bluuebunny/crossref_metadata_2025 huggingface dataset:
Supersonic molecular beam scattering as a probe of thin film deposition processes
Authors: Xia L.-Q. , Jones M. E. , Maity N. , Engstrom J. R.
Published: July 2002

The reactions of silane, SiH4, disilane, Si2H6, and phosphine, PH3, on single crystalline Si(100) and Si(111) surfaces, and methylsilane, SiH3CH3, on a β-SiC surface have been examined employing supersonic molecular beam scattering. The emphasis here is not on any one experimental result, but rather on the specific experimental approaches adopted and a selected set of results that serve to demonstrate the similarities and differences between these systems and the more extensively studied reactions occurring on transition metal surfaces. All reactions have been examined at substrate temperatures characteristic of steady-state thin film growth. Translational activation is observed to be an efficient means to promote the reactivity of the group IV species: SiH4, Si2H6, and SiH3CH3. In all cases, the reactivity increases exponentially with scaled incident kinetic energy, where the scaling analysis specifically takes into account the microcorrugation of the gas-surface potential in terms of how incident kinetic energy and angle of incidence couple to determine the probability of dissociative chemisorption. The reaction probability of SiH4 is described quantitatively over a wide range of reaction conditions by a recently published model that adapts Rice–Ramsperger–Kassel–Marcus theory to translationally activated dissociative chemisorption. In contrast, PH3, due to its coordinative unsaturation, is found to react almost exclusively via a trapping-mediated precursor dissociation channel. By employing a novel analysis scheme, the dependence of PH3 dissociative chemisorption on the fractional coverage of both P(a) and H(a) has been deduced under conditions where the desorption of H2 and P2 are finite. The experimental techniques described here, and the associated conclusions made in this work, should be of tremendous value in future studies directed at examinations of the gas-surface chemistry involved in epitaxial thin film growth.
Monte Carlo calculations of gas rarefaction in a magnetron sputtering discharge
Authors: Turner G. M.
Published: July 2002

Monte Carlo calculations have been made of the rarefaction of the filling gas in a magnetron sputtering discharge due to collisional energy transfer from the flux of sputtered atoms. Temperature profiles of the filling gas between parallel cathode and substrate planes were calculated for both Ar and Ne filling gases and for C, Al, Ti, Cu, W and Au sputtered atoms. The effects of filling gas pressure, discharge voltage and current and cathode-substrate separation were also studied. At constant filling gas pressure, and in the limit of high discharge current, the maximum temperature was approximately proportional to the square root of the discharge current; for constant pressure and discharge voltage and current, the maximum temperature increased linearly with the cathode-substrate separation. The heating of the filling gas was greater for Ar than for Ne, due to differences in the thermal conductivity, sputtering yield, collision cross section, and average fraction of energy transferred from sputtered atoms in a collision. The magnitude of heating also depended strongly on the material being sputtered, primarily being determined by the sputtering yield, particularly at high pressures, and to a lesser extent by the collision cross section, masses, and binding energy of the sputtered and filling gas atom combination. Negligible heating of Ar was calculated for C as the sputtered material, while maximum rarefaction was produced using Au for the same discharge conditions.
Diamond deposition on carbon fibers
Authors: Shah S. Ismat , Waite M. M.
Published: July 2002

Diamond films have been deposited on carbon fibers with diameters as small as 5 μm by microwave plasma assisted chemical vapor deposition. An ultrasonic pretreatment of the fibers in a bath containing methanol and diamond paste was required for successful coating of the fibers. In the absence of such treatment, the fibers were completely etched within a few minutes under the plasma. Raman spectroscopy indicated good quality diamond formation with very little graphitic component. Films with thicknesses between 1 and 30 μm can be reproducibly obtained by this method.
Analysis of the oxygen contamination present in SiNx films deposited by electron cyclotron resonance
Authors: García S. , Martin J. M. , Fernández M. , Mártil I. , González-Diaz G.
Published: July 2002

Silicon nitride (SiNx:H) films are deposited by the electron cyclotron resonance method at different microwave powers and nitrogen to silane gas flow ratio (R). Auger electron spectroscopy (AES), infrared (IR) absorption, and refractive index (n) measurements are used to determine deposition conditions resulting in oxygen contamination of the films as well as those conditions that result in good quality films without oxygen incorporation. Oxygen contamination of the films is produced at high microwave powers and R ratios as shown by the oxygen content determined by AES and different features in the IR spectra: the shift to higher frequencies for the positions of the Si–N and Si–H peaks, the presence of the N–H bending mode, and the broadening of the Si–N peak with its frequency. Low n values confirm the oxygen incorporation into the films, as they decrease when the oxygen content increases. The characteristic dependence of the oxygen presence in the films with the deposition conditions indicate that the oxygen source is the sputtering of the quartz liner located inside the plasma source.
Effect of plasma overetch of polysilicon on gate oxide damage
Authors: Gabriel Calvin T. , McVittie James P.
Published: July 2002

