豊田 紀章

Abstract We would like to improve detection sensitivity by making photoelectron transmission window (SiNx membrane) of liquid cell ultra-thin for liquid measurement using XPS or X-ray PEEM at UHV. In this study, thinning of the membrane using gas cluster ion beams (GCIB) was demonstrated and the burst pressure was compared with those thinned with atomic 400 eV Ar+ ions. It was shown that SiNx membranes thinned by GCIB was 2.5 times higher burst pressure than the Ar+ ions. In addition, improvement of sensitivity of characteristic X-ray from liquid-water induced by low-energy electrons was investigated. By using 4.5 nm thick SiNx membrane etched by GCIB, the X-ray intensity became 1.6 times higher than those from 11 nm thick pristine membrane at electron beam energy of 1.5 keV. This result showed good agreement with Monte Carlo simulation results of the electron-beam-induced X-ray emission from liquid-water beneath SiNx membrane.

Abstract Atomic layer etching (ALE) of silicon nitride film (SiNx) was demonstrated using oxygen gas cluster ion beam (O2-GCIB) with acetylacetone (Hacac) as adsorption gas. GCIB is a beam of aggregates of several thousand atoms, enabling low damage and high energy density irradiation. In this study, we performed the characterization of the ALE, and revealed the etching mechanism. XPS results indicated the following etching process. (i) O2-GCIB irradiation oxidizes the surface of SiNx film, (ii) the oxide layer reacts with Hacac vapor, and (iii) the reaction layer is removed by the GCIB. The ALE can be executed by sequential repetition of the processes (i)~(iii). This technique enables highly accurate control of SiNx film thickness with low irradiation damage.

Abstract 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.

A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.

Low temperature bodings of Cu with the gas cluster ion beam (GCIB) irradiations were studied. Since GCIB exhibits surface smoothing effects without severe damage, it is promising for the surface activated bonding (SAB). Ar-GCIB irradiation at oblique incidence removed native oxide on Cu films without roughening. With increasing the acceleration voltage of Ar-GCIB, the surface roughness of Cu decreased, which resulted in lowering the bonding temperature.

Lithium niobate’s use in integrated optics is somewhat hampered by the lack of a capability to create low loss waveguides with strong lateral index confinement. Thin film single crystal lithium niobate is a promising platform for future applications in integrated optics due to the availability of a strong electro-optic effect in this material coupled with the possibility of strong vertical index confinement. However, sidewalls of etched waveguides are typically rough in most etching procedures, exacerbating propagation losses. In this paper, we propose a fabrication method that creates significantly smoother ridge waveguides. This involves argon ion milling and subsequent gas clustered ion beam smoothening. We have fabricated and characterized ultra-low loss waveguides with this technique, with propagation losses as low as 0.3 dB/cm at 1.55 µm.

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.

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.

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 (O-2-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 O-2-GCIB irradiation at room temperature. Since there was no physical sputtering upon 5 kV O-2-GCIB irradiation, a self-limiting etch stop was observed after removal of the top layer. Conversely, upon 20 kV O-2-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.

Gas cluster ion beam (GCIB) was used for surface activation bonding (SAB). Since GCIB modifies only near surface, low-damage surface modification and activation are expected. In this study, Cu-Cu bonding with GCIB irradiation was selected as a preliminary study. XPS and contact angle measurement showed that surface oxide on Cu was removed efficiently by oblique incidence Ar-GCIB at 5-20 kV. Also, sequential irradiation of GCIB at normal and oblique incidence realized smooth Cu surface. After that Cu-Cu bonding strength was investigated by the tensile test.

Preliminary experiments of gas cluster ion beam (GCIB) irradiation for wafer bonding were conducted. Unique irradiation effects of GCIB, such as low-damage irradiation and surface smoothing effects, will be beneficial for surface activated bonding. From XPS, AFM measurements, Ar-GCIB irradiation at oblique incidence removed native oxide on Cu films efficiently without roughening. Cu-Cu bond increased with the acceleration voltage of Ar-GCIB. There is a correlation between the bond strength and the contact angle reduction due to surface smoothing and oxide removal by Ar-GCIB.

