Annealing Studies of Damage Introduced by High Energy Ion Implantations of Silicon

Ion implantation of dopant impurities into semiconductors offers numerous potential advantages. However, because of the limited knowledge presently available on the annealing of lattice damage, the implantation profile and the electrical characteristics of implanted layers, a considerable amount of investigation is required before this doping technique can be put to practical use. Experimentally obtained implantation profiles and electrical conductivity characteristics of high energy (above 1 Mev) dopant ion implants into silicon are presented. Some preliminary results of ion implantation on silicon dioxide and on the resulting devices are also included.     

Carrier Removal Effects in Neutron-Irradiated Lithium-Doped Silicon

Carrier removal effects in n-type silicon as a result of neutron irradiation and subsequent heat treatment have been monitored by Hall effect and conductivity measurements at a temperature of 275°K. Samples of float-zoned, crucible, and Lopex grown (?=100 to 0.3?-cm) phosphorus-doped silicon and float-zoned and Lopex grown (?= 30 to 0.3?-cm) lithium-doped silicon were irradiated at ambient temperature with ~5-MeV neutrons and, subsequently, heat-treated between 20 and 200°C. The carrier removal rates for the lithium-doped samples, 7 to 75 cm-1 were significantly higher than the removal rates observed in the conventionally-doped samples, 6 to 12 cm-1. In addition, the lithium-doped material exhibited a strong dependence of removal rate on dopant concentration; whereas, the data for the conventional samples were relatively independent of dopant level. Upon subsequent heat-treatment, the lithium-doped samples showed continued carrier removal, while the phosphorus-doped samples tended to recover to a preirradiation condition. The enhanced carrier removal in the lithiumdoped material was found to be consistent with the removal of positively-charged lithium donors from a state of electrical activity by ion-drift to the negatively-charged defect cluster. Relevant parameters yielded by this model are: a defect cluster radius of 300A, a cluster charge of -150e, and an effective capture radius for the lithiumdrift of 2500?. The continued carrier removal in the heattreated, lithium-doped silicon follows kinetics expected for the precipitation of lithium at the neutron-produced defect cluster sites through a diffusion-limited process. The model yields an activation energy of ~0.62 eV which compares well with the ~ 0.     

Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing

High intensity light pulse irradiation of monocrystalline silicon wafers is usually accompanied by inhomogeneous surface melting. The aim of the present work is to induce homogeneous buried melting in silicon by germanium implantation and subsequent flash lamp annealing. For this purpose high dose, high energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp irradiation at high energy densities leads to local melting of the germanium rich buried layer, whereby the thickness of the molten layer depends on the irradiation energy density. During the cooling down epitaxial crystallization takes place resulting in a largely defect-free layer. The combination of buried melting and dopant segregation has the potential to produce unusually buried doping profiles or to create strained silicon structures.     

Electron paramagnetic resonance study of proton implantation induced defects in monocrystalline 4H– and 6H–SiC

Ion implantation is frequently employed in SiC for doping, electrical isolation or in the SiC on isolator technology. The ion implantation process is accompanied by the formation of intrinsic defects, which introduce deep electron and hole traps. They are believed to be mainly multivacancy complexes but the exact microscopic nature of these defects and their distribution versus the ion penetration depth is not well established. We have analyzed by electron paramagnetic resonance spectroscopy the defects introduced by high energy (MeV) proton implantation. In this study we extend the previous investigations on n-type SiC to the case of p-type Al doped bulk samples. Both silicon monovacancy and carbon vacancy related defects are observed. Their nature and introduction rate have been determined. The results obtained will be compared to the published electrical studies in order to correlate the vacancy defects with the known electron and hole traps.     

Surface bioactivity of plasma implanted silicon and amorphous carbon

Plasma immersion ion implantation and deposition (PⅢ&D) has been shown to be an effective technique to enhance the surface bioactivity of materials. In this paper, recent progress made in our laboratory on plasma surface modification single-crystal silicon and amorphous carbon is reviewed. Silicon is the most important material in the integrated circuit industry but its surface biocompatibility has not been investigated in details. We have recently performed hydrogen PⅢ into silicon and observed the biomimetic growth of apatite on its surface in simulated body fluid. Diamond-like carbon (DLC) is widely used in the industry due to its excellent mechanical properties and chemical inertness. The use of this material in biomedical engineering has also attracted much attention. It has been observed in our laboratory that doping DLC with nitrogen by means of PⅢ can improve the surface blood compatibility. The properties as well as in vitro biological test results will be discussed in this article.     

