bluuebunny/crossref_metadata_2025 huggingface dataset:
Applying transform based proximity corrections to electron-beam lithography with 0.2-μm features
Authors: Haslam Michael E. , McDonald John F.
Published: July 2002

This paper examines the application of transform techniques to the problem of compensating for the proximity effect in electron-beam lithography. The patterns examined contain features as small as 0.20 μm. The transform methods employed here have been discussed in earlier papers. However, to date the amount of published experimental evidence documenting the degree of success of the method has been very limited. Therefore, one of the objectives of this paper is to examine thoroughly a set of four patterns containing a number of challenging features which will not develop correctly without some form of compensation. Since very little work on 0.20-μm proximity correction is currently available for comparison, we have attempted to simulate the GHOST method for these same four patterns. The GHOST method is a successful and widely accepted technique for computationless compensation of electron backscattering. It employs a defocused complementary pattern exposure to compensate for this electron backscatter. Thus we can anticipate that it will not adjust for the distortions due to forward scattering, for example, which can affect features in the 0.20-μm range. In addition to forward scattering, we observe that the transform method can compensate for asymmetric astigmatism. We have found asymmetric distortion to be a problem when attempting to write features in the range of 0.20 μm on some commercially available machines. Therefore, the method may have special significance for such machines.
GHOST proximity correction technique: Its parameters, limitations, and process latitude
Authors: Kostelak R. L. , Kung E. H. , Thomson M. G. R. , Vaidya S.
Published: July 2002

The efficacy of the GHOST proximity correction technique for achieving submicron linewidth control in electron beam lithography has been experimentally evaluated. Using the AT&T electron beam exposure systems, the GHOST parameters (correction dose, defocused beam diameter, and overlay accuracy) required for proximity exposure correction at 20 kV were determined via scanning electron microscopy and electrical linewidth measurement techniques. Optimum proximity correction conditions were established from a matrix of correction doses and correction beam diameters on two different substrates: chromium on glass and aluminum on silicon. On chromium, linewidth control of better than ±0.05 μm was obtained using a 3-μm beam and a correction dose between 30% and 40% of incident, or with a 4-μm beam and a 40% correction dose. Even better proximity correction was achieved on aluminum with a 5-μm defocused beam and a 30% correction dose. In conjunction with the experimental data, a computer model was developed to interpret these results. The model assumes an elliptical profile for the incident GHOST beam rather than a Gaussian. Using this model, the tolerances on correction dose and defocused beam diameter for 0.5-μm lithography on aluminum were determined to be 9% and 1.6 μm, respectively. The third GHOST parameter investigated, overlay accuracy between the incident and GHOST exposures, was also found to be critical. A 0.5-μm overlay error resulted in a 0.05-μm linewidth deviation across a 0.5-μm line and space pattern. Last, it was found that with AZ-2400-17 resist the loss of resist thickness and developer latitude upon GHOSTing will not result in pinholes or degrade process latitude as long as the correction dose is maintained at ≤ 40% of the incident dose, and a dilute developer is employed.
Deposition and characterization of silicon dioxide thin films deposited by mercury-arc-source driven photon-activated chemical-vapor deposition
Authors: Scoles Kevin J. , Kim Anderson H. , Jiang Mian-Heng , Lee Brian C.
Published: July 2002

Silicon dioxide thin films have been grown by the technique of photochemical-vapor deposition. Deposition was performed using direct dissociation of oxygen by an ultraviolet arc lamp in the presence of silane. The films were deposited for a temperature range of 150 and 350 °C. Deposition rates peaked at a total pressure of 2 Torr, with a rate of 23 nm/min and 68 nm/min at 150 °C and 250 °C, respectively. Film stress is compressive with 1.04±0.14×109 dynes/cm2. Dielectric constant (εox) and breakdown voltage (VB) were measured as 3.6 and 3.2 MV/cm, respectively. Etch rate in a room temperature 1:5 buffered hydrofluoric acid:deionized water solution was below 50 Å/s. The films have promise for application in integrated circuit devices.
Characterization of electron-beam exposed optical resist
Authors: Tam Nelson N. , Coyne Rick D. , Neureuther Andrew R. , Slayman Charlie W.
Published: July 2002

The behavior of Hitachi RD-2000N negative resist under electron-beam exposure at high-beam current density on the AEBLE-150 has been characterized and modeled through dissolution measurement on the Perkin–Elmer development rate monitor (DRM) and SAMPLE simulation. A three parameter quantitative dissolution rate versus deposited energy model has been established. This model when combined with SAMPLE, can accurately predict the resist thickness versus log dose data and simulate resist profile development. The high-beam current density exposure available with AEBLE-150 give a noticeable increase of resist thickness top loss and rough resist surface topography at 25 Å/cm2. This change in development behavior is consistent with thermal heating of the top of the resist during exposure. Initial data on the AEBLE-150 showed lower contrast (γ) and higher sensitivity than has been reported previously. A factorial experiment of developer type, developer temperature, and prebake temperature showed that they are not the main contributing factors for the discrepancy observed. A combination of process factors especially freshness of developer and time between exposure and development appears to account for this difference. Comparison of simulation and scanning electron micrographs of developed resist profiles gives generally good agreement.
High-precision reticle making by electron-beam lithography
Authors: Hamaguchi Shin-ichi , Kai Jun-ichi , Yasuda Hiroshi
Published: July 2002

