bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and ordering dynamics for Au deposition on Au(110) (1×2)
Authors: Barbier L. , Salanon B. , Sprösser J.
Published: July 2002

The Au(110) surface has a (1×2) missing row reconstruction. It is shown that a metastable (1×1) phase can be formed at 190 K by depositing a one-half Au monolayer to fill the missing rows. Upon annealing (230–450 K) the (1×2) ordering requires extra layer mass transport as is shown by step formation. After deposition of one monolayer, the structure is (1×2) disordered although it includes some (1×1) islands. For that case (1×2) ordering is shown to be slower than the Lifshitz–Allen–Cahn process and occurs between 203 and 273 K.
Ultrahigh vacuum deposition–reflectometer system for the in situ investigation of Y/Mo extreme-ultraviolet multilayer mirrors
Authors: Montcalm Claude , Sullivan Brian T. , Ranger Martial , Pépin Henri
Published: July 2002

An ultrahigh vacuum deposition–reflectometer system was constructed to allow the deposition and subsequent in situ reflectance measurement of extreme-ultraviolet multilayer mirrors. In this article various aspects of the deposition chamber and the reflectance measurement setup are discussed. To demonstrate the capabilities of this system, Y/Mo multilayer mirrors were studied in detail by varying deposition conditions and measuring their subsequent in situ reflectance. By optimizing the deposition conditions, reflectances of 21.3%, 34.7%, and 46.1% were obtained for the Y/Mo mirrors at wavelengths of 7.9, 9.7, and 11.4 nm, respectively.
Effect of grain size and Pb dopant on luminescence in BaTiO3
Authors: Katiyar R. S. , Meng J. F. , Rai Brajesh K.
Published: July 2002

Photoluminescence spectra of Ba1−xPbxTiO3 with grain sizes of 60 nm have been obtained. Different emission bands for pure BaTiO3 have been separately obtained against two excitation lines of 488.0 and 514.5 nm. Based on the dependence of the visible emission band upon Pb content and excitation power, a model that describes the origin of visible emission has been suggested.
Concept of the transmission conductance
Authors: In S. R.
Published: July 2002

The geometric conductance defined in a normal tube is not useful for describing transmission characteristics of a sticky tube with wall pumping in which the gas throughput is not uniform. To find a proper solution to this problem the concept of transmission conductance is introduced instead of the geometric one. The transmission conductance is expressed as a function of the pressures and the throughputs at the inlet and outlet of the sticky tube. Applying the concept of the transmission conductance to the tubes with wall sorption and/or wall outgassing, then a few selected mathematical expressions of the transmission conductance and adsorption speed are derived. A combination rule of the transmission conductance for constructing a composite tube, equivalent to the Oatley’s principle for normal tubes, is also discussed. Comparison of analytic calculations and Monte Carlo simulations shows good correspondence as long as the sticking coefficient on the tube wall is not much larger than 0.1.
Evacuating flat glass panels
Authors: Collins R. E. , Lenzen M. , Ng N.
Published: July 2002

A method of evacuating flat glass panels through a small pumpout tube is described. In order to avoid breakage, the end of this pumpout tube, which is located outside a bakeout oven, has to be mounted in an O-ring fitting, which exerts little force on the tube during evacuation and bakeout. This is achieved first by allowing axial movement of the tube within the O-ring fitting, and second by attaching the vacuum fitting to a bracket, which in turn is fixed to a metal vacuum cup on the glass panel inside the oven. This method has several advantages over conventional evacuation techniques, including enabling the pumpout tube to be situated in a protected location in the edge of the glass panel, and permitting the panel to be baked at high temperatures.
Growth of millimeter-wave GaAs IMPATT structures by molecular beam epitaxy
Authors: Shih H. D. , Bayraktaroglu B. , Duncan W. M.
Published: July 2002

The technique of molecular beam epitaxy (MBE) was applied to the growth of millimeter-wave GaAs double-drift, flat-profile IMPATT structures to meet the stringent doping concentration and thickness requirements. Each structure has five epitaxial layers and was prepared by first growing an undoped AlxGa1−xAs (x∼0.3) layer on a Cr-doped, semi-insulating GaAs(100) substrate held at 600 °C, followed by an n+-GaAs (>1018 cm−3) buffer layer, and n-GaAs (>1017 cm−3) layer, a p-GaAs (>1017 cm−3) layer, and a p+-GaAs (>1018 cm−3) contact layer. Si and Be were used as n-type and p-type dopants, respectively. The AlxGa1−xAs layer acts as an effective ‘‘etch stop’’ during device fabrication, allowing selective removal of the substrate from the epitaxially grown layers in order to reduce the device series resistance. Each device was fabricated with its own ‘‘integral packaging’’ and oscillated in microstrip resonators. The cw oscillations were obtained up to 109 GHz, which is the highest frequency achieved with double-drift-type GaAs IMPATTs.
The growth of high quality Alx Ga1−xAs by molecular beam epitaxy and its application to double-heterojunction lasers
Authors: Collins Douglas M. , Mars Dan E. , Eglash Stephen J.
Published: July 2002

