Gas Cluster Ion Beam Irradiation Research Articles

Pressure resistance evaluation of an ultrathin SiNx membrane etched by a gas cluster ion beam

In this study, reactive etching of a SiNx free-standing membrane with a thickness of a few nanometers was performed using a gas cluster ion beam (GCIB) and the pressure resistance of the membrane with respect to its thickness was evaluated. The low-damage irradiation effect of a 7 keV GCIB in an acetylacetone (Hacac) atmosphere enabled the etching to retain its pressure resistance compared with that of 400 eV Ar+ beam irradiation. In a previous study, it was shown that irradiation of SiNx films with Ar plasma of several hundred eV causes defects in the bonding network of the Si–N bond and the network is easily oxidized. XPS measurements on SiNx films after GCIB etching with Hacac and Ar+ beam irradiation showed that the composition of the Si–O bond was smaller with GCIB irradiation compared to Ar+ beam irradiation. This indicates that GCIB etching with Hacac can suppress the formation of defects in the Si–N network, which reduces the degradation of the pressure resistance.

On the origin of nanoripples on silicon by gas cluster-ion irradiation

The first stage of nanoripples formation on silicon surface under inclined gas cluster ion beam irradiation is investigated. It was shown that ordered ripples appear as the result of emerging and self-organization of single standing protrusions spontaneously developed on the surface. The shapes of protrusions and ripples depending on the ion fluence and the angle of incidence are discussed.

Surface preparation of metal films by gas cluster ion beams using organic acid vapor for Cu–Cu bonding

Surface-activated bonding (SAB) of Cu by gas cluster ion beam (GCIB) irradiation with acetic acid vapor was studied. GCIB irradiation realizes surface smoothing and surface reaction enhancement without severe damage. Therefore, it is promising for SAB. In this study, acetic acid vapor was introduced during Ar-GCIB irradiation to assist the removal of surface oxides on the Cu surface. XPS results showed that Cu(OH)2 was effectively removed by reaction with adsorbed acetic acid, and there was no residue by acetic acid adsorption. In addition, surface roughness decreased by Ar-GCIB irradiation with acetic acid because of the preferential removal of protrusion. Preliminary bonding experiments showed an increase of Cu–Cu bond strength by Ar-GCIB irradiation with acetic acid vapor.

Surface preparation of metal films by gas cluster ion beams using organic acid vapor for Cu-Cu bonding

Abstract Surface activated bonding of Cu by gas cluster ion beam (GCIB) irradiation with acetic acid vapor was studied. GCIB irradiation realizes surface smoothing and surface reaction enhancement without severe damage. Therefore, it is promising for surface-activated bonding (SAB). In this study, acetic acid vapor was introduced during Ar-GCIB irradiation to assist removal of surface oxides on Cu surface. XPS results showed that Cu(OH)2 was effectively removed by reaction with adsorbed acetic acid, and there was no residue by acetic acid adsorption. In addition, surface roughness decreased by Ar-GCIB irradiation with acetic acid because of the preferential removal of protrusion. Preliminary bonding experiments showed increase of Cu-Cu bond strength by Ar-GCIB irradiation with acetic acid vapor.

Ar gas cluster ion beam assisted XPS study of LiNbO3 Z cut surface

XPS combined with profiling by Ar2500+ gas cluster ion beam (GCIB) sputtering has been used to obtain new refined data on the polarization and processing-dependent Li/Nb ratio for the surface of a LiNbO3 single crystal. The most suitable GCIB parameters (normal incidence, 10 keV energy) and irradiation dose (less than or equal to 2.7 × 1016 ions/cm2) have been determined and employed to perform high resolution depth profile analysis without cluster ion-induced Li/Nb changes. The Li/Nb profiles obtained for Z cut wafers with positive and negative faces revealed the presence of two distinct regions. The initial 0.3 nm-thick region had a low Li/Nb ratio due to machining and leaching and did not show a dependence on the polarity direction. The next profile region had a constant Li/Nb ratio, which depended on the crystal polarity. The Li/Nb ratio for the Z+ surface of a wafer and a cleaved sample exceeded the values for the Z– surface of a wafer by 1.2 times. This result confirms theoretical predictions of a different stoichiometry for Z+ and Z– terminations and indicates the ability of GCIB to reach the surface condition that is close to the perfect termination.

