bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of cleanings on the composition of HgCdTe surfaces
Authors: Seelmann-Eggebert M. , Carey G. , Krishnamurthy V. , Helms C. R.
Published: July 2002

The surface chemistry of HgCdTe is investigated with regard to the combined effects of etching, photochemical oxidation, and exposure to acids. The potential of angle-resolved x-ray photoelectron spectroscopy is utilized to characterize the surface region of the processed compound semiconductor with respect to its compositional depth profile. Upon exposure to the acids HNO3, HCl, H2SO4, and lactic acid, the HgCdTe surface does not degrade but becomes chemically passivated by the coverage of up to a monolayer of a native oxide. By such acid treatments, a residue to elemental tellurium, typically present after the Br2/methanol etching process, cannot be removed but becomes partially oxidized. However, the removal of this Te residue is made possible by the employment of a photochemical oxidation step between the etch and the acid treatment. Upon the formation of the photochemical oxide layer, the substrate composition below the interface is not affected. During the oxidation process, HgO segregates to the surface, leaving a Hg deficient oxide region in the bottom part of the layer.
Growth of (111) CdTe on GaAs/Si and Si substrates for HgCdTe epitaxy
Authors: Korenstein R. , Madison P. , Hallock P.
Published: July 2002

(111) CdTe has been grown on both GaAs/Si and Si by hot wall epitaxy. X-ray diffraction, photoluminescence, and defect etching indicate that these layers are of high crystalline quality. For CdTe grown on GaAs/Si, full width at half-maximum of x-ray rocking curves as low as 59 arcsec have been obtained whereas for CdTe grown on Si, x-ray linewidths as narrow as 315 arcsec have been obtained. HgCdTe grown on (111)B CdTe/GaAs/Si by metalorganic chemical vapor deposition is very smooth and devoid of the many defects that plague other orientations.
Fabrication of lateral resonant tunneling devices
Authors: Randall J. N. , Seabaugh A. C. , Luscombe J. H.
Published: July 2002

Lateral resonant tunneling transistors have been fabricated in the InAlAs/InGaAs material system lattice matched to InP. Lateral tunnel barriers are formed in the plane of a two-dimensional electron gas confined at a modulation-doped heterointerface by depletion regions induced by top-contact metal gates. The device is structurally similar to a dual-gate modulation-doped field effect transistor with nanoscale gates. The metal gates are written by e-beam lithography. Device results include multiple negative differential resistance peaks for temperatures as high as 20 K. Using the substrate as a backgate, multiple regions of negative transconductance are also observed.
Engineering sub-50 nm quantum effect devices and single-electron transistors using electron-beam lithography
Authors: Wang Yun , Chou Stephen Y.
Published: July 2002

Fabrication and characteristics of various nanoscale quantum and single-electron devices are described. Using high-resolution electron beam lithography and double layer PMMA resist, we have successfully fabricated a 20 nm split-gate device, a novel 50 nm single barrier single-electron transistor, and a 75 nm triple barrier tunneling device. Effects of beam dose and the number of writing passes on the actual lithography pattern were investigated for various device gate geometries. Pronounced quantum and single-electron effects have been observed in these devices.
Focused ion beam deposition of Pt containing films
Authors: Puretz J. , Swanson L. W.
Published: July 2002

Focused ion beam induced deposition of platinum films from a gas of methylcyclopentadienyl trimethyl platinum is reported. Deposition was carried out with a 25 kV beam of Ga+ with current densities of 2–7 A/cm2 that was controlled by a digital scan generator. Film yields and resistivity were measured as a function of beam current density, gas flux, scan dwell, and loop time. Relatively high yields of 1.4 μm3/nC and resistivities as low as 400 μΩ cm were measured for deposition carried out in 1×10−6 Torr background pressure of residual gas. Auger studies revealed that the films were surprisingly free of oxygen, but contained significant amounts of carbon. A figure-of-merit, Fm=ρ/Y, is defined which enables comparison of films used for interconnects. Fm for the Pt films is superior to that of W(CO)6 deposited W films.
Deep trench plasma etching of single crystal silicon using SF6/O2 gas mixtures
Authors: D’Emic Christopher P. , Chan Kevin K. , Blum Joseph
Published: July 2002

A new magnetron ion etching (MIE) process has been developed to etch 50 μm deep trenches into single crystal silicon. The optimized SF6/O2 gas mixture results in a nearly vertical etch profile with a vertical to horizontal etch rate ratio of 9.4. Similar experiments were carried out on a Drytek reactive ion etching (RIE) system. Results indicate that although the sidewall angle, etch rate ratio, and etch rate of the RIE process for silicon is lower than that of the MIE process, the surfaces of the trench are smoother and more defect-free due to better substrate cooling. The effects of the processing parameters on the silicon etch rate and anisotropy were explored in order to optimize both the MIE and RIE processes. Both processes were used to fabricate single crystal silicon doughnuts of dimensions 25–50 μm thick, 50 μm inner diameter, and 100–200 μm outer diameter.
Novel molecular-beam epitaxially grown GaAs/AlGaAs quantum well structures for infrared detection and integrated optics at 3–5 and 8–12 μm
Authors: Ralston J. D. , Schneider H. , Gallagher D. F. G. , Kheng K. , Fuchs F. , Bittner P. , Dischler B. , Koidl P.
Published: July 2002

