bluuebunny/crossref_metadata_2025 huggingface dataset:
An improved ion source for ion implantation
Authors: Sampayan S. E. , Frisa L. E. , King M. L. , Moore R. A.
Published: July 2002

Modifications to a standard Freeman ion source were made which increased 11B+ scanned wafer current by a minimum factor of 1.4, and 11B2+, 31P2+, and 75As2+ scanned wafer currents by a factor of 4.2. Order of magnitude increases in 31P3+ and 75As3+ scanned wafer currents were also measured in the extracted ion beam. Ion source feed materials were BF3 gas and elemental phosphorus and arsenic. Filament lifetime using BF3 gas has been observed to be in excess of 50 mA h. The apparent increased ionization efficiency was verified by a measured increase in electron density and temperature. In addition, at high extraction current densities (∼30 mA cm−2), the modifications resulted in a symmetric extracted ion beam and uniform filament erosion characteristics. Thus, it was concluded that the plasma uniformity has increased.
Planar vias through Si3N4 fabricated by focused ion beam implantation
Authors: Melngailis John , Herndon Terry O. , Shepard Mark , Lezec Henri
Published: July 2002

Previous work has demonstrated that silicon implanted into Si3N4 at doses above 1017 cm−2 can render the insulator conducting. This has been proposed as a means of making planar vias. Here we report on the use of a focused ion beam to make such planar vias in Si3N4, thus avoiding the need for resist or mask. Implants were carried out at a single energy, 160 keV, using Si++ ions or sequentially at two energies, 80 and 160 keV, using Si+ and Si++ ions, respectively. Films of 0.25-μm-thick Si3N4 over Al metal were implanted. Then the upper layer was deposited, patterned, and the structure was sintered at 425 °C for 30 min. The dose threshold for conduction was between 2×1017 and 5×1017 cm−2 and depended on whether the 160 keV or the two-energy implants were carried out. Interconnects formed in areas 1.6×1.6 μm had resistances as low as 0.15 Ω, while the minimum dimension implants, made with an unscanned beam in 6–12 s, had resistances of 1.5 to 5 Ω. For vias exposed with doses below threshold permanent conduction could be induced by breakdown at voltages well below those needed to break down unimplanted Si3N4. Even with the present state of technology, focused ion beam implantation appears to be a useful technique for making level-to-level interconnects through Si3N4 in limited, critical areas of devices.
Influence of substrate temperature and InAs mole fraction on the incorporation of indium during molecular-beam epitaxial growth of InGaAs single quantum wells on GaAs
Authors: Radulescu D. C. , Schaff W. J. , Eastman L. F. , Ballingall J. M. , Ramseyer G. O. , Hersee S. D.
Published: July 2002

The influence of substrate temperature and InAs mole fraction on the incorporation of indium during molecular-beam epitaxial growth of lattice mismatched InGaAs single quantum wells on GaAs have been investigated. For growth of In0.25Ga0.75As at temperatures <570 °C, a transition from two-dimensional to three-dimensional growth is observed at a certain thickness of InGaAs. This thickness appears to be related to the thickness at which misfit dislocations are generated since it depends upon the substrate temperature during growth. The thickness is largest for quantum wells grown at lower temperature and decreases as the substrate temperature increases. This transition from two-dimensional to three-dimensional growth is not observed at high temperatures (>570 °C) where an indium-induced (4×2) surface reconstruction exists. For growth at 590 °C, Auger electron spectroscopy measurements indicate that the indium atoms reside on the surface of the as-grown layer. However, the growth front of InGaAs remains planar even though indium adatoms do not incorporate into an In0.25Ga0.75As square quantum well. This type of indium surface segregation during growth does eventually degrade the macroscopic morphology of the surface, but only after a capping layer is deposited on top of the InGaAs. Some surface degradation in capped structures is also observed for In0.15Ga0.85As and In0.07Ga0.93As single quantum wells when grown at high temperature (>570 °C), although it is less severe for these lower indium concentrations.
Self-development mechanism of nitrocellulose: Heating effect
Authors: Kaneko H. , Yasuoka Y. , Gamo K. , Namba S.
Published: July 2002

The decomposition of a nitrocellulose resist was achieved by heat treatment in order to investigate the chemical decomposition of the resist due to the electronic collisions in the self-developing process. The decomposition process was evaluated by monitoring the changes in the film thickness and the infrared spectra. A residue left after the heating was quantitatively analyzed. It is concluded that the breakage of the RONO2 bond triggered the decomposition, and the oxidation with the oxygen supplied from NO2 accelerates the decomposition.
Fabrication of low-stress silicon stencil masks for ion beam lithography
Authors: Sen Sudipto , Fong F-O. , Wolfe J. C. , Yen Junling J. , Mauger Philip , Shimkunas Alex R. , Löschner H. , Randall John N.
Published: July 2002

This paper describes the fabrication of stencil masks in large area, low-stress (10 MPa), n-type silicon membranes for demagnifying (4×) ion projection lithography (IPL) and proximity printing. The projection masks have a silicon foil area 95 mm in diameter, thicknesses between 2 and 5 μm, and resolution of 0.6 μm. Proximity printing masks have a 1 cm square membrane area, 0.8 μm thickness, and 80 nm resolution. Measured distortion (3σ) in the IPL masks ranges between 0.23 and 0.65 μm, with an experimental error of 0.20 μm.
Dynamical characteristics of liquid metal ion sources
Authors: Zheng Cui , Linsu Tong
Published: July 2002

