Effect of improved wettability of silicon-based materials with electrolyte for void free copper deposition in high aspect ratio through-vias

We report the improvements in wetting characteristics of silicon-based materials with copper electrolyte by various surface treatments to achieve void free copper deposition in very high aspect ratio through-vias. The contact angles of samples such as native silicon, thermally oxidized silicon, silicon nitride, deep reactive ion etched silicon, etc., with copper electrolyte were measured, before and after the surface treatments. Silicon nitride-coated silicon samples were found to have the best wettability with copper electrolyte and thus silicon nitride was used as an insulating layer instead of commonly used silicon oxide. Wetting characteristics of the samples were further enhanced by SC1 wet surface treatment that makes the surface more suitable for electroplating applications. X-ray photoelectron spectroscopy results verified the presence of polar functional groups on the samples surface, which improved wetting with copper electrolyte. The conclusions drawn by the experimental results were employed in the high aspect ratio, fine pitch through-via copper electroplating and void free copper interconnects having aspect ratio as high as 20 were fabricated.