bluuebunny/crossref_metadata_2025 huggingface dataset:
High-temperature stable W/GaAs interface and application to metal–semiconductor field-effect transistors and digital circuits
Authors: Josefowicz Jack Y. , Rensch David B.
Published: July 2002

The thermal stability of the physical, chemical, and electrical properties of W thin films sputter deposited on GaAs were investigated. A variety of characterization methods, including thin film stress analysis, Auger analysis, Rutherford backscattering spectrometry (RBS) analysis, and Schottky barrier measurements showed that the W/GaAs interface remains stable after high-temperature furnace annealing at 900 °C for 15 min or rapid-lamp annealing at 1000 °C for 11 s. Some refractory metal compounds were also investigated, including, WSi, WNx, and TaSix. Pure W films produced the best Schottky diode characteristics. The average Schottky barrier height was 0.70±0.009 V across a 2-in wafer after furnace annealing at 800 °C/15 min. Pure W self-aligned gate (SAG) metal-semiconductor field-effect transistors (MESFET) and digital circuits were also fabricated. Transconductances as high as 300 mS/mm (Lg =1.0 μm) were measured for enhancement mode SAG MESFET’s. Circuits were fabricated with SAG MESFET enhancement-resistor mode logic using pure W gates, including ring oscillators, with gate delay as low as 25 ps and divide-by-eight circuits that functioned at a frequency >1 GHz.
Refractory metal nitride rectifying contacts on GaAs
Authors: Zhang L. C. , Liang C. L. , Cheung S. K. , Cheung N. W.
Published: July 2002

The electrical characteristics of reactive-sputtered refractory metal nitride contacts on GaAs are investigated for their high-temperature stability after rapid-thermal annealed up to 850 °C for 10 s. It is observed that all the contacts studied, including ZrN/GaAs, TiN/GaAs, and NbN/GaAs systems, show improving rectifying characteristics with annealing temperatures up to 800–850 °C. Not only do they maintain excellent thermal stability and have ideality factors very close to unity, these refractory metal nitride/GaAs contacts actually exhibit a barrier height enhancement ranging from 0.13 eV for NbN/GaAs to 0.30 eV for ZrN/GaAs when contacts are annealed from 500 to 850 °C. Concomitantly, the small-signal capacitance of the contacts decreases with higher annealing temperature. The breakdown characteristics of these contacts become avalanche-like and the breakdown voltages increase by twofold. We have invoked the Shannon contact structure (i.e., metal/p+-GaAs/n-GaAs) to account for these high-temperature induced properties. The p+-GaAs layer formation is attributed to the incorporation of nitrogen into GaAs substrate during sputtering deposition. Comparison between pure refractory metals and their nitride contacts on GaAs are also made with electrical techniques (I–V, C–V) and material characterization techniques (Rutherford backscattering, scanning electron microscopy). Our study suggests that refractory metal nitrides have several advantageous properties for self-aligned GaAs metal–semiconductor field-effect transistor processes.
Low-pressure deposition of high-quality SiO2 films by pyrolysis of tetraethylorthosilicate
Authors: Becker F. S. , Pawlik D. , Anzinger H. , Spitzer A.
Published: July 2002

The deposition of SiO2 by pyrolysis of tetraethylorthosilicate (TEOS) at pressures below 1 Torr was investigated at temperatures between 650 and 800 °C. We found oxide thickness variations of <±5% for suitable process conditions (PD ≤500 mTorr, wafer spacing ≥4.7 mm, TD <730 °C, deposition rate 16 nm min−1). Tests with 150-mm wafers showed that uniformities of ±2% can be achieved if the wafer spacing is increased to 10 mm. Raising the deposition pressure improves the step coverage in deep trenches but degrades the thickness uniformity across the wafer. The investigations of etch rates in different media show strong dependences on the anneal temperature for etchants containing HF but only a slight dependence for plasma etching. The dielectric breakdown strength of the oxides was 8 MV cm−1 and the failure rate after 500-ms current stress at 1 mA cm−2 lower than 20%. We found values for the interface state density of 1×1010 eV−1 cm−2 and for the oxide charge density in the range 3×1010 cm−2 to 2.5×1011 cm−2, depending on the oxide thickness. The hysteresis of C–V scans was <2 mV. No substantial shift of the C–V curve was found after temperature–bias stress. Our I–V investigations showed that the carrier transport is governed by the Poole–Frenkel mechanism. These results as well as secondary ion mass spectroscopy investigations of the layers confirm that Merck TEOS can be used to grow oxide films of sufficient electrical quality for microelectronic applications.
Subsurface cobalt diffusion in silicon single crystal from infinitesimally small cobalt diffusion source
Authors: Appelbaum A. , Malm D. L. , Murarka S. P.
Published: July 2002

The cobalt diffusion, from an infinitesimally thin source, in silicon single crystal has been investigated in the temperature range of 700–1000 °C. Radioactive tracer and secondary ion mass spectroscopic techniques were independently employed to determine diffusion profiles. The diffusion coefficient is given by 0.68–1.35×10−9 exp(−1.5±0.1 eV/RT) cm2/s. These diffusion coefficient values are several orders of magnitude lower than previously reported values obtained using thick cobalt films as the source of diffusion anneals carried out at higher temperatures. The differences in the experimental conditions and their influence on the diffusion coefficients are discussed.
Self-consistent electronic structure of semi-infinite Si(001) (2×1) and Ge(001) (2×1) with model calculations for scanning tunneling microscopy
Authors: Pollmann J. , Krüger P. , Mazur A.
Published: July 2002