Modeling and previous experiments have indicated that charging damage during metal–oxide semiconductor (MOS) polysilicon gate etching occurs just before endpoint when the last of the exposed polysilicon can collect excess plasma currents that cause damage by flowing through the gate oxide. During overetch, this damage mechanism is suppressed by the poor collection efficiency of the exposed polysilicon edges, so damage from this mechanism is expected to remain constant during this period. Although there is an additional edge damage mode where damage can increase during overetch, we here report results showing a decrease in damage with overetch time. The experiment consisted of two lots of fully processed complementary MOS wafers where the polysilicon overetch percentage was varied from 0% to 110%. The etch tool was a triode system that showed antenna dependent charging damage. The test structures were large area capacitors with a 10.5 nm thin oxide whose breakdown statistics were measured after the full process, including anneals. Both the n-channel and p-channel devices showed damage which decreased with overetch time. The damage was significantly worse for the n-channel devices—the mean n-channel gate oxide breakdown voltage was 3 V at endpoint compared to 11.5 V after 110% overetch. The effect was repeated in that both lots showed the same results. The results indicate an apparent annealing during overetch. In the past, radio frequency (rf) annealing has been reported for e-beam damage with a proposed mechanism involving rf heating and carrier motion. We consider this unlikely and suspect that low plasma currents collected by the gate edge could be playing a role in the annealing; however, etching of the exposed gate oxide during overetch may also be important. The n- and p-channel differences can be explained by a voltage drop across the n well which reduces the tunnel current through the p-channel gate oxides.
High density plasma etching of III–V nitrides
Authors: Vartuli C. B. , Pearton S. J. , Abernathy C. R. , Shul R. J. , Howard A. J. , Kilcoyne S. P. , Parmeter J. E. , Hagerott-Crawford M.
Published: July 2002

Two broad classes of plasma chemistry were examined for dry etching of GaN, AlN, and InN. The etch rates for CH4/H2-based plasmas are low (∼ 400 Å/min) even under high microwave power (1000 W) electron cyclotron resonance conditions. Halogen-based plasmas (Cl2, I2, Br2) produce rates up to ∼3000 Å/min with smooth stoichiometric surfaces. Preferential sputtering of N occurs for high ion energies, leading to rough GaN surfaces at rf power above ∼200 W. Etch rates for high ion density discharges are typically an order of magnitude faster than for conventional reactive ion etching.
Simulation model to very low pressure chemical vapor deposition of SiGe alloy
Authors: Gu Shulin , Wang Ronghua , Zhang Rong , Zheng Youdou
Published: July 2002

Kinetics study of very low pressure chemical vapor deposition (VLPCVD) of SiGe alloys has been reported in this article. In this kinetics model, the SiGe alloy deposition process has been treated as three steps: SiH4 and GeH4 adsorption on Si and Ge vacancy sites, hydrogen exchange between silicon and germanium hydrides, and hydrogen desorption from growing surface. The kinetics model is fit to the data of SiGe layers deposited from decomposition of SiH4 and GeH4 by the VLPCVD method. The model agrees well with experimental data.
Reactive ion etching of silica structures for integrated optics applications
Authors: Bazylenko M. V. , Gross M.
Published: July 2002

Reactive ion etching of silica in a hollow cathode reactor using a CHF3/Ar gas mixture has been studied as a function of masking material, rf power, sample temperature, and O2 and CF4 additions. Etch rates in excess of 0.5 μm/min are typically obtained with a selectivity over amorphous silicon and photoresist of more than 10. The sidewall roughness for etching with an amorphous silicon mask is of the order of 0.05 μm, whereas for a photoresist mask, under similar etching conditions, the sidewall roughness is up to 0.1 μm. For the a-Si mask a further improvement in the sidewall roughness down to 0.02 μm can be obtained by adding O2 to the discharge or elevating the sample temperature, however both parameters cause lateral etching of the a-Si mask and therefore linewidth loss. Nonetheless, when using sample temperature as a control parameter, a process window was found which allows smooth sidewalls to be obtained without dimension loss. In the case of O2 additions such a process window was not found. Possible mechanisms accounting for this difference are discussed. Etching in a CHF3/Ar discharge occurs in competition with simultaneous polymer deposition. The polymer deposition rate was measured in areas shielded from ion bombardment. A phenomenological model describing the effects of polymer deposition on etch rates, sidewall slope, and roughness is proposed. This model assumes that a polymer film with different steady-state thickness can form on different etched structure surfaces, as a result of a balance between polymer etching and deposition. The model is used to explain the tendencies in etch rates, profile slope, and sidewall roughness obtained in this study.
Adsorption state of hydrogen sulfide on the GaAs (001)-(4×2) surface
Authors: Chung Chan-Hwa , Yi Sang I. , Weinberg W. Henry
Published: July 2002

We have investigated the mechanism of H2S adsorption and the evolution of a sulfur passivation layer on the GaAs(001)-(4×2) surface using high-resolution electron energy loss spectroscopy, temperature-programmed desorption, Auger electron spectroscopy, and low-energy electron diffraction. The initial H2S adsorption occurs dissociatively to form HS and H with the hydrogen selectively bonded to As at 100 K. Upon annealing to 700 K, vacant Ga sites, which are available for further dissociation of H2S, are monitored by postexposure of atomic hydrogen. The repeated cycles of H2S exposure at 100 K and thermal annealing yielded a sulfur-saturated layer on which only sulfur is available for posthydrogenation. We have also examined the passivation performance of the H2S-treated surface when exposed to water at 100 K.
Work function determination of zinc oxide films
Authors: Sundaram K. B. , Khan Ashamin
Published: July 2002

