Shuji Kiyohara

Plasma etching of CVD diamond films using an ECR-type oxygen source

The etching characteristics of CVD (chemical vapour deposition) diamond films processed with an ECR (electron cyclotron resonance) oxygen plasma are investigated. The etching rate increases linearly with increasing microwave power in the range from 100 to 300 W. For any value of microwave power, the etching rate first increases with increasing gas flow rate, reaches a maximum rate at a gas flow rate of 3 sccm (standard cc min-1), and then decreases gradually with further increase in the gas flow rate. The etching rate increases linearly with increasing negative bias voltage in the range from 0 to -600 V. The etching rate for 100 and 300 W of microwave power and a negative bias of -600 V is 17 and three times greater, respectively, than that for 0 V bias. The surface roughness increases with increasing microwave power in the range from 0 to 300 W. The surface roughness before etching is eight times greater than that obtained after plasma etching with 300 W of microwave power. The Raman spectrum of a CVD diamond film after oxygen plasma etching for 1 h shows not only a diamond (sp3 bonding) peak at 1333 cm-1, but also a broad non-diamond (sp2 bonding) peak around 1500 cm-1. However, as the etching time increases, the broad non-diamond peak around 1500 cm-1 disappears.

Microfabrication of diamond films by localized electron beam chemical vapour deposition

We have investigated the microfabrication of diamond films on silicon substrates using the localized electron beam (EB) chemical vapour deposition (CVD) method with a hydrogen (H2) and methane (CH4) mixed gas source. Micro-Raman spectra at 1, 3 and 5% CH4 concentrations for the accelerating voltage of 10 kV have indicated the presence of a diamond (sp3 bonding) peak at 1333 cm−1, a graphite (sp2 bonding) peak at 1580 cm−1 and a diamond peak, and an amorphous carbon peak at 1360 cm−1 and graphite peak, respectively; those at 7 and 10% concentrations have indicated broad amorphous carbon peaks around 1500 and 1300 cm−1. We have found that the films consist of a mixture of sp3 and sp2 bonded structures. The film quality (sp3) content decreases with increasing CH4 concentration. Consequently, the localized EB CVD diamond films have been fabricated under the following deposition conditions: an accelerating voltage of 10 kV and a CH4 concentration of 1%. The EB was scanned in areas of 2 × 10 µm2 rectangle and 1 × 1 µm2 square on a silicon substrate. The two-dimensional cross-sectional profiles (X–Z axis) of the resulting micro-rectangular diamond patterns were very similar to those of the resulting micro-square diamond patterns. The deposited thickness of the resulting micro-rectangular and square diamond patterns increased linearly with increasing EB irradiation time up to a limit of 10 h. The deposition rate was approximately 0.1 µm h−1 in both cases. The full width at half maximum (FWHM) of the cross-sectional profiles, having the triangular form of the resulting micro-rectangular and square diamond patterns, first increased with increasing EB irradiation time and reached a maximum width at an EB irradiation time of 4 and 6 h, respectively and then decreased gradually with a further increase of the EB irradiation time. The deposited thickness and FWHM of the resulting micro-rectangular and square diamond patterns for a 10 h EB irradiation time were 1.1, 0.98 µm and 3.6, 3.3 µm, respectively.

Micropatterning of Chemical-Vapor-Deposited Diamond Films in Electron Beam Lithography

The micropatterning of chemical-vapor-deposited (CVD) diamond films using electron beam lithography technology has been investigated. The use of metal naphthenates as mask resist materials is proposed, because of their resistance to oxygen plasma in order to form an oxide film on the surface. The exposure characteristics of metal naphthenates, as well as the etching characteristics of CVD diamond and metal naphthenate films processed with electron cyclotron resonance (ECR) oxygen plasma were investigated. Furthermore, the crystal structure of CVD diamond micropatterns fabricated by this process was evaluated using Raman spectroscopy. We found that the metal naphthenates exhibited negative exposure characteristics upon electron beam irradiation. The sensitivity and the gamma value were 2.4×10-3 C/cm2 and 1.6, respectively. A maximum etching selectivity of 10 was obtained under etching conditions of a microwave power of 300 W and oxygen gas flow rate of 3 sccm. Line micropatterns 1 µm and 0.5 µm in width with a height of approximately 1 µm were fabricated with an etching time of 1 h. The crystal structure of the CVD diamond films after etching and the line micropatterns fabricated by this process remained constant; Raman spectra indicated only the presence of a diamond (sp3 bonding) peak at 1333 cm-1.

