bluuebunny/crossref_metadata_2025 huggingface dataset:
Ag2Te/As2S3: A high-contrast, top-surface imaging resist for 193 nm lithography
Authors: Lavine Jerome M. , Buliszak Mark J.
Published: July 2002

At 193 nm, the Ag2Te/As2S3 inorganic resist system exhibits many of the characteristics previously observed at longer wavelengths, namely, a contrast of the order of 10 and the edge effect, both of which contribute to the printing of narrow linewidths. We have observed 0.3 micron lines limited by the resolution capability of the optical system and not by the resist. Under pulsed excimer laser excitation, this system exhibits a threshold of the order of 3 mJ/cm2/pulse. The system does not exhibit reciprocity. While images were printed with two 17 ns pulses of 4 mJ/cm2/pulse, images could not be printed with a single pulse as large as 50 mJ/cm2/pulse. This behavior is not explained by our previously developed model.
Morphological modeling of atomic force microscopy imaging including nanostructure probes and fibrinogen molecules
Authors: Wilson David L. , Kump Kenneth S. , Benard William , Xue Ping , Marchant Roger E. , Eppell Steven J.
Published: July 2002

Due to the finite size of the probe tip, atomic force microscopy (AFM) images of biomolecules, and other structures similar in size, are laterally enlarged. We use mathematical morphology, a non-linear image processing method, to model the interaction between probe tip and sample. In a typical imaging situation, baseline dimensions are most affected by the probe and widths can be 80% tip and 20% molecule. Using the morphological model and a known tip, we can restore the image so that it more closely resembles the actual surface. Morphological restoration is ideal in some regions, giving the exact sample surface, and improved in others. In the case of a carbon probe, restoration increases the perfectly obtained surface area by as much as 160 times. Following restoration, lateral widths at fixed heights are improved by as much as 75%. Restoration greatly improves image resolution even if one uses probes consisting of very small candidate structures, e.g., nanotubes and Bucky balls. The tip imaging process is also modeled, and we find that calibration spheres should be larger than the molecules of interest and that for many tips, there is little or no advantage to using smaller spheres. A blood plasma protein, fibrinogen, is modeled, and AFM and restored images of single molecules are computed.
Effects of oxide overlayer on thermal stress and yield behavior of Al alloy films
Authors: Yeo I.-S. , Anderson S. G. H. , Jawarani D. , Ho P. S. , Clarke A. P. , Saimoto S. , Ramaswami S. , Cheung R.
Published: July 2002

The stress and yield behavior of Al alloys, Al(Cu) and Al(SiCu), have been investigated using bending beam and x-ray diffraction techniques, and the effect of passivation on the stress–temperature behavior of alloys is examined. A stress analysis of trilayer (SiO2/Al alloy film/Si) structure was formulated in order to deduce the stress of the confined metal films from bending beam measurements. The stress–temperature behavior of Al alloy films obtained from bending beam techniques was in agreement with that determined directly by x-ray diffraction techniques. The grain structure and precipitate morphology of these alloy films were studied using transmission electron microscopes. Presence of passivation leads to a change in microstructure of Al alloys, resulting in hardening for the Al(SiCu) films and softening for the Al(Cu) films when compared with the unpassivated films at room temperature. Our results reveal that oxide thickness, Al thickness, and microstructure play an important role in determining the plastic deformation behavior of the metal films, and can satisfactorily explain the contrasting behavior observed for Al(SiCu) and Al(Cu) films.
High phosphorus doping of epitaxial silicon at low temperature and very low pressure
Authors: Huang X. D. , Han P. , Chen H. , Zheng Y. D. , Hu L. Q. , Wang R. H. , Zhu S. M. , Feng D.
Published: July 2002

In situ phosphorus doped Si epitaxial layers have been grown at 600 °C in a very low pressure chemical vapor deposition system, using SiH4 and PH3 diluted in H2. The presence of H2 was found to decelerate the epitaxial growth rates. Secondary-ion mass spectrometry measurement shows that the constant phosphorus concentration with depth for a steady flow of PH3 was achieved. Namely, dopant concentration is a function of gas phase dopant concentration. Chemical concentration as high as 2.5×1020 P/cm3 was obtained in Si epitaxial layers though with very low growth rate. Epilayers with constant doping levels from 1.5×1018 P/cm3 to 1.2×1020 can readily be grown. Despite the relatively low growth rate, there is no evidence of a time-dependent accumulation of phosphorus on the growth surface or the reactor wall. The reasons accounting for this phenomenon are discussed.
Inherent possibilities and restrictions of plasma immersion ion implantation systems
Authors: Mändl S. , Brutscher J. , Günzel R. , Möller W.
Published: July 2002

Design specifications for plasma immersion ion implantation systems are discussed. An analytical model of the plasma sheath evolution is used to deduce restrictions for the dimension of the vacuum chamber and the pressure range. The avoidance of arcing implies an upper limit for the maximum electric field in the sheath and hence for the plasma density. The total fluence per pulse, which determines the implantation duration and the power requirement, is calculated. Furthermore, safety considerations, especially the shielding of x-rays generated by secondary electrons, are discussed.
Atomic force microscopy images obtained with C60 modified tips
Authors: Kim Sanghee , Park Sang-Kyu , Park Chan , Jeon Il Cheol
Published: July 2002

