Soji Miyagawa

Computer simulation of dose effects on composition profiles under ion implantation

Here is presented a computer code ‘‘dynamic sasamal,’’ which has been developed to simulate the dose dependence of concentration profiles and sputtering yields under ion implantations. The model calculations have been applied for high dose implantations of 50‐keV nitrogen into zirconium and aluminum. The results are compared with composition profiles obtained by Rutherford backscattering spectrometry (RBS) and with semiempirical values. In the case of Zr, agreements between calculated composition profiles and experimental profiles obtained by RBS analysis were excellent for all fluences up to 1018 ions/cm2 and the calculated sputtering yield decreased toward the semiempirical value with the increase of the fluence. In the case of Al, for fluences up to 7.5×1017 ions/cm2, the composition profiles obtained by RBS measurements agreed well with the calculated results, but for a fluence of 1×1018 ions/cm2, the measured profile deviated from the calculated one; while the calculations assume a saturation concentration equal to the saturated nitride phase, nitrogen concentrations of 55% were measured within the mean ion range.

Analytical formulas for ionization cross sections and coster-kronig corrected fluorescence yields of the L1, L2, and L3 subshells

We present analytical formulas for three L-subshell ionization cross sections for proton impact based on the recent experimental data and for the Coster-Kronig corrected fluorescence yields based on the theoretical values due to Chen et al. and due to McGuire. Total L X-ray production cross sections were calculated using the analytical formulas and compared with experimental values. As a result, our semi-empirical values using the formulas fitted to the values of Chen et al. coincided with the experimental values very well. Furthermore our values for Lα, Lβ, Lγ, Lη, and Ll X-ray production cross sections calculated using the analytical L1, L2, and L3 Subshell ionization cross sections, and the theoretical values of the fluorescent yields and of the Coster-Kronig transition probabilities due to Chen et al. also agreed with the experimental values.

Surface structure of silicon carbide irradiated with helium ions with monoenergy and continuous energy distributions

Silicon carbide was irradiated at room temperature and 600 °C with helium ions with monoenergy (3–100 keV) and continuous energy distribution ranging from 0.5 keV to 20 keV up to a total dose of 1×1019 ions/cm2 using an ion accelerator controlled by a microcomputer. For room temperature irradiation, porous structures appear on the surface of samples irradiated to dose of ∼5×1018 ions/cm2, and the damaged layer is easily removed from underlying undamaged layer by ultrasonic vibrations. On the other hand, for target temperature of 600 °C, such porous surface structures are not observed, which is due to thermal annealing. It has been shown that the surface deformation depends strongly not only on the implantation profile, but also on irradiation modes of helium ions. Flaking is completely avoided by prebombardment of helium ions with continuous energy distribution, which deliberately produces a pathway for gas release. In order to simulate wall erosion due to helium bombardment, silicon carbide was also irra...

Computer simulation of ion beam penetration in amorphous target

The formalism for a Monte‐Carlo computer code using a liquid model is presented. One of the characteristic features of this program is a constant free flight path length between collisions and the other is the thoroughgoing usage of the fitting formula to the nuclear scattering cross section, minimum energy transfer, and free flight path shortening. This allows for a rapid and accurate assesment of an ion’s direction and energy loss resulting from nuclear collisions. For nuclear scattering, an approximation formula derived by Kalbitzer and Oetzmann was used and the results are compared with those obtained using the formula derived by Winterbon, Sigmund, and Sanders. Both results are compared with experiments, with the results obtained using gas‐like model and also with other well‐established programs marlowe and trim.

Deposition of diamond-like carbon films using plasma source ion implantation with pulsed plasmas

Abstract Recently a pulsed inductively coupled plasma source suitable for plasma-based ion implantation has been developed. The use of a pulsed plasma for plasma source ion implantation (PSII) processing takes advantage of the fact that a high-density plasma can be obtained with low average power because of the shortening of the plasma ignition time. A time resolved plasma density and the spatial profiles of the pulsed inductive RF plasma for the PSII method were measured. Under the optimal condition of the pulsed plasma, DLC thin films were successfully deposited on silicon substrates using Ar, CH 4 and C 7 H 8 gases, and the effects of the implantation voltage on the hydrogen concentration and the deposition rate of DLC coating were measured in the range of 5–20 kV. It was found that the deposition rate decreased with increasing implantation voltage and the hydrogen concentration was within 15–22 at.%.

HIGH-ENERGY CU AND O ION CO-IMPLANTATION INTO SILICA GLASSES

Abstract Optical and structural changes of silica glass substrates implanted with Cu and O ions and subjected to thermal annealing, are examined as a function of the implantation sequence by optical absorption, Rutherford Backscattering Spectrometry (RBS) and thin film X-ray diffraction (XRD) measurements. Before annealing, the distribution of Cu is affected by the implantation sequence and O- followed by Cu-implantation leads to fewer Cu nanoparticles than the Cu- followed by O ion implantation. After annealing, however, the redistribution behavior of Cu and optical absorption features are similar for both co-implanted samples. Nanocrystals of Cu2O are mainly formed by annealing and the absorption peaks at about 340, 450 and 480 nm are observed for the co-implanted samples. The peaks are possibly evidence for the presence of the copper oxide nanocrystals.

