X-ray reflectivity analysis of indium tin oxide thin films on glass

Indium tin oxide (ITO) is a solid solution of indium oxide (In2O3) and tin oxide (SnO2). Due to its high electrical conductivity and optical transparency, ITO is often used to make transparent conductive coatings for applications such as liquid crystal displays and tough panels. The quality of the deposited ITO films is a key factor that determines their electrical and optical properties.

X-ray reflectivity (XRR) is a non-destructive analysis method for the characterization of thin film materials. In particular, XRR measures the density, thickness, and roughness of the film at the same time. In Figure 1 below, the XRR profile of an ITO film deposited on a glass substrate is shown. Nominally, this is a single layer film with a thickness about 20 nm. By applying fast Fourier transform (FFT) to the measured profile, the film thickness can be readily estimated. The result is shown in Figure 2, which suggests that there are two layers of about 4.2 nm and 14.9 nm in the sample with slightly different densities.

XRR profile of an ITO film on a glass substrate

Figure 1: XRR profile of an ITO film on a glass substrate

XRR profile of an ITO film on a glass substrate

Figure 2: FFT of the XRR profile shown in Figure 1.
The numbers on top of the peaks show the calculated layer thicknesses.
The numbers in the parentheses show the depth from the surface.

The data were collected using Rigaku's Ultima IV multipurpose diffraction system.

The Ultima IV represents the state-of-the-art in multipurpose X-ray diffraction (XRD) systems. Incorporating Rigaku's patented cross beam optics (CBO) technology for permanently mounted, permanently aligned and user-selectable parallel and focusing geometries, the Ultima IV X-ray diffractometer can perform many different measurements...fast. Read more...

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