Applications of MeV ion beams to material processing

The development of commercial ion implanters capable of implanting a wide range of elements with multi MeV energies has enabled ion implantation to be applied effectively to the modification of materials to a depth of several micrometers. For a silicon semiconductor technology the depth of penetration enables buried layers to be placed behind device structures to act as electrically isolating barriers. For high mass binary or ternary semiconductors, MeV ion implantation may be the only method of doping without resorting to chemically less pure film deposition techniques which tend to be unsuitable for large scale integration. In metals relatively thick (~1 μm) coatings can be penetrated to improve adhesion. Also, the corrosion properties of metals may be altered by changing the oxidation properties or by the creation of thick amorphous alloy coatings. With these effects come the added advantages that the smoothness and continuity of the surface is retained or may be enhanced. For polymers, MeV implantation enables thick electronic, wear or chemical modifications to be made to the material without loss of bulk integrity or properties.     

Critical issues in the formation of quantum computer test structures by ion implantation

The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO₂/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, ¹²¹Sb²⁵⁺, in SiO₂/Si is also discussed.     

The generation of shallow dopant layers by low-angle implantation

A simple arrangement for the generation of shallow dopant profiled by low-angle ion implantation is described. High resolution Rutherford backscattering has been employed to measure profiles of arsenic and antimony which have been obtained by implantation into (100) silicon at angles of incidence as low as 4° with respect to the wafer surface. These profiles have been compared with Monte Carlo calculations using the TRIM II code and found to be in good agreement. Electrical activity > 5 × 10¹⁹ cm^?3 has been achieved for dopant profiles with peak concentrations within 30 Å of the surface. The technique is amenable to the generation of tailored (e.g. uniform) implantation profiles at constant energy by variation of implant angle.     

The production of non linear damage under molecular ion implantation

Germanium atomic (Ge₁) and molecular ions (Ge₂) of equivalent energy are implanted in silicon at an elevated temperature. The ion induced damage has been characterized by RBS channeling (RBS/C) and positron annihilation spectroscopy. The RBS/C studies indicate that the molecular ion implantation has produced more defects in the near surface regions compared to the atomic ion implantation. This paper reports a first time observation of an enhanced production of vacancy related defects in silicon implanted with molecular ions.     

碳及碳团簇负离子注入硅橡胶细胞相容性研究

通过在GIC4117串列加速器前注入器加装注入靶架以及扫描系统,建立了低能负离子注入平台,实现具有"Charge-up free"优点的负离子以及团簇负离子的注入,从而进行了碳及碳团簇负离子注入硅橡胶细胞相容性研究。水接触角测量表明,随着注入剂量增大到3×1015 cm-2,材料表面的水接触角从108.7°减小到103.1°,表面亲水性得到改善。XPS测试表明,随着注入剂量的增加,样品中碳含量逐渐减小,而氧和氮含量逐渐增加。基于上述结果对负离子注入硅橡胶细胞相容性改善的机制进行了讨论,最后在样品上进行了细胞培养实验。结果表明,负离子注入法是一种简单、有效提升硅橡胶细胞相容性的方法。     

注砷硅片低能电子束退火

本文报道了用低能大面积电子束处理注砷硅片的实验结果。由四探针和背散射、沟道效应测量结果表明，用本方法退火的样品具有电激活率高和砷原子再分布小的优点。     

Surface bioactivity of plasma implanted silicon and amorphous carbon

1 Introduction tors.[10,11] In addition, it has been shown that the criti- cal concentration of ionic products dissolved from the Since the discovery of SiO2-based bioglass in bioactive glass composed of soluble silicon and cal-1969,[1] possible applications of silicon-containing cium ions can enhance osteogenesis th…     

TEM studies of the defects introduced by ion implantation in SiC

We have undertaken a systematic study of the defects formed by ion implantation in SiC for a large variety of experimental conditions. B, N, Al and Ne ions were implanted into 6H–SiC at room temperature RT and at 650°C. Multiple energy implants were carried out in order to obtain “flat” dopant profiles. The samples were annealed from 1100°C to 1750°C for various duration times. Transmission Electron Microscopy (TEM) analysis was carried out on cross-sectional samples using weak beam dark field imaging conditions. All these defects are of interstitial type (clusters or loops). A statistical analysis of digital images was performed to extract the depth-distributions of the defects. The depth-distributions were compared with Monte-Carlo simulations of the ion implantation process. It is shown that when implanted at RT, the defect distributions follow the “damage” profiles i.e., defects appear in regions where atomic displacements occur in the target. In contrast, the defects found after implantation at 650°C always mirror the “range” profile before and after annealing. We show that there is a concentration threshold under which no defect appear. These results are discussed in terms of point defect annihilation, clustering and dopant activation in SiC.     

