豊田 紀章

Gas cluster ion beam technology employs accelerated ions consisting of clusters of a few hundreds to thousands of atoms (gas cluster ion beam technology, GOB). This paper reviews recent novel GCIB process applications for (i) ultra-shallow junction (USJ) formation and doping in Si, (ii) surface smoothing of metals, (iii) selective smoothing of SOI, SiC and other compound semiconductor films, (iv) IC back end of the line (BEOL) processing and (v) high quality thin multi-layer film formation for reliable and durable optical filters. (c) 2005 Elsevier B.V. All rights reserved.

A size-selected gas cluster ion beam (GCIB) system has been developed to study the size effects of energetic cluster ion bombardments on a solid surface. As the typical atomic mass of gas cluster ions exceeds 400,000 amu (10,000 Ar atoms/ion), it had been quite difficult to realize a size-selected GCIB irradiation system. In this study, a bending magnet was employed for mass separation, so that the ion current is sufficient for surface processing. The width of the cluster size distribution, after the magnetic filter, was 400 atoms/cluster, which is 1/20 of the original cluster size distribution. With the size-selected GCIB irradiation system, it was found that the damaged layer thickness of Si substrates dramatically decreased with increasing the cluster size. This result was in good agreement with that obtained from molecular dynamics simulations. (c) 2005 Elsevier B.V. All rights reserved.

In the gas cluster ion beam (GCIB) processes, number of atoms in a cluster ion or "cluster size" is one of the most important parameter on the surface interaction processes because it defines the equivalent bombarding energy of individual atom (eV/atom). In this study, cluster size effects on damage formations, sputtering yields were studied using size controlled GCIB systems. Damage formation in crystalline Si substrate showed significant drop at the cluster size where energy per atom was below 5 eV/atom. Sputtering yields of Au by one Ar atom in cluster showed linear relationship with the energy per atom of cluster ions. Threshold energy for sputtering was far below that with Ar monomer ions due to the near surface energy deposition by Ar cluster ion bombardments.

Irradiation by a Gas Cluster Ion Beam (GCIB) is a promising technique for precise surface etching and planarization of Si wafers. However, it is very important to understand the crystalline structure of Si wafers after GCIB irradiation. In this study, the near surface structure of a Si (100) wafer was analyzed after GCIB irradiation, using a cross-sectional transmission electron microscope (XTEM). Ar-GCIB, that physically sputters Si atoms, and SF6-GCIB, that chemically etches the Si surface, were both used. After GCE3 irradiation, high temperature annealing was performed in a hydrogen atmosphere. From XTEM observations, the surface of a virgin Si wafer exhibited completely crystalline structures, but the existence of an amorphous Si and a transition layer was confirmed after GCIB; irradiation. The thickness of amorphous layer was about 30 nm after Ar-GCIB irradiation at 30 keV. However, a very thin (< 5 nm) layer was observed when 30 keV SF6-GCIB was used. The thickness of the transition layer was the same both Ar and SF6-GCIB irradiation. After annealing, the amorphous Si and transition layers had disappeared, and a complete crystalline structure with an atomically smooth surface was observed.

A newly designed high-current gas cluster ion beam (GCIB) assisted deposition system was developed and O-2 cluster ion current over 100 mu A was obtained with no monomer ions. High-current GCIB realizes high-rate deposition on large substrates. In this system, Ta2O5 and SiO2 films were deposited on Si and glass substrates by O-2-GCIB assisted deposition. Very smooth surface (Ra < 0.5 nm), high refractive index (n = 2.2) and dense structure were obtained by optimizing deposition conditions. Also, more efficient surface smoothing and low damage irradiation effects were obtained by removing O-2 monomer ions from O-2-GCIB by using a permanent magnet. (c) 2005 Elsevier B.V. All rights reserved.

This report reviews a new field of ion beam technology that employs accelerated ions consisting of clusters of a few hundreds to thousands of atoms (Gas Cluster Ion Beam technology, GCIB). Cluster ion-surface collisions have been found to produce low energy bombardment effects at very high density and GCIB processes exhibit unique non-linear effects that are useful for novel surface processing applications. The effects include low energy ion bombardment, lateral sputtering, and low temperature thin film formation. GCIB processing has been successfully applied for shallow junction formation; for high rate etching; for surface smoothing of materials including metals, dielectrics, superconductors and diamond; and for high-k oxide and DLC thin film deposition. Currently, industrial applications of GCIB processes are being conducted by several Japanese companies under the Nanotechnology program called "Advanced Nano-Fabrication Process Technology Using Quantum Beams" of NEDO/METI (New Energy and Industrial Technology Development Organization/the Ministry of economy and Technology Industry). In US, R&D especially for semiconductor applications are under way at Epion Corporation, International SEMATEC and their cooperated associations. Epion is the only company that is developing industrial GCIB equipment and has joined the NEDO/METI project. The review includes recent equipment and process developments. In nano-scale GCIB processes, the effect of cluster size (atoms/cluster) on surface processing, especially damage production, becomes important. In the project, GCIB equipment with cluster size selection system has been developed. Several industrial applications for surface smoothing of magnetic and semiconductor materials by the Japanese government and IC processing by US companies are summarized. (c) 2005 Elsevier B.V. All rights reserved.

