Conventional Ion Implantation Research Articles

Doping of semiconductors using radiation defects produced by irradiation with protons and alpha particles

One of the modern methods for modifying semiconductors using beams of protons and alpha particles is analyzed; this modification is accomplished by the controlled introduction of radiation defects into the semiconductor. It is shown that doping semiconductors with radiation defects produced by irradiation with light ions opens up fresh opportunities for controlling the properties of semiconducting materials and for the development of new devices designed for optoelectronics, microelectronics, and nanoelectronics based on these materials; these devices differ favorably from those obtained by conventional doping methods, i.e., by diffusion, epitaxy, and ion implantation.

A new thermally assisted, plasma based, ionic implantation system of treatment and deposition.

Plasma based ionic implantation (PBII) is a new alternative to conventional ion implantation to produce near-surface treatments, layer growth or semiconductor doping, with the advantage of being non-directional. Furthermore, it can be used for improving the corrosion, friction and wear resisting properties of materials. This paper describes the development of a thermally assisted plasma immersion implantation reactor (TAPIIR). The system aimed at treating samples in the 0.5–60 keV range, with temperature regulation up to 1000°C. Thermochemical treatments, like the nitriding of steels or aluminium, are studied with a separate implantation and diffusion parameter control.

Ultrashallow and Low-Leakage p+n Junction Formation by Plasma Immersion Ion Implantation (PIII) and Low-Temperature Post-Implantation Annealing

p+n junctions are fabricated by the combination of BF3 plasma immersion ion implantation (PIII) and low-temperature post-implantation annealing. Ultrashallow junctions and very low leakage currents (∼10-11 A at -1 V in 1 mm2 junctions) have been obtained. Despite the fact that the activation of the PIII layer is not sufficient, the I–V characteristics obtained are comparable to those of junctions formed by conventional ion implantation. By a combination of Si+ preamorphization and BF3 PIII aimed to improve the dopant activation, a maximum surface concentration of activated boron higher than 1020 cm-3 is obtained in 550°C annealing for p+n junctions with 5 nm depth. The leakage currents, however, are increased by the Si+ implantation in low-temperature post-implantation annealing.

Plasma immersion ion implantation for silicon processing

Plasma Immersion Ion Implantation (PIII) is a technology which is currently widely investigated as an alternative to conventional beam line implantation for ultrashallow doping beyond the 0.15 μm technology. However, there are several other application areas in modern semiconductor processing. In this paper a detailed discussion of the PIII process for semiconductors and of actual as well as future applications is given. Besides the well known advantages of PIII — fast process, implantation of the whole surface, low cost of ownership — several peculiarities — like spread of the implantation energy due to finite rise time or collisions, no mass separation, high secondary electron emission — must be mentioned. However, they can be overcome by adjusting the system and the process parameters. Considering the applications, ultrashallow junction formation by PIII is an established industrial process, whereas SIMOX and Smart-Cut by oxygen and hydrogen implantation are current topics between research and introduction into industry. Further applications of PIII, of which some already are research topics and some are only investigated by conventional ion implantation, include seeding for metal deposition, gettering of metal impurities, etch stop layers and helium implantation for localized lifetime control.

Isotope-beam modification of materials at eV energies

We developed a low energy ion beam deposition system for isotope-selective modification of materials. It consists of a conventional ion implanter (HVEE 500 kV) and an attachable deceleration system. 29(N 2) + ion beams were used for the nitridation of Si(0 0 1) and the resulting 15N retained doses and profiles were determined by narrow nuclear resonance profiling. 29Si was deposited on amorphous carbon films on Si(0 0 1) and the doses evaluated by channeled α particle beams with detection of scattered α at grazing angles. 29Si was also deposited on Si(0 0 1) and the resulting profiles determined by narrow nuclear resonance.

Plasma immersion ion implantation for silicon processing

AbstractPlasma Immersion Ion Implantation (PIII) is a technology which is currently widely investigated as an alternative to conventional beam line implantation for ultrashallow doping beyond the 0.15 μm technology. However, there are several other application areas in modern semiconductor processing. In this paper a detailed discussion of the PIII process for semiconductors and of actual as well as future applications is given. Besides the well known advantages of PIII — fast process, implantation of the whole surface, low cost of ownership — several peculiarities — like spread of the implantation energy due to finite rise time or collisions, no mass separation, high secondary electron emission — must be mentioned. However, they can be overcome by adjusting the system and the process parameters. Considering the applications, ultrashallow junction formation by PIII is an established industrial process, whereas SIMOX and Smart‐Cut by oxygen and hydrogen implantation are current topics between research and introduction into industry. Further applications of PIII, of which some already are research topics and some are only investigated by conventional ion implantation, include seeding for metal deposition, gettering of metal impurities, etch stop layers and helium implantation for localized lifetime control.