We have developed an electron-beam (e-beam) lithography system named ‘‘NOWEL’’ which utilizes very accurate pattern writing method and high-speed data processing. Accordingly NOWEL makes it possible to manufacture reticles for 16-Mbit dynamic random access memories (DRAM’s) or more densely integrated very large scale integrated circuits (VLSI’s). The NOWEL system has three key features: (1) Vertical landing deflection system. This consists of three yokes in series and one short-working-distance lens (M=0.86). The landing angle at the corner of the 5-mm2 main field is <0.0025 rad. Therefore the butting error arising from a 10-μ height variation of the substrate is <0.05 μ. Deflection aberration is about 0.2 μ. (2) Double exposure method called ‘‘A/B mode.’’ We adopted a variable shaped beam. The first exposure is made by serial writing with constant-size rectangular spots, and the second one is made on the previously exposed area by shifting the beam position and reshaping the beam spots. One-half dosage is given in each exposure. By this method the edge roughness of each pattern is improved to be <0.05 μ. (3) Pattern data compression. A hierarchical pattern data structure was developed. In the memory cell area the data can be divided into only a few pattern data for cell units and their repetition data, i.e., start positions, pitch data, and numbers of cell units in the cell area. According to the repetition data in the main field the main deflector moves the positions of cell units, written by the subdeflector, with the same pattern data. We call this exposure method ‘‘main deflection matrix mode.’’ For fine positioning especially in this mode we developed a 20-bit digital-analog convertor (0.005-μ least significant bit). These reduction techniques should compress the amount of total pattern data to 1/10 for a 16-Mbit DRAM. By using NOWEL we made a test reticle which contained 16-Mbit cell patterns with total accuracy within 0.1 μ. In this simplest case only one cell unit with the patterns for 128-bit cells and their repetition data were needed.
The electron-beam column for a high-dose and high-voltage electron-beam exposure system EX-7
Authors: Tamamushi S. , Wada H. , Ogawa Y. , Sasaki I. , Nakasuji M. , Kusakabe H. , Yoshikawa R. , Takigawa T.
Published: July 2002

The electron optical column is designed for the electron-beam (EB) exposure system EX-7 employing a vector scanned variably shaped beam (VSB) on a continuously moving stage. The column, which utilizes a high current density of 200 A/cm2 and a high voltage of 50 kV, has been designed for a 0.25 μm patterning. Generation of triangular shapes in addition to rectangular shapes reduces shot numbers to enhance throughput. An octapole deflector with small deflection distortion, has been developed for beam shaping. The ray tracing method using an analytical expression for the electric and magnetic field was used to design the objective focusing and deflection system, which is composed of a magnetic lens and dual channel electrostatic octapole deflectors. Beam edge resolution including the electron-beam interaction effect is about 0.12 μm and distortion is <0.01 μm at the final beam convergence semiangle of 8 mrad and field size of 600 μm square. As a result, a 0.25 μm resist pattern has been obtained over 600 μm field. Main deflection field stitching error was <±0.04 μm (3σ) without deflection distortion correction.
X-ray lithography using broadband sources
Authors: Hollman Richard
Published: July 2002

A variety of source technologies are currently being proposed for x-ray lithography. Some are broadband sources, producing a continuum spectrum or a broad distribution of wavelengths. The performance of a system using a broadband source is strongly affected by the vacuum window, mask substrate, and resist composition because of the wavelength-selective transmission and absorption of these layers. A desired ‘‘optimum’’ spectrum of energy deposited in the resist can be obtained by proper choice of source parameters, vacuum window, and mask substrate. The calculated performances of different source technologies are compared, using source parameters appropriate to each technology. The effect of vacuum window and mask substrate on performance is shown for a representative broadband source spectrum. The feasibility of x-ray lithography sources for manufacturing use should be viewed in terms of theoretical 0.25-μm patterning capability, which is found to depend principally on three factors: power, geometry (isotropic or collimated), and whether a vacuum window is required.
Sub-half-micron critical dimension control in x-ray lithography mask technology
Authors: Huber H.-L. , Pongratz S. , Trube J. , Windbracke W. , Mescheder U. , Mund F.
Published: July 2002

The main problems in x-ray mask fabrication concern the defect density, the pattern placement accuracy, and the critical dimension (CD) control. To demonstrate the performance of x-ray lithography, it is necessary to fabricate sub-half-micron features with high reproducibility and small linewidth variations. This requires an absorber patterning procedure with extremely high stability and homogeneity and additionally a measuring technique with high accuracy in the sub-half-micron range in order to control the linewidth quality. It has been shown that mask fabrication can fulfill most of the requirements on x-ray mask technology using electron beam (e-beam) writing in a trilevel process with electroplated gold absorbers. Furthermore, a copying procedure was developed which multiplies an e-beam written master mask by using x-ray lithography in a single-layer resist and again gold electroplating. To characterize the linewidths and their variations, an e-beam based measuring technique is presented, which is able to measure quarter-micron CD’s with an accuracy of ∼25 nm as a 3σ value. The aim of this paper is to demonstrate the homogeneity of the running mask technology including the mask copying process and the feasibility of the applied measuring technique. Results are presented showing clearly that linewidth variations can be limited to 50 nm for both master mask and mask copy. X-ray masks with gate lengths down to a quarter-micron dimension have been fabricated in this quality. The technological ways to achieve these results are summarized in this paper.
Analysis by electron energy-loss spectroscopy of poly(methylmethacrylate) electron beam resist
Authors: Martinez Jean-Paul , Camon Henri , Kihn Yolande , Sevely Jean , Balladore Jean-Louis
Published: July 2002

