonselective mesa etch is used as device isolation and selective etch is adopted to open the back-gate contact window. TBGFET works as a MESFET and MISFET with a common channel but separately controlled by top gate and back gate. We can adjust the transconductance and current level at room temperature as we wish by properly applying negative bias to the back gate or top gate. The top gate threshold voltage Vt=−1.6 V and back gate threshold voltage Vbt=−5.4 or −1.5 V are obtained. Either Vt or Vbt can be changed without influencing the other one. Based on the above properties, a number of applications of TBGFET are proposed.
An advanced control system for semiconductor processing equipment
Authors: Parker Ron , Fuhs Clark
Published: July 2002

The move toward more sophisticated semiconductor processing equipment and the industry’s need for ‘‘turnkey’’ operation have put increased demands on the equipment control system and their architecture. There are different needs from four specific groups that must be addressed by today’s control systems. The process engineer should be provided with process flexibility to qualify the process; the system should be simple enough to easily transfer a process to manufacturing and the production fab operator; maintenance engineers need rich diagnostic functions incorporated into the software to provide routine diagnosis and maintenance; and the communication with the control hardware closes the loop, providing a high degree of safety. In addition, future factory automation will require communication from stand-alone systems to host computers. A proven system control architecture has been developed to meet these needs. The control system described has special applications of both hardware and software, paying particular attention to the human needs.
Etching of SiO2 in a narrowly confined plasma of high power density
Authors: Eisele K. M.
Published: July 2002

An etch process for SiO2 in a C6F14+N2 plasma at 1 Torr pressure and with a power of 10 W/cm3 was examined for its etch rate dependence on gas composition, pressure, and electrode separation. Rates larger than 1 μm/min were obtained. The selectivity with respect to silicon could be made infinitely high by choosing various gas mixtures. An axial magnetic field increased the etch rate by 20%. The process was highly anisotropic. Ion and neutral mass spectroscopy was applied to illuminate the differences between this process and the conventional cathode coupled process (RIE) at pressures of 0.05 Torr.
The Cramer–Rao accuracy bound for optimum processing of the edge registration mark signal in electron beam lithography
Authors: McDonald J. , Elminyawi I. , Yemc D. , Haslam M.
Published: July 2002

Experimental data from the IBM direct-write electron beam lithography machine EL-3 are used to evaluate a lower bound on the estimation error resulting from the application of optimal signal processing in determining the mark edge position for registration. The e-beam is swept using a 20 kV accelerating voltage in a raster fashion across a bare rectangular groove of dimensions 5 μm wide×100 μm long×0.5 μm deep. Waveforms for backscattered electrons detected by diodes are processed statistically. The mathematical and numerical techniques are developed to handle a large but sparse noise correlation matrix. The bound obtained decreases exponentially with the sampling rate (at least throughout the range of measurement explored), and it represents the ultimate accuracy achievable with any signal processing technique. The implications of having multiple records of a waveform are included. Comparisons with other approaches are discussed.
Auger electron spectroscopy evaluation of voids in aluminum–1% silicon integrated circuit metallization
Authors: Gasser R. A. , Johnson S. G.
Published: July 2002

The internal surface of voids present in aluminum–1% silicon metallization used in integrated circuits has been examined using Auger electron spectroscopy (AES). This surface was coated with a thin (<20 Å) layer of Al2O3 in addition to nitrogen, which is believed to represent the grain boundary structure prior to void formation. Both the metal fracture surface adjacent to the void and the void surface itself showed nonequilibrium silicon concentrations of 4–6 at. % and oxygen concentrations of 9–17 at. %. The oxygen on the metal fracture surface was not associated with Al2O3 or SiO2; rather, from residual gas analysis (RGA) of the sputtering environment, it is believed to be incorporated as the OH radical or water. High Si and O concentrations indicated the fracture site to be a grain boundary. Thus H, Si, O (or H2O), and N appear to be the contaminants associated with void formation and/or embrittlement in thin aluminum films.
Visible-laser etching of refractory metals by surface modification
Authors: Rothschild M. , Sedlacek J. H. C. , Ehrlich D. J.
Published: July 2002