A high-current gaseous cluster ion beam (GCIB) system with a magnetic size separation function has been developed. This system was equipped with a permanent magnet with a magnetic flux density of 1.2 T. The system consists of a magnetic spectrometer with sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. Depending on the momentum of the cluster ions, positioning of the sample on the guiding rail allows bombardment of the sample with the desired cluster size. In this study, preliminary results demonstrating cluster mass spectra and mass resolution are presented. Finally, scanning tunneling microscopy is used to characterize the morphology of individual cluster impacts after irradiation. (c) 2005 Elsevier B.V. All rights reserved.

The influence of cluster size on damage layer thickness produced by Ar gas cluster ion beam (GCIB) irradiation is presented. The GCIB has a wide cluster size distribution which has been difficult to control. To obtain a narrow size distribution of the GCIB, the mass filter containing a strong permanent magnet is developed. In this study, the size-selected Ar-GCIB irradiates the Si substrates. The cluster size is varied between 500 and 20,000 atoms/cluster. After irradiation, the damage layer thickness on Si substrates is measured by ellipsometry. The results of size-selected Ar-GCIB irradiation on Si substrates at acceleration energy of 5 keV show that the damage decreases very quickly, from 7.9 nm to 0.3 nm with increasing the cluster size from 500 to 5000 atoms/cluster. This tendency is in agreement with the results calculated by molecular dynamics simulation. These results suggest that the GCIB process is promising for low damage processing of semiconductor material. (c) 2005 Elsevier B.V. All rights reserved.

A new cluster size selector is being developed to realize low-damage nano-processing applied gas cluster ion beam (GCIB) technology. The selector consists of several pairs of deflection electrodes and high-frequency deflection biases are applied. Depending on the velocity of a cluster ion, a desired size of cluster can pass through the selector. It can select any target cluster sizes without changing the structure. The length of this device is about 200 nun and it is much smaller than that of traditional mass spectrometers, because of its simple structure. Preliminary experiments showed a good mass resolution and high transmittance for a cluster size selector with this device. (c) 2005 Elsevier B.V. All rights reserved.

Ta2O5 films were deposited with O-2 cluster ion beam assisted deposition at various incidence angles theta, between 0 degrees and 80 degrees from surface normal. The surface morphology and cross-sectional images were studied. The film structure was significantly affected by incidence angle. When theta was between 0 degrees and 30 degrees, dense and flat Ta2O5 films were formed. However, in the case of theta between 30 degrees and 60 degrees, ripples were formed on the surface whose wave vector was in the incidence direction and the film surface was rough. On the other hand, when theta was above 70 degrees, the wave vector of the ripple was rotated to perpendicular and surface roughness decreased to the same value at normal incidence. Ripples formed during thin film assisted deposition were similar to surface morphological evolution during the sputtering process. (c) 2005 Published by Elsevier B.V.

A cluster ion irradiation system with cluster size selection has been developed to study the effects of the cluster size in surface processing using cluster ions. A permanent magnet with a magnetic field of 1.2T was installed for size separation of large cluster ions. Traces formed on a graphite surface by the impact with Ar cluster ions under an acceleration energy of 30 keV were investigated by, scanning tunneling microscopy. The nature of the traces is strongly affected by the number of constituent atoms of the irradiating cluster ion. When the cluster ion is composed of 100-3000 atoms, crater like traces are observed on the irradiated surfaces. In contrast, such traces are not observed at all with the irradiation of the cluster ions composed of over 5000 atoms. This behavior is discussed on the basis of the kinetic energy per constituent atom of the cluster ion.

This report reviews the developing field of ion-beam technology that employs accelerated ions consisting of clusters of a few hundreds to thousands of atoms (gas cluster ion-beam technology, GCIB). Cluster ion-surface collisions have been found to produce low-energy bombardment effects at very high density, and GCIB processes exhibit unique nonlinear effects that are useful for surface processing applications. The effects include low-energy ion bombardment, lateral sputtering, and low-temperature thin-film formation. GCIB processing has been applied to shallow junction formation; high rate etching; surface smoothing of materials including metals, dielectrics, superconductors, and diamonds; and high-k oxide and diamond-like carbon thin-film deposition. We describe the unique characteristics of GCIB-surface interactions and GCIB process applications for (i) ultrashallow junction formation and doping in Si, (ii) surface smoothing of metals, (iii) selective smoothing of silicon-on-insulator SiC, and other compound semiconductor films, (iv) integrated circuit back-end-of-the-line processing, and (v) high-quality multilayer thin-film formation for reliable and durable optical filters. (c) 2005 American Vacuum Society.