Ion beam smoothing of CVD diamond thin films by etchback method

Abstract Smoothing of chemical vapor deposited (CVD) diamond thin films with argon ion beams, and oxygen ion beams, and with both ion beams by the etchback method was investigated. Diamond thin films synthesized by the hot filament CVD method were used as samples. The samples were etched using an ion beam etching apparatus with a Kaufman-type ion source. Consequently, the surface roughness is extremely improved from 0.38 μm Ra (as-grown) to 0.18 μm Ra at the etched depth of 7.2 μm for 1000 eV argon ions at an ion incident angle of 0°. For 1000 eV oxygen ions at an ion incident angle of 80°, the surface roughness is also extremely improved from 0.38 μm Ra (as-grown) to 0.18 μm Ra at the etched depth of 5.5 μm. With the use of the etchback method, the surface roughness decreases rapidly with increasing etched depth and is reduced from 0.38 μm Ra (as-grown) to 0.06 μm Ra at the etched depth of 4.0 μm.

Reactive ion beam machining of diamond using an ECR-type oxygen source

Reactive ion beam machining of diamond chips with oxygen ions using a Kaufman-type apparatus has been investigated. This paper reports machining characteristics of single crystal diamond chips processed with an oxygen ion beam using an electron cyclotron resonance (ECR)-type apparatus. The specific machining rate increases with increase in ion energy, reaches a maximum rate at an ion energy of 300 eV, then decreases gradually with further increase in ion energy. The specific machining rate obtained with 1000 eV oxygen ions increases with increase in ion incident angle and reaches a maximum rate at an ion incident angle of , then decreases with increase in ion incident angle. The specific machining rate obtained with 500 eV oxygen ions decreases with increase in ion incident angle. The specific machining rate for 500 eV oxygen ions at an ion incident angle of is 12 times greater than that for argon ions. Futhermore, the surface roughness of diamond chips before and after oxygen ion beam machining was evaluated using an atomic force microscope (AFM) and a scanning electron microscope (SEM). It was found that the surface roughness increases with increase in ion incident angle, and decreases with increase in ion energy.

Organic Light-Emitting Microdevices Fabricated by Nanoimprinting Technology Using Diamond Molds

The fabrication of organic light-emitting microdevices (micro-OLEDs) by nanoimprint lithography (NIL) using diamond molds fabricated by chemical vapor deposition (CVD) was investigated. The diamond molds used in the NIL process were fabricated with the Bi4Ti3O12 octylate (oxide) mask used in electron beam lithography technology. The diamond molds of convex dots of 30 µm square with 60 µm pitch were fabricated. The optimum imprint conditions were found to be as follows: imprinting pressure, press duration, substrate temperature and removal temperature of 0.8 MPa, 15 min, 180°C and 70°C, respectively. The device structure of 30-µm-square-dot OLEDs fabricated by imprinting is indium tin oxide (ITO) [anode]/poly(9-vinylcarbazole) (PVK) and coumarin-6 (C6) (0.1 µm thick) [hole transport and emitting layers]/8-hydroxyquinoline-aluminum (Alq) (50 nm thick) [electron transport layer]/aluminum (Al) (0.1 µm thick) [cathode]. The fabrication and operation of micro-OLEDs with 30 µm square dots in diamond-mold NIL were successfully demonstrated.

