bluuebunny/crossref_metadata_2025 huggingface dataset:
Field emission from thin film diamond grown using a magnetically enhanced radio frequency plasma source
Authors: Proffitt Simon S. , Probert Simon J. , Whitfield Michael D. , Foord John S. , Jackman Richard B.
Published: July 2002

Nanocrystalline diamond films have been prepared using a novel magnetically enhanced radio frequency assisted plasma chemical vapor deposition source. Such films show field emission at applied fields below 10 V μm−1. Similar results are obtained using methane-hydrogen and methane-nitrogen gas mixtures, suggesting that the nitrogen promoted enhancement in field emission that has been observed in high quality diamond films does not occur for nanocrystalline layers. The design of the source used is easily scaled up for large area deposition, suggesting this could be a useful approach for the preparation of nanocrystalline diamond films for practical field emission purposes.
Enhancement of electron emission from silicon tips by nitrogen doped amorphous carbon coating
Authors: Chi Eung Joon , Shim Jae Yeob , Baik Hong Koo , Lee Heon Young , Lee Sung Man , Lee Se Jong
Published: July 2002

Silicon field emitters have been coated with nitrogenated amorphous carbon (a-C:N) in order to enhance the electron emission current. The coating was produced using a helical resonator plasma enhanced chemical vapor deposition system. The a-C:N film is amorphous and hydrogenated with about 30 at % hydrogen. Nitrogen is also included in the amorphous network and reduces the work function by doping. a-C:N coating enhances significantly the emission current of silicon tips.
Nitrogen and boron implantation into austenitic stainless steel
Authors: Mändl S. , Günzel R. , Richter E. , Möller W.
Published: July 2002

Nitrogen and boron double implantation into austenitic stainless steel were performed to enhance further the beneficial properties of nitrogen implantation, especially to reduce the brittleness of the near surface region. Nitrogen was implanted using plasma immersion ion implantation while boron was subsequently implanted in this first experiment using a conventional ion implanter. The effects of the boron implantation were measured against expanded austenite samples annealed for the same duration as the boron implantation. No significant diffusion of the boron is observed, whereas the preimplanted nitrogen shows additional diffusion during the boron implantation. The boron implanted specimens exhibit an even higher wear resistance correlated with a slightly decreased surface hardness, than the already excellent values for expanded austenite.
Effects of the Ti/Al atomic ratio on the properties of gradient (Ti,Al)N films synthesized by ion beam assisted deposition
Authors: He Xiao-Ming , Shu L. , Xie Z. W.
Published: July 2002

Gradient (Ti,Al)N films were prepared on high speed steel (HSS) and Si (111) wafers by using two Ar+ beams to sputter a titanium target and an aluminum target separately, and a third N+ beam to simultaneously bombard the growing film to assist deposition. The effects of the Ti/Al atomic ratio in the films on properties such as hardness, stress, and adhesion strength were investigated systematically. The results indicated that both the hardness and the adhesion of gradient (Ti,Al)N films to steel substrates exhibited “peak” type changes with an increase of the Ti/Al atomic ratio, and a maximum hardness of 3780 kgf mm−2 was reached at a Ti/Al ratio of 5.35. The compressive stress of gradient (Ti,Al)N films increased with increasing Al content in the films. It was found that extreme hardness, high adhesion strength and low stress gradient (Ti,Al)N films can be synthesized on low temperature HSS steel by using the ion beam assisted deposition process.
High dose rate effects in silicon by plasma source ion implantation
Authors: Chun M. , Kim B. , Conrad J. R. , Matyi R. J. , Malik S. M. , Fetherston P. , Han S.
Published: July 2002

An investigation of high dose rate effects in silicon subsurface morphology has been performed. The unique capability of plasma source ion implantation to operate in the high current/low energy regime, where the near-surface structure can be effectively controlled, has been studied. At an ion energy of ∼40 keV and an estimated dose of 1×1015 cm−2 Ar ions were implanted at various instantaneous dose rates (0.75–8.3 mA/cm2) and two different pulse widths (25–50 μs) into 2 in. diam silicon wafers at a constant repetition rate of 10 Hz. The irradiation damage to the wafers’ structures was characterized by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). A visual observation indicated amorphization of the silicon at 0.75 mA/cm2, but not at 8.3 mA/cm2. The transition from the crystalline-to-amorphous phase was confirmed by TEM electron diffraction studies. RBS data, however, indicated there was a large discrepancy in the total dose retained between the high dose rate (8.3 mA/cm2) and the low dose rate (0.75 mA/cm2). Two simulation methods for the substrate temperature profile have been compared to predict the profile. A comparison of the fraction of irradiation damage from the RBS data indicated that the substrate heating effects are more dominant then the dose rate effects. Improved methods of cooling the wafer are presently being investigated.
Integrated high voltage modulator for plasma immersion ion implantation
Authors: Günzel R.
Published: July 2002