Nano structure formations on An surfaces by Ar gas cluster ion beams (GCIB) irradiation at an oblique incidence were studied. When the incident angle was close to 0 degrees from the surface normal of An targets, the Au surface was smoothed due to the lateral sputtering effects and there were no structure formations. However, ripples were formed on Au surfaces at incident angle of 60 degrees without sample rotation. By irradiations of GCIB at incident angle of 60 degrees with sample rotation, cone like structures with 50 nm in diameters were fabricated. However, the surface roughness suddenly decreased above 60 degrees. Even though the surface roughness was the same, ripple structures were formed parallel to the,incoming GCIB directions at 85 degrees without sample rotation. The incident angle (theta) dependence on the sputtering depth decreased, following cos theta dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence of GCIB. (c) 2005 Elsevier B.V. All rights reserved.

Gas cluster ion beam (GCIB) process has been studied for more than 15 years. But the interest in GCIB process has increased only recently, driven by the nano-technology program. Gas cluster ion bombardment have been applied to offer potential for various industrial applications due to its unique characteristics, i.e. the low energy bombardment, lateral sputtering, surface cleaning and smoothing, and low temperature thin film formation. This paper reviews the current fundamental research related to the GCIB-solid interactions as well as their applications in modern magnetic, optical and semiconductor device fabrications. (c) 2005 Elsevier B.V. All rights reserved.

This chapter discusses the comparison of irradiation effects between cluster and monomer for diamond-like carbon (DLC) film deposition. DLC films have been used as protective coatings for various applications. Especially hard-DLC films are needed for disks and head coatings of hard disk drives. The development of the magnetic media and sensors of reading heads using giant magneto resistive (GMR) or tunnel magneto resistive ('TMR) technologies is very fast and the floating distance between the head and the media is shorter than 3 nm to obtain a higher recording density at present time. The floating space can be reduced by depositing DLC films with thinner thickness. Thinner thickness degrades the film durability and leads to collision of the head with the media surface. Therefore, high wear-resistance DLC films, which have higher hardness than those formed by present deposition method such as plasma CVD are required. © 2005 Elsevier Ltd.

This chapter discusses the high quality thin film formation with gas cluster ion beam assisted deposition system. Demand of optical multilayer thin films increased due to the expansion of broadband optical tele-communication systems. In this application, film characteristic to optical filter have narrow band width, high optical transmission and high durability. The film should be of high density and the film interface should be flat. The chapter is to find the optimum deposition conditions in O2-GCIB (gas cluster ion beam) assisted deposition for high quality Ta2O5 and Nb2O5 optical films with high density, high-refractive index, low extinction coefficient, low surface roughness and high humidity. The film properties and structures are explored under various deposition conditions and environmental test are performed to study the stability of the interference filters. © 2005 Elsevier Ltd.

This chapter discusses the morphology dependence of surface smoothing of argon (Ar) gas cluster ion beams (GCIB), which is used to realize atomic scale surface smoothing and high sputtering yields. Cluster ion beam has a lot of advantages for atomic processes. Smoothing process is one of the promising technologies to be utilized for industrial applications. Cluster consists of a few thousands atoms, and the energy per constituent atom of cluster is the total energy divided by its cluster size. Therefore, very low-energy ion beam can be easily realized by employing large cluster ions. When substrates surface is irradiated with GCIB, sputtering phenomena is developed by lateral sputtering effects. © 2005 Elsevier Ltd.

Glancing angle fluorescence XAFS analysis of Ta and Ti oxide thin films, which were obtained by oxygen gas cluster ion beam assisted deposition techniques (GCIB), was made to analyze the valence states and the structures of the 'amorphous' thin films at atomic level. Glancing angle XAFS measurement was made for Ta L3-edge of the Ta oxide thin films and Ti K-edge of the Ti oxide thin films with 200 nm thickness, respectively, using the detection method of electron yield by conversion with He flow gas counter (CEY) at the beam line BL01B1 in the SPring-8. The Ta L3-XANES results indicate that the assistance of the oxygen GCIB leads to the higher oxidation state of the Ta atom. The Ta L3 and Ti K EXAFS results suggest that these metal oxide films obtained by the oxygen GCIB assisted deposition techniques have amorphous-like structure. © Physica Scripta 2005.

