Atomic layer deposition, characterization, and dielectric properties of HfO2/SiO2 nanolaminates and comparisons with their homogeneous mixtures

摘要

Nanolaminates of HfO2 and SiO2 were prepared using atomic layer deposition (ALD) methods. Successive exposure of substrates maintained at 120 or 160 degrees C to nitrogen flows containing Hf(NO3)(4) and ('BUO)(3)SiOH led to typical bilayer spacings of 2.1 nm, with the majority of each bilayer being SiO2. The density of the SiO2 layers (measured using X-ray reflectometry (XRR)) was slightly higher than expected for amorphous silica, suggesting that as much as 10% HfO2 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(NO3)(4), leading to a SiO2 interfacial layer and the first HfO2 layer. Combining the ALD of Hf(NO3)(4)/('BuO)(3)SiOH with ALD cycles involving Hf(NO3)(4) and H2O allowed the systematic variation of the HfO2 thickness within the nanolaminate structure. This provided all 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 HfO2 in post-deposition annealing treatments. As the HfO2 thickness decreased, the preference for the tetragonal HfO2 phase increased.