Plasma immersion ion implantation for metallurgical and semiconductor research and development

Plasma Source Ion Implantation, also termed Plasma Immersion Ion Implantation, is a rapidly developing material modification technique for treating the near-surface regions of various kinds of materials. It makes use of high-energy ions which are accelerated by a high voltage pulse from a plasma which wraps the workpiece to be treated. The ions are implanted into the material causing effects similar to those of conventional beam-line ion implantation. Research and development of plasma immersion ion implantation has focused in two main fields, treatment of metals for improved wear and corrosion performance, and modification of semiconductors. The paper discusses examples from both fields, with nitrogen PIII of steels and aluminum, and modification of thin metal films. From the semiconductor field, trenchwall doping, ultra-shallow doping with boron, and oxygen ion implantation for SIMOX formation is treated.     

Surface modifications and erosion yields of silicon and titanium doped graphites due to low energy D bombardment

Influences of low energy D⁺ ion bombardment and target temperature on surface topography, surface concentration and erosion yield of carbon based binary compounds were investigated. The samples contained 10 at.% Si and 10 at.% Ti, respectively. The surface concentration was determined in situ by Auger electron spectroscopy and the topography ex situ by scanning electron microscopy. During low energy D⁺ bombardment a pronounced conelike surface developed with silicon respective titanium rich ‘caps’ protecting the underlaying carbon rich shafts from erosion. The average dopant surface concentration was up to 7 × the bulk concentration. The erosion mechanism was determined by surface concentration and chemical state of the surface: At high temperatures carbidic bindings dominated, while at room temperature a mixture of graphite and carbide covered the surface.     

A molecular dynamics study of the clustering of implanted potassium in multiwalled carbon nanotubes

We have studied the low energy irradiation of carbon nanotubes (CNT) with K ions using classical molecular dynamics simulations with analytical potentials. The studied CNTs had diameters of about 0.5–1.2 nm and single or multiple walls. The average penetration depth and probabilities to introduce an impurity atom into CNT were studied with simulations on irradiating the CNT with single K ion. The number of potassium clusters, their average sizes and the damage produced into the CNT due to the irradiation were studied using multiple K ion irradiations. We found that the K ions are mobile in CNTs right after the implantation event and that they cluster together. For CNTs with 1–3 coaxial tubes, the highest ratio of K atoms in clusters per total number of K ions was obtained by using an irradiation energy of about 100 eV. Also the least damage per K ion was found to be produced into the CNT with this energy when those energies high enough for the ion to penetrate the outermost wall of the CNT were considered.     

The point defect engineering approaches for ultra-shallow boron junction formation in silicon

When high energy heavy ions bombard a single crystal, such as MeV Si implantation in Si, the surface region becomes vacancy-rich, while interstitials are mostly distributed near the range of the implants. We have demonstrated that vacancy retards while interstitial enhances boron thermal diffusion in silicon. In this paper we will show experimental results on the modification of boron diffusivity by point defect engineering, and its application in ultra-shallow junction (10 nm) formation. In this paper, we will also show cluster ion, such as GeB and SiB, implantation in silicon, and two-stage annealing in forming ultra shallow junction in Si. RBS, channeling, nuclear reaction, and secondary ion mass spectrometry are used for this studies.     

Mechanisms of damage formation in semiconductors

The damage accumulation in ion-implanted semiconductors is analysed using Rutherford backscattering spectrometry (RBS). When energetic ions are implanted in a material, they transfer their energy mainly into atomic collision processes (nuclear energy loss) and in electronic excitations (electronic energy loss). For a given material this primary energy deposition is determined by the mass and energy of the implanted ions and the ion fluence (number of ions per unit area). However, the damage concentration which is measured after implantation does not only depend on the primary energy deposition, but is strongly influenced by secondary effects like defect annealing and defect transformation. For the latter processes the target temperature and the ion flux (number of ions per unit area and time) play an important role. In this presentation the influence of the various parameters mentioned above on the damage accumulation is demonstrated for various materials. Simple empirical models are applied to get information about the processes occurring and to systematize the results for the various semiconductors.     

Defect Clusters in Electron-Irradiated Silicon

Calculations of the formation of disordered regions in silicon due to irradiation by high energy (15-45 MeV) electrons indicate that a sufficient concentration of defect clusters is produced to affect the electrical properties of the material. Isochronal annealing of room temperature radiation-induced degradation in the short-circuit current of silicon solar cells and in the minority carrier lifetime of the p-type base region is studied up to 500°C. The existence of a low temperature (50-200°C) annealing stage is shown to be independent of dopant and oxygen impurity concentration. It is inferred that this stage, which is similar to those observed in fast neutron- and in proton-irradiated silicon, is characteristic of cluster formation.     

Intensive irradiation of carbon nanotubes by Si ion beam

Multi-walled carbon nanotubes were irradiated with 40 keV Si ion beam to a dose of 1×10^7 cm^-2. The multiple-way carbon nanowire junctions and the Si doping in carbon nanowires were realized. Moreover, the formation processes of carbon nanowire junctions and the corresponding mechanism were studied.