Plasma immersion ion implantation (PIII) on an industrial scale requires negative high voltage pulses in the kA range with voltages up to 200 kV. Hence, the equipment to produce suitable high voltage pulses is rather expensive and shares a considerable part of the total costs of PIII equipment. Reducing the costs of equipment is therefore still a challenge to promote the commercial use of PIII. A new high voltage modulator is presented, which will meet the above requirements. The basic idea of the new modulator is that in case of two floating electrodes, immersed into a plasma and connected to both plates of a charged capacitor, the anode potential will be close to the plasma potential, whereas the cathode potential will become negative compared to the plasma potential. The new modulator works as a triode system, consisting of anode, cathode and grid, all located inside of the working chamber. The plasma is discharged between cathode and grid. As usual in PIII, the sample is immersed into the plasma and works as the cathode in the system. The grid is mounted between plasma and anode, in such a way that ions or electrons from the plasma can get to the anode by passing the grid plane only. Further a capacitor is connected to anode and cathode with both plates and the anode is additionally linked to a positive high voltage source. If the grid is negatively biased, the anode is isolated from the plasma, as electrons from the plasma are reflected by the grid bias, whereas the ions are reflected by the positive potential of the anode. As far as the grid is negatively biased the cathode is at plasma floating potential, and the capacitor may be charged by the positive high voltage source to the capacitor voltage +U0. When the grid potential is switched to ground potential electrons from the plasma can reach the anode and will shift the anode potential to plasma potential. At the same time the cathode is switched to negative high voltage potential −U0. As the performance of the integrated modulator depends on the maximum of the electron current which can be extracted from the plasma by the anode, the basic considerations concerning the anode current and the revealing design parameters of the integrated modulator are given. The experimental results of modulating 20 kV at a maximum current of 4 A confirm the theory.
Inductively coupled plasma etching of III–V antimonides in BCl3/Ar and Cl2/Ar
Authors: Zhang L. , Lester L. F. , Shul R. J. , Willison C. G. , Leavitt R. P.
Published: July 2002

Inductively coupled plasma (ICP) etching characteristics of GaSb and AlGaAsSb have been investigated in BCl3/Ar and Cl2/Ar plasmas. The etch rates and selectivity between GaSb and AlGaAsSb are reported as functions of plasma chemistry, ICP power, rf self-bias, and chamber pressure. It is found that physical sputtering desorption of the etch products plays a dominant role in BCl3/Ar ICP etching, while in Cl2/Ar plasma, the chemical reaction dominates the etching. GaSb etch rates exceeding 2 μm/min are achieved in Cl2/Ar plasmas with smooth surfaces and anisotropic profiles. In BCl3/Ar plasmas, etch rates of 5100 and 4200 Å/min are obtained for GaSb and AlGaAsSb, respectively. The surfaces of both GaSb and AlGaAsSb etched in BCl3/Ar plasmas remain smooth and stoichiometric over the entire range of plasma conditions investigated. This result is attributed to effective removal of etch products by physical sputtering. For a wide range of plasma conditions, the selectivity between GaSb and AlGaAsSb is close to unity, which is desirable for fabricating etched mirrors and gratings for Sb-based midinfrared laser diodes.
Growth and electroluminescent properties of self-organized In0.4Ga0.6As/GaAs quantum dots grown on silicon
Authors: Linder K. K. , Phillips J. , Qasaimeh O. , Liu X. F. , Krishna S. , Bhattacharya P.
Published: July 2002

Our report describes the growth and characterization of self-organized In0.4Ga0.6As/GaAs quantum dots on Si substrates. The size, shape, and density of the dots grown on Si are quite different than dots grown on GaAs substrates under similar conditions. From structural characterization, it is apparent that the dots, themselves, may be defect free. We present electroluminescent characteristics of edge-emitting In0.4Ga0.6As quantum dot lasers grown on Si. The laser spectra indicates the emission wavelength is 1.01 μm at threshold with a linewidth full width at half maximum ∼4 Å. We observe a blueshift towards smaller wavelengths with increasing current, suggesting the filling of smaller dots.
Closed-loop control of composition and temperature during the growth of InGaAs lattice matched to InP
Authors: Johnson S. R. , Grassi E. , Beaudoin M. , Boonzaayer M. D. , Tsakalis K. S. , Zhang Y. H.
Published: July 2002

Spectroscopic ellipsometry (SE) and diffuse reflection spectroscopy (DRS) are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within ±0.002 of its target value and substrate temperature is controlled to within ±2 °C of its target value. The same growth under constant thermocouple control would result in a 50 °C rise in real substrate temperature and a Ga composition 1% above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative (PID) control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased (decreased) 0.2 °C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below (above) the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.
New self-aligned processes for III–V electronic high speed devices
Authors: Etrillard J. , Besombes C. , Bricard L. , Duchenois A. M.
Published: July 2002

We report on two new self-aligned processes intended for microelectronic devices realization exhibiting a significant reduction of the number of elementary technological levels. These processes allow to obtain a very short self-aligned contact separation without using spacers or wet etched mesa overhangs. As an example, only three lithographic masks are used to realize a triple mesa self-aligned heterojunction bipolar transistor (HBT). A bilayer resist process is used to define the specific shape of the upper contact that is used for self-alignment. A combination of selective, isotropic, or anisotropic processes and very simple selective lift-off processes are used to define the mesa and the contacts which are also used as masks during etching. The alloying of contacts may be performed just after deposition and lift-off. These processes can reduce the production cost and increase the reliability for integration in comparison with conventional self-alignment using the selective wet etched emitter overhang in the HBT application. Furthermore, the parasitic access resistance can be reduced both by using thin mesa active layers and decreasing the contacts separation. This separation length can be determined by the aspect ratio of the bilayer resist, the characteristics, and parameters of the contact deposition equipment. At last, low induced damage inductively coupled plasma dry etch processes are partly used to reduce the dry etch damages. © 1999 American Vacuum Society.
High field characteristics of dielectric spacers in thin-film electrode vacuum gaps
Authors: Ma Xianyun , Sudarshan T. S.
Published: July 2002

