Box-like Profiles Research Articles

SN 2018hfm: a low-energy Type II supernova with prominent signatures of circumstellar interaction and dust formation

ABSTRACT We present multiband optical photometric and spectroscopic observations of an unusual Type II supernova, SN 2018hfm, which exploded in the nearby (d ≈ 34.67 Mpc) dwarf galaxy PGC 1297331 with a very low star formation rate (0.0270 M⊙ yr−1) and a subsolar metallicity environment (∼0.5 Z⊙). The V-band light curve of SN 2018hfm reaches a peak with value of −18.69 ± 0.64 mag, followed by a fast decline (4.42 ± 0.13 mag (100 d)−1). After about 50 d, it is found to experience a large flux drop (∼3.0 mag in V), and then enters into an unusually faint tail, which indicates a relatively small amount of 56Ni synthesized during the explosion. From the bolometric light curve, SN 2018hfm is estimated to have low ejecta mass (∼1.3 M⊙) and low explosion energy (∼1050 erg) compared with typical SNe II. The photospheric spectra of SN 2018hfm are similar to those of other SNe II, with P Cygni profiles of the Balmer series and metal lines, while at late phases the spectra are characterized by box-like profiles of H α emission, suggesting significant interaction between the SN ejecta and circumstellar matter. These box-like emission features are found to show increasing asymmetry with time, with the red-side component becoming gradually weaker, indicating that dust is continuously formed in the ejecta. Based on the dust-estimation tool damocles, we find that the dust increases from ∼10−6 M⊙ to 10−4–10−3 M⊙ between +66.7 d and +389.4 d after explosion.

(Invited) P-Type and N-Type Channeling Ion Implantation of SiC and Implications for Device Design and Fabrication

Silicon Carbide is rapidly growing in the power electronics industry. It is fueled by several robust long-term growth markets like renewables, cloud computing and electric vehicles. There is a wide release and proliferation of Diode and MOSFET devices from various companies in the marketplace. There is a continuous push in subsequent generations to improve device performance, reliability and efficiency. Some of the advanced design concepts in Silicon like super-junction technology have significant manufacturing roadblocks like diffusion, epi regrowth and implantation. In this work, we present results of both p-type and n-type channeled implants into 4º offcut N-type SiC substrates and Epitaxial layers using a Nissin Ion Equipment IMPHEAT system. Deep-channeled implants can be considered an enabling technology for the fabrication of advanced device designs including super-junction structures.The use of channeled implants have been reported on on-axis [1] SiC and 4º offcut using primarily low energies [2,3]. One major concern while trying to check the feasibility of channeling and implement it in mass-production is the reliability and variation of the off-cut angle. Fig. 1 shows the off-cut angle reported by the substrate vendor and the actual offcut angle as measured by X-ray diffraction. The actual off-cut variation is comparatively low. However, per wafer inline XRD measurements might be needed for accurate channeling. Fig. 2 shows how a 960kev 1e13cm-2 dose channeled implant changes the wafer shape. This change in shape is consistent with other high temperature treatments like Epi growth. Fig. 3 shows the room temperature channeled and non-channeled implant of triple charged Aluminum at 960 keV with a dose of 1e13cm-2. The offcut angle as measured by XRD of 4.1º gives the maximum range. The implant is also not very sensitive to off-cut disorientation. Fig. 4 shows the channeled implants as a function of implantation temperature. As expected, the range is reduced and thereby restricts very high doses. Fig. 5 shows similar channeled and non-channeled implantation of Boron and Phosphorous. The phosphorous profiles are flat and can be effectively used for n-type doping. A comprehensive review of effects of dose and orientation on the channeled profiles will be presented. Channeled implanted wafers were activated and the activation measured by fabricating Metal Schottky contacts. The effect of high and low warp wafers on channeled implant profiles are also discussed. Further implants at different energies are obtained and combined to get box-like profiles. The error in off-cut degree that can be tolerated for channeled implants in mass-production is estimated for different energies. Implications to super-junction device fabrication is discussed.