A two-step laser etching technique for Mo and W films is described. In the first step, the laser modifies the chemical composition of the metal surface; in the second, deep etching of the pre-exposed areas is by broad-area heating in a reactive ambient. The surface modification takes place in the presence of Cl2, which etches the native-metal oxide and replaces it with a more volatile metal halide. Deep etching is performed with NF3. Since the native oxide is resistant toward etching with NF3, the second step is selective with respect to the laser-halogenated area and is, in effect, a chemical amplification of the surface modification. Well-delineated, high-contrast patterns are obtained with this method.
Ultimate resolution and contrast in ion-beam lithography
Authors: Giles M. D. , Watts R. K. , Labate E.
Published: July 2002

Ion-beam lithography with a stencil mask is capable of very high resolution. We quantify the resolution by calculating the modulation transfer function for protons of energies suitable for patterning resist of useful thickness.
Computer-controlled electron-beam writing system for thin film micro-optics
Authors: Shiono Teruhiro , Setsune Kentaro , Yamazaki Osamu , Wasa Kiyotaka
Published: July 2002

A computer-controlled electron-beam writing system has been developed. The system has various functions for fabricating thin film micro-optical devices. The ability of 0.1-μm patterning, smooth circular and elliptic scanning of an electron beam, and excellent blazing characteristics have been demonstrated. The system has been confirmed to be an efficient means for fabricating micro-optical devices.
Contrast and sensitivity enhancement of resists for high-resolution lithography
Authors: Chiong Kaolin Grace , Petrillo Karen , Hohn Fritz J. , Wilson Alan D. , Moreau Wayne M.
Published: July 2002

Novolac based resists have received much attention in the submicron device fabrication area because of their high dry etch resistance. In high-resolution device fabrication requirements novolac resists suffer from a lack in sensitivity and resolution capability. In order to make use of these high-quality resists, approaches to improve the resolution capability and sensitivity of conventional positive resists have been a major interest of research. Development techniques such as two-step and spray development techniques to improve resist contrast have been reported, but neither is well characterized and well understood. In this paper, we report an interrupted development technique which enhances the contrast of an electron beam (e-beam) exposed diazonapthoquinone novolac, AZ-type resist. As a result of this enhancement, submicron features varying in density can be controlled properly in size and in image profile. The resolution capability of this resist as a single-layer system is extended to the one-quarter micron regime with good linewidth control. In the optically exposed AZ resist, a smaller enhancement in contrast was observed and the resolution improvement is minimal. However, vertical sidewalls are readily obtained by employing appropriate interrupted development schemes on optically as well as e-beam exposed AZ resists. This difference in response to interrupted development is related to the difference in the energy deposited in the resist film due to electron scattering. In the e-beam exposed AZ film, the energy deposited in the resist gradually increases through the bulk of the film. On the other hand, because of the UV absorption characteristics of the novolac resist in optical lithography, the energy deposited is attenuated as it penetrates the resist. Sensitivity enhancement by this technique is on the order of 30% to 50%. A sulfone novolac resist with an inductive effect was examined to try to understand the mechanism of contrast enhancement of AZ resist by interrupted development. No response to interrupted development was observed. Possible mechanisms for the delayed lateral erosion of the AZ resist images are proposed, based on the studies of these resists and

developer interactions. Using this interrupted development technique on a single-layer e-beam exposed resist system, various profiles can be tailored to fit different applications in device processing requirements, namely an undercut profile for metal lift-off, straight sidewalls for etch masks or ion implantation masks.
Electron beam interaction with substrate in electron beam lithography: A scaling experiment to test transport theory
Authors: Schmoranzer H.
Published: July 2002

