Effect of ion irradiation on the structural and magnetic properties of sputtered CoPt alloy

We are interested in studying thin layers of CoPt alloy prepared by co-deposition sputtering. The CoPt layers are deposited on a MgO(001) substrate with a Pt(001) buffer layer. We obtain a layer with the L1₀ tetragonal structure, ordered in the growth direction. This equiatomic L1₀ phase is a “natural” multilayer which consists in a stacking along the (001) direction of pure Co and pure Pt monolayers. In this case, we get an easy magnetization direction perpendicular to the layer plane, which is the required configuration for the perpendicular magneto-optic recording. The order state of these thin films has been modified locally by a low energy ion irradiation. The structural and magnetic properties have changed jointly: with a 40-keV energy and a 4×10¹⁶-ions/cm² flux, the chemical order decreases (the long-range-order (LRO) parameter changed from S=0.80 to S=0.50), the coercive field diminished from 0.090 T down to 0.052 T. Such results show that it is possible to locally change the magnetization easy axis, which is promising for applications.     

Formation of CoNx ultra-thin films during direct-current nitrogen ion sputtering in ultrahigh vacuum

This study reports the formation of ultra-thin cobalt nitride (CoN_x) films on a Co/ZnO(002) crystal by low-energy ion sputtering of nitrogen in an ultrahigh vacuum system. The CoN_x film formed during ion bombardment in which the nitrogen plasma (N⁺) results in both sputtering and implantation in the formation process of CoN_x, especially for the Co adsorbed layers. Auger electron spectroscopy analysis shows that the composition ratio x as a function of sputtering time was highly related to the N⁺ ion energy that was varied from 0.5 to 2 keV. The composition ratio x of CoN_x films is inversely proportional to the ion energy. Low-energy ion sputtering is possible to fabricate ultra-thin CoN_x films and to adjust their chemical compositions.     

Composition profiles of CVD platinum and platinum silicide by Auger electron spectroscopy and secondary ion mass spectrometry

Phosphorus, platinum, silicon and oxygen profiles have been studied in thin film Pt formed on Si by chemical vapor deposition (CVD) from Pt(PF₃)₄, and in the platinum silicide formed by interdiffusion at 450° and 625°C. Low voltage sputtered Pt and its silicide have also been studied. Two profiling techniques have been used: inert ion sputtering with sequential Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS).Phosphorus in as-deposited (225°C) Pt formed by chemical vapor deposition (CVD Pt) was found to be non-uniformly distributed, indicating that some diffusion had already occurred even under these mild conditions. There was a high concentration (10–20 at.%) at the surface, decreasing rapidly to the 0.1% range at a depth of about 50 Å. At the interface with the silicon substrate there was a broad peak with a P concentration of about 1 at.%. When platinum silicide was formed, most of the phosphorus from the interior migrated to the surface, resulting in an enhanced P zone now 150–200 Å thick. The phosphorus did not appear to impede silicide formation in any way. The same $\text{Pt}\text{Si}$ ratio was found in platinum silicide formed from CVD Pt at either 450° or 625°C, in silicide from sputtered Pt and in single-crystal PtSi. The composition of the silicide was essentially constant through most of the film. A strong oxygen signal combined with an Si peak shift was present within 100–200 Å of the surface of the silicide. This is the layer of SiO₂ which has been detected by independent methods earlier, and which protects PtSi from attack by the aqua regia used to remove unreacted Pt from insulator areas. The surface silica coincided with the enhanced phosphorus zone when CVD Pt was used, and thus in this case should be considered as a phosphosilicate glass.     

The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm² with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E_i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti¹⁺, 24% Ti²⁺, 23% Ar¹⁺, and 3% Ar²⁺ ions.     

The Formation of Hollow Lead Structures on the Surface of PbSe Films Treated in Argon Plasma

Conditions for ion sputtering of a PbSe/CaF₂/Si(111) epitaxial system in high-density inductively coupled plasma of high-frequency low-pressure discharge in argon have been established that ensure the formation of submicron-sized hollow lead structures on a lead-selenide surface. The surface was plasma-treated for time periods within 60–240 s at low energy (20–30 eV) of Ar⁺ ions, which is close to their sputtering threshold energy. The properties of the obtained material were studied by the techniques of scanning electron microscopy and energy-dispersive X-ray microanalysis. It is shown that the characteristic size, shape, and density of surface structures can be varied within broad limits depending on the time of plasma treatment and temperature of the material surface. Physical processes responsible for the formation of hollow lead structures under the proposed conditions of plasma sputtering are considered.     

