Focused-ion beam induced deposition of copper

Abstract

As the dimensions of integrated circuits (ICs) decrease into the submicron range, the problems of circuit delay and interconnect reliability become more urgent. Due to its low resistivity (1.67 μΩ cm) and high electromigration resistance, copper has received attention as a candidate metal for the ICs of the future. In addition, the focused-ion beam (FIB), with its capability for milling and deposition at linewidths of 0.1 μm or below, has proved useful as a tool for integrated IC ‘‘microsurgery.’’ FIB induced deposition of copper from a novel organometallic precursor compound, Cu(hfac)TMVS, has been achieved using 25–35 keV Ga+ ions from a liquid metal ion source. Submicron copper lines deposited at room temperature from this precursor exhibit resistivities as low as 50 μΩ cm; a sharp drop in these values is noted for deposition above 67 °C, and deposition on a substrate heated above ∼100 °C yields resistivities near those of pure bulk copper. Composition analysis by Auger electron spectroscopy shows the high temperature deposition to be nearly pure copper. Deposition yields of 14 copper atoms per incident Ga+ ion have been obtained on both silicon and silicon dioxide substrates, with growth rates of up to 2.2 nm/s at an average ion current density of 200 μA/cm2. The quality and microstructure of the deposited film seems to be inextricably tied to the ability of the carbon-containing by-product molecules to desorb from the growing film. For instance, high-temperature deposition results in a low resistivity film with few impurities, most likely because this condition allows greater by-product desorption. Under the proper conditions, this particular precursor compound shows great promise for use in the FIB induced deposition of low resistivity, submicron interconnects on ICs for repair processes.