Approximate static aeroelastic analysis of composite wings

PurposeThe purpose of this paper is to consider divergence of composite plate wings as well as slender wings with thin-walled cross-section of small-size airplanes. The main attention is paid to establishing of closed-form mathematical solutions for models of wings with coupling effects. Simplified solutions for calculating the divergence speed of wings with different geometry are established.Design/methodology/approachThe wings are modeled as anisotropic plate elements and thin-walled beams with closed cross-section. Two-dimensional plate-like models are applied to analysis and design problems for wings of large aspect ratio.FindingsAt first, the equations of elastic deformation for anisotropic slender, plate-like wing with the large aspect ratio are studied. The principal consideration is delivered to the coupled torsion-bending effects. The influence of anisotropic tailoring on the critical divergence speed of the wing is examined in closed form. At second, the method is extended to study the behavior of the large aspect ratio, anisotropic wing with box-like wings. The static equations of the wing with box-like profile are derived using the theory of anisotropic thin-walled beams with closed cross-section. The solutions for forward-swept wing with box-like profiles are given in analytical formulas. The formulas for critical divergence speed demonstrate the dependency upon cross-sectional shape characteristics and anisotropic properties of the wing.Research limitations/implicationsThe following simplifications are used: the simplified aerodynamic theory for the wings of large aspect ratio was applied; the static aeroelastic instability is considered (divergence); according to standard component methodology, only the component of wing was modeled, but not the whole aircraft; the simplified theories (plate-lime model for flat section or thin-walled beam of closed-section) were applied; and a single parameter that defines the rotation of a stack of single layers over the face of the wing.Practical implicationsThe simple, closed-form formulas for an estimation of critical static divergence are derived. The formulas are intended for use in designing of sport aircraft, gliders and small unmanned aircraft (drones). No complex analysis of airflow and advanced structural and aerodynamic models is necessary. The expression for chord length over the span of the wing allows for accounting a board class of wing shapes.Social implicationsThe derived theory facilitates the use of composite materials for popular small-size aircraft, and particularly, for drones and gliders.Originality/valueThe closed-form solutions for thin-walled beams in steady gas flow are delivered in closed form. The explicit formulas for slender wings with variable chord and stiffness along the wing span are derived.

Continuum Modelling of Silicon Diffusion and Activation in in0.53Ga0.47As

A continuum based-model of Silicon diffusion in ion-implanted InGaAs is presented. Several 5×1014 10keV Si+ implants into InGaAs were Rapid Thermal Annealed (RTA) at 750°C ranging from 10-40s. Box-like profiles characteristic of concentration-dependent diffusion were observed, similar to furnace anneals reported previously. Diffusivity extractions were carried out using FLOOPS (Florida Object Oriented Process Simulator), using point defect pairs, and Fermi level effects. Overall consideration of model fits and possible options for further development are suggested.

Problems of N-type Doped Regions in Germanium, their Solutions, and How to Beat the ITRS Roadmap

In this paper the authors discuss the issues surrounding the formation of ultrashallow n-type junctions in Ge. In general the n-type dopants are relatively difficult to activate and diffuse quickly, leading to high access resistances and limited capability to reduce the device dimensions, respectively. Sheet resistance (Rs) was calculated for n-type box-like profiles in Si and Ge. To achieve ITRS Roadmap targets in Si an active doping concentration of 1.5-2×1020 cm-3 is required, but due to the enhanced electron mobility it is predicted approximately 6×1019 cm-3 is sufficient in Ge.

Influence of Lateral Spreading of Implanted Aluminum Ions and Implantation-Induced Defects on Forward Current–Voltage Characteristics of 4H-SiC Junction Barrier Schottky Diodes

Forward current density (JF)-forward voltage (VF) characteristics are experimentally and computationally investigated for 4H-silicon carbide junction barrier Schottky (JBS) diodes with a lightly doped (3 - 5 times1015 cm-3) drift layer and 2-mum-wide p+ stripe regions separated by 1 mum. The JF-VF characteristics of fabricated JBS diodes are compared with those of Schottky barrier diodes simultaneously fabricated on the same epitaxial wafers. These JF-VF characteristics are also compared with those of simulated JBS diodes, assuming boxlike and Monte Carlo-simulated profiles of aluminum. In the simulation of aluminum ion implantation, concentration contours of created interstitials and vacancies are calculated, and their influence on the JF-VF characteristics of JBS diodes is discussed in terms of degradation of electron mobility in the surface region of the drift layer.

