Nicolo Chiodarelli

Measuring the electrical resistivity and contact resistance of vertical carbon nanotube bundles for application as interconnects

Carbon nanotubes (CNT) are known to be materials with potential for manufacturing sub-20 nm high aspect ratio vertical interconnects in future microchips. In order to be successful with respect to contending against established tungsten or copper based interconnects, though, CNT must fulfil their promise of also providing low electrical resistance in integrated structures using scalable integration processes fully compatible with silicon technology. Hence, carefully engineered growth and integration solutions are required before we can fully exploit their potentialities. This work tackles the problem of optimizing a CNT integration process from the electrical perspective. The technique of measuring the CNT resistance as a function of the CNT length is here extended to CNT integrated in vertical contacts. This allows extracting the linear resistivity and the contact resistance of the CNT, two parameters to our knowledge never reported separately for vertical CNT contacts and which are of utmost importance, as they respectively measure the quality of the CNT and that of their metal contacts. The technique proposed allows electrically distinguishing the impact of each processing step individually on the CNT resistivity and the CNT contact resistance. Hence it constitutes a powerful technique for optimizing the process and developing CNT contacts of superior quality. This can be of relevant technological importance not only for interconnects but also for all those applications that rely on the electrical properties of CNT grown with a catalytic chemical vapor deposition method at low temperature.

Integration of Vertical Carbon Nanotube Bundles for Interconnects

Carbon nanotubes (CNTs) are considered a promising material for interconnects for future generation microchips. The integration of vertical CNT in a processing environment is evaluated in this work. Extrapolated performances of CNT-based interconnects are compared with existing technologies at different hierarchy levels including the limitations of present deposition methods for copper and tungsten. For practical implementation, CNT bundles were selectively grown into contact holes using physical vapor deposited and electrochemical deposited cobalt or nickel catalysts. A polishing step was used to control the CNT length after embedding the CNT into an oxide matrix. A CNT metal decoration method based on electrodeposition is presented, which can be used to assess the yield of electrically conductive CNT as well as to form top contacts for electrical characterization. Finally, the importance of having suitable and robust structures for evaluating the integration process is highlighted after the electrical characterization of CNT in a nanoprober station.

Growth mechanism of a hybrid structure consisting of a graphite layer on top of vertical carbon nanotubes

Graphene and carbon nanotubes (CNTs) are both carbon-basedmaterials with remarkable optical and electronic properties which, among others, may find applications as transparent electrodes or as interconnects inmicrochips, respectively. This work reports on the formation of a hybrid structure composed of a graphitic carbon layer on top of vertical CNT in a single deposition process. The mechanism of deposition is explained according to the thickness of catalyst used and the atypical growth conditions. Key factors dictating the hybrid growth are the film thickness and the time dynamic through which the catalyst film dewets and transforms into nanoparticles. The results support the similarities between chemical vapor deposition processes for graphene, graphite, and CNT.

Carbon nanotube interconnects: Electrical characterization of 150 nm CNT contacts with Cu damascene top contact

The integration of Carbon Nanotubes (CNT) in contact holes with TiN underlayer using CMOS compatible processes is discussed. Each process step was optimized by evaluating the electrical results obtained with contact test structures. Subsequently, this process was transferred to 150 nm diameter contact holes. We present the first electrical data obtained from automated probing of 150 nm diameter contacts filled with CNT connected by a Cu damascene top contact module. This constitutes a significant step forward towards the realization of CMOS contact modules with CNT interconnects.