Shizuka Nakano

Ultrasonic Atomic Force Microscope with Overtone Excitation of Cantilever

We propose a novel atomic force microscope (AFM) combined with ultrasonic frequency vibration of a cantilever excited at its support. This method enables both topography and elasticity imaging of stiff samples such as metals and ceramics, without a need for bonding a transducer to the sample. When the sample surface is contacted with a tip attached to the cantilever, the cantilever vibration mode is changed according to the sample properties. It is theoretically predicted that the amplitude and resonant frequency of vibration at higher-order modes are useful parameters for elasticity evaluation of stiff samples. A preliminary experimental verification of this principle is presented using a glass-fiber-reinforced plastic sample. Clear elastic contrast was successfully obtained using a soft cantilever only when it was vibrated at MHz frequency higher-order modes.

Compression test system for a single submicrometer particle

A compression test system was developed for measuring the strength of a single particle with a cross-sectional dimension of less than 1μm. The test system used a small diamond plate that has a flat platen to compress the particle on a diamond substrate. To avoid compressing multiple particles and to avoid direct contact between the platen and the substrate, the flat area was comparable in size to the tested particle. Mechanical processes such as polishing, however, have difficulty in fabricating such a small area. Here, fabrication of a micrometer-sized flat area was achieved by using focused ion beam technology. The resulting compression test system successfully measured the strength of a single submicrometer particle. Results showed that the mean strength of alumina particle with nominal mean diameter of 0.7μm was 2.9GPa.

Atomic Force Microscopy Cantilevers for Sensitive Lateral Force Detection.

In order to enhance the lateral force sensitivity of atomic force microscopy (AFM) to detect atomic or molecular scale interaction, two types of force sensors were fabricated by additional processing of commercial sensors with the help of focused ion beam (FIB) technology. In one type of cantilever, a hinge was fabricated in the middle of the commercial cantilever by FIB milling, resulting in the reduction of the lateral force constant from 1204 N/m to 118 N/m. For further enhancement of the lateral sensitivity without causing snap-in behavior, a novel force sensor was designed and fabricated through a combination of FIB milling and FIB deposition techniques. The lateral force constant was reduced, for example, from 3600 N/m to 20 N/m, and the measured lateral force resolution attained the order of 1 nN.

Advanced micromachine fabrication using ion-implanted layers

Abstract To apply ion implantation to micromachining, we fabricated microstructures using a micropatterned mask and subsequent etching based on the different etch rates of the substrate and of the ion-implanted structure. As examples, a micromesh and cantilever beam were fabricated from a silicon substrate by etching with KOH solution after gold, carbon or titanium ion implantation. Distinctive three-dimensional structures are fabricated by ion implantation at different implantation depths. Although these structures show slight deflections due to residual stresses, they are still applicable in practical uses. The problem of diffraction can be solved by optimizing the fabrication conditions.

Evaluation of the Elastic Properties of a Cantilever Using Resonant Frequencies

A method to evaluate Youngs modulus and Poisons ratio of a micro-cantilever is demonstrated using resonant frequency measurements of deflection and torsional vibrations. Both vibrations of the cantilever were excited by a new cantilever holder, and they were measured separately using an optical lever. Five modes of resonant frequencies for deflection and three modes for torsion were obtained. Youngs modulus and Poisons ratio were estimated by fitting the theoretically calculated resonant frequencies to the experimental results.

SAW velocity measurement of crystals and thin films by the phase velocity scanning of interference fringes

We present principle and application of a novel noncontact velocity measurement of surface acoustic waves (SAW) on crystals and thin films using laser interference fringes scanned at the phase velocity of SAW. The scanning interference fringes (SIF) are produced by intersecting two laser beams with a frequency difference. The SAW velocity within the laser beam spot is measured as the ratio of observed SAW frequency and predetermined wave number of the SIF. The frequency measurement can be quite precise because of a large number of generated SAW carriers and amplitude enhancement effect. The SAW velocity measurement is free from the water loading effect accompanying the leaky SAW measurements. This principle was successfully applied to evaluate Si/sub 3/N/sub 4/ and SiO/sub 2/ films deposited on Si [001] surface.<<ETX>>

High-Power Pulsed Magnetron Sputtering Glow Plasma in Argon Gas and Pulsed Ion Extraction

