Nucleation Enhancement and Area-Selective Atomic Layer Deposition of Ruthenium Using RuO4 and H2 Gas

Abstract

Inherent substrate selectivity is reported for the thermal RuO4 (ToRuS)/H2 gas atomic layer deposition (ALD) process on H-terminated Si (Si–H) versus SiO2. In situ spectroscopic ellipsometry (SE) detected Ru growth from the first cycle on blanket Si–H, whereas on blanket SiO2, 60 cycles were needed to detect growth. Area-selective growth was evaluated on a patterned substrate with 1–10 μm wide Si–H lines separated by 10 μm wide SiO2 regions. Ex situ planar scanning electron microscopy and cross-sectional high-resolution transmission electron microscopy measurements showed that a smooth, continuous Ru film of 4.5 nm could be deposited on Si–H, with no Ru detected on SiO2. The proposed mechanism behind the inherent substrate selectivity is the oxidation of the Si–H surface by RuO4, which was confirmed by in vacuo X-ray photoelectron spectroscopy (XPS) experiments. A methodology to enhance the nucleation of the RuO4/H2 gas process on oxide substrates is also reported. In situ SE and in vacuo XPS experiments ...