Focused ion beam induced deposition of low-resistivity copper material

Focused ion beam (FIB) induced processes for material etching and deposition have proven successful in integrated circuit device modification applications. Current FIB metal deposition processes are typically limited to resistivities in the range of 150–200μΩcm due to included impurities; however, today’s high-frequency devices require very low interconnect resistivity. The organometallic precursor material copper (I) hexafluoroacetylacetonate trimethylvinylsilane, or Cu(hfac)TMVS for FIB-assisted metal deposition was investigated. 50kV Ga+ ions were scanned over a defined area of an Al∕SiO2 resistivity test substrate in the presence of the precursor vapor, using two different 50kV FIB column designs with beam currents from 49to2070pA and current densities of 13–36Acm−2. Resistivity was measured by the four-point probe method. This study verifies prior reported resistivities of ⩽50μΩcm at room T across all deposition parameters for film growth yields ⩽0.18μm3nC−1 ion dose. Depositing on a heated substrate yields considerably lower film resistivity at temperatures near 100°C; resistivities as low as 18.8μΩcm were achieved at the high growth yield of 0.32μm3nC−1 ion dose. At room temperature, the resistivity varied inversely but nonlinearly with growth yield across all depositions. Auger electron spectroscopy revealed Cu content of ∼60at.% in the lowest resistivity films at all substrate temperatures. Via filling with aspect ratios >9:1 is demonstrated.