Ion Implantation Conditions Research Articles

Ballistic self-annealing during ion implantation

Ion implantation conditions are considered during which theenergy, dissipated in the collision cascades, is low enough to ensurethat the defects, which are generated during these collisions,consist primarily of vacancies and interstitial atoms. It is proposedthat ballistic self-annealing is possible when the point defectdensity becomes high enough, provided that none, or very few, of theinterstitial atoms escape from the layer being implanted. Under theseconditions, the fraction of ballistic atoms, generated within thecollision cascades from substitutional sites, decreases withincreasing ion dose. Furthermore, the fraction of ballistic atoms,which finally end up within vacancies, increases with increasingvacancy density. Provided the crystal structure does not collapse, adamage threshold should be approached where just as many atoms areknocked out of substitutional sites as the number of ballistic atomsthat fall back into vacancies. Under these conditions, the averagepoint defect density should approach saturation. This model isapplied to recently published Raman data that have been measured on a3 MeV He+-ion implanted diamond (Orwa et al 2000 Phys. Rev.B 62 5461). The conclusion is reached that this ballisticself-annealing model describes the latter data better than a model inwhich it is assumed that the saturation in radiation damage is causedby amorphization of the implanted layer.

LUMINESCENCE STUDIES IN THERMAL OXIDE FILMS WITH Si IMPLANTATION

The objective of this work is to investigate the origin of the emission bands of Photo and Cathodo - luminescence (PL, CL) in thermal silicon dioxide films implanted with Silicon. The films were obtained by 150 KeV Si implantation into thennal oxide, with doses of 1×1016 cm-2 and 1×1017 cm-2. Thermal treatments of 0, 30, 60 and 180 minutes in nitrogen at 1100°C were applied. We found light emission in the visible range, the bands change with the ion implantation conditions and thermal treatments. The as implanted samples present photoluminescence bands around 1.95 eV and 2.4 eV for both doses, and they disappear width thermal treatments. After annealing, the low dose samples has a photoluminescence band at 2.6 eV, while those of dose of 1×1017 cm-2 has a band centered at 1.7 eV. The intensity of the bands changes with thermal treatment. The cathodoluminescence bands are at 2.7 eV for both implantation doses in samples with and without theermal treatments. A discussion of the results and conclusions that contribute to better understand this nowadays controversial subject is presented.

The removal of ion implanted deuterium from tungsten and stainless steel by transferred-arc cleaning

Tungsten and stainless steel samples have been ion implanted with deuterium in an accelerator to simulate hydrogen isotope ion implantation conditions in magnetic confinement fusion devices. The samples were characterized by ion beam analysis both before and after cleaning to determine deuterium concentrations present. The extent of transferred-arc (TA) cleaning was varied to determine the deuterium removal efficiency, surface roughening and sample erosion rate. The deuterium content was greatly reduced by the cleaning thus demonstrating the possibility of using the TA cleaning technique for removing deuterium from components exposed to D-T fuels.

Acceleration method for gate-disturb degradation on embedded flash EEPROM

A mechanism and acceleration method for read disturb failures induced by Flash EEPROM cycling is reported. The gate-disturb degradation at read depends on program/erase cycle, applied voltage and temperature. It considers that this failure is due to electron tunneling barrier lowering by positive charge trapped during program/erase cycling. The improvement of lifetime has been found by optimizing ion implantation condition at drain.

Conditions of ion implantation into thin amorphous Si gate layers for suppressing threshold voltage shift

We collected data of ion-implantation profiles using Monte Carlo simulation, and showed that these profiles can readily be expressed by a joined half Gaussian function. We extracted parameters of the joined half Gaussian function from the Monte Carlo data. We also derived a model of the shift in threshold voltage caused by the penetration of ion-implanted impurities. Based on the set of profile data, we evaluated the ion-implantation conditions for As, P, B, and BF 2 to suppress the threshold voltage shift.