Dynamic MC simulations of diamond-like carbon film synthesis by plasma-based ion implantation

Abstract By plasma-based ion implantation (PBII) such as low-energy ion beam implantation in plasma, ion beam assisted deposition, and plasma immersed ion implantation, a diamond-like carbon (DLC) film is synthesized. The structure of the DLC film can be characterized by the hydrogen concentration and the relative fractions of sp 2 - and sp 3 -bonded carbon. The energy of the impinging ion plays a crucial role for the film structure and thereby the mechanical, electrical and optical properties of the film. Dynamic Monte Carlo simulations with the binary collision approximation have been applied to the synthesis of DLC films by PBII. It was assumed that energetic CH 3 + ions and CH 3 radicals are incident on the surface alternately. The incident molecular ions dissociated into its individual atoms when colliding with the surface. The radicals adsorbed on the surface are dissociated by the binary collisions with the impinged atoms and a part of hydrogen atoms are released from the surface. It is assumed that only the atoms receiving enough energy to overcome the surface barrier enter the solid. Release of the displaced hydrogen atoms after the subsequent collision cascade is also assumed. The relative fraction of carbon atoms in the sp 2 and sp 3 state were estimated by setting different displacement threshold energy for each state. Effects of the ion/neutral arrival ratio and the ion energy on the deposition rate and on the depth profile of the hydrogen content and the sp 3 /sp 2 ratio in the deposited film are presented.

Formation of β‐Si3N4 by nitrogen implantation into SiC

Polycrystalline β‐SiC samples were implanted with 50 keV 15N ions with fluences ranging from 3×1017 to 1.5×1018 ions/cm2 at elevated temperature up to 1100 °C. Nitrogen depth profiles were measured as a function of implantation temperature and annealing temperature using nuclear reaction analysis, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. It was found that the maximum concentration and the width of nitrogen depth profiles implanted at 1100 °C were reduced distinctly in comparison with the profiles implanted below 930 °C or annealed at 1100 °C. The redistribution of nitrogen implanted in SiC at 1100 °C was ascribed to the formation of β‐Si3N4 crystallites in SiC, which was confirmed by x‐ray diffraction at glancing incidence.

High fluence implantation of nitrogen into titanium: Fluence dependence of sputtering yield, retained fluence and nitrogen depth profile

Abstract Nitrides are formed by high-fluence nitrogen implantation into various metallic targets, and their surface properties are improved. Among them, titanium nitride formation is of great interest in a wide range of technological applications. For nitrogen implantation into Ti with implantation energies of 10 keV to 1 MeV and fluences up to 1 × 1019 ions cm−2, the fluence dependence of sputtering yield, retained fluence and nitrogen depth profiles as well as the implantation energy dependence of saturated thickness of a nitride layer were calculated by computer simulation using the “dynamic SASAMAL” code with various values of threshold displacement energy (Ed) and surface binding energy (Es). The calculated results with Ed = 10 eV and Es = 1.6 eV for nitrogen agreed well with experimental values of the sputtering yield, the depth profile and the retained fluence of nitrogen obtained by Rutherford backscattering spectrometry and resonant nuclear reaction analysis for 50 keV nitrogen implantation at fluences of 6 × 1016 to 2 × 1018 ions cm−2. The thickness of the nitrogen-implanted layer saturated at high fluence and it was nearly equal to the sum of the mean projected range and the straggling value for all energies from 10 keV to 1 MeV.

Thermal behaviour of nitrogen implanted into zirconium

Abstract Zirconium films were implanted with 15 N ions of energy 50 keV to a total fluence of 1 × 10 18 ions cm -2 in an attempt to study the formation process and thermal stability of ZrN layers produced by high fluence implantation of nitrogen. Subsequent to the implantation at room temperature, samples were annealed at temperatures of 300 °C–900 °C. The depth profiles of the implanted nitrogen were measured by nuclear reaction analysis using the 15 N(p,αγ) 12 C at E R = 429 keV, and the surfaces were examined by thin film X-ray diffraction (XRD) and scanning electron microscopy. There were many blisters 0.2–0.4 μm in diameter on the surface of the as-implanted samples and double peaks were observed in the nitrogen depth profiles; they were in both sides of the mean projected range. It was found that most of the blisters became extinct after annealing above 400 °C, and the XRD peak (111) intensity was increased with the increase in the annealing temperature. Moreover, 14 N and 15 N implantations were superimposed on Zr samples in order to study the atomic migration of nitrogen at each stage of high fluence implantation. It was found that the decrease in the peak at the deeper layers was related to blister extinction and nitrogen diffusion into underling zirconium which could be correlated with radiation damage induced by post-implanted ions.