Two novel molecular-beam epitaxially grown quantum well device structures for 3–5 and 8–12 μm photodetection and integrated optics are presented, both of which rely intimately upon the ability of molecular-beam epitaxy to precisely reproduce demanding layer sequences. The first structure combines single-mode infrared waveguiding, grating-coupling, and intersubband absorption at 10 μm in a GaAs/AlGaAs multilayer structure. The second structure demonstrates the feasibility of extending the operating wavelength range of GaAs/AlGaAs infrared detectors into the 3–5 μm atmospheric window by incorporating ultrathin AlAs tunnel barriers. Both growth-induced and intentional inequivalences in the tunnel barriers are found to lead to enhanced photovoltaic detection in these latter devices.
Coherent epitaxy, surface effects, and semiconductor alloy phase diagrams
Authors: Wood David M.
Published: July 2002

Recent theoretical work has made possible a unified understanding of the effects of coherent epitaxy on the phase diagrams of semiconductor alloys. Experimentally observed effects peculiar to coherent epitaxy are briefly reviewed, and an elastic description of this constraint is used to motivate a simple picture of the qualitative effects on phase stability. A rigorous, first principles cluster-based formalism makes possible direct comparison of an alloy phase diagram under bulk and coherent epitaxial conditions. Results for the alloy GaAsxSb1−x are discussed as an example. To understand the details of ordering of such A1−xBxC semiconductor alloys into (AC)4−n(BC)n compounds, however, surface energies, as they are affected by electronically driven reconstructions, and kinetic effects are crucial.
Compositional analysis of HgCdTe epitaxial layers using secondary ion mass spectrometry
Authors: Bubulac L. O. , Edwall D. D. , Cheung J. T. , Viswanathan C. R.
Published: July 2002

The work reported here elaborates on the emission of the secondary Te− ions from secondary ion mass spectrometry (SIMS) analysis of HgCdTe using a Cs+ primary ion beam. Investigations of numerous samples covering a wide compositional range showed excellent linear correlation between negative Te ion yield and Cd mole fraction. These led to the newly developed SIMS analytical method for measuring the changes in the composition of Hg1−xCdxTe with high sensitivity and depth resolution. A physical model describing the emission of secondary Te− ions is proposed. The results can be interpreted by considering the short range interaction between reactive Cs primary beam and the CdTe sublattice via a ‘‘harpoon’’ mechanism. The relevance of this method to the development of Hg1−xCdxTe was demonstrated on metalorganic chemical vapor deposition grown heterostructures.
Properties of CdZnTe crystals grown by a high pressure Bridgman method
Authors: Doty F. P. , Butler J. F. , Schetzina J. F. , Bowers K. A.
Published: July 2002

CdZnTe crystals have been grown over the full range of alloy composition by a high-pressure Bridgman (HPB) method. Use of the inert gas over pressure reduces loss of material from the melt, and permits growth without the use of sealed ampoules, extending the range of possible alloys, and allowing a choice of crucible materials. The HPB method yields high-quality CdZnTe and enables room-temperature gamma radiation detectors to be made over large area wafers of undoped material for the first time.
Two-dimensional delineation of shallow junctions in silicon by selective etching of transmission electron microscopy cross sections
Authors: Cerva Hans
Published: July 2002

The method of junction delineation with thickness fringes in selectively chemical etched transmission electron microscope cross sections is demonstrated on a few examples. Arsenic-doped source and drain regions of metal-oxide-silicon transistors were delineated at a concentration level of about 1×1018 cm−3 both in the as-implanted state and after 900 °C annealing. Calibration was performed with one-dimensional secondary ion mass spectroscopy dopant profiles whereas process simulation was used to examine the experimental two-dimensional results. The lateral extent of the dopant surface concentration at 1×1019 cm−3 under the transistor gate after 900 °C annealing corresponded to the n+/n transition region previously detected by scanning tunneling microscopy. Boron and arsenic junctions were simultaneously delineated in a bipolar transistor.
Improved performance of highly strained InGaAs/GaAs heterostructure devices grown on patterned GaAs substrates
Authors: Li W. Q. , Chan Y. J. , Bhattacharya P. K.
Published: July 2002

Al0.15Ga0.85As/In0.25Ga0.75As pseudomorphic modulation-doped field-effect transistors and strained InxGa1−xAs/GaAs p-i-n photodiodes have been fabricated on patterned (100)-GaAs substrates and characterized. Compared with devices made on planar substrates, small area growth improves the dc transconductance by 40% and current gain cutoff frequency by 50% in the transistors. The photodiodes grown in small recesses (∼30 μm) exhibit 2–4 times higher quantum efficiency than those grown on planar substrates.
Marks for alignment and registration in projection electron lithography
Authors: Farrow R. C. , Liddle J. A. , Berger S. D. , Huggins H. A. , Kraus J. S. , Camarda R. M. , Tarascon R. G. , Jurgensen C. W. , Kola R. R. , Fetter L.
Published: July 2002

This article discusses the relevant criteria for selecting alignment marks for projection electron lithography. The mark material, topography, and pattern layout are considered. Results from experiments and calculations indicate that there is a wide range of acceptable mark configurations suitable for use with short beam dwell times. These results are based on analyses of the available backscattered electron signal and experimentally obtained detection accuracy within the nanometer range.
Reduction and elimination of proximity effects
Authors: Dobisz E. A. , Marrian C. R. K. , Salvino R. E. , Ancona M. A. , Perkins F. K. , Turner N. H.
Published: July 2002

