eV Ion Energy Research Articles

Nanostructure formation on ion-eroded SiGe film surfaces

Ion bombardment of semiconductor substrates gives the possibility to generate ordered nanostructures by self-organization. Here, we investigated ion-beam induced morphology modifications of heteroepitaxial SiGe films on Si(001) that exhibit a distinct surface pattern as a consequence of strain-relief. Morphological changes and evolving surface nanostructures due to ion erosion were characterized by atomic-force microscopy. For SiGe films with mesa structures and for polycrystalline SiGe films, the existence of two characteristic energy regimes is shown. At an ion energy of 250 eV, roughening mechanisms take place. They result in an rms-roughness value exceeding the value of the initial sample surface. In the regime beyond 500 eV ion energy, the morphology smoothens and the pattern vanishes with increasing sputter depth. In both cases, a nanohillock formation in dependence of the sputter depth was found. The average diameter of the hillocks ranges between 14 and 27 nm. The possibility to generate hillocks on the nanometer scale by ion erosion demonstrates the potential of ion-bombardment induced nanopattern formation also for group IV semiconductor substrates.

Dynamics of hyperthermal energy ion–surface collisions: dissociative and non-dissociative scattering of ethanol cations from a self-assembled monolayer surface of fluorinated alkyl thiol on Au (1 1 1)

Dissociation and inelastic scattering of ethanol molecular ions from self-assembled monolayer (SAM) surface of fluorinated alkyl thiol on an Au (111) monocrystal have been studied at 28.9 and 52.9eV collision energies. A single dynamics mechanism for quasi-inelastic scattering was found at both energies. Ions recoil nearly parallel to the surface with very small kinetic energy losses of the order of ≤2eV. Dissociation dynamics features for the main dissociation channel, loss of methyl radical, are dramatically different from that of inelastically scattered primary ions and are different at the two collision energies studied. At 28.9eV two energetically and angularly resolved features are observed, one corresponding to the loss of very large amounts (nearly all) of ion’s translational energy and the other appearing to gain energy (superelastic scattering). This dynamics feature is interpreted as delayed dissociation of ions transmitted through the energy analyzer as molecular ions. This implies a lifetime of such excited ions of more than 5μs. The same dynamics features are observed at 52.9eV ion energy except that a second inelastic process begins to compete with the nearly fully inelastic process. Moreover, at this energy the delayed ion dissociation mechanism is the dominant mechanism. The hypothesis that collision of ethanol cations with the SAM surface initially involves collision of the ion with a single end group of the SAM polymer chain provides a useful rationale for the observed dynamics. Support for this hypothesis is provided by Newton diagrams, which summarize momentum conservation relationships in terms of a common center-of-mass, CMeff, which provides a basis for describing scattering mechanisms for this system. Observation of three energetically distinct scattering processes suggests uniquely different ion–surface interactions contributing to surface-induced dissociation of ethanol ions. Preliminary experiments with Ar+ scattered from the same surface exhibit very similar dynamics features to that observed for ethanol cations. Finally, we note that intensities of scattered primary or fragment ions never approach the specular angle at the energies investigated here.

Ion beam analysis of ion-assisted deposited amorphous GaN

Rutherford backscattering spectrometry and nuclear reaction analysis measurements were done using a 920 keV deuteron beam to investigate amorphous GaN films prepared on Si substrates by an ion assisted deposition technique. Elemental concentrations and depth profiles of O, N, Ga were measured. Films deposited at 750 eV ion energy show that the Ga/N ratios are within 10% of unity and the Ga/O ratios are within 10–15% in the films having thicknesses ranging from 75 to 270 nm. Ga/N and Ga/O ratios in the films deposited at 800 and 900 eV were found to vary more than 10%. The Ga/N ratios of films produced at 400–750 eV are optimal for the production of single-phase a-GaN. There are only minor differences in the optical responses of these films and none at all in the Raman spectra within these levels of variation. Hydrogen analysis was also performed on the films using elastic recoil detection analysis with a 2.5 MeV 4 He + beam. This showed a surface enrichment of H in the thick films and low H concentration values of around 0.9%.

