Boron Profiles Research Articles

Annealing studies of boron implanted emitters for n-silicon solar cells

Effects of annealing on the properties of B-implanted Si for n-type solar cells were investigated by comparing rapid thermal annealing (RTA) and furnace annealing (FA) conditions. Profiles of boron and residual damage were theoretically simulated by technology computer aided design based on boron diffusion kinetics mechanism of transient enhanced diffusion. Compared with the rapid thermally annealed samples, the furnace annealed one showed the lowest remnant damage spectra obtained by channeling Rutherford backscattering spectrometry. Furthermore, the electrical properties of boron implanted samples were characterized by Hall and QSSPC technique, revealing a trend that increasing annealing thermal budget would result in higher active carrier density and lower emitter saturation current density. Finally, passivated emitter solar cells were fabricated to verify the influence of annealing conditions on the performances at device level. The champion cell with efficiency of 18.85% received FA for 20 min, whereas those with lower thermal budgets exhibited significantly lower performance. From diode parameters obtained by fitting dark I–V curves and short wavelength responses of internal quantum efficiency spectrum, it was found that B-implanted samples required an annealing temperature of at least 1000 °C together with a sufficiently long time. Rather low thermal budget such as RTA for dozens of seconds was far enough to realize full activation of boron and removal of implantation damage.

Degradable borate glass polyalkenoate cements

Glass polyalkenoate cements (GPCs) containing aluminum-free borate glasses having the general composition Ag2O-Na2O-CaO-SrO-ZnO-TiO2-B2O3 were evaluated in this work. An initial screening study of sixteen compositions was used to identify regions of glass formation and cement compositions with promising rheological properties. The results of the screening study were used to develop four model borate glass compositions for further study. A second round of rheological experiments was used to identify a preferred GPC formulation for each model glass composition. The model borate glasses containing higher levels of TiO2 (7.5 mol %) tended to have longer working times and shorter setting times. Dissolution behavior of the four model GPC formulations was evaluated by measuring ion release profiles as a function of time. All four GPC formulations showed evidence of incongruent dissolution behavior when considering the relative release profiles of sodium and boron, although the exact dissolution profile of the glass was presumably obscured by the polymeric cement matrix. Compression testing was undertaken to evaluate cement strength over time during immersion in water. The cements containing the borate glass with 7.5 mol % TiO2 had the highest initial compressive strength, ranging between 20 and 30 MPa. No beneficial aging effect was observed-instead, the strength of all four model GPC formulations was found to degrade with time.

Polysilicon thin films fabricated by solid phase crystallization using reformed crystallization annealing technique

In this work, a reformed crystallization annealing technique is presented for the solid phase crystallization (SPC) of amorphous silicon (a-Si) on SiNx-coated quartz substrate. This technique includes a two-step annealing process which consists of a low-temperature (475°C) classical furnace annealing for nucleation of Si and a high-temperature (900°C) grain growth process of polycrystalline silicon (poly-Si) during thermal annealing in classical tube furnace. The aim of this reformed two-step annealing technique is reducing the long (up to 48h) crystallization annealing duration of single step annealing at low temperatures (~600°C) while maintaining the film quality, as low-temperature single step annealing, by using reformed technique. Continuous p-type poly-Si film was formed on quartz substrate thanks to exodiffusion of boron, which was deposited prior to a-Si, through Si film by thermal annealing. The stress and degree of crystallinity of the p-type poly-Si were studied by the micro-Raman Spectroscopy. The crystallization fraction value of 95% was deduced for annealed samples at 900°C, independent from crystallization technique. On the other hand, the Raman analysis points out that compressive stress was induced by increasing the annealing duration at 900°C. X-ray diffraction (XRD) analysis reveals that the preferred crystallite orientation of the films, independent from crystallization temperature and substrates, is <111>. Additionally, the average crystallite size calculated from XRD patterns increases from 69Å to 165Å by using reformed two-step annealing instead of single step annealing at 900°C for 90min. The exodiffusion of boron into the silicon film was deduced from secondary ion mass spectrometry (SIMS) analysis and the p+/p graded boron profile was obtained, which may result higher carrier diffusion length and longer carrier life time. Finally, the annealing duration dramatically decrease to 9h by using reformed two-step annealing technique instead of conventional single step annealing at 600°C. The results show that reformed SPC annealing technique has major advantages by combining the lower annealing duration and high crystal quality.

