Energy Sputtering Research Articles

Emission theory of amorphous-material sputtering. Energy dependence of the sputtering coefficient

The applicability conditions for the Boltzmann kinetic equation in describing the sputtering process are analyzed. The application of the kinetic equation for calculation of the sputtering coefficient is questionable because of the small depth of origin of sputtered particles. A physical model of the emission sputtering theory for amorphous materials is proposed. The threshold sputtering energies and energy dependence of the sputtering coefficient for amorphous materials are calculated in the framework of the proposed model for the case of the normal incidence of primary ions in the energy range of 10 to 105 eV. The calculations are in good agreement with the experimental results.

Sputtering of lithiated and oxidated carbon surfaces by low-energy deuterium irradiation

We study sputtering of lithiated and oxidized amorphous carbon surfaces by deuterium impact in energy range 5–30 eV. Using classical molecular dynamics, we obtain the sputtering yield, the mass and energy spectra, as well as the angular distribution of ejected atoms and molecules of the surfaces saturated by accumulated deuterium impacts. Our results are compared with existing experimental and theoretical data for amorphous a-C:D surfaces, showing that presence of lithium reduces erosion of carbon, while oxygen further enhances this effect.

Modeling of the glow discharge cathode sheath and the cathode surface sputtering in a mixture of argon with mercury vapor

A model of the glow discharge cathode sheath in a mixture of argon with mercury vapor used in gas discharge illuminating lamps is developed. It takes into account that at the stage of lamp ignition the mercury atom density is by several orders lower than the argon atom density and depends on the temperature. The cathode sheath characteristics are calculated and it is shown that at a temperature increase, due to growing contribution of the mercury atom Penning ionization, the discharge cathode voltage drop is decreased and the ratio of the mercury and argon ion current densities at the cathode is increased. The energy spectra of the mixture component ion flows bombarding the cathode surface, as well as their corresponding effective sputtering rates and the sputtered atom flow densities, are found. It is shown that at low values of the discharge current density mercury ions practically do not participate in the cathode sputtering because their energies are less than the threshold sputtering energy. However, at its higher values they can make a significant contribution to the sputtering despite the small mercury content in the mixture.

(Invited) Atomic Layer Etching of SiO2 and Other Materials Using Plasma Process Sequences

Angstrom-level precision in etching of SiO2 is possible using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4F8 molecules and synchronized plasma-based Ar+ ion bombardment.1 The physical sputter rate of SiO2 vanishes for Ar+ ion bombardment with a maximum ion energy of 20 eV and lower, whereas for a fluoroccarbon-coated SiO2 surface, chemical modifications of the SiO2 surface are induced by low energy ion bombardment and SiO2 etching is initiated. The question of SiO2:Si3N4 etching selectivity was studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Since Si3N4 has a lower physical sputtering energy threshold than SiO2, Si3N4 physical sputtering can take place after exhausting the chemical etchant at the end of each cycle for certain ion energies and leads to Si3N4/SiO2 etching selectivity. By optimization of the ALE process parameters, e.g. low ion energies, ESL, and FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for conditions where FC selectively accumulates on Si3N4 surfaces.2Mechanism of the observed ALE behaviors will be discussed using real-time and post-plasma surface analysis data. We will also discuss current challenges with the application of these approaches to other materials. Acknowledgements: I am pleased to acknowledge the essential contributions and collaboration of D. Metzler, C. Li, S. Engelmann, R. Bruce, E. Joseph, C. S. Lai, and E. A. Hudson to this work, and thank National Science Foundation (CBET-1134273), US Department of Energy (DE-SC0001939) and Semiconductor Research Corporation for funding. 1 D. Metzler, R. Bruce, S. Engelmann, E. A. Joseph, and G. S. Oehrlein, J. Vac. Sci. Technol. A 32, 020603 (2014). 2 C. Li, D. Metzler, C. S. Lai, E. A. Hudson, and G. S. Oehrlein, J. Vac. Sci. Technol. A 34, 041307 (2016).

Films Deposited from Reactive Sputtering of Aluminum Acetylacetonate Under Low Energy Ion Bombardment

Films were deposited from aluminum acetylacetonate (Al(acac)3) using a methodology involving reactive sputtering and low energy ion bombardment. The plasma was generated by the application of radiofrequency power to the powder containing electrode and simultaneously, negative pulses were supplied to the electrode where the substrates were attached. It was investigated the effect of the duty cycle of the pulses (Δ) on the properties of the coatings. Association of ion bombardment to the deposition process increased film thickness, structure reticulation and organic content. Ions from the deposition environment were implanted at the film-air interface or underneath it. Morphology and topography were altered depending on Δ. Considering the enhancement of Δ, it affected the flux of ions reaching the depositing interface and then the deposition rate, H content, crosslinking degree and surface microstructure. Alumina groups were detected in the infrared spectra, whereas the precipitation of amorphous alumina was confirmed by X-ray diffraction.

