Study of BEoL dual damascene ULK etch and the correlation to Cu gapfill performance

As logic technology keeps shrinking to 28nm and below, Ultra Low-£ (ULK) dielectric film is widely used in BEoL (Back End of Line) to improve RC performance. To reduce k value damage, weaker post dry-etch cleaning is used to avoid methyl group loss, but the etch by-product removal capability is reduced also. Even with softer cleaning, the trench and via profile still will be affected due to ULK film is more sensitive to wet cleaning compared to low-k and TEOS film. The residual polymer and the sidewall profile will limit the subsequent Cu gap filling process margin, which needs more precise control of etch process. In the this paper, by means of post CMP defect scan, we demonstrate the correlation between Cu void performance and dual damascene profile, etch chemistry combination and loading control. Mechanisms of difference void formations are investigated. Based on that, corresponding tuning methods are investigated.