Carbon nanotube films for extreme ultraviolet lithography and effective heat management in electronic devices

Collaborative paper with imec

A study led by researchers at the ICN2 and published in ‘ACS Applied Materials & Interfaces’ demonstrates that carbon nanotube networks can be used to provide efficient heat dissipation in applications such as extreme ultraviolet lithography, as well as flexible electronics and interconnects in integrated circuits.

Heat dissipation and low power consumption have become key challenges for modern electronics, which must be addressed hand in hand with the development of new integration and miniaturisation technologies for electronic circuits and systems. In particular, as devices become smaller and more powerful, excess heat issues arise, which can compromise operation and durability. In this context, new materials and nanotechnologies can provide solutions for designing high-performance electronic devices that consume little power and are able to manage heat efficiently.

Carbon nanotube (CNT) networks –an emerging class of nanostructured materials that exhibit outstanding electrical and mechanical properties— are promising candidates for applications requiring efficient heat dissipation, such as extreme ultraviolet (EUV) lithography. EUV lithography is a key technology for the miniaturisation of integrated circuits that requires the use of protective films to avoid damaging photomasks during the process. Suitable materials for these shielding pellicles should be transparent to EUV light, mechanically robust, and thermally stable with high thermal conductivity.

As demonstrated in a research paper published today in ACS Applied Materials & Interfacesfree-standing CNT films are strong candidates for this application, due to their high EUV transparency and ability to withstand heat. The authors of this study –a team of researchers from the ICN2 Ultrafast Dynamics in Nanoscale Systems Group (led by Prof. Klaas-Jan Tielrooij), the former ICN2 Phononic and Photonic Nanostructures Group (led by Prof. Clivia Sotomayor-Torres), and from imec (Leuven, Belgium)— employed all-optical Raman thermometry to gain insight into the thermal properties of free-standing CNT networks.

The authors investigated two types of carbon nanotube films: single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs). The first structure consists of a network of nanotubes, whose walls are one atom thick; the second is composed of a network of nanotubes each made of two single-walled nanotubes nested within each other. By Raman thermometry –which is a non-invasive technique— the researchers were able to measure the thermal conductivity of these two types of free-standing CNT films at temperatures ranging from 300 K to 700 K.

The study revealed thermal conductivities up to 50 W m−1 K−1 for films made of double-walled CNTs, a remarkable seven times higher than those of single-walled CNT films. “We believe that this enhanced thermal conduction is due to the additional wall in double-walled carbon nanotube networks, which introduces an extra heat-dissipation channel and reduces the impact of defects,” explains Prof. Klaas-Jan Tielrooij, the coordinator of this research and corresponding author of the paper. “Furthermore, the nanotubes in the studied CNT network films were randomly oriented; we think that aligning the double-walled CNTs within the network would lead to even higher thermal conductivity.”

These outcomes show that free-standing carbon nanotube network films, in particular the double-walled one, provide efficient heat dissipation, demonstrating their suitability for application as EUV pellicle materials. In addition, they hold promise for use in flexible electronics and interconnects in integrated circuits. In fact, the relatively high thermal conductivity of these films makes them ideal for efficient thermal management in devices where traditional materials fall short when dimensions are extremely reduced.