Shizuka Yoshii

Surface Damage on Si Substrates Caused by Reactive Sputter Etching

Surface damage on silicon substrates caused by RSE has been investigated. Defects are classified into four categories in order of destruction, namely, precipitates surrounded by elastic strain field, surface roughness pattern, polycrystalline and amorphous silicon, and no defects, based on the results of TEM and RHEED observation. In particular, precipitates which reach a depth more than 500 A were found to cause OSF. The surface damage consists of contamination (C, F, O) layer, C and defect mixed layer, and defect layer in order from the top. The degree of these defects and contaminations expand with increasing power density and etching duration. RSE conditions, where no defects are formed, were determined, e.g., within 1 minute at 0.4 W cm-2.

TEM, AES and XPS Studies of Si Layer on Buried SiO2 Layer Formed by High-Dose Oxygen Ion-Implantation

Depth distributions of crystallographic and chemical properties in oxygen ion-implanted Si layers have been studied by TEM, AES and XPS. Oxygen ions (16O+) were implanted into (100)-Si wafers at 150 keV to a dose of 1.2×1018/cm2. The dose rate was about 15 µA/cm2. The implanted oxygen forms a buried SiO2 layer after annealing. The Si layer on this buried SiO2 layer is not completely amorphized by implantation, and changes after annealing to a single crystal Si layer at the surface region and a deeper polycrystalline Si layer. A twin layer is formed at the interface region between these two layers. The polycrystalline Si layer consists of a mixture of Si and SiO2.

Nb/Nb oxide/Pb Josephson Tunnel Junctions Fabricated Using CF4 Cleaning Process

Effects of an Ar and CF4 RF plasma mixture, in which the base electrode surface was cleaned prior to oxide barrier formation, on Nb/Nb oxide/Pb Josephson tunnel junction characteristics have been investigated. Good quality junctions with less leakage current (Vm=39.3 mV) and no knee at voltages just above the gap voltage have been obtained using the CF4 cleaning process (CFCP). It is speculated that the chemical etching reaction and a carbon layer generated on the cleaned Nb surface by CF4 plasma play an important role in achieving a cleaned based electrode surface free from damage and the formation of a good quality oxide tunnel barrier, respectively.

Preparation of Perpendicular Magnetic Co–Cr Films by Vacuum Evaporation

The vacuum evaporation technique has been applied to the preparation of perpendicular magnetic hcp Co-Cr films. It was necessary to suppress formation of the tetragonal phase in order to obtain films with high [0001] orientation perpendicular to the substrate.

Quantitative Analysis of Semiconductor Materials with Secondary Ion Mass Spectrometer

A simplified quantitative procedure for SIMS, based on the LTE (Local Thermal Equilibrium) model, was proposed and applied to Na concentration determination in Si and SiO2. The procedure validity was checked using In0.1Ga0.9As and PSG (phospho-silicate glass) films as standard samples. Na concentration determination was carried out using a Si wafer, whose CNa was measured by activation analysis. In the case of SiO2, borosilicate glasses were analyzed taking into account Na ionization yield. Then, Na distribution in SiO2 films was measured by SIMS and was compared with the total amount of Na in SiO2 films obtained by electrical measurement and Atomic Absorption Spectrophotometry (AAS).