The establishment of stable emission in a liquid metal ion source (LMIS) has been analyzed on the basis of electrohydrodynamics. Three requirements for the stabilization of ion emission have been suggested. A computational procedure is developed to simulate the dynamical process with describes how the emission of a LMIS responds to changes in extraction voltage. Some new dynamical characteristics of LMIS’ have been presented and are discussed in detail.
An electron beam measurement and inspection technique for x-ray masks using conductive organic layer
Authors: Watanabe H. , Nikoh H. , Takasu Y. , Todokoro Y.
Published: July 2002

An electron beam (e-beam) measurement and inspection technique for x-ray masks using a conductive organic layer has been developed. This technique consists of spin coating of a conductive organic layer, scanning e-beam probe, detecting the backscattered and secondary electron signals, and removing the conductive layer. By using this technique, x-ray masks are successfully measured and inspected without charging problems. The behavior of incident electrons was also investigated.
Reflection mask technology for x-ray projection lithography
Authors: Hawryluk Andrew M. , Ceglio Natale M. , Gaines David P.
Published: July 2002

We report the first demonstration of the fabrication and characterization of soft x-ray reflecting masks suitable for x-ray projection lithography. We have patterned efficient (R>50%) normal-incidence x-ray mirrors to produce reflecting masks with measured x-ray contrasts>500:1 over a sufficiently wide spectral range. Calculations indicate that masks on silicon substrates are thermally stable for a production-type lithographic facility.
The coherence factors of excimer laser radiation in projection lithography
Authors: Valiev K. A. , Velikov L. V. , Volkov G. S. , Zaroslov D. Yu.
Published: July 2002

The spatial coherence of the excimer laser radiation seriously affects the quality of the images being reproduced by diffraction limited optics in photolithography. It is shown that the coherence parameters of excimer laser radiation exceed the necessary level in 102–103 times. To decrease the coherence down to the optimal level a fly’s eye element is used. The concept of Kirchhoff integrals has been applied to calculate the mutual intensity function transformation by the illuminator of the projection system equipped with fly’s eye element.
Piezo locking stage for nanometer electron-beam lithography
Authors: Kratschmer E. , Rishton S. A. , Luhn H. E. , Kern D. P. , Chang T. H. P.
Published: July 2002

A piezo-actuated locking stage is described, which minimizes stage mechanical vibrations relative to the column in a nanometer electron beam lithography system capable of using large 5-in. diameter substrates. The performance of the piezo locking stage is compared to the performance of a laser position servo system with a resolution of about 5 nm. The measurements show that mechanically locking the stage with respect to the objective lens is far more effective than the servo loop in suppressing mechanical vibrations. With the stage locked, total beam position noise with respect to the substrate has been measured as 2.5-nm peak-to-peak compared to 10-nm peak-to-peak total noise for the servo loop within a bandwidth of 0.25 to 200 Hz. A more detailed analysis of the beam position noise shows that the piezo locking stage reduces the noise component which is caused by mechanical vibrations to 0.4-nm rms.
Anodic oxide metal–insulator–semiconductor structures on n-type InSb
Authors: Chen C. W. , Lile D. L.
Published: July 2002

Anodic oxide metal–insulator–semiconductor (MIS) structures have been prepared on (100)- and (111)B-oriented samples of n-type InSb using either phosphoric or citric acid as the electrolyte. Interface properties have been evaluated using 1-MHz capacitance–voltage (C–V) measurements as a function of temperature from ∼20 to 300 K. By comparing interface state density and fixed charge with preparation conditions for the dielectric, it is concluded that the data are consistent with the presence of elemental Sb at the interface, which acts as a hole trap.
Annealing Ag on GaAs: Interplay between cluster formation and Fermi level unpinning
Authors: Chiang T. T. , Wahi A. K. , Lindau I. , Spicer W. E.
Published: July 2002

It has been shown that upon annealing a 2-monolayer coverage of Ag on UHV-cleaved GaAs at 500 °C, the Ag clusters into islands and the surface Fermi level moves back to within 0.2 eV of the bulk position. In this study, this Fermi level unpinning behavior has been investigated further by using various substrate doping levels and varying the anneal temperature. The Ag clustering process was observed using both ultraviolet photoelectron spectroscopy (UPS) and scanning electron microscopy. Through UPS, the surface Fermi level (Efs) movement was monitored simultaneously with the clustering process. No distinct temperature for the onset of clustering is observed. Rather, the clustering process occurs continuously over the range of temperatures studied (room temperature to 500 °C), with the Ag clusters growing and increasing in separation as anneals are performed at successively higher temperatures. A 10 min annealing time was sufficient to achieve a stable, equilibrium configuration at each annealing temperature. Movement of the Efs back to near the bulk position occurred between 375–450 °C for high doped n-GaAs (6×1018/cm3); whereas no movement of the Efs was observed for low doped n-GaAs (4×1016/cm3) up to 475 °C. Similar results were obtained when the experiment was repeated for high doped p-GaAs (1.4×1019/cm3) and low doped p-GaAs (5×1016/cm3). The absence of movement of Efs in the low doped GaAs is attributed to the longer substrate depletion length, implying that only the areas beneath and within the depletion length of the Ag clusters are pinned.
Surface reactions of trimethylgallium and trimethylarsenic on silicon surfaces
Authors: Förster A. , Lüth H.
Published: July 2002