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 degrees C. (C) 2016 Elsevier B.V. All rights reserved.

The dependence of Ru, CoFe, and SiO2 etching with O-2-GCIB in an acetic acid atmosphere on the angle of incidence was studied. In the case where an acceleration voltage (Va) of 20 kV was used, the depth to which Ru was etched using O-2-GCIB with acetic acid decreased significantly with increasing incident angle. However, the etch depth produced with an acceleration voltage of 5 kV, with O-2-GCIB in acetic acid, did not show a rapid decrease at high incident angles. The etch selectivities of Ru and CoFe to SiO2 at an incident angle of 70 and a Va of 5 kV with acetic acid were 7.6 and 10.4, respectively. This indicates that reactive etching occurred with these metals. Based on XPS and cross-sectional TEM, there was no observable damage to CoFe after O-2-GCIB etching with acetic acid at an incident angle of 70 degrees. (C) 2016 Elsevier B.V. All rights reserved.

Crater-like defects formations with gas cluster ion beams (GCIB) were used as templates for carbon nanotube (CNT) growth. Upon a gas cluster ion impact, dense energy is deposited on a target surface while energy/atom of gas cluster ion is low, which creates crater-like defects. Si and SiO2 were irradiated with Ar-GCIB, subsequently CNTs were grown with an alcohol catalytic CVD using Co and ethanol as catalyst and precursor, respectively. From SEM, AFM and Raman spectroscopy, it was shown that growth of CNT with small diameter was observed on SiO2 with Ar-GCIB irradiation. On Si targets, formation of craters with bottom oxide prevented Co diffusion during CNT growth, as a result, CNT growth was observed only on Si irradiated with high-energy Ar-GCIB. These results showed that isolated defects created by GCIB can be used as templates for nanotube growth. (C) 2015 Elsevier B.V. All rights reserved.

In this paper, preliminary irradiation effects of glancing incidence gas cluster ion beam (GCIB) for surface activated bonding are reported. Unique irradiation effects of GCIB, such as low-damage irradiation and surface smoothing effects, might be beneficial for surface activated bonding. From XPS analysis, Ar-GCIB irradiation at 70 degrees removed native oxide on Si(100) substrate efficiently. On the contrary, mixing of native oxide by normal incidence GCIB occurred, which caused residual oxide layer formation. The surface roughness at oblique incidence showed lowest value (Ra similar to 0.5 nm) without ripple formations. In addition, Cu-Cu bonding were demonstrated as preliminary results of wafer bonding with GCIB.

Crater formations with gas cluster ion beam (GCIB) were used for non-contact hardness measurement of thin films. The crater inner diameter formed with size-selected Ar cluster ions decreased with inverse cube root of film hardness. When the total acceleration energy was the same, cluster size did not affect the crater inner diameter. In addition, high ionization electron voltage (V-e) cause wide distribution of crater depth and diameter due to multiply charged GCIB.

Gas cluster ion beam (GCIB) was used for surface activation bonding (SAB). Since GCIB modifies only near surface, low-damage surface modification and activation are expected. In this study, Cu-Cu bonding with GCIB irradiation was selected as a preliminary study. XPS and contact angle measurement showed that surface oxide on Cu was removed efficiently by oblique incidence Ar-GCIB at 20 kV. Also, sequential irradiation of GCIB at normal and oblique incidence realized smooth Cu surface. Cu-Cu bonding did not succeced without GCIB irradiation or with 5 kV Ar-GCIB irradiation. On the country, Cu-Cu bondings were realized with 10 or 20 kVAr-GCIB irradiations owing to surface oxide removal.

