Low-resistivity molybdenum obtained by atomic layer deposition

Abstract

A novel atomic layer deposition (ALD) process was developed for low-resistivity molybdenum (Mo) from molybdenum dichloride dioxide (MoCl2O2) and atomic hydrogen (at-H). A wide ALD window of self-limiting growth was observed between 150 and 450 °C. No film deposition occurred with molecular hydrogen (H2), demonstrating the necessity to have at-H to efficiently reduce the MoCl2O2 precursor. At 350 °C and above, the film composition was determined at approximately 95 at. % of Mo and 3.5 at % of oxygen (O), with trace amounts (i.e., <1 at. %) of carbon (C), chlorine (Cl), hydrogen (H), and nitrogen (N). The growth per cycle (GPC) was roughly 0.022 nm/cycle. No substrate selectivity or pronounced nucleation delay was observed on silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon carbide (SiC), aluminum oxide (Al2O3), hafnium dioxide (HfO2), and low-k dielectric (SiOC). Film uniformity and conformality were ±5% and ±10%, respectively, while resistivity approached a bulk value of 18.6 μ Ω cm at 24 nm. At 250 °C and below, increased levels of oxygen (up to 33 at. % at 150 °C) and chlorine (2.7 at. % at 150 °C) were detected in the film. This trend coincided with an increase in the GPC, a change in optical properties, a decrease in film density and crystallinity, and an increase in resistivity. While self-limiting growth was observed through the entire ALD window of 150–450 °C, the temperature (T) range for depositing low-resistivity Mo deposition was narrower at T ≥ 250 °C.