The interaction of the electron beam with the silicon substrate is studied by means of a scaling electron scattering experiment in gaseous neon. The scaling factor is given by the ratio of the electron ranges in the gas and in solid silicon and exceeds three orders of magnitude. The spatial intensity distribution of neon light emission excited by electron impact has been recorded and was evaluated as a measure of the spatial distribution of energy deposited. From the scaled measurements the range β of resist exposure by backscattered electrons was determined for primary energies from 10 to 40 keV. The analysis of the experimental data was supported by numerical treatment of the electron transport equation.
A voltage-contrast analyzer using radial magnetic field extraction
Authors: Dinnis A. R. , Khursheed A.
Published: July 2002

Quantitative voltage-contrast work is carried out by detecting the effect which the voltages on conducting tracks on the integrated circuit surface have on the energies of low-energy secondary electrons, i.e., the electrons having energies below ∼20 eV. It is essential that the final lens and the electron energy analyzer should be designed as a unit if satisfactory performance is to be achieved.
High-resolution transmission electron microscope studies of an Al–Ge–Ni Ohmic contact to GaAs
Authors: Graham R. J. , Erkaya H. H. , Edwards J. L. , Roedel R. J.
Published: July 2002

The microstructure of an Al–Ge–Ni Ohmic contact to p-type GaAs has been investigated by cross-sectional high resolution and analytical electron microscopy. The contact is found to consist of a continuous polycrystalline layer of Al3Ni adjacent to the GaAs with single crystals of the same phase and larger Ge rich structures on the surface. The contact interface is extremely planar and uniform with intrusive phases in the GaAs entirely absent. The possible reasons for this and the observed Ohmicity of the contact are discussed.
Boron diffusion within TaSi2 /poly-Si gates
Authors: Schwalke U. , Mazuré C. , Neppl F.
Published: July 2002

The redistribution of boron implanted into TaSi2 /poly-Si gates after high temperature anneals has been investigated as a function of the implantation dose and energy as well as the implantation scheme, i.e., boron implantation either into the silicide or into the poly-Si prior to TaSi2 deposition. Implantation and diffusion profiles were obtained by means of secondary ion mass spectrometry whereas the electrical characterization of the resulting structures was performed using high-frequency capacitance–voltage measurements. The results indicate that boron can easily diffuse from TaSi2 into poly-Si and vice versa at 900 °C. Independent of the implantation scheme, the boron concentration within poly-Si was found to saturate at ∼1×1019 at/cm3 for boron doses >5×1014 at/cm2. The excess of boron always accumulates within the silicide. The solubility limit of boron within TaSi2 was estimated to be >3.5×1020 at/cm3. Boron concentrations of ∼1×1019 at/cm3 within poly-Si were found to be sufficient to realize p+ -polycide gates with stable and reproducible threshold voltages similar to p+ -poly-Si gates. The observed boron redistribution behavior within the polycide is discussed in terms of combined lattice and grain boundary diffusion as well as grain boundary segregation.
Polymer deposition and etching mechanisms in C2F6 radio-frequency plasma as studied by laser-induced fluorescence
Authors: Kitamura Mamoru , Akiya Hideo , Urisu Tsuneo
Published: July 2002

Spatial profiles of CF2 concentration in C2 F6 rf plasma are measured by the laser-induced fluorescence method. The observed profiles are explained by the generation and recombination reaction mechanisms of CF2 . It is found that the deposition rate of fluorocarbon polymer on SiO2 film is proportional to [CF2]n ; n=2.5–3.0, whereas the etch rate of SiO2 is proportional to [CF2]. Both the etching and the deposition reactions proceed at the same time. Based on these observations, reaction mechanisms for fluorocarbon polymer deposition and SiO2 etching are analyzed.
A three-dimensional profile modeling algorithm for positive photoresists
Authors: Barouch E. , Bradie B. , Babu S. V.
Published: July 2002

A numerically efficient version of the WKB algorithm for determining the electric field and the concentration of the photoactive compound within a photoresist film in the presence of standing waves is implemented in three dimensions assuming normal incidence and a flat substrate. This algorithm is combined with the least-action dissolution (LEAD) algorithm to simulate three-dimensional developed resist profiles.
Droplet emission from a gallium liquid metal ion source as observed with an ion streak camera
Authors: Barr D. L. , Brown W. L.
Published: July 2002