In this study, we investigated surface modification of poly ether ether ketone (PEEK) with gas cluster ion beam(GCIB) irradiation. Since GCIB induces high energy density on the irradiated surface, only surface layer is physically or chemically modified without introducing damages in the bulk substrate. The contact angle of water on PEEK decreased with the acceleration voltage of O-2-GCIB, which indicated the improvement of hydrophilicity. This increase of hydrophilicity might be explained by increase of hydrophilic group and microstructure on PEEK surface. Preliminary experiments of cell adhesion tests on PEEK with O-2-GCIB irradiation showed 25 % increase of cell adhesion compared to pristine PEEK substrates.

Low-temperature formation of graphene films with ethane gas cluster ion beam (GCIB) implantations were investigated. Ethane GCIBs realize both shallow carbon implantation and creation of high temperature and high pressure conditions simultaneously, which lead to reduction of substrate temperature for graphene formation. By optimization of deposition conditions, it was found that graphene like films were formed on Ni by 5 keV ethane GCIB irradiations at substrate temperature of 400 degrees C, which was much lower than that required for a typical CVD graphene deposition (800 - 1000 degrees C).

Surface smoothing of Ru used as underlayer of magnetic tunneling junctions (MTJ) in magneto-resistive random access memory (MRAM) was carried out with gas cluster ion beam (GCIB) in order to improve device characteristics. For Ru films, surface smoothing with 5 kV N2-GCIB irradiation was effective, and CoFe films deposited on smoothed Ru surface also showed smooth surface. From the hysteresis loop measurements of MTJ formed on smoothed Ru with N2-GCIB, it showed improvement of inter-layer coupling magnetic field (Hin) with decreasing the surface roughness of underlayer Ru. It is expected that surface roughness of MgO in MTJ was also improved by smoothing of underlayer Ru with N2-GCIB.

Cluster ion beam processing has been extensively developed during the 25 years since the concept originated. Low energy surface interaction effects, lateral sputtering phenomena and high-rate chemical reaction effects have been explored experimentally and have been explained by means of molecular dynamics (MD) modeling. Practical production equipment for a wide range of applications has also been successfully developed. The technology is now advancing rapidly in the fields of sub-nanoscale processing of metals, semiconductors and insulating materials. This paper reviews important events which have taken place during the development with emphasis placed on emerging new advances which have occurred during several recent years. (C) 2014 Elsevier Ltd. All rights reserved.

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. (C) 2014 The Authors. Published by Elsevier B.V.

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.

Effects of water vapor during Ar-GCIB irradiations on poly-methyl methacrylate (PMMA) were investigated. Because of chemical reaction enhancement between PMMA and water vapor adsorbed on PMMA by GCIB irradiations, etching depth of PMMA with water vapor became almost twice as deep as that without water. XPS showed that there was small change in chemical bond after irradiation of Ar-GCIB with water vapor. In addition, large Ar-GCIB irradiation (i.e., low energy/atom) in water vapor also helped to reduce irradiation damage on PMMA. (C) 2014 Elsevier B.V. All rights reserved.

Ion beam assisted deposition (IBAD) has been widely used for high-quality coatings in various areas. In this chapter, we reviewed the fundamental characteristics of IBAD. In addition to the conventional IBAD technique, emerging IBAD techniques such as the gas cluster ion beam (GCIB) assisted deposition and the three-dimensional nanostructure formations with focused ion beam (FIB) were also introduced. IBAD is considered as a mature technology however, new applications of IBAD have been developed using GCIB or FIB. © 2014 Elsevier Ltd All rights reserved.

