Probability of ionization of sputtered particles as a function of their energy: Part I: Negative Si ions

In this study we have investigated how the probability of ionization of sputtered Si atoms to form negative ions depends on the energy of the atoms. We have determined the ionization probability from experimental SIMS energy distributions using a special experimental technique, which included de-convolution of the energy distribution with an instrumental transmission function, found by separate measurements.We found that the ionization probability increases as a power law ∼E^0.677 for particles sputtered with energies of 0-10 eV, then becomes a constant value (within the limits of experimental error) for particles sputtered with energies of 30-100 eV. The energy distributions of Si⁻ ions, measured under argon and cesium ion sputtering, confirmed this radical difference between the yields from low and high-energy ions.To explain these results we have considered ionization mechanisms that are different for the low energy atoms (<10 eV) and for the atoms emitted with higher energy (>30 eV).     

Kinetic electron emission due to perpendicular impact of carbon ions on tungsten surfaces

Total electron yields for perpendicular impact of C⁺ ions on W have been measured for projectile energies from 0.2 keV to 7 keV. The data are compared with the data of C⁺ bombardment of gold and graphite in order to demonstrate general trends in kinetic electron yields at low projectile velocities. The total electron yields in the studied combinations of projectiles and substrates show a similar exponential dependence Γ ∝ (v/A) exp(−A/v), where A is a constant and v is the projectile velocity.     

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

Effects of evolving surface morphology on yield during focused ion beam milling of carbon

We investigate evolving surface morphology during focused ion beam bombardment of C and determine its effects on sputter yield over a large range of ion dose (10¹⁷-10¹⁹ ions/cm²) and incidence angles (Θ = 0-80°). Carbon bombarded by 20 keV Ga⁺ either retains a smooth sputtered surface or develops one of two rough surface morphologies (sinusoidal ripples or steps/terraces) depending on the angle of ion incidence. For conditions that lead to smooth sputter-eroded surfaces there is no change in yield with ion dose after erosion of the solid commences. However, for all conditions that lead to surface roughening we observe coarsening of morphology with increased ion dose and a concomitant decrease in yield. A decrease in yield occurs as surface ripples increase wavelength and, for large Θ, as step/terrace morphologies evolve. The yield also decreases with dose as rippled surfaces transition to have steps and terraces at Θ = 75°. Similar trends of decreasing yield are found for H₂O-assisted focused ion beam milling. The effects of changing surface morphology on yield are explained by the varying incidence angles exposed to the high-energy beam.     

Amorphization of Si (100) under O implantation studied by spectroscopic ellipsometry

The amorphization of crystalline Si (100) under 125 keV O⁺ ion implantation is investigated in the fluence range 1×10¹⁴ ions/cm² to 1×10¹⁶ ions/cm². The microstructure of the O⁺ implanted Si is modeled from ellipsometric data using a two phase, multilayer model within Bruggeman effective medium approximation (BEMA). The transition from the crystalline to the amorphous phase is found to be smooth and progressive. From a detailed analysis of the moments of the dielectric spectra and laser Raman spectroscopy, we infer that the amorphization occurs through a progressive disruption of long-range order caused by the overlap of amorphous nanozones. The dielectric spectrum of the fully amorphous phase is characterized using the Forouhi-Bloomer interband model.     

Estimation of diffusion coefficient by photoemission electron microscopy in ion-implanted nanostructures

We have fabricated parallel stripes of nanostructures in an n-type Si substrate by implanting 30 keV Ga⁺ ions from a focused ion beam (FIB) source. Two sets of implantation were carried out. In one case, during implantation the substrate was held at room temperature and in the other case at 400 °C. Photoemission electron microscopy (PEEM) was carried out on these samples. The implanted parallel stripes, each with a nominal dimension of 4000 nm × 100 nm, appear as bright regions in the PEEM image. Line scans of the intensities from the PEEM image were recorded along and across these stripes. The intensity profile at the edges of a line scan is broader for the implantation carried out at 400 °C compared to room temperature. From the analysis of this intensity profile, the lateral diffusion coefficient of Ga in silicon was estimated assuming that the PEEM intensity is proportional to Ga concentration. The diffusion coefficient at 400 °C has been estimated to be ∼1.3 × 10⁻¹⁵ m²/s. Across the stripes an asymmetric diffusion profile has been observed, which has been related to the sequence of implantation of these stripes and the associated defect distribution due to lateral straggling of the implanted ions.     