We have investigated the irradiation damage depths produced by an Ar gas cluster ion beam (GCIB) and an Ar monomer ion beam (MIB) on GaAs and Gap, in a comparison of the cathode luminescence (CL) spectra of ion-irradiated and nonirradiated areas. The depths of irradiation damage in both substrates were estimated from the relationship between the CL intensity and the electron beam acceleration voltage.

Nano structure formations on Au surfaces by 20 keV At gas cluster ion beam (GCIB) irradiation at an oblique incidence were studied. When the incident angle was close to 0 degrees from the surface normal of Au targets, the Au surface was smoothed due to the lateral sputtering effects and there were no structure formations on the surfaces. However, ripples were formed on Au surfaces at incident angle of 60 degrees without sample rotation. When the Au. samples were irradiated with Ar-GCIB at 60 degrees with sample rotation, cone like structures with 50nm in diameters were fabricated and the surface roughness had a maximum value. However, the surface roughness suddenly decreased over incident angle of 60 degrees. Even though the surface roughness was the same in the cases with and without sample rotations at 85 degrees incidence, ripple structures were formed parallel to the incoming GCIB directions when there was no rotation. The incident angle dependence of the sputtering depth decreased following cos theta dependence. Very efficient surface smoothing without removing materials were realized with oblique incidence.

Glancing angle. uorescence XAFS analysis of Ta and Ti oxide thin films, which were obtained by oxygen gas cluster ion beam assisted deposition techniques (GCIB), was made to analyze the valence states and the structures of the 'amorphous' thin films at atomic level. Glancing angle XAFS measurement was made for Ta L-3-edge of the Ta oxide thin films and Ti K-edge of the Ti oxide thin films with 200nm thickness, respectively, using the detection method of electron yield by conversion with He flow gas counter (CEY) at the beam line BL01B1 in the SPring-8. The Ta L-3-XANES results indicate that the assistance of the oxygen GCIB leads to the higher oxidation state of the Ta atom. The Ta L-3 and Ti K EXAFS results suggest that these metal oxide films obtained by the oxygen GCIB assisted deposition techniques have amorphous-like structure.

Although plasma-virus-RNA level and CD4-positive-T-cell count are useful to monitor clinical status of the human immunodeficiency virus (HIV)-infected individuals, clinical course is often varied among patients and sometimes difficult to predict. To identify additional parameters associated with disease progression, we examined by cDNA microarray the expression profiles of 731 immune-response-related genes in the peripheral blood mononuclear cells (PBMCs) from 21 HIV-positive individuals in Uganda. The analysis enabled the patients to be classified into three distinct groups on the basis of the gene expression patterns. Notably, these groups, clusters I, II and III, were highly associated with clinical status of the patients defined by CDC classification, categories A, B, and C, respectively. Statistical analysis identified 40 genes whose expressions were significantly up- or down-regulated in the Cluster III patients (p < 0.05). Up- and down-regulated genes included ones involved in immature T lymphocytes differentiation, apoptosis signaling, and active HIV replication, suggesting that the levels of active destruction and regeneration of mature T lymphocytes associated with enhanced HIV-1 replication is related to the disease progression. Follow-up study showed that the cluster classification improved prediction of disease prognosis with the CDC classification. These findings provide new clues for studying perturbation of host immunity, pathogenesis, and disease prognosis of HIV-infected individuals. (C) 2004 Elsevier B.V. All rights reserved.

Ta2O5 dielectric films were deposited on Si and quartz substrates by O-2 gas cluster ion beam (O-2-GCIB) assisted deposition at various incidence angles. The film structure and optical properties were significantly influenced by incidence angle. For films deposited using O-2-GCIB at 7 keV energy, when the incidence angle was smaller than 30degrees from the surface normal, a very smooth and dense film was realized and there were no significant difference in optical properties as the films deposited at normal incidence. However, when the incidence angle was higher than 45degrees, surface roughness increased and ripples were formed on the film surface. At a higher acceleration energy, which induces the sputtering of materials, previous reports have shown that in the case of Ar GCIB, ripple formation has been observed at an incidence angle larger than 45degrees. The same result was observed in the case of O-2 cluster ion beam assisted deposition.

Diamond-like carbon (DLC) films with super hardness (>50GPa) were deposited using Ar cluster ion beams at various oblique incident angles irradiated towards substrates on which C-60 was simultaneously deposited. When the incident angles of Ar cluster ions were from 0degrees to 20degrees, the DLC films had a super hardness of approximately 50 GPa, the hardness three times higher than that of conventional DLC films. Furthermore, the films had a flat surface and a low sp(2) content, which was estimated with a near edge X-ray absorption fine structure (NEXAFS). However, in the range of angles above 40degrees, the carbon films had a lower hardness, a rougher surface, and a higher sp(2) content. Therefore, the incident angles of the Ar cluster ions for obtaining super hardness ranged from 0degrees to 20degrees.