This article reports a test setup designed to study the prebreakdown and breakdown characteristics of spacers relevant to field emission displays (FEDs). The electrical characteristics of different spacer structures, bridging vacuum gaps formed by two thin-film electrodes, were studied in an attempt to determine the maximum field to which such gaps can be stressed. An extra low light detection three dimensional imaging system using an intensified charge coupled device camera was developed to diagnose and record the different prebreakdown phases and the breakdown phenomenon. This system enabled us to obtain spatially resolved images of light activities emanating from the electrically stressed surfaces. The experimental results showed that the investigated insulation materials did not introduce significant leakage current under high field stress. Breakdown voltages of fiber, disk-shaped and thick-wall spacers (750 μm high) were 12–14, 13–16, and 15–20 kV, respectively. The insulation capability of the thick-wall structure was limited by the edge effect of the thin-film electrodes and the quality of the thin-film electrodes rather than processes intrinsic to the spacer material or its geometry. This work provides some guidance to the design of spacers for FEDs.
Reduction and creation of paramagnetic centers on surfaces of three different polytypes of SiC
Authors: Macfarlane P. J. , Zvanut M. E.
Published: July 2002

SiC is of interest to create power metal–oxide–semiconductor field-effect transistors because it can be thermally oxidized to form a SiO2 dielectric layer. Previously, we used electron paramagnetic resonance to identify centers in 3C–SiC epilayer samples and 4H–SiC and 6H–SiC wafer samples after oxidation and dry heat treatment [P. J. Macfarlane and M. E. Zvanut, Appl. Phys. Lett. 71, 2148 (1997); Mater. Res. Soc. Symp. Proc. 513, 433 (1998)]. The spectroscopic and thermal characteristics of these centers indicate that they are related to C. Because these centers are activated in a H2O-poor ambient and are passivated in an ambient that is H2O-rich, we suggest that the activation mechanism is release of a hydrogenous species. In this investigation, the effect of repeated oxidations on the concentration of heat-treatment-induced centers is studied. Samples are successively oxidized at 1150 °C in O2 bubbled through de-ionized water for 1, 2, 4, 8, and 16 h. After each oxidation, the samples are heat treated in dry (<0.1 ppm H2O) N2. Prior to the next oxidation, the oxide is removed. Upon oxidation of the samples we observe an order of magnitude reduction in the concentration of centers that are present on the as-prepared substrates. After each oxidation centers are activated by dry heat treatment. We suggest that the centers present on the as-prepared substrates are related to surface damage and are removed during the oxidation as the surface SiC material is converted in the oxidation products. Two models are offered for the source of the centers generated by dry heat treatment. The centers could be activated from C–H bonds related to damage like micropipes, nanopipes, or Si vacancies distributed throughout the SiC substrate, or they could arise from C–H bonds that form during the oxidation. We will discuss the merits of both of these models.
Coherent soft x-ray scattering from InP islands on a semiconductor substrate
Authors: Adamcyk M. , Nicoll C. , Pinnington T. , Tiedje T. , Eisebitt S. , Karl A. , Scherer R. , Eberhardt W.
Published: July 2002

Coherent soft x-ray scattering experiments from a semiconductor sample consisting of InP islands on a smooth semiconductor substrate are described. The soft x-ray scattering was performed with 266 eV photons produced by an undulator source. Using a position sensitive detector, we are able to detect diffusely scattered x rays in the vicinity of the specular reflection, with an in-plane momentum transfer of up to 6 μm−1. Using Huygens–Fresnel theory and atomic force microscope images of the surface structure, we simulated the scattering assuming a finite lateral coherence length for the incident radiation. The lateral coherence length of the incident beam was found to be 20 μm from a fit to the observed diffraction pattern from a pinhole. The effect of changes in the surface morphology on the speckle pattern was simulated to explore the potential of coherent soft x-ray scattering for the study of surface structure dynamics.
Growth characterization of rapid thermal oxides
Authors: Lai W. H. , Li M. F. , Chan L. , Chua T. C.
Published: July 2002

The results of a rapid thermal oxide (RTO) growth study involving 200 mm Si wafers oxidized in three different oxidation ambients (O2, N2O, and NO) at two different pressures (100 and 760 Torr), and a wide range of oxidation temperatures (950–1200 °C) and times (0–480 s) are presented in this work. The variable power law is shown to provide an excellent fit to the characteristics. Enhancement in the O2 RTO over furnace oxidation (FO) growth rates, continued growth in N2O RTO, and growth saturation in NO RTO were observed. Anomalies including higher growth rates at a lower pressure in N2O, higher growth rates at lower temperatures and at a lower pressure in NO, as well as higher growth rates in N2O and NO than in O2 were observed. They may be attributable to the competition between the N incorporation rate and the oxide growth rate for predominance, which might in turn be dependent on the temperature, pressure, thickness of and defect density in the initial oxide layer and the amount of N already incorporated. The growth kinetics exhibit Arrhenius relationships. Those for O2 RTO, O2 FO, and low pressure N2O RTO are similar while those for N2O RTO, N2O FO, and NO RTO are different. Our results suggest the oxide thickness range within which the oxidation is reaction limited decreases in the order of O2 RTO, N2O RTO, and NO RTO.
Chrome on glass mask writing at 75 kV with the IBM EL4+electron-beam system
Authors: Hartley J. G. , Groves T. R.
Published: July 2002

