Energy Ar Ion Research Articles

Calculation of high-energy ions exploded from argon clusters in high intensity femtosecond laser pulses

The modified nanoplasma model has been used to simulate the interaction of large Ar clusters with high intensity femtosecond laser pulses. The modified model has weakened the huge enhancement of electric field inside the clusters, thus provides a more reasonable explanation. The calculated mean kinetic energy of Ar ions is in good agreement with our previous experimental results. For further experimental work, it is the quantitative analysis of the variation of the mean kinetic energy and charge states of Ar ions exploded from the interactions with thecluster size and laser intensity.

Ｃｕ−９％Ａｌ（１１１）上に成長したエピタキシャルアルミナ膜の表面観察

We succeeded in growing the flat Al2O3 film on the Cu-9%Al (111) single crystal surface over a large area using the improved cleaning process, that is, low Ar ion energy and short time sputtering, and investigated the surface morphology and natures of chemical bond of Al2O3 film on the Cu-9%Al by means of Auger electron spectroscopy (AES) and a scanning electron microscopy (SEM). The Al2O3 film surface prepared by this method was uniformly flat, and the maximum thickness was about 4.0 nm. The Al and O KLL Auger peaks from Al2O3 film shifted toward low kinetic energy, and the shift reflected to band bending in the Al203 film near interface.

Theoretical investigation of high-energy ions produced from laser-cluster interactions

By using an effective dielectric constant to modify the nanoplasma model, the interactions of large Ar clusters with high-intensity femtosecond laser pulses have been studied. It is shown that the resonance absorption mechanism plays a predominant role in the production of highly energetic argon ions, and the calculated mean kinetic energy of Ar ions is in good agreement with our previous experimental results. The scaling of mean kinetic energy and charge states of Ar ions against cluster size and laser intensity has also been analyzed. The results indicate the existence of optimum cluster sizes and optimum laser intensities where the best coupling efficiency of the laser energy can be obtained.

Sputtering of SiC with low energy He and Ar ions under grazing incidence

The effect of low energy sputtering under grazing incidence upon the surface composition of SiC was investigated by Auger electron spectroscopy. The energy of the sputtering projectiles (He, Ar) varied from 200 to 1500 eV. Peak shifts to the higher energies with increasing argon ion energy were observed for all silicon and carbon Auger transitions. These shifts were explained by enhanced damage of the surface region within the sampling depth of the Auger electrons. The insensitivity of the Auger peak position to the energy of helium ions indicates that the damage state in the surface region does not change with the increasing energy of helium ions. An increase of the carbon concentration with the decrease of the argon energy was observed. The experiments were accompanied by dynamic Monte Carlo simulations by the TRIDYN code.

Ion beam-induced chemical vapor deposition with hexamethyldisilane for hydrogenated amorphous silicon carbide and silicon carbonitride films

We report on the preparation of hydrogenated amorphous silicon carbide (a-SiC:H) film and silicon carbonitride (a-SiCN:H) film on Si (100) substrate by Ar ion beam-induced chemical vapor deposition (IBICVD) method attached with a bubbling system of hexamethyldisilane (HMDS). Ar ions and HMDS precursor with carrier gases of Ar or N 2 were introduced onto the substrate at room temperature. Fourier transform infrared (FT-IR) spectra revealed that an elimination of an organic compound and the formation of SiC, SiN and CN bonds can be promoted by increasing ion impact energy. Smooth surface with a lower roughness has been achieved when Ar ion energy increases from 50 to 300 eV.

Nucleation and initial growth of platinum islands by plasma sputter deposition

The nucleation and islands growth of platinum have been followed from an early stage through to complete substrate coverage. Thus, this study of initial stages of thin film growth has allowed to improve the understanding of growth mechanisms and to control the final nanomaterials structure. In the presented deposition method, the metal atom source is a negatively biased metal wire submitted to the bombardment of ions created in HF plasma. The originality of this plasma sputtering technique is that in addition to the metal atom flux, the substrate surface is submitted to a high flux of low energy ions, inducing a high atomic surface mobility and modifying the growth mode with respect to conventional deposition techniques (magnetron sputtering or evaporation). Platinum deposits have been investigated by ex situ characterisation techniques: grazing incidence-small angle X-ray scattering (GISAXS) and X-ray diffraction (GIXD) in conjunction with transmission electron microscopy (TEM). Using morphological parameters as coverage rate, islands number density and islands size, different mechanisms (scale laws, islands mobility, coalescence, etc.) governing the growth are described vs. Ar ion and Pt atom energies and fluxes.

