Nobuyuki Kawakami

Preparation of Highly Porous Silica Aerogel Thin Film by Supercritical Drying

Thin film preparation of porous silica aerogel is investigated as super-low dielectric constant material for ultra-large scale integrated circuits. By using Tetramethylorthosilicate based solution mixed with Dimethyl sulphoxide, which effectively suppresses solvent evaporation, thin film is successfully formed on a wafer without cracking. After an optimization of the aging process in water vapor, the film is dried in supercritical fluids of carbon dioxide, which is free from capillary force, and a high porosity aerogel with dielectric constant as low as 1.1 is obtained. Porosity and the dielectric constant of aerogels can be controlled over a wide range by changing the time of aging.

R&D of diamond films in the Frontier Carbon Technology Project and related topics

R&D activities on diamond chemical vapor deposition (CVD) and field emission in the Frontier Carbon Technology Project are presented. The topics are (1) morphology control of diamond films grown by a 60-kW, 915-MHz microwave plasma CVD reactor, (2) growth technology of large single crystal diamond with a low density of defects, (3) heteroepitaxial growth technology of diamond films on Pt, (4) fabrication of sharp emitter tips on single crystal diamond, (5) field emission study from diamond particles, and (6) intense field emission from ion implanted homoepitaxial diamond layer. Research results of field emission obtained by Kyoto University and North Carolina State University are also described.

Fibrous structures on diamond and carbon surfaces formed by hydrogen plasma under direct current bias and field electron-emission properties

Polycrystalline diamond films, single crystal bulk diamonds, and diamond powder were treated in microwave plasma of hydrogen at 1.6 torr under a negative direct-current bias of -150 to -300 V without metal catalyst. It was found that fibrous structures, uniformly elongated along the direction normal to the specimen surface, were formed on the diamond surfaces. Similar experiments for glasslike carbon resulted in conical structures with frizzy fibers at the tops. Transmission electron microscopy measurements indicated that the fibers formed on diamond consisted of randomly oriented diamond nanocrystals with diameters of less than 10 nm, while the conical structures formed on glasslike carbon consisted of graphite nanocrystals. Field emission measurements of the fibrous specimens exhibited better emission efficiency than untreated ones. The field emission electron microscopy of the fibrous glasslike carbon showed a presence of discrete electron emission sites at a density of approximately 10,000 sites/cm 2 .

Diamond Sensors Durable for Continuously Monitoring Intense Vacuum Ultraviolet Radiation

Photoconducting sensors are fabricated using radiation-hard diamond films to measure the intensity of vacuum ultraviolet (VUV) radiation. They are composed of a pair of interdigitated Pt electrodes on highly oriented diamond surfaces. The sensors are examined as monitors of the intensity of VUV radiation (λ=172 nm) from xenon excimer lamps with an output power of greater than 10 mW/cm2. It was demonstrated that the diamond sensors have practical durability: the output signals from the sensors are reproducible and stable under a continuous irradiation from the xenon lamps for more than 500 h.

Formation of fibrous structures on diamond by hydrogen plasma treatment under DC bias

Abstract Diamond films and powders were treated in microwave plasma of hydrogen at 1.6 torr under a negative DC bias of 200 V for 3–6 h. As a result, a fibrous structure was formed on the diamond surface along the direction normal to the surface, while diamond was simultaneously etched at a rate of approximately 1 μm/h. For a 3-h processing, the fiber diameter near the top end was ≤50 nm and the fiber lengths were 2–3 μm. Transmission electron microscopy (TEM) indicated that the fibers consisted of randomly oriented nanocrystals with diameters of

60.4: Single Layer Al‐Ni Interconnections for TFT‐LCDs using Direct Contacts with ITO and a‐Si

It was demonstrated for the first time that the use of Al-Ni alloy films and a-Si surface nitridation for the direct contacts of interconnection lines with both ITO and a-Si were feasible for the TFT technology. The mechanism how the direct contact, described in the present paper, works was studied using various analysis technique.

Focused ion beam/optical‐merged lithographic technique using ladder silicone spin‐on glass

Focused ion beam (FIB) optical‐merged lithography has been developed to improve the throughput in delineating the gate pattern of the metal–oxide–semiconductor field‐effect transistor. In this process, only the critical part of the pattern is delineated with FIB and merged with optically printed noncritical parts. Ladder silicone spin‐on glass (LS‐SOG) has been used as the negative resist for the 200 keV Si2+‐focused ion beam. The 100 nm polysilicon gate was successfully fabricated using the single‐level resist process. The film characteristics of the LS‐SOG were also investigated.

Sub‐100 nm focused ion beam lithography using ladder silicone spin‐on glass

Focused ion beam lithography using ladder silicone spin‐on glass (LS‐SOG) as a negative‐tone resist was investigated. The use of 200 keV Be2+ ion and tetramethylammoniumhydroxide developer resulted an in 80‐nm‐width line pattern with a vertical profile. The pattern collapse during the development was avoided by the use of fluorocarbon‐based solvent. The development mechanism of LS‐SOG was investigated by using nuclear magnetic resonance and gel permeation chromatography analysis.

Focused Ion Beam Lithography Using Ladder Silicone Spin-on Glass as a Positive Resist

Focused ion beam lithography using ladder silicone spin-on glass as a positive resist has been demonstrated. This lithographic technique utilizes the structural change of ladder silicone spin-on glass (LS-SOG) to a silicon-dioxide-like structure. A 60-nm-width space pattern and a 90-nm-diameter hole pattern have been fabricated using ion doses of 6.2 x 10 13 /cm 2 and 1.2 x 10 14 /cm 2 , respectively. The development mechanism and the sensitizing effect of post-exposure baking have been investigated using fourier transform infrared spectroscopy (FTIR).

Current Path Analysis of the Direct Contact Between ITO and Al–Ni Alloy Films

Al-Ni alloys for single-layer interconnections to be used for amorphous silicon thin-film transistors (a-Si TFTs) in liquid-crystal displays have been developed. The developed interconnections make possible a direct electrical contact with an indium-tin oxide (ITO) film without barrier metals, such as Mo and Cr, which are conventionally used for the electrical contacts. In the present paper, we investigated the major current path at the contact between ITO film and the Al-Ni alloy layer using nanoprobes. It was found that the Al 3 Ni precipitations between the ITO film and the Al-Ni alloy layer played an important role of electrically conducting contacts. This led us to a conclusion that it is important to increase local current paths via Al 3 Ni precipitations to achieve a low resistivity at the contact between the ITO film and the Al-Ni alloy layer, which was found to be strongly influenced by the photoresist stripping process successively used for the formation of SiN contact holes in the production of α-Si TFTs.