Ion Mixing Effect Research Articles

1 MeV Au+ ion modification of Fe3O4-based epitaxial films

The effect of 1 MeV Au+ ion irradiations on the layer stability of the Fe3O4-based films grown epitaxially on MgO(001) substrates was investigated by Rutherford backscattering spectroscopy (RBS) and RBS-Channelling (RBS-C). The ion mixing effect leads to an appearance of the additional FeO x layer and a large enlargement of the thickness of the mixed (Fe,Mg,O) layer in the interfaces. Au+ ions were found to be implanted deeply in the MgO substrate. RBS-C experiments have confirmed that the heavy metallic ion irradiations induce a disorder in the crystalline lattice.

1 MeV Ar+ and Kr+ ion irradiation induced intermixing in single- and bi-layer Fe3O4 films grown on MgO(001) single crystals

The layer composition and crystallinity of single-layer Fe3O4(001) and bi-layer Fe3O4/Fe(001) thin films grown epitaxially on MgO(001) substrates have been investigated by Rutherford backscattering spectrometry (RBS), channeling experiments (RBS-C) and X-ray reflectometry (XRR). Four thin films with similar film layer structure but different layer thickness have been irradiated by 1 MeV Ar+ or 1 MeV Kr+ ion beam with ion fluences in the range of ~0.8–20.7 × 1016 ions/cm2 for a detail underlining the ion mixing effect and its influence on the layer stability. The ion fluence of 4.4 × 1016 Ar+/cm2 and 0.8 × 1016 Kr+/cm2 was enough to change the stoichiometry of the Fe3O4 layer in the single-layer Fe3O4 films, while the stoichiometric Fe3O4 layer on the surface of bi-layer films were well preserved at a much higher Ar+ and Kr+ ion fluence (20.7 × 1016 Ar+/cm2 and 2.5 × 1016 Kr+/cm2), despite that such ion fluencies could induce a complete oxidization of the buffer Fe layer. The stability of the Fe3O4 layer and the bilayer structure of the film after Ar+ ion irradiations at an ion fluence about 10 times larger than that of Kr+ ion indicate a high potential for practical applications of the bilayer magnetite films in an argon atmosphere.

Front and back side SIMS analysis of boron-doped delta-layer in diamond

Nowadays the availability of very thin diamond layers in the range of nanometers as well as the possibility to characterize such delta-layer structures are required for the field of photonics and spintronics, but also for the development of next generation high power devices involving boron doping. The fabrication of diamond structures with abrupt interfaces such as superlattices and quantum wells has been recently improved. A very accurate characterization is then essential even though the analysis of such structures is arduous and challenging. SIMS analyses are commonly used to obtain depth profiles of dopants. However, below 10nm in thickness, SIMS induced ion mixing effects which are no longer negligible. Then the raw SIMS profile might differ from the real dopant profile. In this study, we have analyzed a diamond structure containing a thin boron epilayer, especially synthesized to achieve SIMS analysis on both sides and to overcome the effects of ion mixing. We evidence the ion mixing induced by primary ions. Such a structure is a delta diamond layer, comparable to classical boron-doped delta-layer in silicon. Our results show that the growth of boron-doped delta-layer in diamond is now well controlled in terms of thickness and interfaces.

A beneficial application of backside SIMS for the depth profiling characterization of implanted silicon

AbstractAfter ion implantation, annealing is needed to activate dopant and recover crystalline. However, in some annealing conditions there is a possibility that activation annealing forms defects in the implanted region, which may cause errors in SIMS depth profiles. The purpose of this study is to make clear the influence of defects generated during annealing on the conventional front‐side SIMS (FSS) depth profiles, and to provide proper measurement condition to get accurate depth profiles using back‐side SIMS (BSS) technique as another beneficial application. In this study, BF2 were implanted into crystalline silicon, and three different samples were treated, respectively, as implanted, 750 and 900° annealing. In an as‐implanted sample, BSS depth profiles of boron confirmed those obtained by FSS. On the other hand, in annealed samples, BSS depth profiles were steeper than those of FSS. This result suggests that the degradation of depth resolution in FSS cannot be explained only by the effect of ion mixing due to primary ions, but may be related with the crystalline structure in the implanted region. Therefore, BSS techniques can also be indispensable for getting more precise depth profiles in the implanted region of silicon. Copyright © 2010 John Wiley & Sons, Ltd.