Epitaxy of III–V semiconductor layers from gaseous sources metalorganic chemical vapor depsoition and metalorganic molecular-beam epitaxy is essentially determined by surface reactions of metalorganic components on the semiconductor surface. The present paper deals with the decomposition of trimethylgallium [TMGa=Ga(CH3 )3 ] and trimethylarsenic [TMAs=As(CH3 )3 ] on Si(111) and Si(100) surfaces. High-resolution electron energy-loss spectroscopy (HREELS) is used to identify the adsorbed surface species by means of its vibrational spectrum. Adsorption of TMGa and TMAs is performed at 300 K and the surface reaction, in particular its dependence on temperature is studied by measuring HREELS spectra after each step. A comparison with thermal desorbtion data is given in some cases. TMGa and TMAs exhibit a different decomposition pattern and the reaction of TMAs is dependent on the orientation of the Si surface.
Electron beam point spread function determination with a confocal scanning laser microscope
Authors: Fastenau Robert H. , Monahan Kevin M. , Kyser David F. , Phelps Steven
Published: July 2002

The confocal scanning laser microscope (CSLM) was utilized for the measurement of electron beam resist features in over-exposed and normally exposed patterns. Using Fizeau interference, a well defined criterion for the location of resist sidewalls was obtained. Measurement of resist feature sizes in over- and normal exposed patterns, in combination with an accurate determination of the dose required to clear the substrate of positive resist, is shown to be very suitable for an accurate determination of the point spread functions in electron beam lithography. The point spread functions for 20 and 50 kV exposure of 0.5 and 1.0 μm thick resist layers were obtained for a variety of substrate materials; Si and GaAs wafers, an ‘‘x-ray-wafer’’ and Cr masks. Also the effect of resist tone on the point spread function was evaluated.
Dual ion beam deposition of oxide, nitride, and carbide films
Authors: Ito H. , Minowa Y.
Published: July 2002

Compound films such as oxides, nitrides, and carbides have been prepared in a dual ion beam (DIB) deposition system, which contains an ionized cluster beam (ICB) source and an ionized gas beam (IGB) source. The characteristic of the DIB system and the properties of compound films such as SiOx, TiNx, and C were investigated. The ion current density distribution was measured at acceleration voltages from 0 to 10 kV by an array of Faraday cups at the substrate position. Uniform ion current distributions over 5-in. diam substrates have been obtained for ICB of Au, Cu, and Si and IGB of CH4, N2, and O2. The composition of SiOx films prepared by DIB approaches stoichiometric SiO2 with increasing oxygen ion current density. The crystalline structure of TiNx films changes gradually from TiN to Ti2N as the atomic flux ratio of (N/Ti) decreases. The Knoop hardness values of TiN and C films prepared at 200 °C are over 1700 and 3000 kg/mm2, respectively. Therefore the advantages of using the DIB deposition system for low-temperature compound film growth include control over film composition and crystalline structure with excellent physical properties. Ion irradiation during film growth by both metal and gas beams enhances chemical reaction kinetics on the substrate.
Deflection for scanning ion beam systems
Authors: Slingerland H. N.
Published: July 2002

Three achromatic deflectors intended for ion lithography are proposed, in which the beam is incident perpendicular to the target. One of these deflectors uses mixed electrostatic and magnetostatic fields, thereby exhibiting mass dependent deflection. Although this is not favorable for a deflector, this setup works well as an achromatic mass filter. Best performance is obtained using a pre-lens deflector using one lens as a corrector. A two lens corrector has theoretically even better performance, but mechanical and electrical tolerances will probably inhibit good performance.
Effects of light absorption in the resist layer in optical lithography
Authors: Tanaka T. , Fukuda H. , Hasegawa N. , Hashimoto M. , Okazaki S. , Koibuchi S.
Published: July 2002

Effects of light absorption in the resist layer at i-line exposure (wavelength 365 nm) are investigated using a newly developed clear resist. Exposure independent absorption (‘‘B parameter’’ proposed by Dill) at i line of the new resist is ∼ (1)/(3) (0.083 μm−1) that of a conventional g-line-use resist used for comparison. Both resists have nearly equal exposure dependent absorption (‘‘A parameter’’) at i line and development characteristics. The only difference between the two resists from the viewpoint of resolution is the B parameter. Thus, it is clarified that a decrease in the B parameter by a factor of (1)/(3) made a 20% improvement in resolution capability and produced a nearly square shaped resist-pattern profile.
Schottky-like behavior of the GaP(110)/Ag interface
Authors: Chiaradia P. , Fanfoni M. , Nataletti P. , De Padova P. , Viturro R. E. , Brillson L. J.
Published: July 2002

We have performed a photoemission study of the Schottky barrier obtained by depositing Ag onto UHV cleaved GaP(110) at room temperature. The barrier appears to be fully developed at a coverage of ∼2 monolayers and its height is 1.1 eV. This figure is to be compared with higher (lower) values obtained with metals having a larger (smaller) work function than Ag, for example Cu and Au (In and Al) deposited onto the same surface. The result corroborates the idea that the metal–GaP(110) interface is a good example of the Schottky limit in metal–semiconductor junctions. The effective work function model proposed by Woodall and Freeouf provides the best interpretation of the Schottky barrier height in this interface.
An In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistor on GaAs substrate by molecular-beam epitaxy
Authors: Won T. , Agarwala S. , Morkoç H.
Published: July 2002

