Use Of Ion Implantation Research Articles

INFLUENCE OF ION IMPLANTATION ON THE SURFACE CHARACTERISTICS OF POLYCRYSTALLINE CdS LAYERS

PN-heterojunction type solar cells have been fabricated by immersing n-type polycrystalline CdS films in a solution containing copper ions, to form a p-type Cu 2 S layer over the CdS surface. The efficiency and stability of these devices have been found to be very dependent on the grain structure of the initial CdS layers but by the use of ion implantation to modify the structure of the CdS surface significant improvements in cell characteristics have been obtained. Evidence is provided to show that this improvement can be attributed to a reduction in the effective junction area of the cells.

Limitations on the Use of Ion Implantation for the Study of the Reactive Element Effect in β ‐ NiAl

Numerous investigations have used the ion implantation of reactive elements (RE) such as Y or Ce, to study their effect on the growth of external oxide scales on alloys. Ion implantation has, nevertheless, some specific limitations, especially in alloys. The most notable limitation occurs at temperatures >1000°C where, owing to the shallowness of implantation, any effects of the ion‐implanted RE are short‐lived and differ significantly from those observed for an RE alloy addition or an RE oxide dispersion. Additionally, in alumina‐forming alloy systems, particularly , implanted Y stabilizes the first‐forming, metastable . The retention of the scale on Y‐implanted substrates is a chemical effect of the high concentration of Y near the substrate surface and is not a result of the implantation process itself. The loss of the RE effect at high temperatures and long times for implanted alloys is related to the outward diffusion of the RE and the formation of RE‐rich oxides near the gas interface of the scale.

Use of ion implantation to study the corrosion of an austenitic steel in an oxidizing/sulphidizing atmosphere

AbstractThe beneficial effect of the addition by ion implantation of cerium on the corrosion behaviour of a 32Ni‐20Cr austenitic steel in a mixed oxidizing/sulphidizing environment, at 700 °C has been studied. Emphasis was placed on the initial stages of the corrosion process using a wide range of surface analytical techniques. Comparison is made with unimplanted material and also with xenon‐ and chromium‐implanted steel. The latter had no significant effect. In contrast Ce ion implantation improved the corrosion behaviour, which is probably due to a change in the nucleation stage of corrosion, leading to an improved quality of the oxide layer forming under the initial corrosion products. Factors which might contribute to this are discussed.

Ion beam techniques in microelectronics

The use of ion implantation for processing silicon devices and circuits is reviewed. Topics covered include lateral doping by high angle implantation, shallow and deep junction formation, well engineering for CMOS devices, gettering and ion beam synthesis. Applications to III–V compounds and large area electronics are also included.

Disintegration of C60 by heavy-ion irradiation.

The changes in resistivity in fullerene (${\mathrm{C}}_{60}$) films subjected to 320-keV Xe ion irradiation are investigated as a function of ion dose. From a comparison of this dependence with similar data on Xe irradiated diamond and with data on C implanted fused quartz, it is concluded that upon ion impact ${\mathrm{C}}_{60}$ clusters completely disintegrate. This disintegration releases about 60 carbon atoms which disperse among the remaining intact ${\mathrm{C}}_{60}$ spheres giving rise to hopping conductivity between isolated C atoms. The present finding may explain the negative results in the search for fullerenes conjectured to exist in instellar dust and may establish limitations on the use of ion implantation to dope fullerenes with the aim of synthesizing new forms of high-${\mathit{T}}_{\mathit{c}}$ superconductors.

Improvement of tribological properties by ion implantation

Many different measurements confirm that ion implantation changes the friction and wear behaviour, which are the most important properties of tribological systems. Unfortunately, these properties will not always be improved. In industrial application, very often different results of the effects of ion implantation into tools or machine components can be observed, even if the same materials are used. A very important reason for this is the different stresses on the tribological systems. Our own practical experience has so far proved ion implantation to be advantageous in the fields of cutting and milling tools, injection moulds, calibration tools for plastics extrusion, punches and dies, surgical instruments, and wear parts of combustion engines. Year by year, experience of the effective industrial use of ion implantation is gained. However, many investigations of tribometers and real engines using the on-line radionuclide wear measurement technique show us more and more that we are not yet able to understand the complicated physical and chemical reasons for the changes in tribological properties. We do not have a useful theory for the wear processes, so it is not possible to deduce the effects of ion implantation. Predictions can only be made from experience, and are poorly defined. This situation is the main reason for the slow introduction of ion implantation in industry. To find a new applicable theory of friction and wear, much more attention must be given to the following aspects of fundamental importance. o 1. (1) The energy input caused by friction, which is a function of the stress and other parameters of the tribosystem, within a short time leads to the appearance of energy islands, which are statistically distributed over the surfaces. The density of energy within these tiny energy islands is very high. 2. (2) One result of these high energy densities is a mutation of the material's composition and structure within a very thin layer of less than 100 nm underneath the surface. Another result is wear. 3. (3) Ion implantation also changes the composition and structure of the bulk material close to the surface. 4. (4) Together with the wearing surfaces, the mutating compositions and structures migrate into the depth of the material. Thus there is urgent need to increase our knowledge of the tribo-induced mutations of ion-implanted materials and their influence on the tribological properties. For that reason surface analyses have to be carried out to determine the composition and structure of the materials and the mutation caused by friction and wear. Complementary sensitive wear analysis will then enable new models and theories to be developed and corroborated. This is a difficult but interesting challenge to modern physicists, chemists and engineers.