GaInP/GaAs collector-up tunneling-collector heterojunction bipolar transistors (C-up TC-HBTs): optimization of fabrication process and epitaxial layer structure for high-efficiency high-power amplifiers

This paper describes a novel heterojunction bipolar transistor (HBT) structure, the collector-up tunneling-collector HBT (C-up TC-HBT), that minimizes the offset voltage V/sub CE,sat/ and the knee voltage V/sub k/. In this device, a thin GaInP layer is used as a tunnel barrier at the base-collector (BC) junction to suppress hole injection into the collector, which results in small V/sub CE,sat/. Collector-up configuration is used because of the observed asymmetry of the band discontinuity between GaInP and GaAs depending on growth direction. To minimize V/sub k/, we optimized the epitaxial layer structure as well as the conditions of ion implantation into the extrinsic emitter and post-implantation annealing. The best results were obtained when a 5-nm-thick 5/spl times/10/sup 17/-cm/sup -3/-doped GaInP tunnel barrier with a 20-nm-thick undoped GaAs spacer was used at the BC junction, and when 2/spl times/10/sup 12/-cm/sup -2/ 50-keV B implantation was employed followed by 10-min annealing at 390/spl deg/C. Fabricated 40/spl times/40-/spl mu/m/sup 2/ C-up TC-HBTs showed almost zero V/sub CE,sat/ (<10 mV) and a very small V/sub k/ of 0.29 V at a collector current density of 4 kA/cm/sub 2/, which are much lower than those of a typical GaInP/GaAs HBT. The results indicate that the C-up TC-HBT's are attractive candidates for high-efficiency high power amplifiers.

Preparation of DLC gradient biomaterials by means of plasma source ion implant-ion beam enhanced deposition

In this study, a new kind of Ti-TiC-C gradient biomaterial has been prepared by means of plasma source ion implant-ion beam enhanced deposition (PSII-IBED). The experimental results showed that the involved components could be controlled to distribute gradually along the depth through changing ion implantation and deposition conditions. As the result, the intrinsic stress and thermal stress would be remarkably relaxed, and the adhesive strength could be greatly increased. This gradient biomaterial made with PSII-IBED can meet the needs of artificial mechanical heart valves.

Carbon layers formed on steel and Ti alloys after ion implantation of C + at very high doses

Ion implantation is a useful technique to tailor surface properties of steel and Ti alloys. In particular, very high dose C + implantation (in the range of 10 18 ions cm −2) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation of carbon doses up to 8×10 18 ions cm −2 has been performed on 440C martensitic stainless steel and Ti6Al4V substrates under similar conditions and tribological and surface analysis results have been compared. Surface hardening occurred for all ion implantation conditions up to doses of 10 18 ions cm −2 [1–3]. Higher doses resulted in a different behaviour for both materials. The stainless steel showed a softening while a twofold hardness increase was maintained in the Ti alloy. Nevertheless, at the higher implanted dose a decrease in hardness was also observed in the Ti alloy. Small area XPS analyses were performed to evaluate the chemical states after ion implantation and establish a relationship with the observed surface hardening. Depth profile XPS analyses showed that for a dose of 4×10 18 ions cm −2 a carbon layer (with concentration over 85% at. C) was formed in the near surface region for both materials.

Growth of pseudomorphic Si 1− yC y and Si 1− x− yGe xC y alloy layers on < 100 > Si by ion implantation and pulsed excimer laser induced epitaxy

In this work, Si 1− y C y and Si 1− x− y Ge x C y alloy layers were grown by multiple energy ion implantation of Ge and C into single crystal Si followed by pulsed excimer laser induced epitaxy. The properties of the alloy layers obtained by this technique, in terms of film crystallinity, Ge and C redistribution and substitutional incorporation, strain formation or relaxation and C-induced band-gap modification, were demonstrated to depend strongly on both ion implantation and laser processing conditions. The growing of pseudomorphic epitaxial layers from group IV semiconductor alloys was successfully achieved by using the high energy and large area beam (up to 1 J cm −2 per pulse over 40 cm 2) excimer laser developed by SOPRA for industrial applications.

Spatial distribution profiles of defects in cadmium-mercury-tellurium after ion implantation

Defect spatial distributions are investigated after implantation of ions in CdxHg1−xTe under various sets of conditions (radiation dose, type and energy of ions, ion current density, and dose absorption rate). Distribution profiles of electrically active radiation-induced defects are calculated with allowance for the generation of defect complexes of vacancion nature. Defect profiles are determined in experiments after implantation of hydrogen and iron ions at constant low ion current densities, and after implantation of copper, tungsten, and aluminum ions in the case of pulsed bombardment at high ion current densities. Secondary-ion mass spectrometry, electron-positron annihilation, Rutherford backscattering of ions, and differential Hall measurements are used to obtain distribution profiles of interstitial ions, vacancion and extended defects, and electrically active defects, respectively. The profiles of these defects are analyzed for various ion-implantation conditions.