We have investigated surface electronic properties of semi-infinite Si(001) (2×1) and Ge(001) (2×1) using our recently developed self-consistent scattering theoretical method. The calculations are based on local density functional formalism and make use of one-particle Green’s functions. We present results for both symmetric and asymmetric dimer reconstructions of the surfaces to contribute to the current discussion of their structural properties. From comparing our results with photoemission and inverse photoemission data, we find that the asymmetric dimer model agrees better with the data than the symmetric dimer model. These findings are discussed, as well, in light of the recent scanning tunneling microscopy data of Hamers et al. In particular, we use our theory to add to the interpretation of scanning tunneling microscopy and spectroscopy data on Si and Ge(001) (2×1) surfaces.
Crystal orientations and defect structures of GaAs layers grown on misoriented Si substrates by molecular-beam epitaxy
Authors: Lee J. W. , Tsai H. L.
Published: July 2002

The GaAs crystal orientations and the defect structures of the GaAs grown on misoriented (100) Si substrates have been investigated using chemical etching and transmission electron microscopy techniques. It was found that the GaAs orientations were uniquely determined on the (100) Si substrates tilted toward a (011) zone, and the GaAs layers were free from the antiphase domain problem. The reason was ascribed to the misoriented Si surface states, which consist of two-atom steps and preferentially aligned dangling bonds relative to the Si tilt direction. Also it was found that stacking faults and twins formed on the step terraces and propagated along only two out of four (111) planes. Most of them were annihilated near the GaAs/Si interface by crossing each other.
GaAs avalanche photodiodes and the effect of rapid thermal annealing on crystalline quality of GaAs grown on Si by molecular-beam epitaxy
Authors: Chand N. , Allam J. , Gibson J. M. , Capasso F. , Beltram F. , Macrander A. T. , Hutchinson A. L. , Hopkins L. C. , Bethea C. G. , Levine B. F. , Cho Y.
Published: July 2002

Photoluminescence, Rutherford backscattering/channeling, x-ray double crystal rocking curves, and minority carrier lifetime suggest that structural and optical properties of GaAs grown on Si by molecular-beam epitaxy (MBE) improve greatly as a result of postgrowth rapid thermal annealing (RTA). Transmission electron microscopy, in contrast, shows no significant reduction in defect density (∼108 cm−2) after RTA although the defect configuration is affected. Dislocations tend to organize better and combine each other after RTA. The minority carrier (electron) lifetime was found to improve from 2 to 2.7 ns as a result of RTA in p+GaAs(p>1018 cm−3). Annealing at a temperature as low as 750 °C and of a layer as thin as 0.1 μm also produces a significant improvement in photoluminescence (PL) intensity. It is suggested that in situ RTA after a short growth (∼0.1 μm) followed by the growth of the rest of the structure may result in substantial improvement in material quality. To assess the uniformity of the as-grown GaAs on Si and the presence of electrically active defects, avalanche photodiodes (APD’s) were made and tested for spatial uniformity of photoresponse with the help of a flying spot microscope. In devices with thin buffer layer (1.5 μm) microplasma were found to be formed at high reverse field. However, in devices with a thick buffer layer (3 μm) no spatial variation of avalanche gain over the whole device area or formation of microplasmas was detected at the highest reverse field applied. The avalanche gain in APD’s was rather low (∼7) and was limited by the excessive leakage current. The I–V characteristics and the device yield were found to improve significantly on a wafer which was rapidly thermal annealed prior to processing.
Photodeposition rates of metal from metal alkyls
Authors: Krchnavek Robert R. , Gilgen Heinz H. , Chen Julian C. , Shaw Ping S. , Licata Thomas J. , Osgood Richard M.
Published: July 2002

Laser photodeposition of zinc from diethylzinc is experimentally studied. Parametric studies of laser power, intensity, gas pressure, and temperature are evaluated to characterize the deposition process. The results of these experiments verify the trends predicted by a simple theoretical treatment. The investigated deposition process shows contributions from both gas-phase molecules and adsorbed molecular layers. The ability to control the relative contribution from these two media is demonstrated.
Reduction of the concentration of slow insulator states in SiO2/InP metal–insulator semiconductor structures
Authors: Kulisch W. , Kassing R.
Published: July 2002

Spatially distributed states within the insulator are thought to be the origin of the well-known drift phenomena usually found in InP metal–insulator semiconductor (MIS) devices. This paper will show that the concentration of these states can be reduced drastically by applying a suitable deposition technique. Plasma-enhanced chemical vapor deposited SiO2 is used as the insulator in a process involving low substrate temperatures (200 °C), spatial separation of sample and plasma (indirect plasma method), and the addition of phosphorus into the reaction chamber during the initial stage of insulator deposition. The influence of several process parameters on the properties of the silicon dioxide films as well as the SiO2/InP interface characteristics are investigated. Deep level transient spectroscopy and C(V) measurements of InP MIS capacitors yield concentrations of slow insulator states of only 1–2×1011 cm−1 eV−1 for the best of our samples.
Dopant-induced ablation of polymers by a 308 nm excimer laser
Authors: Hiraoka H. , Chuang T. J. , Masuhara H.
Published: July 2002

