Abstract
This paper was to investigate the mechanism of the undercut in the interface between oxide hardmask film and porous low k film and put forward the solution of improving undercut issue. Dilute hydrofluoric acid (DHF) concentration decreased from 300:1 to 1000:1, which did slightly improve the undercut. The dense low k film without O2 plasma was inserted between TEOS hardmask and porous low k film, however, it was not found for undercut profile after dry etching and wet clean. This indicates that O2 plasma caused the carbon loss of porous low k film surface, and porous low k film in the surface was converted into active SiOH. After dry etching and wet clean, dilute hydrofluoric acid (DHF:300:1) removed the SiOH to form the undercut. This clearly showed that oxygen plasma causing porous low k damage played and DHF played the important role of the forming undercut issue.
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