The IBM EL4+mask writer, located in the Advanced Mask Facility in Burlington, Vermont has recently been used to investigate chrome on glass lithography at 75 kV with a current density of 60 A/cm2. One of the main concerns with doing lithography at high beam voltages on a quartz substrate is the effect of beam heating on the resist. Using ZEP7000 resist on both quartz glass and silicon wafer substrates, we have characterized image size control from 0.1 to 3 μm for a large range of pattern geometries.
Perpendicular patterned media in an (Al0.9Ga0.1)2O3/GaAs substrate for magnetic storage
Authors: Wong Joyce , Scherer Axel , Barbic Mladen , Schultz Sheldon
Published: July 2002

By using electron beam lithography, chemically assisted ion beam etching, and electroplating, we have fabricated high aspect ratio magnetic columns, 60–170 nm in diameter, embedded in an aluminum–gallium–oxide/gallium–arsenide [(Al0.9Ga0.1)2O3/GaAs] substrate. In our previous work, we demonstrated storage of data in individual columns spaced 2 μm apart. Here the electroplated Ni columns are in the form of tracks (0.5 and 0.25 μm in the down-track direction, and 1 μm in the cross-track direction), corresponding to areal densities of 1.3 and 2.6 Gbits/in.2, respectively. In this report we describe in more detail the issues in the fabrication of patterned media samples, such as dry etching and oxidation of AlGaAs, and electrodeposition of Ni into GaAs substrate. Initial characterization of the resulting magnets using magnetic force microscopy are also presented.
Progress in x-ray mask technology at NTT
Authors: Oda Masatoshi , Shimada Masaru , Tsuchizawa Tai , Uchiyama Shingo , Okada Ikuo , Yoshihara Hideo
Published: July 2002

This article overviews NTT’s recent progress in membrane and absorber materials for x-ray masks and the fabrication of highly accurate masks for synchrotron radiation lithography. As membrane materials, SiC and diamond films are being studied. Experimental results indicate that diamond films are better than SiC from a mask accuracy point of view because of their higher rigidity. As absorber films, Ta films deposited by electron cyclotron resonance (ECR) sputtering are studied. The Ta films have the α structure and large grains, and are chemically very stable. All masks are produced by a membrane process in which the patterning of absorber films is done after backetching. The absorbers are patterned by a new electron beam (EB) writer with an acceleration voltage of 100 kV and ECR ion stream etching with He gas cooling. Ta patterns with widths below 100 nm are etched accurately. Placement accuracy of absorber patterns produced by this process is confirmed to be about 30 nm, using relatively simple patterns. A technique for inspecting defects on SiC membrane masks using a scanning electron beam and repair using a focused ion beam have also been developed. Ta defects on SiC membrane can be easily detected with high contrast by the system.
Trimethylamine: Novel source for low damage reactive ion beam etching of InP
Authors: Carlström C. F. , Anand S. , Landgren G.
Published: July 2002

A new reactive ion beam etching process using trimethylamine for low damage etching of InP at room temperature has been developed. Characteristics of the etching process, i.e., etch rate, surface morphology, and etch-induced damage are reported. Photoluminescence yield (PLY) was used to characterize the residual damage by using near-surface quantum wells as probes and the etched surface morphologies were quantified by roughness measurements using atomic force microscopy. The etch rate could be varied by over an order of magnitude, from low (∼4 nm/min) at 75 eV up to 100 nm/min at 500 eV. The etched surfaces were extremely smooth (rms roughness <1 nm) independent of ion energy. This was so even for samples etched to a depth of more than 1 μm. Process induced damage as measured by PLY was also significantly smaller than for CH4 based dry etch processes. Further, upon annealing at 650 °C in a PH3 ambient, the etched samples showed near complete PLY recovery, indicating significant damage reduction. Hence, the new process results in a simplified plasma chemistry that provides not only reasonable etch rates but also extremely smooth surfaces and low optical damage.
Inductively coupled plasma reactive ion etching of AlxGa1−xN for application in laser facet formation
Authors: Khan F. A. , Zhou L. , Ping A. T. , Adesida I.
Published: July 2002

The etching characteristics of AlxGa1−xN grown by metal–organic chemical-vapor deposition were investigated in an inductively coupled plasma (ICP) reactive ion etching system using Cl2/Ar gas mixtures. Etch rate variations with substrate bias voltage, ICP coil power, chamber pressure, Cl2/Ar gas mixture ratios, and gas flow rates were investigated. The optimum chamber pressure for etching was found to be dependent on both the substrate bias voltage and ICP coil power. Auger electron spectroscopy analysis showed that the stoichiometries of the etched Al0.22Ga0.78N surfaces were identical, independent of the etching conditions. Etching results were successfully applied to form highly anisotropic and smooth facets in GaN/InGaN/AlGaN heterostructure laser materials.
Fabrication and magneto-transport and SQUID measurements of submicron spin-valve structures
Authors: Park Y. D. , Temple D. , Jung K. B. , Kumar D. , Holloway P. H. , Pearton S. J.
Published: July 2002