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams (GCIB) was investigated with experiments and molecular dynamics (MD) simulations. A new cluster SIMS system with high-intensity cluster ion source has been developed. Ar cluster ion beam with the average size of 2000 was utilized as a primary ion beam. The beam diameter is less than 1 mm at the target position, and a current density of 10 muA/cm(2) is obtained. The etch rate of Si with this current density is more than 20 nm/min, which is far beyond the etch rate in recent low energy SIMS system. The secondary ion intensity linearly increases with the acceleration voltage. A threshold voltage of a few keV for secondary ion emission was found. These results are consistent with previous sputtering experiments. (C) 2004 Elsevier B.V. All rights reserved.

O-2 gas cluster ion beam (O-2-GCIB) assisted depositions were employed to deposit high quality dielectric films (Ta2O5, Nb2O5 and SO2). The optimum irradiation energy and ion current density for Ta2O5 films were 5 to 9 keVand 0.5 muA/cm(2), respectively. The Ta2O5/SiO2 films deposited with O-2-GCIB irradiation showed very uniform and dense structures without columnar or porous structures. Due to the significant surface roughness improvement effect of GCIB, the surface roughness decreased even though the films were deposited on a rough surface. The Nb2O5/SiO2 interference filter deposited with O-2-GCIB assisted deposition was very stable and there was no shift of wavelength before and after environmental tests. (C) 2003 Elsevier B.V. All rights reserved.

Gas cluster ion beam (GCIB) processing has been applied for the ultra-smooth surfaces preparation recently. As GCIB exhibit significantly different physical phenomena from atomic or molecular ion beams, new fields of ion beams have been developed by using GCIB. In this paper, fundamental characteristics of GCIB will be summarized and surface smoothing applications are explained. Additionally, it has been shown that GCIB is suited for assisting ion beams during thin film depositions. Recent results of GCIB assisted depositions are also summarized in the latter part of this paper. (C) 2003 Elsevier B.V. All rights reserved.

Gas cluster ion beam (GCIB) techniques have recently been proposed as new processing methods. We have been investigating the characteristics of GCIB techniques through sputtering GaAs and Gap by Ar gas cluster ion beams as a function of cluster size and acceleration energy. The Ar cluster size was selected by a magnetic spectrometer, and was obtained from the mass spectra measured by a time of flight mass spectrometer. The average sputtering yields of GaAs and Gap were 0-47 and 0-66 atoms/ion for 5-30 kV, respectively. The sputtering yields of GaAs and Gap were higher than those of an Ar monomer ion.

A size-selected gas cluster ion beam (GCIB) system has been developed to study the size effects of energetic large cluster ion bombardments on a solid surface for the first time. This system equipped a permanent magnet with a magnetic flux density of 1.2 T. There is a sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. By locating a sample at a certain position, particular size of cluster ion can be irradiated continuously with affordable ion current density. When the total acceleration energy of Ar-GCIB was 5keV, both amorphous and oxide thickness on Si substrate increased with decreasing cluster size. This result showed good agreement with that obtained from molecular dynamics simulations.

Since the initial study of gas cluster ion beams (GCIB) was started in the Ion Beam Engineering Experimental Laboratory of Kyoto University, more than 15 years have passed. Some of the results of that study have already been applied for industrial use. Unique characteristics of gas cluster ion bombardment have been found to offer potential for various other industrial applications. The impact of an accelerated cluster ion upon a target surface imparts very high energy densities into the impact area and produces non-linear effects that are not associated with the impacts of atomic ions. Among prospective applications for these effects are included shallow ion implantation, high rate sputtering, surface cleaning and smoothing, and low temperature thin film formation.

Diamond-like carbon (DLC) film deposited using C-60 vapor with simultaneous irradiation of an Ar cluster ion beam was characterized by a near edge X-ray absorption fine structure (NAXAFS), in order to optimize the hard DLC film deposition conditions. Contents of sp(2) orbitals in the films, which were estimated from NAXAFS spectra, are 30% lower than that of a conventional DLC film deposited by a RF plasma method. Those contents were obtained under the flux ratio of the C60 molecules to the Ar cluster ions to range from 1 to 20, at 5 keV of Ar cluster ion acceleration energy. Average hardness of the films was 50GPa under these flux ratios. This hardness was three times higher than that of a conventional DLC film. Furthermore, the lowest sp2 content and above-mentioned high hardness were obtained at room temperature of the substrate when the depositions were performed in the range of the substrate temperature from room temperature to 250 degreesC.