The In0.52Al0.48As/In0.53Ga0.47As heterjunction bipolar transistors were grown and fabricated on a GaAs substrate by molecular-beam epitaxy. In order to suppress the propagation of threading dislocations to the surface, a ten-period AlAs/In0.52Al0.48As (20 Å/20 Å) strained layer superlattice was incorporated twice with intervening undoped In0.52Al0.48As layers. The devices with an emitter area of 50×50 μm2 exhibited a typical common emitter current gain of 50, with a maximum of 63, at a collector current density of 2×103 A/cm2.
Modeling of sloped sidewalls formed by simultaneous etching and deposition
Authors: Gross M. , Horwitz C. M.
Published: July 2002

Dry etching of microstructures in various materials has sometimes resulted in sidewalls which slope away from the mask edge. In this paper we model this phenomenon using a process of simultaneous isotropic deposition and anisotropic etching which has been shown by others to give good qualitative agreement with observed etched profiles. A simple analytical relationship between the etch and deposition rates of the deposited material is given and used to deduce a number of features of sloped sidewall etching. We compare these predictions with some experimental results gained using metal based compounds as the deposit material. We provide evidence suggesting that this metal compound deposition can explain a number of previous observations of sloped sidewalls.
Polycide reactive ion etch: Enhanced circuit performance through profile modification
Authors: Roth S. S. , Cullen M. , Reyes J. , Taylor M.
Published: July 2002

A three step, ‘‘profile flexible’’ polycide etch was developed which allowed polycide profiles ranging from vertical to controlled undercut. A pressure controlled HCl+CF4 overetch was achieved which enabled profile adjustment as desired. Vertical and undercut (0.25 μ per side) polycide profiles were fabricated and speed comparisons accomplished. The majority of devices with undercut profiles exhibited an increase in speed from 20.8 to 23.8 MHz as compared to those devices with vertical profiles.
Dependence of the dissolution characteristics of As2S3 as a photoresist on the condensation rate and evaporation temperature
Authors: Mednikarov B.
Published: July 2002

The conditions of evaporation and condensation of thin layers of arsenous sulfide (As2S3) are described. The difference in the selective dissolution of the illuminated and nonilluminated areas found reveals a possibility for the successful application of As2S3 as an evaporated photoresist for microphotolithographic purposes. In this connection the influence of the condensation rate (Vc) and evaporation temperature (tevp) on the selective dissolution is studied. It is shown that the selective dissolution is negligibly influenced by the condensation rate but strongly affected by the temperature of As2S3 evaporation.
Growth and characterization of InxGa1−xAs on Si by molecular-beam epitaxy
Authors: Cheng K. Y. , Hsieh K. C. , Baillargeon J. N.
Published: July 2002

InxGa1−xAs with In composition up to 0.69 has been successfully grown on Si substrates by molecular-beam epitaxy (MBE) using a modified two-step and short-period superlattice process. Double-crystal x-ray diffraction revealed a large residual anisotropic strain in samples containing less than 40% In. The short-period superlattices were effective in reducing dislocations generated near the InxGa1−xAs/Si interface when the In composition was below 0.5.
The growth of high-purity homoepitaxial InSb layers in a molecular-beam epitaxy reactor previously used for CdTe growth
Authors: Williams G. M. , Whitehouse C. R. , Ward J. J. , Brumhead D. , Ashley T.
Published: July 2002

Cross contamination problems can, in certain circumstances, impose a serious limitation for a molecular-beam epitaxy (MBE) system that is utilized to perform the growth of different high-purity semiconductors. Due to the very high capital cost associated with MBE technology it is essential that cross contamination be eliminated to allow continued use of the apparatus. In this paper we provide full details of a major vacuum-system cleaning exercise performed on an MBE reactor, previously used for cadmium telluride growth, which has allowed it to be subsequently and successfully used for the growth of state of the art high-purity InSb epilayers. Secondary ion mass spectroscopy (SIMS) and electrical measurements performed on InSb layers grown prior to the full cleaning process showed them to be heavily contaminated with tellurium. However, corresponding data obtained following the decontamination exercise indicated the successful removal of the previously observed impurities to below the SIMS detection limit. The cleaning process described should be suitable for any laboratory requiring to change the usage of an existing MBE reactor to the growth of alternative materials.
Defining micron-scale platinum contacts on hydrogenated amorphous silicon
Authors: Lecours A. , Meunier M. , Bisson M.
Published: July 2002

A systematic study of the various ways of defining micron scale platinum patterns on a hydrogenated amorphous silicon surface is described. The results of this study indicate that while dry etching is acceptable in certain cases only a combined process(plasma followed by wet etching) is suitable in applications.(AIP)
Error component analysis in the metrology of x-ray masks
Authors: Foss Gordon O.
Published: July 2002

Understanding and minimizing error sources in the fabrication and metrology of sub-half micron lithographic masks will be the challenge of the 1990’s. X-ray masks, with their relatively thick absorber on thin membrane structures, pose the greater challenge in both fabrication and metrology. Registration data for x-ray masks of different formats have been acquired and analyzed for various error components. Measurement error components are machine measurement accuracy, cassette reloading error, and system temperature stability. Fabrication error components are e-beam placement errors, stress related distortion, and e-beam heating of the membrane during writing. This paper will consider primarily the error components related to e-beam writing and metrology. The primary metrology system used was the MEBES III. Machine measurement error has been determined to be relatively independent of format or substrate evaluated. Cassette reloading has been shown to have a significant impact on measurement error and is dependant on format and/or cassette design. Errors due to e-beam heating during pattern writing have been measured and will be discussed. The errors attributed to these components are not limiting to 0.5-μm mask technology, but must be reduced to address 0.25-μm x-ray masks.
All-level electron-beam lithography for trench isolated nano-metal–oxide semiconductor devices
Authors: Perera Asanga H. , Krusius J. Peter
Published: July 2002

