Takeshi Tachibana

Large area deposition of 〈100〉-textured diamond films by a 60-kW microwave plasma CVD reactor

Abstract Diamond films were deposited on silicon wafers of 25–152 mm in diameter by a 60-kW 915-MHz plasma CVD system with a input power of 15–60 kW at a gas pressure of 11.3–17.7 kPa using H 2 CH 4 or H 2 CH 4 CO 2 gas mixtures. Growth orientation of the diamond films and α parameters for the different growth conditions have been investigated in order to control the morphology of the diamond films of 152 mm in diameter. It was clearly seen that the α parameters for the 60-kW system were greater than those for conventional microwave plasma CVD systems in the substrate temperature–CH 4 concentration plane. This means that the contour of the α parameter shifts to the higher substrate temperature and the lower CH 4 concentration, as compared with the results of the conventional CVD systems. It was also found that the parameter range of diamond growth by the 60-kW reactor is broader than that of the conventional CVD systems. Based on the present study, 〈100〉-textured diamond films were successfully grown almost uniformly on the entire surface of a 152-mmφ Si substrate by choosing appropriate process conditions.

Diamond films grown by a 60-kW microwave plasma chemical vapor deposition system

Abstract In order to use chemical vapor deposition (CVD) diamond films for electronic devices, it is necessary to establish technologies for producing diamond wafers with controlled quality. Most of existing diamond CVD systems are, however, designed primarily for laboratory use. To cross the technological gap between the commercial production and the laboratory experiments, the current CVD technologies of diamond must be scaled up and upgraded. Development of large-scale diamond deposition processes was undertaken by using a microwave plasma CVD system, equipped with a 915-MHz, 60-kW generator for generating a large-size plasma. Polycrystalline diamond films were deposited from a hydrogen/methane gas mixture with typical gas pressures and substrate temperatures of 80–120 torr and 800–1050°C, respectively. It was found that depending on the growth conditions, the deposited films have various surface morphologies. Some of the samples have well-defined {111} and {100} facets of up to tens of micrometers in size. The Raman spectra had an intense main peak due to diamond at 1333 cm−1 without a trace of non-diamond carbon. The film quality in terms of Raman spectra was relatively uniform across the samples of 100 mm in diameter. Both 〈111〉 and 〈001〉 textured diamond films were obtained by selected growth conditions.

Correlation between Magnetic Property and Cation Distribution in Z-type Hexagonal Barium-Ferrite (Ba 3 Co 2- x Fe 24+ x O 41 ) by Neutron Diffraction

Abstract : Z-type hexagonal ferrite samples in which cobalt is partially substituted with iron, Ba3Co(2-x)Fe(24+x)O41 (x=0, 0.2, 0.4, 0.6), were prepared by the ceramic process under a sintering oxygen partial pressure, P(O2)=21.3 or 101.3 kPa, at 1573K. The influence of the substitution ratio and oxygen partial pressure on the complex permeability was investigated by examining the cobalt distribution over various cation sites in the Z-type structure with the neutron powder diffraction analysis performed at 294 K (neutron wave length was 1.006 Angstrom). The neutron diffraction pattern was studied with the Rietveld method. A significant difference in the preferential occupation of cobalt on various kind of cation sites was observed between the samples obtained under P(O2)=21.3 and 101.3 kPa. Almost all cobalt atoms are on the 12k octahedral site at the boundary between S- and R-blocks in the sample of x=0, P(O2) 21.3 kPa. On the other hand, in the sample of x=0, P(O2)=101.3 kPa, cobalt atoms are as well on other sites, the 12k octahedral site at the boundary between S- and T-blocks, the 4e tetrahedral site in S-block, the 2a octahedral site in T-block and the 2d five fold (trigonal bypiramid) site in T-block.