Erosion of nanostructured tungsten by laser ablation, sputtering and arcing

Mass loss of nanostructured tungsten, which was formed by helium plasma irradiation, due to laser ablation, sputtering, and arcing was investigated. Below the helium sputtering energy threshold (<117eV), sputtering by impurity gases such as nitrogen and oxygen was dominant. Sputtering yield became closer to theoretical value with increasing the incident ion energy, and sputtering by helium ions became the major contribution when the energy was >200eV. Reduction in sputtering on nanostructured surface was observed. Arcing was initiated using laser pulses, and the erosion rate by arcing was measured. The erosion rate increased with arc current, while the erosion per Coulomb was not affected by arc current.

Morphology of PbTe Crystal Surface Sputtered by Argon Plasma under Secondary Neutral Mass Spectrometry Conditions

We have investigated morphology of the lateral surfaces of PbTe crystal samples grown from melt by the Bridgman method sputtered by Ar+ plasma with ion energy of 50 – 550 eV for 5 - 50 minutes under Secondary Neutral Mass Spectrometry (SNMS) conditions. The sputtered PbTe crystal surface was found to be simultaneously both the source of sputtered material and the efficient substrate for re-deposition of the sputtered material during the depth profiling. During sputtering PbTe crystal surface is forming the dimple relief. To be re-deposited the sputtered Pb and Te form arrays of the microscopic surface structures in the shapes of hillocks, pyramids, cones and others on the PbTe crystal sputtered surface. Correlation between the density of re-deposited microscopic surface structures, their shape, and average size, on the one hand, and the energy and duration of sputtering, on the other, is revealed.

Fluorocarbon based atomic layer etching of Si3N4 and etching selectivity of SiO2 over Si3N4

Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO2 ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar+ ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO2 from the surface. In the present article, the authors describe controlled etching of Si3N4 and SiO2 layers of one to several Angstroms using this cyclic ALE approach. Si3N4 etching and etching selectivity of SiO2 over Si3N4 were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si3N4 were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si3N4 has a lower physical sputtering energy threshold than SiO2, Si3N4 physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si3N4 to SiO2 ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si3N4 surfaces. This highly selective etching is explained by a lower carbon consumption of Si3N4 as compared to SiO2. The comparison of C4F8 and CHF3 only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions, precursor chemistry has a weak impact on etching selectivity. Surface chemistry analysis shows that surface fluorination and FC reduction take place during a single ALE cycle for FC depleted conditions. A fluorine rich carbon layer was observed on the Si3N4 surface after ALE processes for which FC accumulation takes place. The angle resolved-XPS thickness calculations confirmed the results of the ellipsometry measurements in all cases.

Improving the growth of Ge/Si islands by modulating the spacing between screen and accelerator grids in ion beam sputtering deposition system

Ge islands were fabricated on Si buffer layer by ion beam sputtering deposition with a spacing between the screen and accelerator grids of either 1mm or 2mm. The Si buffer layer exhibits mixed-phase microcrystallinity for samples grown with 1mm spacing and crystallinity for those with 2mm spacing. Ge islands are larger and less dense than those grown on the crystalline buffer because of the selective growth mechanism on the microcrystalline buffer. Moreover, the nucleation site of Ge islands formed on the crystalline Si buffer is random. Ge islands grown at different grid-to-grid gaps are characterized by two key factors, namely, divergence half angle of ion beam and crystallinity of buffer layer. High grid-to-grid spacing results in small divergence half angle, thereby enhancing the sputtering energy and redistribution of sputtered atoms. The crystalline volume fraction of the microcrystalline Si buffer was obtained based on the integrated intensity ratio of Raman peaks. The islands show decreased density with decreasing crystalline volume fraction and are difficult to observe at crystalline volume fractions lower than 72%.

Nanopore formation in TiN membranes by the focused electron beam of a transmission electron microscope

The authors fabricated 2-nm nanopores in metallic TiN membranes with and without a SiNx layer using the highly focused electron beam (e-beam) of a transmission electron microscope. Nanopore evolution in TiN membranes was observed as a function of e-beam exposure time at e-beam energies of 200 and 300 kV. To investigate the mechanism of nanopore drilling in TiN membranes, plots of nanopore diameter against exposure time were converted to characteristic contrast curves of normalized drilling volume versus electron dose. The curves indicated that nanopore drilling in TiN metallic membranes using a high-energy focused e-beam is governed by direct atomic displacement or surface sputtering by elastic scattering between electrons and stationary atoms. The sputtering energy of TiN is about 9 eV.