We prepared thioacetate derivatives of C60 for studying tip–substrate interactions in force microscopy. They are expected to make ideal hydrophobic surfaces over tips that are covered with thin gold films. Compound (1) has two attaching points by short chain to minimize damping of forces that is expected to be distinct in the case of long chain molecules, while compound (2) is only one attaching point with a long chain. Adsorption kinetics studies by microgravimetry using a quartz crystal microbalance and by contact angle measurements were performed to confirm chemisorption of the prepared compounds. Topographic images of highly oriented pyrolytic graphite attained using tips coated with these compounds do not show deterioration in resolution compared with images obtained using bare tips. On comparing force-distance curves, compound (2) showed a possibility to be advantageous for force measurement experiments because surfaces covered with compound (2) were found to be more hydrophobic than others.
In situ studies of potassium hydrogen phthalate crystal dissolution using scanning probe microscopy
Authors: Campbell P. A. , Ester G. R. , Halfpenny P. J.
Published: July 2002

Force microscopy has been used to image, both in situ and ex situ, crystals of potassium hydrogen phthalate (KAP) that had been grown from aqueous solution. By introducing water vapor into the growth cell in which the crystals are housed, a localized etching process is seen to occur on the (010) face, which can then be monitored by time-lapse imaging. The etching process results in the development of pits having two distinct morphologies, one that may be linked to local etching at defect sites, and the other reflecting the random nature of the condensation process. The distribution of secondary etch sites is seen to be influenced by the scanning motion of the tip and a model is proposed to explain this observation.
Atomic force microscopy observation of native neurons and modifications induced by glutamate
Authors: Cricenti A. , De Stasio G. , Generosi R. , Scarselli M. A. , Perfetti P. , Ciotti M. T. , Mercanti D.
Published: July 2002

We used an atomic force microscope, in the repulsive regime of contact mode, to take images of uncoated neurons fixed in glutaraldehyde on a gold covered stainless steel substrate. We observed granule cells and their axons with a resolution better than 20 nm. The good stability of the sample and the mechanical reproducibility of the microscope allowed the imaging of a neuron culture area of several square microns. Modifications induced by glutamate on the neuronal culture resulted in observing a drastic reduction in cell granule height (from 1.5–2.0 μm for the unperturbed ones down to 0.7–1.0 μm) and in an increased corrugation of the surface membrane. The atomic force microscope images were very reproducible over repeated scanning acquisition, demonstrating a very good mechanical and thermal stability of the instrument-sample system.
Ballistic electron emission microscopy studies of electron scattering in Au/GaAs Schottky diodes damaged by focused ion beam implantation
Authors: McNabb J. W. , Craighead H. G.
Published: July 2002

Ballistic electron emission microscopy is used to investigate the electron scattering properties of undamaged and focused ion beam implanted Au/GaAs diodes. Implanted regions show decreased ballistic electron transmission attributed to increased scattering. A quantitative model of electron transport is developed that includes quantum mechanical transmission at the interface, scattering effects from optical phonons and implantation induced defects in the semiconductor, and scattering in the metal layer. Model predictions of scattering in undamaged regions show good agreement with the data. However, we conclude additional scattering effects must be included to describe the implanted structures.
Scanning tunneling microscopy of the UO2 (111) surface
Authors: Castell M. R. , Muggelberg C. , Briggs G. A. D. , Goddard D. T.
Published: July 2002

Scanning tunneling microscope (STM) studies of UO2 surfaces have previously not been performed due to insufficient conductivity at room temperature. In order to increase the sample conductivity we have carried out imaging at elevated temperatures in a JEOL 4500XT ultrahigh vacuum STM. With this instrument we can routinely image atomic terraces of the UO2 (111) surface and under exceptional circumstances also resolve atomic structure within the terraces. We have used low-energy electron diffraction and Auger electron spectroscopy to study the surface order and purity and correlated these results with our STM data.
Fabrication and performance of novel monolithic GaAs/AlGaAs microvacuum transmission-mode photoemitters
Authors: Jalonen Marko , Salokatve Arto
Published: July 2002

A novel selective etching method was employed to construct monolithic GaAs/AlGaAs microvacuum structures for transmission-mode photoemitters. These emitters consisted of a photon absorption layer with a window and top contact layers supported by micropillars of about 140 μm2 in cross section areas, a 2-μm-wide vacuum space, and an electron collector. Part of the photoelectrons generated in the absorption layer were emitted into the vacuum space inside the microvacuum structure. They were subsequently accelerated by an applied reverse bias across the vacuum space and collected by a conductive GaAs substrate. The electron emitting surface was protected against contaminants from air by sulfur radicals by a H2SO4 solution treatment. After thermal cleaning at 475 °C and activation with Cs, the microvacuum emitter exhibited an external quantum efficiency of 0.33% at 650 nm wavelength. Photocurrent was a linear function of the power of incident light, and the dark current of the microvacuum emitters remained below 90 pA/cm2 at 20 °C. Experimentally observed spectral quantum efficiencies of the microvacuum and reflection-mode emitters are compared with theoretical diffusion model calculations.
Highly sensitive analytical method for metallic impurities in the thin silicon layer of silicon-on-insulator wafer
Authors: Kodate J. , Machida K. , Imai K. , Tanaka M. , Yabumoto N.
Published: July 2002