Photoablation of polymers by laser beams is a practical process for via holes preparation in polymeric insulators. Excimer laser photochemistry of polymers is actively considered for microlithography. The ablation rate is dependent on the absorption coefficient. By addition of a dopant, photoetching rates of polymers can be increased significantly. In the present study the photoetching rates of poly(dimethyl glutarimide) and chlorinated poly(methylstyrene) are studied with pyrene as a dopant with 308 nm of XeCl excimer laser.
Quantitative i
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u characterization of x-ray mask distortions
Authors: Wells G. M. , Chen G. , So D. , Brodsky E. L. , Kriesel K. , Cerrina F. , Karnezos M.
Published: July 2002

The control of x-ray mask distortion is a central issue in x-ray lithography technology. Three causes of distortion have been examined: the interaction between a stressed absorber and substrate, the heating of the mask during x-ray exposure, and the radiation damage resulting from the cumulative absorption of the x rays. Interferometric techniques have been used to measure both in-plane distortion (IPD) and out-of-plane distortion (OPD). To measure OPD, wave fronts reflected from the mask surface are compared with a reference plane wave. For IPD it is necessary to have a diffraction grating on the mask. IPD causes changes in the grating pitch that result in the changes in the interference pattern. For thermal studies, an in situ shear interferometer was used to measure both OPD and IPD. Temperature increases were monitored using an infrared camera. The results have been modeled using the finite element program ansys. The distortion due to aborber substrate interaction was observed to occur at pattern edges. Thermal distortions were observed to cause IPD in regions with no absorber and both IPD and OPD for areas covered with absorber. Radiation damage was found to cause both IPD and OPD. The OPD was in the form of a plateau and can be modeled assuming the relaxation of the material is dependent on the absorbed dose and taking into account the depth dependence on absorption in the mask.
A vector-scan thermal-field emission nanolithography system
Authors: Gesley M. A. , Hohn F. J. , Viswanathan R. G. , Wilson A. D.
Published: July 2002

A vector-scan Gaussian beam lithography system has been retrofitted with a thermal-field emission electron gun to improve resolution and increase target current density. The design combines a Zr/O/W〈100〉 cathode, three element electrostatic lens, and an octupole stigmator–deflector with the original objective lens and deflection system. Beam voltage is variable up to 25 kV. At high resolution, 1 nA emitted into a gun acceptance semiangle of α0=0.5 mrad is focused to 150 Å at the target with a current density of 500 A/cm2. The current density maximum corresponds to α0=2.2 mrad where a 23 nA, 25 kV probe current is focused to 300 Å with a final convergence angle of 3 mrad at 30-mm working distance. These values imply a current density of 2.6×103 A/cm2 and an effective brightness of 9×107 A/cm2 sr at the target. The conversion is transparent to the original pattern generation–deflection system. This allows the design change to be rapidly incorporated with the existing subsystems. Proximity corrected 750-Å features have been developed.
Characterization of photochemically unpinned GaAs
Authors: Wilmsen C. W. , Kirchner P. D. , Baker J. M. , McInturff D. T. , Pettit G. D. , Woodall J. M.
Published: July 2002

The unpinning of the etched GaAs(100) surface has recently been reported by both photowashing and by Na2S⋅9H2O treatments. Both techniques hold promise of elucidating the mechanism by which GaAs passivation is achieved. We have identified as part of the photowashing process a separate photoactivation step. The activation step did not become apparent until we modified the photowash process in order to minimize light exposure when flowing water was not applied to the substrate. The degree of unpinning produced by this process has been found to be related to the thickness of this oxide, the presence of oxygen and water vapor and the integrated light flux incident on the sample. Photoluminescence experiments clearly show that a photoactivation step involving water vapor is required to achieve the flat-band condition. This process is relatively insensitive to the surface treatment prior to the photowash. We have observed similar photoactivation and insensitivity to surface treatment on GaAs coated with Na2S⋅9H2O. This suggests the possibility of a common passivation process.
The influence of ion scattering on dry etch profiles
Authors: Pelka J. , Weiss M. , Hoppe W. , Mewes D.
Published: July 2002

A simulation study is presented using a new version of the simulation program ADEPT (advanced simulation of dry-etching process technology), which is a subset of the process simulator COMPOSITE. Based on some aspects of plasma physics, a model was developed that allows for the calculation of important properties of a collisional sheath by Monte Carlo methods. These properties have great influence on the anisotropy of dry-etch processes. Angle/energy spectra of ions and fast neutrals can be gained from the model and can be used as input data for profile simulation. A simulation study is presented showing several profile phenomena. A short discussion is included on sidewall protection by polymer deposition, and on surface diffusion.
A fast Monte Carlo beam simulator using exact Coulomb scattering
Authors: Beck Vernon , Gordon Michael , Groves Timothy
Published: July 2002

