Gas Cluster Ion Research Articles

Advancement of Gas Cluster Ion Beam Processes for Chemically Enhanced Surface Modification and Etching

Gas cluster ion beam (GCIB) shows unique irradiation effects such as surface smoothing, surface analysis, shallow implantation, surface smoothing, and thin film formations. Upon GCIB impact, dense energy is deposited on surface layer while energy/atom of GCIB is low. One of the unique characteristics of GCIB is the enhancement of chemical reactions without heating the substrates. When reactive GCIBs are used, high-rate etching of various materials is expected. Not only reactions between molecules in the cluster and target atoms, but also chemical reactions between target atoms and the adsorbed gas on target are enhanced. In this paper, advancement of GCIB process by chemically enhanced surface modification and etching is reported.

Probing the persistence of energy-level control effects at organic semiconductor/electrode interfaces based on photoemission spectroscopy combined with Ar gas cluster ion beam sputtering

Thein situPES – Ar GCIB sputtering combined analysis enable to characterize the persistence of controlled energy-level at organic semiconductor/electrode interfaces.

Retracted: Mass analysis by Ar-GCIB-dynamic SIMS for organic materials

Generally, dynamic secondary ion mass spectrometry (SIMS) has been mainly used as one of the most powerful tools for inorganic mass analysis. On the other hand, an Ar gas cluster ion beam (GCIB) has been developed and spread as a processing tool for surface flattening and also a projectile for time-of-flight (ToF) SIMS. In this study, we newly introduced an Ar-GCIB as a primary ion source to a commercially available dynamic SIMS apparatus, and investigated mass spectra of amino acid films (such as Arginine and Glycine) and polymer films (Polyethylene: PE and Polypropylene: PP) as organic model samples. As a result, each characteristic fragment peak indicating the original molecular organic structure was observed in the acquired mass spectra. In addition, their own molecular ions of the amino acids were also clearly observed. Mass spectra of PE/PP blended-polymer films acquired using Ar-GCIB-dynamic SIMS could be identified between pure PE and PE:PP = 1:3 mixture by applying principal component analysis (PCA). Copyright © 2014 John Wiley & Sons, Ltd.

Retracted: Mass analysis by Ar-GCIB-dynamic SIMS for organic materials

Generally, dynamic secondary ion mass spectrometry (SIMS) has been mainly used as one of the most powerful tools for inorganic mass analysis. On the other hand, an Ar gas cluster ion beam (GCIB) has been developed and spread as a processing tool for surface flattening and also a projectile for time-of-flight (ToF) SIMS. In this study, we newly introduced an Ar-GCIB as a primary ion source to a commercially available dynamic SIMS apparatus, and investigated mass spectra of amino acid films (such as Arginine and Glycine) and polymer films (Polyethylene: PE and Polypropylene: PP) as organic model samples. As a result, each characteristic fragment peak indicating the original molecular organic structure was observed in the acquired mass spectra. In addition, their own molecular ions of the amino acids were also clearly observed. Mass spectra of PE/PP blended-polymer films acquired using Ar-GCIB-dynamic SIMS could be identified between pure PE and PE:PP = 1:3 mixture by applying principal component analysis (PCA). Copyright © 2014 John Wiley & Sons, Ltd.

Angular distributions of particles sputtered from multicomponent targets with gas cluster ions

The experimental angular distributions of atoms sputtered from polycrystalline W, Cd and Ni based alloys with 10keV Ar cluster ions are presented. RBS was used to analyze a material deposited on a collector. It has been found that the mechanism of sputtering, connected with elastic properties of materials, has a significant influence on the angular distributions of sputtered components. The effect of non-stoichiometric sputtering at different emission angles has been found for the alloys under cluster ion bombardment. Substantial smoothing of the surface relief was observed for all targets irradiated with cluster ions.

Mass analysis by Ar‐GCIB‐dynamic SIMS for organic materials

Generally, dynamic secondary ion mass spectrometry (SIMS) has been mainly used as one of the most powerful tools for inorganic mass analysis. On the other hand, an Ar gas cluster ion beam (GCIB) has been developed and spread as a processing tool for surface flattening and also a projectile for time‐of‐flight (ToF) SIMS. In this study, we newly introduced an Ar‐GCIB as a primary ion source to a commercially available dynamic SIMS apparatus, and investigated mass spectra of amino acid films (such as arginine and glycine) and polymer films (polyethylene: PE and polypropylene: PP) as organic model samples. As a result, each characteristic fragment peak indicating the original molecular organic structure was observed in the acquired mass spectra. In addition, their own molecular ions of the amino acids were also clearly observed. Mass spectra of PE/PP blended‐polymer films acquired using Ar‐GCIB‐dynamic SIMS could be identified between pure PE and PE:PP = 1:3 mixture by applying principal components analysis. Copyright © 2014 John Wiley & Sons, Ltd.

