Effects of layer boundaries on x-ray reflectivity in thermally treated ternary gate dielectrics grown by atomic layer deposition

In this study, Si-doped HfO2 (HSO) dielectric films were deposited via thermal atomic layer deposition (ALD) by varying the cycle ratios of SiO2 and HfO2. A carbon-free silicon precursor, trisilylamine (TSA), was employed as the doping source, reacting with ozone to form high-quality SiO2 layers. X-ray reflectivity (XRR) was used to determine key film properties, including thickness, density, surface roughness, and absorptivity in ultrathin films. Although XRR is effective for characterizing layered structures, postdeposition annealing can introduce inaccuracies due to atomic interdiffusion, particularly at low doping levels. To address this, a layer-resolved density model with well-defined interfaces was developed to enable a more accurate analysis of doped high-κ films. The extracted parameters were validated using transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction. XRR results revealed that the doped samples exhibited thicker interfacial layers with higher interfacial layer density and reduced surface roughness compared to pure HfO2, suggesting a lower interface trap density as confirmed by electrical measurements. Furthermore, flatband voltage shifts (ΔVFB) caused by oxide traps showed a correlation with both the Si doping ratio and the overall density of HSO films. These results demonstrate that XRR remains a reliable and insightful technique for evaluating ALD-grown stacks after annealing, offering valuable information prior to detailed structural and electrical characterization.