An electron beam lithography based fabrication technology using highly anisotropic reactive ion etching (RIE) has been developed for the fabrication of exploratory 200 nm metal–oxide semiconductor field effect transistors (MOSFETs), designed to overcome scaling limitations below 0.5 μm. A Cambridge Instruments EBMF 10.5 vector scan system operated at 20 keV and field size of 1.6384 mm is employed. A pattern overlay accuracy of 75 nm (3σ) was obtained using 5×5×1.5 μm2 pit marks etched into the Si substrate. The fabrication process uses four resist systems: a polyimide/PECVD SiO2 based trilayer resist, P[MMA/MAA], the negative novalac resist SAL601-ER7, and a newly developed positive novalac e-beam resist SYSTEM-9, which offers contrasts up to 13.9 and a moderate sensitivity of 29 μC/cm2. This integrated electron beam lithography for device fabrication at 0.2 μm and below, allows a throughput of 2–3 wafer/h writing 256 fields/wafer and a maximum data density (exposed area/total area) of 41%.
Surface dielectric anisotropies and phase diagrams of (001) GaAs
Authors: Aspnes D. E. , Florez L. T. , Studna A. A. , Harbison J. P.
Published: July 2002

Using the double-modulation extension of reflectance-difference spectroscopy, we obtain surface dielectric anisotropy spectra under steady-state conditions for several reconstructions encountered in molecular beam epitaxy on (001) GaAs and follow their evolution with temperature. The changes observed with temperature are gradual, generally not exhibiting distinct boundaries. Marked changes in anisotropy are observed during thermal desorption of the native oxide, indicating that the process is not simple but involves surface roughening.
Effects of interface donors on far infrared photoresponse at cyclotron resonance in a (AlGa)As/GaAs heterojunction
Authors: Grimes R. T. , Chamberlain J. M. , Hughes O. H. , Henini M. , Hill G.
Published: July 2002

The low temperature far infrared photoconductive response of several n-(AlGa)As/GaAs heterojunctions (μ≊2×106 cm2 V−1  s−1 , n≊3×1011 cm−2 ) have been measured at wavelengths between 96 and 255 μm, and at magnetic fields up to 10 T. Under certain bias conditions, splittings of the cyclotron resonance peak are noted, which are attributed to transitions involving an impurity band of energy approximately (1/3)ℏωc below the Landau level. Small anomalies in the de Haas–Shubnikov data are related to these states. Silicon ions, diffusing towards the interface, are thought to be the origin of these states.
Structure, chemistry, and Fermi-level movement at interfaces of epitaxial NiAl and GaAs(001)
Authors: Chambers S. A. , Loebs V. A.
Published: July 2002

We have used x-ray photoemission and low-energy electron diffraction (LEED) to investigate the chemical, structural, and electronic properties of ultrathin epitaxial NiAl overlayers on GaAs(001) grown at ∼250 °C. Approximately 30%–35% of the incident Ni in the first two monolayers (ML) of NiAl diffuses into the substrate. At the same time, most of the first ML of Al binds to the surface arsenic layer to form AlAs, leaving the LEED pattern essentially identical to that exhibited by the substrate. As coverage proceeds, NiAl nucleates on the interfacial AlAs layer and approaches a nearly 1:1 stoichiometry by a coverage of∼10 ML. Interestingly, there is no Al–Ga cation exchange at low coverages. Rather, Ga disruption at the substrate begins at 4 ML, and As disruption is first seen at 10 ML. The Schottky barrier height is within experimental error of the substrate value (0.75±0.05 eV) for coverages up to 6 ML, at which point it begins to increase, reaching a final value of 0.9–1.0 eV by the time the NiAl crystal structure is fully developed in the epilayer. The exact final value of the barrier height depends on the structural quality and doping level in the substrate. NiAl epilayers on GaAs are rather robust with respect to thermal treatments. Although annealing 30 ML films at temperatures up to 570 °C causes some Ni indiffusion, the basic NiAl crystal structure remains in tact and the barrier height stays constant at ∼1 eV. The observed barrier height is consistent with the expectations of Mönch’s modified metal-induced gap states model which takes into account charge transfer across the interface.
Relative core level deformation potentials in strained layer heterojunctions
Authors: Grant R. W. , Waldrop J. R. , Kraut E. A. , Harrison W. A.
Published: July 2002

Accurate determination of the valence-band discontinuity (ΔEv) at a pseudomorphic heterojunction interface from x-ray photoemission spectroscopy (XPS) core level measurements requires knowledge of hydrostatic core level to valence-band centroid binding energy shifts. These shifts can be calculated theoretically. Experiments are reported which measure relative core level deformation potentials in strained layer heterojunctions to test the accuracy of the calculated binding energy shifts. The measurements and calculations are not in good agreement; caution is suggested in deriving ΔEv at pseudomorphic heterojunction interfaces by combining calculated deformation potentials with XPS data until this discrepancy is resolved.
Plasma deposited silicon nitride encapsulant for rapid thermal annealing of Si-implanted GaAs
Authors: Lee Seonghearn , Gopinath Anand
Published: July 2002