Validation of gyrokinetic modelling of light impurity transport including rotation in ASDEX Upgrade

Upgraded spectroscopic hardware and an improved impurity concentration calculation allow accurate determination of boron density in the ASDEX Upgrade tokamak. A database of boron measurements is compared to quasilinear and nonlinear gyrokinetic simulations including Coriolis and centrifugal rotational effects over a range of H-mode plasma regimes. The peaking of the measured boron profiles shows a strong anti-correlation with the plasma rotation gradient, via a relationship explained and reproduced by the theory. It is demonstrated that the rotodiffusive impurity flux driven by the rotation gradient is required for the modelling to reproduce the hollow boron profiles at higher rotation gradients. The nonlinear simulations validate the quasilinear approach, and, with the addition of perpendicular flow shear, demonstrate that each symmetry breaking mechanism that causes momentum transport also couples to rotodiffusion. At lower rotation gradients, the parallel compressive convection is required to match the most peaked boron profiles. The sensitivities of both datasets to possible errors is investigated, and quantitative agreement is found within the estimated uncertainties. The approach used can be considered a template for mitigating uncertainty in quantitative comparisons between simulation and experiment.

Study on excimer laser irradiation for controlled dehydrogenation and crystallization of boron doped hydrogenated amorphous/nanocrystalline silicon multilayers

We report on the excimer laser annealing (ELA) induced temperature gradients, allowing controlled crystallization and dehydrogenation of boron-doped a-Si:H/nc-Si:H multilayers. Depth of the dehydrogenation and crystallization process has been studied numerically and experimentally, showing that temperatures below the monohydride decomposition can be used and that significant changes of the doping profile can be avoided. Calculation of temperature profiles has been achieved through numerical modeling of the heat conduction differential equation. Increase in the amount of nano-crystals, but not in their size, has been demonstrated by Raman spectroscopy. Effective dehydrogenation and shape of the boron profile have been studied by time of flight secondary ion mass spectroscopy. The relatively low temperature threshold for dehydrogenation, below the monohydride decomposition temperature, has been attributed to both, the large hydrogen content of the original films and the partial crystallization during the ELA process. The results of this study show that UV-laser irradiation is an effective tool to improve crystallinity and dopant activation in p+-nc-Si:H films without damaging the substrate.

Classical confinement and outward convection of impurity ions in the MST RFP

Impurity ion dynamics measured with simultaneously high spatial and temporal resolution reveal classical ion transport in the reversed-field pinch. The boron, carbon, oxygen, and aluminum impurity ion density profiles are obtained in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] using a fast, active charge-exchange-recombination-spectroscopy diagnostic. Measurements are made during improved-confinement plasmas obtained using inductive control of tearing instability to mitigate stochastic transport. At the onset of the transition to improved confinement, the impurity ion density profile becomes hollow, with a slow decay in the core region concurrent with an increase in the outer region, implying an outward convection of impurities. Impurity transport from Coulomb collisions in the reversed-field pinch is classical for all collisionality regimes, and analysis shows that the observed hollow profile and outward convection can be explained by the classical temperature screening mechanism. The profile agrees well with classical expectations. Experiments performed with impurity pellet injection provide further evidence for classical impurity ion confinement.

Modeling of the Boron Emitter Formation Process from BCl&lt;sub&gt;3&lt;/sub&gt; Diffusion for N-Type Silicon Solar Cells Processing

This work is devoted to the study of boron doping diffusion process for n-type silicon solar cells applications. Deposition temperature is an important parameter in the diffusion process. In this paper we investigate its influence using an industrial scale furnace [1] (LYDOPTM Boron), which is developed by Semco Engineering. We especially used a numerical model (Sentaurus) in order to further understand the boron diffusion mechanism mainly with respect of the diffusion temperature. The model calibration is based on boron concentration profiles obtained by SIMS (Secondary Ion Mass Spectrometry) analysis. We observed that the boron profiles could be correctly simulated by a single fitting parameter. This parameter, noted kBoron which is connected to the chemical reaction kinetics developed at the interface between the boron silicon glass (BSG) and the silicon substrate

Source Engineering for Tunnel Field-Effect Transistor: Elevated Source with Vertical Silicon–Germanium/Germanium Heterostructure

In this work, we demonstrate by simulation and experiment that the performance of a p+ Si0.5Ge0.5 source tunnel field-effect transistor (TFET) can be improved by inserting an undoped Ge layer between source and channel. The Ge layer suppresses diffusion of boron into the Si channel and it also forms a Si0.5Ge0.5/Ge/Si hole quantum well, leading to an abrupt boron profile and a high hole concentration at the source edge. At the Ge/Si heterojunction, the presence of compressive strain in the Ge layer increases the valence band offset, while the tensile strain in the Si channel increases the conduction band offset, which effectively reduces the tunnel barrier and enhances the tunnel probability. Compared with a control device without the Ge layer, TFETs with a Si0.5Ge0.5/Ge source show a higher on-state current ION and improved threshold voltage VTH and subthreshold characteristics.

