A gallium (Ga) focused ion beam (FIB) has been applied increasingly to 'site-specific' preparation of cross-sectional samples for transmission electron microscopy (TEM), scanning TEM, scanning electron microscopy and scanning ion microscopy. It is absolutely required for FIB cross-sectioning to prepare higher-quality samples in a shorter time without sacrificing the site specificity. The present paper clarifies the parameters that impose limitation on the following performances of the FIB cross-sectioning: milling rate, cross-sectioning at a right angle with respect to the sample surface, curtain structures formed on the cross sections, ion implantation and ion damage. All of these are discussed from the viewpoint of ion-sample interaction. Improvements for these performances achieved by diminishing their limiting origins or by correcting the resultants are described. Especially, the FIB scanning speed is significantly utilizable to improve the milling rate. A microsampling method, which allows the FIB incidence in a sidewards or upwards direction as well as downwards with respect to the microsample surface, is very effective to minimize the curtain structures.

Abstract: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 O.lpm 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.

A new focused-ion-beam (FIB) micro(μ)-sampling technique has recently been developed to facilitate transmission electron microscope (TEM) specimen preparation, while allowing chips or wafer samples to remain intact. A deep trench is FIB-milled to dig out a small, wedge-shaped portion of the sample (or a microwedge) from the samples area of interest, leaving a small, brige-shaped portion (or a microbridge) to support the microwedge. A metal needle is then manipulated into position for lifting the microwedge, i.e., the μ-sample. FIB-assisted deposition (AD) is used to bond the needle to the μ-sample. FIB-milling of the microbridge then separates the μ-sample from the chip or wafer. The separated μ-sample is mounted onto a TEM grid and secured using FIB-AD. The μ-sample is then FIB-thinned further, to a strip of about 0.1 μm thick. All of the above steps are accomplished under vacuum in the FIB system. This design permits a reliable and user-friendly environment for TEM specimen preparation, while keeping chips or wafer samples intact. It also permits operators to repeat TEM inspection and FIB-milling so that precise areas of interest may be made available for TEM inspection. Both cross-sectional and plan view TEM μ-sampling are feasible.

The focused ion beam(FIB) technique, developed for the microelectronics industry has become a major method for site specific transmission electron microscopy(TEM) specimen preparation in a wide range of materials[l]. The FIB lift-out technique has improved the specimen preparation procedures by removing complicated initial fabrication required prior to the FIB milling[2]. However, conventional FIB techniques are still having increased difficulty in meeting failure analysis needs from high technology industries such as microelectronics.We have developed a site specific TEM specimen preparation method using a combination of an FIB instrument and an intermediate voltage TEM equipped with a scanning attachment [3]. In this method, the specimen is mounted on an FIB-TEM compatible specimen holder, so that localization of the specific site can be carried out in the FIB and TEM using the same holder. The scanning electron imaging mode may be used to observe surface structures of the milled area, and the scanning transmission electron microscopy(STEM) mode may be used to observe structures inside of the milled surface.

A boron liquid–metal–ion source is described that uses a combination of a glassy carbon or carbide emitter and a Ni–B base alloy as its source material. The B+ ion emission current is 25%–35% of the total emission current, and the energy spread for B+ ions is 12 eV at a total current of 30 μA. A source lifetime of more than 250 h was achieved with a total current of 30–50 μA. This source mounted on a mass-separated focusing column has led to B+ submicron beams with maximum energies of 20 keV for preliminary experiments on maskless implantation.