Droplets emitted from a gallium liquid metal ion source have been observed using an ion streak camera. The camera records the angle and time of arrival of individual atomic ions at a chevron multichannel plate detector (MCP) with a minimum time resolution of ∼30 ns. The ion hits are recorded with a charge coupled device (CCD) camera observing light from the MCP. Individual droplets are recorded as shadows in the image produced by the broad gallium atomic ion beam. Droplet shadows have large angular widths at times immediately after droplet creation and shrink rapidly in angle with increasing time as the droplets move away from the emitting tip. Associated with each droplet streak is a momentary decrease in atomic ion emission at all angles, as might be anticipated from the perturbation produced by the emission of a droplet. The shape of a droplet streak has been modeled by geometrical shadowing and by Coulomb repulsion shadowing between the droplet and the atomic ions. Through nonlinear fitting methods, both the mass and charge of the droplet may be deduced from this model. Results show that the charge on most large droplets is substantially below the Rayleigh limiting charge. The momentary decreases in atomic ion emission at all angles are roughly periodic under some emission conditions.
Electronic and chemical properties of small silicon clusters in reactions with silane
Authors: Mandich M. L. , Reents W. D. , Kolenbrander K. D.
Published: July 2002

The microscopic surfaces of small silicon clusters offer a model for studying chemistry at highly reactive silicon centers. Positively and negatively charged silicon clusters containing two to seven atoms are prepared by laser evaporation of a solid silicon target located outside of the ion cell of a Fourier transform mass spectrometer. The trapped clusters react with SiD4 at room temperature primarily by addition of SiD2 accompanied by loss of D2. Sequential reactions of bare silicon cluster cations and SiD+3 to form still larger deuterated SixD+y species are also observed. All of the clustering sequences, however, encounter early bottlenecks which prevent further growth. Ab initio electronic structure calculations are used together with phase space theoretical calculations to elucidate the potential surfaces for these reactions. Larger unreactive silicon clusters with six or seven atoms appear to lack the divalent silicon center required to activate Si–D bonds in SiD4 under the mild conditions of these experiments. These findings indicate that ground-state bare silicon clusters and SiH+3 are not the important precursors leading to the formation of hydrogenated silicon dust in silane plasmas.
Thermal and mechanical model of x-ray lithography masks under short pulse irradiation
Authors: Shareef Iqbal , Maldonando Juan R. , Katcoff David
Published: July 2002

The purpose of this paper is to present computer simulations of x-ray mask heating by fast x-ray pulses. In particular, results will be presented of temperature distributions in an x-ray mask during exposure to x-ray pulses generated by a hot plasma. Three mask structures were studied: (i) Si–Au absorber, (ii) Si–polyimide–Au absorber, and (iii) Si–W absorber. The transient thermal analysis results were obtained using finite element modelling techniques (CAEDS and NASTRAN). The x-ray exposure was assumed to have taken place in a helium atmosphere with a 40-μ gap between the mask and the wafer, which was assumed to be a heat sink at constant temperature. The temperature distributions obtained above were subsequently used as input in order to study possible mechanical deformation of the membrane. Again, finite element techniques were used and solutions were obtained by static stress methods. Results indicate a maximum temperature rise on the mask of the order of 18 °C for a 20-ns exposure by a 10 mJ/cm2 x-ray pulse. The maximum temperature was obtained at the end of the x-ray pulse. The temperature decayed quickly, reaching initial ambient temperature after about 10 ms. Mechanical analysis showed that maximum deformation, which was due to maximum temperature differences in the mask layers, also occurred at the end of the pulse. The analysis indicates that there is need for experimental study of x-ray mask distortion during exposure to short x-ray pulses (from a laser plasma or similar source) when the pulse amplitude reaches 10 mJ/cm2.
Fabrication of 0.5 μm n- and p-type metal–oxide semiconductor test devices using x-ray lithography
Authors: Zwicker G. , Windbracke W. , Bernt H. , Friedrich D. , Huber H.-L. , Krullmann E. , Pelka M. , Lange P. , Hemicker P. , Staudt-Fischbach P.
Published: July 2002

