TEM and EDX study of the Al2O3 ultra thin films

The ultra-thin layers of Al2O3 were deposited on a silicon substrates. The method of atomic layer deposition (Beneq TFS 200 ALD system) was chosen as the proper method of dielectric layer deposition. This method provides precise thickness control down to a single atomic layer. The precursors used were trimethylaluminum (Sigma-Aldrich) and purified water. The deposition of the atomic layer was carried out at 200 °C. Samples with a thickness of 2 and 8 nm of alumina were selected for the tests. A high-resolution transmission electron microscope TALOS F200X (HR TEM) equipped with an EDS detector was used for cross-section imaging and chemical composition analyzes. 
A thin layer of natural silicon oxides with a thickness of approx. 2 nm can be detected on the surface of the silicone substrate. The area with a mixture of oxygen, silicon and aluminum concentrations is also clearly visible. The thickness of the aluminum silicate phase boundary was calculated for approx. 1.7 and 4.5 nm for 2 nm and 8 nm films, respectively.