Electrical characterization of Ar-ion-bombardment-induceddamage in Au/Si and PtSi/Si Schottky barriercontacts

Au/Si and PtSi/Si Schottky contacts were prepared onn-Si(100) substrates which had been previously subjected to anAr ion bombardment with well defined energies ranging from100 eV to 1.5 keV. Samples were investigated bycurrent-voltage (I-V) measurements, ballisticelectron emission microscopy (BEEM) and deep-level transientspectroscopy (DLTS). Both I-V and BEEM results showthat the effective Schottky barrier height (SBH) decreases withincreasing Ar ion energy. The lowering of the barrier height isattributed to the bombardment-induced donor-like defects withrelatively high densities near the silicon surface. DLTSspectra show the presence of defect levels both in the formof discrete energy levels and as a continuum of states. Theoxygen-vacancy pair located at 0.16 eV below theconduction band is the dominant defect for the samples bombardedby 100 and 200 eV Ar ions and its peak signal intensity issimilar for the two energies. For 300 eV or higher-energy ion-bombarded samples, other defects develop and become dominant.Their peak signal intensities increase monotonically with Arion energy. The variation of the DLTS spectra is in qualitativeagreement with the tendency of effective SBH lowering forincreasing energy of the bombarding Ar ions.

Fundamental study of ion-irradiation effects on the columnar growth of chromium films prepared by ion-beam and vapor deposition

The effects of ion irradiation during deposition on columnar growth of Cr thin films prepared by ion-beam-assisted deposition were studied. Cr films were prepared by evaporation of Cr metal and simultaneous irradiation of Ar ions onto Si 〈100〉 wafers. The energies of Ar ions were varied over the range of 0.5–20.0 keV, and the transport ratios of irradiating Ar ions to depositing Cr atoms, TR(Ar/Cr), to the substrates were also varied between 0.01 and 0.20. Vaporized Cr atoms were deposited onto substrates at an angle of 45° from the substrate normal and Ar ions were irradiated perpendicular to the substrate surface. Si substrates were not rotated and were kept at low temperature during deposition by a water-cooling system. The experimental results showed that every Cr film had a columnar structure regardless of ion-irradiation conditions. The column size became larger with increasing ion energy and TR(Ar/Cr). The growth direction of the column tilted considerably with increasing ion energy and TR(Ar/Cr) in the cases where the Ar-ion energy was 10.0 keV or less. On the other hand, the column growth direction became perpendicular to the substrate with increasing TR(Ar/Cr) in the case where the ion energy was 20.0 keV. The difference of column growth direction due to ion irradiation conditions could be understood by considering the preferential adatom movements as well as the shadowing effect.

LIF Spectroscopy of a Cylindrical Magnetron Discharge

The energy and density distribution of Ar ions in the plasma of a cylindrical magnetron discharge was investigated by laser induced fluorescence (LIF). It was found that the density of the ions has a broad maximum extending into the negative glow and positive column. The density decrease is much faster towards the cathode than in the opposite direction, consistent with recently published results obtained by Langmuir probe measurements and numerical simulations. The spatial distribution of the “effective ion temperature” estimated from the line profile has a shape similar to that of the ion density distribution, with maximal value also inside the region of the negative glow but closer to the athode surface. The peak value is in the eV range for measurements perpendicular to the electric field and somewhat above 10 eV in the direction of the field.

