Assembling of carbon nanotube structures by chemical anchoring for packaging applications

As IC performance increases, many technical challenges appear in the areas of current-carrying capacities, thermal management, I/O density, and thermal-mechanical reliability. To address these problems, the use of aligned carbon nanotubes (CNTs) has been proposed in IC packaging for electrical interconnect and thermal interface materials (TIMs). The theoretically superior electrical, thermal, and mechanical properties of CNTs promise to reduce the interconnect pitch size, increase thermal conductivity, and enhance system reliability, which is expected to bring about revolutionary improvement to microelectronics. However, the problems with the CVD growth process such as high growth temperature and poor adhesion of CNTs to substrates, challenges in selectively patterning CNT structures, high contact resistance of CNT/electrodes and damage of CNT wall structure by wet chemical functionalization, become barriers for CNT applications. In order to overcome these disadvantages, we proposed the "chemical anchoring" process to directly attach aligned CNTs onto gold-coated substrates. This methodology has the following features: 1) in-situ functionalization of CNTs with reactive functional groups during CVD process, which preserves the perfect CNT wall structure and good alignment of CNTs as well as conrrollably tunes the length of functionalized CNTs; 2) covalently bonded interface by employing a self-assembled monolayer (SAM) as the bridging ligand at the CNT-gold substrate interface; 3) low temperature and simple process. Scanning electron microscopy (SEM) was used to characterize the CNT structures and the SAM-treated gold surface. The effectiveness of the in-situ functionalization was studied by XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectroscopy). Four-point probe testing system was employed to test the electrical performance of the chemically anchored CNT structure. Results showed an Ohmic contact, low electrical resistivity of the - CNT-gold interface structure and improved CNT-substrate adhesion.