The molecular beam epitaxial (MBE) growth of high quality Si-doped (n-type) and Be-doped (p-type) Alx Ga1−xAs with 0<x<0.4 is reported. Room temperature mobilities and radiative recombination efficiencies comparable to those of high quality liquid phase epitaxial (LPE) and organometallic vapor phase epitaxial (OMVPE) material have been obtained. MBE grown double-heterojunction lasers with Al0.07 Ga0.93As active layers have been fabricated. Broad area lasers having threshold current densities between 880 and 1000 A/cm2 and narrow stripe lasers having threshold currents as low as 84 mA are reported. These values are comparable to the best results for LPE and OMVPE lasers with similar structures.
Ultrahigh molecular weight poly(methyl methacrylate) as an electron-beam resist
Authors: Gavens L. M. , Wu B. J. , Hess D. W. , Bell A. T. , Soong D. S.
Published: July 2002

Ultrahigh molecular weight (UHMW) poly(methyl methacrylate) (PMMA) produced by plasma-initiated polymerization was investigated for its suitability as an electron-beam resist. Patterns exposed in this material at low to moderate doses (<5×10−6 C/cm2) displayed distorted features after development in a 1:1 mixture of methyl ethyl ketone and isopropanol. The distorted features are believed to originate from a combination of pattern swelling and stress relief.
SiO2 films deposited on Si by an ionized cluster beam
Authors: Minowa Y. , Yamanishi K. , Tsukamoto K.
Published: July 2002

SiO2 films of 0.1∼1 μm thickness were deposited on Si substrates (4 in. in diameter) by the reactive ionized cluster beam (RICB) developed from the ICB. Fine powder of SiO2 is vaporized to form a jet stream, which, on being ejected from a nozzle into a high vacuum chamber, is cooled and clustered by adiabatic expansion. The clusters thus obtained are ionized in an electron shower, accelerated, and made to bombard the Si substrate. The distribution of film thickness depends on the directivity of the cluster beam and the density distribution of ion current, the latter varying with the density distribution of the electron shower and the lens effect of an accelerating electrode. The optimum design concepts to obtain uniform films are discussed in detail, focusing on the configuration of a nozzle for the cluster beam and an electron extractor and on the location of an accelerating electrode. The physical and chemical properties of SiO2 films obtained varies with ion current, accelerating voltage, substrate temperature, and oxygen partial pressure. Above all, oxygen pressure plays a very important role in the growth of SiO2 films; with approximately 4×10−3 Pa oxygen partial pressure, the SiO2 films formed by the RICB have a refractive index of 1.46, an etching rate of 540 Å/min with a solution of HF/NH4F=1/15, and the infrared spectrum peaked at 1060 cm−1, which indicates that the RICB can form almost the same quality SiO2 films as thermal oxidation but at a very low temperature of below 300 °C. When the RICB technique is applied to deposit SiO2 films as interlevel insulators for multilayer metallization, uniform step coverages are formed at a low temperature, below 300 °C, which is considered to be possible because of the migration of ionized clusters on the surface of the substrate.
Edge contrast: A new definition for comparative lithography tool characterization
Authors: Stickel W. , Langner G. O.
Published: July 2002

A new definition called ‘‘edge contrast’’ is proposed for realistic resolution comparisons between tools of different beam technology. This new quantity does not pre-empt the traditional intensity contrast definition, but extends it. Taken into account are both the intensity levels in areas to be exposed and not to be exposed, as well as the transition variations (edge slope) between them. As a result, it will be shown that, compared to light-optical tools, electron beam systems have a resolving capability already superior in the range of feature dimensions well above 1 μm. A comparison on the basis of the intensity contrast definition would place the point of equivalency in the vicinity of 0.5 μm. The new definition is not only adequate to characterize the lithography tool, but also suitable to encompass the entire process chain provided the functional dependencies between the process parameters are known.
Heating and temperature-induced distortions of silicon x-ray masks
Authors: Heinrich K. , Betz H. , Heuberger A.
Published: July 2002

This paper presents a detailed discussion of problems concerning mask heating, temperature distributions and resulting distortions of a boron-doped silicon mask which is exposed to intense x-ray radiation (from electron storage rings or plasma sources), having different spatial geometries and different distributions over time. For the calculations, all significant heat-loss mechanisms, e.g., radiation, thermal conduction in the mask, and heat transfer through an ambient gas, have been taken into consideration. The line-shaped synchrotron beam has a vertical Gaussian intensity distribution, with nearly time-constant radiation power. The influences of different scan modes on the temperature rise are taken into account. In the case where helium is used as the coolant gas, the temperature rise remains within acceptable limits, even at the highest possible radiation power. The plasma source emits extremely short, high power x-ray pulses having a homogeneous spatial distribution. The short pulse duration leads to a considerable temperature rise in the mask, which would introduce appreciable distortions. However, the homogeneity of the exposure combined with the stress in the mask membrane can suppress this effect.
Trajectory displacement due to local space-charge force
Authors: Sasaki Tateaki
Published: July 2002

Let the space-charge force Fsp acting on a beam of electrons be divided into two parts, average force Fav and local force Floc. The Floc causes stochastic trajectory displacements which cannot be eliminated by refocusing. Recently, the present author developed a theory of local space-charge force and applied it successfully to the energy broadening phenomenon. This paper applies the theory to the trajectory displacement phenomenon and obtains an analytical formula of the trajectory displacement due to local space-charge force. The formula is compared with the simulation data.
Applying optical methods to aid in linewidth control for the development of sub-half-micron geometries
Authors: Ruby Richard
Published: July 2002