A new analytical method for thin Si layer is proposed that uses low temperature oxidation and chemical analysis. The thin Si layer of silicon-on-insulator wafers is oxidized at a low temperature by electron cyclotron resonance oxygen plasma. The oxide is analyzed by vapor phase decomposition method and atomic absorption spectrometry. This approach makes it possible to analyze metallic impurities without the diffusion of contaminants because the oxidation is carried out at a low temperature. The results reveal that metallic impurity concentrations below 1010 atoms/cm2 can be detected with a depth resolution of 4 nm.
Pattern profile control of polysilicon in magnetron reactive ion etching
Authors: Kimizuka Masakatsu , Ozaki Yoshiharu
Published: July 2002

The effects of adding H2 or CBrF3 to Cl2 plasma to control the pattern profile in polysilicon etching are studied using a magnetron reactive ion etching system. It is found that the sidewalls of patterns etched with pure Cl2 plasma at the pressure of 12 Pa are vertical or sloped depending on whether a radio frequency (rf) power of 600 W (0.77 W/cm2) or 700 W (0.9 W/cm2) is applied. By increasing the content of H2, the angle of the sidewall taper of the pattern etched at 600 W rf power reaches 70°. Adding CBrF3 makes it possible to adjust the slope of the sidewall over a range from 77° to 65° at a rf power of 700 W. These observed results are attributed to plasma polymerization.
Lateral range spread of MeV phosphorus ions implanted in silicon measured by time-of-flight secondary ion mass spectrometry
Authors: Shi Bo-Rong , Cue Nelson , Smith Terry L. , Xu Tian-Bing
Published: July 2002

The range profiles of 1.0 MeV P+ implanted into silicon with a dose of 1×1015 cm-2 at angles of 7°, 45°, and 60° were measured by time-of-flight secondary ion mass spectrometry. The longitudinal and lateral range spreads at normal incidence were deduced from the measured profiles at oblique incidence. The measured profiles were systematically shallower and narrower than the TRIM’95(TRansport of Ions in Matter, 1995) predictions, but good agreement can be obtained if the electronic stopping power formula is slightly increased in the higher energy region during the calculations.
I–V
characteristics of modified silicon surface using scanning probe microscopy
Authors: Yasue Takao , Koyama Hiroshi , Kato Tadao , Nishioka Tadashi
Published: July 2002

Using scanning probe microscopy, we have modified a silicon surface and measured its current–voltage (I–V) characteristics. In the modified area, both an increase in film thickness and a decrease in current caused by field-induced oxidation (FIO) have been observed. The I–V characteristics of the FIO film shows a good fit to a Fowler–Nordheim (FN) tunneling current model. The barrier height determined by a FN plot shows a good agreement with that of conventional metal–oxide–semiconductor structure with thermal thick silicon oxide.
New deep-ultraviolet positive photoresists. II. Copolymers of p-trimethylsilylstyrenes and acrylics
Authors: Chiang Wen-Yen , Shann Hwai-Der
Published: July 2002

o -Nitrobenzyl cholate has been widely used as the photoactive component in dissolution inhibition of deep-UV photoresist of poly(methylmethacrylate–co-methacrylic acid) [poly(MMA–co-MAA)]. We wished to promote this system in a bilayer resist application, so we used the copolymers containing silicon instead of poly(MMA–co-MAA). Poly(p-trimethylsilyl–α-methylstyrene–co-methacrylic acid), (PTMSMSMAA, I), poly(p-trimethylsilyl–α-methylstyrene–co-acrylic acid), (PTMSMSAA, II), poly(p-trimethylsilylstyrene–co-methacrylic acid), (PTMSSMAA, III), and poly(p-trimethylsilylstyrene–co-acrylic acid), (PTMSSAA, IV) were synthesized by solution-free radical polymerization of trimethylsilylstyrenic monomers (TMSMS and TMSS) with comonomers (MAA and AA). The preparation of the copolymers in terms of reaction time, thermal initiator, solvent, and the feed mol ratio of reactants was evaluated. The thermal properties of these copolymers were investigated with the differential scanning calorimeter and by thermogravimetric analysis. The chain-stiffening effects of the α-methylstyrene and styrene groups were responsible for high thermal stabilities. The developed patterns exhibited good adhesion to the silicon substrates without the use of any adhesion promoter. The resolution of the resists was at least 0.8 μm and exhibited an oxygen plasma etching rate of 1:15 compared with hard-baked HPR-204.
Efficiency evaluation of postetch metal stack anticorrosion treatments using chemical analyses by x-ray photoelectron spectroscopy and wide dispersive x-ray fluorescence
Authors: Czuprynski P. , Joubert O. , Heitzmann M. , Louis D. , Vizioz C. , Lajoinie E.
Published: July 2002

Chemical analyses by x-ray photoelectron spectroscopy (XPS) combined with wide dispersive x-ray fluorescence (WDXRF) have been used to evaluate the efficiency of metal stack anticorrosion treatments previously etched in a low-pressure high-density plasma source. Analyses demonstrate that residual chlorine is still present in the metal stack showing that corrosion could occur in the subsequent technological steps of the process. In particular, XPS analyses have shown that, after anticorrosion treatment, residual chlorine species are located on the aluminum sidewalls of the features. Combining the results obtained by WDXRF and XPS has allowed a better understanding of the action of anticorrosion treatments.
Magnetic nanostructures fabricated by scanning tunneling microscope-assisted chemical vapor deposition
Authors: Pai Woei Wu , Zhang Jiandi , Wendelken John F. , Warmack R. J.
Published: July 2002

