Silicide formation by Ar+ ion bombardment of Pd/Si

Palladium films, 45 nm thick, evaporated on to Si(111) were irradiated to various doses with 78 keV Ar⁺ ions to promote silicide formation. Rutherford backscattering spectroscopy (RBS) shows that intermixing has occurred across the Pd/Si interface at room temperature. The mixing behaviour is increased with dose which coincides well with the theoretical model of cascade mixing. The absence of deep RBS tails for palladium and the small area of this for silicon spectra indicate that short-range mixing occurs. From the calculated damage profiles computed with TRIM code, the dominant diffusion species is found to be silicon atoms in the Pd/Si system. It is also found that the initial compound formed by Ar⁺ irradiation is Pd₂Si which increases with dose. At a dose of 1×10¹⁶ Ar⁺ cm^–2, a 48 nm thickness of Pd₂Si was formed by ion-beam mixing at room temperature.     

The study of graphite disordering using the temperature dependence of ion-induced electron emission

The temperature dependences of ion-induced electron emission yield γ(T) under 6-30 keV N₂⁺, Ne⁺, Ar⁺ and 15 keV N⁺ high-fluence ion irradiation of polycrystalline graphite at normal ion incidence have been analyzed to trace the structure change dependence depending on irradiation temperature and the level of radiation damage v measured in dpa (displacements per atom). It has been found that, under irradiation at room temperature, the threshold value for graphite lattice disordering equals v_d ≈ 60 dpa for noble gas ions (Ar⁺, Ne⁺) and ν_d ≈ 40 dpa for N₂⁺.     

Effects of ion beam surface modification on water absorption characteristics of perfluorosulfonic acid membranes

The dynamic behavior of water within ion beam (10 keV Ar⁺, 1.0 × 10¹⁶–1.2 × 10¹⁷ ions/cm²) modified perfluorosulfonic acid (PFSA) membranes was investigated at room temperature by combining direct-current (DC) resistance with alternative-current (AC) impedance methods under a water-saturated air atmosphere. The bulk impedance in existing surface sulfonate groups (SO₃⁻) decreased approximately one order of magnitude as a result of Ar⁺ ion irradiation compared to the unirradiated membrane. The enhancement in the proton conductivity results in an improvement of the water absorption characteristics at the Ar⁺ ion-modified surface which showed large superficies as well as hydrophilic radicals. These results can be explained in base of a relative increase in both the water content of the membrane and the change in the interactions of water molecules with sulfonate group at the interface on the proton-transfer process.     

Mechanism of adhesion improvement in ion-beam mixed Cu/SiO2

A thin copper layer (35 nm) deposited on SiO₂ has been subjected to ion-beam mixing with 80 keV Ar⁺ at room temperature, 550 and 650 K. Interfacial properties of irradiated samples were investigated using Rutherford backscattering spectroscopy, grazing-angle X-ray diffraction, X-ray photo-electron spectroscopy and scratch testing. The adhesion of the copper film was improved by a factor of three at a dose of 1.5 × 10¹⁶ Ar⁺ cm^–2 by the ion-beam mixing at room temperature, while the high-temperature ion-beam mixing enhanced the adhesion by a factor of five. Ballistic mixing plays a role in the improvement of adhesion for the room-temperature ion mixing, and the creation of Cu₂O phase induced by ion-beam mixing contributes to the enhancement of adhesion at high temperature.     

The influence of sputtering on FeSi

The effect of different (0.5, 2 and 4 keV) Ar⁺ energy ions on (a) the composition of an FeSi surface, (b) the oxidation of the FeSi surface after bombardment, and (c) the segregation of silicon after bombardment, has been monitored by Auger electron spectroscopy. Silicon was found to be preferentially sputtered by the Ar⁺ ions at all the different energies during bombardment. This effect was more pronounced at the 0.5 keV ion energy bombardment. There was a slight increase in the oxidation rate from the higher to the lower Ar⁺ ion energy at which the sample was sputtered before oxidation. The rate of silicon diffusion to the surface at 593 K after the sample had been sputtered, was lower when the sample had been sputtered by 0.5 keV ions than by 2 keV ions.     