Highly doped Si and Ge formed by GILD (gas immersion laser doping); from GILD to superconducting silicon

Gas Immersion Laser Doping (GILD) of silicon with boron has shown excellent performances in terms of junction depth, box-like profile, dopant concentration and activation. The study of the GILD process is extended to boron and phosphorus doping of silicon on insulator (SOI) and of relaxed Ge films epitaxied on Si or on SOI. The sheet resistances of Si and Ge doped films are measured as a function of the laser energy density and number of laser pulses. The dopant concentration profiles are measured by Secondary Ion Mass Spectrometry (SIMS) in the case of Ge on SOI. Experimental results on Ge show that GILD allows realizing doped layers with sheet resistances of ≈ 10 Ω/□ with nearly boxlike depth profiles, in the case of phosphorus, and of ≈ 40 Ω/□ with depth profiles peaked near the interface of the undoped Ge, in the case of boron. Finally we show that B doping by GILD allows reaching high enough dopant concentrations to make cubic silicon superconductive.

Detailed Analysis and Precise Modeling of Multiple-Energy Al Implantations Through $\hbox{SiO}_{2}$ Layers Into 4H-SiC

This paper presents a detailed analysis and precise modeling of multiple-energy Al implantations necessary for boxlike profiles in the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -region of 4H-SiC power devices. To demonstrate the balance between "scatter-in channeling" and "amorphization-suppressed channeling," a thin-surface SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer is formed on 4H-SiC substrates misoriented by 8deg from (0001) toward [112 macr0]. Experimental, as well as Monte-Carlo-simulated, as-implanted concentration profiles of Al normally incident to the surface suggest that the least ion channeling is realized for implantations without SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in a decreasing energy order. To understand this mechanism, concentration profiles of Al implantations at a single energy with and without SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are modeled using the dual-Pearson approach. Based on the developed model, the Al ion channeling in 4H-SiC is discussed in terms of effects of surface SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers and the sequence of multiple-energy implantations.

Advances in optical carrier profiling through high-frequency modulated optical reflectance

As indicated by the ITRS roadmap, obtaining accurate information on the electrically active dopant profile for sub-30-nm structures is a key issue. Presently, however, there is no conventional, probe-based (destructive) technique available satisfying the ITRS targeted depth (3%) and carrier level (5%−10%) reproducibility and accuracy. In this work, the authors explore the promising capabilities of nondestructive photomodulated optical reflectance (PMOR) techniques, based on the localized (micrometer beam size) detection of variations in the reflectivity of the sample, due to thermal and plasma (excess carrier) effects as can be generated by a modulated pump laser such as the Therma-Probe® (TP) system. Earlier and more recent work using low modulation (1 kHz) frequencies has shown that it is possible, but rather tedious, to extract the electric junction depth (at about 1018 cm−3) and carrier concentration of chemical vapor deposition grown (CVD) (boxlike) structures based on so-called power curves (where the reflected power of the probe laser is plotted versus the power of the pump laser). In this work the authors focus on high-frequency (1 MHz) PMOR, which gives two (instead of one) independent signals, i.e., the amplitude (A) and phase angle (ϕ) of the reflected probe beam. It has been proposed earlier and is confirmed in this work that a single simple measurement allows for the direct and easy extraction of the junction depth (Xj) and carrier concentration (N) of boxlike profiles. Furthermore, the shape of the so-called three-dimensional PMOR offset curves (A and ϕ versus offset), where the distance of the pump relative to the probe beam is varied over several micrometers, might help to obtain information on more complex profiles. The principles allowing for the extraction of arbitrary carrier profiles, with nanometer depth resolution and carrier concentrations between 1018 and 1021 cm−3, from offset curves will be discussed and evidence for the proposed ideas will be given for homogeneously doped material and CVD boxlike structures based on FSEM device simulations.

