Issues with selectivity loss during tungsten plug process integration

This paper reports the causes of selectivity loss during tungsten (W) plug deposition investigated. It was determined that the major cause of selectivity loss was the presence of a sidewall contaminant formed during via etching. Photoresist removal procedures such as oxygen plasma ashing, or an organic stripping solution, did not fully remove this contaminant which supported W growth. Sidewall contaminants that remained on the surface after photoresist stripping resulted in the occurrence of via sidewall creep and W stringers. To completely remove sidewall contaminants after plasma ashing, it was necessary to use additional wet chemical cleaning procedures. This eliminated problems with sidewall creep and W stringers. However, it was also found that wet cleaning procedures could be the cause of other forms of selectivity loss such as W clusters and localized blankets of W metal, when not carefully implemented. The use of wet chemical cleaning procedures in combination with photoresist removal techniques was found to significantly reduce problems with selectivity loss, resulting in improved metallization yields