Plasma-ion processing enhances the functionality of a film, and as such, metal plasma sources are indispensable in film preparation. A magnetron sputtering glow plasma is generated by a pulsed power source in a process called a high-power pulsed magnetron sputtering glow plasma. Metal species are sputtered by energetic argon ions and are ionized. Ions are extracted from the plasma when a substrate holder electrode (SHE) is immersed in the plasma. This process has been referred to as plasma-based ion implantation and deposition (PBII&D). This paper deals with the electrical and optical characteristics of a pulsed magnetron sputtering glow plasma in which pulsed ion extraction is carried out by the PBII&D method. Work is presented showing that the voltage and current characteristics can be represented as a series connection of voltage source, current-limiting resistor, and plasma impedance. As a result, the characteristics are normalized by the peak current and the maximum power consumed in the plasma where a circuit-matching condition is satisfied. However, when the temporary behavior of the current changes by over 20 A/μs under the experimental conditions, a circuit inductance originating from the connecting wire in the circuit can significantly influence the electrical characteristics. As a result, the peak current and the maximum consumed power cannot be used to normalize the electrical characteristics. When an inductive component is considered, the electrical characteristics obtained experimentally are curve fitted to the calculated values. Ion extraction from the glow plasma was successfully observed. This suggests that the PBII&D method can be employed in the case of a high-power pulsed glow plasma. The waveform of the extracted ion current is seen to have a sharp peak at the initial stage of voltage application to the SHE, followed by a stationary state. This confirms that the SHE is immersed in the plasma. The plasma density is on the order of 1017 m-3 and is estimated by the recovery characteristics of the voltage applied to the SHE. The ion density of the glow plasma is found to be proportional to the extracted stationary ion current at the end of the pulse applied to the SHE. The temporary behavior of the optical emission spectrum of the glow plasma confirms that sputtered titanium species are ionized to a singly ionized state and that their appearance is delayed from the appearance of argon ions.

Advanced micromachine fabrication using ion implantation

Abstract Ion-implantation followed by etching was used to fabricate micromachine components from bulk silicon. The size of the ion-modified region was sufficiently small to make microdevices (e.g. devices with submicrometer dimensions). Ion implantation/etching techniques have the advantages of high controllability, high selectivity and non-thermal processing. For 3.1 MeV gold ions implanted into silicon to a dose of 1×10 17 cm −2 , microcantilever beams were fabricated with a Young’s modulus of 60 GPa and a surface resistance of 36 kΩ. The elastic property was lower than conventional materials used for making microdevices, and the electrical resistance was sufficiently low that such components can be used as electrical conductors.

CHARACTERIZATION OF ION IMPLANTED SILICON AND DIAMOND BY VARIABLE WAVELENGTH PHOTOACOUSTIC MICROSCOPY AND SCANNING ACOUSTIC MICROSCOPY

Abstract An ion implanter of a 3 megaelectron-volt energy modifies a subsurface layer of crystalline silicon and diamond-like film. The thickness of layer is up to a few microns. A scanning acoustic microscope and a variable wavelength photoacoustic microscope reveal a change of elastic and thermal property of the layer. The crystalline silicon implanted with silicon ions at a 3 × 1017 cm−2 dose shows a maximum 35% decrease of elasticity and a reduction of thermal conductivity by 3 orders of magnitude. The photoacoustic image of the diamond-like film implanted with nitrogen ions at a 7 × 1016 cm−2 dose shows a variation of film quality.

High-Power Inductively Coupled Impulse Sputtering Glow Plasma

A high-power pulsed glow plasma consisting of ionized metallic species was generated at the sputter target without the use of an externally applied magnetic field. An inductively coupled plasma was produced with a radio frequency (RF) of 200 kHz, and the plasma production was in a burst mode. A pair of titanium electrodes as the sputter target was placed near the RF argon plasma source. A pulsed direct-current (dc) voltage with negative polarity was applied to the target. The metallic plasma, which is referred to as the target plasma, had a density of 1013-1014 cm-3. The electrical characteristics of the target plasma were dependent on the timing of the application of the pulsed dc voltage. The target voltage and the current through the target change based on the plasma density, and the consumed power reaches a maximum when the impedance matches the target plasma circuit, i.e., when the plasma impedance is consistent with the circuit resistance in the target plasma circuit. Optical emission spectra of the target and RF plasma regions were recorded, and titanium and argon ions were observed. Titanium ions were generated within 10 μs after the application of the negative pulse voltage and then diffused into the RF plasma region. The production region for titanium ions occurred within approximately 10 mm of the target surface, and diffusion occurred during the application of the dc pulse in the RF plasma region. However, diffusion was substantially limited to within approximately 35 mm from the target surface. The optical emission intensity of the titanium ions is dependent on the power consumed in the target plasma, and hence, a maximum intensity can be obtained at the maximum power consumption, at which impedance matching is satisfied. The parameters that influence the emission intensity of the metallic species include the plasma density and the sputtering yield.