Kohonen classification applying ‘missing variables’ criterion to evaluate the p‐boronophenylalanine human‐body‐concentration decreasing profile of boron neutron capture therapy patients

AbstractThe irradiation dose in tumor and healthy tissue of a boron neutron capture therapy (BNCT) patient depends on the boron concentration in blood. In most treatments, this concentration is experimentally determined before and after irradiation but not while irradiation is being carried out because it is troublesome to take the blood samples when the patient remains isolated in the irradiation room. A few models are used to predict the boron profile during that period, which until now involves a biexponential decay. For the prediction of decay concentration profiles of the p‐boronophenylalanine (BPA) in the human body during BNCT treatment, a Kohonen‐based neural network method is suggested. The results of various (20 × 20 × 40 Kohonen network) models based on different trainings on the data set of 67 concentration sets (profiles) are described and discussed. The prediction ability and robustness of the modeling method were tested by the leave‐one‐out procedure. The results show that the method is very robust and mostly independent of small variations. It can yield predictions, root mean squared prediction error (RMSPE), with a maximum of 3.30 µg g−1 for the present cases. In order to show the abilities and limitations of the method, the best and the few worst results are discussed in detail. It should be emphasized that one of the main advantages of this method is the automatic improvement in the prediction ability and robustness of the model by feeding it with an increasing number of data. Copyright © 2011 John Wiley &amp; Sons, Ltd.

A beneficial application of backside SIMS for the depth profiling characterization of implanted silicon

AbstractAfter ion implantation, annealing is needed to activate dopant and recover crystalline. However, in some annealing conditions there is a possibility that activation annealing forms defects in the implanted region, which may cause errors in SIMS depth profiles. The purpose of this study is to make clear the influence of defects generated during annealing on the conventional front‐side SIMS (FSS) depth profiles, and to provide proper measurement condition to get accurate depth profiles using back‐side SIMS (BSS) technique as another beneficial application. In this study, BF2 were implanted into crystalline silicon, and three different samples were treated, respectively, as implanted, 750 and 900° annealing. In an as‐implanted sample, BSS depth profiles of boron confirmed those obtained by FSS. On the other hand, in annealed samples, BSS depth profiles were steeper than those of FSS. This result suggests that the degradation of depth resolution in FSS cannot be explained only by the effect of ion mixing due to primary ions, but may be related with the crystalline structure in the implanted region. Therefore, BSS techniques can also be indispensable for getting more precise depth profiles in the implanted region of silicon. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Suppressing the redistribution of boron in crystalline silicon during SIMS analysis

AbstractBoron is one of the most commonly used p‐type dopant in silicon. We found that boron in crystalline silicon does not have identical distribution in depth profile between front side and rear side SIMS analysis. Comparing boron profiles of both analyses, different distributions can be seen at the depth in a few hundreds of nanometers from the surface side. Additionally, we continued analysis to investigate the behavior of boron in homogenously boron‐doped sample, such as p‐type silicon substrate. The result showed that distortion arises at the surface side during analysis and consequently nonuniform distribution was obtained. From the results, we estimate that boron should be redistributed during usual SIMS analysis, and study various analytical conditions in order to suppress such phenomenon. In this study, entire experiments were carried out by CAMECA ims 6f and 7f instruments, known as magnetic sector SIMS. Several ion‐implanted samples having different conditions are prepared for the analyses.As a result of experiments, redistribution of boron in crystalline silicon is suppressed suitably by cooling method using liquid nitrogen. Furthermore, it was revealed that the boron redistribution takes place in activation‐annealing samples, while the redistribution cannot be observed in as‐implanted samples. Copyright © 2010 John Wiley &amp; Sons, Ltd.

