Grazing-incidence small angle x-ray scattering, x-ray reflectivity, and atomic force microscopy: A combined approach to assess atomic-layer-deposited Al2O3 dielectric films

Abstract

Al2O3 dielectric films deposited by atomic layer deposition (ALD) were characterized using grazing-incidence small angle x-ray scattering (GISAXS). Unique to this method, the diffuse scattering from surface and interface roughnesses was calculated with surface parameters (root mean square roughness σ, lateral correlation length ξ, and Hurst parameter h) obtained from atomic force microscopy and layer densities, surface grading, and interface roughness/grading obtained from specular x-ray reflectivity (XRR) simulation. Pore scattering was determined with the measured total diffuse scattering intensity subtracted by the simulated diffuse scattering from roughnesses, from which the pore size distribution was obtained. This GISAXS method was validated with the scanning electron microscopy result of a porous indium phosphide single layer and was applied to two Al2O3 dielectric single layers deposited with different ALD parameters. Both porous and nonporous Al2O3 layers were revealed. The pore size in the porous Al2O3 single layer was determined to disperse in a range of several nanometers with an uncertainty of ∼1 nm. The GISAXS results are correlated with other techniques including specular XRR measurements, spectroscopic ellipsometry, and broadband optical reflectance measurements. Pore size distribution, along with layer thicknesses, densities, and refractive indices, is key to understanding the role of deposition conditions in the optical and electrical properties of Al2O3 dielectric films.