One of the difficulties found in working with the positive e-beam resists in the problem of controlling the linewidth of critical geometries using a fixed time development process. Using the method of interrupted development, where development continues until a particular pattern ‘‘looks right,’’ only somewhat improves linewidth control. Furthermore, the improvement in the sub-half-micron domain remains questionable. Another approach, given here, correlates the disappearance of small islands of unexposed resist (in a ‘‘sea’’ of exposed resist) to the critical dimension (CD) of geometries in the sub-half-micron region. This approach, referred to as SCALES, is a technique that can use an optical microscope for linewidth determination. This, in turn, aids in linewidth control. The existence of these small islands and their subsequent disappearance in the development process can be seen quite easily under the optical microscope. Correlation studies were done comparing the sequential disappearance of the small islands with the CD’s of isolated single-pass lines exposed in polymethylmethacrylate (PMMA). Both random and systematic errors and their sources are discussed and experimental results given. Results based on one carefully controlled in-house e-beam machine yielded a standard deviation (sigma) of less than 0.03 μm. On another machine, the sigma was found to be 0.04 μm. Here, dosage was varied from 40 to 100 μC/cm2, two types of resist were used, and the spot size varied from 0.24 to 0.27 μm during the study. SAMPLE simulations were used to help illuminate certain trends in CD variations due to systematic variations in resist thickness, dosage, and spot size. For comparison, simulations were done for a fixed time development. For the three cases observed, the interrupted development procedure using SCALES showed a superior ability to track CD changes due to process variations over the fixed time development process.
High flatness mask for step and repeat x-ray lithography
Authors: Suzuki K. , Matsui J.
Published: July 2002

A flat and high contrast mask for step and repeat x-ray lithography has been developed. The mask has a 1-μm-thick, 20×20 to 25×25 mm, plasma chemical vapor deposition (PCVD) SiNx membrane, on which x-ray absorber gold patterns are fabricated by selective electropolating. Stress in the SiNx membrane was reduced to about 1×108 dyn/cm2 by optimizing the plasma CVD conditions. Also, stress-free lustrous gold pattern was prepared by optimizing the plating conditions. Furthermore, a stress compensating structure has been employed, which utilized a thermal SiO2 film for compensating a tensile stress in the SiNx membrane. Thus, warpage in the SiNx membrane was reduced to less than 1 μm, regardless of the gold pattern density or of the membrane size. The effective x-ray mask contrast was also much improved by coating the x-ray absorber pattern with another 0.1-μm-thick SiNx film. The SiNx film traps most of the undesirable secondary electrons, which are ejected from the gold pattern during the x-ray exposure process. By using the developed x-ray mask, high aspect ratio half-micron patterns were replicated in the practical x-ray resist, such as negative CPMS (JSR-MES-E) resist or positive NPR (RE-5000P) resist, with high pattern definition.
Electron beam pattern inspection system using digital image processing
Authors: Saitoh K. , Takeuchi S. , Moriizumi K. , Watakabe Y. , Kato T.
Published: July 2002

An electron beam pattern inspection system (EBIS) using digital image processing is presented. A pattern-to-data comparison method is used in this system to detect systematic, random and repeating defects of VLSI circuit patterns. The inspection data are generated from the design data, and transferred from a computer aided design (CAD) system via a computer network. In order to obtain the information of mask or wafer patterns, a low-energy scanning electron microscope, which has the advantage of avoiding damage to the active devices and not charging the surface, is used. Frame memories are installed to store the inspection data and the actual pattern image. An extra image processor preprocesses the pattern image to obtain high signal-to-noise ratio and manipulates these images to extract defects. Two algorithms extracting the defects are studied. Spatial differentiation followed by a thresholding operation is a suitable procedure for the signal with drift.
Substrate rotation and carbon generation in a molecular-beam epitaxy system
Authors: Farley C. W. , Crook G. E. , Kesan V. P. , Block T. R. , Stevens H. A. , Mattord T. J. , Neikirk D. P. , Streetman B. G.
Published: July 2002

This study addresses the tradeoffs involved in using high-substrate rotation speeds to assist in the growth of high-quality heterostructures by molecular-beam epitaxy (MBE). The high rotation speeds desirable to improve the quality of quantum structures are shown to produce high levels of elemental carbon, methane, CO, and CO2 which may incorporate into the MBE layer. The rate of carbon generation cannot be significantly reduced by extended operation at high substrate rotation speeds and temperatures. Therefore, a fundamental tradeoff exists between the benefits obtained from increasing the rotation speed and the resultant increased carbon levels.
Properties of planar magnetron cosputtered silicide films
Authors: Stimmell Jim , Strathman Mike
Published: July 2002