Increased hole trapping in gate oxides as latent damage from plasma charging

With aggressive device scaling and the wide use of plasma-assisted processes, the device damage caused by process-induced charging is receiving growing attention, from both basic understanding and technological points of view. The paper presents results of hole-trapping studies in the thin gate oxide of plasma-damaged NMOS and PMOS transistors. In addition to neutral electron traps and passivated interface damage, which are commonly observed in plasma charging latent damage, we observed and identified hole traps, generated by plasma stress. Enhanced hole trapping in the gate oxide of plasma-damaged devices was studied using Fowler - Nordheim stress and substrate hot-hole injection applied to antenna test structures sensitive to process-induced charging. The number of hole traps increases with increasing antenna ratio, indicating that the mechanism of hole-trap generation is based on electrical stress and current flow, forced through the oxide due to charging under plasma etching or ion implantation conditions.

Equipment and methods of surface modification of the microstructure and properties of metals by adsorption assisted ion implantation

Data on phase and structural transformations in the surface layers of metallic alloys as a function of the conditions of ion implantation are reviewed. It is noted that the ion mixing of the surface-absorbed active elements from the implantational gas medium plays an important role in the formation of the element and phase composition of the ion-doped layers. The most important treatment parameters determining the relative role of ionic mixing in structural-phase transformations in the ion-doped layer are: the elementary composition and pressure of the implantational gas medium, the target temperature, the atomic weight of the implanted ions, and the reactivity of these ions and the target ions to the absorbed elements (C, N, O). The formation of high-energy defect structures and the dispersion of the implanted-layer crystal structure in the strong internal-stress fields generated by the highly nonequilibrium solid solutions and in the course of phase transformation are considered. New possibilities for microstructural modification during high-dose implantation are identified with the formation of high-energy defect (including nanocrystalline) structures; heterophase, completely amorphized and other phase-structural states and their combinations in iondoped layers of metallic alloys. Taking advantage of these possibilities makes it possible to reduce by an order of magnitude the implanted dose necessary to upgrade the performance of the surface, and to raise the productivity and lower the cost of the ionbeam technological treatment.

High-efficiency and low-distortion directly-ion-implanted GaAs power MESFETs for digital personal handy-phone applications

We report a high-efficiency and low-distortion GaAs power MESFET using direct ion implantation technology for the digital wireless personal handy-phone system (PHS). When qualified by 1.9-GHz /spl pi//4-shifted quadrature phase shift keying (QPSK) modulated PHS standard signals, the 2.2-V-operation device with a gate width (Wg) of 2 mm exhibited a power-added efficiency (PAE) of 57.2 % and an adjacent channel leakage power (P/sub adj/) of -58 dBc at an output power of 21.3 dBm. The MESFET with the optimized direct ion implantation conditions and fabrication process achieved the highest PAE for PHS applications. The low-cost MMIC-oriented direct ion implantation technology has demonstrated the state-of-the-art results for new-generation PHS handsets for the first time.

Ion Implantation and Annealing Conditions for Delamination of Silicon Layers by Hydrogen Ion Implantation

The delamination of thin silicon layers by ion implantation and annealing has been studied in implanted silicon layers. Hydrogen ions are implanted into a (100) p‐silicon layer through a 100 nm thick oxide layer at 100 keV with different doses ranging from 1.0 × 1016 to 1.0 × 1017 ion/cm2. Delamination of thin silicon layers was clearly observed in cross‐sectional scanning electron microscope photographs at doses above 5.0 × 1016 ion/cm2. The delamination occurs at 485°C with 10 min annealing for an implantation at 5.0 × 1016 ion/cm2. This temperature, however, can be reduced to 425 and 400°C by increasing annealing time to 60 and 120 min, respectively. Delamination is closely related to the formation of H‐Si defect bonds and the release of a hydrogen atom from these bonds in the hydrogen ion implanted Si layer. Temperature variation of the intensity in the hydrogen desorption shows two intensity peaks at 450 and 650°C.

Montecarlo simulation of ion implantation into SiC-6H single crystal including channeling effect

An ion implantation simulator for single crystal 6H-SiC is presented. This simulator uses a Montecarlo method together with either physically based or semiempirical models to calculate the slowing down of the incoming ions in the crystal. Channeling effect, which appears not to be negligible in SiC single crystal for standard ion implantation conditions, arises naturally as a consequence of the crystal structure and valence electrons distribution. The effect of a native oxide, dynamical amorphization and thermal vibration of the lattice atoms, which affect the channeling behavior of the ions, are also included in the simulation. Recent models for electronic stopping are also used. After calibration, the simulation profiles show good agreement with published SIMS profiles.

