Formation of Ni2Si silicide in Ni/Si bilayers by ion beam mixing

We have studied ion mixing in Ni-Si(1 1 1) bilayers using noble gas ions. Thin Ni films of 45 nm thickness, deposited on a Si (1 1 1) substrate, were irradiated with 175 keV Kr and 110 keV Ar ions at the same fluence of 4×10¹⁶ ions/cm² at room temperature. The formation of the mixing and the elemental depth profile were investigated by Rutherford backscattering spectrometry. In the Ar irradiated sample, there was no structural change. On the other hand, we have noted the formation of Ni₂Si for the sample irradiated with Kr ions. X-ray diffraction measurements confirmed the formation of the Ni₂Si phase. The surface morphology of the Kr irradiated sample was also studied by scanning electron microscopy.     

Influence of incorporated non-metallic impurities on electromigration in copper damascene interconnect lines

Low electromigration in Cu interconnect lines represents one of the major challenges for a good performance of semiconductor devices. Referring to this, experiments were carried out to study the influence of non-metallic impurities like Cl, S, and C incorporated in Cu during the electrochemical deposition. In the case of a lower impurity content a higher resistance against electromigration was verified. The electromigration activation energy for metallizations with small contaminations was found to be (1.00 ± 0.06) eV whereas Cu interconnect lines with high non-metallic impurities revealed an activation energy of (0.65 ± 0.03) eV. The electromigration induced degradation by void formation starts at the top interface between Cu and dielectric cap layer. Probably, this results from high mechanical stresses due to differences in material properties or due to an interface weakening by the segregation of S and C impurities.     

Kinetics of cuprous oxide etching with β-diketones in Supercritical CO2

Cuprous oxide films (Cu₂O) supported on Cu or on SiO₂ were etched using solutions of β-diketones including 1,1,1,5,5,5-hexafluoroacetylacetone, 2,2,6,6-tetramethyl-3,5-heptanedione and 2,2,7-trimethyl-3,5-octanedione (TMOD) in supercritical carbon dioxide at temperatures between 80 and 150 °C and pressures between 20 and 27.5 MPa. The films and etched substrates were analyzed by X-ray photoelectron spectroscopy depth profiling, field emission scanning electron microscopy and spectroscopic ellipsometry. Each of the etching agents was effective. Etching kinetics using TMOD were measured at 100, 125 and 150 °C. At 150 °C the etch rate was 1.5 nm/min. Based on the activation energy obtained from the studies (66 kJ/mol), etching rates of greater than 10.0 nm/min can be obtained at 200 °C.     

Surface reactions between CO2 and H over K-modified Cu(0 0 1)

Low temperature (115-160 K) adsorption of CO on clean Cu(0 0 1), CO₂ on potassium modified Cu(0 0 1) and surface reactions between H₂ and CO₂ were studied. Pre-adsorption of K leads to strong interaction of the interface with arriving carbon dioxide molecules and linear CO₂(phys), bent , CO and are observed as adsorbed species. Annealing of the CO₂/K/Cu(0 0 1) interface causes, successively, desorption of the reaction products. Pre-adsorbed hydrogen on the alkali-modified substrate changes the surface reaction channels, mainly with no presence of CO and creation of surface formate species. Details of surface reactions are compared with results for thick potassium film on a copper substrate.     

Friction and adhesion properties of fluorocarbon polymer thin films prepared by magnetron sputtering

Fluorocarbon polymer thin films were deposited onto a SUS302 substrate with a poly(tetrafluoroethylene) (PTFE) target by three different types of r.f. magnetron sputtering systems with strong, weak and unbalanced magnetic fields. Friction and adhesion properties of these polymer thin films were evaluated.Friction coefficient of polymer thin films prepared with strong magnetic field, unbalanced magnetron and without magnetron (r.f. sputtering) was almost the same level, however, that prepared with the weak magnetic field was slightly lower than those of other thin films. Wear durability of polymer thin film increased with increase of the magnetic field.Adhesion strength between these thin films and SUS302 substrate and shear stress were measured by SAICAS. Both of the adhesion strength and shear stress of polymer thin films prepared with r.f. sputtering (without magnetron) were slightly higher than those prepared by magnetron sputtering systems.     

Growth conditions of the cubic phase cBN in boron nitride films

The nucleation and the subsequent coalescence period of the cubic phase cBN in sputter deposited BN-films is characterized by a shrinking of the film thickness. This is due to the transition of hBN into the denser cBN-phase which occurs inside a highly textured hBN base layer. The corresponding variation of the film thickness with the deposition time is described by a quantitative model. Full BN-stoichiometry in the hBN base layer is shown to be a mandatory condition for the nucleation process and the following growth of the cubic BN-phase. An increase of the substrate temperature fosters the incorporation of nitrogen into the growing film and, thus, the achievement of the stoichiometry condition.     