We have successfully used scanning tunneling microscope-assisted chemical vapor deposition to fabricate magnetic nanostructures as fine as 5 nm wide and <2 nm high using ferrocene [Fe(C5H5)2] as the metal-organic source gas. The physical properties of these nanostructures were qualitatively characterized and ex situ magnetic force microscopy measurements indicate these features are strongly magnetic.
Testing of a rapid fault detection model for quality control: Borophosphosilicate glass thin films monitored by infrared absorption spectroscopy
Authors: Zhang S. , Franke J. E. , Niemczyk T. M. , Haaland D. M. , Cox J. N. , Banerjee I.
Published: July 2002

Infrared absorption spectra of 108 borophosphosilicate glass (BPSG) thin films produced in a multiple-wafer low-pressure chemical vapor deposition (LPCVD) reactor were collected to enable the development and testing of a rapid and inexpensive method for determining if films are within the desired specifications. Classification of samples into good and bad product categories was made by applying principal component analysis to the spectra. Mahalanobis distances were used as the classification metric. The highest overall percentage of correct classification of samples based upon their spectra with two-step classification was 95%. The misclassified samples were, however, within the error of the reference methods that were used in making the original classification against which the infrared (IR) classification methods were tested. The classification errors are thus just as likely to be a result of misclassification by the reference method rather than errors by the IR classification. Although reference measurements were used in this article for the original classification of the samples, these expensive and time-consuming reference methods can be eliminated simply by building classification models on samples determined to produce a product within the correct device specifications. The IR classification methods presented here hold great promise as a tool for rapid quality control of BPSG deposition.
Precise force curves in air and liquid by magnetic force feedback
Authors: Yamamoto Shin-ichi , Yamada Hirofumi , Tokumoto Hiroshi
Published: July 2002

We developed an atomic force microscopy with the tip position was accurately controlled through the magnetic interaction between a coil and the magnet fixed behind the cantilever. By incorporating a feedback system, we could control the motion of a soft cantilever (0.68 N/m) in air and liquid, and obtain force curves without instabilities originating from the strong attractive and adhesive forces between the tip and the sample.
Scanning tunneling microscopy and low energy electron diffraction study of the formation of a ∛×∛R30° reconstruction on the hydrogen etched Si(111) 1×1 surface
Authors: Rogers D. , Tiedje T.
Published: July 2002

The Si(111) 7×7 surface is exposed at room temperature to atomic hydrogen and studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) in ultrahigh vacuum. For increasing exposures, the LEED pattern of the surface changes in well defined steps to a 1×1 pattern. The STM images of the 1×1 surface appear rough and disordered. The 1×1 pattern and rough surface are consistent with an etching of several surface layers by the atomic hydrogen. Heating the 1×1 surface to 560 °C and cooling to room temperature produces a surface with a ∛×∛R30° LEED pattern. The STM images of this surface are consistent with a distribution of adatoms on an ideal Si(111) surface. Further heating results in a 7×7 surface.
Measurement of resist heating in photomask fabrication
Authors: Babin Sergey
Published: July 2002

High-throughput photomask fabrication using 50 kV variably shaped electron-beam lithography was examined for resist heating distortions. Effective absorbed energy changes in the resist due to heating were measured using beam current density and subfield time sequences as parameters. Absorbed energy changes due to short-range heating inside a subfield were also determined. Corresponding linewidth variations caused by resist heating were measured. This showed that the 1 μm gaps had become completely broken. The sublimation of resist during exposure was investigated, and the subsequent reduction in resist thickness was measured as a function of exposure dose. The highly sensitive resist PBS [poly(butene-1 sulfone)], which is used widely for photomask manufacturing, was used for the heating measurements. It was concluded that high-throughput variably shaped electron-beam lithography with a high current density (20–80 A/cm2) may not be suitable for reticle fabrication without taking precautions for heating effects.
Electrostatic accel–decel lens with the advantage of reduced chromatic aberration
Authors: Nomura Setsuo
Published: July 2002

An electrostatic lens, operated in accel–decel mode, is presented. The lens has advantage of low chromatic aberration, which is about 2/3 the amount produced by a conventional einzel lens operated in decel mode. The lens has two pieces of electrodes built in to accelerate and decelerate the beam. The decelerating electrode works as a main lens, while the accelerating electrode enhances the beam energy, reducing the aberration. Calculations for the accel–decel lens provide Cc of 22 mm and f of 10 mm with working distance of 5 mm. The lens is suitable for producing a fine beam with a smaller spot size and with energy of over a few tens of kiloelectron volts. When the lens is applied to a 30 keV focused ion beam with 1 pA current, the spot size is estimated as 4.8 nm in diameter on a target with the above working distance.
Surface characterizations on newly developed copolyester thin films for microelectronics devices
Authors: Shi Frank F. , Economy James
Published: July 2002