Damage buildup in semiconductors bombarded by low-energy ions

The damage buildup in Ge and GaAs bombarded at room and elevated temperatures by keV Ne⁺ and Ar⁺ ions has been studied. Results show that the accumulation of disorder can be considered as a planar growth of an amorphous layer proceeding from the surface. A retardation of amorphous layer growth is experimentally observed in Ge for low ion doses. Results (for the case of room temperature irradiation of GaAs and for all the cases of irradiation of Ge except for the case of irradiation by Ar⁺ ions with high ion flux density) are explained based on the diffusion of mobile point defects to the surface with a subsequent interface segregation process. Calculations based on this model are in good agreement with experimental data.     

Depth profiles and concentration percentages of SiO2 and SiO x induced by ion bombardment of a silicon (100) target

Very thin-film of silicone oxide is of importance in many microelectronics device fabrication. A 9 keV Ar⁺ beam was applied to bombard a silicon (100) target ambient oxygen gas. The measurement was performed with a fixed time of bombardment but different oxygen pressure, beam intensity and temperature. An X-ray Photoelectron Spectroscopy (XPS) was employed to analyze the depth profiles and the concentration percentages of SiO₂ and SiO _x within the bombarded Si (100) samples. The percentage of SiO₂ in different depth of the sample is found to be proportional to the oxygen pressure. The thickness of SiO₂ film formed at room temperature is larger than the thickness at temperature 650 °C. The net percentages of SiO _x , except at the top layer of the surface, are varied in a small difference among different ion-bombardment conditions as the depth below 2 nm.     

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N₂⁺ ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N₂⁺ ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N₂⁺ ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si_xN_y on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N₂⁺ ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates.     

Low-energy Ar ion-beam induced vanadium silicide formation at V/Si interfaces

Vanadium/silicon interfaces produced by V thin film deposition on Si substrates were ion-beam mixed using 2 and 3 keV Ar⁺ ions at room temperature. The ion-beam mixing (IBM) has been studied by means of X-ray photoelectron spectroscopy, factor analysis and TRIDYN simulations. Comparison of the experimental results with those obtained from TRIDYN simulations suggests that, in addition to pure ballistic ion mixing mechanisms, other radiation-enhanced diffusion processes could contribute to the IBM of V/Si interfaces by low-energy Ar⁺ bombardment at room temperature. The kinetics of interface formation by IBM is characterized by two stages. During the first stage, a strong decrease of metallic V species is observed due not only to sputtering but also to the formation of vanadium silicide. The concentration of vanadium silicide related species reaches a maximum at the end of this first stage, decreasing subsequently. Finally, with increasing sputtering time, the signals associated with the silicide slowly decrease, and pure silicon species begin to appear, since no free metallic vanadium atoms are available to react with the unlimited silicon supply from the substrate.     

Effect of heating on the behaviors of hydrogen in C-TiC films with auger electron spectroscopy and secondary ion mass spectroscopy analyses

C-TiC films with a content of 75% TiC were prepared with magnetron sputtering deposition followed by Ar⁺ ion bombardment. Effect of heating on the behaviors of hydrogen in C-TiC films before and after heating was studied with Auger Electron Spectroscopy and Secondary Ion Mass Spectroscopy (SIMS) analyses. SIMS depth profiles of hydrogen after H⁺ ion implantation and thermal treatment show different hydrogen concentrations in C-TiC coatings and stainless steel. SIMS measurements show the existence of TiH, TiH₂, CH₃, CH₄, C₂H₂ bonds in the films after H⁺ ion irradiation and the changes in the Ti LMM, Ti LMV and C KLL Auger line shape reveal that they have a good hydrogen retention ability after heating up to the temperature 393 K. All the results show that C-TiC coatings can be used as a hydrogen retainer or hydrogen permeable barrier on stainless steel to protect it from hydrogen brittleness.     

