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Abstract: Cluster ion beam processes can produce special surface modification effects, such as surface smoothing, high rate sputtering and very shallow implantation. In order to realize high-speed surface processing, a high-energy gas cluster ion beam irradiation system was developed. Since cluster energy depends on chamber pressure, the energy distribution of the high-energy cluster ion beams was measured for various pressure regimes. These distributions show that both cluster size and energy decrease with increasing collisions with residual gas. The number of atoms scattered by one collision with residual gas is proportional to the velocity of the cluster ion. The results suggest that an analytical equation can be used to calculate irradiation energy from the acceleration energy, size of cluster, chamber pressure and transportation length. [Copyright &y& Elsevier]

Abstract: In order to realize high-speed processing, high-energy SF6 cluster ion beam was generated and Si substrates were irradiated with the SF6 cluster ions at acceleration energies of 10–80keV. The sputtering yield increased with acceleration energy and was about 2600 times higher than that of Ar monomer ions. The sputtering yield of SF6 cluster ions was about 3300atoms/ion at acceleration energy of 80keV. The etching ratios of Si/Ni were about 25 at acceleration energy of 20keV. The selectivity of Ni was sufficiently high to use as a mask material for Si etching. Both surfaces of etched material (Si) and mask material (Ni) remained smooth surfaces after high-energy SF6 cluster ion beam irradiation. These results show that the high-energy SF6 cluster ion beam can fabricate patterns of high aspect ratio with high-speed keeping the surfaces smooth. [Copyright &y& Elsevier]

Abstract: The cluster ion beam processes has been shown to produce new surface modification effects, such as surface smoothing, high rate sputtering and very shallow implantation. Now high current is needed to increase the productivity of cluster processing. However, the chamber pressure increases with cluster beam intensity. Energy distributions of the cluster ion beams show that both size and energy of cluster ion decrease by numerous collisions with residual gas. This indicates that it is necessary to reduce the chamber pressure for effective transport of cluster ion beams. [Copyright &y& Elsevier]

Abstract: High ion dose is needed to realize the nano-level smoothing and etching of hard materials using cluster ion beam. Large current is needed to increase the productivity of processing. In order to get the large current cluster ion beam, the cluster generator, ionizer and ion extraction has been studied. The intensity of neutral beams generated from various shapes of nozzles was measured and the orifice diameter of skimmer was adjusted. As a result, the 10 times stronger neutral beams could be generated and a maximum beam current of 2.4mA was achieved at the acceleration voltage of 45kV with the source gas pressure of 15,000Torr. The ratio of monomer ion in the beam was 58%. This result indicates that the beam current of cluster ion except monomer ion is about 1mA. With this beam current, 12-in. wafers can be treated with 2×1015 ions/cm2 in about 4min. The process speed is high enough so that the cluster beam is available for next generation processes. [Copyright &y& Elsevier]

High ion dose is needed to realize the nano-level smoothing and etching of hard materials with increasing the productivity of processing using cluster ion beam. In order to achieve large current cluster ion beam, the cluster generation, ionization and ion transportation were studied. The intensity of neutral cluster beam increased with source gas pressure. The efficient ionization and extraction were realized by structural improvement of the ionizer. As a result, when the gas pressure was 15,000 Torr and the electron emission current is 300 mA, the beam current reached 500 μA. The size distributions of large current Ar cluster ion beam were measured using time-of-flight method. The distributions prove that the neutral beams include clusters with the size up to 160,000 atoms and that the distributions can be controlled by the source gas pressure and ionization condition. [Copyright &y& Elsevier]

Gas cluster ion beam (GCIB) assisted deposition technique has been applied to form titanium-dioxide films. When oxygen cluster ions collide on solid surfaces, oxygen molecules in the clusters enhance oxidation due to high density energy deposition. Metal titanium pellets were used as source material for EB evaporation, because evaporation with metal pellets is much stable than that of oxide pellets. Films were deposited on sapphire (0 0 0 1) substrates with various conditions. Characteristics of the films were examined by use of XRD, RBS and AFM. When film was deposited with the acceleration voltage of 7 kV at 473 K, the well c-oriented rutile TiO2 film was formed with average roughness of 0.4 nm. Without assistance of GCIB rough amorphous film was formed in an atmosphere of oxygen. Very smooth surface films with good crystallinity were formed by GCIB assisted deposition technique. [Copyright &y& Elsevier]