Silicon nitride films were deposited by the plasma-enhanced chemical vapor deposition (PECVD) method in a silane and nitrogen atmosphere as encapsulants for rapid thermal annealing of Si-implanted GaAs. The deposition rate and refractive index of PECVD silicon nitride films were measured with varying the radio-frequency (rf) power, chamber pressure, N2/SiH4 ratio, and substrate temperature. A wide range of deposition parameters was used, and this range of rf power dependence has not been previously reported.
Adhesion enhancement of Ni films on polyimide using ion processing. III. Si intermediate layers and 84Kr+ implantation
Authors: Galuska A. A.
Published: July 2002

The influence of 10 nm Si intermediate layers and 84Kr+ implantation on the adhesion of 30 nm Ni films on poly [N,N-(p,p′-oxydiphenylene) pyromellitimide] (PI) substrates was examined. The Ni/Si/PI specimens were implanted with either 5×1015, 1×1016, or 5×1016 Kr/cm2 at a specimen temperature of less than 100 °C. Surface topography remained smooth after the 5×1015 and 1×1016 Kr/cm2 implants. In contrast, the 5×1016 Kr/cm2 implant resulted in extensive island formation, which destroyed the integrity of the Ni films. Auger electron spectroscopy (AES) depth profiles of the as-deposited films showed graded Ni distributions throughout the Si intermediate layers, which form abrupt interfaces with the PI substrates. After implantation with 5×1015 or 1×1016 Kr/cm2 implants, the Si intermediate layers become highly oxidized. Significant quantities (15 to 20 at. % in the Ni film) of carbon were transferred into the Ni films from the PI substrates, but the interface to the PI substrates remained sharp. The Ni that was present in the as-deposited Si layers appears to segregate out of these layers after the ion-induced oxidation. X-ray photoelectron spectroscopy (XPS) analysis showed that the chemistry of the Si interfacial layers changed from a mixture of SiO and Ni2Si in the as-deposited specimens to almost entirely SiO2 in the implanted specimens. The adhesion of the Ni films was examined using a scratch test. The as-deposited Ni films were removed at a force of 4 N with failure at the Si/PI interface. After ion implantation, the films were removed at a force of only 2 N, and the failure occurred at the Ni/SiO2 interface. This reduction in adhesion, which was in startling contrast to the adhesion enhancement obtained by implanting Ni/PI specimens with 28Si+, was attributed to the preferential formation of SiO2 during the 84Kr+ ion bombardment. It was concluded that the Si must be implanted into both the Ni films and the PI (or other oxygenated polymers) in order to maximize the adhesion enhancement of Ni films.
In0.53Ga0.47As/InP quantum wires: Fabrication and magnetotransport studies
Authors: Menschig A. , Roos B. , Germann R. , Forchel A. , Pressel K. , Heuring W. , Grützmacher D.
Published: July 2002

We have fabricated In0.53 Ga0.47 As/InP quantum wires with geometrical widths down to 80 nm by high resolution electron beam lithography and dry etching. The magnetotransport measurements display four distinct features: (1) The Shubnikov–de Haas oscillations show for narrow wires (<200 nm) a strong deviation from the 1/B periodicity. (2) Over the complete magnetic field range there are nonperiodic universal conductance fluctuations superimposed on the resistance curve. (3) At very low magnetic fields we observe a large negative magetoresistance, which decreases with increasing wire width. (4) In narrow wires we observe a distinct magnetoresistance peak at magnetic fields of about 1 T.
The silylation processes for positive and negative deep ultraviolet resists
Authors: Sviridov S. M. , Timerov M. R. , Valiev K. A. , Velikov L. V. , Zaroslov D. Yu.
Published: July 2002

In this report the experimental results of the resist silylation and O2-plasma development are presented. The Soviet commercial novolac based photoresists of both positive and negative type and gas phase silylation in hexamethyldisilazane (HMDS) were used. The flood exposure of the resist films was made by Hg lamp or KrF laser. It is found that the silylated resist film mass growth (per resist surface square) must exceed 15×10−6 g/cm2 to provide the formation of the etching barrier layer under O2-plasma development. The silylation kinetic is shown to be linear at first period. The dependence of the initial silylation rate on the experimental conditions was studied and results are discussed. Under the silylation of the highly crosslinked resist films the induction effect was observed. For both positive and negative processes the silylation conditions providing selective O2-plasma development are determined. To enhance the contrast of O2-plasma development the three-stage procedure was elaborated.
Absolute flux measurements for x-ray lithography beamlines
Authors: Baszler F. , Hansen M. , Cerrina F.
Published: July 2002

A calorimeter is calibrated for use as an absolute radiometer for synchrotron radiation x-ray lithography (XRL) beamlines. Results of the characterization of two beamlines are reported and compared with theory. Photodiodes and a film detector were calibrated against the calorimeter and the performances of these ordinary radiometers are presented. Using the methods described in this paper an absolute flux reading was obtained with accuracies believed to be better than ±2%. The experimental results are compared with the prediction of a theoretical model called transmit. The code is used to predict the performance of XRL beamlines and is very suitable for ‘‘what if’’ types of scenarios.
Novel process using x-ray lithography for T-shaped gate patterns
Authors: Yoshioka Nobuyuki , Fujino Takeshi , Morimoto Hiroaki , Watakabe Yaichiro , Abe Haruhiko
Published: July 2002

