Surfactant Enabled Supercritical CO2 Cleaning Processes for BEOL Applications: Post-barrier breakthrough

摘要

Supercritical carbon dioxide-based processing is being developed for BEOL cleaning applications. Fluid properties such as zero surface tension and ultra-low viscosity enable a fundamentally new cleaning technology for nano-scale structures and porous Low-k value Dielectrics (LKD). Solvent properties for dense carbon dioxide are dramatically different than those of water typically used in BEOL cleaning applications. Unlikewater, dense CO2 is completely non-polar and comparable to hexane in terms of solvency1. Since non-polar solvents cannot support ionic dissociation, they cannot effectively dissolve ionic residues such as that created in barrier breakthrough etching processes. Alternative approaches must therefore be used if CO2 is to be an effective cleaning media. Simply adding reasonable amounts of semi-polar cosolvents is not effective as these homogeneous mixtures take on intermediate properties that cannot support ionic dissociation (dissolution). This paper will discussthe use of surfactants in CO2 to create discrete polar microdomains useful in removal of etch residues and specifically effective in post-barrier breakthrough cleaning steps. Additionally, we will present processes useful in optimizing cycle time and preventing contaminant re-deposition.