Effects of CPII implantation on the characteristics of diamond-like carbon films

A diamond-like carbon film (DLC) was successfully synthesized using a hybrid PVD process, involving a filter arc deposition source (FAD) and a carbon plasma ion implanter (CPII). A quarter-torus plasma duct filter markedly reduced the density of the macro-particles. Graphite targets were used in FAD. Large electron and ion energies generated from the plasma duct facilitate the activation of carbon plasma and the deposition of high-quality DLC films. M2 tool steel was pre-implanted with 45 kV carbon ions before the DLC was deposited to enhance the adhesive and surface properties of the film. The ion mixing effect, the induction of residual stress and the phase transformation at the interface were significantly improved. The hardness of the DLC increased to 47.7 GPa and 56.5 GPa, and the wear life was prolonged to over 70 km with implantation fluences of 1 × 10 17 ions/cm 2 and 2 × 10 17 ions/cm 2, respectively.

New Approach for Improvement of Secondary Ion Mass Spectrometry Profile Analysis

In this paper, we describe the improvement of secondary ion mass spectrometry (SIMS) profile analysis by a new approach based on partial deconvolution combined with scale-frequency shrinkage. The SIMS profiles are obtained by analysis of the delta layers of boron doped silicon in a silicon matrix, analyzed using Cameca-Ims6f at oblique incidence. These profiles can be approximated closely by exponential-like tail distributions with decay length, which characterizes the collisional mixing effect. The partial deconvolution removes the residual ion mixing effect. The contributions of high-frequency noise are removed by shrinkage to a great extent of the profiles. It is shown that this approach leads to a marked improvement in depth resolution without producing artifacts and aberrations caused principally by noise. Furthermore, it is shown that the asymmetry of the delta layers, caused by the collisional mixing effect, is completely removed, the decay length is decreased by a factor of 4 compared with that before deconvolution.

Influence of ion mixing on the energy dependence of the ion-assisted chemical etch rate in reactive plasmas

Recently, Stafford et al. [Appl. Phys. Lett. 87, 071502 (2005)] have shown that in contrast to the etch yield on a saturated surface, the ion-assisted chemical etch rate cannot universally be modeled by a simple square-root energy dependence. This results from the surface coverage by reactive neutral species being also a function of the ion energy. In this work, we further point out that depending on the plasma-material combination, the etch rate can exhibit two regimes that are characterized by different dependences on the ion energy. While these results are inconsistent with currently available models, we show that they can be interpreted by taking into account ion mixing effects on the desorption rate of volatile reaction products involved in the model of Stafford et al. Application of this rate model to the etching of Si, SiO2, HfO2, and ZrO2 in chlorine and fluorine plasma chemistries provides an excellent description of the simultaneous dependence of the etch rate on ion energy and on ion and reactive neutral fluxes.

The study of ion mixed amorphous carbon films on single crystal silicon by C ion implantation

Amorphous-carbon (a-C) films were deposited on a single-crystal silicon substrate by vacuum vapor deposition system and these amorphous carbon films were implanted with 110 keV C + at fluences of 1 × 10 17 ions/cm 2 . The effect of ion mixing on the surface morphology, friction behavior and adhesion strengths of amorphous carbon films was examined making use of atomic force microscopy (AFM), ball-on-disk reciprocating friction tester, nano-indentation system and scanning electron microscope (SEM). The changes in chemical composition and structure were investigated by using X-ray photoelectron spectroscopy (XPS). The results show that the anti-wear life and adhesion of amorphous carbon films on the Si substrates were significantly increased by C ion implantation. The Si C chemical bonding across the interface plays a key role in the increase of adhesion strength and the anti-wear life of amorphous carbon film. The friction and wear mechanisms of amorphous carbon film under dry friction condition were also discussed.

Skew Ion-Bombardment-Induced Microstructure and Magnetic Anisotropy Evolutions in the Immiscible Co–Cu System during Deposition Process

Co–Cu alloy films with a metastable fcc structure were prepared using the ion beam assisted deposition (IBAD) technique at various ion incidence angles. The films prepared at the ion incidence angles of 15° to 60° showed the {220} out-of-plane texture and in-plane magnetic anisotropy. The fcc phase and hcp phase were obtained in the samples prepared at 75° and glancing incidence angle. It was regarded that the microstructure and magnetic anisotropy evolutions with variations of the ion incidence angle result from three main effects induced by ion interaction, i.e., ion mixing effect, channeling effect and enhancing effect of atomic migration in the ion incidence plane.

