A hierarchy of CO2-based solvents is used to remove post-etch residues from vias and trenches in low-k patterned porous methylsilsesquioxane (pMSQ) interlayer dielectrics. Spectroscopic ellipsometry measurements indicate that, upon pressurization and depressurization with CO2, the thickness and refractive index return to values near the original values indicating that collapse or voiding of the pores did not occur. Post-etch residue could not be removed by pure water, CO2, with or without cosolvent, or dry CO2 with a surfactant. These results suggest that the particles could not be removed by a dissolution mechanism alone. The via And the bottom trench were cleaned with a solvent containing water, CO2, and a hydrocarbon surfactant. In this mild detergent system, particles may be removed both as a suspension and in the dissolved state in microemulsions and macroemulsions. The low interfacial tension prevents collapse of the pMSQ during water removal. This mild detergent system does not produce voids in the pMSQ. Thus, this detergent cleaning technique appears to be selective for post-ash residues on pMSQ dielectrics and is of significant practical interest. (C) 2003 American Vacuum Society.