Zinc oxide-silicon heterojunctions were fabricated using both n- and p-type silicon. The zinc oxide films were deposited by the magnetron sputtering process at various substrate temperatures to form these devices. The electrical properties of these devices were measured and the work function of the zinc oxide was evaluated from these properties.
Observation of surface dissociation of low-energy polyatomic ions relevant to plasma processing
Authors: Sugai H. , Mitsuoka Y. , Toyoda H.
Published: July 2002

To gain insight into surface processes in plasma processing, basic ion beam experiments are performed on two representative polyatomic-ion species: hydrocarbon ions CHx+ for deposition processes and fluorocarbon ions CFx+ for etching processes (x=1,2,…). A single ion species is extracted from an inductive plasma via a mass filter and directed onto aluminum surfaces at energies <150 eV. Significant charge neutralization is observed which leads to backscattering of ∼0.3% CHx+ ions and ∼1% CFx+ ions from the surface bombarded at 100 eV. Most of the ions scattered from the surface have kinetic energies lower than 10 eV. A polyatomic ion impinging on the surface breaks up into smaller ionic fragments. Such surface dissociation is found even at very low incident energies (10–50 eV) in the case of hydrocarbon ions, which is attributed to vibrational excitation of the incident parent ions. In contrast to this, fluorocarbon ions hardly dissociate at such low energies. On the other hand, at high energy (> 100 eV) incidence of both CHx+ and CFx+ species gives rise to dissociation into smaller fragment ions, probably via electronic excitation.
Semiquantitative subplantation model for low energy ion interactions with surfaces. I. Noble gas ion-surface interactions
Authors: Boyd K. J. , Marton D. , Rabalais J. W. , Uhlmann S. , Frauenheim Th.
Published: July 2002

A semiquantitative, phenomenological model for low energy ion interactions with surfaces is developed. The model represents a generalization of the qualitative subplantation model of Lifshitz et al., Phys. Rev. B 41, 10 468 (1989). A general equation for describing ion solid interactions, including film growth processes, is introduced. This model, for the first time, describes the three major contributions to such interactions, i.e., ion penetration, defect production, and radiation enhanced diffusion, in terms of simple analytical equations. In this first article, the basic assumptions of the model are described and the concepts are demonstrated for the example of rare gas ion interaction with graphite. The model is developed in both a simple static form and a more complex dynamic one; the latter is applicable to ion fluence-dependent phenomena. The model provides calculated values of experimentally observable quantities such as the primary ion concentrations retained in the surface and subsurface layers. It also provides estimates of quantities that are difficult to measure such as penetration thresholds, displacement thresholds, and diffusion rates.
Effect of upper hybrid waves on uniform electron cyclotron resonance plasmas
Authors: Ueda Yoko , Kawai Yoshinobu
Published: July 2002

The extraordinary wave (X wave) was found to contribute to the uniformity of an electron cyclotron resonance (ECR) plasma whose electron density is about 1–2×1011 cm−3. The X wave propagated radially in the plasma both before and after an ECR point. The wavelength of the X wave changed radially according to the local electron density. The experimental results indicated a possibility that an upper hybrid resonance (UHR) sustained the very uniform ECR plasma. With increasing input microwave power, the radial profile of the ion saturation current density changed from uniform to convex abruptly, and the electron density at a center increased to about 1012 cm−3 with an electron density jump. Only the whistler wave propagated axially in the high density plasma of about 1012 cm−3. It was found, by measuring electromagnetic waves, that the radial profile of the ion saturation current density abruptly changed when the electron density was nearly equal to the cutoff density of the X wave at the ECR point.
Large-area high-density plasma excitation using standing pure and hybrid surface waves
Authors: Ghanashev I. , Nagatsu M. , Morita S. , Sugai H.
Published: July 2002

Plasma processing of large flat surfaces requires low pressure high density (ne=1011–1012 cm−3) plasmas with uniform plasma density distribution near to the processed surface. Microwave discharges may provide a valuable alternative to the inductively coupled plasmas applied widely now for this purpose. In a recent article [Jpn. J. Appl. Phys., Part 1 35, L341 (1996)] we proposed a plasma source in which the plasma is sustained by a standing surface wave propagating radially and azimuthally along the interface between the plasma and a dielectric plate located at the top wall of a large-diameter cylindrical metal chamber, the wave being launched by a pair of slot antennas cut in the top chamber wall above the dielectric plate. Here we present new experimental results at lower pressures (down to 3 mTorr) and in a non-noble reactive gas (CF4) demonstrating the applicability of the new source for dry etching. The electron density was about one order of magnitude lower than the one observed by previous experiments at 0.2–1 Torr in Ar. We present an eigenmode analysis suggesting that this lower density should cause the appearance of hybrid surface TMmns eigenmodes with an axial mode number s=1, which, in contrast to the case of s=0 of the pure surface modes observed previously at higher electron densities, are evanescent along the chamber axis only in the plasma but not in the dielectric region. Electron density and microwave filed distribution measurements in the plasma confirmed the presence of the hybrid surface modes at low pressures (3–15 mTorr).
Control of the preferred orientation of AlN thin films by collimated sputtering
Authors: Rodrı́guez-Navarro A. , Otaño-Rivera W. , Pilione L. J. , Messier R. , Garcı́a-Ruiz J. M.
Published: July 2002

