Aligned carbon nanotubes for electrical interconnect and thermal management

As IC performance increases, many technical challenges appear in the areas of power delivery, thermal management, I/O density, and thermal-mechanical reliability. To address these problems, the use of aligned carbon nanotubes (CNTs) is proposed in IC packaging as electrical interconnect and thermal interface materials. The superior electrical, thermal, and mechanical properties of CNTs promise to bring revolutionary improvement in reducing the interconnect pitch size, increasing thermal conductivity, and enhancing system reliability. Carbon nanotubes (CNTs) are the fascinating one-dimensional molecular structures that can be either metallic or semiconducting, depending on their diameter and helicity. In order to create interconnect structures comprised of CNTs units, it is necessary to control both the growth of CNTs in predefined orientations and configurations, and the interface with other materials such as metal electrodes. In this paper, the growth of aligned carbon nanotubes (ACNTs) by chemical vapor deposition (CVD) is discussed. It is a promising approach, since CVD growth is scalable and can be adapted to produce well-controlled large-area CNT arrays. Two approaches for CVD nanotube growth were explored. One needs pre-patterning catalysts. By this process, highly-aligned carbon nanotubes (CNTs) with high density were synthesized on Al₂O₃/Fe coated silicon substrates of several square centimeter area. The other process is using vapor-phase mixture of xylene and ferrocene, which avoids pre-patterning the catalysts. The ferrocene was the nanotube nucleation initiator and xylene the carbon source. The as-grown CNTs were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and Raman spectroscopy. The feasibility of ACNT interconnect was investigated through the study of CNT/solder interface after a solder reflow process. Preliminary results indicated that molten Sn/Pb solder could wet the CNT surface and form good solder joints. The ACNT structures will be proposed to develop ultra-fine pitch electrical interconnections and high thermally conductive interface materials.