Direct comparative study on the energy level alignments in unoccupied/occupied states of organic semiconductor/electrode interface by constructing in-situ photoemission spectroscopy and Ar gas cluster ion beam sputtering integrated analysis system

Through the installation of electron gun and photon detector, an in-situ photoemission and damage-free sputtering integrated analysis system is completely constructed. Therefore, this system enables to accurately characterize the energy level alignments including unoccupied/occupied molecular orbital (LUMO/HOMO) levels at interface region of organic semiconductor/electrode according to depth position. Based on Ultraviolet Photoemission Spectroscopy (UPS), Inverse Photoemission Spectroscopy (IPES), and reflective electron energy loss spectroscopy, the occupied/unoccupied state of in-situ deposited Tris[4-(carbazol-9-yl)phenyl]amine (TCTA) organic semiconductors on Au (ELUMO: 2.51 eV and EHOMO: 1.35 eV) and Ti (ELUMO: 2.19 eV and EHOMO: 1.69 eV) electrodes are investigated, and the variation of energy level alignments according to work function of electrode (Au: 4.81 eV and Ti: 4.19 eV) is clearly verified. Subsequently, under the same analysis condition, the unoccupied/occupied states at bulk region of TCTA/Au structures are characterized using different Ar gas cluster ion beam (Ar GCIB) and Ar ion sputtering processes, respectively. While the Ar ion sputtering process critically distorts both occupied and unoccupied states in UPS/IPES spectra, the Ar GCIB sputtering process does not give rise to damage on them. Therefore, we clearly confirm that the in-situ photoemission spectroscopy in combination with Ar GCIB sputtering allows of investigating accurate energy level alignments at bulk/interface region as well as surface region of organic semiconductor/electrode structure.

Depth profiling organic light-emitting devices by gas-cluster ion beam sputtering and X-ray photoelectron spectroscopy

The composition depth profile in organic light-emitting devices (OLEDs) is investigated using X-ray photoelectron spectroscopy (XPS) coupled with gas-cluster Ar-ion beam milling (Ar-GCIB). The XPS technique gives precise information about the surface chemistry of the organic thin films and is capable of differentiating the various charge transport, host and guest materials used in an OLED. The use of large Ar ion clusters (∼1500–2500atoms/cluster) in the milling process allows for small amounts of the organic thin film to be sputtered away without contaminating the surface or damaging the underlying material chemistry. By probing OLEDs as a function of depth, key parameters including emissive layer composition and interface quality can be assessed directly. It is found that the depth profile for graded-composition emissive layer OLEDs closely matches the intended deposition profiles, maintaining both the composition gradient and the intended endpoint compositions. The ability to resolve and correlate subtle changes in film composition to variations in device performance will help inform efforts in device design, while also serving as a diagnostic tool to better understand the mechanisms for device degradation and failure.

Ar cluster ion beam sputtering of InSb investigated by ToF‐SIMS

Ar gas cluster ion beam (GCIB) sputtering of InSb was investigated, and the sputtering rate and depth resolution of time‐of‐flight secondary ion mass spectrometry sputter depth profiling were examined. The practical sputtering rate for InSb using 20 keV Ar2500+ irradiation was confirmed at the incident angles of 0°, 40°, and 60°, and the sputtering rate was too low to perform sputtering at 80°. The preferential sputtering and surface roughness observed under GCIB irradiation was lower than that observed under 3 keV Ar+ irradiation. Characteristic ripple formation was confirmed under 20 keV Ar2500+ irradiation and had a strong influence on the depth resolution. The highest depth resolution was obtained at the incident angle of 0° because no ripple formation occurred and the level of surface roughness was low among the irradiation of GCIB at incident angles of 0°, 40°, and 60°. The present results revealed that GCIB sputtering is an effective method for sputter depth profiling of InSb. Copyright © 2014 John Wiley & Sons, Ltd.

