Koichi Miyata

Selected‐area deposition of diamond films

Selected‐area deposition of diamond film has been accomplished on Si substrates prepared by two different methods: reactive‐ion etching (RIE) and amorphous‐Si masking (ASM). In the RIE method, a Si substrate polished by a diamond paste was patterned with a photoresist mask, and the unprotected areas were etched by RIE, followed by a complete removal of the photoresist films. The diamond deposition was done by electron‐assisted chemical‐vapor deposition (CVD), and diamond films grew only in the areas once covered with the photoresist films and not etched by RIE. In the ASM method, a polished Si substrate was also photolithographically masked with photoresist, followed by a uniform deposition of a hydrogenated amorphous silicon (a‐Si:H) film. The photoresist film was then lifted off together with the overlay of deposited a‐Si:H, leaving the polished Si surface patterned with an a‐Si:H mask. In this case, the diamond deposition was done by microwave plasma CVD, and diamond films grew only in the areas not co...

Heteroepitaxial diamond growth on platinum(111) by the Shintani process

Abstract Diamond films with (111) facets were grown heteroepitaxially on Pt(111) using microwave plasma enhanced chemical vapor deposition. It was observed that many of the neighboring facets coalesced with each other. X-Ray diffraction analyses revealed that the (111) planes of diamond films were parallel to the substrate surface and azimuthally well oriented. The films were confirmed as diamond using Raman spectroscopy.

Fabrication of diamond thin-film thermistors for high-temperature applications

Abstract CVD diamond thin-film thermistors have been fabricated in various geometries and at different doping levels in an effort to achieve practical resistance- vs. -temperature characteristics. Typical activation energy values reported for polycrystalline films were combined with a targeted resistance range to plot an idealized relationship between resistance and temperature for CVD diamond thin films. The optimum device geometry and boron concentration were subsequently approximated from these ideal plots. Fabricated devices were electrically characterized in air at temperatures ranging from 25°C to over 500°C. Repeatability was demonstrated over two temperature cycles and stability was maintained at 500°C for 9 h. Effects of varying thermistor geometry and boron dopant concentration to achieve useful resistance-temperature relationships will be discussed.

Morphology of heavily B-doped diamond films

B-doped diamond films were synthesized by microwave plasma chemical vapor deposition using a mixture of methane (0.5% or 1.2%) and diborane (B 2 H 6 ) below 50 ppm on either Si substrates or undoped diamond films that had been synthesized using 0.5% or 1.2% methane. The surface morphologies of the synthesized films were observed by Secondary Electron Microscopy, and the infrared absorption and Raman spectra were measured. It was found that when diborane concentration was low, B-doped films preferred (111) facets. On the other hand, high diborane concentrations resulted in a deposition of needle-like material that was identified as graphite by x-ray diffraction.

Influence of surface treatment and dopant concentration on field emission characteristics of boron-doped diamond thin films

Field emission characteristics of B-doped diamond thin films terminated with oxygen and hydrogen were investigated. The diamond thin films were prepared by microwave plasma chemical vapor deposition. The dependence of emission characteristics on the surface treatment and on the B concentration was investigated. The turn-on voltage required to extract a current of 0.1 nA depended on these preparation parameters. The emitters with lower B concentration emitted electrons at a lower turn-on voltage, and the H-terminated emitters had a lower turn-on voltage than O-terminated emitters. The analysis of the slope and the intercept of Fowler–Nordheim plot revealed that the dependence of turn-on voltage on the surface treatment is due to the difference of emission barrier height, and that the dependence on B concentration is due not to the emission barrier height but to the surface morphology.

Heteroepitaxial diamond growth process on platinum (111)

Abstract Diamond films were grown on single crystal Pt (111) by microwave plasma chemical vapor deposition. It was found that coalescence between neighboring (111) faces of diamond developed significantly on the film surface. Scanning electron microscopy observations of the growth process showed that the 〈111〉-oriented diamond crystals became dominant on the film surface as a result of the overgrowth of randomly oriented crystals. In early stages of the growth, dissolution and recrystallization of diamond seemed to occur at the Pt surface. It was also observed that some small diamond crystals rotate and translate to take the epitaxial alignment. It was concluded that the dynamic movement and interaction (rotation, translation, dissolution, and recrystallization) of the small diamond crystals are important factors for the epitaxial growth on Pt.

Stability of Field Emission Current from Boron-Doped Diamond Thin Films Terminated with Hydrogen and Oxygen

The stability of field emission current from B-doped diamond thin films terminated with hydrogen and oxygen was measured to investigate the influence of the surface treatment and the dopant concentration on the emission stability. The diamond films were prepared by microwave plasma chemical vapor deposition. The O-termination was performed by acid cleaning in boiling chromic acid and boiling aqua regia. The H-termination was performed by exposing the above sample to hydrogen plasma. The dependence of the emission stability on the B2H6 gas (dopant gas) concentration and the surface treatment was investigated. As a result, little dependence on the B concentration was observed, but dependence on the surface treatment was significant. The field emission of the H-terminated diamond thin films was confirmed to be more stable than the O-terminated films.

Air oxidation of undoped and B-doped polycrystalline diamond films at high temperature

Air oxidation of undoped and B-doped polycrystalline diamond films was investigated at temperatures between 500 and 700 °C. Diamond (111) facets were etched for both undoped and B-doped films after 1 h at 700 °C. The etching rate of (111) facet due to oxidation was approximately 50% lower by B-doping of 1 × 10 19 cm −3 , presumably because of the decrease of sp 2 bands and lattice defects that were identified by Raman and photoluminescence spectroscopy. X-ray photoelectron and electron energy loss spectroscopy revealed that by the high temperature treatment, the diamond surface was initially converted into graphite and successively etched by oxygen.

Effect of Annealing in Air on Electrical Resistances of B-Doped Polycrystalline Diamond Films

The temperature dependent electrical behavior of as-deposited B-doped polycrystalline diamond films was investigated. Diamond films with various atomic B concentrations were deposited using a microwave plasma chemical vapor deposition technique. The atomic B concentrations were determined using secondary ion mass spectroscopy. Resistances were measured between 25 and 525° C in air. Similar electrical behavior was observed for films with atomic B concentrations less than 3×1017 cm-3 in which the resistance increased over 6 orders of magnitude after heating to 525° C. The variation in resistance between the heating and cooling cycles decreased with increasing B concentration. Little or no variation in the resistance was observed for films with atomic B concentrations higher than 4×1018 cm-3. The variable temperature dependent behavior can be explained by a surface conduction mechanism.

Surface Morphology And Defect Structures In Microwave CVD Diamond Films

Polycrystalline diamond films were deposited by the microwave-plasma chemical-vapor-deposition (CVD) on Si substrates using a mixture of methane and hydrogen for the source gas. In the morphology study of diamond films using a scanning electron microscope (SEM), it was found that upon increasing the methane concentration (hereafter denoted by c in units of vol%), the surface texture changed discontinuously from (111) to (100) at around c=0.4%, and gradually from (100) to microcrys-talline above c=1.2%. The diamond-Si interfaces and the defect struc-tures in the films were investigated by transmission electron micro-scopy (TEM). The film growth process was investigated by SEM, and it was found that the appearance of small grains and the formation of well-defined diamond faces took place repeatedly with time during the CVD synthesis. The film morphology of boron-doped diamond films on Si substrates and on non-doped diamond films were also presented.