Satoshi Tomimatsu

Cu film growth on a Si(111) surface studied by scanning tunneling microscopy

We observed a change in growth mode of Cu, while dynamically observing Cu film growth on a Si(111)-7 x 7 surface during Cu deposition at room temperature by scanning tunneling microscopy (STM). Initially, Cu atoms were adsorbed mostly on the faulted halves of the 7 x 7 structure. Then, up to about 2 ML coverage, small Cu islands appeared. As the coverage increased from 2 to 3 ML, the growth mode changed into quasi-layer-by-layer growth. With further deposition, 3-D islands having hexagonal terraces grew.

Capability of ion beam projection optics for microfabrication

Applicability of ion beam projection optics for sputtering fabrication is investigated by using third-order aberration theory. Under the Kohler illumination condition that minimizes off-axial aberration, the total beam current of the shaped beam formed in large-reduction-ratio projection column is larger than that of a conventional focused ion beam. In a preliminary experiment with 50:1-reduction projection optics, the edge blur of the shaped beam is estimated to be less than 0.1 @mm for a total beam current larger than 30 nA. Ion beam projection optics is thought to be suitable for applications that require high-throughput processing.

STM modification of MoS2 in the nanometer-scale using a gas—solid reaction

Abstract We report on the nanometer-scale modification of a MoS 2 surface by scanning tunneling microscopy (STM) with an electric field lower than that required for field evaporation by STM. It is known that a Pt−Ir STM tip dissolves H 2 gas into atomic hydrogen which is chemically active. We applied this phenomenon to STM modification to lower the electric field necessary for atom detachment. A Pt−Ir lip was used to dissolve the H 2 gas on the MoS 2 surface. The gas-solid reaction enhanced the evaporation of the top-layer sulfur atoms, which were removed at a low electric field of about 2.4 V nm −1 . The present study shows that we can control STM modification well with the same feedback loop as that used for STM observation.

Process monitor of 3D-device features by using FIB and CD-SEM

For yield improvement of 3D-device manufacturing, metrology for the variability of individual device-features is on hot issue. Transmission Electron Microscope (TEM) can be used for monitoring the individual cross-section. However, efficiency of process monitoring is limited by the speed of measurement including preparation of lamella sample. In this work we demonstrate speedy 3D-profile measurement of individual line-features without the lamella sampling. For instance, we make a-few-micrometer-wide and 45-degree-descending slope in dense line-features by using Focused Ion Beam (FIB) tool capable of 300mm-wafer. On the descending slope, obliquely cut cross-section of the line features appears. Then, we transfer the wafer to Critical-Dimension Secondary Electron Microscope (CDSEM) to measure the oblique cross-section in normal top-down view. As the descending angle is 45 degrees, the oblique cross-section looks like a cross-section normal to the wafer surface. For every single line-features the 3D dimensions are measured. To the reference metrology of the Scanning TEM (STEM), nanometric linearity and precision are confirmed for the height and the width under the hard mask of the line features. Without cleaving wafer the 60 cells on the wafer can be measured in 3 hours, which allows us of near-line process monitor of in-wafer uniformity.

Development a projection ion beam instrument that uses a gas ion source for metal-contamination-free microsampling

The authors have developed a metal-contamination-free ion beam instrument with a duoplasmatron that serves as a gas ion source and a projection ion beam optical system that generates a shaped gas ion beam. The luminance of the duoplasmatron ion source is low. However, a projection ion beam optical system can increase the ion current with sharp beam edge profiles enough for microsampling fabrication. A metal-contamination-free shaped gas beam can be used to achieve clean inline sampling and wafer return strategy. The irradiation system of the instrument has three electrostatic lenses, an E × B mass separator, and a mechanism for bending the ion beam to prevent neutral particles from irradiating the samples. The instrument also has a gas flow system for ion beam assisted deposition and a needle transport system for microsampling. Experiments using a prototype implementation demonstrated that microsampling can be achieved by using shaped gas ion beams.