Self-heating effect induced by ion bombardment on polycrystalline Al surface nanostructures evolution

We studied the self-heating effect during ion bombardment process on polycrystalline Al foils. An anisotropic surface morphology evolution has been observed. The adjacent peaks?? fusion along the direction perpendicular to the ion beam projection smoothen the surface. Fusion along the parallel direction has been suppressed due to Ar⁺ ion bombardment. It attributes to the result of the competition between the isotropic thermal effect, due to the self-heating effect by energy exchange between incident ions and Al surface, and the suppression by continuous ion bombardment with a certain incident angle. Varying the incident ion beam angle with the angular range 32°?<????<?82°, the ripple wave vector, ??, is found to be parallel to the ion beam direction, whereas for ?? > 82°, ?? is perpendicular to the beam direction. The critical angle, ?? _c , is close to 82°, which is different from Bradley and Harper??s prediction and attributes to the self-heating effect.     

Depth profiling of fullerene-containing structures by time-of-flight secondary ion mass spectrometry

A new variant of depth profiling for thin-film fullerene-containing organic structures by the method of time-of-flight (TOF) secondary ion mass spectrometry (SIMS) on a TOF.SIMS-5 setup is described. The dependence of the yield of C₆₀ molecular ions on the energy of sputtering ions has been revealed and studied. At an energy of sputtering Cs⁺ ions below 1 keV, the intensity of C₆₀ molecular ions is sufficiently high to make possible both elemental and molecular depth profiling of multicomponent (multilayer) thin-film structures. Promising applications of TOF-SIMS depth profiling for obtaining more detailed information on the real molecular composition of functional organic materials are shown.     

Reactive ion etching of Pt electrode using O2-based plasma

We have studied the reactive ion etching (RIE) of Pt electrode using O₂ plasma with additional gases. Dual frequency RIE tool was used to obtain a high-energy ion bombardment. We have investigated the Pt etching profile using O₂/HBr/Ar plasma. We reveal that there is a optimal gas flow ratio for attaining the node separation of Pt electrodes at small critical-dimension (CD) pattern.     

Secondary ion emission of Fe-Ni alloys in the temperature range including the Curie point

The temperature dependence of secondary ion emission was investigated for Fe-Ni ferromagnetic alloys with different Curie points T_c and elemental composition: 35% Ni 65% Fe (T_c=240°C), 40% Ni 60% Fe (T_c=360°C), and 50% Ni 50% Fe (T_c=530°C). The alloy 79% Ni 16% Fe 5% Mo (T_c=345°C) was also studied. The spatial distribution of Ni⁺ and Fe⁺ secondary ions emitted from the (1 1 1) face of invar and permalloy single crystals was shown to be anisotropic with pronounced ion-yield maximum for both components in the 〈1 1 0〉 directions. The shape of the energy distribution of Ni⁺ and Fe⁺ ions was found to be virtually identical for all the alloys under investigation with a most probable energy at 7 eV and a width at half-maximum of 12 eV. The temperature dependence of the Ni⁺ and Fe⁺ emission has a maximum near the Curie point of the investigated alloys and another maximum at the Curie point of nickel which may indicate the precipitation of nickel into microscopic islands on the surface as a result of heating and sputtering. Auger analysis of the surface composition in the surface layers showed a variation in concentration of oxygen and carbon atoms when Fe-Ni alloys pass from the ferromagnetic to the paramagnetic state and this must affect also the secondary ion emission of alloy components.     

Time and energy resolved ion mass spectroscopy studies of the ion flux during high power pulsed magnetron sputtering of Cr in Ar and Ar/N2 atmospheres

Mass spectroscopy was used to analyze the energy and composition of the ion flux during high power pulsed magnetron sputtering (HIPIMS/HPPMS) of a Cr target in an industrial deposition system. The ion energy distribution functions were recorded in the time-averaged and time-resolved mode for Ar⁺, Ar²⁺, Cr⁺, Cr²⁺, N₂⁺ and N⁺ ions. In the metallic mode the dependence on pulse energy (equivalent of peak target current) was studied. In the case of reactive sputtering in an Ar/N₂ atmosphere, variations in ion flux composition were investigated for varying N₂-to-Ar flow ratio at constant pressure and HIPIMS power settings. The number of doubly charged Cr ions is found to increase linearly with increasing pulse energy. An intense flux of energetic N⁺ ions was observed during deposition in the reactive mode. The time evolution of ion flux composition is analyzed in detail and related to the film growth process. The ionization of working gas mixture is hampered during the most energetic phase of discharge by a high flux of sputter-ejected species entering the plasma, causing both gas rarefaction and quenching of the electron energy distribution function. It is suggested that the properties (composition and energy) of the ion flux incident on the substrate can be intentionally adjusted not only by varying the pulse energy (discharge peak current), but also by taking advantage of the observed time variations in the composition of ion flux.     

