Hajime Koyanagi

SPM-based data storage for ultrahigh density recording

The possibility of SPM-based data storage is described regarding both its recording density and readout speed for ultrahigh density data storage. We consider their gap control to achieve high-speed readout. Suitable SPM-based storages are selected and their details are studied. As a result, scanning near-field optical microscope (SNOM)- and atomic force microscope (AFM)-based storages are expected to be candidates for future storage. SNOM-based storage is for . AFM-based storage is for . Using new force modulation AFM pit recording, an ultrahigh recording density of and a readout speed of are demonstrated.

Fabrication of nanostructures using scanning probe microscopes

We present nanostructure fabrication techniques using field evaporation and local heating in scanning probe microscopes, especially the scanning tunneling microscope (STM), atomic force microscope (AFM), and the scanning near‐field optical microscope (SNOM). The detachment of sulfur atoms from the surface of cleaved MoS2 and atomic scale fabrication were demonstrated with a field evaporation in STM. Field evaporation in AFM forms nanometer‐sized gold dots on a SiO2/Si substrate. Local heating with SNOM changes a phase of the GeSbTe recording film from amorphous to crystalline, and forms high reflectivity domains 60 nm in diameter. Moreover, we discuss these applications to a semiconductor process and data storage.

HIGH-DENSITY THERMOMAGNETIC RECORDING METHOD USING A SCANNING TUNNELING MICROSCOPE

A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 μm in diameter are observed using a polarized optical microscope.

FIELD EVAPORATION OF GOLD ATOMS ONTO A SILICON DIOXIDE FILM BY USING AN ATOMIC FORCE MICROSCOPE

To investigate whether field evaporation of gold atoms is responsible for dot formation in an atomic force microscope (AFM) gold‐coated tip/vacuum/SiO2 film/p‐type Si substrate configuration, we have performed elemental analysis of the dots and measured the dependence of the threshold voltage on SiO2 thickness with both polarities for the dot formation. The experiments demonstrate that it is feasible to form gold dots on SiO2 films 17–107 A thick by adjusting the pulsed voltages applied to the gold‐coated AFM tip. Energy dispersive x‐ray spectroscopy (EDX) shows that the dots include gold. The threshold voltages increase almost linearly with the SiO2 thickness. Furthermore, the voltage with negative polarity is lower than that with positive polarity. These results provide evidence that the dot formation on the SiO2 film using AFM occurs by field evaporation.

Megahertz silicon atomic force microscopy (AFM) cantilever and high-speed readout in AFM-based recording

Small atomic force microscopy (AFM) cantilever with a maximum resonant frequency of about 6.6 MHz was developed using a Si microprocess with silicon-on-insulator wafer. The cantilever was triangular in shape with a length of 7–20 μm and a thickness of <0.3 μm and had a tip on the lever. These structures were precisely fabricated by buffer step and prestep and using dual-side aligner. Furthermore, we developed a new optical lever deflection detection system for the small cantilever with a magnifying power of 0.2 μm/A and a spot size of 2 μm. We demonstrate a high resonant frequency of the cantilever and a high speed readout at higher than 5 Mb/s using the prototype of rotation AFM recording system with a new detection system.

Nanometer Recording on Graphite and Si Substrate Using an Atomic Force Microscope in Air

Nanometer recording has been demonstrated with tens nanometer diameter pits and gold mounds formed on graphite and Si substrate using an atomic force microscope at atmospheric pressure. The probe is prepared by means of coating thin gold film on an SiO2 birdbeak-type cantilever probe, fabricated by a Si microprocess. Applications of voltage pulses between the probe and the graphite make about 10-nm diameter pits and Au mounds. Furthermore, about 50-nm to 30-nm diameter Au mound formations on Si wafer covered with natural silicon oxide are also demonstrated. The results indicate that the technique has potentials to achieve Tera-bit/in2 highly packed storage in air, and directly to write nanometer sized patterns on an insulating thin film.

27.4 Gbyte Read-Only Dual-Layer Disc for Blue Lasers

We prototyped a next-generation digital-versatile-disc (DVD) dual-layer disc system using a blue laser diode. Numerous technologies were investigated for our proposal, such as new signal-processing techniques, a disc mastering process using photobleachable dye and silver alloy as a semireflective material. The dual-layer disc for the blue laser system has a 27.4 Gbyte capacity on a 12 cm disc. Where the threshold level of the jitter value was provided at 15%, the radial tilt margin was within ±0.66 degrees on layer 0 and ±0.64 degrees on layer 1, while the tangential tilt margin was within ±0.73 degrees on layer 0 and ±0.70 degrees on layer 1. These values are sufficiently large for the playback system when compared with the DVD system.

Magnetic force microscope combined with a scanning electron microscope

A magnetic force microscope (MFM) using frequency modulation detection was combined with a scanning electron microscope (SEM). The first goal was to facilitate the selection of the MFM imaging field by positioning the magnetic tip using the SEM. The second goal was to improve the performance of the MFM by operating it in a vacuum. The efficiency of the combined SEM was proved by imaging the particular region (about 3 μm in length) on the sample. The improved features of a MFM operated in a vacuum were demonstrated by comparing images taken in air and in a vacuum. The lateral resolution was improved to 50 nm in a vacuum while it was 100 nm in air, although that resolution could possibly be due to atomic force. The dependence of the MFM image on the tip to sample spacing is discussed also.

Formation of nanometer‐sized Au dots on Si substrate in air

Nanometer‐sized Au (gold) dots on a Si substrate were formed by field evaporation using an atomic force microscope (AFM) in air. Theoretical and experimental studies show that field evaporation is possible in the AFM metal probe/vacuum/thin insulator/conductor configuration. Theoretically, the field evaporation is generated by further application of an additional bias voltage less than 30–40 V in a thin insulator. Experiments demonstrated that ultrasmall gold dots were formed on a natural SiO2/Si substrate by the applied voltage less than 10 V, and ultrasmall gold dots of 15 nm in diameter were made on the insulator.

Critical-Dimension Measurement using Multi-Angle-Scanning Method in Atomic Force Microscope

We have developed a new critical dimension (CD) measurement technique using atomic force microscope (AFM) which can measure width-dimensions and examine sidewall-shapes of fine patterns on a wafer. The technique employs a flared-type tip in combination with digital probing and multi-angle scanning mechanism that allows the tip to trace the sidewalls on both sides of a feature (or trench) by making physical contacts with the sidewall surface. First, by using finite element method (FEM) we analyzed deformation of the tip and cantilever to compensate errors caused by the deformation. To verify our compensation method we measured quartz reference patterns either with perpendicular sidewalls or undercuts. In this paper we will describe the applications and usefulness of this multi-angle operation and show some measurement results of ArF resist patterns with 200 nm width and 400 nm depth that were obtained with a flared tip of 120 nm diameter.