Single crystal germanium (Ge) surfaces were irradiated with 100 keV Ga ions at room temperature at doses up to 3×1017 cm-2 and were observed by a scanning electron microscope (SEM) and an atomic force microscope (AFM). It is found that the Ga-irradiated regions swelled and nano-porous structures were formed on the surface after the Ga irradiation up to a dose of about 2×1017 cm-2, but the region was etched by the Ga irradiation for larger doses. The atomic composition of the swelled and etched surfaces was investigated by an Auger electron spectroscopy (AES), but no Ga signal was observed, indicating that the precipitation of Ga did not influence on these characteristics of the Ga-irradiated Ge surfaces. To investigate the water resistance of such nano-porous structures, the sample was dipped in water up to 10 hours, and the surface was observed using SEM and AFM. It is found that the swelled structures were maintained, but the etched region formed by larger-dose irradiation was partially peeled off. This indicates that the nano-porous structures can be used under water environments as a functional surface, such as filters, and deep etching can be performed by larger dose irradiations and dipping the sample in water.

Defects induced by Ga focused ion beam (FIB) irradiation at an energy between 0.1 and IkeV have been characterized by means of deep level transient spectroscopy (DLTS) and related capacitance measurements. Seven different kinds of defect centers were resolved and two centers at 0.33 and O.56eV below the conduction band were dominant in the 100eV Ga implanted sample at doses up to 1015/cm2. Induced defect centers were observed to distribute over the region far beyond the theoretical ion range, which resulted from defect migration during the irradiation. Low energy irradiation induced defects were readily annealed out during low temperature heat treatment in contrast to those induced by high energy irradiations.

Focused ion beam (FIB) techniques have many advantages which stem from being maskless and have attracted much interest for various applications including in situ processing. However, reduction of damage and improvement of throughput are problems awaiting solution. For reduction of damage, low energy FIB is promising and for improvement of throughput, understanding of the basic processes and optimization of process parameters based on this understanding is crucial. This paper discusses characteristics of low energy FIB system, ion beam assisted etching and ion implantation, and effect of damage with putting emphasize on in situ fabrication. Low energy (0.05–25keV) FIB system being developed forms -lOOnm diameter ion beams and is connected with molecular beam epitaxy system. Many results indicate that low damage, maskless ion beam assisted etching is feasible using low energy beams. Recently it was also shown that for ion beam assisted etching of GaAs, pulse irradiation yields very high etching rate of 500/ion. This indicates that the optimization of the relative ratio of ion irradiation and reactant gas supply as important to achieve high etching rate. Low energy FIB is also important for selective doping for high electron mobility heterostructures of GaAs/GaAlAs, because high mobility is significantly degraded by a slight damage.

Beam processing techniques are increasingly important because of their unique capability as nano-device fabrication techniques. These are low temperature processing, high spacial resolution, high material and spacial selectivity and anisotropy, etc. For device fabrication, reduction of processinduced damage is crucial. In the present paper, basic characteristics of electron, ion and photon beam processing for etching and deposition are compared with putting emphasize on the effect of damage and promising techniques to minimize damage.

W films were deposited on n-GaAs by ion beam assisted deposition technique using low energy H2+ and Ar+, and film properties and residual damage in the substrate were investigated by measuring X-ray photoemission, current-voltage characteristics and deep level transient spectroscopy. Films with a resistivity of 1O−5 ohm·cm were formed. It was observed that damage can be reduced using the low energy beams and that Schottky contacts with n-factor of almost 1 and barrier height of 0.88 eV were formed.

The chtaracteristics of ion beam assisted deposition are discussed and compared with those of photon beam assisted deposition. Effects of various deposition parameters including ion species, beam energy and substrate temperature are discussed. Deposited films usually include impurities such as C and O. Inclusion of oxygen takes place by enhanced oxidation by background oxygen and may be reduced by depositing in a clean vacuum. Promising applications of maskless ion beam assisted deposition are also discussed.

Characteristics of ion beam assisted etching (IBAE) for SiO2 have been investigated to reveal'a possibility for maskless etching using focused ion beams. The ion beam assisted etching was done by bombarding 50 keV unfocused ion beams in XeF2 atmosphere and effect of various etching parameter on etching characteristics have been investigated. These are the effects of XeF2 gas pressure, bombarding ion species, bombarding angle and H2 addition, etc. Significant enhancements up to 100 times larger than physical sputtering were achieved. The selectivity of SiO2 to Si could be tailored to specific requirements from 0.1 to 6 by changing the gas mixing ratio. The etching rate was approximately proportional to the energy deposition rate bombarded by ion beam on surface. Carbon contamination on surface after etching were improved by the introduction of XeF2 gas.

Tin oxide deposition was performed by focused argon ion laser irradiation in a tin tetrachloride gas atmosphere. Etching of gallium arsenide and tin oxide deposition were observed in a single scan of a laser beam under specific conditions. The center of the irradiated area was etched and then covered with deposit. Density ratio of 0/Sn obtained from the deposit by AES measurements was about 1.4 - 1.6. Additional hydrogen gas in ambient SnCl4 gas reduced both tin oxide deposition and gallium arsenide etching. Deposition, at first, occurred at the outer side of the irradiated area and gallium arsenide etching occurred at the center of it. The amount of deposit depends on beam dwell time. Additional oxygen in ambient SnCl4 gas improved deposited film quality: the deposited film with additional oxygen proved to be tin dioxide, which is an conductor.

Our experimental results about aperiodic magnetoconductance in narrow n+-GaAs wire are described. These wires are fabricated in an MOCVD grown n+-GaAs film by electron beam lithography and the dry etching technique. It is found that the aperiodic structure arises from the quantum interference which is important in small structures (<1in). The experimental results are compared to the recent theory.

Maskless patterning of Mo and Si was done by implanting 50 keV focused Ga+ ion beam and by plasma etching using CF4 gas. The implantation is done to modify the chemical properties of the sample surface. It was found that Mo films became etch-resistant for the plasma etching after implantation at a dose higher than 4×1015 /cm2. Si crystals showed a positive tone pattern due to a radiation enhanced etching at a dose lower than 5x1016/cm2. At higher doses, the etching rate decreased and above 8 x 1016/cm2, no etching was observed in the implanted region. Patterns with a thickness of a several hundred nanometers were formed by the present maskless patterning technique.

Recent advances of focused ion beam systems and their applications are presented. The applications include maskless ion implantation and various maskless patterning techniques which make use of ion induced chemical effects. These are ion beam assisted etching, deposition and ion beam modification techniques and are promising to improve patterning speed and extend applications of focused ion beams.

A single picosecond pulse laser annealing of ion-implanted Si is reviewed as ultra-short pulse laser annealing, comparing them with nanosecond pulse and picosecond-pulse train annealing. In order to clarify the physical mechanism of pulsed laser annealing, the dynamic behavior of the amorphous to crystalline transition has been investigated by means of time-dependent optical reflectivity measurement at 0.63 µm (cw) and 1.06 µm (30-ps pulse itself) under the irradiation of the annealing beam of a single 30-ps laser pulse at 1.06 µm. A tentative model is proposed for explaining the results and further problems which remain to be resolved are discussed.