The isotopic comparative method (ICM) for SIMS quantification of boron in silicon up to 40 at.%

AbstractThis work extends the Isotopic Comparative Method, which has been previously introduced with the aim of correcting matrix effects, to quantify high concentrations of boron in silicon up to 40 at.% by SIMS technique. It requires a specific sample containing two isotopes of the element to quantify: for this study silicon sample with isotope 10B present in constant, sufficiently dilute concentration, quantifiable with the conventional Relative Sensitivity Factor method and the other isotope 11B implanted at very high concentrations. The intensity of 10B, whose concentration ratio with respect to silicon is known and constant, allows to measure the matrix effects induced by the presence of 11B and to deduce the total boron concentration. The variations of the ion yields of boron YB+ and silicon YSi+ as a function of the boron concentration CB are investigated up to 40 at. %. It is found that under Ar+ sputtering there are no matrix effects on Si+ ions, but a doubling of YB+. Under O2+, YB+ and YSi+ increases almost linearly and similarly up to 2.5 times their value in dilute regime. With saturated O2 flooding under Ar+ or O2+, YB+ and YSi+ increase similarly and weakly. These results allow defining an Extended Relative Sensibility Factor method for the quantification of concentrated boron profiles in silicon. It has been successfully implemented in a ∼5 at.% boron layer obtained by Gas Immersion Laser Doping. ICM has been implemented for quantifying high dose boron implantation in silicon (CB up to 40 at.%). Copyright © 2010 John Wiley &amp; Sons, Ltd.

Spatial variation in fluid flow and geochemical fluxes across the sediment–seawater interface at the Carlos Ribeiro mud volcano (Gulf of Cadiz)

Submarine mud volcanism is an important pathway for transfer of deep-sourced fluids enriched in hydrocarbons and other elements into the ocean. Numerous mud volcanoes (MVs) have been discovered along oceanic plate margins, and integrated elemental fluxes are potentially significant for oceanic chemical budgets. Here, we present the first detailed study of the spatial variation in fluid and chemical fluxes at the Carlos Ribeiro MV in the Gulf of Cadiz. To this end, we combine analyses of the chemical composition of pore fluids with a 1-D transport-reaction model to quantify fluid fluxes, and fluxes of boron, lithium and methane, across the sediment–seawater interface. The pore fluids are significantly depleted in chloride, but enriched in lithium, boron and hydrocarbons, relative to seawater. Pore water profiles of sulphate, hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34–180 cm depth below seafloor. Clay mineral dehydration, and in particular the transformation of smectite to illite, produces pore fluids that are depleted in chloride and potassium. Profiles of boron, lithium and potassium are closely related, which suggests that lithium and boron are released from the sediments during this transformation. Pore fluids are expelled into the water column by advection; fluid flow velocities are 4 cm yr −1 at the apex of the MV but they rapidly decrease to 0.4 cm yr −1 at the periphery. The associated fluxes of boron, lithium and methane vary between 7–301, 0.5–6 and 0–806 mmol m −2 yr −1, respectively. We demonstrate that fluxes of Li and B due to mud volcanism may be important on a global scale, however, release of methane into the overlying water column is suppressed by microbial methanotrophy.

Physical Origins of Threshold Voltage Variation Enhancement in Si(110) n/pMOSFETs

Threshold voltage Vth variations in scaled (110) n/pMOSFETs are systematically investigated. Vth variations in (110) nMOSFETs and pMOSFETs with high channel dose are larger than those in (100) nMOSFETs and pMOSFETs, respectively. Physical origins of Vth variation enhancement in (110) MOSFETs are analyzed on the basis of the substrate impurity concentration dependence of the body effect and S factor variations. It is found that the depletion width variations due to boron ion channeling and the interface trap density variations enhance Vth variations in boron-doped (110) nMOSFETs and that the interface fixed charge variations enhance Vth variations in arsenic-doped (110) pMOSFETs. An undoped channel combined with a steep boron profile and moderate phosphorus doping into the surface are desirable to minimize Vth variations in (110) nMOSFETs and pMOSFETs, respectively.

Atomic-scale boron redistribution during reactive diffusion in Ni–Si

The redistribution of boron during the formation of the Ni silicides was investigated using atom probe tomography and transmission electron microscopy. A 7 nm amorphous intermixed region was found after deposition of a 30 nm thick Ni film at room temperature. The formation of this Ni–Si layer was found to have almost no influence on the boron implantation profile. After heating at 290 °C for 1 h, three types of silicides (Ni2Si, NiSi, and NiSi2) were identified below a thin remaining film of Ni (8 nm). The unexpected presence of the silicon-rich NiSi2 phase at this temperature may be caused by the presence of a thin silicon oxide (SiO2) observed at the Ni/Ni2Si interface that may act as a diffusion barrier. The average boron profile in NiSi2 and NiSi silicides is similar to the profile in the silicon substrate before reaction. A segregation of boron at several interfaces was detected. Small boron clusters (1.5 at. %) were found in NiSi, NiSi2, and Si phases but not in Ni2Si. After a 1 min heat treatment at 450 °C, the NiSi phase is the only silicide present. Boron clusters with a platelet shape and a concentration of 3 to 5 at. % of boron were found in both NiSi and Si. The presence of boron in the Ni silicide and its precipitation in the form of tiny clusters is likely to affect the electrical properties of the contacts.