Development of a compact angle-resolved secondary ion mass spectrometer for Ar sputtering

A compact angle-resolved secondary ion mass spectrometer with a special geometrical configuration, composing of a differentially pumped micro-beam ion gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer, was newly developed. This system enables the measurement of angular distribution (AD) of secondary ions, which are ejected by oblique Ar⁺ sputtering, by a simple tilt operation of the sample stage for ejection angles ranging from 0° to 60° with keeping the ion incidence angle constant 62°±2° from the normal to the surface. Using this system, AD of secondary ions from an HfN film by 3 keV Ar⁺-ion bombardment was measured at room temperature. Since the yield of HfN⁺ dimer ions was almost independent of Hf⁺ and N⁺ monomer ions, it was concluded that the HfN⁺ dimer ions were generated via the “as such” direct emission process.     

Surface morphology analysis of natural single crystal diamond chips bombarded with Ar ion beam

We have studied the surface morphology of natural single crystal diamond chips machined by 0.5-3.0 keV Ar⁺ ion beam irradiation at ion incidence angles of 0°, 30°, 45°, 60°, and 80° with ion doses from 3.4 × 10¹⁸ ions/cm² to 6.8 × 10¹⁸ ions/cm². The surface of diamond chips machined with 0.5 and 1.0 keV Ar⁺ ion beam, at angles of ion incidence from 0° to 45° can be made smooth. Results show that the machined surface at ion dose of 6.8 × 10¹⁸ ions/cm² and beam energy of 0.5 and 1.0 keV become ultra-smooth (surface roughness SR = 0.1 nm rms) compared with unprocessed surface (SR = 0.15-2.1 nm rms). Results also confirm the ripple formation on diamond surface at ion incidence angles of 60°-80° by 0.5-3.0 keV Ar⁺ ion beam. Therefore, the technique of smoothing by choosing ion beam irradiation parameter can be applicable to nano-finishing of diamond tools without ripple formation. This technique can also be applicable in mass production if the diamond surface is mechanically pre-finished.     

Gold films on silicon: Ion-bombardment-induced reactions between gold and silicon

Thin gold films of thickness 80 and 25 nm deposited onto silicon were bombarded with 30 keV Ar⁺ ions to fluences in the range from 4.8 × 10¹⁸ to 1.6 × 10²¹ ions m⁻². Dynamic recoil mixing, i.e. controlled simultaneous deposition of gold and bombardment with Ar⁺ ions, was carried out on gold films 30 nm thick on silicon. All the films were subsequently analysed by Rutherford backscattering spectroscopy, scanning electron microscopy and transmission electron microscopy. The results indicate the formation of a metastable amorphous phase with the composition Au₇₆Si₂₄. The formation of this phase is accompanied by the formation of surface ripples which develop into prominent islands on further ion bombardment. The amorphous phase is stable up to 413 K after which and up to a temperature of 613 K it turns into a stable large-grained polycrystalline compound with a similar composition, and this does not alter on subsequent cooling to room temperature.     

Monitoring the structure-phase changes in graphites using temperature regularities of ion-induced electron emission

The correlation between the temperature dependences of ion-induced electron emission yield, modified surface crystalline structure and morphology of isotropic graphite MPG-8 and highly oriented pyrolytic graphite (HOPG) UPV-1T under high-fluence (F = 10¹⁸-10¹⁹ ion/cm²) 6-30 keV Ar⁺ ion irradiation has been studied and discussed. The target temperature has been varied during continuous irradiation from room temperature to 400 °C. Surface analysis has been performed by the RHEED and SEM techniques. A strong influence of electron transport anisotropy for HOPG has been observed.     

