Search

We prepared two types of trench‐test metal‐oxide semiconductor field‐effect transistor (MOSFET) structures on m‐ and a‐faces in 4H silicon carbide (4H‐SiC) and investigated the anisotropic stress distribution of small trenches with a depth of 1 μm using a scanning near‐field optical Raman microscope (SNOM) that we developed. The stress distributions of σ11 (a‐axis) under the bottom of the trench for m‐face were approximately 100 MPa larger than those for a‐face, and the stress distributions of σ33 (c‐axis) under the bottom of the trench for m‐face were almost the same as those for a‐face. The experimental result agrees well with that calculated by the finite element method (FEM). These results indicate that the anisotropic stress distributions of σ11 components around the apex of the trenches of 4H‐SiC trench‐test MOSFET occur in m‐ and a‐faces. Thus, it is possible that the differences in mobilities for m‐ and a‐faces might be caused by the anisotropic stresses. [ABSTRACT FROM AUTHOR]

Various secondary particles are emitted when the surface of solid matter is irradiated with ions. This phenomenon has been utilized in several methods to analyze target materials. In analytical techniques, the method used to detect secondary ions is called "secondary ion mass spectrometry (SIMS)." In contrast, "secondary ion mass spectrometry with optical emission spectrometry (SIMS‐OES)" detects photons emitted from sputtered, excited atoms. Both SIMS and OES can characterize a sample surface and perform local elemental analysis of the surface, depth profiling of elements, and detection of any atom. SIMS with high sensitivity has mainly been developed for the impurity analyses of semiconductors. However, no research has been reported on applications using SIMS‐OES or a combination of SIMS and SIMS‐OES. In this study, we prove that atomic emission can be observed via ion irradiation. In addition, we show that the composition analysis is possible using the SIMS‐OES method. Herein, impurity and composition analyses were enabled by utilizing atomic emission. Moreover, we proved that an assessment with high‐depth direction resolution is feasible by etching the circumference of a crater in advance. [ABSTRACT FROM AUTHOR]

We developed a reflection‐type tip‐enhanced Raman spectroscopy system with a high spatial resolution to be able to apply for many kinds of opaque samples and obtained Raman images and Raman spectra at the edges of graphene oxide (GO) films using this system. We found that the relative intensity of the D band to the G band (ID/IG) increased 0.6 to 1.5 at the edges of the GO plane and the C‐H stretching mode at approximately 2920 cm−1 was strongly observed at the edges. These results suggest that the graphite network structures are broken down at the edges of the GO plane, resulting in the high ID/IG ratio, and the dangling bonds are mainly terminated by C‐H, C‐O, O‐H, and/or COO‐ groups. [ABSTRACT FROM AUTHOR]

We obtained Raman images at the intersections single‐walled carbon nanotubes (SWCNTs) and Raman spectra using a reflection‐type tip‐enhanced Raman spectroscopy (TERS) system with a high spatial resolution, moving the x–y piezoelectric scanner in steps of 2 nm and with a highly sensitive TERS tip. Consequently, we observed a significant change in the Raman spectra at the intersection between semiconducting and metallic SWCNTs. We observed new G bands at the intersection of SWCNTs. Especially, one of the G bands, which is not observed in isolated metallic and semiconducting SWCNTs, was observed at approximately 1620 cm−1. The G band at approximately 1620 cm−1, which we observed only at the intersection, is considered to be shifted by compressive stresses. The observation of the G band at approximately 1620 cm−1 at the intersection between the semiconducting and metallic SWCNTs suggests that the intersection is at least under a compressive stress of approximately 5 GPa. [ABSTRACT FROM AUTHOR]

To examine precise depth profiles at the interface of SiO2/SiC, a high resolution that can detect slight discrepancies in the distribution is needed. In this study, an experimental method to achieve a high resolution of less than 1 nm was developed by using dual‐beam time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The analysis was preceded by the following three steps: (1) determination of the optimal analytical conditions of the analysis beam (Bi+) and sputtering beam (Cs+), (2) verification of the etching methods to thin the SiO2 layer, and (3) confirmation of the benefits of the low‐energy sputtering beam directed toward SiO2/SiC samples. By using the secondary ion intensity peak‐to‐valley ratio of BN− and BO− of a sample with delta‐doped boron multilayers, the appropriate Bi+/Cs+ condition for a high depth resolution was determined for each energy level of the sputtering beam. Upon verification of the etching methods to thin the SiO2 layer, slight discrepancies were found between samples that were obtained with different etching methods. The difference in the roughness values of the etched surfaces was proactively utilized for the performance confirmation of the low‐energy sputtering beam by means of precise observation of the profiles at the SiO2/SiC interface. The use of a Cs beam with a low energy between 0.25 and 0.5 keV enabled the detection of slight discrepancies in the roughness of less than 1 nm between samples. The aforementioned method has the potential to accurately detect discrepancies in the intrinsic distribution at the SiO2/SiC interface among samples. [ABSTRACT FROM AUTHOR]

With regard to Secondary Ion Mass Spectroscopy (SIMS) measurement of atmospheric gas elements, a problem occurs that the detected signal includes background components caused by residual gas along with contained components. Relating to this issue, an available method to quantify the contained components by separating the background ones had been established for Dynamic SIMS. Time‐of‐Flight SIMS with sputtering ion gun has also applied for depth profiling as well as Dynamic SIMS. However, few studies have attempted to investigate the secondary ion behavior of the atmospheric gas elements for depth profiling by Time‐of‐flight SIMS, especially for low concentration levels. In this study, experimental examinations of the secondary ions of the atmospheric gas elements, such as oxygen, hydrogen, and carbon in the silicon substrate, has been conducted in various analytical conditions of TOF‐SIMS depth profiling mode. Under the analytical conditions of our study, it has been proved that the background intensity of these elements was correlated to the sputtering rate. For the analysis of Floating Zone Silicon substrate, the oxygen intensity of the background component was proportional to the inverse number of the sputtering rate. Based on these facts, the total detected intensity of the atmospheric gas elements was able to be separated into the contained components and background ones by changing the sputtering rate during TOF‐SIMS measurement. An experimental result has shown that the contained oxygen concentration in the Czochralsk Silicon substrate estimated by the “TOF‐SIMS Raster Change Method” has successfully agreed with the result by the Dynamic SIMS. [ABSTRACT FROM AUTHOR]

A room temperature ionic liquid (IL) is a molten salt with melting point below 100 °C and has extremely low vapor pressure, allowing use in a high vacuum chamber. In scanning electron microscopy, the ILs have been found to behave as electrically conductive materials and successfully applied for conductive coating of insulating specimens. It is well known that dynamic SIMS analysis of an insulator causes charge buildup and requires a conductive film coating and electron gun, which can distort depth profiling of metal elements. In this study, 1-ethyl-3-methylimidazolium tetrafluoroborate was employed to test the applicability for charge neutralization in depth profiling of insulators. Mass spectra were successfully obtained from the IL droplets deposited onto a Si substrate without charge buildup. Deposition of the IL onto fiber pulp samples enabled us to acquire continuous secondary ions from the pulp samples. It implies the potential use of the IL as a conductive film for depth profiling of metal elements in insulators such as SiO2 and SiN. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]