Yuji Yoshizako

Chemical Etching of High-Tc Superconducting Y-Ba-Cu-O Films in Phosphoric Acid Solution

Chemical etching properties of a high-Tc Y-Ba-Cu-O film with a phosphoric acid (H3PO4) solution were closely investigated. With an appropriate stirring, the etching developed in proportion to the time. The etching rate R was dependent on the dilution γ of H3PO4: R (µm/s)2γ for γ≤0.5, and otherwise it decreased superlinearly with increasing γ. A 2 µm wide Y-Ba-Cu-O line was fabricated using this technique with a positive-type photoresist such as AZ-1350J. Nosign of degradation of the superconductivity was found in the 50 µm wide etched lines. Rather, they showed an extreme enhancement of the onset temperature after this procedure.

Grain Boundary Josephson Junctions Using Y-Ba-Cu-O Films Operative at 77 K

Grain boundary Josephson junctions were fabricated from superconducting oxide Y-Ba-Cu-O films. The junctions were made by a chemical wet etching technique with phosphoric acid (H3PO4) solution. Typical dimensions of the junctions were a width of 4 µm and a length of 20 µm. The junctions showed the so-called bridge-type Josephson effect. Shapiro steps were observed in the I-V curves at a temperature as high as 77 K.

Role of xenon additive in microwave plasma-assisted (H2+CH4) chemical vapor deposition of diamond thin film

We have examined in detail the role of the Xe additive in microwave plasma-assisted {CH4+H2} chemical vapor deposition (CVD) of diamond film. Effects of Xe addition were evident in the increased growth rate (about 50% increase for 1% Xe), without degradation of the crystallinity, and in the morphological change from the cubic to platelet grain structures. Based on the results of measuring the plasma emission spectra, Raman shift, and microwave plasma impedance, the favorable effects of Xe addition were attributed to its low dissociation and excitation energies (8.28 eV for Xe radicals), which are sufficient for the formation of CH3 but not CH2 radicals. Namely, the addition of Xe caused the CVD plasma to have higher density and lower temperature. This resulted in a large amount of atomic hydrogen and CH3 (precursors for diamond crystallization) and also a smaller amount of CH2, leading to the growth of a good-quality diamond film with a high deposition rate.

Multiple heteroepitaxy and superlattice formation of LnBaCuO/YBaCuO system

Multiple heteroepitaxy and superlattice formation of high-T/sub c/ superconducting films were demonstrated. LnBaCuO/YBaCuO structures (Ln=Er, Nd) were realized as a preliminary stage. Superlattice formation made it clear that the crystal structure of the system strongly depends on the substrate materials. A

High Tc Superconductivity of rf-sputtered Er-Ba-Cu-O Films

High Tc Er-Ba-Cu-O superconducting films were prepared by rf sputtering. The films revealed superconducting transition temperatures for onset and zero resistance of 95 K and 84 K, respectively. Although the X-ray diffraction measurement showed the film consists of an orthorhombic structure with the lattice constants a, b and c, respectively, of 3.883 A, 3.830 A and 11.70 A, most of the surface layer was found by electron spectroscopy for chemical analysis (ESCA) to be significantly Er-deficient.

Effect of Plasma Gases on Insulating Properties of Low-Temperature-Deposited SiOCH Films Prepared by Remote Plasma-Enhanced Chemical Vapor Deposition

Carbon-doped silicon oxide (SiOCH) films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS) at low temperatures (27–53 °C). The structural and insulating properties of the films deposited with Ar or N2 plasma were investigated. In the deposition with low plasma density and low substrate temperature, both plasmas produced films with high hydrocarbon (CHn) content. The films prepared using Ar plasma showed a low leakage current of 7×10-10 A/cm2 at 1 MV/cm due to the incorporation of CHn groups, while the films with high CHn content prepared using N2 plasma showed poor insulating properties. The deposition using N2 plasma formed films with a defective structure, resulting in a higher etch rate than that of the films deposited with Ar plasma. The deposition with the low-density plasma of inert Ar gas is suitable for the low-temperature deposition of SiOCH films with high resistivity.

Low-Temperature Deposition of Amorphous Carbon Films for Surface Passivation of Carbon-Doped Silicon Oxide

Low-temperature plasma-enhanced chemical vapor deposition of amorphous carbon (a-C:H) films was investigated for surface passivation of carbon-doped silicon oxide (SiOCH) films. The a-C:H films were deposited using CH4 and Ar gases at 40–65°C. FT-IR results showed that the deposited films are a-C:H which incorporates hydrocarbon groups. In current−voltage measurements, the a-C:H showed a low leakage current of ~10–10 A/cm2 in air, indicating that the a-C:H films have a potential as a surface passivation layer to prevent moisture absorption in air. The insulating properties of room-temperature deposited SiOCH covered by the a-C:H strongly depended on radio frequency (RF) power in the SiOCH deposition. In the SiOCH film deposited at high RF power of 200 W, the resistivity in air was improved by the a-C:H passivation.

Thermally Stable Carbon-Doped Silicon Oxide Films Deposited at Room Temperature

High CHn content → OH reduction Low leakage current ~10–10 A/cm2 @ 1 MV/cm We have succeeded in growth of the silicon oxide with high resistivity by PECVD using TEOS at 27 ̊C. Carbon incorporation by deposition at low RF power improved their insulating properties. CHn groups contained in the SiOCH films were thermally stable up to 400 ̊C. Necessary for heat-sensitive devices (device integration on flexible plastics, TFT, etc...)

Design of Automatic Matching System for Very High Frequency Plasma-Enhanced Processes

Since it can change electron energy distribution functions, very high frequency (VHF) plasma has gained significant attention as a promising new class of plasma. We demonstrate an automatic matching system for VHF plasma, that works in very wide ranges. A matching system was prepared using conventional variable capacitors. Reflection coefficient at the input of the matching circuits was measured with a directional coupler. A new calculation method for automatic matching based on numerical models for the circuit was developed, and the performance of the automatic matching system was evaluated using a load emulator. These results revealed that the system has an automatic matching capability for the entire range of the covering load area.

Germanium thin film growth onto high T/sub c/ superconducting films

Germanium thin film growth on high-T/sub c/ superconducting films has been studied. The crystallized Ge films were prepared on YBaCuO films at a substrate temperature above 200 degrees C. An ECSA (electron spectroscopy for chemical analysis) study revealed that the Ge films were formed without intense reaction between Fe and YBaCuO. >