The physical processes limiting resolution and causing proximity effects in electron-beam lithography (EBL) are outlined, with the major emphasis on sub-250 nm lithography. A reduction of proximity effects and the enhancement of resolution in the resist can be achieved with a thin intermediate layer (such as 50–300 nm of silicon nitride or silicon dioxide) between the resist and the substrate. This has been observed on a number of substrates (Si, GaAs, W, and InSb) and with two high-resolution e-beam resists. Monte Carlo simulations and experimental results show that secondary electrons play a key role in the understanding of this phenomenon. Furthermore, a large number of fast secondaries (500 eV–3 keV), emitted from substrate–resist interface, enter the resist within a ∼100 nm radius of the primary beam. The thin intermediate layers reduce the number of secondary electrons entering the resist. In contrast, the elimination of proximity effects was observed with very low energy electron beams (≤100 eV) as can be formed by a scanning tunneling microscope (STM), operated in the field emission mode. STM lithography gives a highly localized exposure, which results in very high resist resolution over a wide process latitude. The elements of an implementation of very low voltage EBL are outlined.
Evaluation and application of a very high performance chemically amplified resist for electron-beam lithography
Authors: Lee K. Y. , Huang W. S.
Published: July 2002

This article reports on sub-0.25 μm electron-beam lithography using a new positive-tone chemically amplified resist system called KRS. Unlike conventional chemically amplified resist systems, KRS is immune to N-methylpyrolidone contamination and does not require a postexposure bake step. The resist is aqueous developable and shows a contrast figure of about 10 and a sensitivity of about 12 μC/cm2 at 50 kV. A 0.15 μm feature size with a shaped-beam system in 0.8 μm thick resist on silicon with −0.05 μm print bias was achieved. Sub-100 nm features are resolved in 0.3 μm thick KRS using a high-resolution Gaussian-beam system. The resist was found to be extremely suitable for patterning densely packed, high resolution, and high aspect ratio structures. As examples, the application of this resist for fabricating high resolution x-ray masks and very high performance 0.1 μm gate-length n-metal–oxide–semiconductor field effect transistors are reported.
Simulation of locally enhanced three-dimensional diffusion in chemically amplified resists
Authors: Zuniga M. , Wallraff G. , Tomacruz E. , Smith B. , Larson C. , Hinsburg W. D. , Neureuther A. R.
Published: July 2002

Evidence from simulation, linewidth measurements, and in situ Fourier-transform infrared (FTIR) data are presented which suggests that a type II diffusion front is moving through positive tone t-BOC material during postexposure bake. A steady increase in linespace of 50 nm/min is observed in IBM APEX-E and even faster rates can be found in generic t-BOC resists. The simultaneous reaction and three-dimensional deprotection dependent diffusion simulation was carried out with a massively parallel approach. A novel FTIR measurement of transmission versus time of patterned and unpatterned wafers during postexposure bake corroborated scanning electron microscope linewidth measurements.
Electronic defects induced in p- and n-type silicon by SF6 plasma etching
Authors: Belkacem A. , Arnal Y. , Chantre A. , Pomot C.
Published: July 2002

Electronic defects induced in p- and n-type silicon by SF6 plasma etching in microwave multipolar plasma reactors have been studied by capacitance spectroscopy, spreading resistance, and infrared absorption measurements. A passivation of the boron and phosphorus electrical activity is associated with hydrogen contamination due to residual water traces in the reactor. Deep level transient spectroscopy measurements reveal several deep levels in the gap after etching. They are located at 0.51 and 0.36 eV above the valence band in the p-type boron-doped silicon and at 0.4 and 0.24 eV below the conduction band in the n-type phosphorus-doped silicon. We studied the influence of plasma parameters, gas nature, and postetch thermal annealing on the H(0.51), H(0.36), E(0.4), and E(0.24) levels. The results show that the occurrence of the H(0.51) and E(0.4) levels is correlated with displacement damage production and the presence of SFx species in the plasma. The H(0.36) level is caused by the formation of a carbon-interstitial-related defect whereas the E(0.24) level is attributed to the V–V divacancy.
Evaluation of in situ formed W–Ti and MoSi2 as a diffusion barrier to Al for CoSi2 silicided contact
Authors: Yang Fann-Mei , Chen Mao-Chieh
Published: July 2002

A simple metallization process to form a shallow CoSi2 silicided contact and W–Ti diffusion barrier simultaneously has been developed. The process starts with depositions of a Co–Ti alloy layer and an overlying W layer on silicon wafers using a dual e-beam evaporation system; this is followed by a single-step annealing treatment in a normal flowing-nitrogen furnace. On the other hand, bilayer self-aligned shallow MoSi2/CoSi2/Si silicided contact can be derived from the W/Co–Mo/Si system by a two-step annealing treatment performed in the same environment. I–V characteristics for silicided p+n diodes with the diffusion barriers formed in situ were measured after they had been finished with Al deposition and post-Al annealing at temperatures from 350 to 600 °C in N2. For comparison, Al/CoSi2/p+n and Al/p+n structures were also investigated. It turns out that the integrity of Al/W–Ti/CoSi2/p+n and Al/MoSi2/CoSi2/p+n silicided contacts can be preserved up to 550 and 500 °C, respectively, for a 20 min annealing, while that of Al/CoSi2/p+n can be kept only up to 450 °C.
Dielectric/semiconductor interfaces
Authors: Wieder H. H.
Published: July 2002