The Molecular Dynamics Study for the Damage and Etching Properties of Low Energy Ar Ion Implantation. (Effect of Ion Energy, Polar Angle of the Incident Ion and Substrate Strain).

Molecular dynamics simulations have been performed for the Ar bombardment to Si surface in order to investigate the damage and etching properties. The dependence of the ion energy, the polar angle of the ion and substrate strain was investigated. The averaged number of interstitials was found to be a linear function of the damage energy, and its slope showed good agreement with the Kinchin-Pease model. The averaged number of etched atoms was not linear and its efficiency decreased as the ion energy was increased. It was found that the damages and etchings were caused by the energy injection to the substrate inside and the instantaneous thermal spike of the substrate surface, respectively. Mixing of two types of collision, i.e. binary and many body collisions resulted in increased dispersion of the damage. The damage decreased as the polar angle was increased. Conversely the etching increased, and had the maximum value at 70 degree. The strain dependence showed the symmetrical increased curve both in tension and compression. However, under 10% compressive strain and 1000 eV ion energy, the blocking and instability of the lattice created the significant disorder region.

Chemical erosion of carbon at low temperatures and low ion energies

Investigations of chemical erosion of carbon (EK98) were carried out in hydrogen and deuterium low pressure discharges. Atomic hydrogen fluxes to the surface were obtained from the radiation of the Balmer lines (ΓH = ΓD = 2.6 × 1021 m-2 s-1). From the diffusion flow onto a surface, the reflection coefficients of graphite for H and D atoms were determined to be 40% and 65%, respectively. Erosion yields were derived from weight loss measurements and emission spectroscopy of the CH and C2 bands at ion energies between 5–40 eV in the substrate temperature range of 300–1100 K. Spectroscopic results indicate the influence of higher hydrocarbons. An isotope effect of 2.5–3 was measured, which vanishes at room temperature and approx. 5 eV ion energy. Here, an erosion yield of 0.1% remains. The measurements were compared with model calculations and were in satisfying agreement.

Using a quartz crystal microbalance for low energy ion beam etching studies

A quartz crystal microbalance (QCM) has been used for etching yield measurements in a low energy ion beam system. The goal is to obtain etching yields for ion energies below 150 eV for various ion chemistries and target materials. Typical beam currents are about 0.5 μA, and the mass change per unit time on the QCM is much smaller than that for typical QCM applications. A number of problems with the application of a QCM were encountered and a description of how they were overcome is presented in this article. Quantitative etch yield results for the etching of two different photoresists and SiO2 down to 25 eV ion energy are presented.

Ion acceleration in the radially expanding plasma of the hot refractory anode vacuum arc

The ion energy and plasma potential as a function of radial distance were measured in a vacuum arc mode—the hot refractory anode vacuum arc. A 175 A arc was sustained between a 30-mm-diam water-cooled Cu cathode and a thermally isolated graphite anode. The plasma potential and electron temperature were determined using a triple probe, and the ion energy distribution was measured with a retarding field analyzer. It was found that the electron temperature decreased from 1.2 to 0.6 eV with increasing radial distance from 3 to 18 cm. In the same distance range, the directed ion energy per unit charge increased from 8 to 20 eV. The 12 eV ion energy enhancement significantly exceeded the measured drop of the plasma potential of about 2 V, indicating that the ions were not accelerated electrostatically.

CeO2 thin films grown on biaxially textured nickel (001)

CeO2 films have been grown on biaxially textured Ni substrates at various temperatures. The results show that CeO2 films without IBAD are dominated by (111) orientation from room temperature to 800°C while the preferential orientation of CeO2 films with IBAD is (001) at lower deposition temperature and (111) at deposition temperature higher than 450°C. CeO2 films with better in-plane texture and out-of-plane orientation can be grown at 360°C with 240 eV ion energy and 200 μA/cm2 ion current density.

