Copper Cleaning Process

The introduction of copper for building interconnects requires a reevaluation of back-end cleaning technologies and processes. Traditional solvent-based processing is giving way to aqueous-based cleans for environmental reasons and to meet the rigorous demands of smaller interconnect geometry. Careful selection of chemicals enables effective cleaning without introducing problematic copper corrosion or excessive loss of dielectric material. Furthermore, aqueous cleaning can be cheaper than solvent-based cleaning if economical practices perfected for front-end cleans are applied to the back-end.

Aqueous chemistries are being investigated in open bath systems, but because the chemicals in these systems are exposed to ambient air, dissolved oxygen content is high and the risk of oxidation of exposed metal surfaces is high. Also, ambient light can create a photovoltaic cell at p-n junctions which promotes copper corrosion and redeposition in electrolytic solutions.

Aqueous chemistries are also being investigated in spin-spray type systems, but those systems are known to have limited efficacy in trenches and vias as geometries shrink. Furthermore, these systems have been shown to have substantially higher defects from post-dry watermarks.

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