Nanoscale smoothing of plasmonic films and structures using gas cluster ion beam irradiation

We present a novel method of using gas cluster ion beam irradiation (GCIB) to flatten and widen grains in silver films and structures, while simultaneously, reducing the film thickness with nanometer precision. Ultrathin Ag films produced by GCIB have lower absorbance and better adhesion compared to as-deposited films. By applying the technique post-fabrication to plasmonic color filters, waveguides and disks, we show that an enhanced surface plasmon resonance and propagation length can be achieved.

Observed damage during Argon gas cluster depth profiles of compound semiconductors

Argon Gas Cluster Ion Beam (GCIB) sources have become very popular in XPS and SIMS in recent years, due to the minimal chemical damage they introduce in the depth-profiling of polymer and other organic materials. These GCIB sources are therefore particularly useful for depth-profiling polymer and organic materials, but also (though more slowly) the surfaces of inorganic materials such as semiconductors, due to the lower roughness expected in cluster ion sputtering compared to that introduced by monatomic ions. We have examined experimentally a set of five compound semiconductors, cadmium telluride (CdTe), gallium arsenide (GaAs), gallium phosphide (GaP), indium arsenide (InAs), and zinc selenide (ZnSe) and a high-κ dielectric material, hafnium oxide (HfO), in their response to argon cluster profiling. An experimentally determined HfO etch rate of 0.025 nm/min (3.95 × 10−2 amu/atom in ion) for 6 keV Ar gas clusters is used in the depth scale conversion for the profiles of the semiconductor materials. The assumption has been that, since the damage introduced into polymer materials is low, even though sputter yields are high, then there is little likelihood of damaging inorganic materials at all with cluster ions. This seems true in most cases; however, in this work, we report for the first time that this damage can in fact be very significant in the case of InAs, causing the formation of metallic indium that is readily visible even to the naked eye.

Atomistic modeling of the sputtering of silicon by electrosprayed nanodroplets

The hypervelocity impact of electrosprayed nanodroplets on single-crystal silicon ejects a large number of atoms. Although sputtering by atomic, molecular, and gas cluster ions has been thoroughly studied, the significantly larger size of nanodroplets prevents a straightforward extrapolation of the physics governing the impact of these smaller projectiles. This motivates the present molecular dynamics simulations of nanodroplet impact on silicon, aimed at resolving the mechanisms and the effect of the projectile's size and velocity on sputtering. We find that both collision cascades and thermal sputtering contribute to the overall atom ejection, the former being active during the initial stages of the impact characterized by strong interactions between the molecules of the projectile and the atoms of the target, and the absence of partial thermodynamic equilibrium. In addition, for sufficiently large projectile diameters and impact velocities, conglomerates of atoms are ejected by hydrodynamic forces. The sputtering yield, defined as the average number of target atoms ejected per projectile's molecule, increases monotonically with the kinetic energy of the molecules and, at constant molecular kinetic energy, slightly decreases with projectile diameter as a result of enhanced backscattering of the ejected atoms by the projectile's molecules. For the ionic liquid considered in this study, sputtering is first observed at molecular energies near 12.7 eV and, at the highest energy simulated of 73 eV, the sputtering yield averages to 0.37.

Liquid Phase Epitaxy (LPE) Formation of Localized High Quality and Mobility Ge & SiGe by High Dose Ge-Implantation with Laser Melt Annealing for 10nm and 7nm Node CMOS Technology