Partially scaled 0.5 μm NMOS and PMOS test devices have been fabricated using synchrotron radiation x-ray lithography for all four levels. All exposures were done at the IMT lithography lab at the BESSY storage ring in Berlin, using the Suss MAX I x-ray stepper. The four levels of each device have been processed with the new Hoechst RAY/PF x-ray sensitive resist. A total overlay accuracy of 130 nm (1σ) in x and y direction for all aligned levels and an overall linewidth variation of 23 nm (1σ) across a 100 mm wafer have been achieved. Reproducible NMOS and PMOS processes have been carried out in the CMOS process line of the institute, using gateoxide thicknesses between 15 and 10 nm, appropriate channel implants, and a spacer technology. Electrical results of functional test transistors with effective gate lengths down to 0.25 μm will be presented.
Investigation of the charging effect on thin SiO2 layers with the electron beam lithography system
Authors: Itoh Hiroyuki , Nakamura Kazumitsu , Hayakawa Hajime
Published: July 2002

The charging problem of a dielectric layer during direct exposure with an electron beam lithography system is investigated. Electron beam irradiation on a wafer with a dielectric layer such as SiO2 often causes charge buildup. This excessive accumulation of charge on the sample disturbs placement accuracy, and results in overlay errors. In order to analyze this charging problem, a metrology software package is used to measure the placement error of the exposed patterns on a target plane. Tested sample wafers are deposited with 0.2–1.5 μm SiO2, and then coated with 1 μm resist for exposure. To evaluate the charging dependence on electron beam current, a variable-shaped electron beam lithography system which can easily change beam current is used. The results indicate that nongrounding 0.2 and 0.5 μm SiO2 do not show charge-induced placement errors while 1 and 1.5 μm SiO2 show a definite placement error due to charging. On 1.5 μm Sio2 results indicate an electrostatic breakdown of SiO2, and no charging error is observed after breakdown. These pattern distortions due to charging are evaluated by a statistical analysis, and they are approximated by a simplified equation. To prevent charging, a mechanical contact with the substrate has proven to be effective. This grounding method, using a conductive diamond tip, shows excellent grounding ability.
Nanometer X–Y positioning stages for scanning and stepping
Authors: Chitayat Anwar
Published: July 2002

This paper describes new developments in X–Y stages for scanning or stepping and use in vacuum. The requirement for high dynamic stiffness is analyzed as to its effects on positioning accuracy in dynamically moving stages (scanning) and on settling time for stepping applications. Novel solutions are described to increase the accuracy and stability of the X–Y stages to perform in the nanometer range: (1) the use of piezoelectric locking systems to directly lock the product to the beam producing source (to reduce vibration to the subnanometer level), (2) through-the-chamber wall linear motor drives, where the X–Y stages are located inside the vacuum chamber and linear motor drives are located outside the vacuum chamber, (3) the use of low friction ways with a mirror surface finish so that high smoothness and extremely constant velocity is achieved, and (4) how the combination of these new techniques has resulted in practical systems for nanometer fabrication and inspection.
Electron-beam proximity printing of half-micron devices
Authors: Meissner K. , Haug W. , Silverman S. , Sonchik S.
Published: July 2002