The space charge interaction in a beam can be approximated by summing the scattering between all possible pairs of electrons in the beam. An efficient algorithm is presented for the exact solution to the two-body Coulomb scattering problem. This algorithm is incorporated into a Monte Carlo program to simulate the effects of space charge in electron-beam lithography systems. The results of this algorithm are compared to those obtained using a numerical integration of the Coulomb interaction for the N-body problem. We demonstrate that this approach accurately models the detailed physics for beam currents common to many state-of-the-art e-beam lithography systems.
Measurement of AlAs/InP and InP/In0.52Al0.48As heterojunction band offsets by x-ray photoemission spectroscopy
Authors: Waldrop J. R. , Kraut E. A. , Farley C. W. , Grant R. W.
Published: July 2002

X-ray photoemission spectroscopy (XPS) has been used to measure the valence band offsets at the x=0 and x=0.52 points of the InxAl1−xAs/InP(100) heterojunction system. For the lattice-matched interface we determine a value of ΔEv(InP/In0.52Al0.48As)=0.16 eV (staggered band alignment). Although the pseudomorphic AlAs/InP(100) interface investigated is strained, the ΔEv(AlAs/InP)=−0.27 eV (nested band alignment) value obtained by the XPS analysis method used is interpreted as being characteristic of an unstrained interface.
Studies of GaAs–oxide interfaces with and without Si interlayer
Authors: Freeouf J. L. , Buchanan D. A. , Wright S. L. , Jackson T. N. , Batey J. , Robinson B. , Callegari A. , Paccagnella A. , Woodall J. M.
Published: July 2002

We have studied the properties of metal–oxide–semiconductor structures fabricated by plasma enhanced chemical vapor deposition of SiO2 upon GaAs substrates. We have characterized the dependence of these properties upon the presence of a silicon interlayer, the type and the degree of misorientation of the substrate, and the type of plasma enhancement. We conclude that the presence of a silicon interlayer is beneficial for n-type GaAs if the oxide is deposited by a remote plasma technique. For such oxides on n-type GaAs coated with silicon, integration of the quasi-static capacitance curve suggests a band-bending range of 0.6–0.9 V. Also for these samples, we observe a hysteresis of order 0.6 V, and shifts of only 0.2 V in the midpoint of the rise from minimum to maximum capacitance upon changing frequency from 10 to 200 kHz. The benefits of using a silicon interlayer with a direct plasma deposited SiO2 film are less evident. It is assumed that much of the improvement of these results arises not from a large reduction of the interface density but rather from a shift of the spectrum towards the conduction band edge. This appears evident from the improvement on n-type samples coincident with a degradation on p-type samples. The total band bending change derived from the integral from the quasi-static capcitance–voltage curves is less sensitive to this interlayer than is the frequency dispersion.
A modeling approach to charging in e-beam columns
Authors: Langner G.
Published: July 2002

A fundamental requirement in e-beam lithography is tight control of the electron beam position. Parasitic electrical fields due to charging in the beam environment are a common and often significant cause of position errors. It is difficult to generate controlled conditions to experimentally investigate the problem in a systematic manner. A modeling approach has therefore been taken to calculate the electrical fields generated by surface and space charges in the e-beam column and their effect on the beam position error. A general expression for the effect of perturbing fields on the position error is derived. Perturbing electrical fields of surface charges and space charges generated by ions and secondary electrons are calculated as a function of key parameters (vacuum pressure, temperature, beam current, acceleration voltage, and dimensions) for cases of practical interest. Mechanisms for surface charging are included. From the results, critical areas are identified and conclusions are drawn regarding preventive measures.
Diffraction-limited soft x-ray projection lithography with a laser plasma source
Authors: Kubiak G. D. , Tichenor D. A. , Malinowski M. E. , Stulen R. H. , Haney S. J. , Berger K. W. , Brown L. A. , Bjorkholm J. E. , Freeman R. R. , Mansfield W. M. , Tennant D. M. , Wood O. R. , Bokor J. , Jewell T. E. , White D. L. , Windt D. L. , Waskiewicz W. K.
Published: July 2002

A laser plasma source of extreme ultraviolet and soft x-ray radiation has been used to print diffraction-limited features using soft x-ray projection lithography. A spherical condenser optic, a Si/Ge transmissive mask and a Mo/Si multilayer-coated Schwarzschild objective having 20:1 reduction ratio were employed to pattern selected single-layer and trilevel resists. At a numerical aperture of 0.12, a 0.1-μm line and space pattern is clearly delineated and weak modulation is observed for the analogous 0.05-μm pattern.
Elastic deformation of x-ray lithography masks under external loadings
Authors: Chen A. C. , Lalapet S. N. , Maldonado J. R.
Published: July 2002

This paper describes the elastic deformation of x-ray lithography masks due to external loadings using finite element modeling. The design of the mask support structure is critical to achieve 0.25 μm device design rules, for which the mask contribution to the total overlay budget must be kept below 50 nm. Therefore the mask deformation due to external loads should be below 10 nm. Several three-dimensional finite element models were constructed to simulate x-ray lithography masks under gravity loading and external in-plane loading (an out-of-plane loading can be related to an equivalent in-plane loading via the Poisson ratio of the material). A figure of merit was developed to evaluate the relative stiffness of mask support structures, and to guide future x-ray lithography mask designs.
An electron-beam inspection system for x-ray mask production
Authors: Sandland P. , Meisburger W. D. , Clark D. J. , Simmons R. R. , Smith D. E. A. , Veneklasen L. H. , Becker B. G. , Brodie A. D. , Chadwick C. H. , Chen Z. W. , Chuu L. S. , Emge D. G. , Desai A. A. , Dohse H. J. , Dutta A. , Greene J. D. , Honfi L. A. , Jau J. Y. , Lele S. G. , Ling M. Y. , McMurtry J. E. , Paul R. E. , Pan C.-S. , Robinson M. , Rough J. K. H. , Taylor J. , Wieczorek P. A. , Wong S. C.
Published: July 2002

