Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.     

The effect of boron ion implantation and annealing on the microstructure and electrical characteristics of the diamond films

Diamond films were doped by boron ion-implantation with the energy of 120 keV. The implantation dose ranged from 10¹⁴ to 10¹⁷ cm⁻². After the implantation, the diamond films were annealed at different temperatures (600–750°C) for different times (2–15 min). Scanning Electronic Microscope, Raman and Secondary Ion Mass-spectrum were used to investigate the effect of boron ion implantation and annealing on the microstructure of the diamond films. The electrical resistivities of the diamond films were also measured. It was found that the best dose of boron ion-implantation into the diamond film was around 10¹⁶ cm⁻². The appropriate annealing temperature and time was 700°C and 2–5 min, respectively. After implantation, the resistivities were reduced to 0.1 Ω cm (almost nine orders lower than the unimplanted diamond films). These results show that boron ion implantation can be an effective way to fabricate P-type diamond films.     

Channeling study of boron implanted silicon: Liquid nitrogen temperature implantation

Silicon samples have been boron implanted at 150 keV at liquid nitrogen temperature to a dose of 3.6 × 10¹⁵/cm². This dose rendered the implanted layer amorphous as viewed by helium ion backscattering. Four kinds of room temperature measurements were made on the same set of samples as a function of the isochronal annealing temperature. The measurements made were the determination of the substitutional boron content by the channeling technique using the B¹¹(p, α) nuclear reaction, observation of the disorder by helium ion backscattering, determination of the carrier concentration by van der Pauw Hall measurements, and the sheet resistivity by four point probe measurements. These measurements are compared with results from samples implanted at room temperature. The carrier concentration correlates well with the substitutional boron content for both room temperature and liquid nitrogen temperature implantations. Following annealing temperatures in the 600 to 800°C range, a much larger percentage of the boron lies on substitutional lattice sites, and therefore the carrier concentration is larger, if the implantation is done at liquid nitrogen temperature rather than at room temperature. Following liquid nitrogen temperature implantation, reverse annealing is observed from 600 to 800°C in the substitutional boron content, carrier concentration and sheet resistivity. The boron is more than 90 per cent substitutional after annealing to 1100°C for both the room temperature and liquid nitrogen temperature implantations. The low temperature implantation produced a buried amorphous layer, and this layer was observed to regrow from both the surface and substrate sides at approximately equal rates.     

Possibilities of the formation of carbides and borides by ion implantation

In the system of boron and carbon, the formation of boron carbide was investigated after ion implantation of 25 keV B ions into carbon or of 25 keV C ions into boron and subsequent annealing. TEM and electron diffraction studies showed that the crystallization of boron carbide begins only at temperatures above 1050°C. By implantation of 20 keV C ions into iron (ion dose 10¹⁷ C ions/cm²) only the metastable ε-Fe₂O will be generated, which at above 220°C transforms into the stable cementite Fe₃C. After implantation of 20 keV B ions into iron, no formation of iron boride could be found. These experimental facts can be understood qualitatively with the help of the thermal-spike model. The energy density or the temperature in the thermal spikes is not sufficient for the generation of cementite iron boride or boron carbide.     

Anomalous transient tail diffusion in boron-implanted silicon

Abstract

Anomalous transient tail diffusion is interpreted as being associated with the equilibration of the metastable state formed by the implantation process. During annealing, the sample approaches the thermodynamic equilibrium via quasi-chemical reactions involving radiation defects. The corresponding set of reaction-diffusion equations can be solved giving the space and time evolution of the defect profiles as well as their electrical activity. To exemplify the approach, the tail diffusion of the boron implants with peak concentrations transcending the solubility limit will be discussed in detail. Finally, a simple explanation will be given of the influence of lattice damage on boron diffusion due to pre- or post-implantation of silicon and boron atoms, respectively.     

Modeling of the transient interstitial diffusion of implanted atoms during low-temperature annealing of silicon substrates

It has been shown that many of the phenomena related to the formation of “tails” in the low-concentration region of ion-implanted impurity distribution are due to the anomalous diffusion of nonequilibrium impurity interstitials. These phenomena include boron implantation in preamorphized silicon, a “hot” implantation of indium ions, annealing of ion-implanted layers et cetera. In particular, to verify this microscopic mechanism, a simulation of boron redistribution during low-temperature annealing of ion-implanted layers has been carried out under different conditions of transient enhanced diffusion suppression. Due to the good agreement with the experimental data, the values of the average migration length of nonequilibrium impurity interstitials have been obtained. It has been shown that for boron implanted into a silicon layer preamorphized by germanium ions the average migration length of impurity interstitials at the annealing temperature of 800 °C can be reduced from 11 nm to approximately 6 nm due to additional implantation of nitrogen. The further shortening of the average migration length is observed if the processing temperature is reduced to 750 °C. It is also found that for implantation of BF₂${\mathrm{BF}}_2$ ions into silicon crystal, the value of the average migration length of boron interstitials is equal to 7.2 nm for thermal treatment at a temperature of 800 °C.     