Submicron Ni0.8Fe0.2/Cu/Co spin valves and Co/Cu pseudo spin valves with widths ranging from 200 to 0.5 μm have been realized by direct deposition and liftoff. The resulting configurations were structurally characterized by atomic force microscope and cross-sectional transmission electron microscopy. Transport and magnetic properties of arrays of these spin-valve structures were studied using superconducting quantum interference device magnetometry. Magnetic measurements carried out on several spin-valve structures showed that both coercivity and field at which maximum magnetoresistance (MR) occurs increase with decrease in widths of the spin valves. Comparison of the results obtained from the magnetometry and transport measurements indicated the existence of an offset between the coercive field and field of maximum MR. Resistance versus temperature measurements for varying linewidth show a minimal shift in peak temperature, indicating that processing effects are minimal.
Focus drilling and attenuated phase shift mask for subwavelength contact window printing using positive and negative resists
Authors: Pau S. , Trimble L. E. , Blatchford J. W. , Watson G. P. , Frackoviak J. , Cirelli R. , Nalamasu O.
Published: July 2002

We have investigated the process latitude and resolution limit of printing contact windows using a high numerical aperture KrF stepper and attenuated phase shift mask (APSM). We show that both positive and negative resists can be used depending on the size of the window on the mask. The advantages and disadvantages of using the positive and negative resists are presented. A combination of APSM and focus drilling are shown to extend the focus latitude of subwavelength window printing.
Secondary ion mass spectroscopic analysis of copper migration at the copper/polyimide interface
Authors: Miki Norihiko , Tanaka Keiji , Takahara Atsushi , Kajiyama Tisato
Published: July 2002

Dynamic secondary ion mass spectroscopy (D-SIMS) was applied to analyze the copper (Cu) migration behavior at the interface between polyimide (PI) and Cu. The (PI/Cu) bilayer specimen was prepared by curing polyamic acid (PAA) coated on the Cu substrate. It was found that the Cu deeply migrates into the PI phase across its interface. On the contrary, the Cu migration was not detected at all when the (PI/Cu) bilayer was built up by the vapor deposition of Cu onto the PI film. These results clearly indicate that the Cu migration behavior is strongly dependent on how the bilayer is prepared.
Qualification of spreading resistance probe operations. II
Authors: Clarysse T. , Vandervorst W.
Published: July 2002

In order for spreading resistance probe (SRP) to gain wider credibility, an error of less than 10% (standard deviation) should be routinely achievable on the typical SRP results (dose, sheet, shape carrier profile) irrespective of where, when, or by whom the measurement is performed. Based on the final results from an extensive SRP round robin (see Part I), quantitative specifications have been derived for 14 primary qualification parameters. Since some of these primary parameters are difficult to determine directly (surface roughness, probe penetration, etc.), also a set of electrically verifiable, secondary qualification parameters with appropriate specifications has been defined. These include probe load, linearity and steepness of the calibration curves, noise level and smoothing, junction delineation, junction position, radius calibration, and calibration drift control. In particular the importance of the latter one is frequently overlooked, although essential to achieve the target accuracy (10%). Furthermore, a set of well-characterized and commercially available qualification samples is discussed, which, in combination with the defined qualification parameters, allows each laboratory independently to evaluate its current SRP performance and to monitor the latter as improvements are implemented.
Need to incorporate the real micro-contact distribution in spreading resistance correction schemes
Authors: Clarysse T. , Vandervorst W.
Published: July 2002

It has been known since the early start of the spreading resistance probe (SRP) technique that the metal-silicon probe contact consists typically of a series of small micro contacts. All of the currently applied SRP correction schemes are, however, still based on the assumption of a single large planar circular contact. In this work, we present a new micro-contact correction factor scheme for spreading resistance measurements that is based on a combination of the homogeneous material micro-contact theory of Holm and the Schumann–Gardner multilayer approach traditionally used in SRP. The new model assumes that the measured resistance is composed of three terms: the self-resistance of the micro contacts, the interaction between these contacts, and a contact resistance related to the metal-silicon Schottky contact being used. The validity of the new model has been verified by three-dimensional device simulations for both conducting and insulating boundary conditions. For structures that are several micrometers thick, the new scheme agrees closely with presently used schemes (15%), provided appropriate radius and barrier resistance calibration procedures are applied. For submicron profiles, however, the new scheme solves a series of known artifacts in a consistent and physically acceptable way (i.e., for example, much lower barrier resistance values are needed than before). Hence, the new scheme is recommended for submicron structures. Examples are discussed relating to lightly on heavily doped epilayers and shallow implants in same type, highly doped substrates.
Secondary ion mass spectrometry depth profiling of ultrashallow phosphorous in silicon
Authors: Loesing R. , Guryanov G. M. , Hunter J. L. , Griffis D. P.
Published: July 2002