Noise,resolution and entropy in sputter profiling

Applications of semiconductor sputter profiling in the near future will demand nm or even sub-nm depth resolution, i.e. the ability to distinguish between adjacent features in a concentration profile which are separated by 1 nm or less (not just the ability to achieve a 16-84% width of 1 nm on some edge transient). Recent developments in SIMS indicate that sputter profiling can meet this challenge—provided that instruments with high current microfocus beams less than 1 keV in energy become widely available, and data processing methods are developed to cope with the results. In this paper we discuss the nature of SIMS sputter profile data in detail and explore the consequences of noise, finite sample interval and the destruction of information by processes such as atomic mixing. The use of empirically determined response functions is discussed. We use simple arguments to show that convolution is only a valid model for atomic mixing in the low concentration limit, and contrast the use of Fourier transform and maximum entropy methods for deconvolution in these circumstances. A depth resolution of 1 nm is demonstrated without deconvolution, showing that the technique has real potential for depth resolution on the scale of 1 atomic plane.

Effects of p-type dopants on enhancing AlAs/GaAs superlattice disordering

It is quantitatively shown that the mechanism reponsible for enhancing AlAs/GaAs superlattice disordering by the p-type dopants Zn and Be is essentially the Fermi-level effect occurring in Garich crystals. In the abundance of holes, the Fermi-level effect increases the concentration of the doubly-positively-charged group III element selfinterstitials (designated as I Ga 2+), which govern Al-Ga interdiffusion in crystals rich in group III elements. Under Zn (or Be) indiffusion and ion implantation conditions, the crystal portion where the enhanced Al-Ga inter-diffusion occurs has become rich in group III elements irrespective of whether the annealing ambient is As rich or poor. This is because the incorporation of the Zn (or Be) atoms onto the group III sublattice site will naturally produce crystals rich in group III elements. In the Asrich annealing ambient cases, only the crystal surface region becomes rich in As, while the superlattice disordering reaction occurs in the deeper Zn (or Be) diffusion front region, which is rich in group III elements.

Excitation and De-Excitation Processes in Er Implanted Light Emitting Si Devices

AbstractIn this paper we show that room temperature electroluminescence at 1.54 μm can be obtained in Er and O co-doped Si diodes, fabricated by ion implantation, under both forward and reverse bias conditions. This electroluminescence is particularly strong under reverse bias at the breakdown, when Er is excited through impact with hot carriers. This last mechanism is shown to occur with a cross section of 6×10-17 cm2. The measured decay lifetime of Er ions during pumping is 100 μs at room temperature and this allows to obtain a high internal quantum efficiency. However, when the diode is shut off, the decay lifetime becomes shorter and in particular it is less than 1.2 μs (that is the time response of our system). These results can be explained by the presence of Auger nonradiative de-excitation processes that are inhibited within the depletion region during pumping and set in when, at the shut off, the Er ions are immediately embedded within the heavily doped region (∼1019/cm3) of the device. The long lifetime (100 μs) during pumping and the very fast decay time (≤ 12 μs) at the diode shut off allow us to obtain, in our diode and under reverse bias, both a high efficiency (&gt; 10-4) and a fast modulation (≥ 80 kHz) of the 1.54 μm emission.

The influence of ion implantation conditions on defect formation and amorphisation in silicon

Abstract A phenomenological model describing the dependence of deformation processes on ion implantation conditions is proposed. Experimental results of defect formation as well as amorphisation in silicone for the implantation with Ne+, Ar+ and Kr+ ions in the temperature interval of 150–500 K and for ion current densities of 0.5 to 4.0 μA/cm2 are presented. An analysis of the experimental data within the framework of the proposed model has been carried out. The basic characteristics of the defects appearing at silicon amorphisation also have been defined.

Amorphization of metals by ion implantation and ion mixing methods

In this paper, we present a review of the experimentally determined characteristics of solid-phase amorphization of metals and alloys under ion implantation and ion mixing conditions. For the first time we systematically consider the characteristic features and the thermodynamic, structural, and kinetic criteria for amorphization in different metallic systems, and we demonstrate the expediency of the following classification of alloys undergoing amorphization: “metal-metalloid” systems, intermetallics, heterophase alloys, alloys with high positive heat of mixing. We compare solid-phase amorphization under conditions of bombardment by beams of charged particles, thermal mixing of the alloy components, and mechanical alloying. We consider the phase and structural states preceding amorphization and the possibilities for predicting metallic systems which can undergo amorphization.