3D system integration on 300 mm wafer level: High-aspect-ratio TSVs with ruthenium seed layer by thermal ALD and subsequent copper electroplating

The copper electrochemical deposition (Cu-ECD) filling capability of high aspect ratio through silicon vias (HAR-TSVs) and homogeneity over 300 mm wafers were investigated on a film stack of thermal ALD (thALD) TaxNy barrier with thermal ALD Ru seed in comparison to TixNy barrier with a standard Cu i-PVD seed layer using a commercial 300 mm plating tool. As a first step, Cu-ECD was conducted on wafers with TSV blind holes with aspect ratios (AR) of 10 to 12. To achieve this, a thermal ALD film stack of approximately 6 nm TaxNy and 9 nm Ru (with a sheet resistance of [25.6 ± 1.4] Ω/ϒ) were deposited at 250 °C. The reactants for the barrier layer were (tert-butylimido)tris(diethylamino)tantalum(V) (TBTDET) and ammonia (NH3) as co-reactant. For the Ru seed layer deposition (ethylcyclopentadienyl)(pyrrolyl)ruthenium(II) (ECPR) and molecular oxygen as co-reactant were used supplemented by a hydrogen purge step after every third ALD cycle. The corresponding ALD growth was observed during the entire process by in-situ real-time spectroscopic ellipsometry (irtSE). Blister-free deposition and satisfactory film stack adhesion with no delamination was verified ex situ by scanning electron microscopy (SEM). The deposited copper inside the TSVs was analyzed by focused ion beam (FIB) imaging and X-ray tomography. The Cu ECD filling capability in HAR-TSVs was shown on a film stack of thALD TaxNy thALD Ru seed using a commercial industry standard 300 mm plating tool. A novel blister-free ultra-thin Ru ALD film having good adhesion properties and unique advantages, e. g. high conformity in high-aspect-ratio through-silicon vias large-scale film uniformity over 300 mm wafers, as well as good reproducibility was developed.