Effects of background gas (N-2 or SF6) on ripple formation by oblique incidence gas cluster ion beam (GCIB) irradiation were investigated. When N2 gas was introduced as background gas, both ripple structures and the sputtering yield of Si and SiO2 did not change by Ar-GCIB irradiation at 60 degrees incidence. However, wavelength of ripple became larger when SF6 gas was introduced as background gas. Increase of the sputtering yield in SF6 environment correlates with the change of ripple structures. It is assumed that SF6 molecules adsorbed on ripple structures, and Si or SiO2 ripples were etched preferentially. (C) 2014 The Japan Society of Applied Physics

FeCo films of the type used in spin transfer torque magnetoresistive random access memory were etched by gas cluster ion beam (GCIB) irradiation with acetic acid vapor and characterized by in situ X-ray photoelectron spectroscopy. After 20 keV O-2-GCIB irradiation with acetic acid vapor, etching depth enhancement (10.7x) was observed compared with the results without acetic acid vapor. The etching model of FeCo can be described as follows: (1) FeCo oxide formation with O-2-GCIB irradiation, (2) acetic acid adsorption on FeCo oxide, (3) reactions between FeCo oxide and acetic acid, and (4) the desorption of volatile compounds by local and transient heating owing to O-2-GCIB bombardment. Cross-sectional transmission electron microscopy, transmission electron diffraction analysis, and electron energy loss spectroscopy results showed no significant etching damage or oxidation of FeCo films after etching by O-2-GCIB irradiation with acetic acid vapor. Therefore, the low- damage etching of FeCo can be performed by O-2-GCIB irradiation with acetic acid vapor. (C) 2014 The Japan Society of Applied Physics

A size-selected Ar gas cluster ion beam (GCIB) was applied to secondary ion mass spectrometry (SIMS) of a polystyrene (PS) thin film, a 1,4-didodecylbenzene (DDB) thin film, and an ITO glass sample. Additionally, the samples were analyzed by SIMS using an atomic Ar<sup>+</sup> ion projectile and X-ray photoelectron spectroscopy (XPS). All three samples were contaminated by poly(dimethylsiloxane) (PDMS) on the surface. Compared to the Ar<sup>+</sup> SIMS spectra, the fragments in the PS and DDB SIMS spectra for Ar<sub>1550</sub><sup>+</sup>, including siloxane, were enhanced more than ∼100-fold, while the hydrocarbon fragments were enhanced 10-20-fold. XPS spectra during beam irradiation indicate that Ar-GCIB sputters contaminants on the surface more effectively than the atomic Ar<sup>+</sup> ion beam. These results indicate that a large gas cluster projectile can sputter a much shallower volume of organic material than small projectiles, resulting in an extremely surface-sensitive analysis of organic thin films. The shallow volume sputtering by GCIB is responsible for the preferential enhancement of the surface contaminants.<br>

Halogen free and low-temperature Cu etching was carried out using a gas cluster ion beam (GCIB) with acetic acid vapor. A very shallow Cu surface was oxidized by oxygen GCIB (O-2-GCIB). Simultaneously, reactions between CuO and acetic acid occurred, and reaction products were desorbed by local heating of O-2-GCIB irradiation. Thus, Cu etching at a low-temperature (<60 degrees C) was achieved. From cross-sectional images of Cu pattern with line width of 100 nm, anisotropic Cu etching was carried out with this technique.

We report an alternative method of producing sub-30 nm thick silver films and structures with ultralow loss using gas cluster ion beam irradiation (GCIB). We have direct evidence showing that scattering from grain boundaries and voids rather than surface roughness are the main mechanisms for the increase in loss with reducing thickness. Using GCIB irradiation, we demonstrate the ability to reduce these scattering effects simultaneously through nanoscale surface smoothing, increase in grain width and lower percolation threshold. Significant improvement in electrical and optical properties by up to 4 times is obtained, before deviation from bulk silver properties starts to occur at 12 nm. We show that this is an enabling technology that can be applied post fabrication to metallic films or lithographically patterned nanostructures for enhanced plasmonic performance, especially in the ultrathin regime.

Gas cluster ion beams (GCIB) were used for surface modification of amorphous carbon (a-C) or tetrahedral carbon (ta-C) films, and in-vacuum XPS and near edge X-ray absorption fine structure (NEXAFS) measurements were carried out for evaluation of sp2/sp3 ratio. Since GCIB deposit its kinetic energy at local area, it leads to formation of high energy density state on surface. From XPS analysis, it was shown that sp3 contents in carbon films increased with increasing acceleration voltage (V-a) and it showed highest value at V-a of 10 kV. NEXAFS measurements also showed decrease of sp2 content at V-a of 10 kV. GCIB irradiations can assist to form sp3 rich layer on amorphous carbon surface.