Formation of boron nitride films with various amounts of the cubic phase

Abstract Boron nitride films with various structures have been prepared by low (500–700 eV) and medium energy (5000 eV) ion assisted evaporation on heated silicon substrates. Besides pure nitrogen gas, a mixture of argon/nitrogen was used. By changing the ion current density profile over the substrate area different film types can be grown in one vacuum run. Fourier Transformed Infrared Spectroscopy was carried out to collect information about the B-N bond-structure. For the control of the film stoichiometry and impurity contents Auger Electron Spectroscopy depth profiling analyses were conducted. X-ray Diffraction (XRD) data indicated the effect of different growth conditions (ion current density, ion energy, substrate temperature, gas mixture) on the orientation of the initial h-BN layer. As BN is a potential candidate for tribological applications, the surface topography of films is of major interest. From high resolution Scanning Electron Microscopy (up to 80 000-fold magnification) experiments, information about the effect of the growth conditions on the surface topography was obtained. Profilometer scans in connection with the other characterisation techniques let us get insight into different failures of the film adhesion. At 700 eV ion energy, Ar/N 2 gas mixtures of 40:60 vol.% and substrate temperatures of 450 °C, boron nitride films with more than 80% cubic phase content could be grown. At drastically reduced substrate temperatures of 250 °C, the c-BN growth was also successful. The results are discussed in the light of the effect of the ion assisted processes not only on the cubic phase evolution, but also on the degree of formation of an oriented initial h-BN layer, as monitored by XRD.

Gallium arsenide surface chemistry and surface damage in a chlorine high density plasma etch process

In an effort to monitor ion-driven surface chemistry in the high density plasma etching of GaAs by Cl2/Ar plasma chemistries, we have applied mass spectrometry and careful substrate temperature control. Etch product chlorides were mass analyzed while the substrate temperature was monitored by optical bandgap thermometry and as pressure (neutral flux), microwave power (ion flux) and rf bias of the substrate (ion energy) were varied. By ensuring that the substrate temperature does not deviate during process variations, the changes in product mass peak intensities are a direct measure of changes in the ionassisted surface chemistry which promotes anisotropic etching. Experimental results show that ion-assisted surface chemistry is optimum when sufficient Cl and Cl+ are present in the incident plasma flux. These conditions are met at low coupled microwave powers ( 200 eV. Photoreflectance measurements of the surface Fermi level show significant damage for ion energies >75 eV. However, in situ and ex situ surface passivations can recover the surface Fermi level for up to 200 eV ion energies, in good correlation to the onset of sputtering and subsurface damage. Thus, anisotropic, low damage pattern transfer is possible for ion energies between 50 and 200 eV.

Carbon nucleation on Si(100) using a negative carbon ion beam

The initial nucleation stages of carbon film on Si(100) substrates were investigated by low energy electron diffraction (LEED) and Auger electron spectroscopy. In the initial stages, energetic carbon ions lead to a phase transformation from a two domain p(2×1) to a (1×1) LEED structure pattern after about 6×1015 carbon ion/cm2 dose (3 atomic layers). At room temperature, the energetic carbon ions are deposited as silicon carbide (SiC) up to a thickness of about 10 atomic layers. As the deposition temperature increases to 300 °C, the thickness of the SiC interlayer increases to 30 atomic layers. An increased carbon ion dose leads to the formation of sp3 or sp2 rich carbon film depending on the carbon ion energy and the deposition temperature. Higher energy (150 eV) C− ion beams and lower deposition temperatures (room temperature) produce sp3 rich carbon films. At 150 eV ion energy, the transition temperature from sp3 to sp2 rich carbon film during deposition is about 150 °C. Lower energy (<50 eV) C− ion beams at room temperature produce sp2 rich carbon films. During postdeposition annealing, the sp3 rich carbon film deposited at room temperature was converted to an sp2 rich carbon film above 740 °C.

