Tatsuro Saito

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.

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.

Graphene interconenets selectively grown on catalytic metal damascene structure and its growth mechanism on Ni catalyst

The present work investigated the possibility of the formation of graphene interconnects and studied the behavior of graphene growth in wiring structure. Graphene nucleated on the facet of catalytic metal, and multi layer graphene grew along the terrace surface of catalytic metal. Selective graphene growth served the stacked interconnects structure of graphene / Ni catalytic metal.

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.

Electrical properties of 30 nm width bi-layer interconnects of multi layer graphene and Ni

We have fabricated the stacked interconnects of multi-layer graphene (MLG) and nickel (Ni) at the line width from 30 to 1000 nm in 300 mm wafer. MLG, which was grown by CVD process, was selectively deposited on Ni damascene interconnects by the catalytic reaction of Ni. MLG grown from C2H2 was composed of approximately 20 layers of graphene sheets and covered the overall surface of Ni interconnects. Two processes, one with the gas mixture of C2H2/Ar and the other with only Ar gas, were compared and short failure was observed at the comb structure specifically by the usage of C2H2 gas. Along with the failure analysis, this short failure was suggested to be caused by the unintended growth of carbon material from the Ni nanoparticle on the interconnects. An addition of ashing process improved the electrical performance with the minimum damage to MLG. At last, crystalline analysis of MLG suggests a necessity of a continuous process optimization of CVD process for positive influence on resistivity of the interconnects.

Resistance reduction of CNTs on 300-mm wafer by using two precursors with different growth methods

The process conditions for improving the electrical properties of carbon nanotubes (CNTs) were investigated by using a blanket-structure method for quantifying CNT resistance independently. The growth mechanism of CNTs formed with two different gas precursors was investigated from the viewpoint of crystallinity, growth-length uniformity, and resistance. Although the formed CNTs still require further improvements to obtain a ballistic transport property, it was found that the resistance of CNTs is reduced by using a two-step growth method that produces a multi-wall CNT structure and a uniform micrometer-order growth length.

CMP process for selectively-grown carbon nanotubes in via structure

We have developed a CMP process providing a short polishing time and sufficient uniformity that is applicable to 300 mm scale carbon nanotube (CNT) via integration. To achieve our target, we have developed a new CMP process to make selectively grown CNT in a via hole. Spin on carbon (SOC)film was coated to protect nickel (Ni) catalyst and titanium nitride (TiN) film inside the via hole during SOC-CMP. The SOC-CMP process was used to perform two-step polishing to remove Ni catalyst and TiN film from the field area. CNT-CMP polishing time was reduced from 1690 sec to 200 sec and the yield ratio improved to 100%. CNT-CMP performance improved to a level usable for practical use by selectively growing CNT only from the via. We also evaluated the behavior of CNT-CMP during polishing using a damascene pattern wafer. Step height (Step height means a step between the wiring area and field area) occurred when CNT-SOG (spin-on glass) composite film was appeared upper the via hole but was reduced by concentrating the polishing pressure to project the CNT-SOG composite film. This result indicates that CNT-SOG composite film was polished by mechanical force.