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

Abstract 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) Ta x N y barrier with thermal ALD Ru seed in comparison to Ti x N y 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 Ta x N y 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 ( NH 3 ) 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 Ta x N y 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.