Zr and Hf based high-k films have been identified as promising candidates to replace SiO₂ based dielectrics for the continued down scaling of semiconductor devices. In high-k films, amorphous and crystalline phases coexist depending on the used thermal budget. Hence, different and more complex current conduction mechanisms occur at the nanometer scale and new advanced methods for both, physical and electrical characterization are required. Tunneling atomic force microscopy (TUNA) is a very promising method which allows concurrent locally resolved characterization of the electrical properties and the surface topography of the thin dielectric films. In this work, electrical and surface properties of thin high-k ZrO₂ films were studied using TUNA. The electrical analysis is performed by measuring the tunneling current through the dielectric film in a range of 50 fA to 120 pA with extremely high current sensitivity (noise level of 40 fA). ZrO₂ films in a thickness range of 2 to 10 nm were deposited by atomic layer deposition (ALD) on silicon and annealed (RTA). Their film properties were studied by TUNA mapping. For example, as-deposited 4.8 nm thick amorphous films show smooth surfaces in the topography and randomly distributed leakage current spots in the TUNA current maps. After RTA at 450 and 600°C for 30 to 300 s, all films show a crystalline morphology which is proven by TEM analysis. While the AFM topography measurements do not register the changes in film morphology, TUNA mapping visualizes the film crystallization as ring shaped structures with significantly higher current densities, which are due to grain boundaries. The sensitivity of the TUNA technique will be discussed and a comparison to conventional AFM topography measurements will be performed. Summarizing, the presented results will successfully demonstrate that TUNA is an extremely sensitive mapping tool for the detection of small changes in film morphology of high-k layers at a nanometer scale.

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1. Thermal Stability of thin ALD ZrO₂ Layers as Dielectrics in Deep Trench DRAM Devices Annealed in N₂ and NH₃