Composition and morphology of InP{100} surfaces as a function of low energy Ar + bombardment and annealing

The surface composition and morphology of the InP{001} surface have been studied by in situ Auger electron spectroscopy (AES) and ex situ atomic force microscopy (AFM) as a function of Ar + ion bombardment energy over the range 5 eV to 500 eV and annealing temperatures up to 600°C. Ion bombardment has been performed by means of a low energy, mass-selected, ultrahigh vacuum ion beam system. The surface contamination can be removed by Ar + ion bombardment with ≥ 30 eV ion energies for carbon and ≥ 60 eV ion energies for oxygen species. However, Indium-rich clusters and islanding are observed for Ar + ion energies above ∼ 40 eV. The results show that a combination of 30 eV Ar + ion bombardment and annealing to ∼ 300°C can produce an InP{100} surface which is devoid of observable impurities in AES and devoid of defect features in AFM.

The Effectiveness of Ta Prepared by Ion‐Assisted Deposition as a Diffusion Barrier Between Copper and Silicon

The diffusion barrier properties of Ta, both as deposited without ion bombardment and deposited concurrent with ion energy, were investigated in the Cu/Ta/Si contact system using Auger electron spectroscopy, x‐ray diffraction, optical microscopy, transmission electron microscopy, and sheet resistance measurements. It was found that the ion bombardment during deposition of Ta films influenced the microstructural characteristics, such as the packing density of grain boundaries, the grain size, and the preferred orientation of Ta grains. The Ta film deposited concurrent with 150 eV ion energy (0.13 mA/cm2) showed the increased packing density of grain boundaries, low resistivity, and preferred orientation. The densification of grain boundaries of the Ta barrier layer, followed by an increase of silicide formation temperature, significantly enhanced the barrier property of Ta in the Cu/Ta/Si system.

Organic Surface Analysis by Two-Laser Ion Trap Mass Spectrometry

This paper describes two-laser ion trap mass spectrometry (L2ITMS) for the analysis of organic, polymeric, and biological surfaces. L2ITMS uses one laser to desorb intact molecules from a surface, a second laser for photoionization, and an ion trap for single or tandem mass spectrometric analysis. We demonstrate the capabilities of this instrument by performing laser desorption/photoionization/tandem mass spectrometric analyses of amino acid and mixed polymer thin films. We then use L2ITMS in conjunction with X-ray photoelectron spectroscopy to chemically analyze the surface of an ion-bombarded polystyrene thin film. Low-energy SF5+ ion bombardment causes fluorination of intact polystyrene, partial destruction of the aromaticity of the polystyrene, fluorination of the resultant nonaromatic organic material, and sputtering of the polystyrene. The first of these dominates at 50 eV ion energy, while the latter three dominate at 250 eV.

Microstructure of c-BN Films Deposited by IBAD: IR and Hrem Analyses

ABSTRACTThe in-depth distribution of phases in c-BN films deposited by Ion Beam Assisted Deposition (IBAD) at two different ion energy values (300 and 600 eV) was investigated using the quantitative IR transmission measurements and the HREM technique. Whatever the value of the studied ion energies, the characteristic layered morphology of c-BN film is observed including the interfacial sp2 zone between the substrate and the c-BN volume. In the case of 600 eV ion energy, this interfacial zone is less well-defined in comparison with 300 eV ion energy and the corresponding thickness is more important. Furthermore, the h-BN phase is more diluted within the c-BN film volume showing that the purest phase concentration of c-BN is found for the lowest ion energy, i.e. 300 eV.

Inelastic mean free path of H + and He + with the energy of ∼ 100 keV in carbon film

The energy loss distributions of H + and He + with ∼ 100 keV transmitted through carbon films with a thickness of ∼ 6 nm have been measured by means of high-resolution (∼ 30 eV) ion energy loss spectroscopy. The zero energy loss peaks have been observed. The presence and effect of pinholes in films is inferred from the H 2 + transmission yield. Assuming that the intensity ratio of the zero energy loss peak over the sum of this peak and the main energy loss peak follows an exponential decrease with the film thickness, the inelastic mean free path was derived as 0.6 and 0.9 nm for H + and He + at 100 keV and these values are compared with the experimental values for equivelocity electrons and also with the calculated values for equivelocity electrons, positrons and protons.