SEMSpec is a scanning electron-beam inspection system designed for high-resolution die-to-die inspections of conductive x-ray masks, wafer prints, or stencil masks in a production environment. The inspection sensitivity can be varied from 97% detection of 50-nm defects, at a rate of 27 min cm−2, to 97% detection of 250-nm defects at 1 min cm−2. A thermal-field-emission source produces a Gaussian profile electron beam that is moved by electrostatic deflectors over the continuously moving substrate that is being inspected. Secondary electrons from the substrate are collected in a high-speed detector and the resulting digitized image data is stored in a specialized memory system. Pairs of images to be compared are continuously transferred from the memory to a high-speed defect processor for analysis. Defect reports from the defect processor are analyzed during inspection and stored for subsequent review. We describe the overall system including the electron-beam column with its six-emitter field-emission gun, the deflection system, the secondary-electron detector, the linear-motor drive stage, the control system, the robotic mask handler, and the image-data flow from the high-speed image acquisition subsystem through the analysis system. The electron-beam column is described in detail in a companion paper [W. D. Meisburger, A. A. Desai, and A. D. Brodie, J. Vac. Sci. Technol. B 9, xxxx (1991)]. All functions of the highly automated system—including vacuum control, mask loading, electron-beam column setup, and inspection— can be operated from the system control computer.
Requirements and performance of an electron-beam column designed for x-ray mask inspection
Authors: Meisburger W. D. , Desai A. A. , Brodie A. D.
Published: July 2002

Production viable inspection of x-ray masks requires the resolution of a scanning electron microscope (SEM) at an imaging rate approximately 1000 times that of commercially available systems. This article analyzes the inspection task for x-ray masks and compares the requirements for beam-current density and imaging efficiency necessary to achieve reasonable throughput with technologies available on current SEM and electron-beam lithography systems. The resulting specifications have been translated into an electron-optical column with many novel features. The gun, which contains six thermal field-emission sources mounted on a turret, produces a Gaussian profile beam that is scanned over a continuously moving substrate. Dual electrostatic icosapole deflectors provide high speed telecentric deflection. Secondary electrons are separated from the primary beam by a Wien filter and accelerated into a semiconductor electron detector. An analog optical-fiber link is used to transmit the signal to the image computer for defect detection. Results are presented for the performance of the electron-optical column and imaging system and for the overall defect detection performance of SEMSpec, a dedicated production x-ray mask inspection system.
Scanning noise potentiometry
Authors: Möller R. , Baur C. , Esslinger A. , Kürz P.
Published: July 2002

The thermal noise of the tunneling junction allows to operate a scanning tunneling microscope at exactly zero bias between sample and tunneling tip. Instead of operating at constant direct current the electronic feedback maintains a constant current noise. Already minor differences in the potential lead to a significant dc component of the average current. For any point on the sample the potential can be accurately measured by adjusting the potential such that the dc component of the average tunneling current vanishes. The experiment has been performed on a polycrystalline silver surface. Without applying any external voltages across the sample potential differences of about 50 μV are observed. The resolution obtained in our experiment is in the order of 1 μV.
MEBES IV thermal-field emission tandem optics for electron beam lithography
Authors: Gesley M.
Published: July 2002

The MEBESR IV column design and test results are presented. A new thermal-field emission (TFE) electron gun comprised of a Zr/O/W〈100〉 cathode and a low-aberration, large-aperture electrostatic lens operates as part of a variable-magnification, four-lens ‘‘tandem-optics’’ column. A 10 kV beam with brightness up to 5×106 A/cm2 sr at the mask is produced. The resulting advantage in electron optical performance is divided between a maximum current density of 400 A/cm2 and a convergence angle reduced to 5 mrad at 0.1 μm beam size. System accuracy is enhanced by the improved depth of focus, reduced aberrations, and the ability to reduce address size while maintaining present throughput levels set by the writing time of the serial-exposure, raster-scan machine. Doubling the blanking rate to 160 MHz improves throughput and enables the use of resists having 2.5 μC/cm2 sensitivity. The use of a dual-stigmator column setup and a 7.5 V/ns double-deflection beam blanker maintains beam jitter below 0.01 μm. The four-lens optics can expose masks with a continuously variable beam size over a 0.05–0.30 μm range while maintaining constant current density without adjusting the gun extraction voltage. GhostTM proximity correction of 0.25–0.50 μm features is possible with a fast defocus optic, which forms 0.50–1.0 μm beams and also reduces the exposure current to required values. A beam component analysis provides a measure of the Boersch and radial beam broadening effects.
Application of an x-ray stepper for subquarter micrometer fabrication
Authors: Chen Yong , Haghiri-Gosnet A. M. , Decanini D. , Ravet M. F. , Rousseaux F. , Launois H.
Published: July 2002