A fabrication process capable of forming T-shaped gates useful for high-performance GaAs field-effect transistor devices by exposing a single-layer resist with x rays is proposed in this work. The x-ray mask used in this method has absorber patterns with T-shaped cross sections, which are made up of two absorber layers. This method makes good use of the fact that the x-ray transmittance of materials such as resists and mask absorbers is higher than the ultraviolet/visible light transmittance used in photolithography. In order to confirm the practicality of this method, T-shaped patterns were formed experimentally using the positive resist XPB and an exposure system with an electron-excited x-ray tube (Pd target). The x-ray mask was fabricated by patterning two layers of W-Ti alloy absorber on a BN/polyimide membrane using an electron direct writing technology. It is demonstrated that the T-shaped pattern can be formed easily by using the proposed process.
Contrast amplification of very high resolution x-ray masks
Authors: White V. , Wallace J. , Cerrina F. , Vladimirski Y. , Su Y. , Maldonado J.
Published: July 2002

Future applications of synchrotron based proximity x-ray lithography will require cost effective methods to generate high density patterns with features smaller than 0.25 μ. Masks written with e-beam lithography typically use a trilayer resist system. The process is complicated, defect prone, and expensive, but result in a high contrast proximity x-ray mask. We are investigating an alternative technique involving the e-beam patterning of nanostructure features into a single layer of resist, and its direct metallization to produce a low contrast x-ray mask. This would be used as a master mask for making duplicates. This paper investigates methods that varied spectral and developmental parameters to heighten the contrast sufficiently for pattern transfer into thicker resist providing a potential contrast increase from a dose contrast of 1.7 to on the order of 10.
An investigation of some depth of focus issues in high numerical aperture projection lithography system by experiment and simulation
Authors: Spence C. A. , Ferguson R. A. , Yeung M. , Das S. , Hutchinson J. M. , Neureuther A. R.
Published: July 2002

We have examined the imaging of 0.3 μm equal line/space patterns, in 1 μm of Shipley SN248 resist (referred to as XP8843, in this paper) using projection lithography with deep-UV exposure (248 nm). Experimentally, we have observed some interesting development effects for these small features with high aspect ratios, which highlight the role of developer agitation when using this resist. Our simulations, using a vector model to simulate the exposure, show that because of the high contrast of this resist, there is a greater depth of focus for printing 0.3 μm line space patterns when using a numerical aperture (NA) of 0.42 than 0.6. Interestingly, we see that the process window, when using a NA of 0.6 is only slightly greater when using a thin (0.3 μm) resist than when using a thick (1 μm) resist. This is due to the low absorption of the resist at 248 nm. Unfortunately the low absorption of the resist makes it extremely sensitive to thickness changes when printing on highly reflective substrates, e.g., bare silicon.
Process margins for pulsed laser-induced via filling
Authors: Marella Paul F. , Tuckerman David B. , Pease R. Fabian
Published: July 2002

Process margins have been experimentally determined for pulsed laser-induced filling of Au-coated square vias of varying size (2–15 μm side lengths) and aspect ratio using either a flashlamp-pumped dye laser (λ=490 nm, FWHM pulse duration=600 ns) or an excimer laser (Xe*Cl, λ=308 nm, FWHM pulse duration=35 ns). For 2.0-μm-thick Au coatings, either laser provided comparable process margins (up to ±14%) for the same via diameter. For 3.8-μm-thick coatings, the flashlamp-pumped dye laser exhibited process margins (up to ±21%) nearly twice that of the excimer laser (±12% maximum). Near the damage threshold fluence, excimer laser-induced film damage was localized near irradiated spot edges (the regions of highest intensity gradient), suggesting evaporative recoil effects due to the high peak intensity of this laser. In contrast, the longer, less intense pulse generated by the flashlamp-pumped dye laser did not give rise to these localized effects, instead producing film damage in the regions of highest incident intensity (the damage mechanism has not been identified). Frozen-in capillary waves, produced during the laser-induced flow of the molten metal, are shown to yield information about the metal’s melt duration while suggesting a method for constructing an in-situ process monitor.
A theoretical comparison of the data-acquisition time characteristics of the time of flight voltage contrast detector with retarding field detectors
Authors: Khursheed A. , Dinnis A. R.
Published: July 2002

This paper carries out a theoretical study of the data-acquisition time advantages of the time of flight multichannel voltage contrast detector over conventional retarding field detectors. A theoretical model is developed which can be generalized to apply to other possible multichannel voltage contrast detectors. The results show that where surface field effects are not present or can be eliminated, the data-acquisition times of the time of flight detector can be two orders of magnitude faster than conventional retarding field detectors. Under strong surface field conditions this factor of improvement can fall to below an order of magnitude.
Performance of a combined focused ion and electron beam system
Authors: Sawaragi H. , Mimura R. , Kasahara H. , Aihara R. , Thompson W. , Shearer M. Hassel
Published: July 2002

In order to characterize electron and ion beam induced etching and deposition parameters in a single system a combined focused ion beam (FIB) and electron beam (EB) column has been developed. This system has both an electron gun and a FIB gun with a gallium liquid metal ion (LMI) source integrated on an objective lens and deflector assembly shared by both sources. A cylindrical electrostatic prism was used to position the electron beam on the final lens axis. We have optimized the EB crossover location to minimize chromatic blurring induced by the prism. In addition, the system was configured with a common retarding lens below the objective lens to permit low energy ion and electron beam experimentation. This lens provided the system with an energy range from 1 to 25 keV. The theoretical minimum probe diameters at 1 keV are 20 and 300 nm, respectively, for the electron and focused ion final beam diameters. We will present the experimental scanning electron microscopy (SEM) mode and scanning ion microscopy (SIM) mode image results which compare well to the theoretical predictions at 1 keV.
Intense pulsed plasma x-ray source for lithography
Authors: Kalantar D. H. , Hammer D. A. , Mittal K. C. , Qi N. , Maldonado J. R. , Vladimirsky Y.
Published: July 2002

