| AVS 60th International Symposium and Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM+MI+NS+SS+TF-TuA |
| Session: | High-k Oxides for MOSFETs and Memory Devices II/Oxides and Dielectrics for Novel Devices and Ultra-dense Memory I |
| Presenter: | V. Longo, Eindhoven University of Technology, Netherlands |
| Authors: | V. Longo, Eindhoven University of Technology, Netherlands M.A. Verheijen, Eindhoven University of Technology, Netherlands F. Roozeboom, Eindhoven University of Technology, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
SrTiO3 (STO) has received much attention due to its favorable properties as ferro-electric, para-electric and high-k dielectric material, related to its crystalline perovskite structure. Thin STO films are to be employed as the dielectric layer in metal-insulator-metal (MIM) structures, for example for DRAM and/or RRAM applications. When deposited by Atomic Layer Deposition (ALD), STO films are amorphous and require an annealing step to crystallize. Recent reports have shown that Sr-rich films yield a finer crystalline structure than stoichiometric films upon crystallization by rapid thermal annealing (RTA). The finer grain structure results in reduced nanocrack formation, thus less leakage and improved dielectric properties. A deeper understanding of the crystallization behavior of STO is therefore of crucial importance to further optimize the film properties.
In this work SrTiO3 thin films with different compositions ([Sr]/[Sr]+[Ti] from 0.50 to 0.65) were deposited by plasma-assisted ALD employing cyclopentadienyl-based precursors and an O2 plasma. The crystallization of the as-deposited amorphous films was obtained by RTA in N2 at temperatures ranging from 550 °C to 650 °C. Different annealing times (60 to 600 s) were employed to characterize the crystallization process at different stages. An in-depth analysis of the microstructure of the crystallized STO was carried out by transmission electron microscopy (TEM). As a first step, the analysis was performed on STO films deposited on Si3N4 TEM membranes, either bare or coated by ALD-grown Al2O3, due to the transparency of these materials to the electron beam. It was shown that the STO crystallites had grown in a transrotational manner and that an increased Sr-content resulted in films with reduced grain size and a more compact microstructure. Furthermore, two crystallization regimes were identified: 1) growth-dominated, where the crystallization process is dominated by growth of a low density of crystals, and 2) nucleation-dominated, where a high density of crystals is limited in lateral growth by their proximity. Finally, the STO films were also deposited on Pt-coated TEM windows (Pt prepared by plasma-assisted ALD) to compare the crystallization kinetics on a representative functional bottom electrode material as used in MIM structures. The TEM analysis and the X-ray diffraction patterns evidenced that these films show quite similar crystallization behavior as on Si3N4 and Al2O3 surfaces.