Orientation selection in MgO thin films prepared by ion-beam-deposition without oxygen gas present

Ion assisted MgO film has attracted much attention because of its extensive application. Most of the related work was focused on ion assisted evaporation. In this work, MgO thin films were prepared by ion beam sputtering deposition without oxygen gas present. Effects of sputtering energy, deposition temperature, deposition angle and assisting ions on the orientation were analyzed. The orientation of MgO films is found strongly dependent on these parameters. As the parameters vary, (110), (111), (100) orientation is preferred in turn. The results surface morphology indicate that assisting ions can flatten the film surface and enhance the crystallinity. This orientation selection can be attributed to the energy exchange between assisting ions, deposition atom and adatoms. The results give the possibility to modulate the orientation to meet different demands.

Effect of the nanocrystalline structure type on the optical properties of TiO2:Nd (1 at.%) thin films

Titanium dioxide thin films, each doped with the same amount of neodymium (1at.%) were deposited by Low Pressure Hot Target Reactive Sputtering and High Energy Reactive Magnetron Sputtering processes in order to obtain anatase and rutile thin film structures respectively. The microstructure and phase composition were analyzed using the transmission electron microscopy method including high resolution electron microscopy imaging. The measurements of the optical properties showed, that both prepared thin films were transparent in the visible light range and had a low extinction coefficient of ca. 3⋅10−3. The thin film with the anatase structure had a lower cut-off wavelength and refractive index and a higher value of optical energy band gap as-compared to the TiO2:Nd coating with the rutile structure. Simultaneously, more efficient photoluminescence emission was observed for the rutile thin films.

Factors determining the efficiency of magnetron sputtering. Optimization criteria

We report on the results of experimental study of the dependence of sputtering energy efficiency Kw in a dc planar magnetron sputtering setup on the discharge power, working gas pressure, magnetic field, cathode erosion depth, and the structure of the gas puffing system and anode. We propose that this parameter be used for comparing the degree of perfection of the magnetron design irrespective of the magnetron size and structural features. The results of measurements of Kw in sputtering of Al, Ti, Cr, Cu, Zn, Zr, Nb, Mo, Ag, In, Sn, Ta, W, Pt, and Au are considered. The optimization criterion is worked out for the magnetic system of the magnetron, which ensures the minimal working pressure and the maximal sputtering rate for the cathode. The results are analyzed theoretically.

Holes drilling in gold and silver decahedral nanoparticles by the convergent beam electron diffraction electron beam

The 200 kV focused electron beam in the convergent beam electron diffraction patterns mode in a transmission electron microscope (TEM) with field emission gun is able to drill holes in gold and silver decahedral nanoparticles. However, although they are done under the same circumstances, the holes are shapeless in the silver and faceted in gold nanoparticles. In addition to this, the holes are closed during their high-resolution TEM observation in both materials. To comment their differences, displacement energy considerations are taken into account as function of the sputtering energy in order to modify the displacement cross-section of the processes.

Single material TiO2 double layers antireflection coating with photocatalytic property prepared by magnetron sputtering technique

Single material TiO2 was used to fabricate the double layers antireflection coating with photocatalytic property. TiO2 layers with low and high refractive indices were prepared by the direct reactive magnetron sputtering technique and energy filtrating magnetron sputtering technique, respectively. The structure, surface morphology and optical property were tested by X-ray diffraction, field emission scanning electron microscope and spectroscopic ellipsometer. The photocatalytic property of the coating was evaluated by UV–vis spectrophotometer. Results suggested that the coating had both antireflective and photocatalytic performances. The refractive indices of the top and bottom TiO2 layers were 2.10 and 2.47 (at 600 nm), respectively. The average and max transmissivities were obtained of 88.4% and 98.9% in the wavelength range of 400–800 nm and the degradation rate on Rhodamine B was obtained of 0.0034 min−1.

Quantitative analysis for CIGS thin films by surface analytical techniques

The compound semiconductor Cu(In,Ga)Se2 (CIGS) is well known as the next‐generation solar cell material because of its high absorption coefficient for solar radiation, suitable band gap, ability to be deposited on flexible substrate materials, and producing highly flexible and lightweight solar panels. In order to improve the performance of solar cells, a quantitative and depth‐resolved elemental analysis of photovoltaic thin films is strongly required. In this study, we determined the average concentration of the major elements, Cu, In, Ga, and Se in fabricated CIGS thin films, using inductively coupled plasma atomic emission spectrometry, X‐ray fluorescence, and electron probe microanalysis. Depth profiling results for CIGS samples using AES, XPS, magnetic sector SIMS, and time of flight SIMS were also obtained to compare their atomic concentration results. In the SIMS technique, detection of MCs+ clusters reduced possible matrix effects because of the variant concentrations of In and Ga. The reproducibility and accuracy of quantitative analysis were investigated as a function of ion sputtering energy. The compositional distributions of CIGS absorber layers as measured by MCs+–SIMS showed good agreement with those of AES and XPS. Copyright © 2014 John Wiley &amp; Sons, Ltd.