We report on a study of proximity x-ray lithography with a commercialized x-ray stepper (Karl Suss XRS200) and synchrotron orbital radiation at Super-ACO (Orsay, France). Special attention has been paid to the replication capabilities using SiC/W based high-resolution x-ray masks. The results show that proximity printing at a gap of 40 μm can result in subquarter micrometer replication. Since the resolution of the proximity printing is limited by the Fresnel diffraction, we use a double exposure technique to generate higher density and higher resolution grating structures. Fabrication of sub-100 nm linewidth gratings has been achieved using this technique with a wide exposure latitude.
Evaluation of heterodyne alignment technique for x-ray steppers
Authors: Koga K. , Higashikawa I. , Itoh T. , Araki K. , Fujita K. , Yasui J. , Aoki S.
Published: July 2002

Registration accuracy, as well as resolution capability, is one of the critical factors to identify an appropriate lithography tool. For deep submicron devices represented by the 256 Mbit dynamic random access memory, an alignment accuracy of better than 30 nm is needed. In this article, the alignment accuracy of an x-ray stepper was evaluated using the double-exposure method with a posiresist. The alignment accuracy obtained was better than 38 nm (3σ). Moreover, making a quantitative analysis of alignment error factors, we identified the possibility of improvement toward better than 30 nm (3σ).
Fabrication of n-channel metal–oxide–semiconductor field-effect transistors with 0.2 μm gate lengths in 500 Å thin film silicon on sapphire
Authors: de la Houssaye P. R. , Offord B. W. , Minter J. P. , Imthurn G. P. , Garcia G. A.
Published: July 2002

n-Channel metal–oxide–semiconductor field-effect transistors with gate lengths ranging from 10–0.2 μm were fabricated for the first time on device quality 300–500 Å ultrathin silicon on sapphire (SOS) wafers using electron-beam exposure for the gate level patterning step. Working devices were found over a large area on a group of six 4 in. wafers, including two wafers with approximately 1000 Å thick silicon films used for comparison, each with slightly different fabrication conditions. An arsenic implant was used to dope the source–drain regions of the devices. Threshold voltages were measured across each wafer for a variety of gate lengths, from which both an average value and spread was obtained. Both the average value and spread were seen to correlate with the silicon film thickness and thickness variations measured directly. Similar measurements were obtained for subthreshold slopes. Extrinsic transconductance was measured to be as high as 42 mS/mm for the smaller devices, heavily reduced due to source and contact resistance from the doped thin silicon (at about 250 Ω/square for the 500 Å films) leading up to the channel. Some of the special difficulties of electron-beam patterning on thin-film SOS are addressed.
Fabrication of nonlinearly shaped optical waveguide tapers on InP with precise design-parameter control
Authors: Brückner H. J. , Olzhausen H.-J. , Zengerle R.
Published: July 2002

An entirely integrated reliable and low-loss interconnection between an InP-based optoelectronic circuit and a single-mode optical fiber is presented. This spot transforming device is characterized by a two-layer buried waveguide with laterally tapered geometry. Investigations of the characteristics of the negative tone electron beam resist AZ PN 114 show that it is possible to transfer almost any arbitrary shape of an optical waveguide with a width between 80 and 1200 nm to a directly written mask for dry etching without proximity correction or sophisticated writing strategy. The geometries can be maintained to within 20 nm with respect to the structure design. During subsequent reactive ion etching steps for the InGaAsP-waveguide layers, a very precise etch depth control by a process ellipsometer is possible in the range of 5 nm or less. Optical measurements confirm the spot-size transformation characteristics of our taper device.
Contrast transfer function measurements of deep ultraviolet steppers
Authors: Grassmann Andreas , Moritz Holger
Published: July 2002

The aerial image contrast is a key parameter for the evaluation of the performance of optical projection systems. State-of-the-art deep ultraviolet steppers and some i-line steppers were investigated for comparison by measuring the contrast transfer function, i.e., contrast versus linewidth. Examples are shown how specific weaknesses of an imaging system like astigmatism and sensitivity from internal reflections can be quantified with this technique. For comparison the contrast transfer functions were also calculated, assuming ideal, purely diffraction limited image transfer of the optics, and with the numerical aperture and partial coherence as parameters. Interestingly none of the steppers meet the imaging performance which can be expected from theory.
Helium field ion source for application in a 100 keV focused ion beam system
Authors: Sakata Takahide , Kumagai Kiyohito , Naitou Motohiro , Watanabe Iwao , Ohhashi Yuu , Hosoda Osamu , Kokubo Yasushi , Tanaka Kazumitsu
Published: July 2002

A He gas-phase ion source having a three-electrode acceleration lens that can change the acceleration energy and magnification independently was developed. This source allows application of acceleration voltages up to 100 kV and extraction voltages up to 30 kV. This source is a component of our final objective of development, a nanometer lithography system with a beam diameter of 10 nm and a beam energy of 100 keV. In the present experiment, by using this source, the characteristics of He ion current emitted from W (111) emitter cooled by liquid N2 or liquid He was obtained. Maximum angular intensities of 40 nA/sr and 2.2 μA/sr were obtained at emitter temperatures of ∼100 and 20 K, respectively. In addition, the increase of the gas-phase ion current by emitter treatment (field-emission treatment or field-evaporation treatment) was ascertained.
Novel vertical silicon-membrane structure and its application to Josephson devices
Authors: Rittenhouse G. E. , Early K. , Meyerson B. S. , Smith Henry I. , Graybeal J. M.
Published: July 2002