The effects of collimation on the crystallographic orientation of sputtered aluminum nitride thin films have been studied. The AlN films were deposited on glass at a total gas pressure of 15 mTorr using a rf-diode sputtering system. Collimators with angular widths varying from 31° to 140° were used to decrease the range of impingement angles of the flux of species sputtered and reflected from the sputtering target that arrive on the film surface. The three-dimensional crystallographic orientation of the films was studied by the x-ray pole figure method. All the AlN thin films were deposited under similar conditions, with and without collimators, and produced polycrystalline structures with the c-axis (0001) direction perpendicular to the substrate surface. A comparison of the films’ preferential orientations showed that, as the angular width of the collimator decreases, the full width at half maximum (FWHM) of the χ scan profile of the 0002 diffraction peak decreases linearly, indicating a better alignment of the crystallites in the collimated samples. For a film deposited with a collimator of angular width of 31°, the FWHM is 16°, compared to 33° for a noncollimated deposited film under otherwise identical conditions. For films deposited with a rectangular collimator, crystallites orient in an asymmetric distribution which is directly related to the asymmetry of the collimator opening.
Study of thin film deposition processes employing variable kinetic energy, highly collimated neutral molecular beams
Authors: Roadman S. E. , Maity N. , Carter J. N. , Engstrom J. R.
Published: July 2002

Supersonic molecular beams have been investigated as alternative sources for thin film deposition employing a custom designed ultrahigh vacuum reactor. Molecular beam flux produced in this reactor has been measured as a function of gas flow rate, gas composition, and nozzle temperature. An efficient method to measure kinetics of thin film deposition has been developed that allows a large amount of kinetic data (i.e., deposition rate and incubation time) to be gathered per deposition experiment on a single substrate. Film thickness uniformity has been measured under two limiting conditions, which permitted the estimation of both flux and temperature spatial variations across the substrate. The kinetics of epitaxial silicon thin film deposition using Si2H6 has been examined as a function of incident beam kinetic energy (0.5–2.2 eV) and substrate temperature (550–750 °C). Calculated Si incorporation probabilities agree favorably with reaction probabilities previously measured in our laboratory employing a different apparatus and an alternative technique. The kinetics of Si1−xGex thin film growth using mixtures of Si2H6 and GeH4 were also investigated as a function of substrate temperature. In this case the Ge thin film composition was measured as a function of Ge composition of the beam. The incubation period associated with polycrystalline Si deposition on SiO2 has been investigated as a function of substrate temperature and incident beam kinetic energy. The incubation period decreases with both increasing substrate temperature and incident beam kinetic energy. SiC thin film deposition on Si(100) using SiH3CH3 (Ei=2.0 eV) has been investigated and the growth rate depends rather weakly on substrate temperature. Thin film morphology has been characterized using atomic force microscopy, while film crystallinity for polycrystalline and epitaxial films has been examined using x-ray diffraction and low energy electron diffraction, respectively. Epitaxial Si films exhibit a strong (2×1)+(1×2) pattern and a root-mean-square (rms) roughness of <1 nm, while polycrystalline films show 〈111〉, 〈220〉, and 〈311〉 reflections and a rms roughness of 8–25 nm, which increases with film thickness and deposition temperature.
Pulsed plasma-enhanced chemical vapor deposition from CH2F2, C2H2F4, and CHClF2
Authors: Labelle Catherine B. , Gleason Karen K.
Published: July 2002

Pulsed plasma enhanced chemical vapor deposition films have been grown from 1,1,2,2-C2H2F4, CH2F2, and CHClF2. C 1s x-ray photoelectron spectroscopy indicates a prevalence of C¯–CF species in the films from C2H2F4 and CH2F2, whereas CF2 species dominate the films from CHClF2. The CFx species distributions for the films are largely controlled by the competition between CF2-producing and HF elimination reactions in the pulsed plasmas. Dominance by HF elimination produces films with high C¯–CF and CF concentrations (e.g., CH2F2), whereas dominance by CF2-producing reactions leads to films with higher CF2 concentrations (e.g., CHClF2). The % CF3 in the film is lowest for the precursor having the lowest F:H ratio, CH2F2. Little or no hydrogen was detected in the deposited films. Pulsed plasma films from all three precursors gave dielectric constants of 2.4, with loss tangents on the order of 10−2. Dielectric measurements of pulsed plasma films from hexafluoropropylene oxide gave a dielectric constant of 2.0±0.1 with a loss tangent of 0.009.
Effects of thermal annealing on the microstructure and mechanical properties of carbon–nitrogen films deposited by radio frequency-magnetron sputtering
Authors: Lacerda M. M. , Freire F. L. , Prioli R. , Lepinski C. M. , Mariotto G.
Published: July 2002

Amorphous carbon–nitrogen films deposited by radio frequency-magnetron sputtering were annealed in vacuum for 30 min at temperatures between 300 and 700 °C, without any kind of sequential annealing. The annealing-induced modifications on the chemical composition of the films were followed by ion beam analysis (IBA). Raman scattering and infrared absorption spectroscopies were used to determine the microstructure modifications, while atomic force microscopy (AFM) was used to investigate the surface morphology. The internal stress of the films was obtained by measuring the bending of the substrate and the nanoindentation technique was used to measure the film hardness. Besides the nitrogen loss, determined by IBA analyses, Raman results suggested an increase in the size or in the number of the graphitic domains with the annealing temperature. AFM shows a decrease of the surface roughness as a function of the annealing temperature. The density, the hardness, and the internal stress of the films present a similar dependence on the annealing temperature, i.e., they increase with the temperature of the thermal treatment. The thermal treatment induces a structural modification on the carbon–nitrogen films changing from a soft paracyanogen-like material to a harder and more graphitic one.
Nondestructive characterization of thin silicides using x-ray reflectivity
Authors: Detavernier C. , De Gryse R. , Van Meirhaeghe R. L. , Cardon F. , Ru Guo-Ping , Qu Xin-Ping , Li Bing-Zong , Donaton R. A. , Maex K.
Published: July 2002