Transmission electron microscopy has been used to observe the effects of single ion and Ar cluster impacts. The impact of either single ions or cluster ions produces nanometer-sized craters on Au and ejects nanoparticles. The impact of single ions causes ejection of nanometer-sized particles of gold at the same rate as the rate of cratering leading to the conclusion that the two processes are coupled. The sputtering yield for cluster irradiation of Au exhibits a near cosine dependence on the ejection angle while the amount of Au in visible nanoparticles varies as the cube of the ejection angle. (C) 2003 Elsevier Science B.V. All rights reserved.

Cluster ion implantation using decaborane (B10H14) has been proposed as a shallow implantation technique for LSI devices with gate lengths of several-tens nanometers. Experiments and computer simulations of low-energy boron monomers and decaborane clusters implantation were performed. Molecular dynamics simulations of B-10 cluster implantation have shown similar implant depth but different damage density and damage structure compared to monomer (B-1) ion implantation with the same energy-per-atom. For monomer implantation, point-defects such as vacancy-interstitial pairs are mainly formed. On the other hand, B-10 generates large numbers of defects within a highly-amorphised region at the impact location. This difference in damage structure produced during implantation is expected to cause different annihilation processes. (C) 2003 Elsevier Science B.V. All rights reserved.

Since an initial study of gas cluster ion beam (GCIB) had started in Ion Beam Engineering Experimental Laboratory, Kyoto University, more than 15 years has passed. Some of the results are already been applied for an industrial use. Unique characteristics of GCIB bombardment have been found to offer potential for various industrial applications that cannot be achieved by conventional ion beam processing. Impact of an accelerated cluster ion upon a target surface imparts very high-energy densities into the impact area and produces non-linear effects that are not observed in impacts of atomic ions. Among prospective applications are included shallow ion implantation, high-rate sputtering, surface cleaning and smoothing, and low-temperature thin film formation. Low-energy bombarding effects and sputtering effects produced by the cluster ion impact are particularly important. Cluster ion implantation has been applied to realize ultra-shallow junction formation. High-sputtering yields and lateral sputtering that cause surface smoothing cannot be achieved with monomer ion beams. The surface smoothing process to atomic levels becomes the first production use of GCIB. High-quality thin film formation using GCIB assisted deposition is also the characteristic that is explained mainly due to the very low energy and very high-density ion bombardment. (C) 2003 Elsevier Science B.V. All rights reserved.

O-2 gas cluster ion beam (O-2-GCIB) assisted depositions were studied to deposit high-quality Ta2O5, Nb2O5 and SiO2 films. The optimum irradiation conditions of O-2-GCIB were the acceleration energy of 5-9 keV and the cluster ion current density over 0.5 muA/cm(2), respectively. Nb2O5/SiO2 films deposited with O-2-GCIB assist showed very uniform and dense structures without columnar or porous structures. Due to the significant surface smoothing effect of GCIB, the interface and top surface of Nb2O5/SiO2 multi-layer were quite flat. The interference filter deposited with O-2-GCIB assist deposition was very stable and there was no shift of wavelength before and after environmental tests. As O-2,GCIB is equivalently very low-energy ion beam and is able to deposit flat and dense amorphous films, it is suited to deposit multi-layered films where low-energy assisting ions are required. (C) 2003 Elsevier Science B.V. All rights reserved.

To optimize the flux ratio of C-60 to Ar cluster ion during diamond-like carbon (DLC) film deposition, DLC films deposited under various flux ratios were characterized with Raman spectrometry and near edge X-ray absorption fine structure (NEXAFS). From Raman spectrometry, DLC films were deposited when the flux ratio of C-60 to Ar cluster ion was between 0.7 and 4. When the ratio was over 10, C-60 films were mainly deposited. As it was difficult to do precise characterization of DLC with Raman spectrometry, NEXAFS measurements were performed for the films deposited in the DLC deposition range of flux ratio. From NEXAFS spectra, there was no significant difference in sp(2) contents when the flux ratios were between 1 and 4. Hardness of these DLC films was between 40 and 45 GPa. Therefore very hard DLC film could be deposited with Ar cluster ion beam assist deposition over wide range of flux ratios, and this deposition process was very stable against changes of the flux ratio. (C) 2003 Elsevier Science B.V. All rights reserved.