High-precision quantitative secondary ion mass spectrometry (SIMS) trace analyses of ultrashallow P31 distributions in Si (i.e., junction depths of 50 nm or less) require the ability to eliminate the Si130H mass interference while simultaneously minimizing primary ion impact energy and maximizing sensitivity. Elimination of Si130H requires a relatively high mass resolution SIMS instrument such as the Cameca IMS-6f used in this work. A range of Cs+ primary ion energies ranging from 9.5 to 1.6 keV was investigated to determine which provided the best depth resolution as measured by decay length for ultrashallow depth profiles of 2 keV P in Si. Improvements (or lack thereof) in decay length as the primary ion impact energy was reduced were correlated with crater bottom roughness measurements. Changes in the ion yields of P and Si resulting from both the appreciable fraction of the analyzed depth made up of the surface native oxide and also from the depth required for the primary ion yield enhancing Cs+ to reach a constant level were also investigated utilizing bulk-doped P in Si. The resulting ion yield transients obtained were then used to generate an empirical correction function with the aim of improving the quantitative accuracy of the ultrashallow depth profile selected as having the minimum decay length obtained in this work. Finally, improvements in the P detection limit provided by optimization of the secondary ion postacceleration system are discussed.
Depth profiling of ultra-shallow implants using a Cameca IMS-6f
Authors: McKinley J. M. , Stevie F. A. , Neil T. , Lee J. J. , Wu L. , Sieloff D. , Granger C.
Published: July 2002

We have previously reported measurements of ultra-shallow boron implants in silicon using a magnetic sector Cameca IMS-6f, and excellent depth resolution and dynamic range were obtained for boron implants down to 1 keV using O2+ primary beam. The appropriate impact energy of the primary beam and incidence angle could be easily achieved for an analysis by the choice of several combinations of sample and source voltages, based on calculations governing the penetration depth and incidence angle of the primary ion beam. This article outlines additional low energy analysis results for boron and arsenic implants with either oxygen or cesium low energy beams. Methods for low energy beam alignment have been utilized to allow analysis conditions to be reached quickly while maintaining a good beam shape, and calculations that more accurately describe how the angle of incidence varies with the primary, sample, and deflector voltages are described.
Electrochemical etching of silicon: A powerful tool for delineating junction profiles in silicon devices by transmission electron microscopy
Authors: Spinella Corrado , D’Arrigo Giuseppe
Published: July 2002

In this article, we present in some detail the two-dimensional delineation technique based on selective electrochemical etch and anodic oxidation of silicon. Compared to pure chemical etch, the sensitivity strongly improves and, in the case of boron, the doping profile can be delineated up to a concentration level well below the limit reported for pure chemical etch. We also demonstrate that a proper control of the etching parameters allows us to get effective improvement in delineating As-doped regions, and compared to pure chemical delineation, better sensitivity values are reported.
Structural and process characterization of high voltage operated field emission displays with focus electrodes
Authors: Lee N. S. , Lee H. W. , Kim J1. , Jung S. Y. , Choi J. H. , Park Y. J. , Kim J. W. , Jung J. E. , Park N. S. , Park S. H. , Jin Y. W. , Choi W. B. , Kim J. M. , Chee J. K.
Published: July 2002

Focus electrodes are engaged to improve focusing characteristics of electron beams in 5.2 in. high voltage field emission displays. It is observed experimentally that the electron beam is collimated fairly well on an optimal condition, which is also compared with simulation results. The layout of ceramic spacers is optimized experimentally as well as by simulations. We uniquely develop a carrier gas of Ar and 1.5% H2, which is effective in prohibiting deterioration of device performance during thermal sealing. A luminance in excess of 400 cd/m2 is achieved at an anode voltage of 5000 V. A video running full color image is successfully demonstrated.
Suppression of oxidation of metal emitters by incorporating ruthenium oxide
Authors: Yoon Young Joon , Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man , Song Kie Moon , Lee Se-Jong
Published: July 2002

We fabricated the RuO2 incorporated metal emitters for the cathode of the field emission display in order to improve the drawback of easy oxidation of traditional Spindt-type emitters. The as-deposited RuO2 incorporated Ta film shows the amorphous structure, which is stable up to 800 °C in air ambient. The Ta is bound to oxygen and the RuO2 exists in the form of nanocrystalline and nonstoichiometric phase of RuOx. The RuO2 incorporated Ta film coated emitters and annealed emitters showed good emission results, comparable to pure Ta emitters, and did not oxidize up to 800 °C in air ambient due to their good chemical inertness for the oxygen gas. Therefore, it is expected that the RuO2 incorporated Ta film coated emitters can be easily applied to the fabrication process for field emitters with wide process windows.
Effect of carbon coating on electron field emission from polysilicon
Authors: Chakhovskoi A. G. , Vossough K. , Hunt C. E. , Kosarev A. I. , Vinogradov A. J. , Shutov M. V. , Andronov A. N. , Robozerov S. V.
Published: July 2002

Carbon films deposited at relatively low temperatures were studied as a coating for polysilicon substrates to provide enhancement of the electron field emission. Undoped and phosphor doped polysilicon substrates were coated by carbon films grown by a very high frequency chemical vapor deposition process. Critical process parameters include substrate temperature of 225 °C, pressure of 56 mTorr, loaded power of 2 W/cm2, and discharge frequency of 56 MHz. The substrates were pretreated prior to film deposition, and bias enhanced nucleation was performed in hydrogen/C6H14 plasma. A carbon layer was grown to a thickness of 700 nm. Field emission measurements were performed in an ultrahigh vacuum chamber equipped with an electron gun, a carousel for five samples, and a Faraday cup. A multigrid quasispheric energy analyzer was used for Auger electron spectroscopy and electron energy loss spectroscopy characterization. Additionally, before and after field emission measurements, the secondary emission coefficient σ was measured by a scanning electron beam, which provided a two-dimensional σ map of the sample surface. The field emission current was measured in a diode configuration using a spacer thickness of 45–55 μm through a current collection window 2×5 mm2. Emission current–voltage curves were measured from three different regions of every sample by shifting the current collection window over the sample. A surface conditioning effect was observed, resulting in stabilization and better reproducibility of the emission current–voltage characteristics. The most significant changes in emission characteristics were observed in undoped polysilicon substrates with carbon coatings. Low deposition temperatures make this coating process very attractive because of its compatibility with addressing circuitry based on either silicon or poly-, microcrystalline, or amorphous silicon.
Lateral field emission diode with wedge-type tip and nanogap on separation by implantation of oxygen silicon
Authors: Zang Woo-Jae , Lee Jung-Hee , Lee Jong-Hyun , Bae Young-Ho , Choi Chang-Auck , Hahm Sung-Ho
Published: July 2002