Cu surface segregation in Ni/Cu system

We report experimental evidence of Cu surface segregation in Ni/Cu system, during deposition of Ni film onto Cu substrate at room temperature and during heat treatment in vacuum. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) by Tougaard's analysis results show that surface segregation defeats in competition with increase in Ni thickness and terminates when thickness of Ni increase to more than 4 nm. Surface energy and concentration were calculated using contact angle measurements and the results confirm that segregation reduces the surface energy. Surface segregation during heat treatment at 150-220 °C range as a function of time initially shows linear mass transfer. By solving Fick's equation and taking empirical diffusion coefficient, 125 ± 20 kJ/mol is obtained for activation enthalpy of effective diffusion.     

Irradiation effects on solid surfaces by water cluster ion beams

The interaction between a water cluster ion beam and the surface of a silicon substrate was investigated. The sputtering yield of silicon by a water cluster ion beam was approximately ten times larger than that by an argon monomer ion beam. X-ray photoelectron spectroscopy was used to analyze the silicon surface irradiated with a water cluster ion beam. The analysis revealed that the surface was oxidized, and the oxidation was saturated approximately at the dose of 1 × 10¹⁴ ions/cm². The number of disordered atoms measured by the Rutherford backscattering also supported the result.     

Synthesis, characterization and effect of low energy Ar ion irradiation on gadolinium oxide nanoparticles

In this work, we report on the surfactant assisted synthesis of gadolinium oxide (Gd₂O₃) nanoparticles and their characterization through various microscopic and spectroscopic tools. Exhibiting a monoclinic phase, the nanoscale Gd₂O₃ particles are believed to be comprising of crystallites with an average size of ∼3.2 nm, as revealed from the X-ray diffraction analysis. The transmission electron microscopy has predicted a particle size of ∼9 nm and an interplanar spacing of ∼0.28 nm. Fourier transform infrared spectroscopy studies show that Gd-O inplane vibrations at 536.8 and 413.3 cm⁻¹ were more prominent for 80-keV Ar-ion irradiated Gd₂O₃ nanosystem than unirradiated system. The photoluminescence (PL) spectra of irradiated specimen have revealed an improvement in the symmetry factor owing to significant enhancement of surface-trap emission, compared to the band-edge counterpart. Irradiation induced creation of point defects (oxygen vacancies) were predicted both from PL and electron paramagnetic resonance (EPR) studies. Further, the Raman spectra of the irradiated sample have exhibited notable vibrational features along with the evolution of a new peak at ∼202 cm⁻¹. This can be ascribed to an additional Raman active vibrational response owing to considerable modification of the nanostructure surface as a result of ion bombardment. Probing nanoscale defects through prime spectroscopy tools would find a new avenue for precise tuning of physical properties with generation and annihilation of defects.     

Spontaneous oxide reduction in metal stacks

Aluminum and copper interconnects are widely used for microelectronic applications. A problem can arise when interfacial oxides are present. Such oxides can significantly degrade device performance by increasing electrical resistance. This paper describes analyses of interfacial oxide layers found in Al/Ta and Ta/Cu metal stacks. The analyses were performed through transmission electron microscopy (TEM). The data indicated that the interfacial oxides resulted from spontaneous reductions; that is, Al spontaneously reduced Ta₂O₅ to form Al₂O₃, while Ta spontaneously reduced Cu oxide to form Ta₂O₅.     

Formation and characterization of NaCl-type FeC

Cubic FeC nanoparticles were observed in amorphous iron carbon matrix produced by pulsed laser deposition directly onto electron microscopy grids. The observed lattice constant is close to a theoretically predicted value.     

Atomic layer deposition and post-deposition annealing of PbTiO3 thin films

Lead titanate thin films were deposited by atomic layer deposition on Si(100) using Ph₄Pb and Ti(O-i-Pr)₄ as metal precursors and O₃ and H₂O as oxygen sources. The influence of the Ti : Pb precursor pulsing ratio on the film growth, stoichiometry and quality was studied at two different temperatures, i.e. 250 and 300 °C. Uniform and stoichiometric films were obtained using a Ti : Pb precursor pulsing ratio of 1 : 10 at 250 °C or 1 : 28 at 300 °C. The as-deposited films were amorphous but the crystalline PbTiO₃ phase was obtained by rapid thermal annealing at 600-900 °C both in N₂ and O₂ ambient. Thin PbTiO₃ films were visually uniform and roughness values for as-deposited and annealed films were observed by atomic force microscopy.     

