Atomic Layer Deposition, Characterization, and Dielectric Properties of HfO₂/SiO₂ Nanolaminates and Comparisons with Their Homogeneous Mixtures

Abstract

Abstract Nanolaminates of HfO 2 and SiO 2 were prepared using atomic layer deposition (ALD) methods. Successive exposure of substrates maintained at 120 or 160 °C to nitrogen flows containing Hf(NO 3 ) 4 and ( t BuO) 3 SiOH led to typical bilayer spacings of 2.1 nm, with the majority of each bilayer being SiO 2 . The density of the SiO 2 layers (measured using X‐ray reflectometry (XRR)) was slightly higher than expected for amorphous silica, suggesting that as much as 10 % HfO 2 was incorporated into the silica layers. Based on cross‐sectional transmission electron microscopy (TEM) and XRR, oxidation of the silicon substrate was observed during its first exposure to Hf(NO 3 ) 4 , leading to a SiO 2 interfacial layer and the first HfO 2 layer. Combining the ALD of Hf(NO 3 ) 4 /( t BuO) 3 SiOH with ALD cycles involving Hf(NO 3 ) 4 and H 2 O allowed the systematic variation of the HfO 2 thickness within the nanolaminate structure. This provided an approach towards controlling the dielectric constant of the films. The dielectric constant was modeled by treating the nanolaminate as a stack of capacitors wired in series. The nanolaminate structure inhibited the crystallization of the HfO 2 in post‐deposition annealing treatments. As the HfO 2 thickness decreased, the preference for the tetragonal HfO 2 phase increased.