DLC films formed by hybrid pulse plasma coating (HPPC) system

A new coating system was developed which consists fundamentally of plasma CVD (chemical vapor deposition) and ion-mixing. The system employs pulsed-gas introduction, pulsed-plasma generation and plasma base ion implantation (PBII). In this paper the formation of DLC films by the HPPC system is reported. The plasma densities were measured using a Langmuir probe and a 10-GHz microwave interferometer. DLC films were formed on the surface of workpieces using hydrocarbon gases by the HPPC system, with monitoring plasma density during the coating process. Raman spectra of DLC films by the HPPC system are similar in shape to those by ion-plating, and the fractions of amorphous and graphite components in Raman spectrum gained by segregated four peaks decreased with the decrease of CH 4/C 7H 8 partial pressure ratios. The reason is considered that the larger the deposition rates of films become, the smaller the ion-mixing effects are. Furthermore, as the CH 4/C 7H 8 ratio becomes as low as 1, this phenomenon becomes more apparent. For the further study, the plasma density as well as the change in gas pressure in the chamber must be monitored for the formation of uniform DLC films.

Effect of ion mixing by C + implantation on friction and adhesion of amorphous carbon film on SiO 2

Amorphous carbon films on the SiO 2 substrates have been implanted with C ions with energy of 110 KeV and fluences ranging from 1×10 16 to 1×10 17 C cm −2. The effect of ion mixing on the friction behavior of amorphous carbon film and changes in chemical composition and structure were investigated. The results show that the anti-wear life and adhesion of amorphous carbon films on SiO 2 substrate were significantly increased by C ions implantation, especially when the fluence reached 1×10 17 C cm −2. The Si–C chemical bonding across the interface plays the key role in the increase of adhesion strength and the anti-wear life of amorphous carbon film. The friction and wear mechanism of the amorphous carbon film under dry friction was also discussed.

Ion-beam-assisted sputter deposition of thin oxide films

Experimental results of sputter deposition of thin oxide films of titanium and aluminium are presented and the effects of simultaneous irradiation of thin films by an oxygen ion beam during growth are discussed. The films are deposited on various substrates such as Ti, Si, SUS and quartz using an argon ion beam for sputtering and an oxygen ion beam for producing the mixing effect and control of the stoichiometry of the oxides. The deposition rate was about 0.07 nm s -1 and the oxygen beam currents were a few tens of microamperes per square centimetre. Stable oxide films are produced. Measurement results related to the micromorphology of the interface, film composition and adhesion are presented. Experimental results suggest that the ion mixing effect in the process of ion-beam-assisted sputter deposition strongly influences the adhesion and stoichiometry of the films.

Development in Auger depth profiling technique

The usage of Auger depth profiling technique in its conventional form was limited considerably by surface roughening accompanying the ion sputtering. The depth resolution thus decreased with the thickness of the removed layer. Introducing rotation of the specimen and using glancing-incidence-angle ions the surface roughening was greatly reduced. Applying these conditions, one can study the ion mixing effect, which is another limiting factor for the depth resolution. A Mo 3.6 - Si 3.3 nm multilayer system deposited on a Si substrate has been studied by AES depth profiling with specimen rotation and glancing-incidence-angle ions (87° to the surface normal) in the 1–2 keV electron and 1–5 keV ion energy ranges, using a special ion gun. Depth profiling was followed by plasmon loss and elastic peak electron spectroscopy (EPES). EPES enables variation of the sampling depth, while the AES sampling depth was ≈0.4 nm. Plasmon loss spectra have been recorded on the Mo and Si layers and are considerably different from those obtained on pure Mo and Si, respectively. Simulation of the elastic peak intensity versus profiling depth resulted in good agreement with experimental data. The calculation was based on a single elastic scattering approach and with Liau's ion mixing model.

Problems in the deconvolution of SIMS depth profiles using delta-doped test structures

The notion that the experimentally observed sputter depth profile can be corrected for the distortions introduced by ion mixing, through a deconvolution process using the as-measured result for a delta-function like impurity distribution, is examined critically. Starting point is an existing simple, but conceptually transparent and basically not incorrect, model to describe ion mixing effects. First it is shown that the characteristic exponential rise and decay lengths can be expressed as the fourth power sum of intrinsic and mixing contributions. Then it is demonstrated that the observed variation of the full-width at half-maximum with primary beam parameters (ion type, impact energy and angle of incidence) for delta-like impurity distributions is incompatible with the notion that the mixing efficiency may be estimated from the slopes of the profile. Consequently, the outcome of a deconvolution step does not result in a unique solution, but depends (strongly) on the measurement conditions chosen.

Influence of ion mixing on the depth resolution of sputter depth profiling

During sputter depth profiling, the bombarding ions for sputtering also produce ion mixing at interfaces. As a result, ion bombardment changes the original composition profile of the specimen, setting a limit on the depth resolution of the sputter depth profiling technique. The origin and magnitude of the effect of ion mixing on the depth resolution of sputter depth profiling have been studied using x-ray photoelectron spectroscopy, Auger electron spectroscopy, and Ar+ sputter depth profiling of Pt/Zr, Pt/Mo, Pt/Ti, and Pt/Ni interfaces. It is shown that the effect of ion mixing is an intrinsic limitation on the depth resolution; it depends on the thermodynamic properties, such as the heat of mixing and the cohesive energy, of the solids under examination. The magnitude of the effect of ion mixing is compared with that of the instrument-dependent limitations on the depth resolution of sputter depth profiling.