Synthesis of molybdenum silicide by both ion implantation and ion beam assisted deposition

Two groups of Mo/Si films were deposited on surface of Si(1 0 0) crystal. The first group of the samples was prepared by both ion beam assisted deposition (IBAD) and metal vapor vacuum arc (MEVVA) ion implantation technologies under temperatures from 200 to 400 °C. The deposited species of IBAD were Mo and Si, and different sputtering Ar ion densities were selected. The mixed Mo/Si films were implanted by Mo ion with energy of 94 keV, and fluence of Mo ion was 5 × 10¹⁶ ions/cm². The second group of the samples was prepared only by IBAD under the same test temperature range. The Mo/Si samples were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), sheet resistance, nanohardness, and modulus of the Mo/Si films were also measured. For the Mo/Si films implanted with Mo ion, XRD results indicate that phase of the Mo/Si films prepared at 400 and 300 °C was pure MoSi₂. Sheet resistance of the Mo/Si films implanted with Mo ion was less than that of the Mo/Si films prepared without ion implantation. Nanohardness and modulus of the Mo/Si films were obviously affected by test parameters.     

Synthesis of silicon carbide films by combined implantation with sputtering techniques

Silicon carbide (SiC) films were synthesized by combined metal vapor vacuum arc (MEVVA) ion implantation with ion beam assisted deposition (IBAD) techniques. Carbon ions with 40 keV energy were implanted into Si(1 0 0) substrates at ion fluence of 5 × 10¹⁶ ions/cm². Then silicon and carbon atoms were co-sputtered on the Si(1 0 0) substrate surface, at the same time the samples underwent assistant Ar-ion irradiation at 20 keV energy. A group of samples with substrate temperatures ranging from 400 to 600 °C were used to analyze the effect of temperature on formation of the SiC film. Influence of the assistant Ar-ion irradiation was also investigated. The structure, morphology and mechanical properties of the deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation, respectively. The bond configurations were obtained from IR absorption and Raman spectroscopy. The experimental results indicate that microcrystalline SiC films were synthesized at 600 °C. The substrate temperature and assistant Ar-ion irradiation played a key role in the process. The assistant Ar-ion irradiation also helps increasing the nanohardness and bulk modulus of the SiC films. The best values of nanohardness and bulk modulus were 24.1 and 282.6 GPa, respectively.     

Enhancement effect in photon-stimulated ion desorption for benzene adsorbed on silicon surfaces observed using angle-dependent technique

We have investigated photon-stimulated ion desorption from deuterated benzene (C₆D₆) adsorbed on Si(1 0 0) and Si(1 1 1) surfaces following C 1s core excitation. Using time-of-flight mass spectrometry combined with angle-dependent technique, we measured the dependences of mass-spectra of desorption ions on photon energies and on incident angle (θ) of synchrotron beam. We have found the ion yields for adsorbate-derived fragments of CD⁺ and CD₂⁺ are enhanced in very small angles of incident X-rays. Moreover, molecular orientation effect appeared in excitation energy dependences of D⁺ ions from the Si(1 0 0) and Si(1 1 1) surfaces; that is, ion yield spectra measured at θ = 10° are different from that at θ = 65°. Furthermore, it was found that desorption ion yields increase greatly with decreasing incident angles. The angular dependences are consistently similar for all ion species, excitation energies, and indexes of substrates. Possible desorption processes are described on the basis of the observations.     

Exit angle dependence of charge-state distribution of backscattered He ions

Exit angle and energy dependences of the charge-state distribution of backscattered He ions were investigated when 500 keV He⁺ ions were incident on SiO₂. The energy dependence of the He⁺ fraction was estimated by comparing the measured He⁺ spectra with the simulated spectra of He ions in all charge states at the exit angles of 5-25° with respect to the SiO₂ surface. We found that the He⁺ fraction is almost independent of the exit angle at energies higher than 250 keV and the observed energy dependence of the He⁺ fraction is in good agreement with that for the carbon-foil-transmission experiment. In the low energy region (<250 keV), however, the He⁺ fraction decreases as the exit angle decreases.     

Secondary ion emission from Si bombarded with large Ar cluster ions under UHV conditions

Si was bombarded with size-selected 40 keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si⁺ ions were main species detected under the incidence of 40 keV Ar cluster ions, and the yields of Si cluster ions such as Si₄⁺ were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO⁺ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields.     

A method for the determination of recoil ion ranges needed in DSA measurements

From the yield curve of the²⁷Al(p, γ)²⁸Si reaction obtained with implanted targets, the range distributions and mean ranges of 50 keV Al⁺-ions have been determined in C, Cu, Mo and Ta. The energy straggling of protons has been taken into account in the analysis. The DSA lifetime values in different backing materials are in good agreement when measured ranges are used for the determination of the stopping parameters.     

Photoluminescence spectra of nitrogen implanted GaSe crystals

GaSe single crystals were N-implanted along c-axis with ion beams of 10¹⁴ and 10¹⁶ ions/cm² doses having energy values of 60 and 100 keV. The photoluminescence (PL) spectra of undoped and N-implanted GaSe crystals were measured at different temperatures. The PL intensity was observed to decrease with increasing implantation dose while the FWHM of the exciton peaks increased. In heavily doped crystals, due to the interaction with the radiation induced disorders, the wave vector selection rules are satisfied and an indirect exciton PL band is observed 36 meV below the direct exciton states.     

