Direct plasma-enhanced atomic layer deposition of aluminum nitride for water permeation barriers

Abstract

Oxygen-free, transparent, and insulating thin films at fabrication temperatures below 100 °C are important for sensitive materials and interfaces, like organic electronics. In this work, a capacitive coupled plasma-enhanced atomic layer deposition process of aluminum nitride with trimethylaluminum as a precursor and a mixture of hydrogen/nitrogen as the reactive gas was studied at 80 and 200 °C. The film properties were characterized by spectroscopic ellipsometry, x-ray photoelectron spectroscopy, scanning electron microscopy, and electrical measurements. The growth per cycle stayed constant at around 1 Å, and the refractive index decreased slightly from 1.97 at 200 °C to 1.93 at 80 °C. While the AFM surface roughness was below 0.5 nm at 80 °C deposition temperature, scanning electron microscopy images reveal blister generation at 200 °C on silicon. The x-ray photoemission spectroscopy measurements show a layer composition of Al:N of 1.0:0.9 with a few percent of oxygen and carbon, indicating good air stability and reasonable stoichiometry. The metal-insulator-metal capacitance measurements showed a dielectric constant of 11 at both temperatures. The water vapor transmission rate for a 20 nm thick film on polyethylene naphthalate films was lower than 0.5 mg/(m2⋅day) at 38 °C/90%.