Nano-indentation testing for plasma-based ion-implanted surface of plastics

We have developed a technique to modify the surface of plastics to improve the hardness. Carbon ions were implanted with 20 and 10 keV energy into the plastic surface using the conventional ion-implantation and the plasma-based ion-implantation methods. The modified surface was loaded to 1 mN and unloaded using the diamond tip of the nano-indentation equipment. We found that the deformation of the modified surface was elastic deformation. According to the surface Young's modulus FEM simulation of plastics, surface Young's modulus was improved from 1.8 to 25 GPa using the plasma-based ion-implantation process.

Modeling of the relationship between implantation parameters and implantation dose during plasma immersion ion implantation

Plasma immersion ion implantation (PIII) has attracted wide interests since it emulates conventional ion-beam ion implantation (IBII) in niche applications. For instance, the technique has very high throughput, the implantation time is independent of the sample size, and samples with an irregular shape can be implanted without complex beam scanning or sample manipulation. However, unlike conventional ion-beam ion implantation (IBII), prediction of the implantation dose and consequent process optimization are very difficult without extensive experiments since the incident ion flux is related to the implantation parameters such as accelerating voltage, pulse duration, and so on in a complex manner. Even though individual parameters have been investigated, there has not been a unified and user-friendly model to numerically predict the implantation dose under different plasma and processing conditions. In this letter, we present a one-dimensional analytical model to simulate the effects of parameter variations on the incident ion dose and to predict the implantation dose. The derived model is quite simple and applicable to planar targets such as silicon wafers. It will be an invaluable tool to process engineers in microelectronics working on silicon-on-insulator (SOI) formation by PIII and plasma doping.

Modeling of incident particle energy distribution in plasma immersion ion implantation

Plasma immersion ion implantation is an effective surface modification technique. Unlike conventional beam-line ion implantation, it features ion acceleration/implantation through a plasma sheath in a pulsed mode and non-line-of-sight operation. Consequently, the shape of the sample voltage pulse, especially the finite rise time due to capacitance effects of the hardware, has a large influence on the energy spectra of the incident ions. In this article, we present a simple and effective analytical model to predict and calculate the energy distribution of the incident ions. The validity of the model is corroborated experimentally. Our results indicate that the ion energy distribution is determined by the ratio of the total pulse duration to the sample voltage rise time but independent of the plasma composition, ion species, and implantation voltage, subsequently leading to the simple analytical expressions. The ion energy spectrum has basically two superimposed components, a high-energy one for the majority of the ions implanted during the plateau region of the voltage pulse as well as a low-energy one encompassing ions implanted during the finite rise time of the voltage pulses. The lowest-energy component is attributed to a small initial expanding sheath obeying the Child-Langmuir law. Our model can also deal with broadening of the energy spectra due to molecular ions such as N2+ or O2+, in which case each implanted atom only carries a fraction (in this case, half) of the total acceleration energy.

Plasma-based low-energy ion implantation for low-temperature surface engineering

This paper summarizes the plasma-based low-energy ion implantation technique, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, developed from a combination of two techniques based on conventional plasma-based ion implantation and low-energy ion beam implantation for improvement in wear resistance and corrosion resistance for metals and alloys. An electron cyclotron resonance (ECR) microwave plasma source is used to produce the plasma with the high plasma density, electron temperature and ionization degree. The ions are accelerated from the plasma by a low pulsed negative bias of −0.4–−3 kV, which is similar to the cathode potential of conventional plasma thermo-chemical diffusion processing. The low process temperature is in the range from 150°C to 500°C, which corresponds to the upper limit of conventional ion beam implantation and to the lower limit of plasma thermo-chemical diffusion processing, respectively. Low-energy ion implantation and simultaneous indiffusion is the main mass transfer mechanism, and direct thermo-chemical diffusion absorption is an additional mass transfer mechanism for formation of the nitrided/carburized layer and thin film. It has been proved that plasma-based low-energy ion implantation technique has the potential for applications in industry for surface modification of metals and alloys.