Boron and aluminum diffusion into 4H–SiC substrates

Abstract Boron and aluminum doping by diffusion into n-type 4H–SiC Si-face substrates was carried out at the temperatures of 1800–2000 °C. Secondary ion mass spectroscopy (SIMS) was employed to obtain the impurity profiles, which showed that linearly graded boron profile and shallow aluminum profiles have been achieved, which may be a promising application in SiC device fabrication, such as p–n diode or ohmic contact. Characterization of high temperature processing influence on SiC surface morphology has been performed. Elemental boron and aluminum carbide were determined to be the best candidates as an impurity source materials for realizing p-type diffusion.

F T × BV cbo product modeling for SiGe:C HBTs

The specific aspects of SiGe:C HBT process and device simulation using TCAD are discussed. Cut-off frequency fT and collector junction breakdown voltage BVcbo dependences on carbon concentration in SiGe base area are investigated. The boron and carbon profiles in SiGe base are obtained to provide a trade-off between gain, cut-off frequency and break-down voltage. High values of fT × BVcbo product were achieved.

Evolution of boron-interstitial clusters in preamorphized silicon without the contribution of end-of-range defects

Kinetic Monte Carlo simulations have been used to investigate mechanisms for boron clustering in crystalline and preamorphized Si. We have extended previous boron-interstitial cluster models to include larger and more stable complexes in order to reproduce boron cluster evolution at very high boron concentrations. We have investigated the stoichiometry of boron-interstitial clusters resulting from low temperature recrystallization of preamorphized layers. We have performed a dedicated experiment based on boron implanted into preamorphized Si with end-of-range defects placed far enough from the boron profile to avoid the interaction between end-of-range defects and resulting boron-interstitial clusters after recrystallization. Hall measurements on active B dose combined with a systematic analysis performed by Kinetic Monte Carlo simulations indicate that initial boron-interstitial clusters after recrystallization should not contain a high amount of Si interstitials. Otherwise, boron deactivation and subsequent reactivation will occur faster than experimentally observed. The present results suggest B 3 and B 3I clusters as the most probable configurations after recrystallization.

The impact of nitrogen co-implantation on boron ultra-shallow junction formation and underlying physical understanding

In this paper, we show that boron transient enhanced diffusion can be reduced to different extents by varying the distribution of nitrogen atoms in the junction. This is attributed to the relative location of nitrogen atoms with respect to boron profile and end-of-range defect band, affecting the interactions between dopants and defects upon annealing. In addition, variations in boron dopant activation and deactivation are also observed. Similar to fluorine co-implantation, it is proposed that nitrogen atoms react with vacancy point defects to form nitrogen–vacancy clusters that will trap the interstitials emitted from end-of-range defects. However, we report that the interstitial sink efficiency of nitrogen atoms is not as good as the co-implanted carbon atoms, which is noticed from the dopant deactivation curves. In terms of extended defect evolution, the results clearly indicate that end-of-range defects can be stabilized by choosing the optimized co-implant condition of N. Finally, a deeper physical understanding on the diffusion/clustering pathways of nitrogen co-implantation is achieved to supplement and explain the boron diffusion and deactivation behaviors.

Superdiffusion in Si Crystal Lattice Irradiated by Soft X-Rays

We considered the reasons of superdiffusivity and measured profiles of boron and phosphorus in crystalline silicon at room temperature. The superdiffusivity or ultrafast diffusion of metastable vacancies at room temperature in Si crystal irradiated by soft X-rays was obtained experimentally. In this work, we presented experimentally obtained diffusion coefficients of singly and doubly negatively charged long-lived excited vacancies. These high concentration charged metastable vacancies (about 10 cm−3) at room temperature can very fast diffuse changing electrical conductivity and the Hall mobility of carriers. We measured the superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, which were not affected by X-rays. In this paper, we presented the obtained superdiffusion profiles of boron and phosphorus in crystalline silicon measured with secondary-ion mass spectrometer.