Mass dependence of sputtering characteristics for a number of metals with different properties

Molecular dynamic simulation has been used to study how the sputtering characteristics of metal polycrystals are dependent on the mass m₁ of bombarding ions of low-energy E₀. The influence of target parameters on mass dependence of sputtering has been calculated for Al, Ba, Ce and Au, which were not previously studied. These metals have very different values of density ρ, the lattice constant d, and the surface binding energy E_b (the parameters that define the sputtering process). The features of sputtering characteristics for the metals studied are discussed.     

In situ investigation of magnetron sputtering plasma used for the deposition of multiferroic BiFeO<Subscript>3</Subscript> thin films

Somrani et al. (J. Mater. Sci. 26:3316–3323, 2015) have recently investigated the BiFeO₃ (BFO) thin films growth by RF magnetron sputtering. The role of the processing parameters especially the oxygen flow, deposition temperature and annealing on the microstructure and optical properties of the deposited films has been extensively studied. In this work a detailed investigation of the plasma deposition dynamics of BFO films is presented. A plasma sampling mass spectrometer was inserted into the magnetron sputtering reactor to analyze the nature and energy distribution of each ion species impinging onto the substrate surface. It was find that at very low pressure (<5 mTorr), the ion energy spectra of the sputtered species showed a wide, bimodal distribution with a low energy component corresponding to the sheath potential and a much higher energy component arising from particles ejected from the target and only slightly thermalized in the gas phase. At higher pressure, all energy distributions became narrower due to a nearly complete thermalization. The Bi⁺-to-Fe⁺ ratio was also found to decrease with increasing pressure, going from about 4 at 3 to 1 at 30 mTorr. A similar feature was observed for the O⁺-to-O₂ ⁺ ratio. The plasma dynamic results have been correlated to the Rutherford backscattering spectroscopy characterization of BFO thin films.     

Structure, morphology and electrical characterizations of direct current sputtered ZnO thin films

ZnO thin films were deposited on glass substrates by direct current (DC) sputtering technique at room temperature (RT) to 400 °C with a 99.999% pure ZnO target. Then the samples deposited at RT were annealed in air from the RT to 400 °C. The effects of substrate temperature (T_s) and annealing treatment (T_a) on the crystallization behavior and the morphology have been studied by X-ray diffraction and atomic force microscopy. We also compared the structural properties of samples deposited at 400 °C on glass to those deposited on Pt/silicon substrate. The resistivity, surface roughness and size of the grains have also been studied and correlated to the thickness of ZnO films deposited on Pt/Si substrates. The experimental results reveal that the substrate has a major influence on the structural and morphological properties. For the films deposited on glass, below 400 °C, T_s and T_a have a similar influence on the structure of the films. Moreover, the ZnO samples deposited at RT and annealed in air have poor electrical properties.     

Crystallographic properties of four-fold grain K3Li2Nb5O15 thin films

The structural properties of a potassium lithium niobate (KLN; K₃Li₂Nb₅O₁₅) thin film deposited by rf-magnetron sputtering on a Pt/Ti/SiO₂/Si(100) substrate were investigated. The crystalline structures of the Pt under layer and KLN thin films were examined using θ-2θ, θ-rocking, and mesh scan X-ray diffraction (XRD). The XRD results revealed that the Pt under layer was a strong (111) direction orientated poly crystal. Unlike the Pt under layer film, the KLN(001) peak was found to consist of two separate peaks, one with a broad full width half maximum (FWHM) and the other with a narrow FWHM, indicating that the KLN film had a single crystalline structure. The surface and cross-section morphology were investigated using a scanning electron microscope (SEM). Accordingly, from the results of the SEM and XRD experiments, it was concluded that the KLN film was composed of small single crystals, which had a four-fold symmetry morphology with a c-axis normal to the substrate.     

Molecular dynamics simulations of ion bombardment processes

Abstract

An improved molecular dynamics technique that allows reduction of the computation time required in ion bombardment simulations is presented. This technique has been used to study the influence of the target temperature and structure on the argon sputtering of silicon. Molecular dynamics simulations of l keV Ar+ ion bombardment of silicon were carried out for several types of sample: (100) crystalline at 0 K, (100) crystalline at 300 K, and amorphous at 300 K. The yield of the sputtering process and the energy distribution of the sputtered atoms have been obtained. These results show that the sputtering process depends on the target surface binding energy which, in turn, is very sensitive to the structure of the sample surface.     

