Kaoru Umemura

A FIB Micro-Sampling Technique and a Site Specific TEM Specimen Preparation Method

A FIB micro-sampling technique has been developed to facilitate TEM specimen preparation while allowing samples to remain intact. A deep trench is FIB-milled to remove a portion of the sample containing the region of interest. A micromanipulator is employed for the purpose of lifting out a small portion of the sample, i.e., the micro-sample. FIB assisted metal deposition is used to bond the micro-sample to the micromanipulator. The micro-sample is subsequently lifted out and mounted onto an edge of the micro-sample carrier using FIB assisted metal deposition. The micro-sample is then thinned to the thickness of about 0.1µm for TEM observation. All of the above steps are accomplished under vacuum in the same FIB system. This procedure is a reliable TEM specimen preparation technique when the evaluation or failure analysis of a specific site is required. Both cross sectional and plan view TEM specimen preparations are feasible with this technique. In addition, a technique to prepare TEM specimens from a specific site has also been developed. In this technique, an FIB system equipped with a FIB/TEM(STEM) compatible specimen holder is used for thinning of the samples, e.g., a micro-sample. The compatible specimen holder permits repeated alternating FIB milling and TEM(STEM) observation, enabling TEM specimen preparation from a specific site.

Favorable source material in liquid‐metal‐ion sources for focused beam applications

The variety of ion species is increased by using alloys as well as pure elements as the source material of liquid‐metal‐ion sources (LMIS’s) in focused‐ion‐beam (FIB) technology. Some experiments show that the base elements of the alloy affect the charge and energy distributions of emitted ions. Doubly charged ions, which have a narrower energy spread per charge and smaller energy tail than the singly charged ions, form a finer FIB. The intensity ratio of doubly to singly charged ions is expected to increase with selection of an alloy with higher surface tension, because this will strengthen the electric field at the ion emitting surface. LMIS characteristics in connection with source materials are discussed.

Ion formation in alloy liquid‐metal‐ion sources

Mass and energy analyses are carried out for ions emitted from liquid‐metal‐ion sources (LMISs) using Cu‐P base, Pt‐P, and Ni‐B‐Si alloys. A strong matrix effect of about 10−1 and 1 is observed on the intensity ratio of P++/P+ for Cu‐P and Pt‐P alloys, respectively. The electric field at the ion emitting surface is estimated to be 27–30 V/nm from the post‐ionization model. A difference of only 10% in the field strength between these alloys is responsible for this matrix effect. The Ni‐B‐Si alloy LMIS, on the other hand, does not present an identical field strength for each component. The relationships of [ΔE(M++)/2≤ΔE(M+) <ΔE(M++)] for the energy width and [Ep(M+)≥Ep(M++)/2] for their most probable energy are observed in the energy analysis of mass‐analyzed ions. Most M++ ions are formed in the post‐ionization process on field‐evaporated M+ ions.

Development of Liquid‐Metal‐Ion Sources for Focused‐Ion‐Beam Applications

The luminescence of Y{sub 2}O{sub 3}:Gd under x-ray excitation is reported. Emission is observed from several manifolds. In some cases it is possible to distinguish between emission from Gd{sup 3 +} on the C{sub 2} site and emission from Gd{sup 3 +} on the S{sub 6} site.

Development of Phosphorus Liquid-Metal-Ion Source

A phosphorus liquid-metal-ion source that uses a Cu–P alloy as its source material is described. The P+ ion emission current is about 10% of total emission current, which consists mainly of Cu+ ions. Energy spread of P+ ions is 25 eV at a total current of 30 µA, while that of Cu+ is 28 eV. A source lifetime of more than 20 hours is achieved at a total current of 50–60 µA.

Mass-separated microbeam system with a liquid-metal-ion source

Abstract This paper describes the developement of a mass-separated focusing column, consisting of a liquid-meta-ion (LMI) source, two lenses, an E×B mass filter, and a post-deflector. This system has the ability to produce sub-μm beams with energies up to 20 keV and a maximum current ranging from 10−2 to 1 nA, depending on the source characteristics. Preliminary operation of this focusing system was demonstrated by scanning ion microscope (SIM) images. An image resolution of less than 0.1 μm has been achieved for focused beams of 69Ga+ and 11B+, which were respectively extracted from Ga-LMI and eutectic alloy LMI sources.

Focused phosphorus ion beam implantation into silicon

Abstract Phosphorus implantation into (100) silicon using a 32-keV focused ion beam is investigated from the standpoints of electrical properties and damage to the implanted layers. Phosphorus ions are extracted from the PtPSb alloy liguid-metal-ion source. Electrical properties are measured by isochronal annealing with Hall measurements and radiation damage is evaluated using a transmission electron microscope. Compared with the conventional implantation method, focused ion beam implantation causes heavier radiation damage and forms amorphous layers at a dose of 2 × 10 14 cm −2 due to high current density.

Isotope effect on boron ions emitted from a liquid-metal-ion source

An isotope effect on boron ions emitted from a liquid-metal-ion source utilising Ni-B base alloy is described. The B++ ion intensity is as weak as 1/30 approximately 1/50 that of B-, but the proportion of 10B++ in (10B+10B++) is smaller by 13 approximately 17% than for 11B++. This effect is predicted by the post-ionisation model of field evaporation, although there are certain discrepancies between experimental results and theory.

Mass and Energy Analyses of Gallium-Indium Liquid-Metal-Ion Sources

Mass and energy analyses of ions emitted from Ga-In alloy LMI sources were carried out using a double-focusing mass spectrometer to compare these data with those from single-element Ga and In LMI sources. A more distinct low energy shoulder was observed on the Ga+ energy distribution curve for the Ga-In source at the lower source-current and the higher emitter temperature. A similar shoulder was also observed for the Ga source but not for the In source. The Ga shoulder for the Ga-In source suggests Ga preferential vaporization at the emitter and/or Ga preferential ionization in the vicinity of emitter.

Measurement of energy spread and angular intensity of a cesium liquid metal ion source

This paper determines the optimum range of total ion current for a cesium liquid metal ion source for use as a focused ion beam (FIB). This range is determined from a figure of merit calculated from measurements of the angular intensity and energy spread of emitted ions. Judging from both the figure of merit and the tail of the energy distribution curves, the total emission current should be set near 1 μA for a cesium FIB with a high current density. Assuming that both Cs- and Ga-FIBs have the same diameter, the relative current density of a Cs-FIB is expected to be approximately 80% that of a Ga-FIB.