Drive Current Enhancement in Sub-50 nm CMOS by Reduction of SDE Resistance with Laser Thermal Process

In this paper, we report on the ultrashallow junction profiles and good characteristics of sub-50 nm bulk complementary metal oxide semiconductor (CMOS) devices with n+/p+ source-drain extensions (SDEs) formed by laser thermal processing (LTP). By combining LTP with preamorphization and strong-dosage dopant-ion implantation, CMOS drive current can be improved without incurring a cost in terms of short-channel deterioration. The SDE-junction depth, SDE overlap length, and sheet resistance were controlled by the energy of preamorphization implantation, and the first two of these parameters were independent of dopant dosage. This allowed us to design strongly activated and abrupt box-like dopant profiles. With this technique, we obtain improvements in drive current of 13 and 8%, respectively, for p- and n-metal oxide semiconductor field effect transistors at and without inducing any short-channel deterioration. © 2004 The Electrochemical Society. All rights reserved.

Device Characteristics of Ultra-shallow Junctions Formed by fRTP Annealing

ABSTRACTThe creation of ultra-shallow junction for CMOS devices at the sub-100 nm node is driving significant efforts in developing thermal processing to give rise to high dopant activation in combination with limited diffusion. Flash-assist Rapid Thermal Annealing™ (fRTP™) is a promising new annealing technique, which involves the heating of the bulk of the wafer to an intermediate temperature using rather conventional spike RTP, followed by a short and intense pulse of light localized on the implanted wafer surface.In this work, we have systematically investigated the junction formation of different implants under fRTP anneals in terms of profile and devices. Co-implanted Ge and F species provide more box-like profiles with improved activation. Although leakage currents are higher for fRTP-annealed junctions than for spike-annealed junctions, appropriate fRTP process parameters and correct process conditions provide a critical tool to control and reduce the leakage current of co-implanted fRTP junctions to acceptable levels. Proper implant and anneal are requested for minimizing pattern effect and improving device performance.

Junction and Profile Analysis using Carrier Illumination

AbstractCarrier Illumination™ (CI) is an optical technique for non-destructive in-line monitoring of post-anneal junction depth and pre-anneal PAI depth and dose with wafer mapping capabilities. This work intends to extend the use of the CI-measurements from a range-specific quantitative measurement towards a more universal quantitative analysis of junction depth, profile abruptness and implant dose. For that purpose this paper presents a systematic study of the CI response to a wide variety of post anneal implant processes, varying parameters including implant species, dose and energy, annealing condition, and surface preparation.Samples containing B, BF2 and As-implants with and without Ge PAI layers, with junction depths between 10-120 nm, were measured. In addition near-ideal box-like profiles (as obtained with CVD-growth) were fabricated and measured. For the abrupt CVD profiles, CI measures the junction position with sub-nm resolution independent of the CI-analysis conditions. For more graded profiles resulting from annealed implants, the correlation to the SIMS junction depth becomes a function of generation laser current (which is proportional to the applied power). As the concentration level, at which the correlation is made, can be adjusted over a concentration range of approximately 2x1018 to 2x1019/cm3 by changing the laser current, a route towards correlating the CI measurement with profile abruptness becomes feasible.

Detailed Analysis of Early to Late-Time Spectra of Supernova 1993J

We present a detailed study of line structure in early to late-time spectra of Supernova (SN) 1993J. Spectra during the nebular phase, but within the first two years after explosion, exhibit small-scale structure in the emission lines of some species, notably oxygen and magnesium, showing that the ejecta of SN 1993J are clumpy. On the other hand, a lack of structure in emission lines of calcium implies that the source of calcium emission is uniformly distributed throughout the ejecta. These results are interpreted as evidence that oxygen emission originates in clumpy, newly synthesized material, while calcium emission arises from material pre-existing in the atmosphere of the progenitor. Spectra spanning the range 433-2454 days after the explosion show box-like profiles for the emission lines, clearly indicating circumstellar interaction in a roughly spherical shell. This is interpreted within the Chevalier & Fransson (1994) model for SNe interacting with mass lost during prior stellar winds. At very late times, the emission lines have a two-horned profile, implying the formation of a somewhat flattened or disk-like structure that is a significant source of emission. The very high signal-to-noise ratio spectra are used to demonstrate the potential significance of misinterpretation of telluric absorption lines in the spectra of bright SNe.