Planar magnetron cosputtering (PMC) is a production technique for deposition of refractory metal silicide films. Films produced using this technique consist of alternating layers of metal and silicon, which intermix during subsequent thermal processing to form homogeneous, low-resistivity films. The resulting films have low-resistivities (28, 48, and 52 μΩ cm, respectively, for WSix, TaSix, and MoSx), and have very good oxidation and dry etch properties. This paper describes the PMC process and discusses the important deposition parameters. Two parameters, substrate bias level and substrate carrier rotation speed, produce effects not usually encountered for single-component sputtered films. The influence of these two variables on film stoichiometry, as-deposited resistivity, oxygen content, and density are examined. Changes in bias and rotation speed are found to produce repeatable changes in stoichiometry, as-deposited resistivity, and density but do not appear to effect oxygen content. As-deposited resistivity increases monotonically with silicon content and is a useful production process monitor. Evidence is also presented which suggests that properly prepared films exhibit very rapid interdiffusion during thermal annealing, and that considerable atomic mixing occurs during the deposition process. This conjecture is supported by the results of rapid optical anneals, which show that MoSix films can become homogeneous during 10-s anneals at temperatures as low as 600 °C.
The morphology and characteristics of TaSi2/Si films oxidized at high pressure
Authors: Wang Yangyuan , Chen Jinhua , Tao Jiang , Feng Sunqi , Zhang Ai-Zhen , Stimmell J. B. , Hopkins C. G. , Strathman M. D. , Herman M. H.
Published: July 2002

The oxidation of Ta silicide on Si substrates has been investigated for pressures from 1 to 10.7 atm. The oxidation of these films fits the Deal–Grove linear–parabolic model, with a direct proportionality of the rate constants to the oxidation pressure. In contrast to results reported for single-crystal Si, the activation energies of the rate constants are found to depend upon pressure. Morphologically, transmission electron microscope micrographs show these oxidized silicide films to be rough, and possess SiO2 between grain boundaries. In addition, the dielectric strength of these oxides is found to be between 4 and 8 MV/cm.
X-ray mask heating during electron-beam patterning
Authors: Karnezos M. , Weimar P.
Published: July 2002

Distortions during mask writing can be caused by thermomechanical forces from the pallet and nonuniform heating of the membrane from the e beam. In this paper we present calculated temperature gradients on an x-ray mask that develop during e-beam patterning on trilayer resist. Monte Carlo simulations are used to calculate the energy deposited in the different layers from the 20 kV, 4 mW e beam of the HP raster scan machine. Although more than half of the energy is deposited in the metal layer, the highest local temperature gradients occur in the resist layers (∼270 °C) due to their low heat conductivity. The gradients in tungsten and boron nitride layers are significantly lower (<3 K). The high conductivity of these layers keep the mask in virtual temperature equilibrium conducting the heat away to the mask rim which is thermally anchored to the machine. The worst case overall temperature rise of the mask at the end of the writing period is <1 K. This corresponds to distortions ∼1 ppm over the full field of the mask.
A novel high-speed nanometric electron beam lithography system: EB–F
Authors: Iwadate Kazumi , Yamaguchi Ryoichi , Hirata Kazuo , Harada Katsuhiro
Published: July 2002

An advanced nanometric electron beam lithography system EB–F has been developed for high-speed writing applications beyond the laboratory. The EB–F achieves a minimum beam diameter of 30 nm with a beam current of 3 nA, a deflection field of 2×2 mm. A triple deflection system was developed to achieve the stepping rate of 100 MHz. This system consists of a magnetic main deflector, an electrostatic subdeflector and an electrostatic fill-in deflector. The maximum size of the fill-in field is 2×2 μm, with a minimum positioning step of 10 nm. An electron gun using a new Ti–W thermal field emitter was also adopted. The gun has high brightness of 108 A/cm2/sr and long term stability. The EB–F has two writing modes. They are the high resolution mode with 30 nm at 3 nA and the fast writing mode with 90 nm at 27 nA. They are selected by switching condenser lenses. Acceleration voltages of 20 and 50 kV can also be selected. These new technologies achieve a greater than hundredfold increase in writing speed. A chip consisting of 40% coverage with 0.1 μm feature size in the 2×2 mm field can be written in 162 s on 30 μC/cm2 resist.
Contrast enhancement of resist images by surface cross-linkage
Authors: Hiraoka H. , Hinsberg W. , Clecak N. , Patlach A. , Chiong K. N.
Published: July 2002

A general method of contrast enhancement which provides control of resist image wall profiles and is applicable to both positive and negative working resists may be obtained by surface cross-linking. The cross-linking is used in our process to retard dissolution at the resist surface. The creation of a slower dissolving surface layer affords greater control of wall profiles and enhanced contrast or sensitivity. One method is to use mid- and deep-UV flood exposure. For a negative working electron beam resist this method is the same as surface photo absorption for contrast enhancement. With our experimental resist containing 4,4′-diazido-diphenylsulfide as a sensitizer, the improvement in its electron beam sensitivity was not substantial. For a positive working photoresist, the same aromatic bisazide was added to conventional positive working photoresists composed of a diazo-naphthoquinone-type photosensitizer and novolac resin. A short-300-nm UV flood exposure followed the G-line imagewise exposures. Another method is to use diffusion-controlled chemical reactions by treating imagewise exposed resist films in a multifunctional cross-linking agent prior to image development. Using these methods, a higher contrast and wall profile control have been demonstrated with positive working photo and electron beam resists.
Precisely controlled oscillating mirror system for highly uniform exposure in synchrotron radiation lithography
Authors: Fujii K. , Okada K. , Nagano M. , Kuroda H.
Published: July 2002