Articles you may be interested inDevelopment of liquid-metal-ion source low-energy ion gun/high-temperature ultrahigh vacuum scanning tunneling microscope combined system Rev. Sci. Instrum. 76, 126109 (2005); 10.1063/1.2149001 Favorable source material in liquidmetalion sources for focused beam applications J. Vac. Sci. Technol. B 6, 931 (1988); 10.1116/1.584326 Energy distributions of liquid metal alloy ion sources J. Vac. Sci. Technol. B 6, 919 (1988); 10.1116/1.584323 Movable needle type of liquidmetalion sources for boron and phosphorus ionsMass 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+ + IP+ for Cu-P and Pt-P alloys, respectively. The electric field at the ion emitting surface is estimated to be 27-30 V Inm 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 [.6E(M + + )/2,flE(M +) < AE(M + +) 1 for the energy width and (Ep (M +) ;PEp (M + + )/2] for their most probable energy are observed in the energy analysis of mass-analyzed ions. Most 1i1 + + ions are formed in the post-ionization process on field-evaporated M + ions. 748

In the materials characterization using transmission electron microscope(TEM), FIB technique is demanding more and more as the method to prepare electron transparent specimen 1) . We have developed a dedicated FIB system FB-2000A employing FIB-TEM(STEM) compatible specimen stage 2) and an FIB micro-sampling tehnique [3][4][5] . The FIB-TEM(STEM) compatible specimen stage allowed site specific TEM specimen preparation with a positional accuracy of 0.1µm or better 2) . The FIB micro-sampling allowed extraction of TEM specimen directly from bulk sample without any pre-FIB preparation. Recently, an FIB system FB-2100 with a newly designed 40kV ion optics has been developed to perform high-speed TEM specimen preparation. Accelerating voltage is variable from 10kV to 40kV at a minimum step of 5kV. The maximum ion beam current and maximum ion beam current density of the new ion optics are 30nA and 25A/cm 2 , respectively. The ion milling speed in TEM specimen preparation is approximately twice as high as that of previous model (FB-2000A). No noticeable increase of beam damage for the TEM specimen preparation at 40kV has been confirmed. Figure 1 shows a high resolution TEM image of Si single crystal specimen prepared at 40kV. Crystal lattice and the dumb-bell structure with the spacing of 0.136nm are clearly observed. The requirements for a high-speed TEM specimen preparation are rapidly increasing. One of solutions is employment of automatic fabrication for rough milling of a TEM specimen. We have developed a new automatic fabrication system employing a new marker detection unit based on a phase only correlation(POC) method. The marker detection unit worked for various brightness and sharpness of the images. Figure 2 shows a series of test marker images observed at various images brightness. Images 2-8 were allowable in the marker detection. Figure3 shows a series of test images observed at various Z-position. All markers in these images were identified as the memorized marker. The newly designed ion optics allowed reduction of ion beam diameter together with increase of ion beam current. Minimum probe size and the probe current for the milling are 12nm and 0.02nA, respectively. Additionally, some optimization have been made in settings of voltages, lens for various sizes and accelerating voltages. Those improvements were effectively worked out to improve scanning ion microscopy(SIM) image quality. The SIM image resolution is 6nm or better at 40kV.

A technique to cut out small pieces of samples directly from chips or wafer samples in a focused ion beam (FIB) system has been developed. A deep trench is FIB milled to cut out a small, wedge-shaped portion of the sample from the area of interest A micromanipulator with tungsten (W) probe is employed for lifting the micro-sample. The lifted micro-sample is then mounted on a carrier to prepare electron transparent thin foil specimens for transmission electron microscope (TEM) observation. We have also developed a method for site-specific TEM specimen preparation. In this method, FIB system and TEM/scanning transmission electron microscope (STEM) equipped with secondary electron (SE) detector are employed. An FIB–TEM/STEM compatible specimen holder has also been developed so that a specimen can be milled in the FIB system and observed in a TEM/STEM without remounting the specimen. STEM and scanning electron microscopy (SEM) images are used for locating a specific site on a specimen. SEM image observation at an accelerating voltage of 200kV enabled us to observe not only surface structures but also inner structures near the surface of a cross section with depth of field of around 1 micrometer. The STEM image allows the observation of inner structures of 3-5 micrometer thick specimens. Milling of a specimen by FIB and observation of the milled sample by SEM and STEM are alternately carried out until an electron transparent thin foil specimen is obtained. The position accuracy of the method in TEM specimen preparation is approximately 100nm.