Substrate Effects on the Growth Behavior of Atomic-Layer-Deposited Ru Thin Films Using RuO4 Precursor and N2/H2 Mixed Gas

Abstract

The growth behaviors of atomic-layer-deposited (ALD) Ru thin films using the RuO4 precursor and N2/H2 mixed reduction gas on Ta2O5 thin-film/Si substrates were examined. The Ru films deposited on the Ta2O5 film showed a high growth rate (>0.3 nm/cycle) compared with other ALD Ru processes (∼0.05–0.1 nm/cycle) as well as the characteristic stepwise saturation of the growth rate with respect to the reduction gas (N2/H2) injection time. Detailed analyses revealed that the substrate-involved growth mechanism contributed the extraordinary behavior. The Ta2O5 substrate was reduced to Ta metal by the N2/H2 reduction gas, and the produced Ta atoms were diffused onto the Ru film surface during Ru growth. The proposed reaction mechanism did not significantly affect the electrical properties of the Ru thin film. The process with an exceptionally high growth rate of 0.37 nm/cycle showed a stable self-limited behavior and excellent step coverage, making it suitable for the mass production of the electrode material in a three-dimensional structure. The films showed ∼23 μΩ cm bulk resistivity, which could be maintained down to an extremely low thickness of ∼2.5 nm. This is a highly promising result for its application to the top electrode of the dynamic random access memory (DRAM) capacitor with an ∼10 nm design rule.