MeV高能B+离子注入Si中二次缺陷的抑制与消除

本文研究了MeV高能B⁺离子注入Si中二次缺陷的退火行为。提出一种新型的双重注入退火方法,抑制或消除了MeV高能B⁺离子注入Si样品中的二次缺陷。还对这种二次缺陷的被抑制与被消除的物理机制进行了讨论。 关键词：     

Superhydrophilicity and XPS study of boron-doped TiO2

This study examines the superhydrophilicity and chemical state of boron-doped TiO₂ prepared by the ion implantation method and explores the effect of annealing on them. XRD measurements show that the implanted sample forms a polycrystalline structure of anatase with no trace of rutile. Their water-contact angles are significantly reduced upon irradiation with ultraviolet light. The Ti 2p XPS spectra of the oxide exhibit a shoulder peak at the lower binding energy side of the main peak, whereas no shoulder is observed in single-crystal and annealed TiO₂. This suggests that the titanium ions with lower valences are produced by boron doping and they disappear on subsequent annealing. The SIMS depth profile of boron in the as-implanted TiO₂ exhibits a peak at a depth of 15-20 nm, whereas this peak disappears upon annealing. The water-contact angles increased on annealing under ultraviolet light illumination. It is concluded that the improvement in the superhydrophilicity by boron doping is due to the reduction of titanium, and the deterioration of superhydrophilicity with the subsequent annealing is due to the oxidation of reduced titanium and the inward diffusion of boron.     

Boron implantations in silicon: A comparison of charge carrier and boron concentration profiles

The concentration profiles of boron implanted in silicon were measured using secondary ion mass spectrometry. The accompanying charge carrier profiles were determined by Hall-effect sheet-resistivity measurements combined with layer removal by anodic oxidation and etching. From a mutual comparison of these profiles an electrically inactive boron fraction was found to exist in the region of maximum boron concentration. This fraction can be correlated with boron precipitates. In high dose implantations the precipitates still exist after annealing at 1000°C. In the tail of the profile a small electrically inactive boron fraction was observed. This fraction was correlated with fast diffusing non-substitutional boron. Near the surface a charge carrier peak was found that can be correlated with the damage caused by implantation. The interpretation of the observed electrical effects was facilitated by investigations on boron concentration profiles of layers implanted with different doses and annealed in accordance with different time-temperature schedules.     

Defects formation in the dual B+ and N+ ions implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions (to doses of 1.2×10¹⁴ or 1.2×10¹⁵ cm^–2) and 50 or 100 keV N⁺ ions (to doses from 1.2×10¹⁴ to 1.2×10¹⁵ cm^–2). After implantations, the samples were furnace annealed at temperatures from 100 to 450 °C. The depth profiles of the radiation damages before and after annealing were obtained from random and channeled RBS spectra using standard procedures. Two damaged regions with different annealing behaviour were found for the silicon implanted with boron ions. Present investigations show that surface disordered layer conserves at the annealing temperatures up to 450 °C. The influence of preliminary boron implantation on the concentration of radiation defects created in subsequent nitrogen implantation was studied. It was shown that the annealing behaviour of the dual implanted silicon layers depends on the nitrogen implantation dose.The authors would like to thank the members of the INP accelerator staff for the help during the experiments. The work of two authors (V.H. and J.K.) was partially supported by the Internal Grant Agency of Academy of Science of Czech Republic under grant No. 14805.     

Phosphor preparation by ion implantation

6H silicon carbide crystals have been subjected to ¹¹B⁺ ion implantation and subsequent annealing and found to show the yellow boron photoluminescence.     

Improvement of the Si-SiO2 interface stress resistance of thin gate oxides after channel ion implantation

The effect of phosphorus and boron ion implantation into silicon dioxide films is examined with regard to the resistance of the Si-SiO₂ interface under high field constant current stress conditions. Phosphorus and boron ions of various doses and energies have been implanted through a 35 nm thick oxide. The interface stress resistance is found to decrease with increasing ion dose and increase with implant energy. However, at high energies, the stress resistance of the boron implanted samples is significantly less than the phosphorus equivalents due to the creation of a second interface trap level. Post-implant annealing increases the interface stress resistance but the best performance is observed for the case of sacrificial oxidation.     