Optimization of nitrogenated amorphous carbon films deposited by dual ion beam sputtering

Optimization of deposition conditions for nitrogenated amorphous carbon (a-C:N) films prepared by a dual ion beam sputtering (DIBS) technique is reported. A ripple structure was observed on the surface of a-C:N films, which was believed to be corresponding to the off-normal incidence bombardment by N ions during deposition. Infrared spectra indicated that the nitrogen atoms incorporated were bonded as C–N, CN and CN in the carbon network. The relative intensity of D and G bands obtained by fitting the Raman spectra showed that the sp 3 content in the a-C:N films increased as the Ar ion energy was increased and the sp 3 content was the highest with 100 eV N ion bombardment. The maximum micro-hardness achieved was about 25 GPa for the 200 nm thick a-C:N films deposited under the optimized conditions. The compressive stress ranged from 1 to 3 GPa. The optical band gap determined by spectral ellipsometry ranged from 0.6 to 1.0 eV. The refractive index and extinction coefficient at 633 nm wavelength were about 2.14 and 0.22 for the films deposited under the optimized conditions, respectively. Hardness, stress and optical band gap measurements showed a similar trend with the relative intensity of I D/ I G.

Charge Exchange Ion Energy Distribution at the RF Electrode in a Plasma Etching Chamber

Ar ion energy distribution affected by the charge exchange collision in a sheath was measured by an ion energy analyzer in the rf mode at the rf electrode in a plasma etching chamber. Dependence of the energy distribution on Ar gas pressure ranging from 1.4 to 19.3 mTorr was measured. Under high pressure, an extra peak in addition to the saddle-shaped peaks was observed, and the energy distribution of the ions in the low-energy region increased. These experimental features were adequately explained by a simple calculation model. We also calculated energy distributions of neutrals that were generated by the charge exchange collision, and suggested the connection of the high-energy neutrals with the plasma etching process.

Modification of tetrahedral amorphous carbon film by concurrent Ar ion bombardment during deposition

The surface morphology, mechanical and optical properties of tetrahedral amorphous carbon (ta-C) films by concurrent Ar ion bombardment during filtered cathodic vacuum arc (FCVA) deposition are investigated. The Ar ions were produced by an RF ion beam source at different ion energies ranging from 60 eV to 500 eV, in order to study the Ar ion-induced modification of ta-C films. Atomic force microscopy shows that all films are atomically smooth, with roughnesses (RMS) ranging from 0.17 to 0.43 nm. A rougher film surface has been attributed to a higher Ar ion energy. The compressive stress in the ta-C films ranges from 6.6 to 11.2 GPa and the microhardness from 34 to 67 GPa. A lower compressive stress and microhardness were observed at a higher Ar ion energy. The optical absorption spectrum shows that the edge has shifted to the lower photon energy side with the increasing Ar ion energy. The optical band gap decreases from 2.61 to 1.52 eV as the Ar ion energy is increased from 60 eV to 500 eV. The compressive stress, microhardness, optical absorption and optical band gap information suggests that the sp 2-bonded carbon atoms in the sp 3 matrix increase with the increasing Ar ion energy.

Monte Carlo simulation of angular distribution and fractionation in the zero-fluence isotope sputtering

A static Monte Carlo simulation program has been used to study the influence of primary and secondary knock-on atoms on the angular distribution and the fractionation, for zero-fluence sputtering of 92Mo– 100Mo. At 10 keV Xe ion energy, calculations show that significant depth-dependent momentum asymmetry exists in the near-surface region, as in Refs. (L.P. Zheng, R.S. Li, M.Y.Li, Nucl. Instr. and Meth. B 100 (1995) 490; L.P. Zheng, M.Y. Li, Nucl. Instr. and Meth. B 114 (1996) 28). The calculations also show that at the polar emission angle range between 0° and 90° the probabilities of the sputtered primary knock-on atoms for 92Mo and 100Mo are small (6.1% for 92Mo and 6.6% for 100Mo), especially, between 0° and 30° they are very small (2.5% for 92Mo and 2.8% for 100Mo). At 0.1 keV Ar ion energy, the calculations show that partial momentum flux ratios, for the primary and the secondary knock-on atoms, deviate far from one, through marker plane 1 (about an atomic layer distance from the surface).