In this article, by using surface I–V and C–V characteristics, the levels of moisture uptake and the degree of surface polarization were studied on the newly developed all-aromatic and aromatic/aliphatic copolyester thermosetting thin films with a thickness of 1.0–5.0 μm. The all-aromatic copolyester films which contain more rigid structures appear less polarizable and less hygroscopic compared to aromatic/aliphatic copolyester. It was also found that both the surface current leakage and the polarization are lower than those of the commercially available polyimide systems. The data suggested three types of moisture which could be described by the dehydration conditions required to restore original C–V characteristics. The effects of curing conditions on moisture absorption and polarization are also presented.
Numerical analysis of the pressure dependence of the etch rate in an Al etching reactor equipped with a helicon source
Authors: Ikeda Kei , Oshita Yoshio
Published: July 2002

The pressure dependence of the etch rate in an Al etching reactor has been studied with the goal of developing a method of numerically simulating the etching process. Experimentally, the etch rate was measured at pressures between 3 and 100 mTorr and reached a maximum at about 10 mTorr, whereas the calculated etch rate, which took the etching reaction between Al and Cl2 on an Al surface into account, increased with pressure. To explain the experimental data, the residence time τ0 of the inhibitor adsorbed on the Al surface and time-averaged surface coverage were included in the calculations. In the low-pressure region below 10 mTorr, the etch rate increased with an increase in pressure, due to the increased Cl2 flux on the Al surface. On the other hand, in the high-pressure region over 10 mTorr, the etch rate decreased when the effect of the inhibitor became stronger; this was explained by developing an improved model. Consideration of the inhibitor adsorbed on the Al surface is important, where the increase of τ0 with pressure is necessary to precisely simulate the correlation between the etch rate and pressure.
Nanoscale imaging of the electronic tunneling barrier at a metal surface
Authors: Condon G. R. , Panitz J. A.
Published: July 2002

A photometric field-emission electron microscopy technique is described by which the spatial structure of the surface electronic tunneling barrier can be mapped with nanometer resolution. The technique involves performing a Fowler–Nordheim analysis on luminosity data extracted from a set of digitized field-emission images taken over a range of voltages. This approach is equivalent to older probe-hole methods, but with greatly improved spatial resolution and data accumulation rate. Virtual probe holes of arbitrary size and shape can be constructed by integrating over subregions in the field-emission images. Performance of a system utilizing this technique is demonstrated by measuring the work functions of the (111) and (100) crystallographic planes of a clean tungsten field emitter. Applications of this technique to adsorption phenomena and field-emission display technology are also discussed.
Oxide loss at the gate periphery during high density plasma etching
Authors: Kraft R. , Gupta I. , Kinoshita T.
Published: July 2002

This article describes experimental measurements and computer calculations of the location of microtrenches in the gate oxide at the periphery of a complementary metal-oxide semiconductor gate resulting from a polysilicon gate etch with a low pressure, high density plasma, etch tool. When the oxide is removed at the periphery of a gate with the etch process, it is possible to damage the underlying silicon in the source and drain regions. This damage may not be observable in scanning electron microscope pictures but could still lead to device degradation or failure. To measure the integrity of the oxide at the gate periphery, a modified MOS (MMOS) capacitor test structure was used to measure the electric field breakdown strength of the oxide at the gate periphery. The breakdown voltage can be related to the amount of remaining oxide at the gate periphery. This article describes the use of the MMOS test structure to measure the location of the microtrenches relative to the gate edge in a low pressure, high density plasma, polysilicon gate etch tool.
Maskless sub-μm patterning of silicon carbide using a focused ion beam in combination with wet chemical etching
Authors: Menzel R. , Bachmann T. , Wesch W. , Hobert H.
Published: July 2002

Two methods for maskless patterning of SiC using a focused Ga+ beam are demonstrated: the enhancement of the chemical etching rate by amorphization of c-SiC to a-SiC and physical sputtering if deep structures are required. Both methods are followed by wet chemical etching in HF:HNO3=1:1 at 80 °C to remove the remaining a-SiC. Assuming the critical displacement density for amorphization to be about the same as for the onset of etching, the measured depths of the structures were compared with the depths of amorphization estimated with TRIM 87 calculations. To find optimum sputtering parameters the energy dependence of the sputter yield was investigated and compared with TRIM 87 simulations, too. Damage after implantation and after wet chemical etching was investigated by means of Raman spectroscopy. No damaged material remaining after wet chemical etching could be detected.
Study of the influence of gas chemistry on notching in metal etching
Authors: Tabara Suguru , Kitayama Yoshihiko , Hatakeyama Tadao , Katsuragi Ken , Tanabe Masafumi
Published: July 2002

A comparison of notching of metal etching in Cl2/BCl3 and HCl plasma was made by using a transformer coupled plasma etcher. We found that notches can be reduced by eliminating BCl3 from gases for overetching. Furthermore, the HCl/He overetch process provides notch-free profiles with high selectivities. The reduction in sidewall attack by heavy ions (e.g., BCl2+ or BCl3+) and scavenging of excess Cl radicals by the H radical are considered possible reasons for reduced notching in the HCl/He process.
Efficient surface-emitting cold cathodes based on electroluminescent porous silicon diodes
Authors: Sheng Xia , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