In order to prepare tin-doped indium oxide (ITO) films, we have deposited metallic indium (In) and tin (Sn) on a glass substrate at various substrate temperatures (Ts) in conjunction with irradiation of O2 cluster ions. The temperature dependence of the electrical and optical properties of the ITO films prepared was investigated. The resistivity decreased with increasing substrate temperature, and a resistivity of 1.1×10−4 Ω cm was obtained at Ts=300 °C. This is considered to be due to some improvement of the crystalline state of the films as well as an increase of the carrier density. On the other hand, the transparency was found to be almost constant in the temperature region from room temperature (RT) to 300 °C, and it was higher than 90%. In addition, we have prepared ITO films by the simultaneous use of an O2 cluster ion beam and KrF laser irradiation. High quality ITO films with a lower resistivity of 1.0×10−4 Ω cm and a transparency above 90% was able to be formed at Ts=300 °C. A high carrier density of 2.5×1021 cm−3 was obtained. Laser irradiation during ITO film formation as well as irradiation of O2 cluster ions was effective particularly for annealing and activating doped Sn atoms. [Copyright &y& Elsevier]

Abstract: Cluster ion beam processes exhibit high rate sputtering with low damage, and in particular, extremely high sputtering rates are expected using reactive cluster ion beams. Si could be sputtered at extremely high rates using reactive cluster ion beams, such as SF6, Cl2, CF4, CHF3, and CH2F2. However, processing of metallic materials with reactive cluster ion beams has not been studied yet. It was expected that high-speed etching of metallic materials can be realized with Cl2 cluster ion irradiation, because such a beam would reactively sputter these materials. We generated a Cl2 cluster ion beam and investigated the etching characteristics of various metallic materials, such as Ni and Al films, under this irradiation. The size of the Cl2 cluster, as measured with a time-of-flight (TOF) system, was about 1400 molecules. The sputtering yield for each metal was more than 10 times higher than that obtained with Ar cluster ions, showing that Cl2 cluster ion irradiation reactively sputtered the metallic materials. These results indicated that Cl2 cluster ion irradiation was suitable for high-speed processing of metallic materials. [Copyright &y& Elsevier]

Abstract: Cluster ion beam processes can produce high rate sputtering with low damage compared with monomer ion beam processes. Cl2 cluster ion beams with different size distributions were generated with controlling the ionization conditions. Size distributions were measured using the time-of-flight (TOF) method. Si substrates and SiO2 films were irradiated with the Cl2 cluster ions at acceleration energies of 10–30keV and the etching ratio of Si/SiO2 was investigated. The sputtering yield increased with acceleration energy and was a few thousand times higher than that of Ar monomer ions. The sputtering yield of Cl2 cluster ions was about 4400atoms/ion at 30keV acceleration energy. The etching ratio of Si/SiO2 was above eight at acceleration energies in the range 10–30keV. Thus, SiO2 can be used as a mask for irradiation with Cl2 cluster ion beam, which is an advantage for semiconductor processing. In order to keep high sputtering yield and high etching ratio, the cluster size needs to be sufficiently large and size control is important. [Copyright &y& Elsevier]

Abstract: In order to investigate the dependence of the sputtering yield on cluster size, surfaces were irradiated with cluster ion beams with various size distributions, and the sputtering yields were measured. It was found that there was a threshold energy for sputtering with cluster ion irradiation. When the cluster size was constant, the sputtering yield was proportional to acceleration energy. These results suggested an empirical formula to calculate sputtering yield from the ion energy and the size distribution of the cluster. The empirical formula indicates that the sputtering yield is proportional to the 1.1 power of the size, when the acceleration energy per atom is constant. [Copyright &y& Elsevier]