Localized Ge and SiGe high quality/mobility device surface material region on bulk-Si and SOI wafers are needed for 10nm and 7nm node CMOS technology. Traditionally SiGe and Ge device surface material on bulk-Si or SOI wafers are realized by CVD epitaxial growth or Vapor Phase Epi (VPE) at elevated temperatures. Selective deposition can be achieved with hard mask. To reduce defects strain relaxed buffer (SRB) or aspect ratio trapping (ART) have been employed with bulk-Si or layer transfer wafer bonding for SiGeOI or GeOI. An alternative to VPE is to use either SPE (solid phase epitaxy) or LPE (liquid phase epitaxy) to form SiGe or Ge epitaxial surface layers. Using high dose Ge implantation >E16/cm2 with photoresist soft mask as proposed in 2004 by Borland et al [1,2]. Localized amorphous Ge surface regions can be formed after Ge-infusion doping by Gas Cluster Ion Beam (GCIB) technique followed by low temperature SPE to form single crystal thin surface Ge epitaxial layers but residual end-of-range (EOR) damage remained. Today, laser melt annealing of implanted junctions are currently being used in production for high quality back-side illuminated CMOS image sensors used in smart phone cameras by several IC and foundry semiconductor manufacturers to completely eliminate any residual implant damage/defects with 100% dopant activation provided the melt depth exceeds the implant damage depth [3]. Last year at IWJT-2013 Borland et al [4] reported using Ge-plasma ion implantation at 1E16/cm2 and 1E17/cm2 doses with laser melt annealing to realize up to 55% SiGe by LPE with >4x higher mobility at 160cm2/Vs. One limitation they noted with plasma implantation was poor retained dose due to surface sputtering at low energies which limited the Ge content to <55% for 1E17/cm2 dose. Therefore to overcome this retained dose problem we investigated Ge beamline ion implantation in this paper which should give 100% retained dose. The Ge surface amorphous layer thickness measured by elipsometry was 15nm while the Ge-SIMS depth profile measures 7nm Ge at 100%. Therma-wave analysis was used to monitor the Ge-implant damage recovery and Ge or SiGe recrystallized epitaxial surface layer after various laser melt annealing conditions of varying power level and pulse duration. The Ge-SIMS depth profiles shows we could vary the melt depth for LPE Ge layer from 10nm to >400nm and the Ge layer content from 97% down to 2% respectively. We will also show X-TEM of the Ge-LPE regions. Sb implantation was used to investigate n-type dopant activation in Ge at low and high doses of 3E13/cm2 and 3E15/cm2. Rs measurements were done using a special Hx 4 point probe and SRP (spreading resistance profile) depth profiles. In summary, using high dose beam-line Ge-implantation we realized >7nm amorphous Ge deposition. Epitaxial growth of Ge was achieved by liquid phase epitaxy using shallow laser melt annealing between 10nm and >400nm melt depths.

Influence of surface roughness and coating on the friction properties of nanometer-thick liquid lubricant films

The friction properties of nanometer-thick lubricant films are crucial in the reliability and durability of miniaturized moving mechanical components in micro- and nanoelectromechanical systems and hard disk drives. In this work, gas cluster ion beam treatments were applied to prepare smoothed glass sliding pins and diamond-like carbon (DLC) coated sliding pins for pin-on-disk friction tests to study the effect of the surface roughness and the DLC coating on the friction properties of perfluoropolyether (PFPE) films. The effect of the texture of the solid surface on the friction properties was also investigated. The friction properties were not exclusively determined by the surface energies of the solids. The friction coefficients of the nanometer-thick PFPE films, confined between solid surfaces were sensitive to the surface roughness of the solids. The friction coefficient generally increased with an increasing surface roughness (the composite standard deviation of the surface roughnesses of the pair of solid surfaces). This tendency was reversed when there was a strong longitudinal roughness effect at the contact interface. Moreover, the DLC-coated sliding pins had lower friction coefficients than the glass sliding pins, indicating that the friction properties were noticeably affected by the hardness and Young׳s modulus of the contact materials. The mechanisms for the effects of the surface roughness, surface texture and contact materials on the friction properties are discussed.

The matrix effect in organic secondary ion mass spectrometry

Well defined reference materials consisting of Irganox 1010 and either Irganox 1098 or Fmoc-pentafluoro-l-phenylalanine (Fmoc-PFLPA) are described. These have been analysed with time-of-flight secondary ion mass spectrometry (ToF-SIMS) using argon gas cluster ions, 5keV Ar2000+, as a sputtering source and 25keV Bi3+ ions as a primary source for analysis. We demonstrate that the binary mixtures of Irganox 1010 and Irganox 1098 demonstrate some weak matrix effects whereas the mixtures of Irganox 1010 and Fmoc-PFLPA demonstrate some strong and unusual matrix effects. A parameter, Ξ, is introduced to describe the magnitude of the matrix effect in organic SIMS and a method to correct for the different apparent depths of origin of secondary ions in a depth profile. With some knowledge of the matrix effect magnitude and sign provided by Ξ it becomes possible to select secondary ions for reliable quantitative analysis in binary mixtures. We also indicate how the differences in Ξ between different secondary ions may, in the future, be exploited to assess compositional variation or nanoscale phase separation in materials.