A novel oscillating mirror system in the synchrotron radiation lithography beam line, installed in the Photon Factory storage ring (2.5 GeV), has been studied with special reference to scanning speed control for the synchrotron radiation beam. Concerning an oscillating mirror used in the total reflection region, it should be noted that the cutoff x-ray wavelength depends on the glancing angle. That is, the total photon energy for the reflected varies as a function of the position of the beam irradiating the wafer. An oscillating mirror system has been investigated, in which the scanning speed for the synchrotron radiation beam can be controlled as a function of the glancing angle of the synchrotron radiation beam with reference to the mirror. Exposure result achieved using the oscillating mirror system, showed that extremely high x-ray dose uniformity, ∼±3%, was obtained over the 25-mm-sq. exposure area.
Magnification corrected imaging in synchrotron radiation x-ray lithography
Authors: Müller K.-H. , Brehm K. , Werner K.
Published: July 2002

X-ray masks for ultra-large-scale integration (ULSI) chips having critical dimensions of ∼0.3 μm and field areas of 10 cm2 will be limited by the overlay budget. In this case, a compensation of the linear distortions of mask and wafer can be advantageous. In x-ray lithography, using point sources with divergent radiation, the magnification adaption can be done by slightly varying the proximity gap between mask and wafer. However, this method is insufficient for synchrotron radiation (SR) where the exposing beam is nearly parallel. The illumination is based on a scan motion of the beam with respect to the mask field. We have developed a new technique of magnification correction for SR lithography. In the vertical direction, the correction is done by synchronous shifting of the mask with respect to the wafer. In the horizontal direction, the correction is achieved by bending the wafer by clamping it on a cylindrical chuck. This method compensates for linear overlay deviations in each direction separately; it also holds for trapezoidal errors. In our experiments we used a Suss x-ray stepper and SR of the Berlin electron storage ring (BESSY). Magnification variations on the order of 10 ppm were measured using a Leitz MPV-CD.
Hybrid lithography of a focused ion beam and an electron beam for the fabrication of a GaAs field effect transistor with a mushroom gate
Authors: Hosono K. , Fujino T. , Matsuda S. , Nagahama K. , Sasaki Y. , Morimoto H. , Watakabe Y.
Published: July 2002

The hybrid lithography of a 280-keV Si++ focused ion beam (FIB) and a 20-keV shaped electron beam (EB) has been applied to fabricate a mushroom-shaped gate for a high electron mobility transistor. In this process, a resist in the gate region is reduced to ∼0.2 μm by an FIB lithography (corresponding to ‘‘top-gate’’ formation), and then the center of the top gate is exposed by the EB (corresponding to ‘‘bottom-gate’’ formation). For a thin resist, patterns with smaller dimensions are more easily delineated by an EB exposure than for a thick resist. A 0.2-μm pattern can be obtained by using a shaped EB system with a high throughput. The radiation damage is neglected due to the use of EB for the bottom-gate formation.
Development of a focused ion beam system: Current status and future prospects
Authors: Sawaragi H. , Kasahara H. , Aihara R. , Hassel Shearer M.
Published: July 2002

A computer controlled writing system for a focused ion beam (FIB) has been developed. The system consists of two sets of postlens deflectors, a laser interferometric stage, a high-speed pattern data transfer unit, and a data correction unit. The writing performance was evaluated by the use of a vernier pattern written on a Si wafer coated with 0.6-μm poly(methylmethacrylate) resist with 300-keV, Si++ ions. As a result, an overlay accuracy of 0.22 μm and a stitching accuracy of 0.12 μm were obtained. Throughput of the system is also calculated by assuming simple pattern conditions. This result shows that the current system is impractical for assuming all device processes; however, hybrid utilization of FIB writing combined with conventional processes is an effective way to improve throughput.
Effects of partial coherence on contact hole projection lithography
Authors: White L. K.
Published: July 2002

Calculated image intensity profiles (IIP’s) are presented for contact holes printed with partial coherence levels in the S=0.5 to S=0.7 range and are compared to IIP’s of the correspondingly dimensioned line–space gratings. Improvements in the depth of focus (DOF) latitude and resolution at higher coherence levels (lower pupil fill S) are quantified for contact hole projection lithography with high-numerical aperture (NA), g-line lenses. The relationship between contact and grating DOF is quite complex and changes with the coherence level. Higher pupil fills produce greater differences between the contact and grating DOF. Workable contact hole resolution levels for 0.7, 0.6, and 0.5 pupil fills are estimated to occur at k factors of 0.89, 0.83, and 0.79, respectively, where the k factor normalizes feature size to the resolution factor λ/NA of the lens.
AlGaAs/GaAs heterojunction bipolar transistor with a planar-doped two-dimensional hole gas base grown by molecular-beam epitaxy
Authors: Malik R. J. , Lunardi L. M. , Walker J. F. , Ryan R. W.
Published: July 2002

A new type of AlGaAs/GaAs heterojunction bipolar transistor which employs a two-dimensional-hole gas base formed by planar doping using molecular-beam epitaxy has been demonstrated. The base consists of a submonolayer of Be atoms of sheet concentration 0.5–5×1013 cm−2 which is deposited during growth interruption by molecular-beam epitaxy. Transistor structures exhibit dc current gains up to 700. The effective base transit time is negligible in these transistors and it is postulated that very high speed nonequilibrium transport may occur in the collector region.
High-throughput and fully automated system for molecular-beam epitaxy
Authors: Sakai Junro , Murakami Shun-ichi , Hirama Kimiaki , Ishida Tetsuo , Oda Zenjiro
Published: July 2002