Dark current issues for high gradient C-band medical linac

Simulations of dark current emission for C-band linear accelerating structure were performed taking into account the electric field distributions inside the cavities and the field enhancement factor. Matching calculated dark current energy spectra with the experimentally measured ones made it possible to understand the nature of the dark current and to reveal the areas of the accelerating structure requiring improved surface treatment. Microscopic investigation of the copper accelerating cell surface treated using different techniques showed that gas cluster ion beam irradiation results in the best surface smoothness. Furthermore, it removes the surface insulating layers and prevents from subsequent oxidizing. Both effects can significantly reduce the dark current emission.

(Invited) Reactions on Metal Surface and Diketone Induced By Gas Cluster Ions during Atomic Layer Etching

Gas cluster ion beams (GCIB), which consists of several thousands of gaseous atoms or molecules, have been used as novel low-energy ion beams for surface processing and analysis. Since thousands of low-energy (several eV) atoms bombard a surface at the same time and the same position, the bombarded area experiences transient high-temperature and high-pressure conditions, which enhance sputtering of atoms or enhance surface reactions. In recent years, we have been investigating to apply GCIB as energetic ions for atomic layer etching. We have reported ALE of transition metals (Cu and Ni) with GCIB irradiations and diketone (acetylacetone and hexafluoroacetone). We separated each etching step as following; (1) adsorption of diketone molecules on metal oxide, (2) evacuation of residual vapor, (3) irradiation of oxygen GCIB to remove metal oxide. By using 5 keV oxygen GCIB (~ 2eV/molecules), thin layer of nickel oxide with adsorbed acetylacetone is removed. There is no physical sputtering at this energy region, which realizes self-limiting ALE process. From in-situ XPS study, Ni oxide with adsorbed diketone molecules can be removed by Ar-GCIB irradiation. It means that other oxidation method can be used to form metal oxide, and Ar-GCIB can be used for the removal steps. In this talk, we will report surface reactions between metals and diketone induced by gas cluster ion irradiations, and etching characteristics of various metals using GCIB irradiation and diketone.

Surface topography and composition of NiPd alloys under oblique and normal gas cluster ion beam irradiation

Polycrystalline NiPd and Ni5Pd alloys were irradiated with argon gas cluster ion beam and atomic ion beam. In situ XPS measurements showed surface enrichment with Ni. For cluster ions, the degree of the enrichment was significantly higher, and the ion current density influenced on it. Under oblique cluster ion beam, ripples developed on the surface, and the elements of the alloy redistributed along the surface according to the ripple pattern. For normal cluster ion beam direction, sputtering rate was determined by a crystalline orientation, which limited the smoothing effect.

Surface ripples induced by gas cluster ion beam on copper surface at elevated temperatures

The temperature dependence of the ripples formation on a copper surface under off-normal gas cluster ion beam irradiation was investigated. At room temperature, well developed asymmetric ripples perpendicular to the beam were obtained with “droplets” of copper at the crests. At elevated temperatures, surface smoothing was found instead of rippling. On some grains the ripples perpendicular to the ion beam still remained. To explain this fact, electron backscattered diffraction analysis of the samples surfaces was performed. It showed that the ripple formation at elevated temperatures is governed both by the ion beam direction and by the crystalline orientation of a grain with respect to the beam.

