Atom probe tomography (APT) is a powerful characterization method to obtain three-dimensional (3D) distributions of atoms in materials at nearly atomic-scale resolution by detecting atoms one by one, which are field-evaporated from the apex of needle-shaped specimen. Recent laser-assisted APT system allows analysis of not only metals (conductive materials) but also semiconducting and insulating materials. Advanced sample preparation using focused ion beam apparatus equipped with high resolution scanning electron microscope contributes to site-specific analysis in semiconductor-based nanodevice structures. Such an innovative methodology to visualize elements in 3D has enabled application of APT in the broad area of materials science and engineering. In this article, we focus on recent studies using APT; dopant distribution analysis in modern metal-oxide-semiconductor and fin-type field-effect transistors, ion-implanted deuterium analysis in silicon, and intrinsic spatial resolution evaluation of APT using silicon isotopic multilayers.
The recent applications of argon gas cluster ion beam (GCIB) for X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) are briefly reviewed. Depth profiling of organic materials has been one of the most notable challenges in conventional XPS and TOF-SIMS. Recently, it is getting widely accepted that GCIB has enabled us to obtain the depth profiles of organic materials. GCIB has unique sputtering characteristics, such as extremely low chemical damage, high sputtering yield and surface smoothing capability. These superior characteristics facilitate diverse applications of XPS and TOF-SIMS, increasing the analysis of organic devices and advanced polymers. In this review, the recent applications of GCIB are discussed, focusing on the organic film depth profiling and the surface cleaning effect.
The sensitivity (limit of detection) of high-resolution Rutherford backscattering spectroscopy (HRBS) is mainly determined by the background noise of the spectrometer. There are two major origins of the background noise in HRBS, one is the stray ions scattered from the inner wall of the vacuum chamber of the spectrometer and the other is the dark noise of the micro channel plate (MCP) detector which is commonly used as a focal plane detector of the spectrometer in HRBS. In order to reject the stray ions, several barriers are installed inside the spectrometer and a thin mylar foil is mounted in front of the detector. The dark noise of the MCP detector is rejected by the coincidence measurement with the secondary electrons emitted from the mylar foil upon the ion passage. After these improvements, the background noise is reduced by a factor of 200. The detection limit is improved down to 10 ppm for As in Si.
Scanning transmission electron microscopy (STEM) is a powerful tool for not only imaging but also elemental composition and chemical bonding analysis by energy dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS) with nanometer spatial resolutions. The technique of spherical aberration correction has recently been developed, and angstrom spatial resolutions have been achieved for EDX and EELS measurement as well as imaging. I also introduce other recent trends in STEM related techniques. Low acceleration voltage has often been adopted in order to reduce electron radiation damage. Recent monochrometer has achieved 0.2 eV energy resolution for EELS measurement, which enables us to analyze chemical bonding in more detail. A new type of silicon drift detector (SDD) improves the sensitivity of EDX 10 times higher than conventional detectors. These recent technologies are not independently implemented but combined in an ultimate system which can promote diverse applications of STEM.
Hard X-ray photoelectron spectroscopy (HXPES) has developed to be used in wide ranges of solid state science and technology due to its much larger information depth comparing to the conventional X-ray photoelectron spectroscopy. It enabled to investigate buried layers as deep as more than 20 nm from the surface. Here in this article, various applications of HXPES to the deep layer investigations including chemical state profiling by takeoff angle dependence measurements and standing wave methods, intermixing analysis of metal multilayers, analysis of band bending at the semiconductor hetero interfaces, analysis of 2 dimensional carriers in strongly correlated materials interfaces, electronic structure observations at buried layers and their interfaces in devices. Laboratory HXPES system with monochromatic Cr Kα X-ray excitations is also introduced with its applications to Si MOS gate stack model samples including interface state spectroscopy by electric field application are also introduced.
For realizing higher recording density of perpendicular magnetic recording media, a reduction of the magnetic exchange coupling among magnetic grains in the Co74Pt16Cr10-8 mol%SiO2 granular recording layer (RL) is essential. We propose inserting the thin layer thickness of 1 nm deposited under high Ar gas pressure of 8 Pa into the initial growth region of the RL. Larger perpendicular coercivity of 6.4 kOe and a smaller hysteresis loop gradient at coercivity of 2.1 were obtained, which indicated that magnetically well-isolated media and a significant reduction of the magnetic exchange coupling in the granular RL were realized. By film composition analysis, oxygen content of the insertion layer was found to be very high. These results suggest that magnetic grains are well segregated by forming more oxide mixture of SiO2 and Cr-oxide at the grain boundaries in the insertion layer.
The distribution of the thickness of the films formed by magnetron sputtering depends on elements because the angular distribution of the sputtered atoms depends on elements. In this study, the angular distributions were expressed by cosn θ or cos θ (1+β cos2 θ). The former is appropriate for expressing over-cosine while the latter is appropriate for expressing under-cosine. The parameters n and β were determined so that the thickness distributions calculated reproduce the ones measured in the previous study. Once these parameters are determined, it is expected that the thickness distributions for different geometry of the sputtering apparatus can be predicted by calculation. Thickness distributions were measured for Pt, Cu, and C with the target-to-substrate distance and the diameter of the erosion ring variously changed. They approximately agreed with the calculated ones.
Sensitivity coefficient of a Bayard-Alpert gauge depends on the diameter of its envelope. In our measurement, some gauges with small envelope of diameters 35 mm and 38 mm showed higher sensitivity coefficients by 20%-40% than those with large envelope of diameters 54 mm and 70 mm for nitrogen in high vacuum of about 10−4 Pa. One gauge showed a small dependence of the coefficient on the diameter. In order to explain these results, computer simulations of the generated ion density distribution and the ion collection efficiency inside the grid were performed. Then the sensitivity coefficient was calculated using the ion density distribution and the collection efficiency. The calculated sensitivity coefficient was qualitatively in good agreement with that obtained from experiment.