TOF–SIMS study of polyester/melamine resin with Ar gas cluster ion beam

A pre‐coated steel sheet for household electrical appliances needs to be highly formable and stain resistant. In recent years, secondary ion mass spectrometry (SIMS) with a time‐of‐flight (TOF) mass analyzer with an Ar gas cluster ion beam (Ar–GCIB) has been widely used as a structure analysis technology of organic molecules. In this paper, we looked into the effectiveness of Ar–GCIB–TOF–SIMS as a structure analysis technique of paint film. As a result, we could detect the trimer fragment ions of hexamethoxymethylmelamine in the range of m/z = 400–800 for the first time for the spin‐coating of HMMM on a Si wafer. By evaluation of characteristic monomer fragment ions, we could find out the different surface distributions of melamine‐formaldehyde resin with the different formulations of paint films. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Auger electron nanoscale mapping and x-ray photoelectron spectroscopy combined with gas cluster ion beam sputtering to study an organic bulk heterojunction

The lateral and vertical distributions of organic p/n bulk heterojunctions for an organic solar cell device are, respectively, investigated using nanometer-scale Auger electron mapping and using X-ray photoelectron spectroscopy (XPS) with Ar gas cluster ion beam (GCIB) sputtering. The concentration of sulfur, present only in the p-type material, is traced to verify the distribution of p-type (donor) and n-type (acceptor) materials in the blended structure. In the vertical direction, a considerable change in atomic sulfur concentration is observed using XPS depth profiling with Ar GCIB sputtering. In addition, Auger electron mapping of sulfur reveals the lateral 2-dimensional distribution of p- and n-type materials. The combination of Auger electron mapping with Ar GCIB sputtering should thereby allow the construction of 3-dimensional distributions of p- and n-type materials in organic photovoltaic cells.

A new approach for determining accurate chemical distributions using in‐situ GCIB cross‐section imaging

Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) has become widely used to characterize various kinds of materials, especially organic materials. It has recently become possible to investigate the molecular distributions underneath the surface using Ar‐GCIB (gas cluster ion beam) depth profiling. It is an important new capability for practical use of TOF‐SIMS because the subsurface and interface chemistry plays an important role in the performance of many products. However, it is difficult to obtain accurate chemical depth distributions using sputter depth profiling when the sample has a significant surface roughness and/or inhomogeneous structure. In order to resolve this problem, we proposed an approach to determine the accurate chemical distributions using GCIB cross‐section imaging method. In this study, this approach was demonstrated for practical organic samples, and accurate chemical depth distributions were determined. Copyright © 2014 John Wiley &amp; Sons, Ltd.

High energy gas cluster ions for organic and biological analysis by time-of-flight secondary ion mass spectrometry

There is considerable excitement surrounding the application of gas cluster ion beams (GCIBs) for SIMS analysis in order to study organic materials and biological samples such as cells and tissues. These ion beams, that often comprise several thousand argon atoms in the primary ion, have been used mainly for the etching of organic materials to remove damage from the surface allowing molecular depth profiling experiments to be performed. The energy of the ion beam is normally 2–20keV. There have been relatively few studies reported on the use of GCIB as analysis beams, due to difficulties related to fast pulsing and focusing of the beam along with the sometimes low ionisation efficiency. In this study, we report on the use of a new higher energy (40keV) GCIB operated in a continuous mode. When compared to lower energies depth profiles on thin films of Irganox 1010 show an increase in sputter yield while fragmentation, damage accumulation and ionisation efficiency remains unchanged. Experiments on brain tissues show increased signal levels especially for higher mass secondary ions (m/z 500+) in comparison to C60+ at 40keV and Ar4000+ at 20keV impact energy. The use of higher energies facilitates better focusing of the primary ion beam as demonstrated here on a human hair sample where we achieve a spatial resolution of <3μm. Even with this small spot size, we can detect enough signal from and high mass species for clear localisation. All results indicate that higher energies are beneficial for most aspects of ToF-SIMS applications in biology.

The use of argon cluster bombardment for the surface preparation of paint cross‐sections for analysis by ToF‐SIMS

Surface preparation with gas cluster ion beam (GCIB) sputtering was performed on paint cross‐sections, which belong to the collection of the Royal Institute for Cultural Heritage (KIKIRPA), Brussels, Belgium. Superficial cleaning of cross sections with residual embedding resin surface contamination was studied with different sputtering times in order to obtain a gain in the spectral and imaging mode. Sputtering was made directly through the Time‐of‐Flight‐SIMS apparatus. It was thus demonstrated that GCIB sputtering for a short period was very efficient for the superficial decontamination of cultural heritage cross‐sections without visible damage on the valuable samples. The GCIB sputtering time and dose can be highly decreased when combined with a monoatomic argon ion beam preparation techniques such as the ion milling systems. Copyright © 2014 John Wiley &amp; Sons, Ltd.