X-ray reflectivity (XRR) is a nondestructive method for the characterization of layer thickness, surface and interfacial roughness of thin films. We have applied the XRR technique to the characterization of thin CoSi2 (both epitaxial and polycrystalline) and PtSi layers. The silicide films were prepared by rapid thermal annealing and XRR was used before and after silicidation to measure the layer thickness. The XRR results are compared to results obtained on the same films by Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, profilometry and atomic force microscopy. For silicides which grow by diffusion (CoSi2 formed on amorphous Si and PtSi), we found that XRR may be used to characterize both thin (3 nm) and thick (>50 nm) layers. For polycrystalline CoSi2 formed on single crystalline Si, where not only diffusion but also nucleation is important, roughness was a limiting factor for XRR measurements and only thin layers (<15 nm) could be characterized. For epitaxial CoSi2 layers, which are very smooth, both thin and thick layers could be measured.
X-ray phase lens design and fabrication
Authors: Ceglio N. M. , Hawryluk A. M. , Schattenburg M.
Published: July 2002

We have fabricated the first high resolution phase lens for use at x-ray wavelengths. The lens is a Fresnel phase plate made of silver approximately 5500 Å thick. The structure has 100 zones with a minimum zone width of 3200 Å. The lens is designed for use at the Al Kα line (approximately 1.5 keV) with an anticipated first order diffraction efficiency of ≂25%, and a spatial resolution of 4000 Å. Details of phase lens design and fabrication are presented.
Infrared mesh filters fabricated by electron-beam lithography
Authors: Byrne D. M. , Brouns A. J. , Case F. C. , Tiberio R. C. , Whitehead B. L. , Wolf E. D.
Published: July 2002

Capacitive and inductive infrared mesh filters have been fabricated using electron-beam lithography combined with a lift-off procedure. A single level of PMMA was used to create positive tone patterns while a two-level metal-on-polymer process was used to create negative tone patterns. Resonant structures consisting of arrays of crossed metal dipoles and arrays of crossed slots in otherwise continuous metal films have been fabricated that have linewidths less than 0.25 μm, and which exhibit bandstop and bandpass transmissive properties, respectively.
Submicrometer FET gate fabrication using resistless and focused ion beam techniques
Authors: Rensch David B. , Chen John Y. , Clark William M. , Courtney M. DuChesne
Published: July 2002

We report using a focused ion beam lithography, without the use of organic resists, to produce submicrometer gates. Refractory metal gates of WTi, with a minimum length near 0.1 μm, and p-type polysilicon gates, with lengths down to 0.5 μm, were fabricated. The gate lithography utilizes focused beams of Si++ or B+ ions produced from Au–Si or B–Pt alloy liquid metal ion sources and a three-lens mass-separating focusing column. We found that using proper implant and subsequent etch conditions causes the gate material to behave as a negative resist thus enabling gate definition. NMOS FET’s were fabricated with the WTi and p-type Si gates using these techniques and these devices had gate oxide thicknesses of 38 and ∼13 nm. The gate lengths varied between 2.0 and 0.15 μm. Transconductances as large as 180 mS/mm were obtained.
Experimental focused ion beam system using a gaseous field ion source
Authors: Blackwell R. J. , Kubby J. A. , Lewis G. N. , Siegel B. M.
Published: July 2002

An experimental focused H+2 ion beam system being developed for use in a focused ion beam lithography application is described. The system uses a gaseous field ionization ion source operated at cyrogenic temperatures with a 〈100〉 thermal field built-up tungsten emitter tip to confine the ion emission. A five element cylinder electrode lens is designed to focus the hydrogen ion beam. Modeling results show a 120 Å probe could be scanned over a 0.2 mm square field at 30 keV utilizing the high resolution ion optics that the gaseous field ion source permits. Initial ion optical results from this system are presented.
Heterojunction band offsets and scaling
Authors: Kraut E. A.
Published: July 2002

It is shown that accurate x-ray photoemission spectroscopy values of the valence band offsets ΔEv for Ge/GaAs(110), GaAs/ZnSe(110), and Ge/ZnSe(110) vary linearly with the minimum band-gap difference and obey the simple scaling relation, ΔEv/ΔEg(min)=3/4. This empirical observation is compared with the predictions of current theories of heterojunction band lineups and the results are discussed. A theory relating average bulk crystal Hamiltonians to band offsets is developed and this theory is used to calculate band lineups in the tight-binding limit. It is shown that if only interactions between s and p orbitals on adjacent nearest-neighbor atoms are considered, the band lineups coincide with those predicted by Harrison and Tersoff [J. Vac. Sci. Technol. B 4, 1068 (1986)]. Since the latter do not satisfy the experimentally observed scaling relation, it is concluded that second nearest-neighbor contributions to ΔEv are important in the tight-binding limit.
Development of boron liquid metal ion source for focused ion beam system
Authors: Higuchi-Rusli R. H. , Cadien K. C. , Corelli J. C. , Steckl A. J.
Published: July 2002