A new high-throughput and fully automated system for molecular-beam epitaxy was developed by employing multiple substrate mount pallets and automatic pallet transfer mechanisms. The geometrical configuration between pallet and effusion cells was optimized to achieve the uniformity of thickness and carrier concentration of epitaxial layer better than ±2% within a pallet. The throughput was more than 70 2-in. wafers per day for the growth of AlGaAs/GaAs two-dimensional electron gas structure. In a typical two-dimensional electron gas structure with a 6-nm spacer layer, the variation of sheet electron mobility closed in 7.5 to 10×104 cm2 /V s at 77 K over growth run to run. By improving the heater structure of the Ga effusion cell, the Ga-related oval defect density was found to be reduced <1 cm −2. The total surface defect density was reduced to <50 cm−2 by preventing the particulate contamination on the growth surface. Moreover, unintentionally doped GaAs layer was dominated by a donor, whose concentration was lower than 1×1014 cm−3, and electron mobility was 145 000 cm2 /V s at 77 K.
Fabrication techniques for nanometer scale resistors: A poor man’s nanolithography
Authors: Garfunkel G. A. , Weissman M. B.
Published: July 2002

A variety of techniques were developed to enable the fabrication of submicron resistors suitable for conductance and noise measurements. Small wires with effective diameters of 400 Å and lengths of 750–2000 Å were fabricated by these means. The techniques are suitable for the fabrication of wires with lengths down to less than 500 Å and effective diameters down to less than 150 Å, and require only standard photolithography and thin film deposition equipment. The processing schemes are an offshoot of those previously developed by Prober et al. [Appl. Phys. Lett. 37, 94 (1980)] for the fabrication of long (>1 μm) small-diameter wires. The techniques reported here include an improved method for making long wires, an alternative method for materials that cannot be handled by that approach, and new techniques to enable the fabrication of wires with lengths well below the 1 μm limit of standard photolithography.
Highly reliable oscillating mirror system for synchrotron radiation lithography
Authors: Kuroda H. , Fujii K. , Suzuki K.
Published: July 2002

An oscillating mirror system suitable for a synchrotron radiation (SR) beamline has been developed. The system, enclosed in an ultrahigh vacuum chamber, can be used for SR lithography in subquarter micron device process due to its high reliability and high performance. Preliminary tests indicated that deviation in the driving velocity was ±3% at maximum, when a 2 cps sine wave command signal was applied. Also, vertical dose uniformity within ±3.3% was obtained, when resists were exposed by adequately modified scanning speed.
Composition, growth mechanism, and stability of anodic fluoride films on Hg1−xCdxTe
Authors: Weiss Eliezer , Helms C. R.
Published: July 2002

Fluoridic films produced by the anodization of Hg1−xCdxTe (x∼0.22) surfaces in nonaqueous solutions consist of three distinct regions. A thick uniform region, containing the fluorides of cadmium, mercury, and tellurium, as well as HgTe, is covered by a thin CdF2 layer. The third region—the film–substrate interface—poor in mercury, consists mainly of CdF2 and TeF4. The anodic film is grown by two mechanisms: the dominant one occurs by motion of the film–substrate interface into the semiconductor, consuming the original surface. There is, however, some growth at the film–electrolyte interface which forms the thin CdF2 layer on top of the structure. The CdF2 rich region acts as a diffusion barrier for the indiffusion of oxidizing species. Tellurium ions, on the other hand, diffuse to the outer surface to be oxidized there. This diffusion barrier is overcome when the fluorides are thermally stressed in the presence of traces of oxygen, and the film starts to oxidize. However, the film–substrate interface does not degrade unless the film is heavily oxidized. A model for the anodic fluoride structure is presented and discussed in light of the film stability with respect to room temperature post-growth oxidation and thermal treatments.
Subband spectroscopy and steady-state measurement of dark current in metal–insulator–semiconductor devices
Authors: Schiebel R. A.
Published: July 2002

We demonstrate a steady-state measurement technique of measuring dark current in HgCdTe metal–insulator–semiconductor (MIS) devices, implementing a gated diode. We show that this technique has several advantages over conventional MIS dark current measurement methods. Using this technique we are able to observe subbands due to inversion layer quantization, hence demonstrating a new technique of subband spectroscopy. The tunnel current into these bands is monitored as a function of temperature to deduce the nature of the tunneling transition.
Novel device concept for silicon based infrared detectors
Authors: Scott G. , Mercer D. E. , Helms C. R.
Published: July 2002

We propose a novel device concept for infrared detectors which utilizes a thin film of a narrow gap semiconductor deposited on a p-Si substrate. Such a device would retain the advantages of using a Si-based technology, while operating with higher quantum efficiency. The operation of the device would be similar to a Schottky barrier detector, in that carriers would be excited from the overlayer into the substrate. However, the absence of undesired states near the Fermi level should lead to more efficient generation and transport of photoexcited carriers. Calculations using a recently developed diffusion model for the behavior of Schottky barrier detectors indicate the potential for an order of magnitude improvement in quantum efficiency over PtSi/p-Si detectors at a wavelength of 4 μm.
WNX–Schottky diodes on semiconductor–insulator–semiconductor-like n-GaAs/undoped-AlGaAs/n-GaAs heterostructures
Authors: Steiner Klaus , Mikami Hitoshi , Nishihori Kazuya , Nagaoka Masami , Uchitomi Naotaka
Published: July 2002

