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Characteristics of Polymer Residues Formed at the Via Hole and Photoresist Ashing Properties of Remote Oxygen/Nitrogen Plasma

The low-temperature remote oxygen/nitrogen plasma ashing process that removes both the photoresist and polymer residues containing carbon and fluorine after reactive ion etching (RIE) process was investigated. The fluorocarbon residue was distributed with a depth of several tens of angstroms from the surface with a relatively homogeneous spatial distribution after the RIE process. X-ray photoelectron spectroscopy (XPS) analysis also showed the formation of fluorocarbon films during RIE with mainly C–C, C–CFx (x=1,2,3), CF, and CF2 bonds. The ashing rate increased with increasing amount of nitrogen addition to oxygen gas and showed saturation at approximately 10% of nitrogen addition. Mass spectrometry measurement revealed that the amount of atomic oxygen increased with the addition of nitrogen to oxygen gas. This study revealed that atomic oxygen is the primary reactive species responsible for removal of photoresist in the remote oxygen/nitrogen ashing process.