A field emission diode array with a novel nanometer scale silicon gap in a separation by implantation oxygen structure was fabricated using the thin film stress that had been generated during high-temperature annealing and cooling. In this work, an interelectrode gap ranging from 20 to 100 nm was obtained depending on the width of the pattern when the patterned wafer was cooled after annealing at 1050 °C for 1 h in N2 ambient. The parameters for determining the gap size were identified, and the crystal orientation dependency in forming the gaps was clarified. The proposed nanogap formation technique is very simple and applicable to a field emission (FEA) with a short interelectrode distance. The fabricated FEA exhibited a turn on voltage of 25 V and an emission current of 6 μA per tip at 35 V.
Three-dimensional photon-stimulated field emission theory by transfer matrices and Green’s functions
Authors: Mayer Alexandre , Hagmann Mark J. , Vigneron Jean-Pol
Published: July 2002

For the purpose of simulating photon-stimulated field emission by taking account of three-dimensional aspects, a formalism relying on transfer matrices and Green’s functions is combined with a Floquet expansion of the wave function for taking account of quanta exchanges between the electrons and the external radiation. The main lines of this extended theory and preliminary results are presented.
Optimized design for the scattering with angular limitation in projection electron-beam lithography based electron projection system
Authors: Xiu K. , Gibson J. M.
Published: July 2002

We investigate the design for a scattering with angular limitation in projection electron-beam lithography (SCALPEL) based electron projection system with a demagnification of −4. By a “field-flip” process we can construct a doublet in which the magnetic field has a flat feature in most of the optic column but opposite sign at two sides connected by a sharp transition region. Such a theoretical model can give a near zero chromatic aberration of rotation and much smaller field curvature and astigmatism. Compared with the conventional doublet, the total image blur caused by aberrations at 1/2 mm off-axis distance and 1.5 mrad semiangle aperture at the mask side is about only 24 nm for a column length of 400 mm. A shorter column, less than the current 400 mm, is also favored for further reducing the total aberration. These guarantee that we can choose a much larger aperture angle (compared with present 0.5 mrad) and beam current density in such a SCALPEL projection system to achieve higher throughput while still maintaining current resolution. A practical issue for possible magnetic lens design is also discussed.
Strain relaxation-induced modifications of the optical properties of self-assembled InAs quantum dot superlattices
Authors: Petitprez E. , Moshegov N. T. , Marega E. , Mazel A. , Dorignac D. , Fourmeaux R.
Published: July 2002

We have investigated self-assembled InAs quantum dot superlattices using photoluminescence and transmission electron microscopy. We report results regarding the influence of the dot vertical separation on the optical properties of such structures. The photoluminescence peak shifts toward higher energies and its intensity drops by one order of magnitude when the distance between two consecutive quantum dot layers is reduced below 70 Å. Our transmission electron microscopy images suggest that such unexpected photoluminescence features are related to the formation of structural defects induced by the large amount of strain relieved at small dot separations.
Size distribution of quantum-scale GaAs islands grown by Ga droplet induced chemical beam epitaxy
Authors: Ro Jeong-Rae , Kim Sung-Bock , Park Kyoungwan , Lee Jihwa
Published: July 2002

We report on the size and the size distribution of GaAs nanoislands via Ga droplet induced chemical beam epitaxy. GaAs nanoislands were grown by the direct injection of triethylgallium and the subsequent supply of thermally cracked arsine on a nonpretreated substrate. The size distribution of islands as measured by the quotient σ/da, the standard deviation of the island diameter (σ) divided by the mean island diameter (da), increases with increasing beam equivalent pressure of triethylgallium but is independent of the total amount of triethylgallium supplied. The influence of annealing was not observed on the size distribution of GaAs islands. These results demonstrate that nanoscale GaAs dots with a narrow size distribution can be achieved by the optimization of growth conditions.
Long wavelength pseudomorphic InGaPAsSb type-I and type-II active layers grown on GaAs
Authors: Johnson S. R. , Dowd P. , Braun W. , Koelle U. , Ryu C. M. , Beaudoin M. , Guo C.-Z. , Zhang Y.-H.
Published: July 2002