In electron beam lithography the interactions between the incident electrons and the molecules of the resist lead to a chemical modification of the polymer. In order to understand the various processes which occur, we have used the technique of electron energy-loss spectroscopy (EELS). The detection of plasmons and characteristic signals associated with atomic deep level excitations in the high-energy region of the spectrum allows the chemical elements in a given volume of the specimen to be identified and localized. By measuring the intensity of the characteristic signal associated with a given element it is also possible to estimate the number of atoms of this element present in the volume analyzed. The evolution of the energy-loss spectrum during electron irradiation gives information on the structural modification and on the mass loss of the specimen as a function of the dose. In electron lithography the pattern dimensions vary with the energy deposited in the resist and consequently are related to the time exposure to the beam. The results obtained by EELS allow the evolution of the resist during irradiation to be followed.
Sensitivity-enhanced x-ray lithography using radiation-induced grafting to poly(phenyl methacrylate)
Authors: Mochiji Kozo , Oizumi Hiroaki , Sooda Yasunari , Ogawa Taro , Kimura Takeshi
Published: July 2002

Poly(phenyl methacrylate) (PPhMA) is utilized as a base resist of radiation-induced graft copolymerization for the purpose of high-throughput x-ray lithography. PPhMA has dry-etching resistance due to the aromatic ring in its side chain and, therefore, it can be used for large-scale integration (LSI) fabrication. Gaseous acrylic acid is grafted into PPhMA film to produce a copolymer which is insoluble in the solvent of PPhMA. The graft processing enhances the resist sensitivity by three orders of magnitude to the level of 10 mJ/cm2 . The swelling of the grafted resist during development is drastically minimized by formation of a cross-linked structure in the grafted resist by thermal dehydration of acrylic acids. The above technique successfully provided a negative pattern with feature size down to 0.3 μm.
Integrated data conversion for the electron beam exposure system EX-7
Authors: Koyama K. , Ikenaga O. , Abe T. , Yoshikawa R. , Takigawa T. , Watanabe S.
Published: July 2002

Because pattern data operations for electron beam (EB) lithography requires the knowledge of shape-to-shape correlation with adjacent patterns, the hierarchical structure embedded with the input data is usually expanded. Consequently, drastic increase in both the processing time and data amount has resulted. To overcome this problem a novel data conversion technique has been developed. It can exploit the hierarchical structure and repetitiveness originally incorporated into large-scale integrated designs to efficiently generate EB pattern data. The conversion technique was implemented on a large-scale computer to make pattern data for the EX-7 EB exposure system. As a result, the highest density levels of 1- and 4-Mbit direct random access memories (DRAMS), scaled down to 0.5 μm, were converted within 0.5 h of central processing unit (cpu) time, achieving an average data compaction of (1)/(20) . Overlap elimination and tone reversal were performed at a speed of 108 primitive shapes per hour. The data amount increased to 40 from 17 Mbytes of uncorrected data, when the proximity effect correction was performed on the shrinked 4-Mbit DRAM pattern using this conversion technique.
A thermally assisted field emission electron beam exposure system
Authors: Nakazawa H. , Takemura H. , Isobe M. , Nakagawa Y. , Hassel Shearer M. , Thompson W.
Published: July 2002

Electron beam lithography is widely used to fabricate densely packed devices such as high-frequency transistors, since optical lithography is unable to write the small patterns required for such devices. One major problem with micropattern writing with an electron beam exposure system, however, is slow writing speed; since the system has to write an extremely large number of patterns on low-sensitivity resist with a highly focused beam, exposure times are quite long. To speed up the writing process, we have attached a thermal field emission gun to our electron beam exposure system. This gun is designed to increase the electron source brightness and probe current density. In order to determine this new probe current density, we conducted an extensive evaluation on a complete lithography system which uses a thermal field emission gun. We have measured a current density of ∼1000 A/cm2 at an accelerating voltage of 25 kV and conclude that this lithography system can be put to practical use in production areas requiring high throughput and submicron exposures.
Computational tools to analyze voltage contrast detectors
Authors: Khursheed A. , Dinnis A. R. , Hall D. J. , Knowles W. R.
Published: July 2002

Computer programs have been written to analyze the performance of a wide range of ‘‘in the lens’’ voltage contrast detectors. By plotting electron trajectories for emitted secondaries from the specimen, the programs can calculate important figures of merit for different detectors, such as the efficiency of collecting secondaries which leave the specimen. The programs can also calculate third-order aberrations on the primary beam, and hence determine the spatial resolution capability for each detector.
EBT-1: A highly automated, practical electron beam tester
Authors: Koyama K. , Tojo T. , Sugihara T. , Takigawa T. , Sano T. , Ishikawa M. , Matsuda K.
Published: July 2002