Surface nano-structural modifications and characteristics in nitrogen ion implanted W as a function of temperature and N energy

The surface modifications of tungsten massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16-30 keV with a fluence of 1 × 10¹⁸ N⁺ cm⁻² were implanted in tungsten samples for 1600 s at different temperatures. XRD patterns clearly showed WN₂ (0 1 8) (rhombohedral) very close to W (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from WN₂ (0 1 8) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The surface roughness variation with temperature generally showed a decrease with increasing temperature. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in W studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in W at certain temperatures, which are both consistent with XRD results (i.e., I_{W (2 0 0)}/I_{W (2 1 1)}) for W (bcc). Hence, showing a correlation between XRD and SIMS results.     

Nonlinear optical properties of Cu nanoclusters by ion implantation in silicate glass

Metal nanocluster composite glass prepared by 180 keV Cu ions into silica with dose of 1 × 10¹⁷ ions/cm² has been studied. The microstructural properties of the nanoclusters were analysed by optical absorption spectra and transmission electron microscopy (TEM). Third-order nonlinear optical properties of the nanoclusters were measured at 1064 nm and 532 nm excitations using Z-scan technique. The nonlinear refraction index, nonlinear absorption coefficient, and the real and imaginary parts of the third-order nonlinear susceptibility were deduced. The mechanisms responsible for the nonlinear response were discussed. Absolute third-order nonlinear susceptibility χ⁽³⁾ of this kind of sample was determined to be 2.1 × 10⁻⁷ esu at 532 nm and 1.2 × 10⁻⁷ esu at 1064 nm, respectively.     

铒离子注入6H-SiC的横向离散研究

利用离子注入掺杂技术设计、制作半导体集成器件时,了解离子注入半导体材料的射程分布、射程离散和横向离散规律等是很重要的.用400 keV能量的铒(Er)离子分别与样品表面法线方向成0°,45°和 60°倾角注入碳化硅(6H-SiC)晶体中,利用卢瑟福背散射技术研究了剂量为5×10¹⁵ cm^-2 的400 keV Er离子注入6H-SiC晶体的横向离散.测出的实验值与TRIM98和SRIM 2006得到的理论模拟值进行了比较,发现实验值跟TRIM98和SRIM 关键词： 离子注入 6H-SiC 卢瑟福背散射技术 横向离散     

Formation of nanodots on oblique ion sputtered InP surfaces

Using a field emission gun based scanning electron microscopy, we report the formation of nanodots on the InP surfaces after bombardment by 100 keV Ar⁺ ions under off-normal ion incidence (30° and 60° with respect to the surface normal) condition in the fluence range of 1 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻². Nanodots start forming after a threshold fluence of about 1 × 10¹⁷ ions cm⁻². It is also seen that although the average dot diameter increases with fluence the average number of dots decreases with increasing fluence. Formation of such nanostructured features is attributed due to ion-beam sputtering. X-ray photoelectron spectroscopy analysis of the ion sputtered surface clearly shows In enrichment of the sputtered InP surface. The observation of growth of nanodots on the Ar⁺-ion sputtered InP surface under the present experimental condition matches well with the recent simulation results based on an atomistic model of sputter erosion.     

Damage formation in Ge during Ar and He implantation at 15 K

Ar⁺ and He⁺ ions were implanted into Ge samples with (1 0 0), (1 1 0), (1 1 1) and (1 1 2) orientations at 15 K with fluences ranging from 1×10¹¹ to 1×10¹⁴ cm⁻² for the Ar⁺ ions and fluences ranging from 1×10¹² to 6×10¹⁵ cm⁻² for the He⁺ ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar⁺ and 40 keV He⁺ implantation, RBS analysis was performed with 1.4 MeV He⁺ ions.For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.     

Carbon sputtering yield measurements at grazing incidence

In this investigation, carbon sputtering yields were measured experimentally at varying angles of incidence under Xe⁺ bombardment. The measurements were obtained by etching a coated quartz crystal microbalance (QCM) with a low energy ion beam. The material properties of the carbon targets were characterized with a scanning electron microscope (SEM) and Raman spectroscopy. C sputtering yields measured under Ar⁺ and Xe⁺ bombardment at normal incidence displayed satisfactory agreement with previously published data over an energy range of 200 eV-1 keV. For Xe⁺ ions, the dependence of the yields on angle of incidence θ was determined for 0° ≤ θ ≤ 80°. Over this range, an increase in C sputtering yield by a factor of 4.8 was observed, with the peak in yield occurring at 70°. This is a much higher variation compared to Xe⁺ → Mo yields under similar conditions, a difference that may be attributed to higher scattering of the incident particles transverse to the beam direction than in the case of Xe⁺ → C. In addition, the variation of the yields with θ was not strongly energy dependent. Trapping of Xe in the surface was observed, in contrast to observations using the QCM technique with metallic target materials. Finally, target surface roughness was characterized using atomic force microscope measurements to distinguish between the effects of local and overall angle of incidence of the target.