Broad Beam Ion Research Articles

Characterization of an RF-excited broad beam ion source operated with a mixture of CHF3 and O2

The composition and ion energy distributions of the main ion species of an ion beam were recorded and analyzed. The RF-type broad beam ion source was operated with a mixture of CHF3 and O2. A plasma bridge neutralizer operating with Ar was employed for ion beam neutralization. The data were collected with an energy-selective mass spectrometer (ESMS). The mass spectrum showed numerous ion species, beginning with ionized molecules, dissociation products of the process gases and products from reactions with background gas and the plasma discharge vessel, and the extraction system. For a quantification of the ion beam composition, the mass dependent transmission functions for two ESMS were determined. The ion energy distributions show that, in comparison to operation with inert gases, there are additional slower ions present. These ions can be related to dissociation processes outside of the ion beam source. As a result of their typically lower etching yield, these slower ions affect the etching behavior.

Characterization of a broad beam ion source converted into a high intensity deuterium beam

Avalanche Energy is developing deuterium ion beams for the Orbitron fusion device. For these and similar projects, modification of off-the-shelf high current ion sources enables affordable and rapidly accessible alternatives to custom-built systems. We have successfully operated the Veeco MARK I broad beam source on deuterium to create multi-keV energy ions. Directing this beam through a small aperture required carefully designed optics. Once a narrower beam was created, a faraday cup was used to measure the beam current and profile while a Thomson Parabola was developed to help understand the beam species and energy composition.

Green to deep-red emissive carbon dot formation by C+ ion implantation on nitrogen beam created self-masked nano-template

We report the formation of green to red emissive arrays of carbon dot on silicon-nitride nano-templates by successive implantation of nitrogen and carbon broad ion beams. The patterned nano-templates are formed by 14 keV N2 + ion-bombardment at grazing incident (70°) on Si. Subsequently, 5 keV C+ ions are implanted at the selective sites of the pyramidal nano-template by taking advantage of the self-masking effect. The nano-pyramidal pattern and the implanted carbon dots at the specific sites are confirmed by atomic force microscopy and cross sectional transmission electron microscopy measurements. The developed carbon dots (CDs) are mostly amorphous and consists of SiC and graphitic nitrogen (CN). G-band and D-band carbons are identified by Raman spectroscopy, while the presence of SiC and CN are detected by XPS measurements. A change of band-gap is observed for C-implanted templates by the UV–vis spectroscopy. Excitation wavelength-dependent photoemission from the dots is found in the green to red region. Maximum intense PL is observed in the green–orange region for excitation wavelength of 425 nm and a redshift of PL with decreasing intensity is observed with the increase of excitation wavelength. The observed photoluminescence is described in terms of the combined effects of quantum confinement, graphitic nitrogen and defect induced additional states formation in the carbon dots. The potential applications of CDs are also addressed.

Low-energy ion beam erosion of Si with simultaneous co-deposition of metallic surfactants: Experimental and simulated data

Ion beam erosion of Si under co-deposition circumstances supports the formation of surface patterns on the nano- and micrometer scale. To evaluate the effect of surfactant sputtering within a setup relevant for ultra precision surface finishing, this work is presented. We present data for samples prepared with Ar ion beam erosion, at low ion energy. Al, Cu, steel, Cr, Ni, Mo, Ti, Ta, Zn and Si were chosen as co-deposition material. Simultaneous irradiation of the co-deposition material and the Si samples were performed with a broad beam ion source. The structuring and pattern formation are discussed with SEM and AFM measurements. It was shown that the evolution of structures on the substrate is induced by the silicide-forming metals. This corresponds with a higher surface roughness. Whereas the non-silicide-forming metals did not show patterning, and accordingly, lower surface roughness. Measurements regarding the Si removal rate showed, that it depends on the co-deposition material. Supporting simulation data proposed that the effect of the co-deposition material on the Si removal is determined by the combination of sputtering and scattering properties of the co-deposition material. The ratio of scattered Ar ions to sputtered metal particles describes the effect on the removal change. For metals which tend to higher scattering, the removal is enhanced. This applies for most of the metals with higher atomic number. Whereas the metals with lower atomic number favor self-sputtering, which results in an decreased Si removal.