Shallow junction doping technologies for ULSI

Abstract The fabrication of thin, sub-40 nm doped layers in Si with high concentrations of electrically active dopants and box-like profiles is a major technological challenge. Making these regions without introducing residual defects in the material and without affecting the properties of other material regions in the device is even more difficult. The need to control these properties of doping profiles in ultra-large-scale integrated (ULSI) circuits has driven the study of low energy implantation, transient enhanced diffusion (TED), and focused the search fornew shallow junction doping techniques. In this article, wereview the motivation for shallowjunctions, specific requirements for shallow junctions used in deep sub-micron dimension metal-oxide-semiconductor field effect transistors (MOSFETs), current understanding of implant and diffusion processes, and the state-of-the-art in low energy implantation and a number of alternate doping technologies, including plasma implantation, gas-immersion laser (GILD) doping, rapid vapor-phase doping (RVD), ion shower doping, and decaborane (B10H14) implantation.

Ultra-shallow boxlike profiles fabricated by pulsed ultraviolet-laser doping process

Ultra-shallow, boxlike impurity profiles are produced using gas immersion laser doping (GILD) and then analyzed by spreading resistance profilometry (SRP) and secondary ion mass spectrometry (SIMS) to determine the impurity distribution. At high concentrations, the profiles obtained by SRP exhibit the expected boxlike shape over the entire range of junction depths: The measured concentration within the junction region is uniform while the dopant gradient at the junction exceeds 1 decade/5 nm. In comparison, the same profiles analyzed using high primary ion energy SIMS show a broader transition at the metallurgical junction. Caused by knock-ons and ion mixing during the sputtering process, the inaccuracy is markedly reduced by lowering the acceleration energy of the primary Cs+ ion beam. At lower concentrations (&amp;lt;1019/cm3), profiles analyzed by SRP exhibit shallower junctions than expected. Electrical measurements of diodes and Hall structures show that high-quality, ultra-shallow n+p, np, and pn junctions are fabricated with good dose control using GILD. For complete characterization of GILD, accurate measurement of both chemical and electrically active dopant profiles are required. At present, neither SIMS nor SRP provides an entirely accurate impurity profile.

Thin-base bipolar transistor fabrication using gas immersion laser doping

Gas immersion laser doping (GILD) is used to fabricate the base and emitter regions of narrow-base n-p-n bipolar transistors. The GILD process is unique in that it allows simple fabrication of box-like impurity profiles which can be placed very accurately in the vertical dimension (+or-100 AA). Transistors with base widths ranging from 700 to 1200 AA and DC forward current gains greater than 50 are fabricated. >

The first 7 years (1978–1985) of ice wedge growth, Illisarvik experimental drained lake site, western Arctic coast

A large lake, measuring 600 m × 300 m and with a depth of nearly 5 m, was artificially drained on 13 August 1978. Observations on the formation, width, and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature. The first winter's cracks had box-like profiles, with surface widths to 10 cm and depths to 2.5 m. Some cracks continued to widen and deepen, once opened in early winter, and then narrowed or even closed completely in summer. Mean growth rates for the ice wedges for the first few years have been as much as 3.5 cm/year. Temperature gradients at the time of first cracking have been in the range of 10–15 °C/m. The growth rate of young ice wedges is site specific and temperature dependent, varying with factors such as the temperature gradient, vegetation, and snow cover, so an estimate of the age of an ice wedge from its width will usually be impossible. A study of crack widths indicates that the apparent coefficient of linear expansion of frozen ground may be several times that of ice. Upward cracking has been proven.