WNX –Schottky diodes on semiconductor–insulator–semiconductor-like n-GaAs/undoped-AlGaAs/n-GaAs heterostructures have been fabricated at various annealing temperatures. The barrier characteristics are evaluated and compared with those of WNX –n-GaAs Schottky contacts. At lower annealing temperatures the metal–insulator–semiconductor (MIS) like diodes exhibit superior barrier heights. However, at higher annealing temperatures (TA≥800 °C), both the MIS and WNX –n-GaAs Schottky diodes almost have equivalent barrier heights. The ideality factors of the MIS like diodes are worse over the whole temperature range. Thicker undoped AlGaAs layers result in increased barrier heights at lower annealing temperatures (TA≤800 °C).
Room temperature surface diffusion mechanisms observed by scanning tunneling microscopy
Authors: Trevor Dennis J. , Chidsey Christopher E. D.
Published: July 2002

Using in situ electrochemical scanning tunneling microscopy, we have discovered several processes that mediate room temperature annealing of the gold (111) surface. These process are shown to be governed by motion of step-edge adatoms and not terrace adatoms. This behavior emphasizes the importance of cooperative effects in low temperature crystal growth. A model of pit motion is proposed based on a random walk of step adatoms. This model predicts that the diffusivity is inversely proportional to the cube of the radius of a pit or island.
Optimization and synthesis of electrostatic nonaccelerating two-interval spline lenses
Authors: Kiss L. , Krafcsik I.
Published: July 2002

Optimization and synthesis of electrostatic unipotential and retarding two-interval spline lenses have been carried out from the point of view of the spherical and chromatic aberrations. The figures of merit to express the lens performance are the spherical and chromatic aberration coefficients referred to the object, calculated in infinite magnification mode, and related to the object side focal length. The computations are based on a direct numerical ray tracing method that is suitable to solve either relativistic or nonrelativistic problems. Conditions for the calculations and optimization constraints are prescribed in compliance with the practice. A three-electrode unipotential spline lens and a two-electrode immersion one have been found as optimum according to the spherical aberration, and they are presented as examples. The spherical figures of merit of the unipotential and the immersion lens are Cso/fo=9.17 and Cso/fo=6.70, respectively. The immersion lens has a local minimum chromatic figure of merit too.
A microwave eight-pole transmission line deflector for 100 keV electrons
Authors: Mulder E. H. , van der Mast K. D. , Tauritz J. L.
Published: July 2002

We have studied an eight-pole transmission line deflector, with the aim of obtaining a large bandwidth deflector with higher deflection sensitivity than an electrostatic deflector. We show that each electrode can be designed as a transmission line with a characteristic impedance that is independent of the orientation of the deflection field. In a transmission line deflector, the deflection field travels along the optical axis at the speed of light, either in the same direction as the electrons (conventional field direction, CFD) or in the opposite direction (opposite field direction, OFD). We show that at high frequencies neither CFD nor OFD improves the deflection sensitivity, due to the magnetic field in a transverse electromagnetic (TEM) wave. Therefore, this deflector is not suitable for achieving the goal of increased sensitivity. However, the OFD achieves the same sensitivity as an electrostatic deflector using a shorter axial length. Finally, the deflection sensitivity of the transmission line deflector proves to be frequency dependent in the frequency range between 100 Hz and 200 kHz, which is illustrated in the experimental results presented.
Improving projection lithography image illumination by using sources far from the optical axis
Authors: Asai Satoru , Hanyu Isamu , Hikosaka Kohki
Published: July 2002

In a projection lithography system having fly-eye elements, a virtual source is created as an array of approximately mutually incoherent point sources. This paper describes simulated results of the light amplitude and phase of the mask-projected image for a point source and discusses the dependence on the point source location on a plane situated perpendicular to the optical axis. We showed that the projected image illuminated by point sources far from the optical axis was improved by the effect of interference between multiple apertures. Resolution of the 0.4 μm lines and spaces was improved theoretically and experimentally at a wavelength of 435.8 nm and a numerical aperture of 0.45.
Correlation of HgCdTe epilayer defects with underlying substrate defects by synchrotron x-ray topography
Authors: Dean B. E. , Johnson C. J. , McDevitt S. C. , Neugebauer G. T. , Sepich J. L. , Dobbyn R. C. , Kuriyama M. , Ellsworth J. , Vydyanath H. R. , Kennedy J. J.
Published: July 2002

Synchrotron x-ray topography studies have been conducted at the National Synchrotron Light Source at Brookhaven National Laboratory to correlate defects in HgCdTe epilayers with those in underlying CdTe family substrates. Infrared detectors have been fabricated on these epilayers to investigate the performance impact of specific defects. This paper describes synchrotron x-ray facilities and methods. Images of substrates and epilayers are discussed and mapping of epilayer/substrate defects, such as microtwins, subgrain boundaries and slip lines, is demonstrated. Efforts to map detector array performance to epilayer and substrate topographs are described.
A study of GaAsSb/InAlAs interfaces grown by molecular-beam epitaxy
Authors: Stutz C. E. , Evans K. R. , Martinez M. J. , Taylor E. N. , Ehret J. E. , Yu P. W. , Wie C. R.
Published: July 2002

