Junichiro Sameshima

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.

The behavior and mechanism of background signals during depth profiling of atmospheric elements using dual‐beam time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) have been experimentally investigated for silicon wafers. The background signals of atmospheric elements were found to be inversely proportional to the sputtering rate. Most of the background signals are largely attributable to the accumulation of components through adsorption and ion bombardment in the pre‐equilibrium state. On the other hand, the contribution of real‐time adsorption during the instant after the last sputtering in the equilibrium state is negligible under the present experimental conditions. H ₂ O is dominant in the background formation process of hydrogen and oxygen, which is supported by the higher adsorption coefficients. The background levels of carbon and nitrogen are lower than those of hydrogen and oxygen. Furthermore, the background signal of carbon with respect to the sputtering rate shows a different trend than the other elements. This could be attributed to accumulation in the pre‐equilibrium state. These results indicate that the background levels can be lowered close to those of dynamic‐SIMS by using an extremely high sputtering rate in dual‐beam TOF‐SIMS.

Degradation analysis was conducted to p‐i‐n type OLED devices. PL, LDI‐MS, and GCIB‐TOF‐SIMS revealed the degraded layer was EML and molecular formula of the degradation product. GCIB‐TOF‐SIMS clarified the change of n‐dopant with the degradation.

To examine precise depth profiles at the interface of SiO ₂ /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 SiO ₂ layer, and (3) confirmation of the benefits of the low‐energy sputtering beam directed toward SiO ₂ /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 SiO ₂ 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 SiO ₂ /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 SiO ₂ /SiC interface among samples.

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.