Boron liquid metal ion sources (LMIS) for the recently acquired VG focused ion beam system have been developed, and Pd73B27 binary eutectic alloy was selected as the p-type dopant source. A lifetime of more than 120 h has been recorded and three different emitter tip radii were used to test boron ion beam stability. Microstructure examination of the Pd73B27 binary alloy proved that boron LMIS instability was caused primarily by the formation of solid precipitates due to a change in alloy stoichiometry. Auger electron spectroscopy (AES) analysis of boron beam deposited on a flat silicon substrate shows rhenium emitter erosion as well as other elements (Fe, Ni, and Cr) resulting from extractor sputtering. In this paper, greater attention is placed on the metallurgical aspects of LMIS in order to develop more reliable boron LMIS.
The dependence of droplet charge distribution on frequency in liquid metal ion sources
Authors: Bahasadri A. , Brown W. L. , Saedi R. , Pourrezaei K.
Published: July 2002

The charge distribution of microdroplets emitted from liquid metal ion sources (LMIS’s) has been investigated as a function of total beam current. For microdroplets with charges of more than 10 000 electronic units, the distribution changes rapidly with total beam current for currents of more than 60 μA. The charge distribution has also been examined when the extractor of the LMIS is driven with an external ac voltage. The total emission of highly charged microdroplets shows a resonance at ∼4 kHz. This resonant behavior may be related to surface wave instabilities that have been suggested as a primary mechanism of droplet formation.
Focused ion implantation of gallium arsenide metal–semiconductor field effect transistors with laterally graded doping profiles
Authors: Evason A. F. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

Implantation with finely focused beams of dopant ions scanned under computer control enables laterally graded doping profiles to be formed. A 150-nm-diam beam of silicon ions from a gold–silicon–beryllium liquid metal ion source has been used to fabricate GaAs metal–semiconductor field effect transistors (MESFET’s) incorporating a number of different laterally graded doping profiles. It is seen experimentally that, when compared with uniformly implanted devices, these MESFET’s display increased available output power and transductance.
Spatial resolution limit for focused ion-beam lithography from secondary-electron energy measurements
Authors: Ando Masaaki , Muray Julius J.
Published: July 2002

The energy distributions of secondary electrons emitted from silicon and other metals when bombarded by gallium, indium, or gold ions have been measured. With these data, a semiempirical theory then enables the effective range of the secondary electrons in a resist layer to be estimated. Typical values lie in the range 0.5–10 nm, and are in agreement with the measured spatial resolution limit for focused-ion-beam lithography.
Reactive ion etching of GaAs and AlGaAs in a BCl3–Ar discharge
Authors: Cooperman S. S. , Choi H. K. , Sawin H. H. , Kolesar D. F.
Published: July 2002

Reactive ion etching of GaAs and AlGaAs has been performed in a BCl3 –Ar discharge. Etching properties have been studied as functions of BCl3 percentage (0%–100%), total pressure (2.5–30.0 mTorr), and power density (0.06–0.22 W/cm2 ). At low pressures (2.5–12.5 mTorr) and intermediate BCl3 percentages (25%–75%), profiles exhibiting a high degree of anisotropy are achieved. Under anisotropic conditions, etch rates are about 0.05–0.1 μm/min (at power density of 0.22 W/cm2 ), somewhat lower than for other chlorine-containing gases. Conditions for etching GaAs and AlGaAs at equal rates have been determined. There is a small lag time between ignition of the glow discharge and the start of etching. The relative concentration of Cl atoms in the plasma, as measured by optical emission actinometry, correlates well with the etch rate for various operating parameters.
Charging effects from electron beam lithography
Authors: Cummings K. D. , Kiersh M.
Published: July 2002

This paper discusses initial results from a study of pattern placement errors due to substrate charging in fixed spot direct write electron beam systems. Experimental results obtained from small crosses written with 20 keV electrons near large pads indicate charging-induced errors of 0.2 μm can occur over 1 mm away from the pad. We present a simple theory that describes the placement errors for large cross-pad separations. The theory suggests that the substrate–electron interaction is strong and long range. Finally, we give some insights on how 50 keV electrons effectively reduce charging effects.
Construction and operation of an ultrahigh vacuum chemical vapor deposition epitaxial reactor for growth of GexSi1−x
Authors: Greve D. W. , Racanelli Marco
Published: July 2002

An ultrahigh vacuum chemical vapor deposition system suitable for deposition of epitaxial GexSi1−x has been constructed. We report details of its construction and operation and demonstrate deposition of epitaxial silicon and GexSi1−x at temperatures as low as 577 °C. Measurements of thickness uniformity both across and between wafers are also presented.
High-performance synchrotron orbital radiation x-ray stepper
Authors: Koga K. , Nomura N. , Yasui J. , Terui Y. , Nagano H. , Fujita K. , Kusumoto S. , Nakano K. , Nakatani S. , Mizuguchi S. , Aoki S. , Yamamoto M. , Yamaguchi K. , Sato T. , Matsuo K. , Yanagida K.
Published: July 2002