Use of ion implantation for improving the adhesion of diamond-like carbon films deposited by means of other techniques

Nanoindentation and friction tests have been used to establish the beneficial effect of pre-implantation of low C fluences upon the adhesion of diamond-like coatings synthesized by a laser plasma or by plasma enhanced chemical vapour deposition. The improvement is attributed to an interfacial layer of carbide.

Oxygen ion source with plasma cathode

An ion source with a plasma cathode has been developed for long lifetime use in ion implanters. In this ion source, a plasma cathode replaces the conventional metallic filament used in a Freeman-type ion source. This ion source consists of two compartments, namely a plasma generator and an ion source chambers interconnected by a tapered narrow duct. The pressure difference between the two parts, maintained by differential pumping, prevents the feed gas from flowing into the plasma generator. With any combination of an argon plasma cathode and a feed gas of either fluoride (AsF 5, PF 5) or oxygen, the lifetime was found to be more than 90 h with an extraction voltage of 40 kV and a correspoding ion current density of 20 mA/cm 2, and a considerable amount of As +, P +, O +, and O 2 + ions were observed in mass spectra.

Effects of ion implantation on the hydration of Na beta "-alumina crystals

The ion-induced modifications of the water dissolution process and sodium release have been thoroughly investigated in sodium beta "-alumina single crystals by applying depth profiling techniques (Rutherford backscattering spectrometry, elastic recoil detection analysis and resonant nuclear reactions) for the characterization of leached surfaces. The authors observe modifications of etching and leaching rates in the case of irradiated samples, both depending on the energy deposited by the projectile. Combined with new results of the sodium profile modifications induced by ion implantation, such ion-induced effects give additional information on the processes which govern the surface modification of irradiated beta "-alumina crystals and which could be detrimental for the use of ion implantation in the development of micro-ionic devices.

The fate of implanted 19F ions in diamond and their theoretical modelling

The ubiquitous use of ion implantation and the simultaneous interest in the emplacement of selected impurities in the matrix of choice bring added emphasis to the need for a quantitative understanding of the residence sites adopted by such imputities. The time-dependent perturbed angular distribution technique has been used to study the case of fluorine implanted in diamond. Careful examination is presented of the dependence of the perturbation parameters on the characteristics of the implant sites. These comprehensive investigations reveal the power of the technique in the richness of detail exposed and make possible the theoretical modelling of the data.

Surface-emitting laser-based optical bistable switching device

The first experimental demonstration of a surface-normal bistable optical switching device based on the monolithic integration of a vertical-cavity surface-emitting laser and a pnpn photothyristor is reported. By the use of ion implantation, it is shown that the positive feedback in the photothyristor can be controlled, thus enabling the integration of both bistable and latching optical switches on the same epitaxial structure. High contrast (30 dB) and an optical gain of 8 are demonstrated.

An ion-implanted diamond metal-insulator-semiconductor field-effect transistor

A p-type conducting layer has been formed in a substrate of semi-insulating natural diamond (type IIa) by boron implantation. Silicon dioxide was deposited over this layer to make an insulated-gate field-effect transistor. Saturation and pinch-off were both observed at room temperature. The transconductance was 3.9 mu S-mm/sup -1/ and the output conductance was 60 nS-mm/sup -1/. This is the first reported use of ion implantation to successfully fabricate a field-effect device in diamond. >

In situ studies of silicide-mediated crystallization of amorphous Si

Metal silicides in thin films play an essential role in the increasingly fine-scale fabrication of integrated circuits. Although commonly produced by interfacial reaction between metal films and silicon, buried metal silicides have recently been produced in crystalline Si by ion-implantation. Cammarata et al., have reported the use of ion-implantation to form buried nickel silicide precipitates in amorphous Si thin films, in which the first (and only) phase to form was NiSi2. The kinetics of the nucleation and growth of NiSi2 precipitates were investigated and an enhancement of the crystallization kinetics of the amorphous Si, apparently due to the migration of silicide precipitates, was found. In this paper, we describe the results of an in-situ transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) investigation of the silicide-mediated crystallization of amorphous Si.