A retrospective and chronological review will be presented of the scientific and technological evolution of metal/insulator/semiconductor structures with emphasis on the interfaces between compound semiconductors, homomorphic, heteromorphic, and heterojunction quasi-insulators. The Conference on the Physics and Chemistry of Semiconductor Interfaces has provided for the past 20 years a forum for the synthesis of worldwide research on the nature of dielectric/semiconductor interfaces. The current status of such research and some of the many unresolved fundamental and applications-oriented issues that remain to be explored will be introduced, as well.
Sb-induced surface stabilization of InP(100) wafer beyond 500 °C
Authors: Soukiassian P. , Mangat P. S. , Huttel Y. , Hurych Z. , Gruzza B. , Porte A.
Published: July 2002

This article investigates the effect of Sb deposition on the surface thermal stability of an InP(100) wafer by core-level and valence-band photoemission spectroscopy using synchrotron radiation. Ion bombardment of the InP(100) surface removes the native oxides and induces the formation of three dimensional indium clusters. After room-temperature Sb deposition and subsequent thermal annealings, the system undergoes surface restructuring which includes removal of the In islands by Sb, establishment of In–Sb bonds and formation of a InSb/InP(100) interface at 400 °C. This system is found to be stable beyond 500 °C, i.e., well above the thermal decomposition temperature (370 °C) of the clean InP(100). In these conditions, P atoms migration from the bulk and their desorption resulting in P depletion layer at the surface occurs only at higher temperatures around 600 °C.
Measurement of GaAs temperature-dependent optical constants by spectroscopic ellipsometry
Authors: Kuo C. H. , Anand S. , Droopad R. , Choi K. Y. , Maracas G. N.
Published: July 2002

Temperature-dependent optical constants (30 °C<T<650 °C) of semi-insulating GaAs in the range of 1.24–5.00 eV were measured using spectroscopic ellipsometry (SE) inside a specially designed molecular beam epitaxy chamber. Because of the lack of native oxides and surface adsorbates, a simple two-phase model (vacuum/substrate) could be used to calculate optical constants from the ellipsometry data. A Lorentz oscillator model with seven oscillators was used to fit the ε1 and ε2 experimental data to determine the temperature-dependent interband transition energies, E1 and E1+Δ1. Changes in the dielectric function at different surface temperatures would allow SE to be used as a tool to accurately measure the surface temperature of GaAs. Accurate knowledge of the temperature-dependent optical constants is also useful for the design of optical devices.
Room temperature photoluminescence in strained Si1−xGex/Si quantum wells
Authors: Fukatsu S. , Sunamura H. , Shiraki Y.
Published: July 2002

Photoluminescence (PL) observation at room temperature is reported in strained Si1−xGex/Si multiple quantum wells (MQWs) grown by gas source Si molecular beam epitaxy. It was found that QW PL is enhanced when MQWs are arranged so that photogenerated carriers are trapped efficiently to QWs without significant loss. This was achieved by locating MQWs over the penetration depth of the excitation light. QW PL was found to develop with a power exponent of 1.8 for lower excitation. QW PL was observed at room temperature for MQW samples with x up to 0.69.
Application of the digital alloy composition grading technique to strained InGaAs/GaAs/AlGaAs diode laser active regions
Authors: Cody Jeffrey G. , Mathine David L. , Droopad Ravi , Maracas George N. , Rajesh Ramamurti , Carpenter Ray W.
Published: July 2002

Molecular-beam epitaxy (MBE) growth, lasing performance, and transmission electron microscopy (TEM) of In0.25Ga0.75As asymmetric triangular quantum well (ATQW) active regions is reported. The digital alloy technique was utilized to form three active regions of widths 200, 300, and 400 Å. Each structure lased with a threshold current density of 313, 152, and 241 A/cm2, respectively. The lasing wavelength range was 979–1030 nm. This is the first demonstration that controlled, digitally graded quantum wells can be incorporated into laser diode active regions.
Growth optimization of molecular beam epitaxy grown InAlAs on InP
Authors: Choi Woo-Young , Fonstad Clifton G.
Published: July 2002

The effects of different molecular beam epitaxy (MBE) growth conditions on material qualities of In0.52Al0.48As on InP were investigated. Investigated parameters were growth temperature and As overpressure. A range of these two parameters within which InAlAs grows under the As-rich condition was first determined by reflection high-energy electron diffraction. Five different InAlAs samples were grown within this range and characterized by double crystal x-ray diffraction, Hall measurement, and photoluminescence. Based on the results of these characterizations, the optimal MBE growth condition for InAlAs was determined.
Influences of δ -doping time and spacer thickness on the mobility and two-dimensional electron gas concentration in δ -doped GaAs/InGaAs/GaAs pseudomorphic heterostructures
Authors: Shieh H. M. , Hsu W. C. , Kao M. J. , Wu C. L.
Published: July 2002