Improving broad-beam ion etching equipment through innovative ion optics design

Ion beam etching (IBE) is a crucial technique used for the manufacturing of nanostructures, including blazed gratings and slanted gratings. In the overall design of a complete IBE system, the ion optics play an important role. To achieve a high-performance broad-beam ion source, the design of the ion optics presents greater challenges. In this study, a full-particle three-dimensional model was utilized to calculate the extraction of the ion beam from the discharge plasma, with the presentation of the influence of ion optics parameters on beam current. To enhance the beam current of broad-beam equipment, a novel approach to the design of the ion optics with chamfered apertures was proposed, followed by an investigation into the influence of chamfering parameters on the ion optics. The research provides a significant theoretical basis and a wide range of possibilities for the design and performance improvement of IBE ion optics.

Characterization of a broad beam Kaufman-type ion source operated with CHF3 and O2

Process stability and reproducibility are essential for highly precise manufacturing with reactive ion beam etching (RIBE) in optics industry. Therefore, the ion beam source characteristic must be well known. For this study, a Kaufman-type broad beam ion source operated with CHF3 and O2 is characterized with energy selective mass spectrometry and Faraday measurements. These results are compared with etching experiments on SiO2, Si, and AZ®1505 photo resist. The influence of the source setup and process conditions on ion beam composition, ion energy distribution, and the etch selectivity are discussed. It was found that etch selectivity applying different ion beam currents at a fixed feed gas composition correlate with resulting ion beam composition. Due to a change in ion beam composition, selectivity also changes with the total volumetric mass flow of the feed gas at a fixed ion beam current and constant mixing ratio of CHF3 and O2.

Methods to expose subsurface objects of interest identified from 3D imaging: The intermediate sample preparation stage in the correlative microscopy workflow.

The correlative imaging workflow is a method of combining information and data across modes (e.g. SEM, X-ray CT, FIB-SEM), scales (cm to nm) and dimensions (2D-3D-4D), providing a more holistic interpretation of the research question. Often, subsurface objects of interest (e.g. inclusions, pores, cracks, defects in multilayered samples) are identified from initial exploratory nondestructive 3D tomographic imaging (e.g. X-ray CT, XRM), and those objects need to be studied using additional techniques to obtain, for example, 2D chemical or crystallographic data. Consequently, an intermediate sample preparation step needs to be completed, where a targeted amount of sample surface material is removed, exposing and revealing the object of interest. At present, there is not one singular technique for removing varied thicknesses at high resolution and on a range of scales from cm to nm. Here, we review the manual and automated options currently available for targeted sample material removal, with a focus on those methods which are readily accessible in most laboratories. We summarise the approaches for manual grinding and polishing, automated grinding and polishing, microtome/ultramicrotome, and broad-beam ion milling (BBIM), with further review of other more specialist techniques including serial block face electron microscopy (SBF-SEM), and ion milling and laser approaches such as FIB-SEM, Xe plasma FIB-SEM, and femtosecond laser/LaserFIB. We also address factors which may influence the decision on a particular technique, including the composition, shape and size of the samples, sample mounting limitations, the amount of surface material to be removed, the accuracy and/or resolution of peripheral parts, the accuracy and/or resolution of the technique/instrumentation, and other more general factors such as accessibility to instrumentation, costs, and the time taken for experimentation. It is hoped that this study will provide researchers with a range of options for removal of specific amounts of sample surface material to reach subsurface objects of interest in both correlative and non-correlative workflows.

Emerging Technologies for Advanced 3D Package Characterization to Enable the More-Than-Moore Era