We demonstrate the use of Gas Cluster Ion Beam (GCIB) nanoprocessing technology for producing ultrathin silver waveguide and disk structures with smoother surfaces and wider grain sizes for enhanced surface plasmon propagation.

Irradiation effects of gas cluster ion beam (GCIB) were studied on Co 3Fe7 films as a novel etching process. Etching depth of Co 3Fe7 increased with increasing the acceleration voltage (Va) and the ionization electron voltage (Ve), however, there is a tradeoff between etching rate and the surface roughness. Because multiply charged GCIBs were formed at high Ve (200 V), the surface layer and interface became rough. When low Ve (50 V) was applied for ionization of Ar-GCIB, crystalline CoFe2O 4 layer (10nm thick) was formed by Ar-GCIB irradiations at room temperature. Oxidation was due to water vapors during GCIB irradiation, which will be eliminated in ultra high vacuum. It is expected that gentle etching of magnetic films is possible with Ar-GCIB ionized at low Ve. © 2013 The Japan Society of Applied Physics.

Gas cluster ion beam (GCIB) irradiation was performed on Fe7Co3 films to examine the magnetic properties. After Ar ion beam etching, the coercive force (H-c) increased from the initial value; this may have been caused by irradiation damage from high-energy Ar ions. H-c decreased after Ar-GCIB irradiation (acceleration voltage (V-a): 20 kV, ion fluence (F): 1 x 10(15) ions/cm(2)). Since GCIB is an equivalent low-energy (several eV/atom) ion beam, it shows a damage-recovery effect. When the ionization electron voltage (V-e) was reduced from 200 to 60 V, H-c was observed to further decrease. Since the fraction of multiply charged Ar-GCIB decreased with decreasing V-e, severe damage of Fe7Co3 films can be minimized by employing low V-e. (C) 2013 American Institute of Physics.

Gas cluster ion beam (GCIB) etching of etch-resistant materials under acetic acid vapor was studied for development of new manufacturing process of future nonvolatile memory. Etching depths of various etch-resistant materials (Pt, Ru, Ta, CoFe) with acetic acid vapor during O-2-GCIB irradiations were 1.8-10.7 times higher than those without acetic acid. Also, etching depths of Ru, Ta, CoFe by Ar-GCIB with acetic acid vapor were 2.2-16.1 times higher than those without acetic acid. Even after etching of Pt, smoothing of Pt was realized using O-2-GCIB under acetic acid. From XPS and angular distribution of sputtered Pt, it was shown that PtOx layer was formed on Pt after O-2-GCIB irradiation. PtOx reacted with acetic acid by GCIB bombardments; as a result, increase of etching depth was observed. (C) 2013 The Japan Society of Applied Physics

The dependence of surface morphology and sputtering yield of SiO 2 thin films on the incident angle of gas cluster ion beams (GCIBs) was studied. When the incident angles (h) were either 0° or 30° ripples did not form on the surface of SiO2, and the sputtering depth increased linearly with increasing ion fluence. When θ = 45°, ripples formed in the direction perpendicular to that of the incident beam. The ripple pattern became shaper and wider with increasing θ-60°. When θ = 60°, the ripple wavelength and amplitude increased linearly with increasing ion fluence. However when θ = 80°, ripples formed in the direction parallel to that of the GCIB. When θ = 60°, the etching depth decreased with increasing ion fluence. This change in the sputtering rate can be associated with the change in the structure of the ripples. © 2013 Published by Elsevier B.V.