Molecular dynamics simulations of low-energy (25–200 eV) argon ion interactions with silicon surfaces: Sputter yields and product formation pathways

The etch yield and subsurface damage are important issues in low energy (200 < eV) ion interactions with surfaces. In particular, atomic layer etching requires etching of electronic materials with monolayer precision and minimal interlayer atomic mixing. In this study, the molecular dynamics technique is used to simulate the impact of argon ions on chlorine-free and chlorine-passivated silicon surfaces, under conditions relevant to atomic layer etching. Thousands of individual ion impact simulations are performed on a massively parallel supercomputer. The silicon sputter yield is obtained for Ar ion energies ranging from 25 to 200 eV. Where possible, simulation results are compared to available experimental data. Volatile product formation during ion bombardment of ordered surfaces tends to follow distinct local trajectories. For example, the formation of products due to 120 eV Ar ions impacting onto Si(001)(2×1) at normal incidence has been found to occur mainly by a mechanism in which the Ar ion impacts directly in-between a surface silicon dimer pair. The energetic recoiled silicon atoms undercut nearby silicon atoms resulting in product formation. Several other product formation pathways have also been observed.

Incidence angle distributions of ions bombarding grounded surfaces in high density plasma reactors

Ion incidence angle distribution on surfaces in plasma etching reactors determines the shape evolution of via holes and trenches through its effects on the spatial variation of ion fluxes along the walls of these microscopic features. We describe a novel retarding-field energy analyzer design that is capable of measuring the energy and the incidence angle distributions of ions bombarding grounded surfaces in plasma reactors with sub-0.5° resolution. Using this analyzer we measured the energy and angle distributions of Ar ions incident onto a Si surface in a low-pressure helicon wave excited Ar plasma. Ion angle distributions are approximately Gaussian. In absence of collisions in the sheath, the width of the ion angle distribution function is determined by the ratio of the directed energy gained in the sheath to the random ion energy in the plasma. Variation of the ion angle distribution width as a function of plasma power and pressure is determined by the dependence of the sheath potential and the ion temperature on these externally controlled parameters. In low pressure Ar plasmas, the ion angle distribution broadens with increasing power and shows a maximum as a function of pressure in the range 0.5–4 mTorr.

Al-doped zinc oxide films deposited by simultaneous rf and dc excitation of a magnetron plasma: Relationships between plasma parameters and structural and electrical film properties

A new technique of the simultaneous excitation of a magnetron sputtering discharge by rf and dc was used for the deposition of undoped ZnO- and Al-doped ZnO (ZnO:Al) films. By this technique, it was possible to change the ion-to-neutral ratio ji/jn on the substrates during the film growth by more than a factor of ten, which was revealed by plasma monitor and Langmuir probe measurements. While for a pure dc discharge the ions impinging onto a floating substrate have energies of about Ei≈17 eV, the rf discharge is characterized by Ar-ion energies of about 35 eV. Furthermore, the ion current density for the rf excitation is higher by a factor of about five, which is caused by the higher plasma density in front of the substrate. This leads to a much higher ion-to-neutral ratio ji/jn on the growing film in the case of the rf discharge, which strongly influences the structural and electrical properties of the ZnO(:Al) films. The rf-grown films exhibit about the three times lower specific resistances (ρ≈6×10−4 Ω cm), due to lower mechanical stress, leading to higher charge carrier concentrations and mobilities. Undoped ZnO films exhibited the largest compressive stress values up to 2.8 GPa. The aluminium-doped films have a better (001) texture and larger grains (dg≈38 nm), which can be attributed to the beneficial role of Al as a surfactant. The better crystalline film quality of the ZnO:Al films is the reason for the much lower compressive stress of <0.5 GPa in these layers.