Preparation and antibacterial properties of Ag-containing diamond-like carbon films prepared by a combination of magnetron sputtering and plasma source ion implantation

Ag-containing diamond-like carbon (DLC) films were prepared on austenitic type stainless steel SUS316L and silicon wafer substrates by a process combining reactive magnetron sputtering with plasma source ion implantation (PSII). An Ag disc was used as a target for the sputter source with an RF power of 100 W. A mixture of the gases Ar and C₂H₂ was introduced into the discharge chamber while a negative high voltage pulse was applied to the substrate holder. By changing the gas flow ratios the resulting Ag content of the films could be varied. The prepared films were composed of amorphous carbon with crystalline Ag, as observed by X-ray diffractometry and TEM. Additional sample characterizations were performed by X-ray photoelectron spectroscopy, secondary ion mass spectrometry and Raman spectroscopy. The surface morphology was observed by scanning electron microscopy. The antibacterial activity was determined using Staphylococcus aureus bacteria. All Ag-containing diamond-like carbon films exhibited an antibacterial activity with only small variations depending on the Ag content.     

Detection of Al and Mg contamination in sputtered Pt films by Auger electron spectroscopy and secondary ion mass spectrometry

Traces of metallic contaminants, codeposited during the sputtering of Pt in Si integrated circuit fabrication, can cause deleterious metallurgical reactions during subsequent processing. Anomalous lateral diffusion and evidence of the formation of a liquid phase during sintering have been observed. Wafers exhibiting these symptoms have been found to undergo gross PtSi attack during the subsequent Pt etch in aqua regia. Silicide damage is then followed by a high probability of AuSi eutectic alloy formation which causes resistive paths that shunt many emitter-base junctions and Schottky diodes.The principal metallic contamination observed in this study originated from the wafer trays and other parts of the sputtering station, which were constructed from standard commercial grades of Al alloys containing Al, Mg and Cu. Within sputtered films of Pt 500Åthick, Al has been identified and profiled by means of Auger electron spectroscopy (AES) and secondary ion mass spectrometry. The degree of metallic contamination could be varied by modifying the sputtering procedure; this was confirmed by AES and successfully correlated with subsequent PtSi attack.In the series of experiments described in this paper, any contamination of Pt layers by Al and Mg was virtually eliminated by coating the wafer trays and adjacent parts of the sputtering station with approximately 1 μm of Pt before deposition of the 500Ålayer on the device slices. The Auger signal from Al in Pt films deposited on device wafers, after the above-described precaution, dropped to a level below noise but still detectable. At these contamination levels, PtSi attack by aqua regia was eliminated. Close monitoring of the matallic contamination should therfore be maintained in all sputtering facilities used for Si integrated circuit manufacture.     

The energy spectra of the secondary ion emission for transition metals of the fourth period

The energy spectra of the secondary ion emission (SIE) for transition metals of the fourth period are calculated under the assumption that SIE is caused by the joint action of electron-exchange and kinetic ion emission (KIE) mechanisms. Some improvement of the KIE theory is carried out for the cases of high (of the order of tens of keV) and low (less than 2 keV) energies E_O of bombarding ions. It is found that the KIE plays an essential role in SIE, starting from the E_O value of the order of tens of keV. It is shown that the KIE energy spectra (1) are broader than the sputtering energy spectra by an order of magnitude, (2) differ essentially in both cases indicated, (3) show a peak (at high E_O in accordance with an experiment) or a break (at low E_O) near to the secondary ion energy corresponding to the KIE threshold.     

The possibility of using platinum foils with a rippled surface as diffraction gratings

The atomic structure and surface relief of thin cold-rolled platinum foils upon recrystallization annealing and loading under ultrahigh vacuum conditions have been studied by low energy electron diffraction (LEED), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The surface of samples upon high-temperature annealing and subsequent uniaxial extension of recrystallized Pt foils represents a fractal structure of unidirectional ripples on various spatial scales. The total fractal dimension of this surface is D _GW = 2.3, while the fractal dimensions along and across ripples are D _‖ ≈ 1 and D _⊥ ≈ 1.3, respectively. The optical spectra of a halogen lamp and a PRK-2 mercury lamp were recorded using these rippled Pt foils as reflection diffraction gratings. It is shown that Pt foils with this surface relief can be used as reflection diffraction gratings for electromagnetic radiation in a broad spectral range.