Effect of ion mixing on the depth resolution of sputter depth profiling

The effect of ion mixing on the depth resolution of sputter depth profiling has been studied using x-ray photoelectron spectroscopy and Ar+ sputtering of Pt/Zr, Pt/Mo, Pt/Ti, and Pt/Ni interfaces. It is shown that the heat of mixing of binary alloys plays an important role in depth resolution. The measured interface width of bilayers consisting of metals with a large and negative heat of mixing (Pt/Zr and Pt/Ti) is significantly broader than that of metals with a nearly zero heat of mixing (Pt/Mo and Pt/Ni). This observation suggests that the mechanism of ion mixing during sputter depth profiling with ion energies of a few keV is the same as ion mixing with ion energies of several hundred keV; diffusion in thermal spikes is the dominant contribution to ion mixing in the systems investigated.

Modeling the effect of ion mixing and surface roughening on depth profiles

AbstractA simple instrument transfer function is proposed to convolute hypothesized profiles (e.g. sharp interfaces). The convoluted profiles can then be compared to measured profiles. The convolution involves an ion mixing factor which has a constant value independent of the sputter depth and a roughening factor which is a fixed fraction of the sputter depth. Electron escape depth is also included in the convolution. Measured profiles for silicon dioxide films varying form 23 to 1000 angstroms were obtained with AES and argon ion sputtering, and are compared to the convoluted hypothesized profiles. An ion mixing factor of 10 angstroms and a roughening factor of 1% of the sputter depth were obtained. This roughness factor is significantly lower than usually obtained for many other materials, e.g. metal films.

Ion mixing effects on the electrochemical behavior of tin coated nickel

Nickel substrates were coated with a thin Sn layer and implanted with 100 keV xenon ions, leading to the formation of new surface phases, mainly Ni 3Sn. Electrochemical measurements were carried out on Ni samples submitted to each of the following surface modifications: Sn-deposition, Xe +-implantation, ion-mixing (combined treatment), and on untreated Ni. The test solution was 0.5 M NaCl. Both the potentiodynamic anodic and cathodic polarization curves show that the implantation on uncoated Ni improves the anodic passivation with respect to the Sn deposition on Ni; comparable results are obtained by surface alloying induced by ion-mixing. The cathodic behaviour is in agreement with the presence of both galvanic couples and active sites for H 2 evolution due to defect spreading. Only the alloyed surface shows a clearly different behaviour, i.e. a high hydrogen reduction overvoltage. The electrochemical measurements were repeated in the presence of sulphide ions.

Correlation between chemistry and the amount of mixing in bilayers submitted to ion bombardment

Experiments conducted with bilayers of elements so chosen as to maximize chemical differences and to minimize physical differences (e.g., atomic weights) demonstrate the importance of chemistry in determining the amount of interaction which results from ion mixing experiments. These results emphasize the dominance of chemical factors which are at least neglected, if not totally ignored, in the modeling of ion mixing effects. Ion bombardment of Pd/Hf bilayers causes the formation of Pd3Hf; the existence of such compounds was not detected in other bilayers of ‘‘similar’’ elements.

Formation of GaAs Ohmic Contacts by Using Ion Beam Mixing

ABSTRACTIon beam mixing effects on metals and highly doped semiconductors on GaAs for formation of ohmic contacts have been studied. In this study, we have principally selected Pt as metal and Ge as semiconductors electrodes for GaAs. In Pt/GaAs system, we observed alloying phenomena induced by Si+, Ar+, Ge+ ion mixing effects. The amount of GaAs reacted with Pt was found to be proportional to the mass of the incident ions for constant dose. Concernig with the formation of ohmic contacts, only in the case of Si implantation through Pt films, the conversion from Schottky- to ohmic-contact was observed due to ion beam mixing effects. In Ge/GaAs system, we observad the solid state epitaxy for implanted Ge layer by the first annealing at 450°C in the two step annealing, but no activation of the implanted species. For activating implanted species, the second annealing at 800°C was effective. Concerning with the formation of ohmic contacts, we observed that the ohmic I-V characteristics for Ge/GaAs system could be obtainable when the following conditions were satisfied at the same time: 1) high dose implantation of As+ into Ge layer, 2) low dose implantation of Si into Ge/GaAs boundary and 3) relatively short period annealing in the second annealing step. From such study, it is concluded that ion beam mixing in conjunction with rapid annealing would be most promising for forming stable and reproducible ohmic contacts.