Electron-beam proximity printing (EBP), a lithographic shadow projection method, has demonstrated the capability to print structures with dimensions below 0.5 μm, to achieve level-to-level overlay better than 50 nm (1σ) and to perform with very high throughput. Four sequential EBP mask levels have been exposed and functional n-type metal–oxide semiconductor (NMOS) devices have been produced. This paper describes the overall process as well as the operation of the EBP tool. It presents process and lithography data for these devices and shows that the overlay capability exceeds the requirements for half-micron ground rules. EBP has the unique capability to continuously change the direction of the electron beam and so to laterally displace the image of mask structures on the wafer. This feature makes it possible to correct distortions of the IC pattern in the mask (e.g., magnification, rotation, higher-order distortions) to adapt a new pattern level to one former level already on the wafer and to achieve a fast precise pattern alignment independent of the precision of the stage step. The achievable level-to-level overlay was predicted through both calculation of the mask and tool dependent errors and simulation of the EBP correction feature. This theoretical result was confirmed with experimental data from the processed half-micron devices. Both the theoretical prediction and the method to measure the level-to-level overlay will be described.
Scanning tunneling microscope images of native defects on the ZnSe(110) surface
Authors: Hu Wei-Min , Dow John D.
Published: July 2002

Scanning tunneling microscope images of native antisite defects at the relaxed (110) surface of ZnSe are predicted. The images of a particular sample depend on the sign of the voltage bias and the voltage sweep of the sample relative to the microscope tip, and whether that sweep causes a deep level to actively participate in the tunneling. Under certain conditions the images give the appearance of two defects at incorrect sites.
Surface intervalley scattering on GaAs(110) studied with picosecond laser photoemission
Authors: Haight R. , Silberman J. A.
Published: July 2002

Investigations of the laser excited GaAs(110) surface with angle resolved, picosecond laser photoemission have revealed a previously unobserved valley of the C3 surface band. The valley minimum is at the X̄ point in the surface Brillouin zone and resides within the band gap at this location. Electron population in this valley increases only as a result of scattering from the directly photoexcited valley at Γ̄. With high momentum resolution we have been able to isolate the dynamic electron population changes at both Γ̄ and X̄ and deduced the scattering time between the two valleys.
Epitaxial growth of Bi on GaAs(100) surfaces
Authors: Horng S. , Kahn A.
Published: July 2002

Bi layers deposited on (100) GaAs are investigated with low-energy electron diffraction, Auger electron spectroscopy, and electron energy-loss spectroscopy. The (100) substrates are prepared by simultaneous Ar+ sputtering and annealing. The deposition of Bi on room-temperature (100) GaAs eliminates the reconstruction spots at 0.5 monolayer. No long-range order is obtained in the room temperature grown Bi layer. Post-growth annealing at 250 °C restores long-range order and produces a sixfold symmetric hexagonal pattern characteristic of the rhombohedral structure of bulk Bi. The attenuation of the Auger peak intensities as a function of Bi thickness indicates that the film grows in a quasi-laminar fashion. The deposition of Bi on high-temperature (100) GaAs (250 °C) produces a two-dimensional ordered growth. The GaAs (4×6) structure is replaced by a (2×1) structure after deposition of one-half monolayer Bi. These (2×1) structure remains visible up to coverages of at least 25 monolayers. Auger measurements indicate island formation, while the sharpness of the electron diffraction spots indicates good crystallinity at the surface of the Bi crystal.
High-aspect-ratio resist pattern fabrication by alkaline surface treatment
Authors: Endo M. , Sasago M. , Matsuoka K. , Nomura N.
Published: July 2002

A new and simple high-aspect-ratio, single-layer resist process for the manufacture of very large scale integration (VLSI) devices is described. Before the exposure step in the conventional process, an alkaline surface treatment is added to the positive photoresist. This treatment inhibits the dissolution of the unexposed resist layer during development, which leads to a high-aspect-ratio resist pattern. Excellent submicron resist patterns are obtained with a large focus latitude using this simple method.
Overlay precision between electron beam and optical lithography systems for a mix and match GaAs technology
Authors: Patrick W. , Glorer K. , Schneider J.
Published: July 2002

