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Manipulation of Ni catalyst particle size, shape and areal density on TiN support layer for growth of vertical aligned CNTs

: Tittmann, J.; Hermann, S.; Fiedler, H.; Schulz, S.E.; Gessner, T.

Aalto University School of Science, Aalto:
NT13. Fourteenth International Conference on the Science and Applications of Nanotubes 2014 : 24–28 June 2013 Dipoli Congress Center, Espoo, Finland
International Conference on the Science and Application of Nanotubes <14, 2014, Helsinki>
Fraunhofer ENAS ()

Due to their promising electronic properties, vertical grown carbon nanotubes (CNTs) can be applied as vertical interconnects in integrated circuits. The main reason against the replacement of copper by CNTs in this technology is the still too low areal density. Consequently, the electrical resistance of CNT-Vias is larger than that of copper interconnects.

Here we show investigations of vertical CNTs grown on TiN/ Ni layers. This system is not only known to give a small contact resistance between metallization and CNTs but also to produce CNTs with high quality. Based on AFM measurements, changes in catalyst particle height and shape as well as in their areal density are determined. REM and Raman measurements demonstrate the dependence of the CNT length and quality on the thickness of both layers. To further increase the number of catalyst particles per area, an approach similar to [1] is tested. In this procedure a second catalyst layer is deposited on top of the already formed first catalyst particles. In contrast
to Esconjauregui’s combination of Al2O3 with Fe, Co and Ni, we use TiN and Ni to check the general validity of this approach for different systems. Besides that, we apply the approach for growth of multi- instead of single-walled
nanotubes. We find that this leads to increase in the particle density by up to 600 %. But depending on the starting configuration of the system, shrinking to less than 50 % is also possible. By combining observations from several states of sample preparation, we draw the conclusion, that the first catalyst layer and the particles formed by it have a drastic impact on the final appearance and therefore on the final areal particle density.

[1] S. Esconjauregui, M. Fouquet, C. Bayer, ACS Nano. Vol. 4, No. 12 (2010) 7431-7436