Ta2O5 films were deposited on a rough surface with O-2 cluster ion beam assisted deposition and the reduction of surface roughness was studied. Stoichiometric Ta2O5 thin films were deposited with O-2 cluster ion assisted deposition, and the film structure was very dense without porous and columnar structures. Smooth Ta2O5 surfaces were realized even though they were deposited on a rough surface when O-2 cluster ion energy was 7 keV. As the surface smoothing effect by O-2 cluster ion irradiation was not dominant at O-2 cluster ion energy of 7 keV, smooth Ta2O5 surface was mainly originated by additional deposition of very thin Ta2O5 films. (C) 2003 Elsevier Science B.V. All rights reserved.

In order to study the influences of residual Ar monomer ion (Ar+) on sp(2) content and hardness of diamond like carbon (DLC) films formed by Ar cluster ion beam assisted deposition, Ar cluster ion, Ar+ and their mixed ions (Ar cluster ion and Ar+) bombardments were performed during evaporation of C-60. From near edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopy measurements, lower sp(2) content in the carbon films was obtained with Ar cluster ion bombardment than that with Ar+ and mixed ion. Furthermore higher hardness and smooth surface were shown with Ar cluster ion bombardments. Therefore it was important to reduce Ar+ in Ar cluster ion beams to obtain hard DLC films with flat surface. (C) 2003 Elsevier Science B.V. All rights reserved.

Diamond-like carbon (DLC) films with high hardness were formed by Ar cluster ion beam assisted deposition at room temperature, using C-60 as a carbon source. The gas cluster ion beam (GCIB) assisted deposition was useful to form hard DLC films, as the bombardments induced high-pressure and high-temperature effects at the impact surface, and ultra low energy effects. When the acceleration energy of Ar cluster ion was 5 keV, the hardness of 50 GPa was obtained. This value was approximately two times higher than that of the films deposited with conventional methods. Wear-resistance properties were also higher than that of conventional films. Rough estimations of sp(2) orbital in the films were carried out with Raman spectra, the films formed with Ar cluster ion bombardment had lower sp(2) contents, which meant films had low fraction of graphite bonding. Thus DLC films exhibiting higher physical characteristics and lower graphite bonding were obtained with GCIB assisted deposition. (C) 2002 Elsevier Science B.V. All rights reserved.

In this paper, the incident angle dependence of assisting O2 cluster ion beams for various film properties was reported. Surface roughness and AFM image of Ta2O5films was shown.

O-2 gas cluster ion beam (O-2-GCIB) assisted depositions were studied to form high quality Ta2O5, Nb2O5 and SiO2 films. The optimum irradiation conditions for Ta2O5 and Nb2O5 film depositions were the acceleration energy of 5 to 9keV and the cluster ion current density over 0.5muA/cm(2), respectively. The Nb2O5/SiO2 films deposited with O-2-GCIB irradiations showed very uniform and dense structures without columnar or porous structures. Due to the significant surface smoothing effect of GCIB, the interface and top surface of Nb2O5/SiO2 multi-layer were quite flat. The interference filter deposited with O-2-GCIB assist deposition was very stable and there was no shift of wavelength before and after environmental tests. As O-2-GCIB is equivalently very low-energy ion beam and is able to deposit flat and dense amorphous films at low substrate temperature, it is suited to deposit multi-layered films where low-energy assisting ions are required.

To study the influence of the flux ratio of C-60 molecule to Ar cluster ion on DLC film characteristics, DLC films deposited under various flux ratios were characterized with Raman spectrometry and Near Edge X-ray Absorption Fine Structure (NEXAFS). From results of these measurements, hard DLC films were deposited when the flux ratio of C-60 to Ar cluster ion was between 0.7 and 4. Furthermore the DLC film with constant sp(2) content was obtained in the range of the ratio from 0.7 to 4, which contents are lower values than that of conventional films such as RF plasma. DLC films deposited under the ratio from 1 to 4 had hardness from 40 to 45GPa. It was shown that DLC films with stable properties of low sp(2) content and high hardness were formed even when the fluxes were varied from 1 to 4 during deposition. It was indicated that this process was useful in the view of industrial application.

O-2 gas cluster ion beam (O-2-GCIB) assisted depositions were employed to deposit high quality dielectric films (Ta2O5, Nb2O5 and SiO2). The optimum irradiation energy and ion current density for Ta2O5 and Nb2O5 film were 5 to 9 keV 2 and 0.5 muA/cm(2), respectively. The Nb2O5/SiO2 films deposited with O-2-GCIB irradiation showed very uniform and dense structures without columnar or porous structures. Due to the significant surface roughness improvement effect of GOB, the interface and top surface of Nb2O5/SiO2 multi-layer were quite flat. The interference filter deposited with O-2-GCIB assist deposition was very stable and there was no shift of wavelength before and after environmental tests. As O-2-GCIB is equivalently very low-energy ion beam and is able to deposit flat and dense amorphous films at low substrate temperature, it suitable for deposition of multi-layered films where low-energy assisting ions are required.