The x-pinch soft x-ray source is described for application in submicron resolution lithography. Experiments have been performed to measure and characterize the radiation emitted from the magnesium wire x-pinch plasma using an 80 ns, ≤500 kA pulse. Soft x-ray yields of 14.2 J averaged over three independent calibrated diagnostics at 445 kA have been measured in magnesium K-shell radiation (predominantly 8.4–9.4 Å or 1.5–1.3 keV) from a submillimeter source, with as little as 5–10% of the yield below the 6.74 Å silicon absorption edge. Samples of high sensitivity x-ray resist have been exposed in as few as two pulses at a 10 cm distance. Observed scaling of the yield indicates the possibility of effectively exposing a resist at a distance of 40 cm using a<750 kA pulser.
Process characteristics of an all-organic chemically amplified deep-ultraviolet resist
Authors: Cheng M. , Nalamasu O. , Timko A. G. , Pol V. , Kometani J. M. , Reichmanis E. , Thompson L. F.
Published: July 2002

An all-organic chemically amplified positive deep-ultraviolet resist has been developed that demonstrates 0.35 μm resolution at a dose of ∼18 mJ/cm2 of 248 nm KrF laser radiation. Good critical dimension uniformity and process latitude were demonstrated. Additionally, use of an overcoat material applied immediately after resist coating reduces the dependence of the resist on the time delay between exposure and post-exposure bake. Efforts relating to process optimization will be described in conjunction with current process performance capabilities and limitations. Additionally, a comparison between triphenylsulfonium hexafluoroarsenate onium salt and nitrobenzyl ester resist formulations will be discussed for select process steps.
Carbon removal from as-received Si samples in ultrahigh vacuum using ultraviolet light and an ozone beam
Authors: Lenssinck J. M. , Hoeven A. J. , van Loenen E. J. , Dijkkamp D.
Published: July 2002

A novel Si-sample cleaning method is described. This low-temperature process uses ultraviolet (UV) radiation and an ozone beam to remove carbonaceous components from the native oxide of as-received Si samples. Because the cleaning process is implemented as an ultrahigh vacuum (UHV) process in a UHV process chamber, the sample does not need to be reexposed to atmospheric conditions between the carbon removal and the desorption of the native oxide, which results in very low contamination levels. The efficiency of this carbon removal-method is determined.
Characterization of PbTe/p-Si and SnTe/p-Si heterostructures
Authors: Scott G. , Helms C. R.
Published: July 2002

Heterostructures which utilize a thin film of narrow-gap semiconductor deposited on a p-Si substrate have the potential to function as high-efficiency, easily fabricated infrared detectors. We have characterized two such systems, namely PbTe and SnTe. The structures were prepared by congruently evaporating films of PbTe and SnTe from single sources of the compounds onto 〈100〉 p-Si wafers which were chemically cleaned prior to deposition. We have analyzed the composition and electrical properties of the deposited films, as well as the electrical and photoresponse properties of the heterostructures. Current–voltage measurements indicated rectifying behavior with good ideality factor and low leakage down to 77 K for the case of SnTe/Si. High series resistance of the PbTe/Si structures made electrical characterization difficult, though they also showed rectifying behavior and low reverse leakage. Photoresponse measurements indicate a threshold of 0.36–0.4 eV for SnTe/p-Si and 0.3 eV for PbTe/p-Si. These results indicate that the PbSnTe alloy on p-Si will have a lower energy threshold than either of the binary compounds.
Resist development simulation treated as a boundary value problem
Authors: Bergner K.
Published: July 2002

A very efficient method is described for the simulation of the resist development process in electron beam lithography. This method is based on Fermat’s principle of geometric optics, and the derived systems of differential equations are solved as boundary value problems. By way of this new idea, a compact representation of the computed results is obtained, the difficulties with the ‘‘loops’’ are avoided, and an efficient mathematical algorithm leads to a very small calculation time. This approach is applicable to optical lithography also. The results of typical examples are presented and briefly discussed.
Selective annealing for the planar processing of HgCdTe devices
Authors: Parat K. K. , Ehsani H. , Bhat I. B. , Ghandhi S. K.
Published: July 2002

Hg1−xCdxTe layers grown by organometallic vapor phase epitaxy are p type with carrier concentrations around 4×1016 /cm3 due to group II vacancies. Following a Hg saturated anneal at 220 °C for 25 h, these layers become n type with carrier concentrations around 5×1014/ cm3 . However, the presence of a 0.5–0.8 μm thick CdTe cap inhibits the annealing of the underlying Hg1−xCdxTe layer, since it acts as a barrier for Hg diffusion. By opening windows in this cap, the underlying Hg1−xCdxTe layer can be annealed and converted to n type in a selective manner. P–N junction photodiodes were fabricated using this planar technique. Some of these diodes employed the CdTe cap itself as the surface passivant; in others, the CdTe cap was stripped and anodic sulfide was used as the junction passivant. In both the cases, diodes had R0A values comparable to the best values reported in literature. N-channel enhancement mode metal–insulator semiconductor field effect transistors were also fabricated using anodic sulfide as the surface passivant. Here, the n-type source and drain regions were formed by selectively annealing the as grown p-type Hg1−xCdxTe layer.