Cathodoluminescence and photoluminescence of swift ion irradiation modified zinc oxide-porous silicon nanocomposite

We report the room temperature cathodoluminescence and photoluminescence of swift ion irradiated (130 MeV Nickel ion) porous silicon zinc oxide nanocomposites. The evolution of a broad and flat emission band from 1.5 to 3.5 eV is demonstrated. Annealing effect of irradiation is found to result in a relative increase in the band edge emission. Emission wavelength can be tuned in the complete visible range by changing the substrate characteristics.     

Enhanced luminescence from encapsulated silicon nanocrystals in SiO2 with rapid thermal anneal

It is well known that Si ion implantation into SiO₂ and subsequent high-temperature anneals induce the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of rapid thermal annealing to enhance the photoluminescence intensity have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing excess Si with different concentrations. Si precipitation to form nanocrystals in implanted samples takes place with a conventional furnace anneal. The photoluminescence intensity and the peak energy of emission from Si nanocrystals depend on implanted ion dose. Moreover, the luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence and that the luminescence peak energy is found to be dependent, but only by a small factor, on the thermal history of specimens. Enhancement is found to be typical for low dose samples. Furthermore, the observation that the prolonged anneal induces saturation and a blue shift of the luminescence strongly indicates the emission is not simply due to electron-hole recombination inside the Si nanocrystals. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism of photoemission.     

Improved microstructural properties of a ZnO thin film using a buffer layer in-situ annealed in argon ambient

ZnO films with improved crystallinity were grown on a Si (111) substrate by a two-step growth process using low-temperature ZnO buffer layers. The effect of the ambient gas during the temperature elevation and the in-situ thermal annealing after the growth of the low-temperature buffer layers on the optical and structural properties of the films was investigated by X-ray diffraction (XRD), photoluminescence, and transmission electron microscopy. The use of argon as the ambient gas during the thermal treatment of the buffer layer leads to the enhancement of the (0002) diffraction peak intensity at 2θ ∼ 34.4° and the reduction of the full width at half maximum value in the XRD rocking curve, which means that well-defined and c-axis oriented ZnO film was obtained. The relationship between the thickness of the SiO₂ layer between the ZnO buffer layers and Si substrates and the structural and optical properties of the ZnO films is discussed.     

Effect of substrate temperature and deposited thickness on the formation of iron silicide prepared by ion beam sputter deposition

Ion beam sputter deposition (IBSD) method was employed to find optimum conditions for the formation of epitaxial β-FeSi₂ films on Si(100) substrate. It was found that crystal structure of the films as determined by X-ray diffraction (XRD) analysis is dependent on the substrate temperature as well as on the deposited thickness of sputtered Fe. The film with best crystal properties was obtained either at 873 K with the deposited Fe thickness of 15 nm, or at 973 K with the deposited Fe thickness of 30 nm. The obtained results indicate the importance of Fe and/or Si diffusion in determining the crystal properties of β-FeSi₂ film.     

A model for energy loss and straggling of slow ions in electron gas with intraband exchange

Influence of ferro-paramagnetic phase transition on the electronic energy loss and the straggling of ions in the electron gas subjected to magnetic ordering is reported. The linear response (LR) theory was used in application to low velocity ions. The medium was described by the Lindhard dielectric function ε(k,ω). The magnetic interactions were included in the model by means of the Stoner treatment of itinerant electrons. The intraband exchange interaction was shown to shift the energy levels, change degeneracy, shift the Fermi level and thus contribute to the change of electron gas stopping characteristics. Results of the calculations were critically compared to change of stopping at the Curie temperature measured for Ni and Gd foils in transmission experiments.     

Comparison of ordered structure in buried oxide layers in high-dose, low-dose, and internal-thermal-oxidation separation-by-implanted-oxygen wafers

The ordered SiO₂ in the buried oxide (BOX) layer of high-dose, low-dose, and internal-thermal-oxidation (ITOX) separation-by-implanted-oxygen (SIMOX) wafers was investigated by X-ray diffraction. From the results, it was found that the SiO₂ molecules in the low-dose and ITOX SIMOX wafers are better ordered than those in the high-dose SIMOX wafer and that the ordered structure of the ITOX layer is different from that of the originally formed BOX layer, suggesting that the ITOX layer has a structure similar to that of the ordered SiO₂ in the thermal oxide layer.     

Preparation, characterization and photocatalytic activity of in situ Fe-doped TiO2 thin films

Fe-doped TiO₂ thin films were prepared in situ on stainless steel substrates by liquid phase deposition, followed by calcination at various temperatures. It was found that some Fe³⁺ ions were in situ doped into the TiO₂ thin films. At 400 °C, the film became photoactive due to the formation of anatase phase. At 500 °C, the film showed the highest photocatalytic activity due to an optimal Fe³⁺ ion concentration in the film. At 900 °C, the photocatalytic activity of the films decreased significantly due to the further increase of Fe³⁺ ion concentration, the formation of rutile phase and the sintering and growth of TiO₂ crystallites.