Cell Adhesion on PEEK Surface with Gas Cluster Ion Beam Irradiation

Cell Adhesion on PEEK Surface with Gas Cluster Ion Beam Irradiation

Surface Planarization with Gas Cluster Ion Beams and Application to Wide-Bandgap Semiconductors

In this study, the fundamental sputtering effects of gas cluster ion beams (GCIBs), especially for surface planarization, are reported. Because gas cluster ions are aggregates of thousands of gas atoms, the collision process for a GCIB, with dense and multiple collisions, differs from that of atomic ions via collision cascading; thus, GCIBs have many unique irradiation effects. Among them, the low-damage and surface smoothing effects are beneficial for the planarization of wide-bandgap semiconductor wafers. The planarization of SiC, diamond, and GaN has been demonstrated using GCIB irradiation.

Irradiation conditions of gas cluster ion beam for surface-activated bonding

The irradiation conditions of gas cluster ion beam (GCIB) for surface-activated bonding (SAB) were investigated. Since GCIB realizes bombardment with low energy (∼several eV/atom) and dense-energy deposition, it modifies the near-surface layer with low damage, which will be beneficial for surface-activated bonding. In this study, Cu–Cu bonding with GCIB irradiation was carried out as a preliminary study, and the irradiation conditions of Ar-GCIB were investigated. X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that the surface oxide on Cu was removed efficiently by oblique-incidence Ar-GCIB irradiations. Also, it was shown that sequential Ar-GCIB irradiations at normal and oblique incidences realized a smooth Cu surface. Cu–Cu bonding did not succeed for the pristine Cu or Cu irradiated with Ar monomer ions. In contrast, Cu–Cu bonding was realized with Ar-GCIB irradiation owing to surface oxide removal and smoothing effects.

Fabrication of optically smooth surface on the cleavage of porous silicon by gas cluster ion irradiation

Electrochemical etching of Si is a promising method of fabricating multilayer photonic structures with hundreds of layers. Nevertheless, the natural cleavage of the porous silicon structure has roughness and then high optical scattering that embarrasses the usage of porous silicon in optical devices. In this study, gas cluster ion beam irradiation was suggested as a polishing technique. The bombardment results in surface smoothing and consequent enhancement of light reflection without significant difference in sputtering rate of layers with different porosity. Increasing irradiation dose results in different behavior of porous layers: densification of low-porosity structures and nano-rods formation in high-porosity layers.

Atomic layer etching of Cu film using gas cluster ion beam

In this work, atomic layer etching (ALE) with a gas cluster ion beam (GCIB) was investigated for the first time. Since gas cluster ions produce dense energy deposition without severe damage, effective, low-damage, and low-temperature removal of chemically altered surface layers is expected. In this study, ALE of Cu films upon oxygen GCIB (O2-GCIB) irradiation in the presence of acetic acid vapor was investigated. Cu atoms were removed from the surface layer, owing to chemical reactions between adsorbed acetic acid molecules and Cu atoms upon O2-GCIB irradiation at room temperature. Since there was no physical sputtering upon 5 kV O2-GCIB irradiation, a self-limiting etch stop was observed after removal of the top layer. Conversely, upon 20 kV O2-GCIB irradiation, Cu atoms were physically sputtered after removal of the chemically altered surface layer. By applying low-energy (5 kV) GCIB irradiation, ALE with GCIB was achieved at room temperature.

A new technique to detect antibody-antigen reaction (biological interactions) on a localized surface plasmon resonance (LSPR) based nano ripple gold chip

We demonstrate that the gold nano-ripple localized surface plasmon resonance (LSPR) chip is a low cost and a label-free method for detecting the presence of an antigen. A uniform stable layer of an antibody was coated on the surface of a nano-ripple gold pattern chip followed by the addition of different concentrations of the antigen. A red shift was observed in the LSPR spectral peak caused by the change in the local refractive index in the vicinity of the nanostructure. The LSPR chip was fabricated using oblique gas cluster ion beam (GCIB) irradiation. The plasmon-resonance intensity of the scattered light was measured by a simple optical spectroscope. The gold nano ripple chip shows monolayer scale sensitivity and high selectivity. The LSPR substrate was used to detect antibody-antigen reaction of rabbit X-DENTT antibody and DENTT blocking peptide (antigen).