• Quadrupole-ToF-SIMS was applied with gas cluster ion beam (GCIB). • Ar-GCIB sputtered 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC) sample. • He or N2 gas of varied pressures was used at travelling-wave ion guide. • DSPC mass spectra and ion yields in MS and MS/MS modes were measured. • Secondary ion or fragment energy was cooled depending on the gas and pressure. The work was aimed at using gas to cool the secondary ions emitted from gas cluster ion beam (GCIB) bombardment of biosamples for lowering the ion energy distribution and thus enhancing the detection sensitivity for secondary ion mass spectrometry (SIMS). An Ar-cluster ion source at energy in an order of keV was installed with the Q-ToF (Quadrupole Time-of-Flight) premier at the Quantum Science and Engineering Center, Kyoto University. The main component of the Q-ToF premier consisted of a travelling-wave ion guide, a mass filter quadrupole lens, a travelling-wave collision cell, and a ToF analyzer. A 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC) sample was used in the study on cooling the secondary ions at the travelling-wave ion guide by using helium and molecular nitrogen gas. The DSPC sample was impinged with primary Ar-cluster ions at energy 10 keV and sputtered for secondary ions in an energy range from zero to several hundred eV. Sputtering-emitted secondary ions were extracted to the Q-ToF mass spectrometer. The experiment was carried out to measure DSPC secondary ion mass spectra in two modes at varied pressures of helium or molecular nitrogen gas. The first mode was the MS mode and the other was the MS/MS mode which defined the m / z = 790.6 Da for the protonated molecule at the mass filter quadrupole lens. The experiment found that the secondary ion yields (SIYs) in the MS mode reached the maximum at 2.0 and 0.35 Pa for helium and molecular nitrogen, respectively. In the MS/MS mode, the SIYs reached the maximum at 2.5 and 0.35 Pa for helium and molecular nitrogen, respectively, and however, some fragments could not be eliminated by the cooling molecular nitrogen gas. The cooling of the secondary ions for lowering the energy distribution and the transverse direction of the secondary ions by using helium was more effective and stable than by using molecular nitrogen. [ABSTRACT FROM AUTHOR]

Cluster ion beam effect on large biomolecules is interesting due to differences in ion beam characters from normal ion beams and applications in analysis of the molecules as the cluster ion beam should be more effective in fragmenting large and complicated biomolecules to make study of the complex molecular structure possible. Argon gas cluster ion beam (Ar-GCIB) at 10 keV bombarded samples of DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine, C 44 H 88 NO 8 P, monoisotopic molecular weight 789.6 Da), angiotensin II (C 50 H 71 N 13 O 12 , monoisotopic molecular weight 1045.5 Da) and leucine enkephalin (C 28 H 37 N 5 O 7 , monoisotopic molecular weight 555.6 Da). The bombardment-generated fragments were in-situ analyzed and measured using the tandem quadrupole – time-of-flight secondary ion mass spectrometry (Q-ToF-SIMS) technique. The experiment was operated within an integrated system of Ar-GCIB and Q-ToF-SIMS. Two modes, i.e. MS (quadruple off) and MS/MS (quadrupole on), were applied in the ToF-SIMS measurement. Particularly, the secondary ion fragmentation with the collision energy dependence was focused in the study. [ABSTRACT FROM AUTHOR]

Abstract: A mass spectrometric technique using nuclear microprobes is presented in this paper for biological applications. In recent years, imaging mass spectrometry has become an increasingly important technique for visualizing the spatial distribution of molecular species in biological tissues and cells. However, due to low yields of large molecular ions, the conventional secondary ion mass spectrometry (SIMS), that uses keV primary ion beams, is typically applied for imaging of either elements or low mass compounds. In this study, we performed imaging mass spectrometry using MeV ion beams collimated to about 10μm, and successfully obtained molecular ion images from plant and animal cell sections. The molecular ion imaging of the pollen section showed high intensities of ions in the pollen cytoplasm, compared to the pollen wall, and indicated the heterogeneous distribution in the cytoplasm. The 3T3-L1 cell image revealed the high intensity of ions, in particular from the cell nucleus. The result showed that not only the individual cell, but also the cell nucleus could be identified with the present imaging technique. [Copyright &y& Elsevier]