A systematic study has been carried out to determine the feasibility of a mix and match GaAs technology where only the gate level is defined by electron beam (e-beam). The overlay accuracy between e-beam and optically defined patterns was determined for a range of marker field sizes up to 8×8 mm. Ti/Au markers, which are ideal for e-beam registration and alloyed Au/Ge/Ni/Au markers (Ohmic contact on GaAs), which are not normally considered suitable for registration, were used in the study. Using Ohmic metal markers the gate can be aligned directly to the source-drain contact mask level, thus eliminating optical-to-optical overlay errors which would occur if a zero level alignment mask were used. A ‘‘mix and match’’ technology has been used to fabricate 0.2 μm gate-length metal–semiconductor field effect transistor (MESFET) devices with 0.3 μm source-gate spacing.
A novel scanning tunneling microscope controlled field emission microlens electron source
Authors: McCord M. A. , Chang T. H. P. , Kern D. P. , Speidell J. L.
Published: July 2002

A field emission electron source that combines scanning tunneling microscope (STM) technology with a micromachined aperture has been explored. The STM is used to position the field emission tip over a metal aperture of 0.4–2.5 μm diam. An extraction voltage ranging from 50 to 200 V applied between the tip and the aperture results in the field emission of electrons, which pass through the aperture and can be collected on the other side. The aperture is fabricated on a silicon nitride membrane using electron beam lithography and reactive ion etching. Such a source can potentially provide a very bright, high current, low voltage source of electrons. The simple aperture can be replaced by a microlens consisting of a stacked structure of two or three thin film electrodes separated by thin film insulating spacers, and a compact, high performance electron source or complete optical system can be realized. While the concept of a miniature field emission cathode is well known, incorporation of an STM into the design gives several advantages. These include fine positioning of the tip with respect to the aperture, both vertically and horizontally; active feedback stabilization of the emission current by adjusting the tip position without changing the extraction voltage; and replacability of the tip. Source characteristics as a function of aperture diameter, tip radius, and extraction voltage as well as data on noise, lifetime, maximum total current, and operating pressure are presented. An accompanying paper will present detailed calculations of the electron–optical performance.
Energy broadening of an electron optical line source
Authors: Brodie A. D. , Nixon W. C.
Published: July 2002

The energy broadening due to electron–electron interactions of an electron optical line source and a line shaped beam have been theoretically analyzed and compared to its axially symmetric counterpart. An analytical approach was developed to evaluate the energy spread in an electron source. Monte Carlo methods were used to evaluate the energy broadening induced in a thin electron optical lens of 10× magnification. The results predict that the focusing of line shaped beams have an induced energy spread up to 27% lower than round beams.
Practical optimization of multielectrode lenses
Authors: van der Steen H. W. G. , Barth J. E.
Published: July 2002

In a previous publication the second order electrode method (SOEM) was demonstrated to give practical designs for three electrode electrostatic lenses. Here the extension of the method is presented to include optimization of multielectrode lenses. The method uses a cubic spline approximation to calculate the axial potential distribution from the electrode shape. The optimization is carried out with respect to a practical-application dependent merit function. The main constraints of the optimization algorithm are the first-order optical properties of the lens, such as fixed object and image position. The smoothness of the electrode surface is a requirement incorporated in the algorithm as a constraint. Scaling the dimensions of the lens is used to focus it. A computer program has been developed, which can optimize up to nine electrode lens systems.
Differential metrology of very large scale integration, oxide isolation structures using a confocal scanning laser microscope
Authors: Monahan K. M. , Fastenau R. H. , Tien T.
Published: July 2002

A confocal scanning laser microscope (CSLM) has been used to study a variety of oxide isolation structures, including LOCOS and SLOCOS, by means of a confocal differential Fizeau metrology (CDFM) technique recently developed at Philips Research Laboratories Sunnyvale (PRLS). This technique permits measurement between Fizeau fringes less than 200 nm in width (FWHM), with less than 50 nm of optical offset, greater than 50% contrast, and mean standard errors in the nanometer range. Comparisons are made between measurement tools (CSLM and SEM), between processes (LOCOS and SLOCOS), between process steps (nitride mask definition and local thermal oxidation), between individual wafers (levels of nitride mask thickness), and between individual features on a wafer (levels of nitride mask linewidth). Unique metrological evidence is presented for a stress-related deformation mechanism in both LOCOS and SLOCOS structures at nitride mask thicknesses greater than about 250 nm.