Gold nano-ripple structure with potential for bio molecular sensing applications

We introduce a simple and cost-effective scheme for bio-sensing using nano-ripple structures. One dimensional metallic nano-ripple structures formed by gas cluster ion beam irradiation have shown polarization of light as well as localized surface plasmon resonance. These localized surface plasmon resonance based bio sensors not only are capable of label free real time analytical detection but also show high sensitivity. The nano-surface morphology determines the changes in the plasmonic properties of nano-structures hence the plasmonic response is tunable. By adsorbing a mono-layer of thiolated organic compound on the surface of these substrates we identified the shift in the localized surface plasmon resonance peaks triggered by the change of dielectric function in the neighborhood of the structures. These plasmonic nano-metallic structures can be utilized to observe the change of localized surface plasmon resonance frequency due to the cycle of adsorption, re-adsorption and reactions taking place on the surface that can potentially be mapped in to reaction mechanics. The bio-sensor has monolayer molecule-coating sensitivity and specific selectivity. This study can be extended to sensing biological molecules such as proteins, DNAs, antibodies and antigens.

Surface Activation and Planarization with Gas Cluster Ion Beam for Wafer Bonding

Surface activated bonding (SAB) has been widely used for various semiconductor wafers. In the SAB process, atomic Ar ions bombard wafer surface to form activated surface. In order to form activated surface on materials which are susceptible to irradiation damage, we have been investigating the gas cluster ion beam (GCIB) as an alternative to atomic ion beams. Gas clusters are aggregates of several thousands of gaseous atoms. Therefore, energy per atom of a gas cluster ion can be easily reduced to several eV. Although energy/atom of a gas cluster ion is low, thousands of low-energy atoms bombard a target surface at the same location simultaneously. As a result, the energy density on the target surface became extremely high and non-linear collisions of atoms are induced. They induces unique irradiation effects of GCIB such as high-yield sputtering, surface analysis of organic materials, thin film deposition at low temperature, and surface smoothing, which are beneficial for surface activated bonding. In this paper, preliminary irradiation effects of surface activation and planarization with glancing incidence GCIBs will be reported. From in-situ XPS analysis of O1s peak intensity on Si(100) with native oxide, Ar-GCIB irradiation at 70o removed native oxide efficiently. On the contrary, mixing of native oxide by normal incidence GCIB might occur, which caused residual oxide layer formation. In addition, the surface roughness at oblique incidence showed lowest value (Ra < 0.5 nm) without ripple formations. Cross-sectional TEM observation with oblique incidence GCIB irradiation showed that the sub-surface damage was almost negligible. These results indicated the possibility of use of GCIB as low-energy ions for wafer bonding.

Relatively low temperature deposition of graphene like films with ethane GCIB irradiation

Abstract Relatively low-temperature depositions of graphene like film on Ni substrate were studied using ethane gas cluster ion beam (GCIB). Ethane GCIBs realize shallow carbon implantation and create high temperature and high pressure conditions, which lead to reduction of substrate temperature. By optimization of deposition conditions, it was found that graphene like films were formed on Ni by 5 keV ethane GCIB irradiation at substrate temperature of 400 °C. Abstract code: (given by the organizing committee).

Chemical stability of polymers under argon gas cluster ion beam and x-ray irradiation

In this work, the authors examine chemical stability of polymers under x-ray photoemission spectroscopy (XPS) depth profiling coupled with argon gas cluster ion sputtering. The depth profiles measured for polystyrene, poly(3-dodecylthiophene), and poly(methyl methacrylate) thin films do not reveal changes in the XPS spectra due to cluster bombardment. Nevertheless, x-ray irradiation influences the shape of the sputter craters. The observed features are attributed to cross-linking or chain scission occurring in the polymers.

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 &amp; Sons, Ltd.