The porosity-modulation technique has been applied to improve the emission properties of the previously reported surface-emitting cold cathodes based on electroluminescent porous silicon (PS) diodes. It is demonstrated here that by introducing a modified structure into the PS layer, the emission efficiency is significantly improved. An extremely high efficiency of 12% has been obtained. A significant decrease in the emission current fluctuation and a consequent increase in the durability of the emission are also observed. These results are due to a regulated electric field distribution near the outer surface of the PS layer.
Calculation of bulk states contributions to field emission from GaN
Authors: Chung M. S. , Yoon B.-G. , Park J. M. , Cutler P. H. , Miskovsky N. M.
Published: July 2002

The field emission current from an n-type GaN is theoretically calculated as a function of carrier concentration n. The obtained emission current density j increases slowly with increasing n even though the band bending has the opposite n dependence. In evaluating the n dependence of field emission, the internal voltage drop due to field penetration is found to be crucial. The current density j is also calculated for several electron affinities χ. It seems that at the lowest χ and at high field, F, the calculated emission currents from the bulk states can be close to the measured values. The electric field at the GaN conical tip is found to be very high in the large area and yield such a large emission current as measured in experiment.
Molecular beam epitaxy growth and properties of GaN, InGaN, and GaN/InGaN quantum well structures
Authors: Johnson M. A. L. , Brown J. D. , El-Masry N. A. , Cook J. W. , Schetzina J. F. , Kong H. S. , Edmond J. A.
Published: July 2002

Growth of III–V nitrides by molecular beam epitaxy (MBE) was studied using rf nitrogen plasma sources. Plasma sources from three different vendors have been tested. All three of the sources have been used to grow high quality GaN. However, the EPI rf source produces an optical emission spectrum that is very rich in the active nitrogen species of 1st-positive excited nitrogen molecules and nitrogen atoms. GaN growth rates at 800 °C of 1 μm/h have been achieved using this source. The MBE-grown GaN films are deposited homoepitaxially on high quality metalorganic vapor phase epitaxy-grown GaN/SiC substrates. With the growth conditions for high quality undoped GaN as a base line, a detailed study of Mg doping for p-type GaN was performed. An acceptor incorporation of 2×1019 cm−3 was measured by both capacitance–voltage and secondary ion mass spectroscopy for a doping source temperature of 290 °C. However, a faceted three-dimensional growth mode was observed by reflection high energy electron diffraction during Mg doping of GaN. Additional studies suggest an interdependence between Mg incorporation and growth surface morphology. Quantum well structures made from the InGaN ternary alloy were grown using a modulated beam MBE method. With this technique, quantum well compositions were controllable, grown with visible luminescence ranging from 400 to 515 nm depending on indium mole fraction. Light emitting diode test structures, combining Mg p-type doping with InGaN quantum wells, were fabricated and tested.
Nature of Stranski–Krastanow growth of InAs on GaAs(001)
Authors: Ramachandran T. R. , Madhukar A. , Mukhametzhanov I. , Heitz R. , Kalburge A. , Xie Q. , Chen P.
Published: July 2002

The nature of the two-dimensional (2D) to three-dimensional (3D) morphological transition in the highly strained epitaxy of InAs on GaAs(001) is discussed, based on in situ scanning tunneling microscope and atomic force microscope studies, combined with photoluminescence (PL) and PL excitation spectroscopy results. A re-entrant 2D–3D morphology change is observed, in which quasi-3D (Q3D) clusters appear, disappear, and reappear well in advance of the formation of 3D islands. We suggest that the Q3D clusters may act as a kinetic pathway to 3D island formation, spreading out the 2D–3D transition over a delivery range of ∼0.3 monolayers. Large (>∼50 nm wide) 2D clusters sitting on top of the wetting layer (WL) undergo morphological changes with increasing strain and ultimately lose their material to 3D islands. Small (<20 nm) 2D clusters decorating the WL appear to contribute to the commonly observed redshift of the InAs WL PL peak prior to 3D island formation. A diffusion-limited formation of 3D islands for our growth conditions is indicated by the behavior of the 3D island density as a function of growth rate.
Voltage-tunable near-infrared photodetector: Versatile component for optical communication systems
Authors: Masini G. , Colace L. , Assanto G. , Pearsall T. P. , Presting H.
Published: July 2002

We present a voltage-tunable wavelength-selective photodetector (VWP) for the near-infrared (NIR), realized by engineering the optical properties of Si and Ge. The structure exhibits a wide tunability by varying the applied voltage and weighting the photocurrents generated by two back-to-back diodes. We demonstrate its versatility in deconvolving signals of different wavelengths and a preliminary study on the applications of the VWP as a solid-state spectrum analyzer. The spectrum of NIR light impinging the device can be resolved from a set of photocurrent measurements for different bias voltages.
Role of Te on the morphology of InAs self-assembled islands
Authors: Sáfar G. A. M. , Rodrigues W. N. , Moreira M. V. B. , de Oliveira A. G. , Neves B. R. A. , Vilela J. M. , Andrade M. S. , Rochet F.
Published: July 2002