A gas cluster is an aggregate of a few to several thousands of gaseous atoms or molecules, and it can be accelerated to a desired energy after ionization. Since the kinetic energy of an atom in a cluster is equal to the total energy divided by the cluster size, a quite-low-energy ion beam can be realized. Although it is difficult to obtain low-energy monomer ion beams due to the space charge effect, equivalently low-energy ion beams can be realized by using cluster ion beams at relatively high acceleration voltages. Not only the low-energy feature but also the dense energy depositions at a local area are important characteristics of the irradiation by gas cluster ions. All of the impinging energy of a gas cluster ion is deposited at the surface region, and this dense energy deposition is the origin of enhanced sputtering yields, crater formation, shockwave generation, and other non-linear effects. GCIBs are being used for industrial applications where a nano-fabrication process is required. Surface smoothing, shallow doping, low-damage etching, trimming, and thin-film formations are promising applications of GCIBs. In this paper, fundamental irradiation effects of GCIB are discussed from the viewpoint of low-energy irradiation, sputtering, and dense energy depositions. Also, various applications of GCIB for nano-fabrications are explained.

In this study, charge states of gas cluster ions were evaluated from observations of individual impact craters. Since the diameter of craters formed by gas cluster ion impact increases in proportion to the cubic root of the acceleration energy, and is not dependent on cluster size when energy is greater than 10 eV/atom, the charge state of a cluster ion can be evaluated from the diameter of its individual crater. From AFM images of SiO2 irradiated with Ar cluster ions produced using low electron ionization voltages (Ve), craters with diameters of about 4 nm were observed. However, larger diameter craters started to appear with increasing Ve. From the distribution of charge states at Ve of 200 V, it was shown that there were some Ar cluster ions with six charges. There was no apparent dependence of charge state of Ar-GCIB on electron ionization current (Ie). This result indicates that ionization electron bias is the key parameter to control charge states of gas cluster ions. © 2013 Elsevier B.V. All rights reserved.

Cu etching was carried out at a low substrate temperature using a gas cluster ion beam (GCIB) under an acetic acid gas atmosphere. A very shallow Cu surface was oxidized by O-2-GCIB irradiation. Reactions between copper oxide and acetic acid occurred, and the reaction products were desorbed by local heating owing to the O-2-GCIB irradiation. Thus, Cu etching at a low substrate temperature (<60 degrees C) was achieved. By introducing acetic acid gas during O-2-GCIB irradiation, the etching depth of Cu became almost 29 times higher than the depth achieved when the etching was carried out using O-2-GCIB alone at an acceleration voltage of 5 kV. In addition to the etching of Cu, there was no surface roughening after O-2-GCIB irradiation under acetic acid atmosphere. (C) 2012 The Japan Society of Applied Physics

This paper reports on low damage sputtering of Si and an organic material (polyimide) using a nitrogen gas cluster ion beam (N-2-GCIB). In the case of N-2-GCIB irradiation, the thickness of the amorphous and rough interlayer on Si reduced by a greater amount than that in the case of irradiation with Ar cluster ions of the same size and acceleration energy. Similarly, the chemical damage to and surface roughness of polyimide irradiated with N-2-GCIB were smaller than those of polyimide irradiated with Ar-GCIB having the same energy per atom. It was thus demonstrated that N-2-GCIB is promising for low-damage sputtering of various materials. (C) 2011 Elsevier B.V. All rights reserved.

We propose a gas cluster ion beam treatment for silicon waveguide trimming and demonstrated this treatment can effectively trim the silicon waveguides. This GCIB method is promising to trim resonators for a designed add/drop wavelength. © 2012 IEEE.

Mixed gas cluster ion beams were formed using pickup cell for metal etching. O-2 neutral clusters pick up acetic acid and formed mixed cluster beam. By using O-2-GCIB with acetic acid, enhancement of Cu etching was observed. Because of dense energy deposition by GCIB, etching of Cu proceeds by CuO formation, enhancement of chemical reaction with acetic acid and desorption of etching products. Surface roughening was not observed on poly crystalline Cu because of the small dependence of etching rate on crystal orientation. Halogen free and low-temperature metal etching with GCIB using pickup cell is possible.