Abstract: This paper proposes a low damage smoothing process for magnetic materials using a gas cluster ion beam (GCIB). In order to achieve low damage processing, the effect of incident angle was investigated. Depth profiles of major elements constituting the films were measured by secondary ion mass spectroscopy (SIMS). The film structure and the lattice spacing were obtained by X-ray reflectivity (XRR) and grazing incident X-ray diffraction (XRD), respectively. After the GCIB irradiation at an acceleration voltage of 20kV and incident angle of 80° with simultaneous rotation, a smooth surface of a PtMn film was obtained, with an average roughness of 1.2nm. A damaged layer thickness of less than 1.5nm was achieved under these conditions. Using the oblique GCIB irradiation, the PtMn film was etched without any change in the strain profile. Thus, the GCIB could be utilized to obtain surfaces of magnetic devices with extremely shallow damage. [Copyright &y& Elsevier]

Abstract: Surface smoothing of laser crystallized polycrystalline silicon (poly-Si) films using gas cluster ion beam (GCIB) technology has been studied. It is found that both SF6-GCIB and O2-GCIB decrease the height of hillocks and reduce the surface roughness of the irradiated films. The mean surface roughness value of poly-Si films was reduced from 10.8nm to 2.8nm by SF6-GCIB irradiation at 80°. Ultraviolet reflectance measurement reveals that GCIB irradiation causes damage near-surface of the poly-Si films. Formation of the damage, however, can be suppressed by using GCIB irradiation at high incident angle. Effect of GCIB irradiation in a metal–insulator–semiconductor (MIS) capacitor has also been investigated. The capacitance–voltage curves of MIS capacitor with SF6-GCIB irradiation are distorted. On the contrary, the distortion is reduced by O2-GCIB irradiation at 80, which suggests that electrical-activated damage of the films can be decreased by using O2-GCIB irradiation. [Copyright &y& Elsevier]

Abstract: Oblique irradiation of gas cluster ion beam (GCIB) is a promising technique for polishing of vertical mirrors in micro-electro-mechanical-systems (MEMS) optical devices. The relationship between reflection properties and surface profiles was examined for gold mirrors fabricated by a similar process to MEMS vertical mirrors. The intensity of the diffuse light reflected by the gold mirror was substantially reduced by the oblique irradiation of GCIB, which could be explained in terms of the decrease of the surface roughness. By comparing surface profiles of the mirror after GCIB irradiation at different incident angles and using two gas species, characteristics of the oblique irradiation of GCIB were clarified. [Copyright &y& Elsevier]

Smoothing effect is one of the advantages of cluster ion beam. It is important to estimate an ion dose to achieve required surface smoothness. The smoothing rate with cluster ion beam depends on surface profiles. In this work, modeling of surface smoothing process with cluster ion beams was examined. Ar cluster ions with an energy of 20 keV was irradiated on rough Si Surface. Fast Fourier transform was applied to atomic force microscope data of 100 × 100 μm2, and power spectra were calculated. Smoothing rate depends on the wave number as well as the ion dose. Relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of the wave number dependence of the smoothing rate. The calculated and the experimental surface profiles are in good agreements. [Copyright &y& Elsevier]

Abstract: We measured the sputtering yield, surface roughness and surface damage of thin leucine films bombarded with Ar cluster ions and examined the usefulness of large gas cluster ions for the depth profiling of organic compounds. Ar cluster ion beams with a mean size of 2000atoms/cluster and energies from 5 to 30keV were used. Sputtering yields increased linearly with incident ion energy and were extremely high compared to inorganic materials. Surface damage was investigated by measuring positive secondary ions emitted from the leucine film before and after cluster ion irradiation. After irradiation the leucine surface became smoother. The yield ratio of protonated leucine ions to other fragment ions kept constant before and after Ar cluster ion irradiation. These results indicate that large gas cluster ions are useful for depth profiling of organic compounds. [Copyright &y& Elsevier]

Abstract: Argon gas cluster ion beam (GCIB) was employed to improve the surface smoothness of indium tin oxide (ITO) substrates. The dependence of the smoothness as well as of the sputtered depth on cluster ion energy and dose has been studied. Results show that relatively low-energy (10keV) clusters with mean size of 2000 Ar atoms are sufficient to reduce the mean roughness of the ITO surface to about one fourth of its initial value. Organic electroluminescent (EL) devices (α-NPD/Alq3/Mg–Ag) were formed on the smoothed surfaces and a considerable improve of the devices’ EL efficiency was observed. [Copyright &y& Elsevier]