A newly designed synchrotron orbital radiation x-ray stepper system has been developed to establish practical quarter-micrometer x-ray lithography and installed in the Tsukuba Research Laboratory for SORTEC Corporation, Japan. This stepper features the newly devised high-precision real-time full-closed alignment system and the ultraprecision vertical wafer stage which can be operated at an atmospheric helium pressure. In order to realize precision positioning of the wafer stage, we developed a 10-axis stage by combining a coarse XY positioning stage guided by hydrostatic air bearings and a fine positioning stage driven by six piezoelectric actuators. We also developed holographic alignment error detection optics, which consists of a three-axis Fourier transform lens system. Alignment error between the mask and the wafer can be detected during exposure and is fed back to the servo control system. By this real-time alignment error correction, an alignment precision of 0.06 μm(3σ) was successfully achieved.
Electron beam induced modification of GaAs surfaces for maskless thermal Cl2 etching
Authors: Clausen E. M. , Harbison J. P. , Chang C. C. , Craighead H. G. , Florez L. T.
Published: July 2002

We have investigated how exposure to an electron beam can modify the surface of a GaAs epitaxial layer, causing the irradiated areas to later show a variable reaction to Cl2 gas at elevated temperatures. In the work presented here, electron beam exposure and thermal Cl2 etching are performed sequentially in two separate vacuum systems. The reaction to Cl2 at elevated temperatures is moderated by the electron beam dose. Below a critical dose we observe that the areas which have been exposed to the electron beam begin etching much sooner than the nonexposed areas. Above the critical dose, a masking effect takes place so that the irradiated areas become more resistant to etching by Cl2 than the unexposed areas. Both positive and negative lithographic patterns can thus be produced in adjacent areas with high contrast. These effects are attributed to changes in a native oxide only a few monolayers thick. The electron beam exposure forms a latent image which is not found in our experiments to be altered or healed by exposure to the atmosphere. The process presents possibilities for maskless patterning and simplification for in situ processing, possibly removing the need for the e-beam system to be directly connected to the growth chamber. Its use would eliminate the difficult sample transfer mechanics permiting separate high resolution e-beam writing machines to be used for pattern generation.
Characterization of a new electron cyclotron resonance source working with permanent magnets
Authors: Neumann G. , Kretschmer K.-H.
Published: July 2002

Most electron cyclotron resonance (ECR) sources available today are working with electromagnets. A new source, developed for etch applications, is supplied with permanent magnets. This leads to strong short-range magnetic fields and the ECR condition is fulfilled on a ring near the chamber wall. Having the maximum electric field strength of the 2.45 GHz along this ring in the microwave radiator leads to efficient plasma production. The principle source characteristics are demonstrated with oxygen plasmas. At low pressure (some 10−4—some 10−3 mbar) and moderate microwave power (100–500 W) the plasma burns as a ring plasma. Increasing pressure and/or microwave power over the above mentioned values leads to a ‘‘bulk’’-type plasma. The change from ‘‘ring’’-type to bulk-type plasma occurs discontinuously and is connected (a) with a discontinuity in the run of the reflected power and (b) with a sudden change in the relative ion flux densities of different ionic fragments measured by mass spectrometry. Absolute ion densities up to 5×1010 cm−3 have been found by Langmuir probe measurements in a bulk plasma at a pressure of 1×10−3 mbar. Anisotropic etching of polysilicon over SiO2 was performed in the ring mode with pure Cl2 as feed gas and applying a radio-frequency (rf) extraction to the ECR plasma. Low damage etching was achieved due to the low direct-current (dc)-bias voltage of 150–200 V with very good anisotropy. The poly-Si etchrate was 85 nm/min with a selectivity of 18:1 to SiO2 and a uniformity of ±7.5% over 200 mm wafers.
Can nuclear magnetic resonance resolve epitaxial layers?
Authors: Buratto Steven K. , Shykind David N. , Weitekamp Daniel P.
Published: July 2002

The recently demonstrated technique of time-sequenced optical nuclear magnetic resonance in GaAs has made possible the detection of spectra free of the line shape distortions that accompanied earlier steady-state methods with an improvement in sensitivity as well. This work examines the possibility of even higher spectral resolution by means of selective averaging with radio frequency-optical multiple-pulse techniques with the aim of isolating the site-specific changes in the spin Hamiltonian associated with excitation to localized states of the conduction band, as in quantum wells. Simulations are presented to evaluate the approach proposed. It is concluded that such experiments are capable of the sensitivity and resolution to resolve individual epitaxial layers in high-quality structures and would provide unprecedented detail on the electronic structure and its uniformity by way of the nuclear quadrupole and spin-averaged hyperfine interactions.
Surface morphology study on CdZnTe single crystals by atomic force microscopy
Authors: Azoulay M. , George M. A. , Burger A. , Collins W. E. , Silberman E.
Published: July 2002

The study of the crystal surface morphology of CdZnTe is important for the understanding of the fundamentals of crystal growth in order to improve the crystal quality which is essential in applications such as substrates for epitaxy or performance of devices, i.e., room temperature nuclear spectrometers. We present here a first atomic force microscopy study on CdZnTe. Cleaved (110) surfaces were imaged in the ambient and an atomic layer step structure was revealed. The effects of thermal annealing on the atomic steps together with Te precipitation along these steps are discussed in terms of deformation due to stress relief and the diffusion of tellurium precipitates.
Kinetics and mechanism for desorption of H2O from spin-on-glass
Authors: Tompkins Harland G. , Deal Paul W.
Published: July 2002