The Rectification Studies on the P+-Ion Implanted C60/Si Films

Abstract

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^?2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

Effect of surface treatment on segregation of impurities in haematite

Surface segregation of various impurities such as Mg, Si, Ca, Al and Cr were determined for the haematite phase (Fe₂O₃) annealed in two different gas compositions involving (1) air at 1173 K, and (2) a gas mixture containing sulphur at 773 K. The objective of work was to establish the effect of the gas-phase composition on segregation of lattice defects. The near-surface segregation profiles of the impurities were determined by secondary ion mass spectrometry. The depth profile analysis was made by sputtering using an Ar⁺ primary beam of energy 30 keV. The surface charge was neutralized by an electron gun. It was found that annealing Fe₂O₃ under a gas phase containing sulphur resulted in the formation of an Fe(SO₄)₃ surface layer. It was observed that the two surface treatment procedures applied (both with and without sulphur) result in Mg enrichment in the near-surface region of Fe₂O₃. Si and Ca exhibit an enrichment and impoverishment after the surface treatments 1 and 2, respectively. Finally, the near-surface layer is impoverished in Cr and Al after both types of surface treatment. Experimental results are discussed in terms of segregation driving forces of the respective elements and the possible effect of sulphur on the gas-solid heterogeneous kinetics.     

Ar assisted carbidization of TiO2 (1 1 0) supported Mo nanoparticles by decomposition of C2H4

Ar⁺ assisted carbidization of Mo nanoparticles supported on TiO₂ (1 1 0) is studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In order to activate the diffusion of carbon into the bulk of Mo nanoparticles we applied Ar ions (1 keV) during the exposure of C₂H₄. XPS exhibited that the decomposition of C₂H₄ at 850 K accompanied by ion bombardment results in an almost complete carbidization of nanocrystalline Mo while this treatment performed without ion bombardment results only in the carbidization of the particle surface. The modification of the crystallinity of the Mo-carbide particles was deduced from STM measurements.     

BF2 ion implantation in silicon through surface oxides,behaviour of the fluorine with rapid thermal annealing

BF₂ ion implantation through surface oxides has been investigated to form shallow p⁺/n junctions. BF₂ ion implantation was performed at 25 keV at a dose of 5.4 × 10¹⁴cm⁻² through surface oxides of different thicknesses into crystalline silicon. Rapid thermal annealing (1000°C/10 s) was used for dopant activation and radiation damage removal. Secondary ion mass spectroscopy (SIMS) was used to obtain the boron and fluorine distribution profiles. p⁺/n junctions as shallow as 0.12 μm were formed with reasonable sheet resistance. The study shows that, as expected, dopant loss in the surface oxide during ion implantation results in higher values of sheet resistance. Out-diffusion of fluorine during RTA resulted in a fluorine loss of 50 to 65% from the silicon. Also, fluorine was found to segregate at the oxide/silicon interface.     

Surface texturing of silicon by dynamic recoil mixing

A technique known as dynamic recoil mixing is used in which a film of constant mass of gold can be maintained on a silicon substrate whilst it is being bombarded by energetic ions. The technique is used to produce surface texturing of silicon. Scanning electron microscopy and Rutherford backscattering techniques have been used to study the development of surface texture as a function of 10 keV Ar⁺ ion fluence. The results show the regrowth of silicon crystallites into the gold film as the Ar⁺ ion fluence increases until at high doses of 1 × 10¹⁷ ions cm^-2 the silicon crystallites coalesce and overlap the initial layer burying some of the gold beneath them. IR transmission of the silicon textured surface shows an increase of 4% for an ion fluence of (1–6) × 10¹⁶ ions cm^-2 in the wavelenght range 2.5–3 μm.     

A new method for determining the sharpness of InGaAs/GaAs heterojunctions by auger depth profiling

It is established for the first time that the phenomenon of ion-stimulated surface segregation can be used to increase the depth resolution of Auger profiling during analysis of the In_x Ga_{1 − x} As/GaAs heterostructures. It is demonstrated that, by varying the energy of the sputtering Ar⁺ ion beam from 1 to 0.5 keV in the region of the GaAs/InGaAs heterojunction, the junction sharpness can be estimated at a resolution on the order of 0.5 nm determined by a difference in the projected range of Ar⁺ ions and independent of the escape depth of the Auger electrons.