Solid source molecular-beam epitaxy was used to grow GaAsSb wells of various thicknesses with InAlAs barriers nominally lattice-matched to InP substrates. As-grown quantum wells (QWs) were measured by photoluminescence (PL) to have a monotonic increase in PL peak energy for a decrease in GaAsSb well thickness, indicating QW confinement. Growth interrupts at the GaAsSb/InAlAs interface, using arsenic and/or antimony overpressure, were found to degrade material quality as measured by PL. Thermal annealing up to the substrate growth temperature had no effect on the QW PL peak energies.
Arsenic passivation of silicon by photo-assisted metalorganic vapor-phase epitaxy
Authors: Rodway D. C. , Mackey K. J. , Smith P. C. , Vere A. W.
Published: July 2002

Earlier work by Bringans et al. [R. D. Bringans and M. A. Olmstead, J. Vac. Sci. Technol. B 7, 1232 (1989); R. I. C. Uhrberg, R. D. Bringans, M. A. Olmstead, R. Z. Bachrach, and J. E. Northrup, Phys. Rev. B 35, 3945 (1987)] and by Woolf [D. A. Woolf, D. I. Westwood, and R. H. Williams, Semicond. Sci. Technol. 4, 1127 (1989)] has shown that molecular-beam epitaxy deposition of arsenic may be used to provide a capping and passivation layer on clean silicon surfaces both to protect the clean surface and to allow the transport of samples between laboratories for characterization purposes. In the present work we have shown that it is also possible to carry out such capping by means of photoassisted metalorganic vapor phase epitaxy using excimer laser radiation to decompose arsine. Suitable control of the laser beam intensity allows the deposition of films varying in thickness from one monolayer to several hundreds of angstroms.
Silylation of novolac based resists: Influence of deep-ultraviolet induced crosslinking
Authors: Op de Beeck Maaike , Van den hove Luc
Published: July 2002

Most surface imaging resist schemes are based on the selective diffusion of a Si-containing compound into the resist. In the diffusion enhanced silylated resist process hexamethyldisilazane is being incorporated in the exposed regions during the silylation treatment. Upon deep ultraviolet irradiation (at 248 nm), novolac based resists will however crosslink to some extent. The crosslinking reaction influences the degree of silicon incorporation in the exposed resist and hence plays an important role in the imaging properties. The crosslinking reaction has been studied in detail in this work for two types of Plasmask deep-ultraviolet resists, along with its consequences on resist imaging. A decrease in silicon incorporation due to crosslinking puts a serious limitation on the useful process window for Plasmask 150u, but the process window is not limited by crosslinking for Plasmask 301u. A thorough investigation of the influence of crosslinking on the pattern deformation is also carried out.
Selective regrowth of InP and GaAs by organometallic vapor phase epitaxy and metalorganic molecular beam epitaxy around dry etched features
Authors: Hobson W. S. , Pearton S. J. , Abernathy C. R. , Ren F. , Lothian J. R.
Published: July 2002

Epitaxial growth of InP and GaAs (AlGaAs) in narrow (∼1 μm wide) trenches and around mesas formed by highly anisotropic dry etching was performed by low-pressure (30 Torr) organometallic vapor phase epitaxy (OMVPE) and metalorganic molecular beam epitaxy (MOMBE). For the [110] oriented trenches and mesas, MOMBE produced highly selective regrowth of both materials under normal growth conditions. By contrast, it was necessary to add CCl4 to the growth chemistry in OMVPE to eliminate deposition on the SiNx mask during growth in trenches and around mesas. Due to growth rate enhancement near the edge of the masked regions, acceptable control of the growth thickness in OMVPE could only be obtained for the case of mesas, but not for narrow trenches.
Improved inverted AlInGa/GaInAs two-dimensional electron gas structures for high quality pseudomorphic double heterojunction AlInAs/GaInAs high electron mobility transistor devices
Authors: Künzel H. , Bach H.-G. , Böttcher J. , Heedt C.
Published: July 2002

Molecular beam epitaxy grown AlInAs/GaInAs single quantum well high electron mobility transistor structures (SQW-HEMT) on InP were developed for transistor applications with high current drive capability. Use of low growth temperatures for the layers below the GaInAs channel in case of the inverted interface proved to be essential to achieve simultaneously high electron concentrations in the channel region and mobilities equal to those of normal single heterojunction HEMT structures. The mobilities obtained in SQW-HEMT structures which employed Si δ-doping on both sides of the SQW channel were found to be only weakly dependent on the channel thickness down to 16 nm whereas below the mobility tended to degrade. Based on theoretical calculations an optimum spatial distribution of the carriers is deduced aiming at high channel electron density and low parallel concentration in the lower supply region by optimizing the thickness of the spacers and the asymmetric distribution of the donors above and below the channel. Further improvements of the SQW-HEMT structures were obtained by incorporating elastically strained In-rich channels. In this way, increased mobilities and concomitantly enhanced electron concentrations have been achieved. Unsurpassed 77 K mobilities amounting up to 55.000 cm2/V s in conjunction with a Hall carrier density of 6.0×1012 cm−2, which compares with a simulated channel density of 5.4×1012 cm−2, were attained. 0.6 μm gate length devices fabricated on the optimized SQW-HEMT layer structures clearly demonstrate the superior performance of the SQW design in terms of saturation current without compromising the pinch-off behavior.