To continue Moore’s Law, semiconductor packaging is adopting new architectures, materials, and structures. Package dimensions are becoming thinner and smaller while going 3D to enable higher performance in smaller footprints. New package technologies such as chiplets, hybrid bonding, TSV silicon interposers and silicon interconnect bridges enable heterogenous integration of diverse functions, such as RF and logic, into a single package. The advanced electrical systems known as system-in-package (SiP) are comprised of many components and materials, each offering unique failure modes and challenges for diagnosis and analysis.The pace of materials and device development today, combined with the central role of IC packaging to meet the demands of system performance through More-than-Moore innovations, drives an urgent need for improved package characterization of structures and defects to aid fast development of reliable 3D packages. Traditional non-destructive techniques like 2D X-ray and scanning acoustic microscopy are hitting limits for 3D package analysis due to resolution and throughput limits. Focused ion beam scanning electron microscopes (FIB-SEM) enabled decades of technology advances for front-end-of-line (FEOL) and back-end-of-line (BEOL) processes, but their usefulness for packaging analysis is limited by slow FIB milling rates relative to the millimeter volumes of material that must be removed.As the line between packaging and silicon interconnects blurs, it becomes more difficult to localize and image defects and structures throughout the package life cycle, starting from material selection through development and on to high volume production and field failure diagnostics. Characterization and failure analysis instruments must work synergistically to provide fast results for rapid package development of products meeting the required electrical and mechanical specifications with high yield, high quality and high reliability.X-ray Computed Tomography (CT) has become a key enabler to solve 3D packaging challenges, because it can non-destructively image the interior of objects in 3D. X-ray Microscopy (XRM) extends this capability through higher resolution and increased versatility. Although 3D XRM achieves submicron resolution on full-sized intact packages, the trade-off for this performance is throughput. Traditional 3D XRM approaches can take many hours at the extreme end of highest resolution for largest package sizes. Meanwhile, the requirement for artifact-free cross sections of fast-shrinking package structures drives the use of ion beam technologies, such as broad Ar ion beams and Ga+ or Xe+ focused ion beams. Advances in packaging technology are pushing standard ion beam approaches beyond their limits, due to the combined need for precise end-pointing and rapid site-specific removal of millimeter volumes of material. Microbumps in 3D packages are 8,000 times smaller than solder balls, and 124 times smaller than C4 bumps [1], while I/O pitches are approaching 1 µm [Figure 1]. Broad Ar+ ion beams can be applied to large areas but lack the end-pointing specificity required by today’s advanced fine-pitch high density interconnect. While Ga+ FIB (used for semiconductor analysis) and Xe+ PFIB (used for far-BEOL structure analysis) deliver excellent end-pointing on the nanometer scale, both are unable to deliver the required milling rates to enable rapid site-specific cross-sectional analysis of structures deeply buried within 2.5/3D and other SiP packages.We present advanced microscopy innovations for 3D package analysis. 3D XRM data acquisition speeds can be increased by 4X and sometimes more than 10X when using artificial intelligence for reconstruction of 3D XRM data [2,3] [Figure 2]. In addition, the recent integration of a fs-laser onto a FIB-SEM enables site-specific material removal rates that are orders of magnitude faster than a FIB alone [4] [Figure 3]. Enabled by the high-accuracy end-pointing and fast milling achievable with a 100nA Ga+ beam, the new laser-integrated FIB-SEM, or LaserFIB, enables site-specific cross sectioning for SiP and complex package structures with high throughput. We show that when combining the 3D XRM and LaserFIB advances into a package analysis workflow, unprecedented capability emerges for rapid, high-resolution characterization of large structures and deeply buried features. This supports fast development of reliable next-generation package technology by providing the combination of speed, site targeting, and end-pointing accuracy required to address increasingly complex devices with higher throughput and analysis success rates. References ASE Group; accessed April 8, 2022 from https://ase.aseglobal.com/en/technology/advanced_25dic Harris et al., Putting AI to Work: A Practical and Simple Application to Improve 3D X-ray FA; International Reliability Physics Symposium (IRPS); Dallas, TX (2022).Gu et al., Accelerate Your 3D X-ray Failure Analysis by Deep Learning High Resolution Reconstruction. ISTFA (2021). https://doi.org/10.31399/asm.cp.istfa2021p0291 Tordoff et al., The LaserFIB: new application opportunities combining a high-performance FIB-SEM with femtosecond laser processing in an integrated second chamber. Applied Microscopy. 50(1), 24 (2020) Figure 1

Erratum: “Characterization of an RF excited broad beam ion source operating with inert gases” [J. Appl. Phys. 129, 223305 (2021)

Erratum: “Characterization of an RF excited broad beam ion source operating with inert gases” [J. Appl. Phys. 129, 223305 (2021)

Exploring the Infiltration Features of Perovskite within Mesoporous Carbon Stack Solar Cells Using Broad Beam Ion Milling.