The effect of Te presence on the morphology and distribution of InAs islands grown by molecular beam epitaxy on GaAs is investigated. Atomic force microscopy was used to follow the dependence of height, radius, and surface density on Te and InAs coverages. They ranged from zero to 0.45 monolayers (ML) of Te, and from 1.8 to 3.5 ML for InAs. We obtained a higher density of islands for samples covered with 0.3 ML of Te. The number of islands is essentially the same for samples covered with 0 and 0.45 ML of Te. A delay on the onset of island growth is observed for samples with θTe=0.45 ML. The surface morphology is also different for samples with Te when compared with the Te free sample. We suggest that for θTe=0.45 ML the coherence-incoherence transition is either delayed or absent for the InAs coverage range studied.
Optical absorption of Ag nanoclusters in Ag+-implanted c-SiO2
Authors: Feng Xiao-Dong , Tian Min-Bo , Liu Zheng-Xin
Published: July 2002

c- SiO 2 samples were implanted with Ag+ at an energy of 200 keV to doses in the range of 2.3–9×1016 ions/cm2 at room temperature. At a dose of 6.7×1016 ions/cm2, the transmission electron microscopy image shows that the implanted layer consists of two major sizes of nanoclusters: the large clusters, found in the deeper layer, are about 20 nm in diameter; the smaller clusters, found near the surface, are about 5 nm in diameter. At the relatively low dose of 2.3×1016 ions/cm2, there is only one optical absorption band caused by surface plasmon resonance. At a higher dose, a splitting of the absorption band and the redshift are attributed to a dipole interaction between nanoclusters for a high density of nanoclusters.
Evidence for liquid indium nanoparticles on Ge(001) at room temperature
Authors: Bottomley D. J. , Iwami M. , Uehara Y. , Ushioda S.
Published: July 2002

Indium films up to 6 ML thick on the Ge(001) surface in ultrahigh vacuum have been both deposited at and investigated at room temperature. The investigation techniques used were scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and low energy electron diffraction. Correlated AES and STM observations strongly suggest In–Ge intermixing, while XPS rules out compound formation. For a film 5 ML thick, nanoparticles approximately 15 nm high and 60 nm across with a pronounced faceted shape were observed in STM using a Pt–Ir tip scanning as far from the surface as possible. For smaller tip-sample distances, a dynamic tip-sample interaction was observed which resulted in sawtooth topographic data inconsistent with the topography observed at larger tip-sample separations. The evidence is that the epitaxial film is in the liquid phase at room temperature, in spite of the In bulk melting point at atmospheric pressure being 430 K. The liquid phase hypothesis is supported by a thermodynamic calculation which considers the impact of heteroepitaxial stress on the melting point.
Numerical modeling of electron transport in a cylindrical cell
Authors: Fedirko V. A. , Belova N. G.
Published: July 2002

A physical and mathematical model is developed for the numerical simulation of electron transport in a multielectrode microcell with a circular emitter. Two circular grid electrodes are included in the model to control the electron beam. A target plate face electrode is considered as a secondary electron source. Electron beam transport in a self-consistent electric field is simulated using a cylindrical particle mesh code. Some typical examples are calculated to demonstrate the effectiveness of the proposed technique for optimization of beam control. The influence of a magnetic field on the static and dynamic characteristics of the microcell is also studied. Split anode difference current is predicted in a magnetic field and thus the microvacuum cell may be used as a magnetosensitive element.
Contact hole model for etch depth dependence
Authors: Abraham-Shrauner Barbara
Published: July 2002

The dependence of the etch depth of a contact hole or circular via on the diameter of the hole opening is derived for a simple model which includes the effect of the bombarding ions and the neutral radicals on the etching. The ion etch rate at the center of the contact hole is proportional to the ion energy flux and the neutral etch rate is proportional to the neutral flux expression for molecular flow in a pipe. The total etch rate expression is found by Langmuir kinetics. The linear experimental relation for the etch depth versus the inverse diameter holds in this model for etching in the near ion flux-limited regime. The dependence of the etch depth and average etch rate on the etch time is given for this model.
Integrating system and feature scale models to study copper reflow
Authors: Friedrich L. J. , Dew S. K. , Brett M. J. , Smy T.
Published: July 2002

The reflow of sputtered copper is a microelectronics metallization procedure compatible with damascene processing [Murarka et al., MRS Bull. 18, 46 (1993)]. During the reflow process, copper films are deposited via traditional sputter technologies and subsequently made to fill submicron trenches and vias through surface diffusion enhanced by annealing [Gardner and Fraser, in 1995 Proceedings of the VLSI Multilevel Interconnection Conference, edited by T. E. Wade (VMIC, Tampa, FL, 1995), p. 287]. This article studies the copper reflow processing parameters through simulation using the process simulators SIMSPUD and GROFILMS. Simulation results are presented as depictions of the film on the feature scale and as an analysis of the process parameter space. In particular, factors such as initial film profiles and anneal temperatures are shown to be important considerations in developing a successful Cu reflow process. The effects of the deposition procedure on the reflow process are presented regarding system configuration, copper film thickness, and trench aspect ratios. The deposition system parameters are shown to be important when multiple feature sizes are to be filled concurrently.
Low temperature in situ boron doped Si epitaxial growth by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition
Authors: Park Jin-Won , Hwang Ki-Hyun , Yoon Euijoon
Published: July 2002

