A study on the polymer residues formation at the via-hole and its removal by remote oxygen/nitrogen and hydrogen plasma

Abstract

For multilevel device fabrication, via-holes are generally dry etched for electrical connection between the upper and lower metal layers. The ashing and photo resist (PR) strip processes are generally followed to remove the PR and polymerized residues, respectively. However, the PR strip is the wet chemical process and causes environmental problems. In this study, low temperature remote plasma dry cleaning process that removes both the PR and polymer residues containing carbon and fluorine will be described. The radio frequency remote oxygen/nitrogen plasma was used to remove the PR and polymer residues simultaneously. The cleaning efficiency was systematically evaluated at various conditions such as the oxygen and nitrogen ratio, plasma power, exposure time, gas flow rate and sample temperature. The hydrogen plasma treatment was also carried out to remove polymerized residues formed at the bottom nitride layer oxygen/nitrogen plasma cleaning. In-situ Auger electron microscopy, x-ray photoelectron spectroscopy, atomic force microscope analysis systems were used to evaluate the cleaning effects and to avoid recontamination such as carbon absorption in the air. Scanning electron microscope provided a preliminary assessment of cleaning performance. Preliminary results indicated that the hydrogen plasma treatment subsequent to oxygen/nitrogen PR ashing process was very efficient to remove the polymerized residues formed at the bottom nitride.