Carbon perovskite solar cells (C-PSCs) are a popular photovoltaic technology currently undergoing extensive development on the global research scene. Whilst their record efficiency now rivals that of silicon PV in small-scale devices, C-PSCs still require considerable development to progress to a commercial-scale product. This study is the first of its kind to use broad beam ion milling for C-PSCs. It investigates how the carbon ink, usually optimised for maximum sheet conductivity, impacts the infiltration of the perovskite into the active layers, which in turn impacts the performance of the cells. Through the use of secondary electron microscopy with energy-dispersive X-ray spectroscopy, infiltration defects were revealed relating to carbon flake orientation. The cross sections imaged showed between a 2% and 100% inactive area within the C-PSCs due to this carbon blocking effect. The impact of these defects on the performance of solar cells is considerable, and by better understanding these defects devices can be improved for mass manufacture.

Impact of ion species on ion beam sputtered Ta2O5 layer quality parameters and on corresponding process productivity: A preinvestigation for large-area coatings

The demand for ion beam sputtering-coated substrates is growing. In order to introduce ion beam sputter deposition (IBSD) technology into new fields of application, the deposition area must be further increased. In this context, the ion species applied for the sputtering process is an important parameter. In the present investigation, an industrial scale IBSD process was characterized with respect to productivity and layer quality by varying the ion species. Ar, Kr, or Xe broad ion beams at an ion energy of 1.8 keV were used, and the evaluation was carried out on the basis of Ta2O5 layers. The dielectric films were produced in a reactive process through the sputtering of a metallic Ta target, and their two-dimensional distributions of the coating rate R, the refractive index n(320nm), and the extinction coefficient k(320nm) were determined over a planar area of 0.9 × 1.0 m2 above the target by the collection method. R served as a measure of productivity, while n(320nm) and k(320nm) were quality parameters. Additionally, the layer composition was determined for selected samples on the collector by an electron probe microanalyzer (EPMA). As expected, the different ion-solid interaction mechanisms resulted in significant differences with regard to productivity. Linear scaling of productivity as a function of ion mass was observed. Calculations of the sputtering yield with semiempirical models or SRIM-2013, a binary collision Monte Carlo simulation program, did not confirm the observed linearity. Furthermore, the configuration with the highest productivity, Xe, led to a locally occurring and significant reduction in layer quality, more precisely, an increase of k(320nm). Additionally, the layer compositions determined with EPMA confirmed that ions originating from the ion source were implanted in the thin films during their formation. A detailed evaluation of the angle-resolved energy distributions of the involved particles, simulated with SRIM-2013, was performed. However, the determination of the energies carried away from the target by backscattered ions and sputtered target atoms does not explain the observed degradation mechanism. This concludes that for the realization of future large-area coatings with IBSD, not all relevant mechanisms are yet understood in sufficient detail.

Comparative analysis of different charged particles emerging from a broad beam ion source

In this research, the ion-source is modified to produce differently charged particles; that could be successfully used in a variety of applications. The different parameters affecting the particles; neutral charge, electron, and positive ion emerging from a broad beam cold cathode ion source are studied using argon and nitrogen gases. The neutral and the electron current are measured using a simple technique. It is found that the neutral particles and the electrons depend on the positive ion current, gas pressure, and gas type. Also, the ratio of the neutral to the positive charge is increased by increasing the gas pressure and its reach to 1.2 at pressure 4 × 10-4 mbar in case of argon and reach to 1.45 at pressure 5 × 10-4mbar in case of nitrogen gas. Also; it is found that the ratio of the electron to the positive charge is inversely proportional to the gas pressure in the case of argon gas. But in the case of the nitrogen gas it is found that this ratio is directly proportional and reaches 2.1 at pressure 5 × 10-4mbar.