The authors present novel techniques for fabricating vertical silicon membranes having thicknesses below 100 nm and, in some cases, ∼40 nm. The combination of extreme membrane facet smoothness, near perfect parallelism, compatibility with epitaxial doped layers, and ability to be fabricated in either single structures or in dense arrays present unusual properties for application. As one specific application of this structure, the authors have fabricated a hybrid superconductor/semiconductor short-channel Josephson device. Since these vertical membrane structures are also compatible with high-mobility Si/Ge channel layers, the authors are currently extending this work to study the ballistic transport of Cooper pairs through discrete energy eigenstates formed by the quantum confinement within the thin semiconductor membrane.
Multiconcens: An exposure method for submicron contact-hole layers, using variable-shape electron-beam direct-write and single-layer resist
Authors: Heinlein F. , Gross G. , Höfflinger B. , Irmscher M. , Reuter C. , Springer R.
Published: July 2002

With Multiconcens (multiple concentric shots), a novel exposure method is presented, which is especially tailored for variable-shape electron-beam lithography of submicron contact-hole layers, exposed into single-layer positive resist. The goal is to provide a critical dimension-accurate, technological processable resist mask with minimum effort in order to generate functioning contact and via holes. Typical experiments demonstrate, after comparison with results from conventional uncorrected single-shot exposure, the advantage of the method, which guarantees better stability with respect to process fluctuations, for the desired resist profile. Together with a convenient data preparation, the Multiconcens exposure principle can correct topography influences occuring with planarization effects of single layer resist. The feasabilty of contact holes with dimensions required for submicron technologies using thick single-layer resist is also shown.
Electron beam lithography system with new correction techniques
Authors: Takahashi Y. , Yamada A. , Oae Y. , Yasuda H. , Kawashima K.
Published: July 2002

In our electron exposure system, the focal length of the final projection lens is designed to be very short. To decrease aberrations due to beam deflections, which cannot be corrected by a dynamic focus coil or a stigmator, deflection coil parameters are determined by a simulation, which used the conditions: coma length=0, transverse chromatic aberration coefficient=0, and beam incidence is normal to the sample surface. Patterns of the size under 0.2 μm are well resolved inside the whole deflection field of 1.6×1.6 mm. Current density of the system is more than 40 A/cm2. Refocusing and refocus–flyback are necessary to utilize the high current density for spot size between 0.1 and 3.0 μm. Large spot defocusing is refocused by small refocus coils, and refocused beam position shifts are corrected by a refocus–flyback method. Beam-settling retardation caused by an eddy current occurs after an electromagnetic jump. A differentiated electromagnetic signal is added to electrostatic deflectors to compensate for the transitional beam positions between the jump. The beam-settling time is less than 100 μs for a 1 mm jump, about a tenth of that without the compensation.
Electrical characterization of low temperature GaAs layers, and observation of the extremely large carrier concentrations in undoped material
Authors: Tadayon Bijan , Fatemi Mohammad , Tadayon Saied , Moore F. , Dietrich Harry
Published: July 2002

We present here the results of a study on the effect of substrate temperature Ts on the electrical and physical characteristics of low temperature molecular-beam epitaxy GaAs layers. Based on the x-ray results, three temperature ranges have been defined for Ts: 1) high range (Ts≥ 460 °C), 2) intermediate range (260 ≤ Ts ≤ 450 °C), and 3) low range (the amorphous range) (Ts ≤ 250 °C). Hall measurements have been performed on the as-grown samples and on samples annealed at 610 and 850 °C. Si implantation into these layers has also been investigated. From an electrical stand point, the most striking difference between the low range and the intermediate range is the fact that after annealing at 850 °C, the undoped layers grown below or at 250 °C have a low resistivity (net electron concentrations as high as 1.5×1018 cm−3 and mobilities as high as 920 cm2 V−1 s−1), while after anneal the undoped layers grown in the intermediate range have extremely high resistivity (about 8×105 Ω cm).
Dissociative attachment and surface reactions induced by low-energy electrons
Authors: Sanche Léon
Published: July 2002

The mechanisms leading to anion electron stimulated desorption (ESD) at low energies (0–20 eV) are discussed with emphasis on the formation of transitory anions at surfaces decaying by dissociative attachment (DA). The results of recent measurements are summarized and briefly explained using as examples data on O− ESD from O2 condensed on Pt and H−, CH−, and CH−2 desorption from hydrocarbons also physisorbed on Pt. It is shown that, when O2 and hydrocarbons are coadsorbed on Pt, O− ions formed by DA can undergo reactive scattering with other surface molecules; this reaction leads to the product OH− some of which desorb from the surface.
Molecular dynamics simulations of deep penetration by channeled ions during low-energy ion bombardment of III–V semiconductors
Authors: Stoffel N. G.
Published: July 2002