A highly automated electron beam testing system EBT-1 was built for measuring internal voltages of very large scale integrated (VLSI) devices in both wafer and package forms. Voltage measurement and its associated operations are performed by the computer with a minimum of operator intervention. The mother-board probe-card system has been incorporated for easy signal connection and the six-axis stages are specially designed. The upper X, Y stages, Z stage, and piezo-drive θ stage are used to precisely align the probe card to an arbitrary chip on a 6-in.-wafer, whereas the lower X, Y stages are used to shift the area of observation. The electron optical column with four magnetic lenses uses a single-crystal LaB6 cathode to generate sufficient beam current at low accelerating voltages of 1 to 3 kV. The device drive signals are supplied from conventional LSI testers via more than 160 vacuum-tight connectors. EBT-1 has achieved a voltage resolution of < 50 mV and a time resolution of 0.5 ns at the device clock frequency of 25 MHz. The system has been extensively used in the development of VLSI devices, including 1-Mbit dynamic random access memory.
A heating model for excimer laser projection processing
Authors: Palmer S. , Matteson S.
Published: July 2002

The reaction rates for laser-induced desorption, etching, and deposition are dependent on the local substrate temperature. Accurate predictions of the spatial and temporal temperature profiles on the wafer are necessary in order to optimize the process conditions. We report on the solution of the transient heat conduction equation using an adaptation of HEATING5, a program developed at the Oak Ridge National Laboratory.1 The solution includes the full temperature dependence of the material parameters. The aerial and temporal distribution of the incident laser radiation is used in the heating program to calculate the temporal and spatial dependence of the thermal profiles. From the results of the heating model, a process model for laser-induced etching is constructed and used to explain our results on projection pattern etching of silicon using the KrF laser and fluorine gas mixture.
Electrostatic focusing and electrostatic deflection systems with reduced aperture aberrations
Authors: Oku Kentaro , Maruyama Masanori , Fukushima Masakazu
Published: July 2002

Electrostatic focusing and electrostatic deflection (SS) electron beam systems have been investigated to increase the resolution of SS camera tubes. SS camera tubes have pattern electrodes formed on their inner walls. The pattern electrodes comprise deflection electrodes and a cylindrical electrode. The deflection electrodes form a band around the inner wall at one end of the tube. Four leads project longitudinally from this band, dividing the cylindrical electrode into four parts. An octopole lens is created around the leads of the deflection electrodes. To increase tube resolution, the electron optical characteristics were evaluated, taking into account the effects of the octopole lens. It was revealed that, due to the octopole lens, the aberration spot is not isotropic and its diameter is about three times that produced by a cylindrical lens. New pattern electrodes with zig-zag shaped leads were devised. It was found that the aberration spot became almost round and its diameter was reduced to the value obtained with a cylindrical lens.
Selectively silicided vertical power double-diffused metal–oxide semiconductor field effect transistors for high-frequency power switching applications
Authors: Shenai K. , Piacente P. A. , Korman C. S. , Baliga B. J.
Published: July 2002

A new power field effect transistor (FET) structure with selectively silicided gate and source regions is described. This structure simultaneously lowers the gate sheet resistance and source contact resistance. Vertical power double-diffused metal-oxide semiconductor field effect transistors fabricated using this technology have a specific on-resistance of 0.53 mΩ cm2 for devices capable of blocking 50 V in the off-state. Devices with cell density as high as 4 million cells/in.2 and die size as large as 200×220 mil have been successfully fabricated with excellent gate yield. These results represent the best ever reported forward conductivities for any type of power FET in the 50-V reverse blocking range. Comparison of selectively silicided power FET’s with state of the art commercial nonsilicided FET’s indicates that the former have an order-of-magnitude lower gate sheet resistance, 8× smaller on-resistance, and 2× smaller input capacitance.
The morphologies and characteristics of reactively formed TaSi2 films
Authors: Jiang Tao , Guobin Zhang , Guoying Wu , Anyan Du
Published: July 2002

Morphologies and characteristics of the surface and interface of TaSi2/Si and TaSi2/poly-Si structures reactively formed by furnace annealing and rapid thermal annealing (RTA) have been investigated thoroughly. Scanning electron microscopy and transmission electron microscopy (cross section) results show that the morphologies of the annealed samples were uneven, but the surface and interface of RTA samples were better than that of furnace annealed samples. The specific contact resistivity of TaSi2 to n+ -Si substrates with Kelvin structure was measured. The contact resistivity increased as the annealing temperature increased, but was lower for RTA samples than for furnace annealed samples. Sheet resistance measurement, x-ray diffraction, and Auger electron spectroscopy analysis techniques were used to monitor the formation of TaSi2 films.
Fabrication of epitaxial GaAs/AlGaAs diaphragms by selective dry etching
Authors: Ade R. W. , Fossum E. R. , Tischler M. A.
Published: July 2002