In this study, the rate equation is considered for outgassing of H2O from spin-on-glass during heating cycles. Also considered is the identity of the film species which desorbs. Previous studies have provided processing engineering information about how much the samples must be heated to desorb the water and how long the samples can be exposed to room temperature before readsorption. In this study, residual gas analyzer thermal analysis data are analyzed using methods suggested recently in the technical literature and it is determined that the desorption reaction is second order with an activation energy of ∼19 kcal/mol. Using Fourier-transform infrared, it is shown that the desorption reaction which gives off the H2O during heating involves the reduction of near-neighbor hydrogen bonded silanols to produce Si–O–Si and a water molecule.
Surface core-level shifts in CaF2-on-Si(111) films: Experiment and theory
Authors: Rotenberg Eli , Denlinger J. D. , Hessinger Uwe , Leskovar M. , Olmstead Marjorie A.
Published: July 2002

Using a combination of in situ x-ray photoelectron spectroscopy and x-ray photoelectron diffraction, we have resolved surface core-level shifts for Ca and F atoms in thin (three–eight layers) CaF2-on-Si(111) films. These values are 0.7±0.1 eV towards higher binding energy for Ca 2p electrons and 0.6±0.1 eV towards lower kinetic energy for F KVV electrons. These shifts are in good agreement with a simple extra-atomic electrostatic model in which the shifts are due to the change in both the Madelung potential and the polarization response (relaxation) at the surface. We find no evidence for altered ionicity at the CaF2(111) surface.
Probing the CaF2 density of states at Au/CaF2/n-Si(111) interfaces with photoelectron spectroscopy and ballistic-electron emission microscopy
Authors: Cuberes M. T. , Bauer A. , Wen H. J. , Prietsch M. , Kaindl G.
Published: July 2002

The electronic properties, chemistry, and spatial structure of Au/CaF2/n-Si(111) metal–insulator–semiconductor (MIS) structures, with epitaxially grown CaF2 layers of a few monolayers (ML) thickness, have been studied by photoelectron spectroscopy, scanning-tunneling microscopy, and ballistic-electron emission microscopy. CaF2 films on Si are characterized by flat surfaces with defect lines about 500 Å apart, and band bending in Si reduces gradually with increasing CaF2 layer thickness. Au grows on top of the CaF2 layer in the form of hexagonal terraces. A Si segregation to the surface, as observed in case of the bare Au/Si interface, is strongly reduced by the CaF2 intralayer. Ballistic-electron emission microscopy shows a strong influence of the CaF2 density of states for electron transport through the intralayer. For a 4 ML thick CaF2 intralayer, the position of the CaF2conduction-band minimum is derived from the onset of the collector current at 3.3 V. The valence-band offset at the CaF2/Si interface is derived from the valance-band edge observed in photoelectron spectroscopy.
Two-dimensional fluid modeling of time-dependent plasma sheath
Authors: Hong MunPyo , Emmert G. A.
Published: July 2002

A two-dimensional code is developed for simulating the nonuniformly expanding plasma sheath when a negative potential is applied to a two-dimensional target immersed in a plasma. The code uses fluid equations for the cold, collisionless ions coupled with the Boltzmann relationship for the electrons and Poisson’s equation. The evolution of the sheath at a square target is simulated numerically. The nonuniformity of the incident dose and the angular distribution of the ions striking the surface near the corner are calculated. The incident dose is higher near the corner of the square target but has its maximum value at a slight distance from the corner. In addition, the angle at which the ions strike the surface is more oblique near the corner and the area over which the oblique angle occurs broadens as the sheath grows.
Electron-beam cell projection lithography: Its accuracy and its throughput
Authors: Someda Y. , Satoh H. , Sohda Y. , Nakayama Y. , Saitou N. , Itoh H. , Sasaki M.
Published: July 2002

The cell projection electron-beam lithography system HL-800D has been developed for 0.2 μm ultralarge scale integration circuit and application specific integrated circuit use. This system is formed by a conventional variable shaped beam and cell beams for using five apertures. To achieve high resolution and high-stitching accuracy between the cell beams, and between variable shaped beam and cell beam, we developed the automatic tuning method for cell beams. Included in the method are: (1) rotation and magnification correction, (2) beam alignment for cell beams, (3) space-charge effect correction, and (4) mask position alignment. This method realized a system for easy handling of cell projection tuning. As a result, stitching accuracy under 0.05 μm and resolution under 0.2 μm for cell beams have been achieved. The contact hole layer and the wiring layer of a 0.35 μm DRAM pattern have been overlaid with an accuracy of 0.04 μm (maximum value).
Statics and dynamics of ferroelectric domains studied with scanning force microscopy
Authors: Lüthi R. , Haefke H. , Gutmannsbauer W. , Meyer E. , Howald L. , Güntherodt H.-J.
Published: July 2002

Scanning force microscopy for studying ferroelectric domain structures is applied. The force microscope was operated in the contact static mode (repulsive force regime) and in the noncontact dynamic mode (attractive force regime). These two techniques were applied to study cleavage faces of ferroelectric crystals of GASH (guanidinium aluminum sulfate hexahydrate) and TGS (triglycine sulfate) crystals. Using the contact mode, the positive and negative domains are revealed by opposite contrast. In the dynamic noncontact mode, the domain walls are revealed. The experimental setup allows in situ experiments to study the dynamics of ferroelectric domains. First results on the time dependence of the domains motion in TGS will be presented.