A series of GaAs/In0.25Ga0.75As/GaAs pseudomorphic high electron mobility transistors (HEMTs) was grown by low-pressure metalorganic chemical vapor deposition. The respective influences of δ-doping time and spacer thickness on the two-dimensional electron gas concentrations and the mobilities were studied. The maximum mobilities, μ=5600 and 22 000 cm2/V s at 300 and 77 K, respectively, appeared at a spacer thickness of 100 Å with a δ-doping time of 0.2 min. A δ-doped GaAs/In0.25Ga0.75As/GaAs pseudomorphic HEMT with the above parameters was fabricated. This device revealed high saturation current density of 350 mA/mm, transconductance of 95 mS/mm, and broad maximum transconductance region of 2.5 V with geometry of 2×100 μm2 at room temperature. In addition, very high breakdown voltage (26 V) and low leakage current (≤2 μA at −26 V) were achieved.
The ADEQUAT project for development and transfer of 0.25 μm logic complementary metal–oxide–semiconductor modules
Authors: DeKeersmaecker R. , Declerck G. , Félix P. , Haond M. , Hill C. , Janssen G. , Lorenz J. , Maes H. , Montree A. , Neppl F. , Patruno P. , Rudan M. , Ryssel H. , Van den hove L. , Vandervorst W. , van Ommen A.
Published: July 2002

The ADEQUAT project [Advanced Developments for Quarter Micron complementary metal–oxide–semiconductor (CMOS) Technologies] is executed by a European consortium under the JESSI/ESPRIT programs. It aims at developing new device structures and process modules for the 0.35 and 0.25 μm CMOS logic technology generations, offering improved performance while meeting the reliability and manufacturability constraints. Several examples of choices illustrating this optimization process are presented together with the overall project organization and roadmap.
Sensor integration into plasma etch reactors of a developmental pilot line
Authors: Barna G. G. , Loewenstein L. M. , Brankner K. J. , Butler S. W. , Mozumder P. K. , Stefani J. A. , Henck S. A. , Chapados P. , Buck D. , Maung S. , Saxena S. , Unruh A.
Published: July 2002

During the course of the Microelectronics Manufacturing Science and Technology (MMST) program, a number of sensors have been integrated into various test-bed plasma etch reactors with the goal of monitoring, diagnosing, and controlling these processes. These sensors include single wavelength and spectral ellipsometers for real-time in situ etch rate and endpoint determination; a standard monochromator for etch rate and nonuniformity measurements; an eddy current sensor for incoming metal thickness control; a rf monitor for rf current and voltage diagnostics; and a scatterometry-based critical dimension sensor for linewidth measurements. The full integration of these sensors turned out to be a complex and time-consuming task including hardware, optical, software, material, and processing issues. Once integrated into the reactor, and the appropriate process modeling completed, these sensors enabled the monitoring, diagnosis, and model-based control of these processes. Besides maintaining specific process observables at their target values, running under process control has highlighted phenomena such as equipment aging and first-wafer effects. This work has clearly shown that the full implementation of sensors into commercial manufacturing equipment is essential for the model-based control and diagnosis of semiconductor processes.
Effects of sulfur passivation and rapid thermal annealing on the electrical properties of InP metal–insulator semiconductor Schottky diodes
Authors: Eftekhari G.
Published: July 2002

The effects of sulfur passivation and rapid thermal annealing on the electrical characteristics of InP metal–insulator semiconductor Schottky diodes are investigated. Passivation causes a moderate increase in barrier height and decrease in reverse current. Further reduction in the reverse current is obtained after rapid thermal annealing. The passivated diodes show a very good thermal stability. Bond formation at the interface and charge injection into the oxide are used to explain the observations.
Microstructures of nanosize hydrogenated crystalline silicon studied by scanning tunneling microscopy
Authors: Bai C. L. , Wang Z. H. , Dai C. C. , Zhang P. C. , He Y. L.
Published: July 2002

The morphology of nanosize hydrogenated crystalline silicon (nc-Si:H) films have been investigated by scanning tunneling microscopy (STM) without hydrofluoric acid etching under atmospheric conditions. Images from submicrometer scale down to atomic scale have been represented. On a large scale, the nc-Si:H films are found to be consisted of microcrystallites separated by different interfacial regions from STM results. The mean size of microcrystallites is about 3–5 nm, which is in agreement with high-resolution electron microscopy studies. In addition, near-atomic resolution STM images provide some information on the interfacial region, which seems to be crucial for the atomic structure and many properties of nanocrystalline materials. The results show that the arrangements of the atoms on nanocrystallites are well ordered, while atoms in the interfacial regions are randomly distributed. The mechanism for imaging nc-Si:H is discussed.
Atomic force microscopy and friction force microscopy of Langmuir–Blodgett films for microlithography
Authors: Fujihira Masamichi , Takano Hajime
Published: July 2002

We describe the study of microlithography of a thin chromium film on a quartz plate by an atomic force microscope (AFM) and a friction force microscope (FFM). The scratching of Langmuir–Blodgett (LB) films of ω-tricosenoic acid deposited on the chromium films was carried out by scanning an AFM tip under a high normal force of ∼5×10−8 N. The scratched depth was measured by a topographic AFM image recorded by scanning with a new tip under a low normal force of 1×10−8 N. The surface properties of the scratched surfaces created in the multilayered LB films were studied by the FFM. From (1) the wear patterns observed on the scratched surface of the multilayer and (2) the high resistance against scratching of the single monolayer observed by AFM and FFM, it was concluded that the first monolayer always remained even after scratching under the high normal force. Etching resistance of the chromium surfaces covered with LB films with a various number of monolayers was also studied by measuring elapsed times required for complete etching. A drastic change in the etching resistance was observed between the bare or the single monolayer covered chromium films and the multilayer covered ones.
Schottky barrier study of ion implantation damage in GaAs
Authors: Wang Y. G. , Ashok S.
Published: July 2002