Study of Low-energy Atomic Mixing by Means of Auger Depth Profiling, XTEM and TRIM Simulation on Ge/Si Multilayer System

Low-energy atomic mixing is experimentally studied on a Ge/Si amorphous multilayer system by means of Auger depth profiling and XTEM. The ion etching was performed by using Ar ions of energy 500 eV (XTEM) and 618 eV (Auger) and angle of incidence >84° and the specimen was rotated during sputtering. Applying these conditions it is believed that the interface broadening occurs mainly because of atomic mixing because the surface roughening is negligible. The Auger depth profile was carried out on a specimen containing Ge/Si strips parallel to the surface. The extent of the atomic mixing was determined by comparing the depth profile to profiles provided by dynamic TRIM simulation. For ion milling another geometry was used ; the Ge/Si strips were perpendicular to the surface. A very thin (2 nm) TEM specimen was prepared and the thickness of the completely mixed region could be directly estimated from the TEM image : 1 nm at 500 eV ion energy and 85° angle of incidence. The TEM image also shows that the atomic mixed region is asymmetric.

Growth and Characterization of AlN on 6H-SiC Substrates

ABSTRACTAIN/SiC structures are of current importance for the development of high temperature electronic devices. A systematic study of the growth and structure of AIN on Lely grown 6H-SiC was performed. The SiC substrates were chemically etched followed by thermal desorption at 875 °C under UHV conditions. AFM and RHEED images show the relative improvement in surface morphology following the cleaning procedure. AIN films were grown on 6H-SiC substrates using plasma source molecular beam epitaxy (PSMBE). Substrate temperatures were varied from 400 °C to 800 °C and deposition energies from 1 eV to 25 eV during AIN growth. The AIN crystal structure and topology were analyzed by RHEED and AFM. The AIN/SiC film microstructure are correlated with the quality of the SiC surface and the parameters of the AIN deposition process. Epitaxial growth of AIN(0002) was strongly dependent on the SiC surface quality and deposition energy. The highest quality AIN was achieved at growth temperatures of approximately 600 °C and 15 eV ion energy. Higher ion energy resulted in amorphous film growth.

Low-Energy Focused Ion Beam Doping during Molecular Beam Epitaxial Growth for the Fabrication of Three-Dimensional Devices: The Effect of Dopant Surface Segregation

An extreme example of surface segregation is found in Sn-doped GaAs grown by molecular beam epitaxy (MBE). Abrupt changes in the doping profile are not possible, instead the dopant concentration decreases exponentially towards the wafer surface from the point at which doping was terminated. In this work it is shown that segregation can be suppressed by implanting the Sn from a very-low-energy (50 to 300 eV) ion beam during growth. The effect of ion implantation energy is studied using secondary ion mass spectroscopy (SIMS) to measure the depth profile of the implanted Sn. It is found that the level of incorporation can be increased by up to a factor of eight using a 300 eV ion energy.

Uniform And Large Area Deposition Of Diamond-Like Carbon Using Rf Source Ion Beam

AbstractWe have designed and constructed a large area ion beam apparatus to deposit DLC films onto 1000 cm2surfaces with various geometries. The use of an efficient RF excited ion gun (13.56 MHz, 1 kW power, 50-3000 eV ion energy) with a diameter of 20 cm, enables us to generate various hydrocarbon ions with high ion beam currents, varying ionic species and less maintenance. The use of a four axis (Χ-ϒ-Θϒ-ΘZ) substrate scanner with computer control can produce uniform DLC films on large areas and curved surfaces. The effects of RF power, ion energy, gaseous composition, and total pressure on the properties of DLC have been systematically investigated.