Molecular dynamics simulations are used to model the formation of deep crystalline damage during the low-energy ion bombardment of semiconductor crystals. For beams of heavy ions at energies below a kilovolt, the average penetration range of the simulated trajectories is only a few nanometers. However, a small, but significant, fraction of the ions are found to scatter into 〈011〉 axial channels through which they propagate tens of nanometers below the surface. A model is developed to convert the simulated ion channeling probabilities into predictions of optical damage as a function of depth in the crystal. The results are used to explain the recent measurements of anomalous degradation of deep quantum wells during dry etching of III–V semiconductor heterostructures. The model is also used to evaluate several strategies intended to avoid this unintentional ion channeling and to reduce the creation of deep damage during low-energy ion bombardment.
Optical properties of strained-layer InxGa1−xSb/GaSb heterostructures with x≤0.4
Authors: Qian L. Q. , Wessels B. W.
Published: July 2002

The optical emission characteristics of strained-layer InxGa1−xSb/GaSb quantum well structures have been studied. For the In0.18Ga0.82Sb/GaSb strained-layer quantum well structures with well thicknesses from 5.9 to 15.4 nm, intense and narrow photoluminescence emission was observed with energies ranging from 0.723 to 0.758 eV. The full width at half- maximum of the emission peaks is of the order of 10 meV. The dependence of emission energy on well thickness was compared with the prediction of a finite square well model, taking into account strain. Good agreement was obtained for a valence band offset of ΔEv=0.35ΔEg. Temperature dependent photoluminescence measurements were used to verify the band offset parameters. The activation energies measured from the temperature dependent photoluminescence measurements were consistent with the prediction of finite square well model using a valence band offset of ΔEv=0.35ΔEg.
New technique for dry etch damage assessment of semiconductors
Authors: Foad M. A. , Thoms S. , Wilkinson C. D. W.
Published: July 2002

Surface conductance measurements, using the transmission line model (TLM) technique, have been used to assess surface electrical damage in GaAs resulting from dry etching. Reactive ion etching (RIE) in CH4/H2 and SiCl4, ion beam etching in Ne and Ar and electron cyclotron resonance etching (ECR-RIE) in CCl2F2/He have been investigated. A phenomenological model is proposed for determining the extent of the surface etching damage. It is found that the use of slow etch rates, high bias/accelerating voltage and light ions in etching increases the electrical damage in GaAs. Possible causes for the creation of deep damage are discussed, and the criteria for low damage etching are suggested. The TLM method is a powerful technique for assessing etching processes used for semiconductors.
High mobility electron gases and modulation-doped field effect transistors fabricated in Si/Si1−xGex by rapid thermal chemical vapor deposition
Authors: Venkataraman V. , Liu C. W. , Sturm J. C.
Published: July 2002

High mobility n-type Si0.62Ge0.38/strained Si modulation-doped structures have been fabricated on relaxed graded Si1−xGex buffers by rapid thermal chemical vapor deposition. The mobility and density of the two-dimensional electron gas was studied as a function of spacer thickness of the modulation-doped structure. Mobilities exceeding 40 000 cm2/V s at a density of 1.7×1012 cm−2 (10 K) and 15 000 cm2/V s at a density of 2.9×1012 cm−2 (77 K) were observed, giving a record low sheet resistivity of 140 Ω/⧠ at 77 K. Self-aligned depletion and enhancement mode modulation-doped field effect transistors were fabricated in similar structures using a novel two-step lithography process. Good saturation characteristics with low gate leakage currents were achieved, but the maximum room-temperature transconductance was limited by parasitic source and drain resistances.
X-ray photoelectron spectroscopy investigation of the mixed anion GaSb/InAs heterointerface
Authors: Wang M. W. , Collins D. A. , McGill T. C. , Grant R. W.
Published: July 2002

X-ray photoelectron spectroscopy has been used to measure levels of anion cross-incorporation and to study interface formation for the mixed anion GaSb/InAs heterojunction. Anion cross-incorporation was measured in 20 Å thick GaSb layers grown on InAs, and 20 Å thick InAs layers grown on GaSb for cracked and uncracked sources. It was found that significantly less anion cross-incorporation occurs in structures grown with cracked sources. Interface formation was investigated by studying Sb soaks of InAs surfaces and As soaks of GaSb surfaces as a function of cracker power and soak time. Exchange of the group V surface atoms was found to be an increasing function of both cracker power and soak time. We find that further optimization of current growth parameters may be possible by modifying the soak time used at interfaces.
Feasibility study of new graybeam writing strategies for raster scan mask generation
Authors: Murray Andrew , Abboud Frank , Raymond Frederick , Berglund C. N.
Published: July 2002

The simplicity of the raster scan beam technology has made it the dominant choice for maskmaking production tools. Nevertheless, building patterns on a grid resolution determined by the address of the raster scan mask generator places limitations on the location of pattern edges. Furthermore, as pattern dimensions shrink to 0.5 μm, and eventually to 0.15 μm, the standard technique of decreasing the address unit size decreases write time throughput. One promising approach to avoid this throughput bottleneck is pixel-level intensity and position modulation (graybeam plus pixel deflection to displace edge locations of patterns at a resolution smaller than the address grid size. In this article, methods for modulating the intensity and position of writing pixels are shown, along with simulation and experimental results using test patterns. Simulation results are presented that show the relationship between grid size and the discrete intensity levels needed to achieve a given edge placement requirement. Intensity and position modulation opens the possibility of using fewer pixels per pattern (larger address size) for a given edge placement requirement in comparison to conventional raster scan exposure techniques. Sensitivity of the displacement to lithography parameters and patterns are also determined and compared to experimental results. Finally, feasibility for hardware implementation on a raster scan e-beam system is presented.