正极性电火花加工时能量及电极损耗机理分析

本文基于场致发射理论对阳极表面材的料溅射能量进行建模和分析。设计并进行了紫铜电极和A3#钢电极正极性单孔电火花加工对比实验，实验表明：电极损耗的原因主要是入射电子的溅射能引起的组织结合键断裂；紫铜电极比A3#钢电极加工时的极间放电能量大，故其加工效率也快。实验结果很好的验证了建立的模型分析的有效性。 In this paper, the work power was modeled and its related parameters were analyzed based on the field emission theory. The contrast experiments of single-hole EDM with different electrode materials as copper and A3 # steel were designed. The experimental results show that the main reason for electrode loss mainly was the fracture of organization combination key caused by incident electronic sputtering energy; and the processing efficiency of copper electrode is faster than A3 # steel electrode, because interelectrode discharge energy of copper electrode is more. The experimental phenomena and results verify the rationality and effectiveness of the proposed model.

Comparison of fullerene and large argon clusters for the molecular depth profiling of amino acid multilayers

A major challenge regarding the characterization of multilayer films is to perform high-resolution molecular depth profiling of, in particular, organic materials. This experimental work compares the performance of C60(+) and Ar1700(+) for the depth profiling of model multilayer organic films. In particular, the conditions under which the original interface widths (depth resolution) were preserved were investigated as a function of the sputtering energy. The multilayer samples consisted of three thin δ-layers (~8 nm) of the amino acid tyrosine embedded between four thicker layers (~93 nm) of the amino acid phenylalanine, all evaporated on to a silicon substrate under high vacuum. When C60(+) was used for sputtering, the interface quality degraded with depth through an increase of the apparent width and a decay of the signal intensity. Due to the continuous sputtering yield decline with increasing the C60(+) dose, the second and third δ-layers were shifted with respect to the first one; this deterioration was more pronounced at 10 keV, when the third δ-layer, and a fortiori the silicon substrate, could not be reached even after prolonged sputtering. When large argon clusters, Ar1700(+), were used for sputtering, a stable molecular signal and constant sputtering yield were achieved throughout the erosion process. The depth resolution parameters calculated for all δ-layers were very similar irrespective of the impact energy. The experimental interface widths of approximately 10 nm were barely larger than the theoretical thickness of 8 nm for the evaporated δ-layers.

Optical characterization and laser damage of fused silica optics after ion beam sputtering

The sputtering process of fused silica bombarded by Ar ion beam is simulated with the SRIM software. The effects of ion beam energy and incident angle on sputtering yield and surface damage are computed. Since ion beam sputtering will result in defects in fused silica, such as E′ color centers and other lattice defects and probably Argon bubbles, the optimized sputtering energy is selected below 1keV so that the projected range of Ar ions is less than 10Å. The experimental results show that the scratches in subsurface of fused silica can be smoothed obviously and better surface can be obtained as the optimized parameters are used for ion beam sputtering. The laser induced damage threshold of fused silica increases by about 18% after ion beam sputtering.

Simulations of micrometeoroid interactions with the Earth atmosphere

Micrometeoroids (cosmic dust with size between a few $\mu$m and $\sim$1 mm) dominate the annual extraterrestrial mass flux to the Earth. We investigate the range of physical processes occurring when micrometeoroids traverse the atmosphere. We compute the time (and altitude) dependent mass loss, energy balance, and dynamics to identify which processes determine their survival for a range of entry conditions. We develop a general numerical model for the micrometeoroid-atmosphere interaction. The equations of motion, energy, and mass balance are simultaneously solved for different entry conditions (e.g. initial radii, incident speeds and angles). Several different physical processes are taken into account in the equation of energy and in the mass balance, in order to understand their relative roles and evolution during the micrometeoroid-atmosphere interaction. In particular, to analyze the micrometeoroid thermal history we include in the energy balance: collisions with atmospheric particles, micrometeoroid radiation emission, evaporation, melting, sputtering and kinetic energy of the ablated mass. Low entry velocities and grazing incidence angles favor micrometeoroid survival. Among those that survive, our model distinguishes (1) micrometeoroids who reach the melting temperature and for which melting is the most effective mass loss mechanism, and (2) micrometeoroids for which ablation due to evaporation causes most of the the mass loss. Melting is the most effective cooling mechanism. Sputtering-induced mass loss is negligible.