Characterization of an RF excited broad beam ion source operating with inert gases

Ion current density distributions, mass spectra, and ion energy distribution functions (IEDFs) for the use of Ar and mixtures of Ar/He and Ar/Ne in an RF broad beam ion source have been measured as a function of the extracted ion beam current and the applied RF-power. For the measurements, an array of Faraday probes and an energy-selective mass spectrometer have been used. Regardless of the gases or gas mixtures used, a broadening of the ion current density profile is measured at constant grid voltages with increasing RF-power. The IEDFs of all species are also dependent on the applied RF-power and show a bimodal shape with an increasing energy shift for a higher RF-power. The data show a significant contribution of charge exchange processes after the ions left the ion beam source. Besides ions of the process gas, additional species of ions originating from the erosion processes of the ion beam source, can be found in the mass spectrum. The measurements show that the operating conditions of the ion source have a significant influence on the beam properties and thus can also affect the results of ultraprecise ion beam-assisted processes.

Nanoscale dynamics during self-organized ion beam patterning of Si. II. Kr+ bombardment

Despite extensive study, fundamental understanding of self-organized patterning by broad-beam ion bombardment is still incomplete and controversial. Understanding the nanopatterning of elemental semiconductors, particularly silicon, is both foundational for the broader field and of intrinsic scientific and technological interest itself. This is the second component of a two-part investigation of the kinetics and fluctuation dynamics of self-organized nanoscale ripple development on silicon during 1 keV Ar$^+$ (Part I) and Kr$^+$ bombardment. Here, it's found that the ion-enhanced viscous flow relaxation is essentially equal for Kr$^+$-induced patterning as previously found for Ar$^+$ patterning. The magnitude of the surface curvature dependent roughening rate in the early stage kinetics is larger for Kr$^+$ than for Ar$^+$, qualitatively consistent with expectations for erosive and mass redistributive contributions to the initial surface instability. As with the Ar$^+$ case, fluctuation dynamics in the late stage show a peak in correlation time at the length scale corresponding to the dominant structural feature on the surface -- the ripples. Analogy is made to the phenomenon of de Gennes narrowing in liquids, but significant differences are also pointed out. Finally, it's shown that speckle motion during the surface evolution can be analyzed to determine spatial inhomogeneities in erosion rate and ripple velocity on the surface. This allows the direction and speed of ripple motion to be measured in real time, a unique capability for measuring these fundamental parameters outside the specialized environment of FIB/SEM systems.

Nanoscale pattern formation on solid surfaces bombarded by two broad ion beams in the regime in which sputtering is negligible

We study nanoscale pattern formation on the surface of a solid that is bombarded with two diametrically opposed, broad ion beams for ion energies low enough that sputtering can be neglected. We focus on the case in which the angle of ion incidence is just above the threshold angle for pattern formation. The equation of motion at sufficiently long times is derived using a generalized crater function formalism. This formalism also yields expressions for the coefficients in the equation of motion in terms of crater function moments. We find that virtually defect-free ripples with a sawtooth profile can emerge at sufficiently long times. The ripples also coarsen as time passes, in contrast to the near-threshold behavior of ripples in the higher energy regime in which sputtering is significant.

Parameter estimation for pattern formation induced by ion bombardment of solid surfaces using deep learning

The nanostructures produced by oblique-incidence broad beam ion bombardment of a solid surface are usually modelled by the anisotropic Kuramoto–Sivashinsky equation. This equation has five parameters, each of which depend on the target material and the ion species, energy, and angle of incidence. We have developed a deep learning model that uses a single image of the surface to estimate all five parameters in the equation of motion with root-mean-square errors that are under 3% of the parameter ranges used for training. This provides a tool that will allow experimentalists to quickly ascertain the parameters for a given sputtering experiment. It could also provide an independent check on other methods of estimating parameters such as atomistic simulations combined with the crater function formalism.

