Aluminum–4% Cu interconnect etching in a low‐pressure magnetically enhanced reactor

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A novel approach has been used to obtain residue‐free dry etching of Al–4% Cu alloy interconnects with chlorine‐based plasmas. The addition of external aluminum in a magnetically enhanced plasma etch reactor was used to form AlCuClx, a volatile etch by‐product. Response surface methodology was used to explore the parameter space for a hydrocarbon‐free BCl3/Cl2‐based chemistry. Total gas flows between 60 and 80 sccm, rf power levels between 800 and 1000 W, and BCl3/Cl2 ratios of 0.1–0.25 were found to lead to optimal etches. The response variables studied were Al etch rate, photoresist etch rate, SiO2 selectivity, and post‐etch residue. Al etch rates of 4500 Å/min, photoresist selectivities of 1.5:1, and SiO2 selectivities better than 5:1 were obtained. Optical emission spectroscopy was used to monitor the removal of the Cu‐rich residue by observing emission intensities of the 325‐nm Cu line.