Determination of the Ion Sputtering-induced In-depth Distribution by Means of Elastic Peak Electron Spectroscopy

Elastic peak depth profiling was carried out on an Mo/Si multilayer system using a rotating specimen, grazing angle of incidence (86° with respect to the surface normal) and 0.5 keV Ar ion energy. The depth profiling was simulated by dynamic TRIM (T-DYN) code. The T-DYN code provided the in-depth distribution of the elements in any moment of the depth profiling process. Direct Monte Carlo calculation was developed to calculate the intensity of the elastic peak emitted from the distribution determined by the T-DYN code. Good agreement was found between the calculated and measured elastic peak depth profiles, proving that the Monte Carlo routine developed is readily applicable to inhomogeneous layers and the mixing of the Mo/Si layer is well described by the T-DYN code.

Determination of the Ion Sputteringinduced Indepth Distribution by Means of Elastic Peak Electron Spectroscopy

Elastic peak depth profiling was carried out on an Mo/Si multilayer system using a rotating specimen, grazing angle of incidence (86° with respect to the surface normal) and 0.5 keV Ar ion energy. The depth profiling was simulated by dynamic TRIM (T-DYN) code. The T-DYN code provided the in-depth distribution of the elements in any moment of the depth profiling process. Direct Monte Carlo calculation was developed to calculate the intensity of the elastic peak emitted from the distribution determined by the T-DYN code. Good agreement was found between the calculated and measured elastic peak depth profiles, proving that the Monte Carlo routine developed is readily applicable to inhomogeneous layers and the mixing of the Mo/Si layer is well described by the T-DYN code. © 1997 by John Wiley & Sons, Ltd.

Kinetic study of low energy argon ion-enhanced plasma etching of polysilicon with atomic/molecular chlorine

Surface kinetics of ion-enhanced chlorine plasma etching in the low ion energy regime was studied by utilizing Ar+ for ion bombardment and Cl and Cl2 as reactants. The argon ion and chlorine atom (molecular) fluxes were controlled independently over more than an order of magnitude and at flux levels within an order of magnitude of that typically used in high density plasma processes. The ion-enhanced etching yield was characterized as a function of Ar ion energy, ion flux, neutral-to-ion flux ratio, and the ion incident angle. Possible reaction pathways are proposed and reduced into a two-parameter model which is useable in a profile simulator. The etching yield increases with the increase of flux ratio but gradually saturates at higher flux ratios as the ion flux limits the etching yield. The ion energy dependence was found to scale linearly with (Eion1/2−Eth1/2), where the threshold energy Eth is found to be 16 eV. The etching yield of Cl is found to be similar to that of Cl2 at flux ratios below 10, but 4–5 times higher than that of Cl2 at higher flux ratios. The sticking coefficient of Cl2 is similar to that of Cl for smaller neutral-to-ion flux ratios where the ion bombardment produces highly reactive surface silicon sites for both atomic and molecular chlorine. At high neutral-to-ion flux ratios, however, the dissociative adsorption of molecular chlorine is slower than the adsorption of atomic chlorine on the highly chlorinated surfaces. The angular dependence of ion-enhanced etching yield was also measured. The etching yield was reduced by approximately 35% when an ion impingement angle was changed from normal impingement to 60° off-normal.

Effects of Ar bombardment on magnetic properties of Fe films deposited by double-ion-beam sputtering

The microstructure and magnetic properties of polycrystalline Fe films have been investigated in detail by controlling the condition of ion-beam sputtering with an Ar bombardment with a constant ratio of arrival rate of Fe to Ar. To control the Fe crystallite size, Fe films have been deposited at an Ar bombardment voltage VA in the range of 80–2000 V with the condition that the ratios of the arrival rate RA (atoms of Fe/atoms of Ar) were 1 to 1 (RA of 1) and 1 to 0.1 (RA of 0.1). Fe films with excellent soft magnetic characteristics for 4πMs of about 21.5 kG and HC of 2.5 Oe were deposited on the substrate bombarded by Ar ions with VA of 200 V at Rs of 1 and 400 V at RA of 0.1. The Ar bombardment had the two effects of raising the local temperature of the film surface and decreasing the Fe crystallite size. The orientation of crystals in the films may be related to the bombardment energy and amount of Ar ions. The high-energy bombardment formed a mixing layer between the deposited film and the surface of the substrate. These results imply that Ar bombardment by the proper energy and amount of Ar ions assists in improving the soft magnetic properties in the films.