A selective dry process is used to fabricate epitaxial diaphragms by etching anisotropic cavities through a GaAs substrate to an AlGaAs stop-etch layer. Active devices are built directly on the layers comprising the diaphragm. The etching process follows the device fabrication sequence, facilitating integration of these structures with pre-existing electronic circuitry. Potential applications in optoelectronic and acoustic wave devices are discussed, and an optical interconnection technique based on the diaphragm structure is described.
Lithography issues in fabricating high-performance sub-100-nm channel metal–oxide semiconductor field effect transistors
Authors: Kern D. P. , Rishton S. A. , Chang T. H. P. , Sai-Halasz G. A. , Wordeman M. R. , Ganin E.
Published: July 2002

Specific issues related to achieving high device performance in extremely small channel length field effect transistor circuits are discussed. Ultrahigh resolution electron beam lithography is needed to obtain the ultrashort channels which are key for fast devices, and for the important gate area, double-layer poly(methylmethacrylate) for lift-off of a metal reactive ion etching mask has proven to be a suitable technique. Good level to level overlay and dimensional control in the contact process allow miniaturization of all device elements, in particular, reduction of the distance between source/drain contacts and optimization of the contact size and geometry. These are key factors in minimizing parasitic effects. The design considerations are discussed and the fabrication techniques are described which resulted in devices with a maximum measured transconductance of 910 mS/mm at 77 K for a 70-nm gate device, exhibiting the clearest evidence so far for electron velocity overshoot, and unloaded ring oscillators with 13-ps switching time per stage.
Electron wave diffraction by nanometer grating and its application for high-speed transistors
Authors: Furuya Kazuhito , Kurishima Kenji
Published: July 2002

This paper describes a new phenomenon about the diffraction of the ballistic electron by a transverse grating in the semiconductor. As a theoretical result, the diffraction efficiency changes almost between one and zero owing to a slight change in the average potential energy of the grating. For the grating of a 19-nm pitch in GaInAs, we can change the diffraction efficiency between 0.88 and 0.001 by 0.1 V in the grating layer voltage. Applying this phenomenon to control of the electron transport, a new type of transistor is described.
Synthesis and evaluation of Co–P and Co–As organometallics as precursors for metal pnictides
Authors: Gross M. E. , Lewis J.
Published: July 2002

The compounds [Co(CO)3XEt3]2,X=P,As, have been evaluated as possible precursors for the deposition of the cobalt pnictides, CoX. Thermogravimetric analysis and x-ray diffraction reveal loss of the 1:1 Co:X stoichiometry of the starting material upon thermal decomposition. The decomposition products consist of mixed Co and Co2X phases.
The common-anion rule and the role of cation states: Binary versus ternary semiconductors
Authors: Kilday D. G. , Margaritondo G. , Ciszek T. F. , Deb S. K.
Published: July 2002

The failure of the common-anion rule for heterojunction interfaces involving binary semiconductors has been demonstrated by many recent experiments. Wei and Zunger have explained this puzzling result in terms of a substantial role of the cation d states in determining the valence-band edge position. The same approach predicts that the valence-band edge position of certain ternary semiconductors and of their quaternary alloys depends weakly on the composition. We present synchrotron-radiation photoemission tests of these predictions.
Accommodation of lattice mismatch in GexSi1−x/Si superlattices
Authors: Miles R. H. , Chow P. P. , Johnson D. C. , Hauenstein R. J. , Marsh O. J. , Nieh C. W. , Strathman M. D. , McGill T. C.
Published: July 2002

We present evidence that the critical thickness for the appearance of misfit defects in a given material and heteroepitaxial structure is not simply a function of lattice mismatch. We report substantial differences in the relaxation of mismatch stress in Ge0.5 Si0.5 /Si superlattices grown at different temperatures on (100) Si substrates. Samples have been analyzed by x-ray diffraction, channeled Rutherford backscattering, and transmission electron microscopy. While a superlattice grown at 365 °C demonstrates a high degree of elastic strain, with a dislocation density <105 cm−2 , structures grown at higher temperatures show increasing numbers of structural defects, with densities reaching 2×1010 cm−2 at a growth temperature of 530 °C. Our results suggest that it is possible to freeze a lattice-mismatched structure in a highly strained metastable state. Thus it is not surprising that experimentally observed critical thicknesses are rarely in agreement with those predicted by equilibrium theories.
Extended fine structures in the electron energy loss spectrum of InAs
Authors: Schowengerdt F. D. , Grunthaner F. J.
Published: July 2002

Extended fine structures have been observed in the electron energy loss spectrum of InAs. The structures consist of oscillations extending several hundred eV above the In M4,5 edge. They are of the type recently observed by others in a variety of materials and are attributed to the same phenomenon responsible for extended x-ray absorption fine structure (EXAFS); namely, an interference between the outgoing and backscattered parts of the ejected core electron wave function, which in this case is observed as a modulation of the energy distribution of the inelastically scattered electrons above the core edge. Because the backscattering occurs mainly in the near-neighbor environment of the In atoms and the excitation takes place in the surface region, these oscillations carry surface structural information. We have analyzed the data in the standard EXAFS context and have obtained radial distribution functions for In atoms at the surface of the bulk InAs. The measured nearest-neighbor distance, uncorrected for the phase shifts, of 2.40±0.04 Å agrees well with the results of K-shell EXAFS. This is the first reported measurement of fine structure associated with M-shell excitations involving d electrons.
The effect of strain on the band structure of InxGa1−xAs
Authors: Hwang J. , Pianetta P. , Kubiak G. D. , Stulen R. H. , Shih C. K. , Pao Y.-C. , Shen Z-X. , Lindberg P. A. P. , Chow R.
Published: July 2002