HgCdTe photovoltaic detectors fabricated using a new junction formation technology

The current–voltage characteristics measured over a wide temperature range are reported for HgCdTe mid-wavelength infrared n-on-p photodiodes fabricated using a novel junction formation technology. The planar homojunction device junctions were formed on LPE grown vacancy doped HgCdTe using a reactive ion etching (RIE) plasma induced conversion process. The zero bias dynamic resistance–junction area product, RoA, was 4.6×107Ωcm2 at 80K and is comparable to the best planar diodes reported using conventional ion implantation junction formation technology. Arrhenius plots of RoA exhibit an activation energy equal to the bandgap, Eg, and show that the diodes are diffusion limited for temperatures ≥135K. A series of temperature dependent 1/f noise measurements were performed, indicating that the activation energy for 1/f noise in the region where the diodes are diffusion limited is 0.7Eg. Energies close to this value have previously been associated with Hg vacancies in HgCdTe. These results are similar to those obtained from high quality HgCdTe photodiodes fabricated using mature ion implantation technology. However, the plasma based technology used in this work is significantly less complex and does not require any high temperature annealing steps.

Characterisation of dark current in novel Hg 1− xCd xTe mid-wavelength infrared photovoltaic detectors based on n-on-p junctions formed by plasma-induced type conversion

This paper reports initial characterisation results for planar mid-wavelength infrared (MWIR) photodiodes fabricated using a novel reactive ion plasma-induced n-on-p junction formation technology on vacancy-doped p-type HgCdTe grown by LPE on CdZnTe substrates. The junction is formed without the need for post-implant annealing typically required by ion implantation junction formation techniques to repair damage or to move the junction away from damaged regions. The dark current and dynamic resistance, R d, of the fabricated photodiodes have been characterised as a function of temperature. At 80 K, the zero-bias dynamic resistance–junction area product ( R 0 A) of the diodes is 4.6×10 7 Ω cm 2, with the devices being diffusion limited down to ∼135 K. Dynamic resistance has been measured for temperatures between 80 and 195 K and biases between −200 and +150 mV. Modelling of the observed dark current has been undertaken using three distinct mechanisms, diffusion, generation–recombination, and trap-assisted tunnelling. The results show that the plasma-induced junction formation technique can produce high-performance planar HgCdTe photodiodes. The dark current mechanisms found in these devices are similar to those found in diodes formed using conventional ion implantation techniques.

Direct current plasma implantation using a grounded conducting grid

A novel plasma implantation technique performed in a low pressure steady state dc mode utilizing a grounded conducting grid on top of the wafer stage is presented. By numerically simulating the ion paths by the particle-in-cell method, it is observed that the ion paths are optimized for certain implant geometry. In the optimal configuration, the directional angle of the acceleration vector does not depend on the mass and charge state of the ions, and the ratio of the partial differential of the scalar potential φ along the radial and longitudinal directions remains constant for varying applied voltages. The retained dose and impact energy uniformity are totally determined by the ratio of the radius of the wafer stage r, radius of the vacuum chamber R, distance between the wafer stage and the grid H, and thickness of the wafer stage D. The optimal ratio is r:R:H:D=1:4:2.5:2, that is, suggesting a disk shape vacuum chamber, which is quite different from that of a conventional plasma immersion ion implanter. In addition to retaining the large area and parallel processing advantages of plasma immersion ion implantation (PIII), the implantation energy can be extended far beyond the limit of PIII as the technique obviates the use of the power modulator, which not only limits the implantation energy but also is the most expensive and technologically complex hardware component in a PIII system.

Single-Crystalline CoSi2 Layer Formation by Focused Ion Beam Synthesis

The effects of accumulated radiation damage which arise from the excessive current density employed during focused ion beam implantation are described. The dwell time during beam scanning significantly influences the focused ion beam synthesis of CoSi2 in Si. At sufficiently low accumulated damage, single-crystalline CoSi2 layers are obtained, similarly to conventional ion implantation. A procedure is described which enables the reduction of radiation damage induced by a focused ion beam to the level of conventional ion implantation. This is of importance for the formation of single-crystalline CoSi2 layers.

Pure high dose metal ion implantation using the plasma immersion technique

High energy implantation of metal ions can be carried out using conventional ion implantation with a mass-selected ion beam in scanned-spot mode by employing a broad-beam approach such as with a vacuum arc ion source, or by utilizing plasma immersion ion implantation with a metal plasma. For many high dose applications, the use of plasma immersion techniques offers a high-rate process, but the formation of a surface film along with the subsurface implanted layer is sometimes a severe or even fatal detriment. We describe here an operating mode of the metal plasma immersion approach by which pure implantation can be obtained. We have demonstrated the technique by carrying out Ti and Ta implantations at energies of about 80 and 120 keV for Ti and Ta, respectively, and doses on the order of 1×1017 ions/cm2. Our experiments show that virtually pure implantation without simultaneous surface deposition can be accomplished. Using proper synchronization of the metal arc and sample voltage pulse, the applied dose that deposits as a film versus the part that is energetically implanted (the deposition-to-implantation ratio) can be precisely controlled.

