Tetsuya Akasaka

In Situ Ellipsometric Observations of the Growth of Silicon Thin Films from Fluorinated Precursors, SiFnHm (n+m≤3)

The growth of silicon thin films fabricated from fluorinated precursors SiFnHm (m+n≤3), was investigated for the first time by in situ ellipsometric observation. Specific dependencies were recognized of the ellipsometric trajectories in the (Ψ, Δ) plane on chemical species used as the precursors. Under certain film preparation condition wherein the structures formed depend greatly on parameters such as the substrate temperature and the substrate material, the film structure was altered from amorphous to polycrystalline or epitaxial. The ordering of the structure was gradually improved with an increase in the thickness. Under the other condition, µ-crystalline films with columnar texture were fabricated independently of substrate temperature or material.

Boron Nitride Thin Films Grown on Graphitized 6H–SiC Substrates by Metalorganic Vapor Phase Epitaxy

The growth of thin boron nitride (BN) films on graphitized 6H–SiC substrates was investigated in an attempt to reduce the large lattice mismatch between 6H–SiC and BN, which would improve the three-dimensional ordering in BN thin films grown by metalorganic vapor phase epitaxy (MOVPE). BN thin films were grown by low-pressure (300 Torr) MOVPE using triethylboron and ammonia on graphitized 6H–SiC substrates with surfaces displaying (1×1) reconstruction as determined by low energy electron diffraction (LEED). The (1×1) surfaces were formed by annealing at 1500 °C in ultrahigh vacuum with a base pressure of 10-10 Torr. The LEED patterns showed that the surfaces were covered with single-crystal graphite several monolayers thick. X-ray diffraction revealed that the c-axis lattice constant of the BN was 6.72 A, which is close to the 6.66 A of bulk hexagonal BN. In contrast, BN films grown on non-graphitized 6H–SiC substrates by MOVPE under the same conditions were mostly amorphous. Use of a graphitized 6H–SiC substrate covered with graphite several monolayers thick improves the degree of three-dimensional ordering in BN thin films grown by MOVPE.

Measurement and Analysis of Vibrations on Surface of Phantom Induced by Piezoelectric Extracorporeal Shock Wave Lithotripter

We investigated the sound radiated from an object, induced by a piezoelectric extracorporeal shock wave lithotripter (ESWL). However, it was found that more direct measurement is necessary to analyze the sounds in piezoelectric ESWL. Therefore, we investigate the vibrations of a phantom, which are directly measured using laser Doppler velocimetry. The results show that the peak frequency in the power spectrum shifts as the number of shots increases from high frequency to low frequency. The previous results are confirmed by detecting the characteristic peaks obtained from the vibrations of bronze models. The bronze models are used to simulate the phantom during the breaking process. It is found that it is more difficult to make the models vibrate exactly at the focal point than above or below the focal region. These results will be applied to the monitoring of the breaking process and the choice of the optimum focal point on the calculus.

Si Epitaxy below 400°C from Fluorinated Precursors SiFnHm (n+m=< 3) under In Situ Observation with Ellipsometry

A systematic study of Si epitaxy below 400°C was performed under in situ observation with ellipsometry. From the fluorinated precursors SiFn Hm (m+n≤3), epitaxial films were fabricated on (100)-oriented Si substrates in the temperature range from 260 to 400°C. According to in situ ellipsometric observation, a highly ordered crystalline layer over 500 nm thick was grown on a partially fluctuating initial layer 8 nm thick. On the other hand, epitaxial growth was limited to within 50 nm thick on both (110)- and (111)-oriented substrates. Polycrystalline Si with columnar texture was finally grown with increasing thickness on these substrates. In situ ellipsometry is very useful for monitoring crystalline growth in chemical vapor deposition (CVD) techniques.