Focused ion beam induced deposition of low-resistivity copper material

摘要

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 150-200 μΩ 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. 50 kV Ga~+ ions were scanned over a defined area of an Al/SiO~2 resistivity test substrate in the presence of the precursor vapor, using two different 50 kV FIB column designs with beam currents from 49 to 2070 pA and current densities of 13-36 A cm~(-2). Resistivity was measured by the four-point probe method. This study verifies prior reported resistivities of ≤ 50 μΩ cm at room T across all deposition parameters for film growth yields ≤0.18 μm~3 nC~(-1) ion dose. Depositing on a heated substrate yields considerably lower film resistivity at temperatures near 100℃; resistivities as low as 18.8 μΩ cm were achieved at the high growth yield of 0.32 μm~3 nC~(-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 ～ 60 at. % in the lowest resistivity films at all substrate temperatures. Via filling with aspect ratios > 9:1 is demonstrated.