Artifact-free microstructures of the Cu–In reaction by using cryogenic broad argon beam ion polishing

Metallurgical systems containing substantial amounts of metallic indium have always been very challenging to investigate due to the difficulties involved with sample characterization caused by the substantial softness of indium. Such difficulties are overcome in this study, and artifact-free microstructures are successfully obtained for the first time by using cryogenic broad Ar beam ion polishing for the reactions between Cu and molten indium at 180 ℃. A two-phase layer consisting of Cu11In9 and In forms at the Cu/In interface. The growth of this layer follows parabolic kinetics, indicating that it is a diffusion-controlled process. Within the layer, Cu11In9 islands are larger near the In side than those near the Cu side, suggesting that coarsening of the Cu11In9 islands occurs. During the cooling process after the reaction, large faceted Cu11In9 islands heterogeneously precipitate over the two-phase layer. Simultaneously, nonfaceted Cu11In9 particles homogeneously precipitate within the In phase.

ION BEAM IRRADIATION EFFECTS ON SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF ZnO/PVA COMPOSITES

Polymer nanocomposites composed of zinc oxide nanoparticles (ZnO NPs)-doped polyvinyl alcohol (PVA) polymer matrix have been synthesized using solvent casting preparation method. The ZnO/PVA polymer nanocomposite films are irradiated with different argon ion beam fluences using broad-beam ion source. The prepared films are characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and UV–visible spectroscopy. The XRD shows that ZnO NPs are successfully formed on PVA polymer and the mean size of ZnO NPs is 31.2[Formula: see text]nm. The FTIR peaks indicate that ZnO NPs are attached to the polymer chains, whereas the SEM analysis shows that ZnO NPs are homogeneously dispersed into the PVA polymer surface. The optical bandgap, band tail width and number of carbon atoms in cluster are obtained and discussed using UV–visible spectroscopy. The transmittance is shown with low transmittance intensity in the UV region with the addition of ZnO NPs and ion beam irradiation. The optical bandgap [Formula: see text] showed significant decrease from 5.25[Formula: see text]eV for pristine PVA to 3.10[Formula: see text]eV by adding ZnO and from 3.10[Formula: see text]eV for un-irradiated ZnO/PVA to 2.98[Formula: see text]eV after being irradiated by [Formula: see text][Formula: see text]cm[Formula: see text]. The number of carbon atoms in cluster [Formula: see text] is increased by ZnO addition, whereas the Urbach energy [Formula: see text] is decreased. These results confirmed that there are significant modifications in PVA polymer, and the produced flexible ZnO/PVA is a good polymer nanocomposite film for technological applications.

In situ XRD measurements to explore phase formation in the near surface region

Though X-ray diffraction (XRD) is a well-established technique—yet still continuously evolving—for characterization of thin films and diffusion layers, there are two inherent limitations due to the underlying physical principles leading to the diffraction: (i) all data are a weighted integral across the information depth and (ii) X-ray amorphous or nanocrystalline phases are very difficult to be detected. The purpose of this Perspective is to show how a straightforward combination of in situ XRD with depth profiling using a laboratory experiment in combination with a low-energy broad-beam ion source may allow us to overcome these limitations for functional surfaces. Whereas time-resolved investigations of diffusion and phase formation during ion implantation using reactive species are well established, using ion beam sputtering with nonreactive species for depth profiling of the phase composition during the measurements is a rather recent development. While employing analysis of differential spectra leads to a depth resolution below the information depth, ongoing in situ sputtering will lead to information obtained from layers deeper than the information depth. Keeping track of the total diffraction intensity permits the identification of phases without reflections in the XRD measurements, i.e., they appear to be amorphous, and their depth distribution. Selected examples drawn mainly from investigations of the nitriding kinetics of austenitic stainless steel will be used to demonstrate the potential and possible limitations of this method.

Characterization and optimization of low-energy broad-beam ion source

In this work, a cold-cathode ion source was modified to produce a broad beam that could be successfully used in a variety of applications. The ion source features gave reliable, long-term, maintenance-free operation. The ion source was surrounded by a magnetic field to produce uniform plasma in limited volume at low gas pressures (10−3 torr). The output ion beam current was up to 700 μA, and the diameter of the cold cathode was broad (∼25 mm). The stainless steel cathode disk and the cylindrical anode were separated by a Teflon flange. The fabrication of the source was simple, and a stable discharge medium was obtained by adjusting the operating conditions, such as discharge voltage, magnetic field intensity and argon (Ar) gas pressure. Also, the output ion beam was measured at different acceleration voltages. Moreover, the ion beam profile is characterized at different magnetic field intensities.