Visible photoluminescence in ion beam mixed SiO 2/Si/SiO 2 layers

Visible photoluminescence from silicon nanocrystals embedded in SiO 2 matrix by ion beam mixing was investigated. Photoluminescence spectra of ion beam mixed SiO 2/Si/SiO 2 films excited by an Ar-laser (457.9 nm) showed more intense luminescence with a peak centered at 720 nm than that prepared by the conventional ion implantation method. The formation of nanocrystals in SiO 2 matrix was confirmed by cross-sectional high resolution transmission electron microscopy. The red luminescence is attributed to the silicon nanocrystals produced by ion beam mixing.

Plasma nitriding of stainless steels at low temperatures

To avoid the drop in corrosion resistance of stainless steels in conventional nitriding (precipitation of CrN), low-temperature techniques like ion implantation, plasma immersion ion implantation (PIII, PI3) and low-temperature plasma nitriding were developed. In this investigation, four stainless-steel grades (ferritic: X6Cr17, austenitic–ferritic: X2CrNiMoN22.5.3, austenitic: X8CrNiTi18.10 and X5CrNi18.10) were plasma-nitrided between 250 and 500°C. Nitrogen-enriched layers with a high nitrogen content were produced, leading to a significant increase in surface hardness. X-ray diffraction indicated that CrN did not precipitate if treatment temperatures did not exceed 400°C. ‘Expanded austenite’ formed in the austenitic and duplex steels and Ë-nitride (Fe2N1−x) in the ferritic steel. The optically visible structure of the nitrided cases is comparable with that of the PIII layers, with higher charging densities being possible in the plasma nitriding. Also, in comparison to conventional ion implantation, large charges and parts with complicated shapes can be treated.

In situ sample temperature measurement in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an excellent surface modification technique because it is not restricted by the line-of-sight limitation that plagues conventional beamline ion implantation. However, the lack of in situ monitoring has hampered wider acceptance of the technique in industry. It is known that the implantation temperature has a large influence on the surface properties of the treated specimens in addition to the more obvious parameters such as implantation voltage, pulse duration, pulsing frequency, and so on. Direct measurement of the target temperature is complicated by the sample high voltage as well as by interference from the electromagnetic field and plasma. In this article, we present a novel interference-free, in situ temperature measurement technique employing a shielded thermocouple directly attached to the sample stage. Our experiments show that the setup can monitor the target temperature in real time, even under severe arcing conditions. Our results also indicate that in a hot filament glow discharge radiation heating is quite small, and sample heating is primarily caused by ion bombardment during the PIII cycles. The new design will open up other possibilities such as in situ dose monitoring if, for example, the thermocouple is replaced by a Faraday cup.

Ion implantation post-processing of amorphous carbon films

Abstract Ion implantation techniques were used to improve the hardness and wear resistance of sputtered hydrogenated amorphous carbon films and cathodic-arc non-hydrogenated amorphous carbon films. Conventional ion implantation and plasma immersion ion implantation and deposition techniques were used to implant the films with Si, Ti, Hf and W ions of mean energies in the ranges of 28–72 and 3–6 keV, respectively, and doses between 1×1015 and 1×1017 cm−2. Nanohardness measurements demonstrated an increase in the apparent film hardness, depending on the type, kinetic energy, and dose of implanted ions. The effect of the ion dose on the microstructure characteristics of implanted carbon films was studied by Raman spectroscopy. Continuous sliding tests and non-contact profilometry revealed an appreciable increase in the wear resistance of the ion implanted films. Differences in the hardness of implanted films are interpreted in terms of microstructural changes caused by competing mechanisms responsible for film densification, irradiation damage and increase of tetrahedral (sp3) bond configurations. It is shown that, under certain conditions, ion implantation post-processing techniques may significantly improve the nanohardness and sliding wear resistance of amorphous carbon films.

Nitrogen and boron implantation into austenitic stainless steel

Nitrogen and boron double implantation into austenitic stainless steel were performed to enhance further the beneficial properties of nitrogen implantation, especially to reduce the brittleness of the near surface region. Nitrogen was implanted using plasma immersion ion implantation while boron was subsequently implanted in this first experiment using a conventional ion implanter. The effects of the boron implantation were measured against expanded austenite samples annealed for the same duration as the boron implantation. No significant diffusion of the boron is observed, whereas the preimplanted nitrogen shows additional diffusion during the boron implantation. The boron implanted specimens exhibit an even higher wear resistance correlated with a slightly decreased surface hardness, than the already excellent values for expanded austenite.