Masayuki Katagiri

Lightly phosphorus-doped homoepitaxial diamond films grown by chemical vapor deposition

Lightly phosphorus-doped {111} homoepitaxial diamond films have been grown by microwave plasma-assisted chemical vapor deposition under optimized growth conditions. The Phosphorus concentration in the film can be controlled at a low doping level of the order of 1016cm−3. N-type conductivity of the films with phosphorus concentrations above 1×1016cm−3 is reproducibly confirmed by Hall-effect measurements in the temperature range from 300to873K. The highest value of the Hall mobility at room temperature is 660cm2∕Vs obtained for a film with a phosphorus concentration of 7×1016cm−3.

Low-Temperature Graphene Growth Originating at Crystalline Facets of Catalytic Metal

We explored the characteristic behavior of low-temperature graphene growth on catalytic metal films. The results suggested that graphene growth originates from the crystalline facets with specific angles with respect to the crystalline orientation of the catalytic metals at low temperatures, which is different from the conventional growth models. The G/D ratio of the Raman spectrum of the graphene film was affected by both the number of specific facets and the width of the terrace. Because of this behavior, it is important to prepare the surface conditions with a smaller number of facets and a wider terrace for high-quality graphene growth at low temperatures.

Fabrication and Characterization of Planarized Carbon Nanotube Via Interconnects

We fabricate planarized carbon nanotube (CNT) via interconnects using chemical mechanical polishing (CMP). The selective growth of CNT bundles in via holes and the filling of spin-on-glass into the space among the CNTs are performed, followed by a CMP process. The via resistance is reduced by post-CMP treatment and post-annealing due to the improvement in the top contact formation. The measured CNT via resistance is higher than the CNT bundle resistance estimated from the measured resistance of an individual CNT. This indicates that contact resistance is higher than the CNT resistance in the CNT via interconnect.

Electrical properties of multilayer graphene interconnects prepared by chemical vapor deposition

We fabricate multilayer graphene interconnects with 100-nm-class line widths. Multilayer graphene is grown on a Ni catalyst layer using remote plasma-enhanced chemical vapor deposition (CVD) at a low temperature of 600°C and transferred onto a SiO2/Si substrate after exfoliation from the Ni layer. The sheet resistance of the CVD graphene interconnects is as low as 500 Ω sq. The temperature dependence of resistance reveals that the CVD graphene exhibits half-metallic transport properties.

Selective carbon nanotube growth in via structure using novel arrangement of catalytic metal

We fabricated a carbon nanotube (CNT) via structure on a 300-mm wafer. We investigated the CNT chemical-mechanical polishing (CNT-CMP) behavior in an actual via pattern structure and clarified the technical issues of the CNT-CMP process. We developed a fabrication process of CNT via structures using selective CNT growth, which has a high potential for applying CNTs to high aspect ratio via structures.

Electrical Resistivity Measurements of Layer Number Determined Multilayer Graphene Wiring for Future Large Scale Integrated Circuit Interconnects

To investigate the feasibility of nanocarbon interconnects for future LSIs, the electrical resistance of exfoliated multilayer graphene (MLG) wirings has been studied with accurate measurements of the number of layers. We employed transmission electron microscopy (TEM) as an exact number determination method, atomic force microscopy (AFM) as a simple method, and an extended optical contrast method as an easy distinction method, which we proposed for determining the number of layers. The sheet resistance of MLG wirings, including TEM determined 3-, 54-, and 341-layer MLGs, has been measured using the four-probe method and the layer number dependence of sheet resistance was discussed on the basis of a ladder circuit model simulation. It is shown that the dependence agrees well with the simulations, suggesting parallel conduction in MLG wirings, even if the probe electrodes are deposited just on the top layer of MLG.

A Study on Electrical Resistance of Carbon Nanotubes and Their Metal Contacts Using Simplified Test Structure

In order to realize a high conductive carbon nanotube (CNT) via structure, an accurate evaluation of electrical properties of CNTs and their metal contacts is essential. We succeeded in evaluating the resistance of CNTs and their contacts individually by using our proposed test method and test structure. The contact resistance of CNTs to metals was dependent on the types of contacting metals, which can be explained by the Gibbs energy of oxide formation and differences in work functions of each metal with CNTs and adhesion property. Ti and Pd had common chemical and mechanical characteristics and showed the lowest contact resistance with CNTs among contact metals we used.

Imaging and nanoprobing of graphene layers on Ni damascene interconnects by conductive atomic force microscopy

Graphene is a promising material to replace copper interconnect metallization under 10 nm in width. We report a method for evaluating graphene interconnect wiring structure by conductive atomic force microscopy (C-AFM), which enables direct measurement of the 2D-resistance distribution and coverage evaluation of multilayer graphene (MLG) grown on Ni interconnects using a 300 mm damascene process. It is demonstrated that the coverage of MLG upon Ni can be estimated more precisely by C-AFM than that by back-scattered electron scanning electron microscopy (BSE-SEM) observation. We also measured the resistance of the MLG/Ni conductor and confirmed conduction paths of the MLG/Ni interconnect. Process dependence of MLG shows that lower local resistance corresponds to higher G band and D band intensity ratio (G/D ratio) in Raman spectra. C-AFM is demonstrated to be a potential technique for local conductance evaluation of next generation interconnects.

Shallow P donors in 3C-, 4H-, and 6H-SiC

EPR spectra originating from phosphorus shallow donors occupying silicon sites in 3C-, 4H-, and 6H-SiC are identified by using CVD grown films in which the interference from the signals from the nitrogen shallow donors is practically absent. Phosphorus donors occupying both silicon and carbon sites are observed in high-energy phosphorus ion implanted semi-insulating 6H-SiC which was also free from the interference from the signals from the nitrogen shallow donors.

Imaging and nanoprobing of graphene layers for interconnects by conductive atomic force microscopy

Graphene is a promising material to replace Cu-interconnect metallization under a width of 10 nm. We report a method for evaluating the graphene interconnect wiring structure by conductive atomic force microscopy (C-AFM), which enables the direct measurement of the two-dimensional (2D) resistance distribution and the coverage evaluation of multilayer graphene (MLG) grown on Ni interconnects using a 300 mm damascene process. The resistivity of exfoliated two-layer graphene was measured and a reasonable value of 30 µΩcm was obtained. We also measured the resistance of the MLG/Ni stack of 350 nm L/S patterns and confirmed the conduction paths of the MLG/Ni stack. It is demonstrated that the coverage of MLG on Ni interconnects can be estimated more precisely by C-AFM than by backscattered electron scanning electron microscopy (BSE-SEM) observation. C-AFM is demonstrated to be a potential technique for the local conductance evaluation of next-generation interconnects.