Ta2O5 films were deposited on a rough surface (average roughness 1.3nm, peak-to-valley 14nm) and surface roughness evolutions and improvements by O-2 gas cluster ion beam (O-2-GCIB) assisted deposition was studied. The average roughness dramatically decreased from 1.3nm to 0.5nm after deposition of Ta2O5 films 20nm in thickness with 7 keV of O-2 Cluster ion beams. As there was no etching or sputtering of Ta2O5 film by 7keV O-2-GCIB irradiations, O-2-GCIB assist deposition realized significant improvement of surface roughness by additional deposition of TA(2)O(5) film whose thickness was close to the peak-to-valley of original surface. It is expected that morphological evolution of the film by GCIB assist deposition becomes completely different from conventional ion assist deposition due to energetic cluster ion impacts.

Multiscale simulation method (MSM) has been used for modeling impacts of Ar clusters, with energies ranging from 20-500eV/atom, impacting Si surfaces. Our simulation predicts that on a Si (100), craters are nearly triangular in cross-section, with the facets directed along the close-packed (111) planes. The Si (100) craters exhibit four-fold symmetry. The craters on Si (111) surface are well rounded in cross-section and the top-view shows a complicated star-like image. The simulation results for individual gas cluster impacts were compared with experiments at low dose (10(10) ions/cm(2) charge fluence) for Ar cluster impacts into Si (100) and Si (111) substrate surfaces. Atomic force microscopy (AFM) and cross-sectional high-resolution transmission electron microscope (TEM) imaging of individual gas cluster ion impacts into Si (100) and Si (111) substrate surfaces revealed faceting properties of the craters and are in agreement with the theoretical prediction.

Since the initial study of gas cluster ion beams (GCIB) was started in the Ion Beam Engineering Experimental Laboratory of Kyoto University, more than 15 years have passed. Some of the results of that study have already been applied for industrial use. Unique characteristics of gas cluster ion bombardment have been found to offer potential for various other industrial applications. The impact of an accelerated cluster ion upon a target surface imparts very high energy densities into the impact area and produces non-linear effects that are not associated with the impacts of atomic ions. Among prospective applications for these effects are included shallow ion implantation, high rate sputtering, surface cleaning and smoothing, and low temperature thin film formation.

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams (GCIB) was studied with experiments and molecular dynamics (MD) simulations to achieve a high-resolution depth profiling. From MD simulations of Ar cluster ion impact on a Si substrate, the ion beam mixing by a cluster ion was heavier than that by Ar+ at the same energy per atom, because the energy density at the impact point by clusters was extremely high. However, the sputtering yield with an Ar cluster ion was one or two orders of magnitude higher than that with Ar+ at the same energy per atom. Comparing at the ion energy where the altered layer thickness was the same by both Ar cluster and Ar+ impact, a cluster ion showed almost 10 times higher sputtering yield than Ar+. Preliminary experiment was performed with a conventional SIMS detector and a mass resolution of several nanometer was achieved with Ar cluster ions as a primary ion beam. (C) 2002 Elsevier Science B.V. All rights reserved.

In order to study the influences of Ar monomer ion (Ar+) on carbon film properties induced by ion beams assisted deposition, At cluster ion, Ar+, and their mixed ions (Ar cluster ion and Ar+) irradiated surface during evaporation and deposition of C-60. From Near Edge X-ray Absorption Fine Structure (NEXAFS) and Raman spectroscopy measurements, lower sp(2) content in carbon films was obtained via Ar cluster ion beam bombardment in comparison with bombardment by Ar+ and mixed ion beams. Furthermore higher hardness and smoothness of surface were demonstrated via Ar cluster ion bombardments. Thus, it was important to irradiate using higher fraction Ar cluster ions in the beam, in order to obtain hard DLC films with flat surface.

Diamond Like Carbon (DLC) films were formed by Ar cluster ion beam assisted vapor deposition of C(60). To study the effects of contaminating Ar monomer ions (Ar) in the cluster beam on the sp(2) content, film hardness, and surface morphology of the films, beams of Ar cluster ions, Ar(+), and a mixture of cluster ions and Ar+ were used for the bombardment, during evaporation of C(60). From the Near Edge X-ray Absorption Fine Structure (NEXAFS) and Raman spectroscopy measurements, lower sp(2) contents in carbon films were obtained for the cases when Ar cluster ion beams were used. The usage of single Ar+ and mixed ion beams showed higher sp(2) contents. Furthermore, higher hardness and smoother surfaces were obtained with Ar cluster ion irradiations. Therefore, the increase of the fraction of Ar cluster ions in the beams was important to obtain hard DLC films with flat surfaces.