GaPAsSb type-I quantum wells and symmetric InGaAs/GaPAsSb/InGaAs type-II quantum wells are proposed as long wavelength active layers for GaAs based optoelectronic devices. Room temperature photoluminescence from 1.2 to 1.5 μm is observed from the type-II quantum wells, while low temperature photoluminescence at 1.25 μm is observed from type-I quantum wells. A reflection high-energy electron diffraction peak that is extended parallel to the surface, while its width is perpendicular to the surface is narrow, suggests that spontaneous lateral composition modulation occurs in the GaPAsSb layers.
In
0.18
Ga
0.82
As/GaAs
1−y
P
y
quantum wells grown on (n11)A GaAs substrates by molecular beam epitaxy
Authors: Kamimoto H. , Tatsuoka Y. , Kitada T. , Shimomura S. , Hiyamizu S.
Published: July 2002

We have investigated the influence of V(As4+P2)/III(Ga) pressure ratio on interface flatness of In0.18Ga0.82As/GaAs1−yPy (2.9 nm/20 nm) single quantum wells (SQWs) (y=0.18–0.32) grown on (100)- and (n11)A-oriented GaAs substrates (n=3, 4, and 5) by molecular beam epitaxy. With decreasing V(As4+P2)/III(Ga) pressure ratio from 8 to 4, full width at half maximum (FWHM) of 11 K photoluminescence (PL) peak of the (411)A SQW was dramatically reduced to 7.8 meV, while those of the (311)A and (100) SQWs increased from their best FWHM (7.3 and 6.8 meV). This is different from those in the other SQWs. The best values of FWHM of the (311)A and (411)A SQWs were as small as those of the (100) In0.18Ga0.82As/GaAs1−yPy and In0.17Ga0.83As/Al0.3Ga0.7As QWs. The highest PL intensity was observed for the (411)A SQW grown under V(As4+P2)/III(Ga)=4. The (311)A SQWs grown under V(As4+P2)/III(Ga)=4 to 8 have 60%–70% smaller PL intensity than the (411)A SQW, but they have much higher PL intensity than the (100) and (511)A SQWs. This implies that the (311)A and (411)A In0.18Ga0.82As/GaAs1−yPy QWs have a good optical quality.
As
4
pressure dependence of surface segregation of indium atoms during molecular beam epitaxy of In0.08Ga0.92As/GaAs superlattices on (411)A GaAs substrates
Authors: Kitada Takahiro , Tatsuoka Yasuaki , Shimomura Satoshi , Hiyamizu Satoshi
Published: July 2002

As 4 pressure dependence of surface segregation of In atoms during molecular beam epitaxy (MBE) growth of pseudomorphic In0.08Ga0.92As/GaAs (7.5 nm/11.2 nm) superlattices (SLs) on (411)A GaAs substrates was investigated by high resolution x-ray diffraction (HRXRD) and 12 K photoluminescence measurements. Surface segregation lengths of In atoms (λ: 1/e decay length of In content profile along the growth direction) determined by HRXRD decrease with increasing V/III ratio for both the (411)A and simultaneously grown (100) SLs. λ for the (411)A SL grown under V/III (As4/Ga) pressure ratio of 10 was 2.32 nm, which is 1.4 times larger than that for the (100) SL, while λ was almost the same for both the (411)A and (100) SLs grown under V/III=30. With decreasing V/III ratio, In surface segregation increased, and InGaAs/GaAs interface flatness was improved in the (411)A InGaAs/GaAs SLs. Reduced As4 pressure results in enhanced surface segregation of In atoms as well as enhanced surface migration of In atoms during MBE growth of the (411)A InGaAs/GaAs SLs.
Fabrication of GaAs-based photonic band gap materials
Authors: Zhou W. D. , Bhattacharya P. , Sabarinathan J. , Zhu D. H.
Published: July 2002

A relatively simple technique for fabrication of GaAs-based quasi-three-dimensional photonic crystals has been investigated. Selective impurity-induced layer disordering and wet oxidation techniques are utilized. Fourier-transform infrared spectroscopy measurement reveals a stop band between 15 and 20 μm for a sample with scattering center spacing of 6.3 μm. Another narrow transmittance dip is observable in the wavelength range of 1.1–1.58 μm, with an attenuation of 12 dB at 1.18 μm. The process is reproducible and lends itself to integration with other optoelectronic and electronic devices on the same substrate.
The Origin and Evolution of the Woolly Mammoth
Authors: Lister Adrian M. , Sher Andrei V.
Published: July 2002

The mammoth lineage provides an example of rapid adaptive evolution in response to the changing environments of the Pleistocene. Using well-dated samples from across the mammoth's Eurasian range, we document geographical and chronological variation in adaptive morphology. This work illustrates an incremental (if mosaic) evolutionary sequence but also reveals a complex interplay of local morphological innovation, migration, and extirpation in the origin and evolution of a mammalian species. In particular, northeastern Siberia is identified as an area of successive allopatric innovations that apparently spread to Europe, where they contributed to a complex pattern of stasis, replacement, and transformation.
In the Beginning Was the Word
Authors: Lewontin R. C.
Published: July 2002

Who Wrote the Book of Life?
A History of the Genetic Code. Lily E. Kay. Stanford University Press, Stanford, CA 2000. 470 pp. $60, £45. ISBN 0-8047-3384-8. Paper, $24.95, £17.95. ISBN 0-8047-3417-8.

On the basis of a careful examination of archives, publications, and interviews, Kay presents a history of the research between 1953 and 1970 that explained how DNA sequences specify the amino acid sequences that form proteins. She pays particular attention to the influence of information theory on this work, and concludes that, strictly speaking, "the genetic code is not a code, DNA is not a language, and the genome is not an information system."