Feb 19, 2009
Slimmer nanorods lead to low-temperature bonding
A new technique for growing slimmer copper nanorods could lead to interesting new applications for advancing integrated 3D chip technology. Periodically exposing fledgling copper nanorods to oxygen during the vapor-deposition process results in nanorods with a reduced diameter and increased density. These slimline nanorods have diameters between 10 nm and 50 nm, far smaller than the typical 100 nm diameter of conventionally grown copper nanorods.
The reduced diameter nanorods exhibit the low annealing temperature of around 300 °C, making them attractive for use in semiconductor and chip applications that employ copper and require relatively low temperatures. In their annealed state, the nanorods grow denser and form a continuous film. This sintering characteristic suggests the slimmer nanorods will be an effective bonding agent or adhesive to use in the development or fabrication of 3D integrated devices.
The arrays of copper nanorods are produced by vapor deposition at an oblique angle. In a conventional setting, with an uninterrupted stream of copper atoms deposited in a vacuum onto a substrate, the deposition angle naturally results in taller, thicker nanorods that shade – and in turn stunt the growth of – shorter rods. This process is guided by the surface roughness of the substrate.
Periodically interrupting the deposition, and exposing the ambient air, however, leads to oxygen being absorbed into the surface of the copper nanorods. During subsequent depositions, this oxidized copper helps to prevent the vaporized copper atoms from migrating away from the very tips of the nanorods. This ensures that the nanorods grow taller, without necessarily growing in diameter. Thinner rods result in less shading of adjacent nanorods, leading to higher rod densities.
By increasing the number of growth interruptions, copper nanorods with an average diameter of 10 nm can be obtained. These thinner nanorods anneal at around 300 °C, at which a continuous film is formed. Such a film made from copper nanorod arrays could feasibly be used as an adhesive layer for wafer bonding because of the nanorods' low temperature sintering characteristics.
The researchers presented their work in Nanotechnology.
About the author
Pei-I Wang is a research associate working with Prof. Toh-Ming Lu at the Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, NY, USA. In addition to Lu and Pei-I Wang, co-authors on the paper include Rensselaer physics professor and chair Gwo-Ching Wang, graduate student Thomas C Parker and Prof. Tansel Karabacak of the University of Arkansas at Little Rock, Little Rock, USA. This work was collaborated with Prof. Jian-Qiang Lu of Rensselaer Polytechnic Institute.