Masatoshi Asari

Focused ion beam direct deposition of gold

Focused ion beam direct deposition has been developed as a new technique for making patterned metal film directly on substrates. The 20 keV Au+ ion beam is focused, deflected, and finally decelerated to 30–200 eV between the objective lens and substrate. The decelerated beam is deposited on the substrate at room temperature. The beam diameter can be tuned between 0.5 and 8 μm and the beam current varies from 40 pA to 10 nA, corresponding to the beam diameter. Current density was about 20 mA/cm2, so that the deposition rate in the beam spot was estimated about 0.02 μm/s. The purity of gold film was measured with Auger electron spectroscopy and contents of carbon and oxygen, undesirable impurities, were below detection limits. The resistivity was constant at 3.7±0.1 μΩ cm for deposition over the ion energy range of 34–194 eV.

Layer-by-layer growth of GaAs studied by glancing angle scattering of fast ions

Angular distribution of scattered ions at glancing angle incidence of 3 keV He ions on a (001) surface of GaAs is studied during its molecular beam epitaxial growth. We report observation of intensity oscillations of the scattered ions from the growing surface. The period of the oscillations corresponds to the growth time of one monomolecular layer. The oscillations of the intensity is due to the oscillatory change in surface step density during layer‐by‐layer growth of the surface. This observation is in agreement with the intensity oscillations of reflection high‐energy electron diffraction (RHEED) from epitaxially growing surface of GaAs.

Focused ion beam direct deposition of superconductive thin film

Focused ion beam direct deposition of niobium has been developed as a technique for fabricating superconductive thin films. A Nb2+ ion beam extracted from a Nb10–Au50–Cu40 liquid metal ion source was accelerated to 40 keV, focused, deflected and finally decelerated to 50–1000 eV. The beam current density was 0.4–2 mA/cm2 and the minimum deposited linewidth was about 0.5 μm. The sticking probability of the Nb2+ ion beam and the critical temperature of deposited niobium films were measured. The deposition at different deposition rates and different residual gas pressure were performed. A clear relation was obtained between the critical temperature and the concentration of contaminations. This relation is consistent with the published relation for bulk niobium if it is assumed that the sticking probability of residual gas is 0.2. However, dependence of the critical temperature on ion energy was not observed.

ICB deposition and epitaxial growth of GaAs thin films

Abstract The hetero- and homoepitaxial deposition of GaAs films by the ionized cluster beam technique in connection with subsequent neutral beam deposition forming a double layer structure have been studied. It is found that ICB-deposited films have superior quality in comparison with conventional ion beam deposited films and comparable quality like MBE or MOCVD-deposited films. By the fabrication of device structures, it has been proved that the start of film growth from an interface formed by an ICB-deposited As layer is advantageous. Additionally, surface cleaning by low-energy ionized cluster beams has been studied. For the first time, defect-free surface cleaning by low-energy cluster ion beams has been realized.

The MeV ion implantation system “RFQ-1000” and its applications

Abstract Advanced VLSI devices are nowadays required to raise switching speed, to improve noise immunity and to minimize chip size. Presently, MeV ion implantation attracts much technological attention in the field of VLSI fabrication, because it is expected to be one of the most feasible solutions to those demanding requirements. In order to realize such prospective expectations, an RFQ (radio-frequency quadrupole) accelerator was applied for the first time to the field of ion implantation and a MeV ion implantation system “RFQ-1000” has been developed. First, we briefly refer to the background of the system development, putting emphasis on the RFQ. Next an outline is given of the system configuration and features. Following, detailed performances of the system are described, i.e., beam current capability, energy variability, dose uniformity, particle performance and so on. Then we move onto the viewpoint of applications. The current status of device applications by the MeV ion implantation are briefly reviewed. Finally future applications of the system to the field of compound semiconductors and to the surface modification of materials are presented.

An RFQ accelerator system for MeV ion implantation

Abstract A 4-vane-type Radio-Frequency Quadrupole (RFQ) accelerator system for MeV ion implantation has been constructed and ion beams of boron and nitrogen have been accelerated successfully up to an energy of 1.01 and 1.22 MeV, respectively. The acceleration of phosphorus is now ongoing. The design was performed with two computer codes called SUPERFISH and PARMTEQ. The energy of the accelerated ions was measured by Rutherford backscattering spectroscopy. The obtained values agreed well with the designed ones. Thus we have confirmed the validity of our design and have found the possibility that the present RFQ will break through the production-use difficulty of MeV ion implantation.

In-Situ Study of Growing Surface by Glancing Angle Scattering of Fast Ions

At glancing angle incidence of fast ions on a clean single crystal surface, most of the ions are reflected from the topmost atomic layer without penetrating the crystal surface. This phenomenon is utilized for in-situ study of growing surface. Angular distribution of scattered ions at glancing angle incidence of 3 keV neutral He and He+ ions on the (001) surface of GaAs is studied during its molecular beam epitaxial growth (MBE). The intensity oscillations of the scattered ions are observed during the growth. The period of the oscillations corresponds to the growth time of one mono-molecular layer. The oscillations of the intensity are attributed to the oscillatory change in surface step density during layer-by-layer growth of the surface.