Ion bombardment damage on GaAs surface has been studied with Ar ion implantation, followed by controlled removal of the damaged GaAs surface layer by anodic oxidation/stripping prior to Schottky metallization. The electrical characteristics of subsequently fabricated Au/n-GaAs Schottky barriers display progressive recovery towards those of undamaged control samples as a function of implanted Ar dose. The recovery depth for different material/device parameters are well in excess of the projected range for 10-keV Ar ions (10.5 nm) in GaAs. Deep level transient spectroscopy measurements of the Ar-implanted samples show both suppression and enhancement of deep levels in the GaAs surface region. A Ga-rich surface region introduced by low-energy Ar implantation appears to be responsible for the modification of deep level traps. The recovery in Schottky barrier height with a postimplantation rapid thermal anneal process is very poor at temperatures below 600 °C and significant degradation occurs at a higher temperature of 700 °C. Carrier compensation and suppression of donorlike antisite defects AsGa have been found in a Ga-rich region resulting from either ion bombardment or high-temperature annealing.
Laser system for fine pitch Tape Automated Bonding
Authors: Economikos Laertis
Published: July 2002

A system has been developed for implementing a solderless fine pitch Tape Automated Bonding (TAB) process. The process was applied to multichip module (MCM) packages with lead pitch of 100 μm. The technology can be extended to ultrafine pitch as low as 25 μm and can be used for both inner lead bonding and outer lead bonding. The technology is based on metal to metal diffusion at the lead to pad interface using a ‘‘hot’’ tip energized by a laser. A closed end flat tip was used to comply with safety requirements and provide uniform temperature distribution across the footprint of the tip. The tip has shown no degradation during the initial testing of 25 000 bonds. The technology is much simpler compared to the solder based TAB process. It is easily controlled, does not require any pretreatment of the pads and is less sensitive to pad contamination and surface nonplanarity. It can be applied to various sets of pad-lead metallurgies such as Au–Au, Au–Sn, Cu–Au, and Ni–Au. The study shows that the process can be designed to be reworkable which makes it suitable for MCM applications.
Design of an atom-cluster generator for a transmission electron microscope and in situ observation of the deposition process of large atom clusters
Authors: Mori H. , Fujii K. , Komatsu M. , Miyauchi K.
Published: July 2002

An atom-cluster generator which can be set in the specimen chamber of a transmission electron microscope has been designed and constructed. The generator essentially consists of two vacuum chambers; one is the chamber for differential pumping and the other the cluster source chamber. The former plays an essential role in keeping the column of a microscope in a high vacuum. The latter is kept in a gas atmosphere and nm-sized metal clusters are produced in this chamber by evaporating a metal element from a tungsten filament. With this apparatus, preliminary in situ deposition experiments were carried out, and it was observed that isolated gold clusters, ejected from the atom-cluster generator, landed sequentially on a substrate.
Simulations of trench-filling profiles under ionized magnetron sputter metal deposition
Authors: Hamaguchi S. , Rossnagel S. M.
Published: July 2002

Numerical simulation results are presented for microscopic profile evolutions of deposited metal films in trench structures under ionized magnetron sputter deposition. The model used for the simulations takes account of the deposition of both ionized and neutral metal species and sputtering (i.e., etching) of the deposited film by the bombardment of metal and inert-gas (such as argon) ions. The evolution of the surface topography is calculated numerically using the shock- tracking algorithm. Numerical results are also compared with experimental observations. A primary application of this metal deposition technique is interconnect metallization on semiconductors.
Plasma development of a silylated bilayer resist: Effects of etch chemistry on critical dimension control and feature profiles
Authors: Hutton Richard S. , Boyce Craig H. , Taylor Gary N.
Published: July 2002

We have previously described a positive-tone, silylated, dry-developed bilayer resist process for which 0.2 μm features with an aspect ration of 4.5 were obtained using deep-UV (248 nm) exposure. The plasma development of the resist is comprised of two steps: an initial etch with a mixture of Ar and Cl2 to remove the thin layer of silylated resist in the exposed regions followed by pattern transfer using an oxidative plasma. In this process feature profiles with minimal undercut were obtained when CO2 was used instead of O2 in the pattern transfer step. We have investigated the mechanism of these etching processes using x-ray photoelectron spectroscopy (XPS) and trilevel resist processing and found that there was little deposition and that the selectivity of the silylated resist decreased by a factor of 2 in the CO2 plasma compared to the O2 plasma. The lower selectivity leads to increased erosion of the silicon-containing mask and reduced critical dimension (CD) control. In order to obtain good CD control and further improve the feature profiles we have evaluated other etching gases which are considered to undergo sidewall deposition during the pattern transfer step, including SO2 and mixtures of O2 with N2 and SO2. Using trilevel resist structures, the degree of lateral etching was determined for each plasma. The extent of deposition in each plasma was monitored through surface analysis using XPS. In the silylated bilayer resist, the feature profiles are significantly influenced by the etching rates, selectivities, and degree of overetch which were studied by varying the etcher power levels, and etching times. In this article we will discuss the results of these studies and show how 0.2 μm features with nearly vertical sidewalls were obtained.
Effect of remaining solvent on sensitivity, diffusion of acid, and resolution in chemical amplification resists
Authors: Asakawa Koji , Ushirogouchi Tohru , Nakase Makoto
Published: July 2002

