Improving electrical contact of vertically aligned carbon nanotubes with bonding metals in thermocompression bonding through oxygen plasma treatment

Abstract

Vertically aligned carbon nanotubes (VACNTs) are being widely studied due to their exceptional mechanical, electrical, and thermal properties. The application of thermocompression bonding (TCB) technique has positioned VACNTs as promising candidates for 3D heterogeneous integration, interconnects, and nanopackaging. However, challenges arise from a CNT-cluster layer covering the top surface of the as-grown VACNTs, adversely affecting wettability and electrical contact between the VACNTs and the bonding metals used in the TCB process. To mitigate this issue, we propose using oxygen plasma reactive ion etching (RIE) to treat the top and/or bottom surfaces of the VACNTs. Scanning electron microscopy and Raman spectroscopy characterizations confirm the successful removal of the CNT-cluster layer from the top surface following the RIE treatment, and excessive RIE treatment may cause partial damage to the graphitic structures of the VACNT surface. Direct-current measurements on fabricated VACNT wall π-bridge structures further validate the enhancement in electrical contact between the top surface-treated VACNTs and the bonding metals. This improvement is attributed to the effective removal of the CNT-cluster layer and the relative minimal damage to the graphitic structures, particularly in comparison to the bottom surface-treated VACNTs.