Boron electrical activation in dual B+ + N+ + and B+ + Ar+ ion-implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions and then with 50 keV N⁺ or 100 keV Ar+ ions to doses from 1.2 x 1014 to 1.2 x 1015 cm^–2. The implanted samples were studied using the Hall effect and standard van der Pauw methods. The dependences of the sheet resistivity and the sheet concentration of charge carriers on the annealing temperature in the range from 700 to 1300 K were obtained. Models describing the influence of additional implantation of nitrogen and argon ions on the process of boron electrical activation during annealing are proposed.     

Controlling boron diffusion during rapid thermal annealing with co-implantation by amphoteric impurity atoms

A model for simulating the rapid thermal annealing of silicon structures implanted with boron and carbon is developed. The model provides a fair approximation of the process of boron diffusion in silicon, allowing for such effects as the electric field, the impact of the implanted carbon, and the clustering of boron. The migration process of interstitials is described according to their drift in the field of internal elastic stress.     

Damage dependent electrical activation of boron implanted silicon

The important role of damage dependent electrical activation in the case of boron implanted silicon layers is whown by comparing measured acceptor concentration profiles in differently amorphized silicon layers. It is shown that the amorphous layer is completely recrystallized after a 650° C anneal for 10 min and the implanted boron is electrically active. In the heavily damaged but not amorphous region underneath the amorphous layer the implanted boron is hardly electrically active after this temperature treatment. At higher annealing temperatures the electrical activity increases, but 900° C are required for complete activation of the implanted boron. These results indicate that the process to activate the implanted boron electrically is strongly damage dependent. We thus found a new contribution to the understanding of the annealing behavior of implanted layers.     

Charge state of intrinsic interstitial defects and their substitution of boron atoms in the silicon lattice

The displacement of boron atoms from silicon lattice sites by silicon interstitial atoms was studied, by galvanomagnetic and x-ray methods. The substitution is controlled by the charge state of the interstitial defects. The charge transfer was effected by a change in the level of ionization during implantation by varying the ion-beam density and during annealing by additional electron bombardment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 55–59, April, 1991.     

Study of a nTHGEM-based thermal neutron detector

With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in ~3He gas supply, research on new types of neutron detector as an alternative to ~3He is a research hotspot in the field of particle detection. GEM(Gaseous Electron Multiplier) neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant 4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic n THGEM(neutron THick GEM) for neutron detection. The performance of the n THGEM working in different Ar/CO_2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single n THGEM has been tested for 2-D imaging using a ~(252)Cf neutron source. The key parameters of the performance of the n THGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector.     

Efficient silicon light emitting diodes made by dislocation engineering

Efficient silicon-based light emitting diodes have been fabricated using the dislocation engineering method. Crucially this technique uses entirely conventional ULSI processes. The devices were fabricated by conventional low-energy boron implantation into silicon substrates followed by high-temperature annealing, and strong silicon band edge luminescence was observed. Dislocation engineering is also shown to reduce the thermal quenching for other material systems. Dislocation engineered β-FeSi₂ and Er light emitting devices were fabricated and room temperature electroluminescence at 1.5 μm was observed in both cases.     

Effects of Additional Vacancy-Like Defects Produced by Ion Impealations on Boron Thermal Diffusion in Silicon

The effects of additional vacancy-like defects on thermal diffusion of B atoms in silicon were investigated by using secondary ion mass spectroscopy. B atoms were introduced into silicon by 30keV B ion implantation at a dose of 2×10¹⁴cm^－2, while the additional vacancy-like defects were produced by two different ways. One was via 40 or 160keV He ion implantation at a dose of 5×10¹⁶cm－2 and followed by an annealing at 800°C for 1h, which produced a well-defined cavity band near the projected range of He ions. The other was via 0.5MeV F or O ion implantation at a dose of 5×10¹⁵cm^－2,which creates excess vacancy-like defects around the 1/2 projected range of F or O ions. Our results clearly show that the additional vacancy-like defects could suppress the boron diffusion during subsequent thermal annealing at 800°C for 30 min. The suppressing effects were found to depend on both the ion type and ion energy. The results were qualitatively discussed in combination with the results obtained by using transmission electron microscopy and Rutherford backscattering spectroscopy.     

Fabrication of particular structures of hexagonal boron nitride and boron–carbon–nitrogen layers by anisotropic etching

Anisotropic etching of hexagonal boron nitride (h-BN) and boron–carbon–nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H₂ and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.