Angle-resolved photoemission spectroscopy has been used to study strained InxGa1−xAs(001) layers in pseudomorphic heterostructures grown by molecular-beam epitaxy. It is found that the Δ3+Δ4 bands and the Δ1 band respond differently to the strain perturbation. For strained GaAs(001), the Δ3+Δ4 bands (Px +Py- like) are shifted upward in energy by a maximum amount of 0.3 eV, while in contrast, the Δ1 band (Pz- like) is shifted downward by about 0.5 eV. For both strained In0.2Ga0.8As(001) and In0.9Ga0.1As(001), the band shifts are in the opposite direction to that in the GaAs case, consistent with the opposite strain conditions. The strain-induced effects due to cation (Ga or In) alloying are also discussed.
Metal d-level induced mid-gap Fermi level pinning on GaAs(110)
Authors: McLean A. B. , Williams R. H. , McGilp J. F.
Published: July 2002

The transport properties of a diverse range of metal/GaAs(110) Schottky diodes have been examined using the conventional current–voltage and capacitance–voltage techniques. The metals we have examined include Cu, Ag, Au, Al, Ga, In, Sn, Ti, Sb, Y, V, Cr, Mn, Fe, Co, Ni, Pd, and Na. The data are used to test for correlations between the Schottky barrier height and the interface heat of reaction, the metal work function, and the metal electronegativity. We have found that central transition metals, situated between groups V A–VIII of the periodic table, pin the Fermi level near mid-gap. The barrier heights obtained from most other metals exhibit a near-linear dependence on electronegativity. These findings are discussed in the light of recent photoemission and inverse photoemission studies and in terms of existing microscopic theories of Schottky barrier formation.
Reaction of dimers and diatomic molecules with GaAs(110): Molecular dynamics computer simulations
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

Simulations have been performed for dimers and diatomic molecules adsorbing on the (110) surface of GaAs. Al2 usually remains together after adsorption, indicating a tendency toward cluster formation. In one run, this dimer broke up, but the energy was found to be substantially higher; i.e., the dissociated atoms are metastable with respect to the metallic cluster. On the other hand, O2 tends to dissociate immediately upon adsorption, in ways that suggest the beginning of oxide formation. Molecular chemisorption of O2 was observed in one run, but found to be metastable.
X-ray photoemission study of Hg clusters on Hg1−xCdxTe surfaces
Authors: Sporken R. , Sivananthan S. , Reno J. , Faurie J. P.
Published: July 2002

Hg1−xCdxTe (111)B surfaces have been studied with x-ray photoelectron spectroscopy (XPS). A surface shift is deduced from a careful analysis of Te 4d core-level spectra. The presence of small Hg clusters on these surfaces is observed, and the size is estimated from the XPS data (R=5–20 Å). The positive binding energy shift for these clusters agrees very well with the calculated Coulomb energy due to the positive charge which appears on the clusters during the photoemission process. The origin of these clusters is briefly discussed.
Stabilization of an electrostatic lens for a focused ion beam system
Authors: Aihara R. , Obata M. , Sawaragi H. , Shearer M. H.
Published: July 2002

An electrostatic lens is used as the focusing lens for focused ion beam (FIB) systems. The lens action against charged particles is caused by creating a high-electric field between the electrodes. To improve the stability of the electrostatic lens, it is necessary to raise the withstand voltages of the insulator and the electrodes in the electrostatic lens. We have improved the withstand voltage of the insulator by covering the triple junction with a dielectric and using the conditioning procedure described in this paper. As a result, a stable electrostatic lens system for manufacturing application of FIB has been developed.
Nitrocellulose as a self-developing resist for focused ion beam lithography
Authors: Kaneko H. , Yasuoka Y. , Gamo K. , Namba S.
Published: July 2002

In order to obtain reproducibility of self-development of nitrocellulose, a method of controlling the focused ion beam by monitoring the absorption current was investigated. The change of the absorption current and the progress of self-development were observed as a function of the irradiation time of the focused ion beam, and an appropriate end point of irradiation by the ion beam was decided. Using this method, line patterns with a width of 160 nm were fabricated.
Focused ion beam exposure characteristics of Langmuir–Blodgett films
Authors: Shiokawa T. , Kim P. H. , Toyoda K. , Namba S. , Suzuki M. , Matsui S.
Published: July 2002

Exposure characteristics of 75-layer ω-tricosenoic acid Langmuir–Blodgett (LB) films on Al film deposited on a Si substrate have been investigated with 100-kV Be++, Si++, and Au++ focused ion beams. The dependence of the remaining film thickness on the ion dose has a peak because of the etching of the LB film at high ion doses. The sensitivity and contrast show the highest values for Au++ exposure and are 2.1×1012 cm−2 and 0.91, respectively. The etch depth at nominal ion dose is negligibly small compared with the initial and the remaining film thicknesses. The LB film pattern fabricated by exposure with the focused ion beam can be used as the mask in dry etching and in phosphoric acid etchant. From the above results, it is found that the LB film can be used as a negative resist in 100-kV Be++, Si++, and Au++ focused beam lithography.
The influence of electrode geometry on liquid metal ion source performance
Authors: Swanson L. W. , Li Jia Zheng
Published: July 2002