ION BEAM ASSISTED CHEMICAL ETCHING OF SINGLE CRYSTAL DIAMOND CHIPS

Abstract Ion beam assisted chemical etching (IBACE) of diamond chips with an argon ion beam and a reactive oxygen gas flux was investigated. The specific etching rate of single crystal diamond chips with a (100) oriented face increases with increasing ion energy ranging from 300 to 1000 eV. The specific etching rates of the chip processed with 500 eV and 1000 eV Ar + ions increase with increasing oxygen partial pressure, and reach a maximum rate at an oxygen partial pressure of approximately 0.02 and 0.05 Pa, respectively, and then decrease gradually with increasing oxygen partial pressure. The specific etching rate of the chip for IBACE which includes both physical and chemical reactions is approximately two times greater than that for ion beam etching (IBE) which causes only a physical sputtering reaction. Futhermore, the surface roughness of diamond chips before and after IBACE was evaluated using an atomic force microscope (AFM). Consequently, the surface roughness of the chip for IBACE increases with increasing substrate temperature, whereas that for IBE (only Ar + ions) is almost constant as a function of the substrate temperature ranging from room temperature to 400°C.

Oxygen ion beam assisted etching of single crystal diamond chips using reactive oxygen gas

The etching characteristics of single crystal diamond chips processed using an oxygen ion beam with reactive oxygen gas flux were investigated. The specific etching rate increased linearly with increasing ion energy in the range of 250 to 1000 eV. The specific etching rates processed in a 1000-eV oxygen ion beam with oxygen gas was approximately twice that processed only in a 1000-eV oxygen ion beam. The angular dependences of only a 500-eV oxygen ion beam (no assist), and a 500-eV argon ion beam with oxygen gas were quite different from that of the other conditions. The specific etching rates were almost constant as a function of ion incident angle in the range of 0 to 50°. Those for the other conditions first increased with increasing ion incident angle, and reached a maximum rate at an ion incident angle of 40° or 50°, and then decreased gradually with further increase in ion incident angle. The specific etching rates using an argon ion beam with oxygen gas first increased with increasing gas partial pressure and then reached a saturation level at a gas partial pressure above 0.015 Pa, whereas those for the other conditions increased linearly with increasing gas partial pressure in the range of 0 to 0.06 Pa. The specific etching rates using an oxygen ion beam increased linearly with increasing substrate temperature in the range of 100 to 500 °C. The specific surface roughness was almost constant as a function of the substrate temperature, in the range of 100 to 500 °C. The specific surface roughness after assisted etching using oxygen or hydrogen gases was approximately half that processed in only oxygen or argon ion beams (no assist).

Ultra-precision processing of diamond with oxygen ion beams

In order to apply the reactive ion beam etching with oxygen ions to ultra-precision processing of diamond tools, the dependences of the etching rate of the (100) face of single crystal diamond on the ion energy, the ion incidence angle, the ion current density and the work-piece temperature were investigated. The etching rate for “reactive” oxygen ion beam etching which includes both physical sputtering and chemical etching is about ten times larger than that for ion beam etching using “inert” argon ions which causes only physical sputtering. Moreover, the surface roughness of the diamond chip after oxygen ion beam etching which was measured using Atomic Force Microscope is about six times smaller than that before etching.

Fabrication of nitrogen-containing diamond-like carbon film by filtered arc deposition as conductive hard-coating film

Diamond-like carbon (DLC) films, which are amorphous carbon films, have been used as hard-coating films for protecting the surface of mechanical parts. Nitrogen-containing DLC (N-DLC) films are expected as conductive hard-coating materials. N-DLC films are expected in applications such as protective films for contact pins, which are used in the electrical check process of integrated circuit chips. In this study, N-DLC films are prepared using the T-shaped filtered arc deposition (T-FAD) method, and film properties are investigated. Film hardness and film density decreased when the N content increased in the films because the number of graphite structures in the DLC film increased as the N content increased. These trends are similar to the results of a previous study. The electrical resistivity of N-DLC films changed from 0.26 to 8.8 Ω cm with a change in the nanoindentation hardness from 17 to 27 GPa. The N-DLC films fabricated by the T-FAD method showed high mechanical hardness and low electrical resistivity.