The effect of the remaining solvent on the diffusion of the catalytically active acid within the chemical amplification resists is discussed. A range of solvents was investigated from the viewpoint of sensitivity, diffusion, and resolution. The solvent remaining after the coating and baking processes is thought to one of the most probable factors among the several possible causes in the determination of the performance of the resists. It is also considered to result in the environmental instability which is currently one of the most serious problems in the use of the resists of this type. The remaining solvent drastically enhances the thermal diffusion of acid generated from photo-acid generators upon photoanalysis. The log of the diffusion range of the acid is found to be proportional to the concentration of the remaining solvent. This phenomenon may be described by a theory which combines the hole theory of liquids and the free volume theory of polymers and was also found to be the correlation energy between resin, solvent, and acid. In practice, this enhancement of diffusion range by remaining solvent does not result in higher sensitivity but rather degrades the performance of the resists.
Tip-induced lifting of the Au{100} (hex)-phase reconstruction in a low temperature ultrahigh vacuum scanning tunneling microscope
Authors: Buisset J. , Rust H.-P. , Schweizer E. K. , Cramer L. , Bradshaw A. M.
Published: July 2002

The clean Au{100} surface is known to be reconstructed, forming a pseudohexagonal (5×27) outermost layer. This structure is observed both in ultrahigh vacuum (UHV) and in the electrochemical environment at potentials corresponding to small negative surface electronic charges. Using a UHV scanning tunneling microscope (STM) at 77 K we have observed that the reconstruction can be lifted at large positive sample biases. The 20% less dense bulk-terminated surface is produced and the excess material appears as irregularly shaped gold clusters. Over a period of a few minutes, however, the surface relaxes back to the pseudo-hexagonal phase, a process that can also be followed with the STM.
Independent parallel lithography using the atomic force microscope
Authors: Minne S. C. , Manalis S. R. , Atalar A. , Quate C. F.
Published: July 2002

Independent parallel features have been lithographically patterned with a 2×1 array of individually controlled cantilevers using an atomic force microscope. Control of the individual cantilevers was achieved with an integrated piezoelectric actuator in feedback with a piezoresistive sensor. Patterns were formed on 〈100〉 single crystal silicon by using a computer controlled tip voltage to locally enhance the oxidation of the silicon. Using the piezoresistor directly as a force sensor, parallel images can be simultaneously acquired in the constant force mode. A discussion of electrostatic forces due to applied tip voltages, hysteresis characteristics of the actuator, and the cantilever system is also presented.
Molecular beam epitaxy growth and properties of GaN, AlxGa1−xN, and AlN on GaN/SiC substrates
Authors: Johnson M. A. L. , Fujita Shizuo , Rowland W. H. , Bowers K. A. , Hughes W. C. , He Y. W. , El-Masry N. A. , Cook J. W. , Schetzina J. F. , Ren J. , Edmond J. A.
Published: July 2002

The thin film growth of GaN, AlGaN, and AlN on GaN/SiC substrates by molecular beam epitaxy (MBE) has been studied. The GaN/SiC substrates consisted of 3-μm-thick GaN buffer layers grown on 6H-SiC wafers by metal organic vapor phase epitaxy (MOVPE) at Cree Research, Inc. A radio frequency plasma source was employed to generate active nitrogen species for MBE growth. The high quality of the MBE grown GaN epilayers was evident from the intense room temperature photoluminescence (PL) dominated by a sharp band-edge peak at 3.409 eV having a full width at half maximum (FWHM) of 29.7 meV and the double-crystal x-ray rocking curve (0002) diffraction peak having FWHM as narrow as 156 arcsec. Vertical cross-section TEM clearly showed these MBE grown GaN epilayers to have replicated the quality of the underlying MOVPE grown GaN buffer layer on SiC. The room temperature PL spectra from Mg doped p-type films showed a dominant peak at 3.2 eV. AlxGa1−xN films were also grown on GaN/SiC substrates. Two-dimensional nucleation and growth was monitored by reflection high energy electron diffraction for GaN, AlxGa1−xN, and AlN epilayer deposition, and featured (2×2) surface reconstruction during the growth of GaN/AlN strained layer superlattices. Light emitting diodes (LEDs) based on vertical AlxGa1−xN/GaN double heterostructures have been demonstrated for the first time using MBE grown III–V nitrides on conducting GaN/SiC substrate materials. The typical turn-on voltage among these LEDs was 3.2 V. The forward bias voltage was 4.7 V at 20 mA. The peak wavelength of the electroluminescence (EL) spectrum was 400 nm at 77 K. These results demonstrate that MBE may be used to produce GaN, AlxGa1−xN and AlN based epitaxial structures which are comparable in crystalline quality to those grown by MOVPE.
Field emission from ZrC films on Si and Mo single emitters and emitter arrays
Authors: Xie Tianbao , Mackie W. A. , Davis P. R.
Published: July 2002

Field emission from ZrC films deposited on Si and Mo single emitters and field emitter arrays (FEAs) has been studied. For single emitters, the results show dramatic improvements in emitter performance by reducing work functions—on the order of 1 eV—and increasing stability. For FEAs, deposition of a ZrC film reduced the operating voltage 30%–50% at an emission current of 1.0 μA/tip and increased the emission stability.
Direct patterning of Si(001) surfaces by atomic manipulation
Authors: Salling Craig T.
Published: July 2002