The surface electric field distribution along the axis of a wetted needle type liquid metal ion source has been determined by numerical methods and is shown to exhibit a secondary maximum at the intersection of the cylindrical and conical sections. It is shown that the volume flow rate of the liquid metal film along the cylindrical portion of the emitter is adequate to resupply the ionized portion at the needle apex. However, a pressure minimum in the liquid film, which decreases with increasing apex cone angle, occurs at the cone/cylinder intersection and the pressure gradient formed on the conical section of the emitter opposes flow to the apex region. It is shown that, by chemically roughening the conical section of the emitter, liquid film flow via microcapillary action occurs in such a way as to provide a low flow impedance to the apex.
Submicron pattern dimension determination using a total waveform comparison method
Authors: Hasegawa Shinya , Iida Yasuo , Hidaka Toshiharu
Published: July 2002

A pattern dimension determination method has been developed. The three parameters, linewidth, wall angle, and film thickness represent pattern dimension. The total waveform of a measured backscattered electron signal is compared with a standard signal data base. Two methods are adopted to reduce data base construction time. (1) The data base was constructed with Monte Carlo simulation by a supercomputer. (2) Data base size is reduced using a waveform approximation method. The two improvements result in fast data base construction (26 min) for a specified material sample. This data base construction method is more practical than preparing signal data base from real standard sample due to data base construction time. Obtained dimensional accuracies are found to be 0.02 μm, 5 deg, and 0.1 μm for linewidth, wall angle, and film thickness, respectively, with scanning electron micrograph comparisons. Deduction time for obtaining physical dimensions from a signal was 17 s.
Antenna properties of thin-film warm-carrier devices fabricated by using focused ion beam milling
Authors: Yasuoka Y. , Harakawa K. , Gamo K. , Namba S.
Published: July 2002

A thin-film warm-carrier device, which has a contact area smaller than any other thin-film antenna coupled device yet conceived, was fabricated by a combination of electron beam lithography and focused ion beam milling. The device exhibited a distinguishing antenna pattern for CO2 laser radiation, and the pattern shifted in accordance with the long-wire antenna theory when the length of the thin-film antenna was reduced. These results indicate that the device works as an antenna coupled detector for CO2 laser radiation.
Oxidation of TiSi2: The role of implanted As and its behavior during oxidation
Authors: Holland O. W. , Fathy D. , Withrow S. P. , Sjoreen T. P.
Published: July 2002

The influence of As+ ion implantation on the oxidation of TiSi2 films was investigated. It is shown that implantation of As leads to a greatly increased rate of oxidation in a dry O2 ambient. Oxidation of a silicide implanted with inert Ar+ ions showed that the effect is not solely due to ion-induced damage but depends on the presence of As in the film. The microstructure of these films, before and after oxidation, was studied using high-resolution transmission electron microscopy and Rutherford backscattering. Also, the morphology of As+-implanted films after rapid thermal annealing will be discussed. Under certain conditions, the morphology is substantially affected by the implant.
Aluminum oxides as imaging materials for 193-nm excimer laser lithography
Authors: Pang S. W. , Kunz R. R. , Rothschild M. , Goodman R. B. , Horn M. W.
Published: July 2002

Aluminum oxide films deposited over amorphous carbon(a-C:H) planarizing layers have been investigated as imaging layers for 193-nm excimer laser lithography. The AlOx films were deposited by ion beam deposition, e-beam evaporation, or sputter deposition. The films have been analyzed by Auger electron spectroscopy and x-ray photoelectron spectroscopy. Depending on the deposition conditions, AlOx films with compositions varying from metallic to fully oxidized Al can be formed. The optical appearance of these films varies from highly reflective for metallic Al to highly transparent for fully oxidized layers. Using pulsed 193-nm radiation from an ArF excimer laser, the single-pulse self-development threshold energy is similar for films with different compositions when the film reflectivity is taken into account. It was found that pure Al films and highly oxidized Al films do not provide good adhesion on a-C:H layers and have a tendency to peel during laser exposure. In contrast, films with intermediate compositions consisting of a mixture of Al and aluminum oxides provide good adhesion, high etch resistance during O2 reactive ion etching, and submicrometer resolution when exposed with the 193-nm excimer laser. Features as small as 0.1 μm have been patterned on these films in projection, and can be transferred through a 1-μm-thick a-C:H planarizing layer with vertical profiles.
Application of photoacid generating chemistry to photobleachable deep-ultraviolet resist
Authors: Endo Masayuki , Tani Yoshiyuki , Sasago Masaru , Nomura Noboru , Das Siddhartha
Published: July 2002