The influence of rapid thermal annealing on oxygen implant profiles in copper

This work is part of a general study examining the use of ion implantation and rapid thermal annealing (RTA) to produce high- T c films on copper substrates. The behavior of implanted oxygen in copper and also copper oxidation during rapid thermal annealing (10–30 s) is investigated. Samples of single-crystal copper were implanted with 60 keV 18O to a fluence of 2.5 × 10 16ions/cm 2. These samples were then subjected to rapid thermal annealing for 10 s in a protective atmosphere in order to determine how the oxygen profile alters during the course of the anneal. Copper oxidation during RTA was investigated using unimplanted samples which were annealed in air for 30 s time periods. Characterization of the implanted and oxidized layers was made using the 18O(p, α) 15N nuclear reaction. RBS. SIMS and glancing-angle X-ray diffraction.

Effects of ion implantation on the photoelectrochemical properties of TiO 2

The possible use of ion implantation for the control of photoelectrochemical properties has been studied for single-crystalline TiO 2. Thermionic ions (Na +, Li +) are implanted into TiO 2 (rutile) at energies of about 10 keV. Effects of ion implantation are evaluated in terms of the optical absorption spectra, the interfacial capacitance-voltage characteristics, and the photoelectrochemical current-voltage characteristics. It is shown that ion implantation is useful both for an enhancement in the absorption of visible light and for a shift of the flatband potential toward the negative side with respect to the reference electrode. Further studies are necessary in order to obtain the photoelectrochemical activation without the influence of irradiation damage.

Ion implanted Nd:YAG waveguide lasers

A detailed description of the use of ion implantation to create optical waveguides in laser crystals is given. Calculated mode profiles and lasing thresholds are shown to be in good agreement with experimental results in a monolithic planar waveguide Nd:YAG laser. The first fabrication and characterization of ion implanted channel waveguides in Nd:YAG is also reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Use of Ion Implantation for Lifetime Control in Silicon Devices

The Use of Ion Implantation for Lifetime Control in Silicon Devices

Development of Plasma Filament Ion Source for High Current Implanter.

A plasma filament ion source has been developed as a long-lived ion source for use in ion implantation. This ion source uses a primary discharge to serve as an electron source for a second discharge, which is formed into a plasma filament replacing a thermionic metallic filament used in the Freeman type ion source. The operation is relatively facile and good beam stability can be obtained. With any combination of a plasma filament of either argon or neon and a feed gas of either fluoride (AsF5, PF5, PF3, or BF3) or hydride (AsH3), the lifetime was found to be more than 90 hours with an extraction voltage of 40kV and the corresponding ion current density over 20mA/cm2. Mass spectrometry results show that this ion source has an ability of generating a considerable amount of As+ and P+ ions from AsF5 and PF5, and hence will be useful for realizing a fully cryopumped ion implanter system. This ion source is also eminently suitable for use in oxygen ion production.

Formation of AlGaAs by ion beam mixing of Al films on GaAs

There is considerable interest in the use of ion implantation for material synthesis. The synthesis of AlGaAs by dual implants of As+ and Al+ into GaAs followed by rapid thermal annealing (RTA) has been reported recently. In this paper results relating to the formation of AlxGa1-xAs by depositing thin Al films on GaAs substrates and irradiating with arsenic ions followed by RTA are presented.Aluminium layers of 580Å or 650Å in thickness were deposited onto liquid encapsulated Czochralski (LEC) grown samples of semi-insulating &lt;100&gt; GaAs. The deposition was done using pure aluminium on a heated filament at a chamber pressure of ∽10−6 Torr with the thickness being measured using a talystep. Subsquently As+ implants were performed at room temperature using an energy of 150, 200 or 300 keV and a dose of 3x1016 or 1x1017 cm−2. The implantation energy was selected to ensure that the projected depth exceeded the thickness of the Al overlayer employed.

Low-cost process for fabricating polysilicon transistors

A process for the fabrication of p-channel polysilicon MOS transistors is described. The process is compatible with the use of low-temperature glass substrates and replaces the use of ion implantation for the source/drain doping with in situ doped polysilicon. MOS transistors made with this process exhibit an on/off current ratio of 2.5*10/sup 5/, a mobility of 16 cm/sup 2//V-s, and a subthreshold slope of 1.3 V/decade.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>