The ability to create atomic-scale structures with the scanning tunneling microscope (STM) plays an important role in the development of a future nanoscale technology. I briefly review the various modes of STM-based fabrication and atomic manipulation. I focus on using an ultrahigh vacuum STM to directly pattern the Si(001) surface by atomic manipulation at room temperature. By carefully adjusting the tip morphology and pulse voltage, a single atomic layer can be removed from the sample surface to define features one atom deep. Segments of individual dimer rows can be removed to create structures with atomically straight edges and with lateral features as small as one dimer wide. Trenches ∼3 nm wide and 2–3 atomic layers deep can be created with less stringent control of patterning parameters. Direct patterning provides a straightforward route to the fabrication of nanoscale test structures under ultrahigh vacuum conditions of cleanliness.
Electrical evaluation of InP surface damage caused by reactive ion etching with a mixture of methane (CH4) or ethane (C2H6) and hydrogen (H2)
Authors: Yamamoto N. , Kishi K. , Matsumoto S. , Kadota Y. , Iga R. , Okamoto H. , Mawatari H.
Published: July 2002

The electrical properties of a (100) InP surface were studied based on the fabrication process of a buried heterostructure (BH) laser diode (LD). The current–voltage (I–V) and capacitance–voltage (C–V) characteristics were measured for Schottky barriers on the surface at each step of the process—reactive ion etching (RIE) with a mixture of methane (CH4) or ethane (C2H6) and hydrogen (H2), oxygen plasma treatment, chemical etching, and annealing—under conditions which produce almost the same surface as that immediately before the BH regrowth. From the characteristics, it was found that CH4/H2 and C2H6/H2 RIEs caused the appearance of almost the same damage layers as a result of phosphorus desorption and hydrogen passivation in the near-surface region. Furthermore, it was found that only annealing can remove the hydrogen passivation. These results suggest that to obtain a high-quality regrowth interface it is essential to chemically etch the damage layers resulting from phosphorus desorption prior to BH regrowth in the fabrication process of BH-LDs.
Numerical study of optical transmission in sandwich slabs: Implication to photon scanning tunneling microscopy
Authors: Wang Shu , Xiao Mufei , Siqueiros Jesús M.
Published: July 2002

In this work, we present a numerical simulation of scanning near-field optical microscopy. The simulation is based on a recently developed macroscopic theory which rigorously solves the electromagnetic field in a two-dimensional dielectric-air-dielectric sandwich system with arbitrary one-dimensional structures at its two interfaces. A tiny dielectric triangular is added on one interface to represent the probe tip in the device, while on the other interface, two identical topographic defects with various profiles are attached to represent the sample surface. The probe tip is assumed scanning at a constant height above the sample surface which is illuminated by a p-polarized light. The intensity of the local field averaged along a cross section inside the tip is calculated to represent the signal level of the microscope. The feasibility of the theoretical scheme is numerically demonstrated, and various aspects in the microscopy, such as the effects of the separation of the two objects, and of the shape differences between ridges and grooves are discussed.
Near-field optical microscopy with uncoated tips: Calibration, chemical contrast on organic crystals, and photolithography
Authors: Kaupp G. , Herrmann A. , Haak M.
Published: July 2002

Reflection-back-through-the-fiber scanning near-field optical microscopy (SNOM) measurements with uncoated tapered fiber tips, that remain cold, were performed under shear-force distance control for opaque and transparent rough samples. The feedback dynamics of the commercial (DME) RASTERSCOPE SNOM were tested with a 3000/500 nm gold grating at very high scan rates. Slow rates give rise to thermal broadening due to heating of the gold surface by partial light absorption. Enhancement of the light intensity at the base by reflection from steep walls on four sides is reported, the steepness contrast being less important. Doped gallium arsenide substrates give materials contrast. Extremely rough porous silicon has been probed. Organic chemical contrast is seen for the first time with SNOM on partly oxidized anthracene at large dislocations. Anthracene, anthraquinone, and their charge-transfer complex are clearly discriminated by different reflectivities. Irradiated α-cinnamic acid exhibits a chemically uniform surface and, thus, no SNOM contrast despite the anisotropic μm high features that are observed. Photolithography on light-absorbing 2,5-dibenzylidene-cyclopentanone crystals with the tip illuminated at an ≈10 nm distance provides an easy, inexpensive, and rapid performance test of single tips. Very long local irradiation creates features that widen and reach heights of 300 nm.
Structure and phonon density of states in nanoclusters: Molecular dynamics study for Al
Authors: Schommers W. , Rieth M.
Published: July 2002

The generalized phonon density of states for Al nanoclusters was studied theoretically using molecular dynamics. By doing this anharmonic effects could be fully considered. In order to investigate the structure of the clusters we have also calculated the structure factor S(q)(Fourier transform of the pair correlation function). The calculations were done for systems consisting of 500 atoms and at several temperatures. Stable and metastable cluster states are observed: The clusters in the metastable state show a well defined peak in the structure factor S(q) which we interpret as superstructure. The appearance of the superstructure in the metastable state is accompanied by substantial change in the phonon density of states.
GaN field emitter array diode with integrated anode
Authors: Underwood Robert D. , Keller S. , Mishra U. K. , Kapolnek D. , Keller B. P. , DenBaars S. P.
Published: July 2002

GaN field emission pyramids are grown by self-limiting, selective-area metalorganic chemical vapor deposition. The self-limitation provides the potential of high uniformity of the pyramids and the selective-area growth allows one to define regular arrays of GaN pyramids for field emitter arrays (FEAs). Fabrication of an integrated anode lowered the operating voltage of the FEAs by narrowing the anode-cathode distance compared to devices with an external anode. A maximum emission current of 0.15 μA/tip has been observed for voltages of 570 V with an emitter-anode separation of 2 μm.