The high optical density of the conventional positive resist in the deep UV region (190 nm to 300 nm) prevents its use in the fabrication of high contrast patterns. The photobleachable deep UV resist composed of a 1,3-dicarbonyl-2-diazo compound as the alkaline dissolution inhibitor and an alkaline-soluble styrene polymer as the resin matrix, which we developed, is one promising approach to resolve these problems. Using this resist, high contrast 0.5 μm patterns were obtained with a KrF excimer laser stepper. In this paper, we have applied photoacid generators to such photobleachable resists. The photoacid generator used was triphenylsulfonium hexafluoroarsenate, and it greatly enhanced the sensitivity and contrast of the resist. The decomposition of diazo compound in the resist was significantly enhanced (and the dissolution characteristics improved) in the presence of the onium salt. This novel positive resist utilizing chemical amplification more than meets the requirements for KrF excimer laser lithography.
Electron optical performance of electron beam lithography columns predicted by a simple model
Authors: Langner Guenther , Stickel Werner
Published: July 2002

A simple model is presented which predicts the maximum attainable current density and associated optimum brightness and semi-angle in a variable shaped spot (VSS) and a Gaussian spot (GS) electron beam lithography system for a given resolution (edge width). For a GS the optimum source demagnification factor is also predicted. The contribution of the forward scattering in the resist is taken into consideration. The model allows the assessment of the sensitivity of the attainable current density to various design and operation parameters. The model is based on the quadratic sum of uncorrelated and uncorrectable aberrations and solves the expression for the sum for the current density using the reduced brightness as variable. VSS systems are characterized by an optimum brightness and a high sensitivity to stochastic trajectory displacement due to electron–electron interaction. The acceleration potential has a paramount effect on the attainable current density, still enhanced when forward scattering due to the resist is included. In GS systems the chromatic and geometrical aberrations limit the attainable density. The brightness attainable with Lanthanum–hexaboride emitters is satisfactory for VSS systems but GS systems require very high brightness guns (e.g., TFE) to exploit the potential for achieving a high current density.
Molecular-beam epitaxy growth of high-quality two-dimensional electron system
Authors: Shayegan M. , Engel L. , Goldman V. J. , Santos M. , Suen Y-W. , Sajoto T.
Published: July 2002

We report on the growth of modulation-doped GaAs/AlxGa1−x As heterostructures with extremely low disorder by molecular-beam epitaxy. In growing these structures we employed (1) ultrathick (≳1000 Å) spacer layers with graded composition; (2) modulation doping with two atomic planes of Si; and (3) other techniques to minimize the disorder. The structures have mobilities (μ) on the order of 1×106 cm2/V s (at 4.2 K) for areal densities (ns ) as low as 4×1010 cm−2. Quantum transport measurements in these structures demonstrate their exceptionally high quality.
Window cleaning and fluorine incorporation by XeF2 in photochemical vapor deposition
Authors: Langford A. A. , Bender J. , Fleet M. L. , Stafford B. L.
Published: July 2002

A new method of maintaining window transparency in photochemical vapor deposition (photo-CVD) has been developed in which the window is continuously etched clean during the deposition process. This technique is demonstrated in the deposition of a-Si:H(F) by direct photo-CVD of Si2H6 using XeF2 as an etchant. XeF2 is also used to clean the chamber between runs. Fluorine may be incorporated in the films via either gas phase or surface reactions with XeF2. The optoelectronic quality of a-Si:H:F decreases with F incorporation, which suggests that this technique may be particularly suited to the deposition of μc-Si:H(F) and a-SiGe :H(F) and a-SiC :H(F) alloys wherein fluorinated process gases are preferentially employed.
Silicon deposition in diode and hollow-cathode systems
Authors: Horwitz Chris M.
Published: July 2002

Deposition of silicon from silane discharges is studied in diode and hollow-cathode systems. Using the single-target (‘‘diode’’) configuration as a reference, it is shown that discharge confinement results in substantial increases in deposition rate and efficiency. The ‘‘target-confined hollow cathode’’ exhibits the best performance; in comparison with a diode discharge at 2-Pa silane pressure, rates are 20–50× higher at fixed applied rf voltage and 5× higher at fixed input power density. Alternatively, for a fixed deposition rate this new configuration allows the applied rf voltage to be reduced by ∼10 and the power density to be reduced by ∼20, again at a 2-Pa pressure. Planarizing films are obtained at low pressures and/or low gas flows, while high pressures yield more directional deposition over surface steps. Good agreement with this profile study, and with our deposition rate data, is given by a model wherein ion bombardment is the dominant film forming and etching mechanism at low pressures, and wherein trapping of both excited neutrals and of electrons may contribute to the high efficiencies and rates observed.
Characterization of diazonaphthoquinone–novolac resin-type positive photoresist for g-line and i-line exposure using water-soluble contrast enhancement materials
Authors: Endo M. , Sasago M. , Ueno A. , Nomura N.
Published: July 2002

We describe the characterization of conventional diazonaphthoguinone–novolac resin-type positive photoresist for g-line (436-nm) and i-line (365-nm) exposure using water-soluble contrast enhancement materials. In the experiments, the Rayleigh’s theoretical resolution and contrast enhancement capability of the water-soluble contrast enhancement materials were set to be equal between the each wavelength exposure. As a result, the pattern profiles of the resist were better, however, the latitude of depth of focus was worse for g-line exposure than for i-line exposure. Mask linearity had no difference between them. It was found that the improvement of the pattern profiles for i-line exposure was achieved by using a higher photobleachable photoresist at i-line.