Boron-doped silicon epitaxial layers were grown by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition at 440–510 °C. Reflection high-energy electron diffraction and transmission electron microscopy (TEM) were used to study the effect of boron doping on the crystalline quality of silicon epitaxial layers. At growth conditions where undoped defect-free Si epitaxial layers were successfully obtained at 440 °C, in situ boron-doped epitaxial layers were replete with twins. However, at conditions with increased ion energy flux and at a higher temperature, 470 °C, no twins were observed. TEM analysis revealed the presence of an amorphous phase in the twinned epitaxial layers. It is believed that the amorphous phase formation, presumably from the reaction between B and O during the doping process, appeared to hinder the growth of the epitaxial layer, leading to degradation of the Si crystalline quality. Defect-free boron-doped Si epitaxial layers were able to be obtained by suppressing the amorphous phase formation at conditions with increased growth temperature and higher ion energy flux.
Transport phenomena related to electron field emission from semiconductors through thick oxide layers
Authors: Filip V. , Nicolaescu D. , Okuyama F. , Plavitu C. N. , Itoh J.
Published: July 2002

In this article the field electron emission from a semiconductor (with special emphasis on silicon) occurring through a thick oxide layer is considered. The oxide thickness is taken large enough (as compared to the electron mean free path) to allow for transport effects. The electrons are injected from the conduction band of the semiconductor into the conduction band of the oxide, through the interfacial potential barrier. Finally they are emitted through the oxide–vacuum interface. Owing to the small density of conduction electrons in the oxide layer, the electric field deeply penetrates it. For a more refined model, field penetration into the base semiconductor can also be considered. Comparative computations of the emission current density are performed for these two models. No essential differences are found in the high field range. For relatively low field strength, however, significant improvement can be obtained by considering field penetration into the semiconductor. These observations may be of use in designing electron field emission devices.
Integral and local field emission analyses of nanodiamond coatings for power applications
Authors: Göhl A. , Alimova A. N. , Habermann T. , Mescheryakova A. L. , Nau D. , Zhirnov V. V. , Müller G.
Published: July 2002

Nanodiamond (ND) powder coatings are very promising for cold cathode applications. The suitability of a (di)electrophoretically deposited ND coating (crystallite size: 1–10 nm) for high current applications was analyzed depending on three types of Si substrates (flat, rough, Si tip array). Nondestructive direct current field emission (FE) investigations were performed by means of a field emission scanning microscope. FE properties like the electrical onset field strength Eon (at 0.5 nA), current I vs E behavior, maximum current carrying ability as well as the local distribution and uniformity of emitters were analyzed by using anodes of different apex diameters D. A decrease of Eon for D=10/100/1000 μm from 203/190/109 V/μm of the flat to 67/44/20 V/μm of the rough, and to ≈7/6.7/4.5 V/μm of the tip array sample is achieved by the geometrical field enhancement of the structures. The reproducible high-current density JREP>15 A/cm2 for D=10 μm of the flat and rough sample exhibits the large potential of the ND coating for power applications. Their nonuniformity due to the μm-roughness results, however, in a low JREP for large areas. In contrast, ND coated tips showed a good uniformity over mm2 size and a moderate JREP≈0.2 A/cm2, basing on about 40% of significantly emitting tips.
Investigation of ion implanted electroplated chromium from a trivalent bath
Authors: Hamdi A. H. , Malaczynski G. W. , Elmoursi A. A. , Leung C. H. , Campbell A. B. , Shpuniarsky D. , Simko S. J. , Militello M. C. , Balogh M. P. , Lindsay J. H.
Published: July 2002

The objective of this work is to compare chromium electroplated from a hexavalent bath, Cr(+6), with a more environmentally friendly process; nitrogen plasma source ion implantation of chromium from a trivalent bath Cr(+3) which transforms it into a material that is harder than as-deposited Cr(+6) with equal or better wear resistance properties. As-deposited, the hardness of a Cr(+6) layer is higher (1200–1500 Knoop) than that of an as-deposited Cr(+3) layer (950–1100 Knoop). Nitrogen-ion implantation at 120 kV to a dose higher than 3×1017 N/cm2 increases the hardness of the Cr(+3) to 2300 Knoop. Wear resistance measurements show that under the same wear conditions a N-ion-implanted Cr(+3) layer has about twice the wear resistance than the as-deposited Cr(+3) and Cr(+6) layer. Specifically, the width of the wear groove in a pin-on-disk test of an implanted Cr(+3) plated layer is 60 μm for a 100 g load while for an as-deposited Cr(+6) under the same load, the groove width is 114 μm. In this report we also demonstrate that nitrogen ion implantation into trivalent-deposited Cr(+3) achieves the same chromium nitride phases and hardness as nitrogen-implanted Cr(+6).
Process window and mechanism of surface property enhancement of 9Cr18 steel using plasma immersion ion implantation
Authors: Zeng Z. M. , Tang B. Y. , Chu P. K. , Tian X. B. , Wang S. Y. , Wang X. F.
Published: July 2002

9Cr18 martensite steel is commonly used as a bearing material in the aerospace industry in China. Because of its ability to treat large and irregular industrial components, plasma immersion ion implantation (PIII) is a good technique to enhance the wear resistance of 9Cr18 precision bearings to extend the working lifetime. We have recently conducted a systematic investigation to determine the process window of nitrogen PIII as well as to identify the enhancement mechanism. The surface properties of 9Cr18 steel after nitrogen PIII under different dosage and plasma conditions (filament hot electron discharge and radio frequency glow discharge) are evaluated by measuring the microhardness, wear property, coefficient of friction, corrosion resistance, as well as elemental depth profiles. Our data indicate that the degree of improvement does not differ substantially under the various PIII conditions thereby suggesting a fairly large process window as long as enough nitrogen is incorporated to form nitride phases.